Thread leaks occur when resolve address failed.

import org.apache.zookeeper.ClientCnxn; import org.apache.zookeeper.ZooKeeper; import org.apache.zookeeper.server.ZooKeeperThread; import java.lang.reflect.Field; public class Main extends Thread { public static void main( String [] args) { new Main().start(); } @Override public void run() { System .setProperty( "zookeeper.serverCnxnFactory" , "org.apache.zookeeper.server.NettyServerCnxnFactory" ); System .setProperty( "zookeeper.clientCnxnSocket" , "org.apache.zookeeper.ClientCnxnSocketNetty" ); ZooKeeperThread eventThread = null ; try { ZooKeeper zooKeeper = new ZooKeeper( "a.local:4096" , 50000, watchedEvent -> { }); Field cnxnField = zooKeeper.getClass().getDeclaredField( "cnxn" ); cnxnField.setAccessible( true ); ClientCnxn clientCnxn = (ClientCnxn) cnxnField.get(zooKeeper); Field eventThreadField = clientCnxn.getClass().getDeclaredField( "eventThread" ); eventThreadField.setAccessible( true ); eventThread = (ZooKeeperThread) eventThreadField.get(clientCnxn); zooKeeper.close(); } catch (Exception ignore) { ignore.printStackTrace(); } System .out.println(eventThread.getState()); } }