ZOOKEEPER-3883: new UncaughtExceptionHandler object with lambda

Author: ZWShuai91 <17610028856@163.com>

Reviewers: Enrico Olivelli <eolivelli@apache.org>, Norbert Kalmar <nkalmar@apache.org>

Closes #1396 from ZWShuai91/ZOOKEEPER-3883

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

@@ -82,11 +82,7 @@ public class NIOServerCnxnFactory extends ServerCnxnFactory {
     public static final String ZOOKEEPER_NIO_SHUTDOWN_TIMEOUT = "zookeeper.nio.shutdownTimeout";
 
     static {
-        Thread.setDefaultUncaughtExceptionHandler(new Thread.UncaughtExceptionHandler() {
-            public void uncaughtException(Thread t, Throwable e) {
-                LOG.error("Thread {} died", t, e);
-            }
-        });
+        Thread.setDefaultUncaughtExceptionHandler((t, e) -> LOG.error("Thread {} died", t, e));
 
         /**
          * Value of 0 disables use of direct buffers and instead uses

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

@@ -29,13 +29,7 @@ public class ZooKeeperThread extends Thread {
 
     private static final Logger LOG = LoggerFactory.getLogger(ZooKeeperThread.class);
 
-    private UncaughtExceptionHandler uncaughtExceptionalHandler = new UncaughtExceptionHandler() {
-
-        @Override
-        public void uncaughtException(Thread t, Throwable e) {
-            handleException(t.getName(), e);
-        }
-    };
+    private UncaughtExceptionHandler uncaughtExceptionalHandler = (t, e) -> handleException(t.getName(), e);
 
     public ZooKeeperThread(String threadName) {
         super(threadName);