ZOOKEEPER-4427: Migrate to Logback

This is the first commit of Logback migration task.

1. Replaced log4j dependencies with logback alternatives,
2. Replaced log4j.properties files with logback.xml
3. Refactored unit tests to use logback for log capturing.

This patch doesn't cover the zookeeper-contrib projects, only the main codebase.

Author: Andor Molnar <andor@apache.org>

Reviewers: Enrico Olivelli <eolivelli@apache.org>, Chris Nauroth <cnauroth@apache.org>, Mate Szalay-Beko <symat@apache.org>

Closes #1793 from anmolnar/ZOOKEEPER-4427

bin/zkCleanup.sh

@@ -43,11 +43,11 @@ ZOO_LOG_FILE=zookeeper-$USER-cleanup-$HOSTNAME.log
 
 if [ "x$ZOODATALOGDIR" = "x" ]
 then
-"$JAVA" "-Dzookeeper.log.dir=${ZOO_LOG_DIR}" "-Dzookeeper.root.logger=${ZOO_LOG4J_PROP}" "-Dzookeeper.log.file=${ZOO_LOG_FILE}" \
+"$JAVA" "-Dzookeeper.log.dir=${ZOO_LOG_DIR}" "-Dzookeeper.log.file=${ZOO_LOG_FILE}" \
      -cp "$CLASSPATH" $JVMFLAGS \
      org.apache.zookeeper.server.PurgeTxnLog "$ZOODATADIR" $*
 else
-"$JAVA" "-Dzookeeper.log.dir=${ZOO_LOG_DIR}" "-Dzookeeper.root.logger=${ZOO_LOG4J_PROP}" "-Dzookeeper.log.file=${ZOO_LOG_FILE}" \
+"$JAVA" "-Dzookeeper.log.dir=${ZOO_LOG_DIR}" "-Dzookeeper.log.file=${ZOO_LOG_FILE}" \
      -cp "$CLASSPATH" $JVMFLAGS \
      org.apache.zookeeper.server.PurgeTxnLog "$ZOODATALOGDIR" "$ZOODATADIR" $*
 fi

bin/zkCli.cmd

@@ -20,7 +20,7 @@ call "%~dp0zkEnv.cmd"
 set ZOO_LOG_FILE=zookeeper-%USERNAME%-cli-%COMPUTERNAME%.log
 
 set ZOOMAIN=org.apache.zookeeper.ZooKeeperMain
-call %JAVA% "-Dzookeeper.log.dir=%ZOO_LOG_DIR%" "-Dzookeeper.root.logger=%ZOO_LOG4J_PROP%" "-Dzookeeper.log.file=%ZOO_LOG_FILE%" -cp "%CLASSPATH%" %ZOOMAIN% %*
+call %JAVA% "-Dzookeeper.log.dir=%ZOO_LOG_DIR%" "-Dzookeeper.log.file=%ZOO_LOG_FILE%" -cp "%CLASSPATH%" %ZOOMAIN% %*
 
 endlocal
 

bin/zkCli.sh

@@ -38,6 +38,6 @@ fi
 
 ZOO_LOG_FILE=zookeeper-$USER-cli-$HOSTNAME.log
 
-"$JAVA" "-Dzookeeper.log.dir=${ZOO_LOG_DIR}" "-Dzookeeper.root.logger=${ZOO_LOG4J_PROP}" "-Dzookeeper.log.file=${ZOO_LOG_FILE}" \
+"$JAVA" "-Dzookeeper.log.dir=${ZOO_LOG_DIR}" "-Dzookeeper.log.file=${ZOO_LOG_FILE}" \
      -cp "$CLASSPATH" $CLIENT_JVMFLAGS $JVMFLAGS \
      org.apache.zookeeper.ZooKeeperMain "$@"

bin/zkEnv.cmd

@@ -16,7 +16,6 @@ REM limitations under the License.
 
 set ZOOCFGDIR=%~dp0%..\conf
 set ZOO_LOG_DIR=%~dp0%..\logs
-set ZOO_LOG4J_PROP=INFO,CONSOLE
 
 REM for sanity sake assume Java 1.6
 REM see: http://java.sun.com/javase/6/docs/technotes/tools/windows/java.html

bin/zkEnv.sh

@@ -70,11 +70,6 @@ then
     ZOO_LOG_DIR="$ZOOKEEPER_PREFIX/logs"
 fi
 
-if [ "x${ZOO_LOG4J_PROP}" = "x" ]
-then
-    ZOO_LOG4J_PROP="INFO,CONSOLE"
-fi
-
 if [[ -n "$JAVA_HOME" ]] && [[ -x "$JAVA_HOME/bin/java" ]];  then
     JAVA="$JAVA_HOME/bin/java"
 elif type -p java; then

bin/zkServer.cmd

@@ -21,6 +21,6 @@ set ZOOMAIN=org.apache.zookeeper.server.quorum.QuorumPeerMain
 set ZOO_LOG_FILE=zookeeper-%USERNAME%-server-%COMPUTERNAME%.log
 
 echo on
-call %JAVA% "-Dzookeeper.log.dir=%ZOO_LOG_DIR%" "-Dzookeeper.root.logger=%ZOO_LOG4J_PROP%" "-Dzookeeper.log.file=%ZOO_LOG_FILE%" "-XX:+HeapDumpOnOutOfMemoryError" "-XX:OnOutOfMemoryError=cmd /c taskkill /pid %%%%p /t /f" -cp "%CLASSPATH%" %ZOOMAIN% "%ZOOCFG%" %*
+call %JAVA% "-Dzookeeper.log.dir=%ZOO_LOG_DIR%" "-Dzookeeper.log.file=%ZOO_LOG_FILE%" "-XX:+HeapDumpOnOutOfMemoryError" "-XX:OnOutOfMemoryError=cmd /c taskkill /pid %%%%p /t /f" -cp "%CLASSPATH%" %ZOOMAIN% "%ZOOCFG%" %*
 
 endlocal

bin/zkServer.sh

@@ -162,7 +162,7 @@ start)
       fi
     fi
     nohup "$JAVA" $ZOO_DATADIR_AUTOCREATE "-Dzookeeper.log.dir=${ZOO_LOG_DIR}" \
-    "-Dzookeeper.log.file=${ZOO_LOG_FILE}" "-Dzookeeper.root.logger=${ZOO_LOG4J_PROP}" \
+    "-Dzookeeper.log.file=${ZOO_LOG_FILE}" \
     -XX:+HeapDumpOnOutOfMemoryError -XX:OnOutOfMemoryError='kill -9 %p' \
     -cp "$CLASSPATH" $JVMFLAGS $ZOOMAIN "$ZOOCFG" > "$_ZOO_DAEMON_OUT" 2>&1 < /dev/null &
     if [ $? -eq 0 ]
@@ -200,13 +200,13 @@ start-foreground)
       ZOO_CMD=("$JAVA")
     fi
     "${ZOO_CMD[@]}" $ZOO_DATADIR_AUTOCREATE "-Dzookeeper.log.dir=${ZOO_LOG_DIR}" \
-    "-Dzookeeper.log.file=${ZOO_LOG_FILE}" "-Dzookeeper.root.logger=${ZOO_LOG4J_PROP}" \
+    "-Dzookeeper.log.file=${ZOO_LOG_FILE}" \
     -XX:+HeapDumpOnOutOfMemoryError -XX:OnOutOfMemoryError='kill -9 %p' \
     -cp "$CLASSPATH" $JVMFLAGS $ZOOMAIN "$ZOOCFG"
     ;;
 print-cmd)
     echo "\"$JAVA\" $ZOO_DATADIR_AUTOCREATE -Dzookeeper.log.dir=\"${ZOO_LOG_DIR}\" \
-    -Dzookeeper.log.file=\"${ZOO_LOG_FILE}\" -Dzookeeper.root.logger=\"${ZOO_LOG4J_PROP}\" \
+    -Dzookeeper.log.file=\"${ZOO_LOG_FILE}\" \
     -XX:+HeapDumpOnOutOfMemoryError -XX:OnOutOfMemoryError='kill -9 %p' \
     -cp \"$CLASSPATH\" $JVMFLAGS $ZOOMAIN \"$ZOOCFG\" > \"$_ZOO_DAEMON_OUT\" 2>&1 < /dev/null"
     ;;
@@ -287,7 +287,7 @@ status)
       fi
     fi
     echo "Client port found: $clientPort. Client address: $clientPortAddress. Client SSL: $isSSL."
-    STAT=`"$JAVA" "-Dzookeeper.log.dir=${ZOO_LOG_DIR}" "-Dzookeeper.root.logger=${ZOO_LOG4J_PROP}" "-Dzookeeper.log.file=${ZOO_LOG_FILE}" \
+    STAT=`"$JAVA" "-Dzookeeper.log.dir=${ZOO_LOG_DIR}" "-Dzookeeper.log.file=${ZOO_LOG_FILE}" \
           -cp "$CLASSPATH" $CLIENT_JVMFLAGS $JVMFLAGS org.apache.zookeeper.client.FourLetterWordMain \
           $clientPortAddress $clientPort srvr $isSSL 2> /dev/null    \
           | $GREP Mode`

conf/log4j.properties

@@ -1,82 +0,0 @@
-# Copyright 2012 The Apache Software Foundation
-# 
-# Licensed to the Apache Software Foundation (ASF) under one
-# or more contributor license agreements.  See the NOTICE file
-# distributed with this work for additional information
-# regarding copyright ownership.  The ASF licenses this file
-# to you under the Apache License, Version 2.0 (the
-# "License"); you may not use this file except in compliance
-# with the License.  You may obtain a copy of the License at
-#
-#     http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-
-# Define some default values that can be overridden by system properties
-zookeeper.root.logger=INFO, CONSOLE
-
-zookeeper.console.threshold=INFO
-
-zookeeper.log.dir=.
-zookeeper.log.file=zookeeper.log
-zookeeper.log.threshold=INFO
-zookeeper.log.maxfilesize=256MB
-zookeeper.log.maxbackupindex=20
-
-zookeeper.tracelog.dir=${zookeeper.log.dir}
-zookeeper.tracelog.file=zookeeper_trace.log
-
-log4j.rootLogger=${zookeeper.root.logger}
-
-#
-# console
-# Add "console" to rootlogger above if you want to use this 
-#
-log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender
-log4j.appender.CONSOLE.Threshold=${zookeeper.console.threshold}
-log4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayout
-log4j.appender.CONSOLE.layout.ConversionPattern=%d{ISO8601} [myid:%X{myid}] - %-5p [%t:%C{1}@%L] - %m%n
-
-#
-# Add ROLLINGFILE to rootLogger to get log file output
-#
-log4j.appender.ROLLINGFILE=org.apache.log4j.RollingFileAppender
-log4j.appender.ROLLINGFILE.Threshold=${zookeeper.log.threshold}
-log4j.appender.ROLLINGFILE.File=${zookeeper.log.dir}/${zookeeper.log.file}
-log4j.appender.ROLLINGFILE.MaxFileSize=${zookeeper.log.maxfilesize}
-log4j.appender.ROLLINGFILE.MaxBackupIndex=${zookeeper.log.maxbackupindex}
-log4j.appender.ROLLINGFILE.layout=org.apache.log4j.PatternLayout
-log4j.appender.ROLLINGFILE.layout.ConversionPattern=%d{ISO8601} [myid:%X{myid}] - %-5p [%t:%C{1}@%L] - %m%n
-
-#
-# Add TRACEFILE to rootLogger to get log file output
-#    Log TRACE level and above messages to a log file
-#
-log4j.appender.TRACEFILE=org.apache.log4j.FileAppender
-log4j.appender.TRACEFILE.Threshold=TRACE
-log4j.appender.TRACEFILE.File=${zookeeper.tracelog.dir}/${zookeeper.tracelog.file}
-
-log4j.appender.TRACEFILE.layout=org.apache.log4j.PatternLayout
-### Notice we are including log4j's NDC here (%x)
-log4j.appender.TRACEFILE.layout.ConversionPattern=%d{ISO8601} [myid:%X{myid}] - %-5p [%t:%C{1}@%L][%x] - %m%n
-#
-# zk audit logging
-#
-zookeeper.auditlog.file=zookeeper_audit.log
-zookeeper.auditlog.threshold=INFO
-audit.logger=INFO, RFAAUDIT
-log4j.logger.org.apache.zookeeper.audit.Log4jAuditLogger=${audit.logger}
-log4j.additivity.org.apache.zookeeper.audit.Log4jAuditLogger=false
-log4j.appender.RFAAUDIT=org.apache.log4j.RollingFileAppender
-log4j.appender.RFAAUDIT.File=${zookeeper.log.dir}/${zookeeper.auditlog.file}
-log4j.appender.RFAAUDIT.layout=org.apache.log4j.PatternLayout
-log4j.appender.RFAAUDIT.layout.ConversionPattern=%d{ISO8601} %p %c{2}: %m%n
-log4j.appender.RFAAUDIT.Threshold=${zookeeper.auditlog.threshold}
-
-# Max log file size of 10MB
-log4j.appender.RFAAUDIT.MaxFileSize=10MB
-log4j.appender.RFAAUDIT.MaxBackupIndex=10

conf/logback.xml

@@ -0,0 +1,114 @@
+<!--
+ Copyright 2022 The Apache Software Foundation
+
+ Licensed to the Apache Software Foundation (ASF) under one
+ or more contributor license agreements.  See the NOTICE file
+ distributed with this work for additional information
+ regarding copyright ownership.  The ASF licenses this file
+ to you under the Apache License, Version 2.0 (the
+ "License"); you may not use this file except in compliance
+ with the License.  You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+ Unless required by applicable law or agreed to in writing, software
+ distributed under the License is distributed on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ See the License for the specific language governing permissions and
+ limitations under the License.
+
+ Define some default values that can be overridden by system properties
+-->
+<configuration>
+  <!-- Uncomment this if you would like to expose Logback JMX beans -->
+  <!--jmxConfigurator /-->
+
+  <property name="zookeeper.console.threshold" value="INFO" />
+
+  <property name="zookeeper.log.dir" value="." />
+  <property name="zookeeper.log.file" value="zookeeper.log" />
+  <property name="zookeeper.log.threshold" value="INFO" />
+  <property name="zookeeper.log.maxfilesize" value="256MB" />
+  <property name="zookeeper.log.maxbackupindex" value="20" />
+
+  <!--
+    console
+    Add "console" to root logger if you want to use this
+  -->
+  <appender name="CONSOLE" class="ch.qos.logback.core.ConsoleAppender">
+    <encoder>
+      <pattern>%d{ISO8601} [myid:%X{myid}] - %-5p [%t:%C{1}@%L] - %m%n</pattern>
+    </encoder>
+    <filter class="ch.qos.logback.classic.filter.ThresholdFilter">
+      <level>${zookeeper.console.threshold}</level>
+    </filter>
+  </appender>
+
+  <!--
+    Add ROLLINGFILE to root logger to get log file output
+  -->
+  <!--appender name="ROLLINGFILE" class="ch.qos.logback.core.rolling.RollingFileAppender">
+    <File>${zookeeper.log.dir}/${zookeeper.log.file}</File>
+    <encoder>
+      <pattern>%d{ISO8601} [myid:%X{myid}] - %-5p [%t:%C{1}@%L] - %m%n</pattern>
+    </encoder>
+    <filter class="ch.qos.logback.classic.filter.ThresholdFilter">
+      <level>${zookeeper.log.threshold}</level>
+    </filter>
+    <rollingPolicy class="ch.qos.logback.core.rolling.FixedWindowRollingPolicy">
+      <maxIndex>${zookeeper.log.maxbackupindex}</maxIndex>
+      <FileNamePattern>${zookeeper.log.dir}/${zookeeper.log.file}.%i</FileNamePattern>
+    </rollingPolicy>
+    <triggeringPolicy class="ch.qos.logback.core.rolling.SizeBasedTriggeringPolicy">
+      <MaxFileSize>${zookeeper.log.maxfilesize}</MaxFileSize>
+    </triggeringPolicy>
+  </appender-->
+
+  <!--
+    Add TRACEFILE to root logger to get log file output
+    Log TRACE level and above messages to a log file
+  -->
+  <!--property name="zookeeper.tracelog.dir" value="${zookeeper.log.dir}" />
+  <property name="zookeeper.tracelog.file" value="zookeeper_trace.log" />
+  <appender name="TRACEFILE" class="ch.qos.logback.core.FileAppender">
+    <File>${zookeeper.tracelog.dir}/${zookeeper.tracelog.file}</File>
+    <encoder>
+      <pattern>%d{ISO8601} [myid:%X{myid}] - %-5p [%t:%C{1}@%L] - %m%n</pattern>
+    </encoder>
+    <filter class="ch.qos.logback.classic.filter.ThresholdFilter">
+      <level>TRACE</level>
+    </filter>
+  </appender-->
+
+  <!--
+    zk audit logging
+  -->
+  <!--property name="zookeeper.auditlog.file" value="zookeeper_audit.log" />
+  <property name="zookeeper.auditlog.threshold" value="INFO" />
+  <property name="audit.logger" value="INFO, RFAAUDIT" />
+
+  <appender name="RFAAUDIT" class="ch.qos.logback.core.rolling.RollingFileAppender">
+    <File>${zookeeper.log.dir}/${zookeeper.auditlog.file}</File>
+    <encoder>
+      <pattern>%d{ISO8601} %p %c{2}: %m%n</pattern>
+    </encoder>
+    <filter class="ch.qos.logback.classic.filter.ThresholdFilter">
+      <level>${zookeeper.auditlog.threshold}</level>
+    </filter>
+    <rollingPolicy class="ch.qos.logback.core.rolling.FixedWindowRollingPolicy">
+      <maxIndex>10</maxIndex>
+      <FileNamePattern>${zookeeper.log.dir}/${zookeeper.auditlog.file}.%i</FileNamePattern>
+    </rollingPolicy>
+    <triggeringPolicy class="ch.qos.logback.core.rolling.SizeBasedTriggeringPolicy">
+      <MaxFileSize>10MB</MaxFileSize>
+    </triggeringPolicy>
+  </appender>
+
+  <logger name="org.apache.zookeeper.audit.Slf4jAuditLogger" additivity="false" level="${audit.logger}">
+    <appender-ref ref="RFAAUDIT" />
+  </logger-->
+
+  <root level="INFO">
+    <appender-ref ref="CONSOLE" />
+  </root>
+</configuration>

owaspSuppressions.xml

@@ -41,14 +41,4 @@
            this writing  -->
       <cve>CVE-2019-3826</cve>
    </suppress>
-   <suppress>
-      <!-- false positive for us, it is about log4j server in log4j-1.2.17.jar
-           ZOOKEEPER-3677 -->
-      <cve>CVE-2019-17571</cve>
-   </suppress>
-   <suppress>
-      <!-- it only affects the log4j SmtpAppender users. As Log4J 1.2 is EOL now, we can't fix this unless we
-           upgrade to log4j 2. See ZOOKEEPER-3817 -->
-      <cve>CVE-2020-9488</cve>
-   </suppress>
 </suppressions>

pom.xml

@@ -459,6 +459,7 @@
 
     <!-- dependency versions -->
     <slf4j.version>1.7.30</slf4j.version>
+    <logback-version>1.2.10</logback-version>
     <audience-annotations.version>0.12.0</audience-annotations.version>
     <jmockit.version>1.48</jmockit.version>
     <junit.version>5.6.2</junit.version>
@@ -577,6 +578,16 @@
         <artifactId>log4j</artifactId>
         <version>${log4j.version}</version>
       </dependency>
+      <dependency>
+        <groupId>ch.qos.logback</groupId>
+        <artifactId>logback-core</artifactId>
+        <version>${logback-version}</version>
+      </dependency>
+      <dependency>
+        <groupId>ch.qos.logback</groupId>
+        <artifactId>logback-classic</artifactId>
+        <version>${logback-version}</version>
+      </dependency>
       <dependency>
         <groupId>org.jmockit</groupId>
         <artifactId>jmockit</artifactId>

zookeeper-docs/src/main/resources/markdown/zookeeperAdmin.md

@@ -1,5 +1,5 @@
 <!--
-Copyright 2002-2004 The Apache Software Foundation
+Copyright 2002-2022 The Apache Software Foundation
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -33,7 +33,7 @@ limitations under the License.
     * [Administering](#sc_administering)
     * [Maintenance](#sc_maintenance)
         * [Ongoing Data Directory Cleanup](#Ongoing+Data+Directory+Cleanup)
-        * [Debug Log Cleanup (log4j)](#Debug+Log+Cleanup+%28log4j%29)
+        * [Debug Log Cleanup (logback)](#Debug+Log+Cleanup+Logback)
     * [Supervision](#sc_supervision)
     * [Monitoring](#sc_monitoring)
     * [Logging](#sc_logging)
@@ -436,7 +436,7 @@ in the unlikely event a recent log has become corrupted). This
 can be run as a cron job on the ZooKeeper server machines to
 clean up the logs daily.
 
-    java -cp zookeeper.jar:lib/slf4j-api-1.7.5.jar:lib/slf4j-log4j12-1.7.5.jar:lib/log4j-1.2.17.jar:conf org.apache.zookeeper.server.PurgeTxnLog <dataDir> <snapDir> -n <count>
+    java -cp zookeeper.jar:lib/slf4j-api-1.7.30.jar:lib/logback-classic-1.2.10.jar:lib/logback-core-1.2.10.jar:conf org.apache.zookeeper.server.PurgeTxnLog <dataDir> <snapDir> -n <count>
 
 
 Automatic purging of the snapshots and corresponding
@@ -445,14 +445,14 @@ enabled via the following configuration parameters **autopurge.snapRetainCount**
 this, see [Advanced Configuration](#sc_advancedConfiguration)
 below.
 
-<a name="Debug+Log+Cleanup+%28log4j%29"></a>
+<a name="Debug+Log+Cleanup+Logback"></a>
 
-#### Debug Log Cleanup (log4j)
+#### Debug Log Cleanup (logback)
 
 See the section on [logging](#sc_logging) in this document. It is
 expected that you will setup a rolling file appender using the
-in-built log4j feature. The sample configuration file in the
-release tar's conf/log4j.properties provides an example of
+in-built logback feature. The sample configuration file in the
+release tar's `conf/logback.xml` provides an example of
 this.
 
 <a name="sc_supervision"></a>
@@ -504,22 +504,20 @@ The ZooKeeper service can be monitored in one of three primary ways:
 ### Logging
 
 ZooKeeper uses **[SLF4J](http://www.slf4j.org)**
-version 1.7.5 as its logging infrastructure. For backward compatibility it is bound to
-**LOG4J** but you can use
-**[LOGBack](http://logback.qos.ch/)**
-or any other supported logging framework of your choice.
-
-The ZooKeeper default *log4j.properties*
-file resides in the *conf* directory. Log4j requires that
-*log4j.properties* either be in the working directory
+version 1.7 as its logging infrastructure. By default ZooKeeper is shipped with
+**[LOGBack](http://logback.qos.ch/)** as the logging backend, but you can use
+any other supported logging framework of your choice.
+
+The ZooKeeper default *logback.xml*
+file resides in the *conf* directory. Logback requires that
+*logback.xml* either be in the working directory
 (the directory from which ZooKeeper is run) or be accessible from the classpath.
 
 For more information about SLF4J, see
 [its manual](http://www.slf4j.org/manual.html).
 
-For more information about LOG4J, see
-[Log4j Default Initialization Procedure](http://logging.apache.org/log4j/1.2/manual.html#defaultInit)
-of the log4j manual.
+For more information about Logback, see
+[Logback website](http://logback.qos.ch/).
 
 <a name="sc_troubleshooting"></a>
 
@@ -1141,8 +1139,8 @@ property, when available, is noted below.
 * *audit.impl.class* :
     (Java system property: **zookeeper.audit.impl.class**)
     **New in 3.6.0:**
-    Class to implement the audit logger. By default log4j based audit logger org.apache.zookeeper.audit
-    .Log4jAuditLogger is used.
+    Class to implement the audit logger. By default logback based audit logger org.apache.zookeeper.audit
+    .Slf4jAuditLogger is used.
     See the [ZooKeeper audit logs](zookeeperAuditLogs.html) for more information.
 
 * *largeRequestMaxBytes* :
@@ -2427,7 +2425,7 @@ The output contains multiple lines with the following format:
 * *stmk* :
     Sets the current trace mask.  The trace mask is 64 bits,
     where each bit enables or disables a specific category of trace
-    logging on the server.  Log4J must be configured to enable
+    logging on the server. Logback must be configured to enable
     `TRACE` level first in order to see trace logging
     messages.  The bits of the trace mask correspond to the following
     trace logging categories.

zookeeper-docs/src/main/resources/markdown/zookeeperAuditLogs.md

@@ -1,5 +1,5 @@
 <!--
-Copyright 2002-2004 The Apache Software Foundation
+Copyright 2002-2022 The Apache Software Foundation
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -66,25 +66,36 @@ Below are sample audit logs for all operations, where client is connected from 1
 
 ## ZooKeeper Audit Log Configuration
 
-By default audit logs are disabled. To enable audit logs configure audit.enable=true in conf/zoo.cfg. Audit logging is done using log4j. Following is the default log4j configuration for audit logs in conf/log4j.properties
-
-    #
-    # zk audit logging
-    #
-    zookeeper.auditlog.file=zookeeper_audit.log
-    zookeeper.auditlog.threshold=INFO
-    audit.logger=INFO, RFAAUDIT
-    log4j.logger.org.apache.zookeeper.audit.Log4jAuditLogger=${audit.logger}
-    log4j.additivity.org.apache.zookeeper.audit.Log4jAuditLogger=false
-    log4j.appender.RFAAUDIT=org.apache.log4j.RollingFileAppender
-    log4j.appender.RFAAUDIT.File=${zookeeper.log.dir}/${zookeeper.auditlog.file}
-    log4j.appender.RFAAUDIT.layout=org.apache.log4j.PatternLayout
-    log4j.appender.RFAAUDIT.layout.ConversionPattern=%d{ISO8601} %p %c{2}: %m%n
-    log4j.appender.RFAAUDIT.Threshold=${zookeeper.auditlog.threshold}
+By default audit logs are disabled. To enable audit logs configure `audit.enable=true` in _conf/zoo.cfg_. 
+Audit logging is done using logback. Following is the default logback configuration for audit logs in `conf/logback.xml`
+
+    <!--
+      zk audit logging
+    -->
+    <!--property name="zookeeper.auditlog.file" value="zookeeper_audit.log" />
+    <property name="zookeeper.auditlog.threshold" value="INFO" />
+    <property name="audit.logger" value="INFO, RFAAUDIT" />
+    
+    <appender name="RFAAUDIT" class="ch.qos.logback.core.rolling.RollingFileAppender">
+      <File>${zookeeper.log.dir}/${zookeeper.auditlog.file}</File>
+      <encoder>
+        <pattern>%d{ISO8601} %p %c{2}: %m%n</pattern>
+      </encoder>
+      <filter class="ch.qos.logback.classic.filter.ThresholdFilter">
+        <level>${zookeeper.auditlog.threshold}</level>
+      </filter>
+      <rollingPolicy class="ch.qos.logback.core.rolling.FixedWindowRollingPolicy">
+        <maxIndex>10</maxIndex>
+        <FileNamePattern>${zookeeper.log.dir}/${zookeeper.auditlog.file}.%i</FileNamePattern>
+      </rollingPolicy>
+      <triggeringPolicy class="ch.qos.logback.core.rolling.SizeBasedTriggeringPolicy">
+        <MaxFileSize>10MB</MaxFileSize>
+      </triggeringPolicy>
+    </appender>
     
-    # Max log file size of 10MB
-    log4j.appender.RFAAUDIT.MaxFileSize=10MB
-    log4j.appender.RFAAUDIT.MaxBackupIndex=10
+    <logger name="org.apache.zookeeper.audit.Slf4jAuditLogger" additivity="false" level="${audit.logger}">
+      <appender-ref ref="RFAAUDIT" />
+    </logger-->
 
 Change above configuration to customize the auditlog file, number of backups, max file size, custom audit logger etc.
 

zookeeper-docs/src/main/resources/markdown/zookeeperInternals.md

@@ -1,5 +1,5 @@
 <!--
-Copyright 2002-2004 The Apache Software Foundation
+Copyright 2002-2022 The Apache Software Foundation
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -312,11 +312,12 @@ hierarchy of groups.
 
 ## Logging
 
-Zookeeper uses [slf4j](http://www.slf4j.org/index.html) as an abstraction layer for logging. [log4j](http://logging.apache.org/log4j) in version 1.2 is chosen as the final logging implementation for now.
+Zookeeper uses [slf4j](http://www.slf4j.org/index.html) as an abstraction layer for logging. 
+[Logback](https://logback.qos.ch/) is chosen the logging backend since ZooKeeper version 3.8.0.
 For better embedding support, it is planned in the future to leave the decision of choosing the final logging implementation to the end user.
-Therefore, always use the slf4j api to write log statements in the code, but configure log4j for how to log at runtime.
+Therefore, always use the slf4j api to write log statements in the code, but configure logback for how to log at runtime.
 Note that slf4j has no FATAL level, former messages at FATAL level have been moved to ERROR level.
-For information on configuring log4j for
+For information on configuring logback for
 ZooKeeper, see the [Logging](zookeeperAdmin.html#sc_logging) section
 of the [ZooKeeper Administrator's Guide.](zookeeperAdmin.html)
 

zookeeper-docs/src/main/resources/markdown/zookeeperJMX.md

@@ -1,5 +1,5 @@
 <!--
-Copyright 2002-2004 The Apache Software Foundation
+Copyright 2002-2022 The Apache Software Foundation
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -77,8 +77,17 @@ on the left hand side. Expand this item and depending on how you've
 started the server you will be able to monitor and manage various
 service related features.
 
+#### Logback MBeans registration _(new in 3.8.0)_
+
+Logback is the default logging backend of ZooKeeper since version 3.8.0. 
+It can be configured to register JMX MBeans by adding `<jmxConfigurator />` to _logback.xml_. More
+information can be found on Logback's [website](https://logback.qos.ch/manual/jmxConfig.html).
+
+#### Log4j MBeans _(deprecated)_
+
 Also note that ZooKeeper will register log4j MBeans as
-well. In the same section along the left hand side you will see
+well if log4j1 is configured as the logging backend of SLF4j. 
+In the same section along the left hand side you will see
 "log4j". Expand that to manage log4j through JMX. Of particular
 interest is the ability to dynamically change the logging levels
 used by editing the appender and root thresholds. Log4j MBean

zookeeper-docs/src/main/resources/markdown/zookeeperStarted.md

@@ -1,5 +1,5 @@
 <!--
-Copyright 2002-2004 The Apache Software Foundation
+Copyright 2002-2022 The Apache Software Foundation
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -101,12 +101,12 @@ ZooKeeper:
     bin/zkServer.sh start
 
 
-ZooKeeper logs messages using log4j -- more detail
+ZooKeeper logs messages using _logback_ -- more detail
 available in the
 [Logging](zookeeperProgrammers.html#Logging)
 section of the Programmer's Guide. You will see log messages
 coming to the console (default) and/or a log file depending on
-the log4j configuration.
+the logback configuration.
 
 The steps outlined here run ZooKeeper in standalone mode. There is
 no replication, so if ZooKeeper process fails, the service will go down.
@@ -137,8 +137,7 @@ Once you have connected, you should see something like:
 
 
     Connecting to localhost:2181
-    log4j:WARN No appenders could be found for logger (org.apache.zookeeper.ZooKeeper).
-    log4j:WARN Please initialize the log4j system properly.
+    ...
     Welcome to ZooKeeper!
     JLine support is enabled
     [zkshell: 0]

zookeeper-docs/src/main/resources/markdown/zookeeperTools.md

@@ -1,5 +1,5 @@
 <!--
-Copyright 2002-2021 The Apache Software Foundation
+Copyright 2002-2022 The Apache Software Foundation
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -96,7 +96,6 @@ The environment setting for the ZooKeeper server
 ```bash
 # the setting of log property
 ZOO_LOG_DIR: the directory to store the logs
-ZOO_LOG4J_PROP: the level of logs to print
 ```
 
 <a name="zkCleanup"></a>

zookeeper-metrics-providers/zookeeper-prometheus-metrics/src/test/resources/log4j.properties

@@ -1,65 +0,0 @@
-# Copyright 2012 The Apache Software Foundation
-#
-# Licensed to the Apache Software Foundation (ASF) under one
-# or more contributor license agreements.  See the NOTICE file
-# distributed with this work for additional information
-# regarding copyright ownership.  The ASF licenses this file
-# to you under the Apache License, Version 2.0 (the
-# "License"); you may not use this file except in compliance
-# with the License.  You may obtain a copy of the License at
-#
-#     http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-
-# Define some default values that can be overridden by system properties
-zookeeper.root.logger=INFO, CONSOLE
-
-zookeeper.console.threshold=INFO
-
-zookeeper.log.dir=.
-zookeeper.log.file=zookeeper.log
-zookeeper.log.threshold=INFO
-zookeeper.log.maxfilesize=256MB
-zookeeper.log.maxbackupindex=20
-
-zookeeper.tracelog.dir=${zookeeper.log.dir}
-zookeeper.tracelog.file=zookeeper_trace.log
-
-log4j.rootLogger=${zookeeper.root.logger}
-
-#
-# console
-# Add "console" to rootlogger above if you want to use this
-#
-log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender
-log4j.appender.CONSOLE.Threshold=${zookeeper.console.threshold}
-log4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayout
-log4j.appender.CONSOLE.layout.ConversionPattern=%d{ISO8601} [myid:%X{myid}] - %-5p [%t:%C{1}@%L] - %m%n
-
-#
-# Add ROLLINGFILE to rootLogger to get log file output
-#
-log4j.appender.ROLLINGFILE=org.apache.log4j.RollingFileAppender
-log4j.appender.ROLLINGFILE.Threshold=${zookeeper.log.threshold}
-log4j.appender.ROLLINGFILE.File=${zookeeper.log.dir}/${zookeeper.log.file}
-log4j.appender.ROLLINGFILE.MaxFileSize=${zookeeper.log.maxfilesize}
-log4j.appender.ROLLINGFILE.MaxBackupIndex=${zookeeper.log.maxbackupindex}
-log4j.appender.ROLLINGFILE.layout=org.apache.log4j.PatternLayout
-log4j.appender.ROLLINGFILE.layout.ConversionPattern=%d{ISO8601} [myid:%X{myid}] - %-5p [%t:%C{1}@%L] - %m%n
-
-#
-# Add TRACEFILE to rootLogger to get log file output
-#    Log TRACE level and above messages to a log file
-#
-log4j.appender.TRACEFILE=org.apache.log4j.FileAppender
-log4j.appender.TRACEFILE.Threshold=TRACE
-log4j.appender.TRACEFILE.File=${zookeeper.tracelog.dir}/${zookeeper.tracelog.file}
-
-log4j.appender.TRACEFILE.layout=org.apache.log4j.PatternLayout
-### Notice we are including log4j's NDC here (%x)
-log4j.appender.TRACEFILE.layout.ConversionPattern=%d{ISO8601} [myid:%X{myid}] - %-5p [%t:%C{1}@%L][%x] - %m%n

zookeeper-metrics-providers/zookeeper-prometheus-metrics/src/test/resources/logback.xml

@@ -0,0 +1,36 @@
+<!--
+ Copyright 2022 The Apache Software Foundation
+
+ Licensed to the Apache Software Foundation (ASF) under one
+ or more contributor license agreements.  See the NOTICE file
+ distributed with this work for additional information
+ regarding copyright ownership.  The ASF licenses this file
+ to you under the Apache License, Version 2.0 (the
+ "License"); you may not use this file except in compliance
+ with the License.  You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+ Unless required by applicable law or agreed to in writing, software
+ distributed under the License is distributed on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ See the License for the specific language governing permissions and
+ limitations under the License.
+
+ Define some default values that can be overridden by system properties
+-->
+<configuration>
+
+  <appender name="CONSOLE" class="ch.qos.logback.core.ConsoleAppender">
+    <encoder>
+      <pattern>%d{ISO8601} [myid:%X{myid}] - %-5p [%t:%C{1}@%L] - %m%n</pattern>
+    </encoder>
+    <filter class="ch.qos.logback.classic.filter.ThresholdFilter">
+      <level>INFO</level>
+    </filter>
+  </appender>
+
+  <root level="INFO">
+    <appender-ref ref="CONSOLE" />
+  </root>
+</configuration>

zookeeper-server/pom.xml

@@ -75,8 +75,12 @@
       <artifactId>slf4j-api</artifactId>
     </dependency>
     <dependency>
-      <groupId>org.slf4j</groupId>
-      <artifactId>slf4j-log4j12</artifactId>
+      <groupId>ch.qos.logback</groupId>
+      <artifactId>logback-core</artifactId>
+    </dependency>
+    <dependency>
+      <groupId>ch.qos.logback</groupId>
+      <artifactId>logback-classic</artifactId>
     </dependency>
     <dependency>
       <groupId>org.eclipse.jetty</groupId>
@@ -118,10 +122,6 @@
        <artifactId>metrics-core</artifactId>
        <scope>provided</scope>
     </dependency>
-    <dependency>
-      <groupId>log4j</groupId>
-      <artifactId>log4j</artifactId>
-    </dependency>
     <dependency>
       <groupId>org.apache.kerby</groupId>
       <artifactId>kerb-core</artifactId>

zookeeper-server/src/main/java/org/apache/zookeeper/audit/Log4jAuditLogger.java → zookeeper-server/src/main/java/org/apache/zookeeper/audit/Slf4jAuditLogger.java

@@ -22,10 +22,10 @@ import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 /**
- * Log4j based audit logger
+ * Slf4j based audit logger
  */
-public class Log4jAuditLogger implements AuditLogger {
-    private static final Logger LOG = LoggerFactory.getLogger(Log4jAuditLogger.class);
+public class Slf4jAuditLogger implements AuditLogger {
+    private static final Logger LOG = LoggerFactory.getLogger(Slf4jAuditLogger.class);
 
     @Override
     public void logAuditEvent(AuditEvent auditEvent) {

zookeeper-server/src/main/java/org/apache/zookeeper/audit/ZKAuditProvider.java

@@ -46,7 +46,7 @@ public class ZKAuditProvider {
     private static AuditLogger getAuditLogger() {
         String auditLoggerClass = System.getProperty(AUDIT_IMPL_CLASS);
         if (auditLoggerClass == null) {
-            auditLoggerClass = Log4jAuditLogger.class.getName();
+            auditLoggerClass = Slf4jAuditLogger.class.getName();
         }
         try {
             Constructor<?> clientCxnConstructor = Class.forName(auditLoggerClass)

zookeeper-server/src/main/java/org/apache/zookeeper/server/ZooTrace.java

@@ -27,7 +27,7 @@ import org.slf4j.LoggerFactory;
  * This class encapsulates and centralizes tracing for the ZooKeeper server.
  * Trace messages go to the log with TRACE level.
  * <p>
- * Log4j must be correctly configured to capture the TRACE messages.
+ * Logback must be correctly configured to capture the TRACE messages.
  */
 public class ZooTrace {
 

zookeeper-server/src/main/resources/NOTICE.txt

@@ -81,13 +81,13 @@ framework, which can be obtained at:
   * HOMEPAGE:
     * http://commons.apache.org/logging/
 
-This product optionally depends on 'Apache Log4J', a logging framework,
+This product optionally depends on 'Apache Logback', a logging framework,
 which can be obtained at:
 
   * LICENSE:
-    * license/LICENSE.log4j.txt (Apache License 2.0)
+    * license/LICENSE.logback.txt (Eclipse Public License 1.0)
   * HOMEPAGE:
-    * http://logging.apache.org/log4j/
+    * https://logback.qos.ch/
 
 This product optionally depends on 'JBoss Logging', a logging framework,
 which can be obtained at:

zookeeper-server/src/main/resources/lib/log4j-1.2.17.LICENSE.txt

@@ -1,202 +0,0 @@
-
-                                 Apache License
-                           Version 2.0, January 2004
-                        http://www.apache.org/licenses/
-
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-      outstanding shares, or (iii) beneficial ownership of such entity.
-
-      "You" (or "Your") shall mean an individual or Legal Entity
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zookeeper-server/src/main/resources/lib/logback-classic-1.2.10.LICENSE.txt

@@ -0,0 +1,414 @@
+This program and the accompanying materials are made available under the
+terms of the Eclipse Public License 2.0 which is available at
+http://www.eclipse.org/legal/epl-2.0, or the Apache Software License
+2.0 which is available at https://www.apache.org/licenses/LICENSE-2.0.
+
+
+
+Eclipse Public License - v 1.0
+
+THE ACCOMPANYING PROGRAM IS PROVIDED UNDER THE TERMS OF THIS ECLIPSE PUBLIC
+LICENSE ("AGREEMENT"). ANY USE, REPRODUCTION OR DISTRIBUTION OF THE PROGRAM
+CONSTITUTES RECIPIENT'S ACCEPTANCE OF THIS AGREEMENT.
+
+1. DEFINITIONS
+
+"Contribution" means:
+
+a) in the case of the initial Contributor, the initial code and documentation
+   distributed under this Agreement, and
+b) in the case of each subsequent Contributor:
+    i) changes to the Program, and
+   ii) additions to the Program;
+
+   where such changes and/or additions to the Program originate from and are
+   distributed by that particular Contributor. A Contribution 'originates'
+   from a Contributor if it was added to the Program by such Contributor
+   itself or anyone acting on such Contributor's behalf. Contributions do not
+   include additions to the Program which: (i) are separate modules of
+   software distributed in conjunction with the Program under their own
+   license agreement, and (ii) are not derivative works of the Program.
+
+"Contributor" means any person or entity that distributes the Program.
+
+"Licensed Patents" mean patent claims licensable by a Contributor which are
+necessarily infringed by the use or sale of its Contribution alone or when
+combined with the Program.
+
+"Program" means the Contributions distributed in accordance with this
+Agreement.
+
+"Recipient" means anyone who receives the Program under this Agreement,
+including all Contributors.
+
+2. GRANT OF RIGHTS
+  a) Subject to the terms of this Agreement, each Contributor hereby grants
+     Recipient a non-exclusive, worldwide, royalty-free copyright license to
+     reproduce, prepare derivative works of, publicly display, publicly
+     perform, distribute and sublicense the Contribution of such Contributor,
+     if any, and such derivative works, in source code and object code form.
+  b) Subject to the terms of this Agreement, each Contributor hereby grants
+     Recipient a non-exclusive, worldwide, royalty-free patent license under
+     Licensed Patents to make, use, sell, offer to sell, import and otherwise
+     transfer the Contribution of such Contributor, if any, in source code and
+     object code form. This patent license shall apply to the combination of
+     the Contribution and the Program if, at the time the Contribution is
+     added by the Contributor, such addition of the Contribution causes such
+     combination to be covered by the Licensed Patents. The patent license
+     shall not apply to any other combinations which include the Contribution.
+     No hardware per se is licensed hereunder.
+  c) Recipient understands that although each Contributor grants the licenses
+     to its Contributions set forth herein, no assurances are provided by any
+     Contributor that the Program does not infringe the patent or other
+     intellectual property rights of any other entity. Each Contributor
+     disclaims any liability to Recipient for claims brought by any other
+     entity based on infringement of intellectual property rights or
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+     any other intellectual property rights needed, if any. For example, if a
+     third party patent license is required to allow Recipient to distribute
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+     copyright rights in its Contribution, if any, to grant the copyright
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+4. COMMERCIAL DISTRIBUTION
+
+Commercial distributors of software may accept certain responsibilities with
+respect to end users, business partners and the like. While this license is
+intended to facilitate the commercial use of the Program, the Contributor who
+includes the Program in a commercial product offering should do so in a manner
+which does not create potential liability for other Contributors. Therefore,
+if a Contributor includes the Program in a commercial product offering, such
+Contributor ("Commercial Contributor") hereby agrees to defend and indemnify
+every other Contributor ("Indemnified Contributor") against any losses,
+damages and costs (collectively "Losses") arising from claims, lawsuits and
+other legal actions brought by a third party against the Indemnified
+Contributor to the extent caused by the acts or omissions of such Commercial
+Contributor in connection with its distribution of the Program in a commercial
+product offering. The obligations in this section do not apply to any claims
+or Losses relating to any actual or alleged intellectual property
+infringement. In order to qualify, an Indemnified Contributor must:
+a) promptly notify the Commercial Contributor in writing of such claim, and
+b) allow the Commercial Contributor to control, and cooperate with the
+Commercial Contributor in, the defense and any related settlement
+negotiations. The Indemnified Contributor may participate in any such claim at
+its own expense.
+
+For example, a Contributor might include the Program in a commercial product
+offering, Product X. That Contributor is then a Commercial Contributor. If
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zookeeper-server/src/main/resources/lib/logback-core-1.2.10.LICENSE.txt

@@ -0,0 +1,414 @@
+This program and the accompanying materials are made available under the
+terms of the Eclipse Public License 2.0 which is available at
+http://www.eclipse.org/legal/epl-2.0, or the Apache Software License
+2.0 which is available at https://www.apache.org/licenses/LICENSE-2.0.
+
+
+
+Eclipse Public License - v 1.0
+
+THE ACCOMPANYING PROGRAM IS PROVIDED UNDER THE TERMS OF THIS ECLIPSE PUBLIC
+LICENSE ("AGREEMENT"). ANY USE, REPRODUCTION OR DISTRIBUTION OF THE PROGRAM
+CONSTITUTES RECIPIENT'S ACCEPTANCE OF THIS AGREEMENT.
+
+1. DEFINITIONS
+
+"Contribution" means:
+
+a) in the case of the initial Contributor, the initial code and documentation
+   distributed under this Agreement, and
+b) in the case of each subsequent Contributor:
+    i) changes to the Program, and
+   ii) additions to the Program;
+
+   where such changes and/or additions to the Program originate from and are
+   distributed by that particular Contributor. A Contribution 'originates'
+   from a Contributor if it was added to the Program by such Contributor
+   itself or anyone acting on such Contributor's behalf. Contributions do not
+   include additions to the Program which: (i) are separate modules of
+   software distributed in conjunction with the Program under their own
+   license agreement, and (ii) are not derivative works of the Program.
+
+"Contributor" means any person or entity that distributes the Program.
+
+"Licensed Patents" mean patent claims licensable by a Contributor which are
+necessarily infringed by the use or sale of its Contribution alone or when
+combined with the Program.
+
+"Program" means the Contributions distributed in accordance with this
+Agreement.
+
+"Recipient" means anyone who receives the Program under this Agreement,
+including all Contributors.
+
+2. GRANT OF RIGHTS
+  a) Subject to the terms of this Agreement, each Contributor hereby grants
+     Recipient a non-exclusive, worldwide, royalty-free copyright license to
+     reproduce, prepare derivative works of, publicly display, publicly
+     perform, distribute and sublicense the Contribution of such Contributor,
+     if any, and such derivative works, in source code and object code form.
+  b) Subject to the terms of this Agreement, each Contributor hereby grants
+     Recipient a non-exclusive, worldwide, royalty-free patent license under
+     Licensed Patents to make, use, sell, offer to sell, import and otherwise
+     transfer the Contribution of such Contributor, if any, in source code and
+     object code form. This patent license shall apply to the combination of
+     the Contribution and the Program if, at the time the Contribution is
+     added by the Contributor, such addition of the Contribution causes such
+     combination to be covered by the Licensed Patents. The patent license
+     shall not apply to any other combinations which include the Contribution.
+     No hardware per se is licensed hereunder.
+  c) Recipient understands that although each Contributor grants the licenses
+     to its Contributions set forth herein, no assurances are provided by any
+     Contributor that the Program does not infringe the patent or other
+     intellectual property rights of any other entity. Each Contributor
+     disclaims any liability to Recipient for claims brought by any other
+     entity based on infringement of intellectual property rights or
+     otherwise. As a condition to exercising the rights and licenses granted
+     hereunder, each Recipient hereby assumes sole responsibility to secure
+     any other intellectual property rights needed, if any. For example, if a
+     third party patent license is required to allow Recipient to distribute
+     the Program, it is Recipient's responsibility to acquire that license
+     before distributing the Program.
+  d) Each Contributor represents that to its knowledge it has sufficient
+     copyright rights in its Contribution, if any, to grant the copyright
+     license set forth in this Agreement.
+
+3. REQUIREMENTS
+
+A Contributor may choose to distribute the Program in object code form under
+its own license agreement, provided that:
+
+  a) it complies with the terms and conditions of this Agreement; and
+  b) its license agreement:
+      i) effectively disclaims on behalf of all Contributors all warranties
+         and conditions, express and implied, including warranties or
+         conditions of title and non-infringement, and implied warranties or
+         conditions of merchantability and fitness for a particular purpose;
+     ii) effectively excludes on behalf of all Contributors all liability for
+         damages, including direct, indirect, special, incidental and
+         consequential damages, such as lost profits;
+    iii) states that any provisions which differ from this Agreement are
+         offered by that Contributor alone and not by any other party; and
+     iv) states that source code for the Program is available from such
+         Contributor, and informs licensees how to obtain it in a reasonable
+         manner on or through a medium customarily used for software exchange.
+
+When the Program is made available in source code form:
+
+  a) it must be made available under this Agreement; and
+  b) a copy of this Agreement must be included with each copy of the Program.
+     Contributors may not remove or alter any copyright notices contained
+     within the Program.
+
+Each Contributor must identify itself as the originator of its Contribution,
+if
+any, in a manner that reasonably allows subsequent Recipients to identify the
+originator of the Contribution.
+
+4. COMMERCIAL DISTRIBUTION
+
+Commercial distributors of software may accept certain responsibilities with
+respect to end users, business partners and the like. While this license is
+intended to facilitate the commercial use of the Program, the Contributor who
+includes the Program in a commercial product offering should do so in a manner
+which does not create potential liability for other Contributors. Therefore,
+if a Contributor includes the Program in a commercial product offering, such
+Contributor ("Commercial Contributor") hereby agrees to defend and indemnify
+every other Contributor ("Indemnified Contributor") against any losses,
+damages and costs (collectively "Losses") arising from claims, lawsuits and
+other legal actions brought by a third party against the Indemnified
+Contributor to the extent caused by the acts or omissions of such Commercial
+Contributor in connection with its distribution of the Program in a commercial
+product offering. The obligations in this section do not apply to any claims
+or Losses relating to any actual or alleged intellectual property
+infringement. In order to qualify, an Indemnified Contributor must:
+a) promptly notify the Commercial Contributor in writing of such claim, and
+b) allow the Commercial Contributor to control, and cooperate with the
+Commercial Contributor in, the defense and any related settlement
+negotiations. The Indemnified Contributor may participate in any such claim at
+its own expense.
+
+For example, a Contributor might include the Program in a commercial product
+offering, Product X. That Contributor is then a Commercial Contributor. If
+that Commercial Contributor then makes performance claims, or offers
+warranties related to Product X, those performance claims and warranties are
+such Commercial Contributor's responsibility alone. Under this section, the
+Commercial Contributor would have to defend claims against the other
+Contributors related to those performance claims and warranties, and if a
+court requires any other Contributor to pay any damages as a result, the
+Commercial Contributor must pay those damages.
+
+5. NO WARRANTY
+
+EXCEPT AS EXPRESSLY SET FORTH IN THIS AGREEMENT, THE PROGRAM IS PROVIDED ON AN
+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, EITHER EXPRESS OR
+IMPLIED INCLUDING, WITHOUT LIMITATION, ANY WARRANTIES OR CONDITIONS OF TITLE,
+NON-INFRINGEMENT, MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Each
+Recipient is solely responsible for determining the appropriateness of using
+and distributing the Program and assumes all risks associated with its
+exercise of rights under this Agreement , including but not limited to the
+risks and costs of program errors, compliance with applicable laws, damage to
+or loss of data, programs or equipment, and unavailability or interruption of
+operations.
+
+6. DISCLAIMER OF LIABILITY
+
+EXCEPT AS EXPRESSLY SET FORTH IN THIS AGREEMENT, NEITHER RECIPIENT NOR ANY
+CONTRIBUTORS SHALL HAVE ANY LIABILITY FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING WITHOUT LIMITATION
+LOST PROFITS), HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ARISING IN ANY WAY OUT OF THE USE OR DISTRIBUTION OF THE PROGRAM OR THE
+EXERCISE OF ANY RIGHTS GRANTED HEREUNDER, EVEN IF ADVISED OF THE POSSIBILITY
+OF SUCH DAMAGES.
+
+7. GENERAL
+
+If any provision of this Agreement is invalid or unenforceable under
+applicable law, it shall not affect the validity or enforceability of the
+remainder of the terms of this Agreement, and without further action by the
+parties hereto, such provision shall be reformed to the minimum extent
+necessary to make such provision valid and enforceable.
+
+If Recipient institutes patent litigation against any entity (including a
+cross-claim or counterclaim in a lawsuit) alleging that the Program itself
+(excluding combinations of the Program with other software or hardware)
+infringes such Recipient's patent(s), then such Recipient's rights granted
+under Section 2(b) shall terminate as of the date such litigation is filed.
+
+All Recipient's rights under this Agreement shall terminate if it fails to
+comply with any of the material terms or conditions of this Agreement and does
+not cure such failure in a reasonable period of time after becoming aware of
+such noncompliance. If all Recipient's rights under this Agreement terminate,
+Recipient agrees to cease use and distribution of the Program as soon as
+reasonably practicable. However, Recipient's obligations under this Agreement
+and any licenses granted by Recipient relating to the Program shall continue
+and survive.
+
+Everyone is permitted to copy and distribute copies of this Agreement, but in
+order to avoid inconsistency the Agreement is copyrighted and may only be
+modified in the following manner. The Agreement Steward reserves the right to
+publish new versions (including revisions) of this Agreement from time to
+time. No one other than the Agreement Steward has the right to modify this
+Agreement. The Eclipse Foundation is the initial Agreement Steward. The
+Eclipse Foundation may assign the responsibility to serve as the Agreement
+Steward to a suitable separate entity. Each new version of the Agreement will
+be given a distinguishing version number. The Program (including
+Contributions) may always be distributed subject to the version of the
+Agreement under which it was received. In addition, after a new version of the
+Agreement is published, Contributor may elect to distribute the Program
+(including its Contributions) under the new version. Except as expressly
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zookeeper-server/src/test/java/org/apache/zookeeper/audit/Log4jAuditLoggerTest.java → zookeeper-server/src/test/java/org/apache/zookeeper/audit/Slf4JAuditLoggerTest.java

@@ -19,6 +19,7 @@ package org.apache.zookeeper.audit;
 
 import static org.apache.zookeeper.test.ClientBase.CONNECTION_TIMEOUT;
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.io.LineNumberReader;
@@ -27,11 +28,6 @@ import java.net.InetAddress;
 import java.net.InetSocketAddress;
 import java.util.ArrayList;
 import java.util.List;
-import org.apache.log4j.Layout;
-import org.apache.log4j.Level;
-import org.apache.log4j.Logger;
-import org.apache.log4j.SimpleLayout;
-import org.apache.log4j.WriterAppender;
 import org.apache.zookeeper.CreateMode;
 import org.apache.zookeeper.KeeperException;
 import org.apache.zookeeper.KeeperException.Code;
@@ -48,33 +44,28 @@ import org.apache.zookeeper.server.ServerCnxn;
 import org.apache.zookeeper.server.quorum.QuorumPeerTestBase;
 import org.apache.zookeeper.test.ClientBase;
 import org.apache.zookeeper.test.ClientBase.CountdownWatcher;
+import org.apache.zookeeper.test.LoggerTestTool;
 import org.junit.jupiter.api.AfterAll;
 import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.BeforeAll;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
-
-public class Log4jAuditLoggerTest extends QuorumPeerTestBase {
-    private static final Logger LOG = Logger.getLogger(Log4jAuditLoggerTest.class);
+public class Slf4JAuditLoggerTest extends QuorumPeerTestBase {
+    private static final Logger LOG = LoggerFactory.getLogger(Slf4JAuditLoggerTest.class);
     private static int SERVER_COUNT = 3;
     private static MainThread[] mt;
     private static ZooKeeper zk;
-    private static Logger zlogger;
-    private static WriterAppender appender;
     private static ByteArrayOutputStream os;
 
     @BeforeAll
     public static void setUpBeforeClass() throws Exception {
         System.setProperty(ZKAuditProvider.AUDIT_ENABLE, "true");
         // setup the logger to capture all logs
-        Layout layout = new SimpleLayout();
-        os = new ByteArrayOutputStream();
-        appender = new WriterAppender(layout, os);
-        appender.setImmediateFlush(true);
-        appender.setThreshold(Level.INFO);
-        zlogger = Logger.getLogger(Log4jAuditLogger.class);
-        zlogger.addAppender(appender);
+        LoggerTestTool loggerTestTool = new LoggerTestTool(Slf4jAuditLogger.class);
+        os = loggerTestTool.getOutputStream();
         mt = startQuorum();
         zk = ClientBase.createZKClient("127.0.0.1:" + mt[0].getQuorumPeer().getClientPort());
         //Verify start audit log here itself
@@ -322,8 +313,7 @@ public class Log4jAuditLoggerTest extends QuorumPeerTestBase {
         String searchString = " - ";
         int logStartIndex = log.indexOf(searchString);
         String auditLog = log.substring(logStartIndex + searchString.length());
-        assertEquals(expectedLog, auditLog);
-
+        assertTrue(auditLog.endsWith(expectedLog));
     }
 
     private static void verifyLogs(String expectedLog, List<String> logs) {
@@ -428,12 +418,5 @@ public class Log4jAuditLoggerTest extends QuorumPeerTestBase {
                 e.printStackTrace();
             }
         }
-        try {
-            zlogger.removeAppender(appender);
-            os.close();
-        } catch (IOException e) {
-            e.printStackTrace();
-        }
     }
-
 }

zookeeper-server/src/test/java/org/apache/zookeeper/audit/StandaloneServerAuditTest.java

@@ -18,7 +18,6 @@
 
 package org.apache.zookeeper.audit;
 
-
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 import java.io.ByteArrayOutputStream;
@@ -27,36 +26,24 @@ import java.io.LineNumberReader;
 import java.io.StringReader;
 import java.util.ArrayList;
 import java.util.List;
-import org.apache.log4j.Layout;
-import org.apache.log4j.Level;
-import org.apache.log4j.Logger;
-import org.apache.log4j.SimpleLayout;
-import org.apache.log4j.WriterAppender;
 import org.apache.zookeeper.CreateMode;
 import org.apache.zookeeper.KeeperException;
 import org.apache.zookeeper.ZooDefs;
 import org.apache.zookeeper.ZooKeeper;
 import org.apache.zookeeper.test.ClientBase;
+import org.apache.zookeeper.test.LoggerTestTool;
 import org.junit.jupiter.api.AfterAll;
 import org.junit.jupiter.api.BeforeAll;
 import org.junit.jupiter.api.Test;
 
-
-
 public class StandaloneServerAuditTest extends ClientBase {
     private static ByteArrayOutputStream os;
 
     @BeforeAll
     public static void setup() {
         System.setProperty(ZKAuditProvider.AUDIT_ENABLE, "true");
-        // setup the logger to capture all the logs
-        Layout layout = new SimpleLayout();
-        os = new ByteArrayOutputStream();
-        WriterAppender appender = new WriterAppender(layout, os);
-        appender.setImmediateFlush(true);
-        appender.setThreshold(Level.INFO);
-        Logger zLogger = Logger.getLogger(Log4jAuditLogger.class);
-        zLogger.addAppender(appender);
+        LoggerTestTool loggerTestTool = new LoggerTestTool(Slf4jAuditLogger.class);
+        os = loggerTestTool.getOutputStream();
     }
 
     @AfterAll

zookeeper-server/src/test/java/org/apache/zookeeper/server/quorum/QuorumPeerMainTest.java

@@ -47,10 +47,6 @@ import java.util.concurrent.TimeoutException;
 import java.util.regex.Pattern;
 import javax.security.sasl.SaslException;
 import org.apache.commons.io.FileUtils;
-import org.apache.log4j.Level;
-import org.apache.log4j.Logger;
-import org.apache.log4j.PatternLayout;
-import org.apache.log4j.WriterAppender;
 import org.apache.zookeeper.CreateMode;
 import org.apache.zookeeper.KeeperException;
 import org.apache.zookeeper.PortAssignment;
@@ -66,6 +62,7 @@ import org.apache.zookeeper.server.ServerMetrics;
 import org.apache.zookeeper.server.persistence.FileTxnSnapLog;
 import org.apache.zookeeper.server.quorum.Leader.Proposal;
 import org.apache.zookeeper.test.ClientBase;
+import org.apache.zookeeper.test.LoggerTestTool;
 import org.junit.jupiter.api.Test;
 
 /**
@@ -339,13 +336,7 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
      * @throws InterruptedException
      */
     @Test
-    public void testElectionFraud() throws IOException, InterruptedException {
-        // capture QuorumPeer logging
-        ByteArrayOutputStream os = new ByteArrayOutputStream();
-        WriterAppender appender = getConsoleAppender(os, Level.INFO);
-        Logger qlogger = Logger.getLogger(QuorumPeer.class);
-        qlogger.addAppender(appender);
-
+    public void testElectionFraud() throws Exception {
         numServers = 3;
 
         // used for assertions later
@@ -353,7 +344,9 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
         boolean foundLooking = false;
         boolean foundFollowing = false;
 
-        try {
+        try (LoggerTestTool loggerTestTool = new LoggerTestTool(QuorumPeer.class)) {
+            ByteArrayOutputStream os = loggerTestTool.getOutputStream();
+
             // spin up a quorum, we use a small ticktime to make the test run faster
             servers = LaunchServers(numServers, 500);
 
@@ -411,8 +404,6 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
                     break;
                 }
             }
-        } finally {
-            qlogger.removeAppender(appender);
         }
 
         assertTrue(foundLeading, "falseLeader never attempts to become leader");
@@ -427,13 +418,9 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
     public void testBadPeerAddressInQuorum() throws Exception {
         ClientBase.setupTestEnv();
 
-        // setup the logger to capture all logs
-        ByteArrayOutputStream os = new ByteArrayOutputStream();
-        WriterAppender appender = getConsoleAppender(os, Level.WARN);
-        Logger qlogger = Logger.getLogger("org.apache.zookeeper.server.quorum");
-        qlogger.addAppender(appender);
+        try (LoggerTestTool loggerTestTool = new LoggerTestTool("org.apache.zookeeper.server.quorum")) {
+            ByteArrayOutputStream os = loggerTestTool.getOutputStream();
 
-        try {
             final int CLIENT_PORT_QP1 = PortAssignment.unique();
             final int CLIENT_PORT_QP2 = PortAssignment.unique();
 
@@ -452,21 +439,18 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
             assertTrue(ClientBase.waitForServerDown("127.0.0.1:" + CLIENT_PORT_QP1, ClientBase.CONNECTION_TIMEOUT),
                     "waiting for server 1 down");
 
-        } finally {
-            qlogger.removeAppender(appender);
-        }
-
-        LineNumberReader r = new LineNumberReader(new StringReader(os.toString()));
-        String line;
-        boolean found = false;
-        Pattern p = Pattern.compile(".*Cannot open channel to .* at election address .*");
-        while ((line = r.readLine()) != null) {
-            found = p.matcher(line).matches();
-            if (found) {
-                break;
+            LineNumberReader r = new LineNumberReader(new StringReader(os.toString()));
+            String line;
+            boolean found = false;
+            Pattern p = Pattern.compile(".*Cannot open channel to .* at election address .*");
+            while ((line = r.readLine()) != null) {
+                found = p.matcher(line).matches();
+                if (found) {
+                    break;
+                }
             }
+            assertTrue(found, "complains about host");
         }
-        assertTrue(found, "complains about host");
     }
 
     /**
@@ -476,15 +460,11 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
     public void testInconsistentPeerType() throws Exception {
         ClientBase.setupTestEnv();
 
-        // setup the logger to capture all logs
-        ByteArrayOutputStream os = new ByteArrayOutputStream();
-        WriterAppender appender = getConsoleAppender(os, Level.INFO);
-        Logger qlogger = Logger.getLogger("org.apache.zookeeper.server.quorum");
-        qlogger.addAppender(appender);
-
         // test the most likely situation only: server is stated as observer in
         // servers list, but there's no "peerType=observer" token in config
-        try {
+        try (LoggerTestTool loggerTestTool = new LoggerTestTool("org.apache.zookeeper.server.quorum")) {
+            ByteArrayOutputStream os = loggerTestTool.getOutputStream();
+
             final int CLIENT_PORT_QP1 = PortAssignment.unique();
             final int CLIENT_PORT_QP2 = PortAssignment.unique();
             final int CLIENT_PORT_QP3 = PortAssignment.unique();
@@ -518,28 +498,25 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
             assertTrue(ClientBase.waitForServerDown("127.0.0.1:" + CLIENT_PORT_QP3, ClientBase.CONNECTION_TIMEOUT),
                     "waiting for server 3 down");
 
-        } finally {
-            qlogger.removeAppender(appender);
-        }
-
-        LineNumberReader r = new LineNumberReader(new StringReader(os.toString()));
-        String line;
-        boolean warningPresent = false;
-        boolean defaultedToObserver = false;
-        Pattern pWarn = Pattern.compile(".*Peer type from servers list.* doesn't match peerType.*");
-        Pattern pObserve = Pattern.compile(".*OBSERVING.*");
-        while ((line = r.readLine()) != null) {
-            if (pWarn.matcher(line).matches()) {
-                warningPresent = true;
-            }
-            if (pObserve.matcher(line).matches()) {
-                defaultedToObserver = true;
-            }
-            if (warningPresent && defaultedToObserver) {
-                break;
+            LineNumberReader r = new LineNumberReader(new StringReader(os.toString()));
+            String line;
+            boolean warningPresent = false;
+            boolean defaultedToObserver = false;
+            Pattern pWarn = Pattern.compile(".*Peer type from servers list.* doesn't match peerType.*");
+            Pattern pObserve = Pattern.compile(".*OBSERVING.*");
+            while ((line = r.readLine()) != null) {
+                if (pWarn.matcher(line).matches()) {
+                    warningPresent = true;
+                }
+                if (pObserve.matcher(line).matches()) {
+                    defaultedToObserver = true;
+                }
+                if (warningPresent && defaultedToObserver) {
+                    break;
+                }
             }
+            assertTrue(warningPresent && defaultedToObserver, "Should warn about inconsistent peer type");
         }
-        assertTrue(warningPresent && defaultedToObserver, "Should warn about inconsistent peer type");
     }
 
     /**
@@ -597,14 +574,9 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
     public void testQuorumDefaults() throws Exception {
         ClientBase.setupTestEnv();
 
-        // setup the logger to capture all logs
-        ByteArrayOutputStream os = new ByteArrayOutputStream();
-        WriterAppender appender = getConsoleAppender(os, Level.INFO);
-        appender.setImmediateFlush(true);
-        Logger zlogger = Logger.getLogger("org.apache.zookeeper");
-        zlogger.addAppender(appender);
+        try (LoggerTestTool loggerTestTool = new LoggerTestTool("org.apache.zookeeper")) {
+            ByteArrayOutputStream os = loggerTestTool.getOutputStream();
 
-        try {
             final int CLIENT_PORT_QP1 = PortAssignment.unique();
             final int CLIENT_PORT_QP2 = PortAssignment.unique();
 
@@ -629,21 +601,19 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
             assertTrue(ClientBase.waitForServerDown("127.0.0.1:" + CLIENT_PORT_QP2, ClientBase.CONNECTION_TIMEOUT),
                     "waiting for server 2 down");
 
-        } finally {
-            zlogger.removeAppender(appender);
-        }
-        os.close();
-        LineNumberReader r = new LineNumberReader(new StringReader(os.toString()));
-        String line;
-        boolean found = false;
-        Pattern p = Pattern.compile(".*FastLeaderElection.*");
-        while ((line = r.readLine()) != null) {
-            found = p.matcher(line).matches();
-            if (found) {
-                break;
+            os.close();
+            LineNumberReader r = new LineNumberReader(new StringReader(os.toString()));
+            String line;
+            boolean found = false;
+            Pattern p = Pattern.compile(".*FastLeaderElection.*");
+            while ((line = r.readLine()) != null) {
+                found = p.matcher(line).matches();
+                if (found) {
+                    break;
+                }
             }
+            assertTrue(found, "fastleaderelection used");
         }
-        assertTrue(found, "fastleaderelection used");
     }
 
     /**
@@ -858,13 +828,8 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
         boolean foundLeading = false;
         boolean foundFollowing = false;
 
-        // capture QuorumPeer logging
-        ByteArrayOutputStream os = new ByteArrayOutputStream();
-        WriterAppender appender = getConsoleAppender(os, Level.DEBUG);
-        Logger qlogger = Logger.getLogger("org.apache.zookeeper.server.quorum");
-        qlogger.addAppender(appender);
-
-        try {
+        try (LoggerTestTool loggerTestTool = new LoggerTestTool(QuorumPeerMainTest.class)) {
+            ByteArrayOutputStream os = loggerTestTool.getOutputStream();
             Servers svrs = new Servers();
             svrs.clientPorts = new int[numServers];
             for (int i = 0; i < numServers; i++) {
@@ -944,8 +909,6 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
                     "Corrupt peer should not attempt connection to out of view leader");
             }
 
-        } finally {
-            qlogger.removeAppender(appender);
         }
     }
 
@@ -995,13 +958,6 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
 
     }
 
-    private WriterAppender getConsoleAppender(ByteArrayOutputStream os, Level level) {
-        String loggingPattern = ((PatternLayout) Logger.getRootLogger().getAppender("CONSOLE").getLayout()).getConversionPattern();
-        WriterAppender appender = new WriterAppender(new PatternLayout(loggingPattern), os);
-        appender.setThreshold(level);
-        return appender;
-    }
-
     private String getUniquePortCfgForId(int id) {
         return String.format("server.%d=127.0.0.1:%d:%d", id, PortAssignment.unique(), PortAssignment.unique());
     }
@@ -1291,44 +1247,34 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
         ClientBase.setupTestEnv();
         BaseTestMetricsProvider.MetricsProviderCapturingLifecycle.reset();
 
-        // setup the logger to capture all logs
-        ByteArrayOutputStream os = new ByteArrayOutputStream();
-        WriterAppender appender = getConsoleAppender(os, Level.WARN);
-        Logger qlogger = Logger.getLogger("org.apache.zookeeper.server.quorum");
-        qlogger.addAppender(appender);
-
-        try {
-            final int CLIENT_PORT_QP1 = PortAssignment.unique();
-            final int CLIENT_PORT_QP2 = PortAssignment.unique();
+        final int CLIENT_PORT_QP1 = PortAssignment.unique();
+        final int CLIENT_PORT_QP2 = PortAssignment.unique();
 
-            String quorumCfgSectionServer = "server.1=127.0.0.1:" + PortAssignment.unique() + ":" + PortAssignment.unique() + ";" + CLIENT_PORT_QP1
-                                            + "\nserver.2=127.0.0.1:" + PortAssignment.unique() + ":" + PortAssignment.unique() + ";" + CLIENT_PORT_QP2 + "\n";
+        String quorumCfgSectionServer = "server.1=127.0.0.1:" + PortAssignment.unique() + ":" + PortAssignment.unique() + ";" + CLIENT_PORT_QP1
+                                        + "\nserver.2=127.0.0.1:" + PortAssignment.unique() + ":" + PortAssignment.unique() + ";" + CLIENT_PORT_QP2 + "\n";
 
-            // server 1 boots with a MetricsProvider
-            String quorumCfgSectionServer1 = quorumCfgSectionServer
-                                             + "metricsProvider.className=" + BaseTestMetricsProvider.MetricsProviderCapturingLifecycle.class.getName() + "\n";
+        // server 1 boots with a MetricsProvider
+        String quorumCfgSectionServer1 = quorumCfgSectionServer
+                                         + "metricsProvider.className=" + BaseTestMetricsProvider.MetricsProviderCapturingLifecycle.class.getName() + "\n";
 
-            MainThread q1 = new MainThread(1, CLIENT_PORT_QP1, quorumCfgSectionServer1);
-            MainThread q2 = new MainThread(2, CLIENT_PORT_QP2, quorumCfgSectionServer);
-            q1.start();
-            q2.start();
+        MainThread q1 = new MainThread(1, CLIENT_PORT_QP1, quorumCfgSectionServer1);
+        MainThread q2 = new MainThread(2, CLIENT_PORT_QP2, quorumCfgSectionServer);
+        q1.start();
+        q2.start();
 
-            boolean isup1 = ClientBase.waitForServerUp("127.0.0.1:" + CLIENT_PORT_QP1, 30000);
-            boolean isup2 = ClientBase.waitForServerUp("127.0.0.1:" + CLIENT_PORT_QP2, 30000);
-            assertTrue(isup1, "Server 1 never came up");
-            assertTrue(isup2, "Server 2 never came up");
+        boolean isup1 = ClientBase.waitForServerUp("127.0.0.1:" + CLIENT_PORT_QP1, 30000);
+        boolean isup2 = ClientBase.waitForServerUp("127.0.0.1:" + CLIENT_PORT_QP2, 30000);
+        assertTrue(isup1, "Server 1 never came up");
+        assertTrue(isup2, "Server 2 never came up");
 
-            q1.shutdown();
-            q2.shutdown();
+        q1.shutdown();
+        q2.shutdown();
 
-            assertTrue(ClientBase.waitForServerDown("127.0.0.1:" + CLIENT_PORT_QP1, ClientBase.CONNECTION_TIMEOUT),
-                    "waiting for server 1 down");
+        assertTrue(ClientBase.waitForServerDown("127.0.0.1:" + CLIENT_PORT_QP1, ClientBase.CONNECTION_TIMEOUT),
+                "waiting for server 1 down");
 
-            assertTrue(ClientBase.waitForServerDown("127.0.0.1:" + CLIENT_PORT_QP2, ClientBase.CONNECTION_TIMEOUT),
-                    "waiting for server 2 down");
-        } finally {
-            qlogger.removeAppender(appender);
-        }
+        assertTrue(ClientBase.waitForServerDown("127.0.0.1:" + CLIENT_PORT_QP2, ClientBase.CONNECTION_TIMEOUT),
+                "waiting for server 2 down");
 
         assertTrue(BaseTestMetricsProvider.MetricsProviderCapturingLifecycle.configureCalled.get(), "metrics provider lifecycle error");
         assertTrue(BaseTestMetricsProvider.MetricsProviderCapturingLifecycle.startCalled.get(), "metrics provider lifecycle error");
@@ -1344,46 +1290,36 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
         ClientBase.setupTestEnv();
         BaseTestMetricsProvider.MetricsProviderWithConfiguration.httpPort.set(0);
 
-        // setup the logger to capture all logs
-        ByteArrayOutputStream os = new ByteArrayOutputStream();
-        WriterAppender appender = getConsoleAppender(os, Level.WARN);
-        Logger qlogger = Logger.getLogger("org.apache.zookeeper.server.quorum");
-        qlogger.addAppender(appender);
+        final int CLIENT_PORT_QP1 = PortAssignment.unique();
+        final int CLIENT_PORT_QP2 = PortAssignment.unique();
 
-        try {
-            final int CLIENT_PORT_QP1 = PortAssignment.unique();
-            final int CLIENT_PORT_QP2 = PortAssignment.unique();
+        String quorumCfgSectionServer = "server.1=127.0.0.1:" + PortAssignment.unique() + ":" + PortAssignment.unique() + ";" + CLIENT_PORT_QP1 + "\n"
+                                        + "server.2=127.0.0.1:" + PortAssignment.unique() + ":" + PortAssignment.unique() + ";" + CLIENT_PORT_QP2 + "\n";
 
-            String quorumCfgSectionServer = "server.1=127.0.0.1:" + PortAssignment.unique() + ":" + PortAssignment.unique() + ";" + CLIENT_PORT_QP1 + "\n"
-                                            + "server.2=127.0.0.1:" + PortAssignment.unique() + ":" + PortAssignment.unique() + ";" + CLIENT_PORT_QP2 + "\n";
+        // server 1 boots with a MetricsProvider
+        String quorumCfgSectionServer1 = quorumCfgSectionServer
+                                         + "metricsProvider.className="
+                                         + BaseTestMetricsProvider.MetricsProviderWithConfiguration.class.getName()
+                                         + "\n" + "metricsProvider.httpPort=1234";
 
-            // server 1 boots with a MetricsProvider
-            String quorumCfgSectionServer1 = quorumCfgSectionServer
-                                             + "metricsProvider.className="
-                                             + BaseTestMetricsProvider.MetricsProviderWithConfiguration.class.getName()
-                                             + "\n" + "metricsProvider.httpPort=1234";
+        MainThread q1 = new MainThread(1, CLIENT_PORT_QP1, quorumCfgSectionServer1);
+        MainThread q2 = new MainThread(2, CLIENT_PORT_QP2, quorumCfgSectionServer);
+        q1.start();
+        q2.start();
 
-            MainThread q1 = new MainThread(1, CLIENT_PORT_QP1, quorumCfgSectionServer1);
-            MainThread q2 = new MainThread(2, CLIENT_PORT_QP2, quorumCfgSectionServer);
-            q1.start();
-            q2.start();
+        boolean isup1 = ClientBase.waitForServerUp("127.0.0.1:" + CLIENT_PORT_QP1, 30000);
+        boolean isup2 = ClientBase.waitForServerUp("127.0.0.1:" + CLIENT_PORT_QP2, 30000);
+        assertTrue(isup1, "Server 1 never came up");
+        assertTrue(isup2, "Server 2 never came up");
 
-            boolean isup1 = ClientBase.waitForServerUp("127.0.0.1:" + CLIENT_PORT_QP1, 30000);
-            boolean isup2 = ClientBase.waitForServerUp("127.0.0.1:" + CLIENT_PORT_QP2, 30000);
-            assertTrue(isup1, "Server 1 never came up");
-            assertTrue(isup2, "Server 2 never came up");
-
-            q1.shutdown();
-            q2.shutdown();
+        q1.shutdown();
+        q2.shutdown();
 
-            assertTrue(ClientBase.waitForServerDown("127.0.0.1:" + CLIENT_PORT_QP1, ClientBase.CONNECTION_TIMEOUT),
-                    "waiting for server 1 down");
+        assertTrue(ClientBase.waitForServerDown("127.0.0.1:" + CLIENT_PORT_QP1, ClientBase.CONNECTION_TIMEOUT),
+                "waiting for server 1 down");
 
-            assertTrue(ClientBase.waitForServerDown("127.0.0.1:" + CLIENT_PORT_QP2, ClientBase.CONNECTION_TIMEOUT),
-                    "waiting for server 2 down");
-        } finally {
-            qlogger.removeAppender(appender);
-        }
+        assertTrue(ClientBase.waitForServerDown("127.0.0.1:" + CLIENT_PORT_QP2, ClientBase.CONNECTION_TIMEOUT),
+                "waiting for server 2 down");
 
         assertEquals(1234, BaseTestMetricsProvider.MetricsProviderWithConfiguration.httpPort.get());
     }
@@ -1396,13 +1332,9 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
         ClientBase.setupTestEnv();
         BaseTestMetricsProvider.MetricsProviderCapturingLifecycle.reset();
 
-        // setup the logger to capture all logs
-        ByteArrayOutputStream os = new ByteArrayOutputStream();
-        WriterAppender appender = getConsoleAppender(os, Level.WARN);
-        Logger qlogger = Logger.getLogger("org.apache.zookeeper.server.quorum");
-        qlogger.addAppender(appender);
+        try (LoggerTestTool loggerTestTool = new LoggerTestTool("org.apache.zookeeper.server.quorum")) {
+            ByteArrayOutputStream os = loggerTestTool.getOutputStream();
 
-        try {
             final int CLIENT_PORT_QP1 = PortAssignment.unique();
             final int CLIENT_PORT_QP2 = PortAssignment.unique();
 
@@ -1433,23 +1365,20 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
 
             assertTrue(ClientBase.waitForServerDown("127.0.0.1:" + CLIENT_PORT_QP2, ClientBase.CONNECTION_TIMEOUT),
                     "waiting for server 2 down");
-        } finally {
-            qlogger.removeAppender(appender);
-        }
-
-        assertTrue(BaseTestMetricsProvider.MetricsProviderWithErrorInStop.stopCalled.get(), "metrics provider lifecycle error");
+            assertTrue(BaseTestMetricsProvider.MetricsProviderWithErrorInStop.stopCalled.get(), "metrics provider lifecycle error");
 
-        LineNumberReader r = new LineNumberReader(new StringReader(os.toString()));
-        String line;
-        boolean found = false;
-        Pattern p = Pattern.compile(".*Error while stopping metrics.*");
-        while ((line = r.readLine()) != null) {
-            found = p.matcher(line).matches();
-            if (found) {
-                break;
+            LineNumberReader r = new LineNumberReader(new StringReader(os.toString()));
+            String line;
+            boolean found = false;
+            Pattern p = Pattern.compile(".*Error while stopping metrics.*");
+            while ((line = r.readLine()) != null) {
+                found = p.matcher(line).matches();
+                if (found) {
+                    break;
+                }
             }
+            assertTrue(found, "complains about metrics provider");
         }
-        assertTrue(found, "complains about metrics provider");
     }
 
     /**
@@ -1459,13 +1388,9 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
     public void testInvalidMetricsProvider() throws Exception {
         ClientBase.setupTestEnv();
 
-        // setup the logger to capture all logs
-        ByteArrayOutputStream os = new ByteArrayOutputStream();
-        WriterAppender appender = getConsoleAppender(os, Level.WARN);
-        Logger qlogger = Logger.getLogger("org.apache.zookeeper.server.quorum");
-        qlogger.addAppender(appender);
+        try (LoggerTestTool loggerTestTool = new LoggerTestTool("org.apache.zookeeper.server.quorum")) {
+            ByteArrayOutputStream os = loggerTestTool.getOutputStream();
 
-        try {
             final int CLIENT_PORT_QP1 = PortAssignment.unique();
 
             String quorumCfgSection = "server.1=127.0.0.1:" + PortAssignment.unique() + ":" + PortAssignment.unique() + ";" + CLIENT_PORT_QP1
@@ -1484,21 +1409,18 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
             assertTrue(ClientBase.waitForServerDown("127.0.0.1:" + CLIENT_PORT_QP1, ClientBase.CONNECTION_TIMEOUT),
                     "waiting for server 1 down");
 
-        } finally {
-            qlogger.removeAppender(appender);
-        }
-
-        LineNumberReader r = new LineNumberReader(new StringReader(os.toString()));
-        String line;
-        boolean found = false;
-        Pattern p = Pattern.compile(".*BadClass.*");
-        while ((line = r.readLine()) != null) {
-            found = p.matcher(line).matches();
-            if (found) {
-                break;
+            LineNumberReader r = new LineNumberReader(new StringReader(os.toString()));
+            String line;
+            boolean found = false;
+            Pattern p = Pattern.compile(".*BadClass.*");
+            while ((line = r.readLine()) != null) {
+                found = p.matcher(line).matches();
+                if (found) {
+                    break;
+                }
             }
+            assertTrue(found, "complains about metrics provider");
         }
-        assertTrue(found, "complains about metrics provider");
     }
 
     /**
@@ -1508,13 +1430,9 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
     public void testFaultyMetricsProviderOnStart() throws Exception {
         ClientBase.setupTestEnv();
 
-        // setup the logger to capture all logs
-        ByteArrayOutputStream os = new ByteArrayOutputStream();
-        WriterAppender appender = getConsoleAppender(os, Level.WARN);
-        Logger qlogger = Logger.getLogger("org.apache.zookeeper.server.quorum");
-        qlogger.addAppender(appender);
+        try (LoggerTestTool loggerTestTool = new LoggerTestTool("org.apache.zookeeper.server.quorum")) {
+            ByteArrayOutputStream os = loggerTestTool.getOutputStream();
 
-        try {
             final int CLIENT_PORT_QP1 = PortAssignment.unique();
 
             String quorumCfgSection = "server.1=127.0.0.1:" + PortAssignment.unique() + ":" + PortAssignment.unique() + ";" + CLIENT_PORT_QP1
@@ -1534,21 +1452,18 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
             assertTrue(ClientBase.waitForServerDown("127.0.0.1:" + CLIENT_PORT_QP1, ClientBase.CONNECTION_TIMEOUT),
                     "waiting for server 1 down");
 
-        } finally {
-            qlogger.removeAppender(appender);
-        }
-
-        LineNumberReader r = new LineNumberReader(new StringReader(os.toString()));
-        String line;
-        boolean found = false;
-        Pattern p = Pattern.compile(".*MetricsProviderLifeCycleException.*");
-        while ((line = r.readLine()) != null) {
-            found = p.matcher(line).matches();
-            if (found) {
-                break;
+            LineNumberReader r = new LineNumberReader(new StringReader(os.toString()));
+            String line;
+            boolean found = false;
+            Pattern p = Pattern.compile(".*MetricsProviderLifeCycleException.*");
+            while ((line = r.readLine()) != null) {
+                found = p.matcher(line).matches();
+                if (found) {
+                    break;
+                }
             }
+            assertTrue(found, "complains about metrics provider MetricsProviderLifeCycleException");
         }
-        assertTrue(found, "complains about metrics provider MetricsProviderLifeCycleException");
     }
 
     /**
@@ -1558,13 +1473,9 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
     public void testFaultyMetricsProviderOnConfigure() throws Exception {
         ClientBase.setupTestEnv();
 
-        // setup the logger to capture all logs
-        ByteArrayOutputStream os = new ByteArrayOutputStream();
-        WriterAppender appender = getConsoleAppender(os, Level.WARN);
-        Logger qlogger = Logger.getLogger("org.apache.zookeeper.server.quorum");
-        qlogger.addAppender(appender);
+        try (LoggerTestTool loggerTestTool = new LoggerTestTool("org.apache.zookeeper.server.quorum")) {
+            ByteArrayOutputStream os = loggerTestTool.getOutputStream();
 
-        try {
             final int CLIENT_PORT_QP1 = PortAssignment.unique();
 
             String quorumCfgSection = "server.1=127.0.0.1:" + PortAssignment.unique() + ":" + PortAssignment.unique() + ";" + CLIENT_PORT_QP1
@@ -1584,21 +1495,18 @@ public class QuorumPeerMainTest extends QuorumPeerTestBase {
             assertTrue(ClientBase.waitForServerDown("127.0.0.1:" + CLIENT_PORT_QP1, ClientBase.CONNECTION_TIMEOUT),
                     "waiting for server 1 down");
 
-        } finally {
-            qlogger.removeAppender(appender);
-        }
-
-        LineNumberReader r = new LineNumberReader(new StringReader(os.toString()));
-        String line;
-        boolean found = false;
-        Pattern p = Pattern.compile(".*MetricsProviderLifeCycleException.*");
-        while ((line = r.readLine()) != null) {
-            found = p.matcher(line).matches();
-            if (found) {
-                break;
+            LineNumberReader r = new LineNumberReader(new StringReader(os.toString()));
+            String line;
+            boolean found = false;
+            Pattern p = Pattern.compile(".*MetricsProviderLifeCycleException.*");
+            while ((line = r.readLine()) != null) {
+                found = p.matcher(line).matches();
+                if (found) {
+                    break;
+                }
             }
+            assertTrue(found, "complains about metrics provider MetricsProviderLifeCycleException");
         }
-        assertTrue(found, "complains about metrics provider MetricsProviderLifeCycleException");
     }
 
     /**

zookeeper-server/src/test/java/org/apache/zookeeper/test/LoggerTestTool.java

@@ -0,0 +1,88 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.zookeeper.test;
+
+import ch.qos.logback.classic.Level;
+import ch.qos.logback.classic.Logger;
+import ch.qos.logback.classic.LoggerContext;
+import ch.qos.logback.classic.spi.ILoggingEvent;
+import ch.qos.logback.core.Appender;
+import ch.qos.logback.core.Layout;
+import ch.qos.logback.core.OutputStreamAppender;
+import ch.qos.logback.core.encoder.LayoutWrappingEncoder;
+import java.io.ByteArrayOutputStream;
+import org.slf4j.LoggerFactory;
+
+public class LoggerTestTool implements AutoCloseable {
+  private final ByteArrayOutputStream os;
+  private Appender<ILoggingEvent> appender;
+  private Logger qlogger;
+
+  public LoggerTestTool(Class<?> cls) {
+    os = createLoggingStream(cls);
+  }
+
+  public LoggerTestTool(String cls) {
+    os = createLoggingStream(cls);
+  }
+
+  public ByteArrayOutputStream getOutputStream() {
+    return os;
+  }
+
+  private ByteArrayOutputStream createLoggingStream(Class<?> cls) {
+    ByteArrayOutputStream os = new ByteArrayOutputStream();
+    appender = getConsoleAppender(os);
+    qlogger = (ch.qos.logback.classic.Logger) LoggerFactory.getLogger(cls);
+    qlogger.addAppender(appender);
+    qlogger.setLevel(Level.INFO);
+    appender.start();
+    return os;
+  }
+
+  private ByteArrayOutputStream createLoggingStream(String cls) {
+    ByteArrayOutputStream os = new ByteArrayOutputStream();
+    appender = getConsoleAppender(os);
+    qlogger = (ch.qos.logback.classic.Logger) LoggerFactory.getLogger(cls);
+    qlogger.addAppender(appender);
+    qlogger.setLevel(Level.INFO);
+    appender.start();
+    return os;
+  }
+
+  private OutputStreamAppender<ILoggingEvent> getConsoleAppender(ByteArrayOutputStream os) {
+    Logger rootLogger =
+        (ch.qos.logback.classic.Logger) LoggerFactory.getLogger(org.slf4j.Logger.ROOT_LOGGER_NAME);
+    Layout<ILoggingEvent> layout = ((LayoutWrappingEncoder<ILoggingEvent>)
+        ((OutputStreamAppender<ILoggingEvent>) rootLogger.getAppender("CONSOLE")).getEncoder()).getLayout();
+
+    OutputStreamAppender<ILoggingEvent> appender = new OutputStreamAppender<>();
+    appender.setContext((LoggerContext) LoggerFactory.getILoggerFactory());
+    appender.setOutputStream(os);
+    appender.setLayout(layout);
+
+    return appender;
+  }
+
+  @Override
+  public void close() throws Exception {
+    qlogger.detachAppender(appender);
+    os.close();
+  }
+}

zookeeper-server/src/test/java/org/apache/zookeeper/test/ReadOnlyModeTest.java

@@ -29,10 +29,6 @@ import java.io.LineNumberReader;
 import java.io.StringReader;
 import java.util.concurrent.TimeoutException;
 import java.util.regex.Pattern;
-import org.apache.log4j.Layout;
-import org.apache.log4j.Level;
-import org.apache.log4j.Logger;
-import org.apache.log4j.WriterAppender;
 import org.apache.zookeeper.CreateMode;
 import org.apache.zookeeper.KeeperException;
 import org.apache.zookeeper.KeeperException.NotReadOnlyException;
@@ -41,6 +37,7 @@ import org.apache.zookeeper.ZKTestCase;
 import org.apache.zookeeper.ZooDefs;
 import org.apache.zookeeper.ZooKeeper;
 import org.apache.zookeeper.ZooKeeper.States;
+import org.apache.zookeeper.common.StringUtils;
 import org.apache.zookeeper.common.Time;
 import org.apache.zookeeper.test.ClientBase.CountdownWatcher;
 import org.junit.jupiter.api.AfterEach;
@@ -294,16 +291,9 @@ public class ReadOnlyModeTest extends ZKTestCase {
         qu.enableLocalSession(true);
         qu.startQuorum();
 
-        // setup the logger to capture all logs
-        Layout layout = Logger.getRootLogger().getAppender("CONSOLE").getLayout();
-        ByteArrayOutputStream os = new ByteArrayOutputStream();
-        WriterAppender appender = new WriterAppender(layout, os);
-        appender.setImmediateFlush(true);
-        appender.setThreshold(Level.INFO);
-        Logger zlogger = Logger.getLogger("org.apache.zookeeper");
-        zlogger.addAppender(appender);
+        try (LoggerTestTool loggerTestTool = new LoggerTestTool("org.apache.zookeeper")) {
+            ByteArrayOutputStream os = loggerTestTool.getOutputStream();
 
-        try {
             qu.shutdown(2);
             CountdownWatcher watcher = new CountdownWatcher();
             ZooKeeper zk = new ZooKeeper(qu.getConnString(), CONNECTION_TIMEOUT, watcher, true);
@@ -323,22 +313,21 @@ public class ReadOnlyModeTest extends ZKTestCase {
 
             // resume poor fellow
             qu.getPeer(1).peer.resume();
-        } finally {
-            zlogger.removeAppender(appender);
-        }
 
-        os.close();
-        LineNumberReader r = new LineNumberReader(new StringReader(os.toString()));
-        String line;
-        Pattern p = Pattern.compile(".*Majority server found.*");
-        boolean found = false;
-        while ((line = r.readLine()) != null) {
-            if (p.matcher(line).matches()) {
-                found = true;
-                break;
+            String log = os.toString();
+            assertFalse(StringUtils.isEmpty(log), "OutputStream doesn't have any log messages");
+
+            LineNumberReader r = new LineNumberReader(new StringReader(log));
+            String line;
+            Pattern p = Pattern.compile(".*Majority server found.*");
+            boolean found = false;
+            while ((line = r.readLine()) != null) {
+                if (p.matcher(line).matches()) {
+                    found = true;
+                    break;
+                }
             }
+            assertTrue(found, "Majority server wasn't found while connected to r/o server");
         }
-        assertTrue(found, "Majority server wasn't found while connected to r/o server");
     }
-
 }

zookeeper-server/src/test/java/org/apache/zookeeper/test/ReconfigExceptionTest.java

@@ -48,8 +48,8 @@ public class ReconfigExceptionTest extends ZKTestCase {
     // Use DigestAuthenticationProvider.base64Encode or
     // run ZooKeeper jar with org.apache.zookeeper.server.auth.DigestAuthenticationProvider to generate password.
     // An example:
-    // java -cp zookeeper-3.6.0-SNAPSHOT.jar:lib/log4j-1.2.17.jar:lib/slf4j-log4j12-1.7.5.jar:
-    // lib/slf4j-api-1.7.5.jar org.apache.zookeeper.server.auth.DigestAuthenticationProvider super:test
+    // java -cp zookeeper.jar:lib/slf4j-api-1.7.30.jar:lib/logback-classic-1.2.10.jar:lib/logback-core-1.2.10.jar:conf
+    // org.apache.zookeeper.server.auth.DigestAuthenticationProvider super:test
     // The password here is 'test'.
     private static String superDigest = "super:D/InIHSb7yEEbrWz8b9l71RjZJU=";
     private QuorumUtil qu;

zookeeper-server/src/test/resources/log4j.properties

@@ -1,65 +0,0 @@
-# Copyright 2012 The Apache Software Foundation
-# 
-# Licensed to the Apache Software Foundation (ASF) under one
-# or more contributor license agreements.  See the NOTICE file
-# distributed with this work for additional information
-# regarding copyright ownership.  The ASF licenses this file
-# to you under the Apache License, Version 2.0 (the
-# "License"); you may not use this file except in compliance
-# with the License.  You may obtain a copy of the License at
-#
-#     http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-
-# Define some default values that can be overridden by system properties
-zookeeper.root.logger=INFO, CONSOLE
-
-zookeeper.console.threshold=INFO
-
-zookeeper.log.dir=.
-zookeeper.log.file=zookeeper.log
-zookeeper.log.threshold=INFO
-zookeeper.log.maxfilesize=256MB
-zookeeper.log.maxbackupindex=20
-
-zookeeper.tracelog.dir=${zookeeper.log.dir}
-zookeeper.tracelog.file=zookeeper_trace.log
-
-log4j.rootLogger=${zookeeper.root.logger}
-
-#
-# console
-# Add "console" to rootlogger above if you want to use this 
-#
-log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender
-log4j.appender.CONSOLE.Threshold=${zookeeper.console.threshold}
-log4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayout
-log4j.appender.CONSOLE.layout.ConversionPattern=%d{ISO8601} [myid:%X{myid}] - %-5p [%t:%C{1}@%L] - %m%n
-
-#
-# Add ROLLINGFILE to rootLogger to get log file output
-#
-log4j.appender.ROLLINGFILE=org.apache.log4j.RollingFileAppender
-log4j.appender.ROLLINGFILE.Threshold=${zookeeper.log.threshold}
-log4j.appender.ROLLINGFILE.File=${zookeeper.log.dir}/${zookeeper.log.file}
-log4j.appender.ROLLINGFILE.MaxFileSize=${zookeeper.log.maxfilesize}
-log4j.appender.ROLLINGFILE.MaxBackupIndex=${zookeeper.log.maxbackupindex}
-log4j.appender.ROLLINGFILE.layout=org.apache.log4j.PatternLayout
-log4j.appender.ROLLINGFILE.layout.ConversionPattern=%d{ISO8601} [myid:%X{myid}] - %-5p [%t:%C{1}@%L] - %m%n
-
-#
-# Add TRACEFILE to rootLogger to get log file output
-#    Log TRACE level and above messages to a log file
-#
-log4j.appender.TRACEFILE=org.apache.log4j.FileAppender
-log4j.appender.TRACEFILE.Threshold=TRACE
-log4j.appender.TRACEFILE.File=${zookeeper.tracelog.dir}/${zookeeper.tracelog.file}
-
-log4j.appender.TRACEFILE.layout=org.apache.log4j.PatternLayout
-### Notice we are including log4j's NDC here (%x)
-log4j.appender.TRACEFILE.layout.ConversionPattern=%d{ISO8601} [myid:%X{myid}] - %-5p [%t:%C{1}@%L][%x] - %m%n

zookeeper-server/src/test/resources/logback.xml

@@ -0,0 +1,36 @@
+<!--
+ Copyright 2022 The Apache Software Foundation
+
+ Licensed to the Apache Software Foundation (ASF) under one
+ or more contributor license agreements.  See the NOTICE file
+ distributed with this work for additional information
+ regarding copyright ownership.  The ASF licenses this file
+ to you under the Apache License, Version 2.0 (the
+ "License"); you may not use this file except in compliance
+ with the License.  You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+ Unless required by applicable law or agreed to in writing, software
+ distributed under the License is distributed on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ See the License for the specific language governing permissions and
+ limitations under the License.
+
+ Define some default values that can be overridden by system properties
+-->
+<configuration>
+
+  <appender name="CONSOLE" class="ch.qos.logback.core.ConsoleAppender">
+    <encoder>
+      <pattern>%d{ISO8601} [myid:%X{myid}] - %-5p [%t:%C{1}@%L] - %m%n</pattern>
+    </encoder>
+    <filter class="ch.qos.logback.classic.filter.ThresholdFilter">
+      <level>INFO</level>
+    </filter>
+  </appender>
+
+  <root level="INFO">
+    <appender-ref ref="CONSOLE" />
+  </root>
+</configuration>