HDDS-922. Create isolated classloder to use ozonefs with any older hadoop versions. Contributed by Elek, Marton.

hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/conf/OzoneConfiguration.java

@@ -47,6 +47,8 @@ public class OzoneConfiguration extends Configuration {
 
   public OzoneConfiguration(Configuration conf) {
     super(conf);
+    //load the configuration from the classloader of the original conf.
+    setClassLoader(conf.getClassLoader());
   }
 
   public List<Property> readPropertyFromXml(URL url) throws JAXBException {

hadoop-hdds/common/src/main/java/org/apache/hadoop/ozone/OzoneConfigKeys.java

@@ -371,6 +371,13 @@ public final class OzoneConfigKeys {
   public static final boolean OZONE_ACL_ENABLED_DEFAULT =
       false;
 
+  //For technical reasons this is unused and hardcoded to the
+  // OzoneFileSystem.initialize.
+  public static final String OZONE_FS_ISOLATED_CLASSLOADER =
+      "ozone.fs.isolated-classloader";
+
+
+
   /**
    * There is no need to instantiate this class.
    */

hadoop-hdds/common/src/main/resources/ozone-default.xml

@@ -1806,4 +1806,19 @@
       not be renewed.
     </description>
   </property>
+
+  <property>
+    <name>ozone.fs.isolated-classloader</name>
+    <value></value>
+    <tag>OZONE, OZONEFS</tag>
+    <description>
+      Enable it for older hadoops to separate the classloading of all the
+      Ozone classes. With 'true' value, ozonefs can be used with older
+      hadoop versions as the hadoop3/ozone related classes are loaded by
+      an isolated classloader.
+
+      Default depends from the used jar. true for ozone-filesystem-lib-legacy
+      jar and false for the ozone-filesystem-lib.jar
+    </description>
+  </property>
 </configuration>

hadoop-hdds/docs/content/OzoneFS.md

@@ -56,12 +56,11 @@ This will make this bucket to be the default file system for HDFS dfs commands a
 You also need to add the ozone-filesystem.jar file to the classpath:
 
 {{< highlight bash >}}
-export HADOOP_CLASSPATH=/opt/ozone/share/hadoop/ozonefs/hadoop-ozone-filesystem.jar:$HADOOP_CLASSPATH
+export HADOOP_CLASSPATH=/opt/ozone/share/ozonefs/lib/hadoop-ozone-filesystem-lib-.*.jar:$HADOOP_CLASSPATH
 {{< /highlight >}}
 
 
 
-
 Once the default Filesystem has been setup, users can run commands like ls, put, mkdir, etc.
 For example,
 
@@ -78,3 +77,19 @@ hdfs dfs -mkdir /users
 
 Or put command etc. In other words, all programs like Hive, Spark, and Distcp will work against this file system.
 Please note that any keys created/deleted in the bucket using methods apart from OzoneFileSystem will show up as diectories and files in the Ozone File System.
+
+## Legacy mode
+
+There are two ozonefs files which includes all the dependencies:
+
+ * share/ozone/lib/hadoop-ozone-filesystem-lib-VERSION.jar
+ * share/ozone/lib/hadoop-ozone-filesystem-lib-legacy-VERSION.jar
+
+ The first one contains all the required dependency to use ozonefs with a
+ compatible hadoop version (hadoop 3.2 / 3.1).
+
+ The second one contains all the dependency in an internal, separated directory,
+ and a special class loader is used to load all the classes from the location.
+
+ With this method the hadoop-ozone-filesystem-lib-legacy.jar can be used from
+ any older hadoop version (eg. hadoop 2.7 or spark+hadoop 2.7)

hadoop-ozone/dist/dev-support/bin/dist-layout-stitching

@@ -106,10 +106,6 @@ run cp "${ROOT}/hadoop-common-project/hadoop-common/src/main/bin/workers.sh" "sb
 run cp "${ROOT}/hadoop-ozone/common/src/main/bin/start-ozone.sh" "sbin/"
 run cp "${ROOT}/hadoop-ozone/common/src/main/bin/stop-ozone.sh" "sbin/"
 
-#shaded ozonefs
-run mkdir -p "./share/hadoop/ozonefs"
-run cp "${ROOT}/hadoop-ozone/ozonefs/target/hadoop-ozone-filesystem-${HDDS_VERSION}.jar" "./share/hadoop/ozonefs/hadoop-ozone-filesystem-${HDDS_VERSION}.jar"
-
 #shaded datanode service
 run mkdir -p "./share/hadoop/ozoneplugin"
 run cp "${ROOT}/hadoop-ozone/objectstore-service/target/hadoop-ozone-objectstore-service-${HDDS_VERSION}-plugin.jar" "./share/hadoop/ozoneplugin/hadoop-ozone-datanode-plugin-${HDDS_VERSION}.jar"

hadoop-ozone/dist/pom.xml

@@ -82,6 +82,13 @@
                   <classifier>classpath</classifier>
                   <destFileName>hadoop-ozone-tools.classpath</destFileName>
                 </artifactItem>
+                <artifactItem>
+                  <groupId>org.apache.hadoop</groupId>
+                  <artifactId>hadoop-ozone-filesystem</artifactId>
+                  <version>${ozone.version}</version>
+                  <classifier>classpath</classifier>
+                  <destFileName>hadoop-ozone-filesystem.classpath</destFileName>
+                </artifactItem>
                 <artifactItem>
                   <groupId>org.apache.hadoop</groupId>
                   <artifactId>hadoop-ozone-common</artifactId>
@@ -183,6 +190,14 @@
       <groupId>org.apache.hadoop</groupId>
       <artifactId>hadoop-ozone-tools</artifactId>
     </dependency>
+    <dependency>
+      <groupId>org.apache.hadoop</groupId>
+      <artifactId>hadoop-ozone-filesystem-lib</artifactId>
+    </dependency>
+    <dependency>
+      <groupId>org.apache.hadoop</groupId>
+      <artifactId>hadoop-ozone-filesystem-lib-legacy</artifactId>
+    </dependency>
     <dependency>
       <groupId>org.apache.hadoop</groupId>
       <artifactId>hadoop-ozone-common</artifactId>

hadoop-ozone/dist/src/main/compose/ozonefs/docker-compose.yaml

@@ -19,12 +19,12 @@ services:
    datanode:
       image: apache/hadoop-runner
       volumes:
-        - ../..:/opt/hadoop
+         - ../..:/opt/hadoop
       ports:
-        - 9864
+         - 9864
       command: ["/opt/hadoop/bin/ozone","datanode"]
       env_file:
-        - ./docker-config
+         - ./docker-config
    ozoneManager:
       image: apache/hadoop-runner
       hostname: ozoneManager
@@ -36,7 +36,7 @@ services:
          ENSURE_OM_INITIALIZED: /data/metadata/ozoneManager/current/VERSION
          WAITFOR: scm:9876
       env_file:
-          - ./docker-config
+         - ./docker-config
       command: ["/opt/hadoop/bin/ozone","om"]
    scm:
       image: apache/hadoop-runner
@@ -45,16 +45,25 @@ services:
       ports:
          - 9876
       env_file:
-          - ./docker-config
+         - ./docker-config
       environment:
-          ENSURE_SCM_INITIALIZED: /data/metadata/scm/current/VERSION
+         ENSURE_SCM_INITIALIZED: /data/metadata/scm/current/VERSION
       command: ["/opt/hadoop/bin/ozone","scm"]
-   hadooplast:
+   hadoop3:
       image: flokkr/hadoop:3.1.0
       volumes:
-        - ../..:/opt/ozone
+         - ../..:/opt/ozone
+      env_file:
+         - ./docker-config
+      environment:
+         HADOOP_CLASSPATH: /opt/ozone/share/ozone/lib/hadoop-ozone-filesystem-lib-0*.jar
+      command: ["watch","-n","100000","ls"]
+   hadoop2:
+      image: flokkr/hadoop:2.9.0
+      volumes:
+         - ../..:/opt/ozone
       env_file:
-        - ./docker-config
+         - ./docker-config
       environment:
-         HADOOP_CLASSPATH: /opt/ozone/share/hadoop/ozonefs/*.jar
+         HADOOP_CLASSPATH: /opt/ozone/share/ozone/lib/hadoop-ozone-filesystem-lib-legacy*.jar
       command: ["watch","-n","100000","ls"]

hadoop-ozone/ozonefs-lib-legacy/pom.xml

@@ -0,0 +1,104 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+  Licensed 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. See accompanying LICENSE file.
+-->
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+  <parent>
+    <groupId>org.apache.hadoop</groupId>
+    <artifactId>hadoop-ozone</artifactId>
+    <version>0.4.0-SNAPSHOT</version>
+  </parent>
+  <artifactId>hadoop-ozone-filesystem-lib-legacy</artifactId>
+  <name>Apache Hadoop Ozone FileSystem Legacy Jar Library</name>
+  <description>This projects creates an uberjar from ozonefs with all the
+    dependencies, but the dependencies are located in an isolated subdir
+    and loaded by a custom class loader. Can be used together with Hadoop 2.x
+  </description>
+  <packaging>jar</packaging>
+  <version>0.4.0-SNAPSHOT</version>
+  <properties>
+    <file.encoding>UTF-8</file.encoding>
+    <downloadSources>true</downloadSources>
+  </properties>
+
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-jar-plugin</artifactId>
+        <executions>
+          <execution>
+            <goals>
+              <goal>test-jar</goal>
+            </goals>
+          </execution>
+        </executions>
+      </plugin>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-dependency-plugin</artifactId>
+        <executions>
+          <execution>
+            <id>include-dependencies</id>
+            <goals>
+              <goal>unpack-dependencies</goal>
+            </goals>
+            <phase>prepare-package</phase>
+            <configuration>
+              <outputDirectory>target/classes/libs</outputDirectory>
+              <includeScope>compile</includeScope>
+              <excludes>META-INF/*.SF</excludes>
+              <excludeArtifactIds>
+                slf4j-api,slf4j-log4j12,log4j-api,log4j-core,log4j,hadoop-ozone-filesystem
+              </excludeArtifactIds>
+            </configuration>
+          </execution>
+          <execution>
+            <id>include-ozonefs</id>
+            <goals>
+              <goal>unpack-dependencies</goal>
+            </goals>
+            <phase>prepare-package</phase>
+            <configuration>
+              <outputDirectory>target/classes</outputDirectory>
+              <includeArtifactIds>hadoop-ozone-filesystem</includeArtifactIds>
+              <includeScope>compile</includeScope>
+              <excludes>META-INF/*.SF</excludes>
+            </configuration>
+          </execution>
+        </executions>
+      </plugin>
+      <plugin>
+        <groupId>org.codehaus.mojo</groupId>
+        <artifactId>animal-sniffer-maven-plugin</artifactId>
+        <executions>
+          <execution>
+            <id>signature-check</id>
+            <phase></phase>
+          </execution>
+        </executions>
+      </plugin>
+    </plugins>
+  </build>
+
+  <dependencies>
+    <dependency>
+      <groupId>org.apache.hadoop</groupId>
+      <artifactId>hadoop-ozone-filesystem</artifactId>
+      <scope>compile</scope>
+    </dependency>
+  </dependencies>
+</project>

hadoop-ozone/ozonefs-lib-legacy/src/main/resources/ozonefs.txt

@@ -0,0 +1,21 @@
+<!--
+  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.
+-->
+
+Apache Hadoop Ozone placeholder file.
+
+The usage of the legacy version of the uber jar can be detected based on
+the existence of this file.

hadoop-ozone/ozonefs-lib/pom.xml

@@ -0,0 +1,89 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+  Licensed 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. See accompanying LICENSE file.
+-->
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+  <parent>
+    <groupId>org.apache.hadoop</groupId>
+    <artifactId>hadoop-ozone</artifactId>
+    <version>0.4.0-SNAPSHOT</version>
+  </parent>
+  <artifactId>hadoop-ozone-filesystem-lib</artifactId>
+  <name>Apache Hadoop Ozone FileSystem Single Jar Library</name>
+  <packaging>jar</packaging>
+  <description>This projects creates an uber jar from ozonefs with all the
+    dependencies.
+  </description>
+  <version>0.4.0-SNAPSHOT</version>
+  <properties>
+    <file.encoding>UTF-8</file.encoding>
+    <downloadSources>true</downloadSources>
+  </properties>
+
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-jar-plugin</artifactId>
+        <executions>
+          <execution>
+            <goals>
+              <goal>test-jar</goal>
+            </goals>
+          </execution>
+        </executions>
+      </plugin>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-dependency-plugin</artifactId>
+        <executions>
+          <execution>
+            <goals>
+              <goal>unpack-dependencies</goal>
+            </goals>
+            <phase>prepare-package</phase>
+            <configuration>
+              <outputDirectory>target/classes</outputDirectory>
+              <includeScope>compile</includeScope>
+              <excludes>META-INF/*.SF</excludes>
+              <excludeArtifactIds>
+                slf4j-api,slf4j-log4j12,log4j-api,log4j-core,log4j
+              </excludeArtifactIds>
+            </configuration>
+          </execution>
+        </executions>
+      </plugin>
+      <plugin>
+        <groupId>org.codehaus.mojo</groupId>
+        <artifactId>animal-sniffer-maven-plugin</artifactId>
+        <executions>
+          <execution>
+            <id>signature-check</id>
+            <phase></phase>
+          </execution>
+        </executions>
+      </plugin>
+    </plugins>
+  </build>
+
+  <dependencies>
+    <dependency>
+      <groupId>org.apache.hadoop</groupId>
+      <artifactId>hadoop-ozone-filesystem</artifactId>
+      <scope>compile</scope>
+    </dependency>
+  </dependencies>
+</project>

hadoop-ozone/ozonefs/pom.xml

@@ -43,46 +43,6 @@
           </execution>
         </executions>
       </plugin>
-      <plugin>
-        <groupId>org.apache.maven.plugins</groupId>
-        <artifactId>maven-shade-plugin</artifactId>
-        <version>3.1.1</version>
-        <configuration>
-          <artifactSet>
-            <includes>
-              <include>com.google.guava:guava</include>
-              <include>org.slf4j:slf4j-api</include>
-              <include>com.google.protobuf:protobuf-java</include>
-              <include>com.nimbusds:nimbus-jose-jwt</include>
-              <include>com.github.stephenc.jcip:jcip-annotations</include>
-              <include>com.google.code.findbugs:jsr305</include>
-              <include>org.apache.hadoop:hadoop-ozone-client</include>
-              <include>org.apache.hadoop:hadoop-hdds-client</include>
-              <include>org.apache.hadoop:hadoop-hdds-common</include>
-              <include>org.fusesource.leveldbjni:leveldbjni-all</include>
-              <include>org.apache.ratis:ratis-server</include>
-              <include>org.apache.ratis:ratis-proto-shaded</include>
-              <include>com.google.auto.value:auto-value-annotations</include>
-              <include>com.squareup:javapoet</include>
-              <include>org.jctools:jctools-core</include>
-              <include>org.apache.ratis:ratis-common</include>
-              <include>org.apache.ratis:ratis-client</include>
-              <include>org.apache.ratis:ratis-netty</include>
-              <include>org.apache.ratis:ratis-grpc</include>
-              <include>org.rocksdb:rocksdbjni</include>
-              <include>org.apache.hadoop:hadoop-ozone-common</include>
-            </includes>
-          </artifactSet>
-        </configuration>
-        <executions>
-          <execution>
-            <phase>package</phase>
-            <goals>
-              <goal>shade</goal>
-            </goals>
-          </execution>
-        </executions>
-      </plugin>
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-dependency-plugin</artifactId>
@@ -96,7 +56,7 @@
             <configuration>
               <!-- build a shellprofile -->
               <outputFile>
-                ${project.basedir}/target/hadoop-tools-deps/${project.artifactId}.tools-optional.txt
+                ${project.basedir}/target/1hadoop-tools-deps/${project.artifactId}.tools-optional.txt
               </outputFile>
             </configuration>
           </execution>
@@ -110,7 +70,17 @@
             <include>ITestOzoneContract*.java</include>
           </includes>          
         </configuration>
-      </plugin>      
+      </plugin>
+      <plugin>
+        <groupId>org.codehaus.mojo</groupId>
+        <artifactId>animal-sniffer-maven-plugin</artifactId>
+        <executions>
+          <execution>
+            <id>signature-check</id>
+            <phase></phase>
+          </execution>
+        </executions>
+      </plugin>
     </plugins>
   </build>
 
@@ -118,17 +88,17 @@
     <dependency>
       <groupId>org.apache.hadoop</groupId>
       <artifactId>hadoop-common</artifactId>
-      <scope>provided</scope>
+      <scope>compile</scope>
     </dependency>
     <dependency>
       <groupId>org.apache.hadoop</groupId>
       <artifactId>hadoop-hdfs</artifactId>
-      <scope>provided</scope>
+      <scope>compile</scope>
     </dependency>
     <dependency>
       <groupId>org.apache.hadoop</groupId>
       <artifactId>hadoop-hdfs-client</artifactId>
-      <scope>provided</scope>
+      <scope>compile</scope>
     </dependency>
     <dependency>
       <groupId>org.apache.hadoop</groupId>

hadoop-ozone/ozonefs/src/main/java/org/apache/hadoop/fs/ozone/BasicKeyInfo.java

@@ -0,0 +1,53 @@
+/**
+ * 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
+ * <p>
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * 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.hadoop.fs.ozone;
+
+/**
+ * Minimum set of Ozone key information attributes.
+ * <p>
+ * This class doesn't depend on any other ozone class just on primitive
+ * java types. It could be used easily in the signature of OzoneClientAdapter
+ * as even if a separated class loader is loaded it it won't cause any
+ * dependency problem.
+ */
+public class BasicKeyInfo {
+
+  private String name;
+
+  private long modificationTime;
+
+  private long dataSize;
+
+  public BasicKeyInfo(String name, long modificationTime, long size) {
+    this.name = name;
+    this.modificationTime = modificationTime;
+    this.dataSize = size;
+  }
+
+  public String getName() {
+    return name;
+  }
+
+  public long getModificationTime() {
+    return modificationTime;
+  }
+
+  public long getDataSize() {
+    return dataSize;
+  }
+}

hadoop-ozone/ozonefs/src/main/java/org/apache/hadoop/fs/ozone/FilteredClassLoader.java

@@ -0,0 +1,84 @@
+/**
+ * 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
+ * <p>
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * 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.hadoop.fs.ozone;
+
+import java.net.URL;
+import java.net.URLClassLoader;
+import java.util.HashSet;
+import java.util.Set;
+
+/**
+ * Class loader which delegates the loading only for the selected class.
+ *
+ * <p>
+ * By default java classloader delegates first all the class loading to the
+ * parent, and loads the class only if it's not found in the class.
+ * <p>
+ * This simple class loader do the opposit. Everything is loaded with this
+ * class loader without delegation _except_ the few classes which are defined
+ * in the constructor.
+ * <p>
+ * With this method we can use two separated class loader (the original main
+ * classloader and instance of this which loaded separated classes, but the
+ * few selected classes are shared between the two class loaders.
+ * <p>
+ * With this approach it's possible to use any older hadoop version
+ * (main classloader) together with ozonefs (instance of this classloader) as
+ * only the selected classes are selected between the class loaders.
+ */
+public class FilteredClassLoader extends URLClassLoader {
+
+  private final ClassLoader systemClassLoader;
+
+  private final ClassLoader delegate;
+  private Set<String> delegatedClasses = new HashSet<>();
+
+  public FilteredClassLoader(URL[] urls, ClassLoader parent) {
+    super(urls, null);
+    delegatedClasses.add("org.apache.hadoop.fs.ozone.OzoneClientAdapter");
+    delegatedClasses.add("org.apache.hadoop.fs.ozone.BasicKeyInfo");
+    delegatedClasses.add("org.apache.hadoop.fs.ozone.OzoneFSOutputStream");
+    delegatedClasses.add("org.apache.hadoop.fs.Seekable");
+    this.delegate = parent;
+    systemClassLoader = getSystemClassLoader();
+
+  }
+
+  @Override
+  public Class<?> loadClass(String name) throws ClassNotFoundException {
+    if (delegatedClasses.contains(name) ||
+        name.startsWith("org.apache.log4j") ||
+        name.startsWith("org.slf4j")) {
+      return delegate.loadClass(name);
+    }
+    return super.loadClass(name);
+  }
+
+  private Class<?> loadFromSystem(String name) {
+    if (systemClassLoader != null) {
+      try {
+        return systemClassLoader.loadClass(name);
+      } catch (ClassNotFoundException ex) {
+        //no problem
+        return null;
+      }
+    } else {
+      return null;
+    }
+  }
+}

hadoop-ozone/ozonefs/src/main/java/org/apache/hadoop/fs/ozone/OzoneClientAdapter.java

@@ -0,0 +1,55 @@
+/**
+ * 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
+ * <p>
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * 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.hadoop.fs.ozone;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.Iterator;
+
+/**
+ * Lightweight adapter to separte hadoop/ozone classes.
+ * <p>
+ * This class contains only the bare minimum Ozone classes in the signature.
+ * It could be loaded by a different classloader because only the objects in
+ * the method signatures should be shared between the classloader.
+ */
+public interface OzoneClientAdapter {
+
+  void close() throws IOException;
+
+  InputStream createInputStream(String key) throws IOException;
+
+  OzoneFSOutputStream createKey(String key) throws IOException;
+
+  void renameKey(String key, String newKeyName) throws IOException;
+
+  BasicKeyInfo getKeyInfo(String keyName);
+
+  boolean isDirectory(BasicKeyInfo key);
+
+  boolean createDirectory(String keyName);
+
+  boolean deleteObject(String keyName);
+
+  long getCreationTime();
+
+  boolean hasNextKey(String key);
+
+  Iterator<BasicKeyInfo> listKeys(String pathKey);
+
+}

hadoop-ozone/ozonefs/src/main/java/org/apache/hadoop/fs/ozone/OzoneClientAdapterFactory.java

@@ -0,0 +1,119 @@
+/**
+ * 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
+ * <p>
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * 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.hadoop.fs.ozone;
+
+import java.io.IOException;
+import java.net.MalformedURLException;
+import java.net.URL;
+import java.util.ArrayList;
+import java.util.Enumeration;
+import java.util.List;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Creates OzoneClientAdapter with classloader separation.
+ */
+public final class OzoneClientAdapterFactory {
+
+  static final Logger LOG =
+      LoggerFactory.getLogger(OzoneClientAdapterFactory.class);
+
+  private OzoneClientAdapterFactory() {
+  }
+
+  public static OzoneClientAdapter createAdapter(
+      String volumeStr,
+      String bucketStr)
+      throws IOException {
+
+    ClassLoader currentClassLoader = OzoneFileSystem.class.getClassLoader();
+    List<URL> urls = new ArrayList<>();
+
+    findEmbeddedLibsUrl(urls, currentClassLoader);
+
+    findConfigDirUrl(urls, currentClassLoader);
+
+    ClassLoader classLoader =
+        new FilteredClassLoader(urls.toArray(new URL[0]), currentClassLoader);
+
+    try {
+
+      ClassLoader contextClassLoader =
+          Thread.currentThread().getContextClassLoader();
+      Thread.currentThread().setContextClassLoader(classLoader);
+
+      //this class caches the context classloader during the first load
+      //call it here when the context class loader is set to the isoloated
+      //loader to make sure the grpc class will be loaded by the right
+      //loader
+      Class<?> reflectionUtils =
+          classLoader.loadClass("org.apache.ratis.util.ReflectionUtils");
+      reflectionUtils.getMethod("getClassByName", String.class)
+          .invoke(null, "org.apache.ratis.grpc.GrpcFactory");
+
+      OzoneClientAdapter ozoneClientAdapter = (OzoneClientAdapter) classLoader
+          .loadClass("org.apache.hadoop.fs.ozone.OzoneClientAdapterImpl")
+          .getConstructor(String.class, String.class)
+          .newInstance(
+              volumeStr,
+              bucketStr);
+
+      Thread.currentThread().setContextClassLoader(contextClassLoader);
+
+      return ozoneClientAdapter;
+    } catch (Exception e) {
+      LOG.error("Can't initialize the ozoneClientAdapter", e);
+      throw new IOException(
+          "Can't initialize the OzoneClientAdapter implementation", e);
+    }
+
+  }
+
+  private static void findConfigDirUrl(List<URL> urls,
+      ClassLoader currentClassLoader) throws IOException {
+    Enumeration<URL> conf =
+        currentClassLoader.getResources("ozone-site.xml");
+    while (conf.hasMoreElements()) {
+      urls.add(
+          new URL(
+              conf.nextElement().toString().replace("ozone-site.xml", "")));
+
+    }
+  }
+
+  private static void findEmbeddedLibsUrl(List<URL> urls,
+      ClassLoader currentClassloader)
+      throws MalformedURLException {
+
+    //marker file is added to the jar to make it easier to find the URL
+    // for the current jar.
+    String markerFile = "ozonefs.txt";
+    ClassLoader currentClassLoader = OzoneFileSystem.class.getClassLoader();
+
+    URL ozFs = currentClassLoader
+        .getResource(markerFile);
+    String rootPath = ozFs.toString().replace(markerFile, "");
+    urls.add(new URL(rootPath));
+
+    urls.add(new URL(rootPath + "libs/"));
+
+  }
+
+}

hadoop-ozone/ozonefs/src/main/java/org/apache/hadoop/fs/ozone/OzoneClientAdapterImpl.java

@@ -0,0 +1,235 @@
+/**
+ * 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
+ * <p>
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * 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.hadoop.fs.ozone;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.HashMap;
+import java.util.Iterator;
+
+import org.apache.hadoop.hdds.client.ReplicationFactor;
+import org.apache.hadoop.hdds.client.ReplicationType;
+import org.apache.hadoop.hdds.conf.OzoneConfiguration;
+import org.apache.hadoop.ozone.OzoneConfigKeys;
+import org.apache.hadoop.ozone.client.ObjectStore;
+import org.apache.hadoop.ozone.client.OzoneBucket;
+import org.apache.hadoop.ozone.client.OzoneClient;
+import org.apache.hadoop.ozone.client.OzoneClientFactory;
+import org.apache.hadoop.ozone.client.OzoneKey;
+import org.apache.hadoop.ozone.client.OzoneVolume;
+import org.apache.hadoop.ozone.client.io.OzoneOutputStream;
+
+import static org.apache.hadoop.ozone.OzoneConsts.OZONE_URI_DELIMITER;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Implementation of the OzoneFileSystem calls.
+ */
+public class OzoneClientAdapterImpl implements OzoneClientAdapter {
+
+  static final Logger LOG =
+      LoggerFactory.getLogger(OzoneClientAdapterImpl.class);
+
+  private OzoneClient ozoneClient;
+  private ObjectStore objectStore;
+  private OzoneVolume volume;
+  private OzoneBucket bucket;
+  private ReplicationType replicationType;
+  private ReplicationFactor replicationFactor;
+
+  public OzoneClientAdapterImpl(String volumeStr, String bucketStr)
+      throws IOException {
+    this(createConf(), volumeStr, bucketStr);
+  }
+
+  private static OzoneConfiguration createConf() {
+    ClassLoader contextClassLoader =
+        Thread.currentThread().getContextClassLoader();
+    Thread.currentThread().setContextClassLoader(null);
+    OzoneConfiguration conf = new OzoneConfiguration();
+    Thread.currentThread().setContextClassLoader(contextClassLoader);
+    return conf;
+  }
+
+  public OzoneClientAdapterImpl(OzoneConfiguration conf, String volumeStr,
+      String bucketStr) throws IOException {
+    ClassLoader contextClassLoader =
+        Thread.currentThread().getContextClassLoader();
+    Thread.currentThread().setContextClassLoader(null);
+    try {
+      String replicationTypeConf =
+          conf.get(OzoneConfigKeys.OZONE_REPLICATION_TYPE,
+              OzoneConfigKeys.OZONE_REPLICATION_TYPE_DEFAULT);
+
+      int replicationCountConf = conf.getInt(OzoneConfigKeys.OZONE_REPLICATION,
+          OzoneConfigKeys.OZONE_REPLICATION_DEFAULT);
+      this.ozoneClient =
+          OzoneClientFactory.getRpcClient(conf);
+      objectStore = ozoneClient.getObjectStore();
+      this.volume = objectStore.getVolume(volumeStr);
+      this.bucket = volume.getBucket(bucketStr);
+      this.replicationType = ReplicationType.valueOf(replicationTypeConf);
+      this.replicationFactor = ReplicationFactor.valueOf(replicationCountConf);
+    } finally {
+      Thread.currentThread().setContextClassLoader(contextClassLoader);
+    }
+
+  }
+
+  @Override
+  public void close() throws IOException {
+    ozoneClient.close();
+  }
+
+  @Override
+  public InputStream createInputStream(String key) throws IOException {
+    return bucket.readKey(key).getInputStream();
+  }
+
+  @Override
+  public OzoneFSOutputStream createKey(String key) throws IOException {
+    OzoneOutputStream ozoneOutputStream =
+        bucket.createKey(key, 0, replicationType, replicationFactor,
+            new HashMap<>());
+    return new OzoneFSOutputStream(ozoneOutputStream.getOutputStream());
+  }
+
+  @Override
+  public void renameKey(String key, String newKeyName) throws IOException {
+    bucket.renameKey(key, newKeyName);
+  }
+
+  /**
+   * Helper method to fetch the key metadata info.
+   *
+   * @param keyName key whose metadata information needs to be fetched
+   * @return metadata info of the key
+   */
+  @Override
+  public BasicKeyInfo getKeyInfo(String keyName) {
+    try {
+      OzoneKey key = bucket.getKey(keyName);
+      return new BasicKeyInfo(
+          keyName,
+          key.getModificationTime(),
+          key.getDataSize()
+      );
+    } catch (IOException e) {
+      LOG.trace("Key:{} does not exist", keyName);
+      return null;
+    }
+  }
+
+  /**
+   * Helper method to check if an Ozone key is representing a directory.
+   *
+   * @param key key to be checked as a directory
+   * @return true if key is a directory, false otherwise
+   */
+  @Override
+  public boolean isDirectory(BasicKeyInfo key) {
+    LOG.trace("key name:{} size:{}", key.getName(),
+        key.getDataSize());
+    return key.getName().endsWith(OZONE_URI_DELIMITER)
+        && (key.getDataSize() == 0);
+  }
+
+  /**
+   * Helper method to create an directory specified by key name in bucket.
+   *
+   * @param keyName key name to be created as directory
+   * @return true if the key is created, false otherwise
+   */
+  @Override
+  public boolean createDirectory(String keyName) {
+    try {
+      LOG.trace("creating dir for key:{}", keyName);
+      bucket.createKey(keyName, 0, replicationType, replicationFactor,
+          new HashMap<>()).close();
+      return true;
+    } catch (IOException ioe) {
+      LOG.error("create key failed for key:{}", keyName, ioe);
+      return false;
+    }
+  }
+
+  /**
+   * Helper method to delete an object specified by key name in bucket.
+   *
+   * @param keyName key name to be deleted
+   * @return true if the key is deleted, false otherwise
+   */
+  @Override
+  public boolean deleteObject(String keyName) {
+    LOG.trace("issuing delete for key" + keyName);
+    try {
+      bucket.deleteKey(keyName);
+      return true;
+    } catch (IOException ioe) {
+      LOG.error("delete key failed " + ioe.getMessage());
+      return false;
+    }
+  }
+
+  @Override
+  public long getCreationTime() {
+    return bucket.getCreationTime();
+  }
+
+  @Override
+  public boolean hasNextKey(String key) {
+    return bucket.listKeys(key).hasNext();
+  }
+
+  @Override
+  public Iterator<BasicKeyInfo> listKeys(String pathKey) {
+    return new IteratorAdapter(bucket.listKeys(pathKey));
+  }
+
+  /**
+   * Adapter to conver OzoneKey to a safe and simple Key implementation.
+   */
+  public static class IteratorAdapter implements Iterator<BasicKeyInfo> {
+
+    private Iterator<? extends OzoneKey> original;
+
+    public IteratorAdapter(Iterator<? extends OzoneKey> listKeys) {
+      this.original = listKeys;
+    }
+
+    @Override
+    public boolean hasNext() {
+      return original.hasNext();
+    }
+
+    @Override
+    public BasicKeyInfo next() {
+      OzoneKey next = original.next();
+      if (next == null) {
+        return null;
+      } else {
+        return new BasicKeyInfo(
+            next.getName(),
+            next.getModificationTime(),
+            next.getDataSize()
+        );
+      }
+    }
+  }
+}

hadoop-ozone/ozonefs/src/main/java/org/apache/hadoop/fs/ozone/OzoneFSInputStream.java

@@ -18,13 +18,13 @@
 
 package org.apache.hadoop.fs.ozone;
 
+import java.io.IOException;
+import java.io.InputStream;
+
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.classification.InterfaceStability;
 import org.apache.hadoop.fs.FSInputStream;
-import org.apache.hadoop.ozone.client.io.KeyInputStream;
-
-import java.io.IOException;
-import java.io.InputStream;
+import org.apache.hadoop.fs.Seekable;
 
 /**
  * The input stream for Ozone file system.
@@ -36,10 +36,10 @@ import java.io.InputStream;
 @InterfaceStability.Evolving
 public final class OzoneFSInputStream extends FSInputStream {
 
-  private final KeyInputStream inputStream;
+  private final InputStream inputStream;
 
   public OzoneFSInputStream(InputStream inputStream) {
-    this.inputStream = (KeyInputStream)inputStream;
+    this.inputStream = inputStream;
   }
 
   @Override
@@ -59,12 +59,12 @@ public final class OzoneFSInputStream extends FSInputStream {
 
   @Override
   public void seek(long pos) throws IOException {
-    inputStream.seek(pos);
+    ((Seekable) inputStream).seek(pos);
   }
 
   @Override
   public long getPos() throws IOException {
-    return inputStream.getPos();
+    return ((Seekable) inputStream).getPos();
   }
 
   @Override

hadoop-ozone/ozonefs/src/main/java/org/apache/hadoop/fs/ozone/OzoneFSOutputStream.java

@@ -20,7 +20,6 @@ package org.apache.hadoop.fs.ozone;
 
 import java.io.IOException;
 import java.io.OutputStream;
-import org.apache.hadoop.ozone.client.io.KeyOutputStream;
 
 
 /**
@@ -31,10 +30,10 @@ import org.apache.hadoop.ozone.client.io.KeyOutputStream;
  */
 public class OzoneFSOutputStream extends OutputStream {
 
-  private final KeyOutputStream outputStream;
+  private final OutputStream outputStream;
 
   public OzoneFSOutputStream(OutputStream outputStream) {
-    this.outputStream = (KeyOutputStream)outputStream;
+    this.outputStream = outputStream;
   }
 
   @Override

hadoop-ozone/ozonefs/src/main/java/org/apache/hadoop/fs/ozone/OzoneFileSystem.java

@@ -25,20 +25,18 @@ import java.net.URISyntaxException;
 import java.util.ArrayList;
 import java.util.EnumSet;
 import java.util.HashMap;
+import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
-import java.util.Iterator;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
-
-import com.google.common.base.Preconditions;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
-import org.apache.hadoop.hdds.conf.OzoneConfiguration;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
 
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.classification.InterfaceStability;
+import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.fs.CreateFlag;
 import org.apache.hadoop.fs.FSDataInputStream;
 import org.apache.hadoop.fs.FSDataOutputStream;
@@ -47,34 +45,25 @@ import org.apache.hadoop.fs.FileStatus;
 import org.apache.hadoop.fs.FileSystem;
 import org.apache.hadoop.fs.Path;
 import org.apache.hadoop.fs.PathIsNotEmptyDirectoryException;
-import org.apache.hadoop.ozone.client.ObjectStore;
-import org.apache.hadoop.ozone.client.OzoneBucket;
-import org.apache.hadoop.ozone.client.OzoneClient;
-import org.apache.hadoop.ozone.client.OzoneClientFactory;
-import org.apache.hadoop.ozone.OzoneConfigKeys;
-import org.apache.hadoop.ozone.client.OzoneKey;
-import org.apache.hadoop.ozone.client.OzoneVolume;
-import org.apache.hadoop.hdds.client.ReplicationFactor;
-import org.apache.hadoop.hdds.client.ReplicationType;
-import org.apache.http.client.utils.URIBuilder;
-import org.apache.commons.lang3.StringUtils;
-import org.apache.hadoop.classification.InterfaceAudience;
-import org.apache.hadoop.classification.InterfaceStability;
-import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.fs.permission.FsPermission;
+import org.apache.hadoop.hdds.conf.OzoneConfiguration;
 import org.apache.hadoop.security.UserGroupInformation;
 import org.apache.hadoop.util.Progressable;
-import org.apache.hadoop.ozone.client.io.OzoneOutputStream;
 
+import com.google.common.base.Preconditions;
+import org.apache.commons.lang3.StringUtils;
+import static org.apache.hadoop.fs.ozone.Constants.LISTING_PAGE_SIZE;
 import static org.apache.hadoop.fs.ozone.Constants.OZONE_DEFAULT_USER;
-import static org.apache.hadoop.ozone.OzoneConsts.OZONE_URI_SCHEME;
 import static org.apache.hadoop.fs.ozone.Constants.OZONE_USER_DIR;
 import static org.apache.hadoop.ozone.OzoneConsts.OZONE_URI_DELIMITER;
-import static org.apache.hadoop.fs.ozone.Constants.LISTING_PAGE_SIZE;
+import static org.apache.hadoop.ozone.OzoneConsts.OZONE_URI_SCHEME;
+import org.apache.http.client.utils.URIBuilder;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 /**
  * The Ozone Filesystem implementation.
- *
+ * <p>
  * This subclass is marked as private as code should not be creating it
  * directly; use {@link FileSystem#get(Configuration)} and variants to create
  * one. If cast to {@link OzoneFileSystem}, extra methods and features may be
@@ -85,16 +74,15 @@ import static org.apache.hadoop.fs.ozone.Constants.LISTING_PAGE_SIZE;
 public class OzoneFileSystem extends FileSystem {
   static final Logger LOG = LoggerFactory.getLogger(OzoneFileSystem.class);
 
-  /** The Ozone client for connecting to Ozone server. */
-  private OzoneClient ozoneClient;
-  private ObjectStore objectStore;
-  private OzoneVolume volume;
-  private OzoneBucket bucket;
+  /**
+   * The Ozone client for connecting to Ozone server.
+   */
+
   private URI uri;
   private String userName;
   private Path workingDir;
-  private ReplicationType replicationType;
-  private ReplicationFactor replicationFactor;
+
+  private OzoneClientAdapter adapter;
 
   private static final Pattern URL_SCHEMA_PATTERN =
       Pattern.compile("(.+)\\.([^\\.]+)");
@@ -102,11 +90,7 @@ public class OzoneFileSystem extends FileSystem {
   @Override
   public void initialize(URI name, Configuration conf) throws IOException {
     super.initialize(name, conf);
-    if(!(conf instanceof OzoneConfiguration)) {
-      setConf(new OzoneConfiguration(conf));
-    } else {
-      setConf(conf);
-    }
+    setConf(conf);
     Objects.requireNonNull(name.getScheme(), "No scheme provided in " + name);
     assert getScheme().equals(name.getScheme());
 
@@ -125,16 +109,32 @@ public class OzoneFileSystem extends FileSystem {
       uri = new URIBuilder().setScheme(OZONE_URI_SCHEME)
           .setHost(authority).build();
       LOG.trace("Ozone URI for ozfs initialization is " + uri);
-      this.ozoneClient = OzoneClientFactory.getRpcClient(getConf());
-      objectStore = ozoneClient.getObjectStore();
-      this.volume = objectStore.getVolume(volumeStr);
-      this.bucket = volume.getBucket(bucketStr);
-      this.replicationType = ReplicationType.valueOf(
-          getConf().get(OzoneConfigKeys.OZONE_REPLICATION_TYPE,
-              OzoneConfigKeys.OZONE_REPLICATION_TYPE_DEFAULT));
-      this.replicationFactor = ReplicationFactor.valueOf(
-          getConf().getInt(OzoneConfigKeys.OZONE_REPLICATION,
-              OzoneConfigKeys.OZONE_REPLICATION_DEFAULT));
+
+      //isolated is the default for ozonefs-lib-legacy which includes the
+      // /ozonefs.txt, otherwise the default is false. It could be overridden.
+      boolean defaultValue =
+          OzoneFileSystem.class.getClassLoader().getResource("ozonefs.txt")
+              != null;
+
+      //Use string here instead of the constant as constant may not be available
+      //on the classpath of a hadoop 2.7
+      boolean isolatedClassloader =
+          conf.getBoolean("ozone.fs.isolated-classloader", defaultValue);
+
+      if (isolatedClassloader) {
+        this.adapter =
+            OzoneClientAdapterFactory.createAdapter(volumeStr, bucketStr);
+      } else {
+        OzoneConfiguration ozoneConfiguration;
+        if (conf instanceof OzoneConfiguration) {
+          ozoneConfiguration = (OzoneConfiguration) conf;
+        } else {
+          ozoneConfiguration = new OzoneConfiguration(conf);
+        }
+        this.adapter = new OzoneClientAdapterImpl(ozoneConfiguration,
+            volumeStr, bucketStr);
+      }
+
       try {
         this.userName =
             UserGroupInformation.getCurrentUser().getShortUserName();
@@ -142,7 +142,7 @@ public class OzoneFileSystem extends FileSystem {
         this.userName = OZONE_DEFAULT_USER;
       }
       this.workingDir = new Path(OZONE_USER_DIR, this.userName)
-              .makeQualified(this.uri, this.workingDir);
+          .makeQualified(this.uri, this.workingDir);
     } catch (URISyntaxException ue) {
       final String msg = "Invalid Ozone endpoint " + name;
       LOG.error(msg, ue);
@@ -153,7 +153,7 @@ public class OzoneFileSystem extends FileSystem {
   @Override
   public void close() throws IOException {
     try {
-      ozoneClient.close();
+      adapter.close();
     } finally {
       super.close();
     }
@@ -179,7 +179,7 @@ public class OzoneFileSystem extends FileSystem {
     }
 
     return new FSDataInputStream(
-        new OzoneFSInputStream(bucket.readKey(key).getInputStream()));
+        new OzoneFSInputStream(adapter.createInputStream(key)));
   }
 
   @Override
@@ -200,19 +200,16 @@ public class OzoneFileSystem extends FileSystem {
           throw new FileAlreadyExistsException(f + " already exists");
         }
         LOG.trace("Overwriting file {}", f);
-        deleteObject(key);
+        adapter.deleteObject(key);
       }
     } catch (FileNotFoundException ignored) {
       // this means the file is not found
     }
 
-    OzoneOutputStream ozoneOutputStream =
-        bucket.createKey(key, 0, replicationType, replicationFactor,
-            new HashMap<>());
     // We pass null to FSDataOutputStream so it won't count writes that
     // are being buffered to a file
     return new FSDataOutputStream(
-        new OzoneFSOutputStream(ozoneOutputStream.getOutputStream()), null);
+        adapter.createKey(key), null);
   }
 
   @Override
@@ -236,7 +233,7 @@ public class OzoneFileSystem extends FileSystem {
 
   @Override
   public FSDataOutputStream append(Path f, int bufferSize,
-      Progressable progress) throws IOException {
+                                   Progressable progress) throws IOException {
     throw new UnsupportedOperationException("append() Not implemented by the "
         + getClass().getSimpleName() + " FileSystem implementation");
   }
@@ -256,7 +253,7 @@ public class OzoneFileSystem extends FileSystem {
     @Override
     boolean processKey(String key) throws IOException {
       String newKeyName = dstKey.concat(key.substring(srcKey.length()));
-      bucket.renameKey(key, newKeyName);
+      adapter.renameKey(key, newKeyName);
       return true;
     }
   }
@@ -264,7 +261,7 @@ public class OzoneFileSystem extends FileSystem {
   /**
    * Check whether the source and destination path are valid and then perform
    * rename from source path to destination path.
-   *
+   * <p>
    * The rename operation is performed by renaming the keys with src as prefix.
    * For such keys the prefix is changed from src to dst.
    *
@@ -361,6 +358,7 @@ public class OzoneFileSystem extends FileSystem {
 
   private class DeleteIterator extends OzoneListingIterator {
     private boolean recursive;
+
     DeleteIterator(Path f, boolean recursive)
         throws IOException {
       super(f);
@@ -379,7 +377,7 @@ public class OzoneFileSystem extends FileSystem {
         return true;
       } else {
         LOG.trace("deleting key:" + key);
-        boolean succeed = deleteObject(key);
+        boolean succeed = adapter.deleteObject(key);
         // if recursive delete is requested ignore the return value of
         // deleteObject and issue deletes for other keys.
         return recursive || succeed;
@@ -390,6 +388,7 @@ public class OzoneFileSystem extends FileSystem {
   /**
    * Deletes the children of the input dir path by iterating though the
    * DeleteIterator.
+   *
    * @param f directory path to be deleted
    * @return true if successfully deletes all required keys, false otherwise
    * @throws IOException
@@ -431,7 +430,7 @@ public class OzoneFileSystem extends FileSystem {
       result = innerDelete(f, recursive);
     } else {
       LOG.debug("delete: Path is a file: {}", f);
-      result = deleteObject(key);
+      result = adapter.deleteObject(key);
     }
 
     if (result) {
@@ -449,6 +448,7 @@ public class OzoneFileSystem extends FileSystem {
   /**
    * Create a fake parent directory key if it does not already exist and no
    * other child of this parent directory exists.
+   *
    * @param f path to the fake parent directory
    * @throws IOException
    */
@@ -457,12 +457,13 @@ public class OzoneFileSystem extends FileSystem {
     if (!key.isEmpty() && !o3Exists(f)) {
       LOG.debug("Creating new fake directory at {}", f);
       String dirKey = addTrailingSlashIfNeeded(key);
-      createDirectory(dirKey);
+      adapter.createDirectory(dirKey);
     }
   }
 
   /**
    * Check if a file or directory exists corresponding to given path.
+   *
    * @param f path to file/directory.
    * @return true if it exists, false otherwise.
    * @throws IOException
@@ -487,7 +488,7 @@ public class OzoneFileSystem extends FileSystem {
         new HashMap<>(LISTING_PAGE_SIZE);
     private Path f; // the input path
 
-    ListStatusIterator(Path f) throws IOException  {
+    ListStatusIterator(Path f) throws IOException {
       super(f);
       this.f = f;
     }
@@ -495,6 +496,7 @@ public class OzoneFileSystem extends FileSystem {
     /**
      * Add the key to the listStatus result if the key corresponds to the
      * input path or is an immediate child of the input path.
+     *
      * @param key key to be processed
      * @return always returns true
      * @throws IOException
@@ -518,7 +520,7 @@ public class OzoneFileSystem extends FileSystem {
       if (pathToKey(keyPath.getParent()).equals(pathToKey(f))) {
         // This key is an immediate child. Can be file or directory
         if (key.endsWith(OZONE_URI_DELIMITER)) {
-         // Key is a directory
+          // Key is a directory
           addSubDirStatus(keyPath);
         } else {
           addFileStatus(keyPath);
@@ -537,6 +539,7 @@ public class OzoneFileSystem extends FileSystem {
 
     /**
      * Adds the FileStatus of keyPath to final result of listStatus.
+     *
      * @param filePath path to the file
      * @throws FileNotFoundException
      */
@@ -547,6 +550,7 @@ public class OzoneFileSystem extends FileSystem {
     /**
      * Adds the FileStatus of the subdir to final result of listStatus, if not
      * already included.
+     *
      * @param dirPath path to the dir
      * @throws FileNotFoundException
      */
@@ -560,9 +564,9 @@ public class OzoneFileSystem extends FileSystem {
     /**
      * Traverse the parent directory structure of keyPath to determine the
      * which parent/ grand-parent/.. is the immediate child of the input path f.
+     *
      * @param keyPath path whose parent directory structure should be traversed.
      * @return immediate child path of the input path f.
-     * @return immediate child path of the input path f.
      */
     Path getImmediateChildPath(Path keyPath) {
       Path path = keyPath;
@@ -610,6 +614,7 @@ public class OzoneFileSystem extends FileSystem {
 
   /**
    * Get the username of the FS.
+   *
    * @return the short name of the user who instantiated the FS
    */
   public String getUsername() {
@@ -648,7 +653,7 @@ public class OzoneFileSystem extends FileSystem {
         LOG.trace("creating directory for fpart:{}", fPart);
         String key = pathToKey(fPart);
         String dirKey = addTrailingSlashIfNeeded(key);
-        if (!createDirectory(dirKey)) {
+        if (!adapter.createDirectory(dirKey)) {
           // Directory creation failed here,
           // rollback and delete newly created directories
           LOG.trace("Directory creation failed, path:{}", fPart);
@@ -682,11 +687,11 @@ public class OzoneFileSystem extends FileSystem {
 
     if (key.length() == 0) {
       return new FileStatus(0, true, 1, 0,
-          bucket.getCreationTime(), qualifiedPath);
+          adapter.getCreationTime(), qualifiedPath);
     }
 
     // Check if the key exists
-    OzoneKey ozoneKey = getKeyInfo(key);
+    BasicKeyInfo ozoneKey = adapter.getKeyInfo(key);
     if (ozoneKey != null) {
       LOG.debug("Found exact file for path {}: normal file", f);
       return new FileStatus(ozoneKey.getDataSize(), false, 1,
@@ -702,6 +707,7 @@ public class OzoneFileSystem extends FileSystem {
    * Get the FileStatus for input directory path.
    * They key corresponding to input path is appended with a trailing slash
    * to return only the corresponding directory key in the bucket.
+   *
    * @param f directory path
    * @return FileStatus for the input directory path
    * @throws FileNotFoundException
@@ -712,9 +718,9 @@ public class OzoneFileSystem extends FileSystem {
     String key = pathToKey(qualifiedPath);
     key = addTrailingSlashIfNeeded(key);
 
-    OzoneKey ozoneKey = getKeyInfo(key);
-    if(ozoneKey != null) {
-      if (isDirectory(ozoneKey)) {
+    BasicKeyInfo ozoneKey = adapter.getKeyInfo(key);
+    if (ozoneKey != null) {
+      if (adapter.isDirectory(ozoneKey)) {
         // Key is a directory
         LOG.debug("Found file (with /) for path {}: fake directory", f);
       } else {
@@ -730,7 +736,7 @@ public class OzoneFileSystem extends FileSystem {
 
     // File or directory corresponding to input path does not exist.
     // Check if there exists a key prefixed with this key.
-    boolean hasChildren = bucket.listKeys(key).hasNext();
+    boolean hasChildren = adapter.hasNextKey(key);
     if (hasChildren) {
       return new FileStatus(0, true, 1, 0, 0, 0, FsPermission.getDirDefault(),
           getUsername(), getUsername(), qualifiedPath);
@@ -739,65 +745,6 @@ public class OzoneFileSystem extends FileSystem {
     throw new FileNotFoundException(f + ": No such file or directory!");
   }
 
-  /**
-   * Helper method to fetch the key metadata info.
-   * @param key key whose metadata information needs to be fetched
-   * @return metadata info of the key
-   */
-  private OzoneKey getKeyInfo(String key) {
-    try {
-      return bucket.getKey(key);
-    } catch (IOException e) {
-      LOG.trace("Key:{} does not exist", key);
-      return null;
-    }
-  }
-
-  /**
-   * Helper method to check if an Ozone key is representing a directory.
-   * @param key key to be checked as a directory
-   * @return true if key is a directory, false otherwise
-   */
-  private boolean isDirectory(OzoneKey key) {
-    LOG.trace("key name:{} size:{}", key.getName(),
-        key.getDataSize());
-    return key.getName().endsWith(OZONE_URI_DELIMITER)
-        && (key.getDataSize() == 0);
-  }
-
-  /**
-   * Helper method to create an directory specified by key name in bucket.
-   * @param keyName key name to be created as directory
-   * @return true if the key is created, false otherwise
-   */
-  private boolean createDirectory(String keyName) {
-    try {
-      LOG.trace("creating dir for key:{}", keyName);
-      bucket.createKey(keyName, 0, replicationType, replicationFactor,
-          new HashMap<>()).close();
-      return true;
-    } catch (IOException ioe) {
-      LOG.error("create key failed for key:{}", keyName, ioe);
-      return false;
-    }
-  }
-
-  /**
-   * Helper method to delete an object specified by key name in bucket.
-   * @param keyName key name to be deleted
-   * @return true if the key is deleted, false otherwise
-   */
-  private boolean deleteObject(String keyName) {
-    LOG.trace("issuing delete for key" + keyName);
-    try {
-      bucket.deleteKey(keyName);
-      return true;
-    } catch (IOException ioe) {
-      LOG.error("delete key failed " + ioe.getMessage());
-      return false;
-    }
-  }
-
   /**
    * Turn a path (relative or otherwise) into an Ozone key.
    *
@@ -805,7 +752,7 @@ public class OzoneFileSystem extends FileSystem {
    * @return the key of the object that represents the file.
    */
   public String pathToKey(Path path) {
-    Objects.requireNonNull(path, "Path can not be null!");
+    Objects.requireNonNull(path, "Path canf not be null!");
     if (!path.isAbsolute()) {
       path = new Path(workingDir, path);
     }
@@ -839,17 +786,17 @@ public class OzoneFileSystem extends FileSystem {
   }
 
   /**
-   *  This class provides an interface to iterate through all the keys in the
-   *  bucket prefixed with the input path key and process them.
-   *
-   *  Each implementing class should define how the keys should be processed
-   *  through the processKey() function.
+   * This class provides an interface to iterate through all the keys in the
+   * bucket prefixed with the input path key and process them.
+   * <p>
+   * Each implementing class should define how the keys should be processed
+   * through the processKey() function.
    */
   private abstract class OzoneListingIterator {
     private final Path path;
     private final FileStatus status;
     private String pathKey;
-    private Iterator<? extends OzoneKey> keyIterator;
+    private Iterator<BasicKeyInfo> keyIterator;
 
     OzoneListingIterator(Path path)
         throws IOException {
@@ -859,12 +806,13 @@ public class OzoneFileSystem extends FileSystem {
       if (status.isDirectory()) {
         this.pathKey = addTrailingSlashIfNeeded(pathKey);
       }
-      keyIterator = bucket.listKeys(pathKey);
+      keyIterator = adapter.listKeys(pathKey);
     }
 
     /**
      * The output of processKey determines if further iteration through the
      * keys should be done or not.
+     *
      * @return true if we should continue iteration of keys, false otherwise.
      * @throws IOException
      */
@@ -876,6 +824,7 @@ public class OzoneFileSystem extends FileSystem {
      * If for any key, the processKey() returns false, then the iteration is
      * stopped and returned with false indicating that all the keys could not
      * be processed successfully.
+     *
      * @return true if all keys are processed successfully, false otherwise.
      * @throws IOException
      */
@@ -884,7 +833,7 @@ public class OzoneFileSystem extends FileSystem {
       if (status.isDirectory()) {
         LOG.trace("Iterating directory:{}", pathKey);
         while (keyIterator.hasNext()) {
-          OzoneKey key = keyIterator.next();
+          BasicKeyInfo key = keyIterator.next();
           LOG.trace("iterating key:{}", key.getName());
           if (!processKey(key.getName())) {
             return false;

hadoop-ozone/pom.xml

@@ -11,11 +11,7 @@
   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. See accompanying LICENSE file.
--->
-<project xmlns="http://maven.apache.org/POM/4.0.0"
-         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
-http://maven.apache.org/xsd/maven-4.0.0.xsd">
+--><project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>org.apache.hadoop</groupId>
@@ -43,8 +39,10 @@ http://maven.apache.org/xsd/maven-4.0.0.xsd">
     <module>common</module>
     <module>client</module>
     <module>ozone-manager</module>
-    <module>tools</module>
     <module>ozonefs</module>
+    <module>ozonefs-lib</module>
+    <module>ozonefs-lib-legacy</module>
+    <module>tools</module>
     <module>integration-test</module>
     <module>objectstore-service</module>
     <module>datanode</module>
@@ -102,6 +100,16 @@ http://maven.apache.org/xsd/maven-4.0.0.xsd">
         <artifactId>hadoop-ozone-filesystem</artifactId>
         <version>${ozone.version}</version>
       </dependency>
+      <dependency>
+        <groupId>org.apache.hadoop</groupId>
+        <artifactId>hadoop-ozone-filesystem-lib</artifactId>
+        <version>${ozone.version}</version>
+      </dependency>
+      <dependency>
+        <groupId>org.apache.hadoop</groupId>
+        <artifactId>hadoop-ozone-filesystem-lib-legacy</artifactId>
+        <version>${ozone.version}</version>
+      </dependency>
       <dependency>
         <groupId>org.apache.hadoop</groupId>
         <artifactId>hadoop-ozone-integration-test</artifactId>
@@ -207,6 +215,7 @@ http://maven.apache.org/xsd/maven-4.0.0.xsd">
       <groupId>org.apache.hadoop</groupId>
       <artifactId>hadoop-hdds-tools</artifactId>
     </dependency>
+
     <dependency>
       <groupId>org.apache.hadoop</groupId>
       <artifactId>hadoop-common</artifactId>
@@ -304,7 +313,7 @@ http://maven.apache.org/xsd/maven-4.0.0.xsd">
         <groupId>org.codehaus.mojo</groupId>
         <artifactId>findbugs-maven-plugin</artifactId>
         <configuration>
-          <excludeFilterFile combine.self="override"></excludeFilterFile>
+          <excludeFilterFile combine.self="override"/>
         </configuration>
       </plugin>
       <plugin>