我正在开发部署在Tomcat上的应用程序。我使用Smack在XMPP上实现CCS FCM。我正在监视关闭挂钩，并在关闭时运行connection.disconnect（）。但是在取消部署时，我在catalina日志中得到了这个痕迹。
10-Oct-2017 17:44:06.952 WARNING [https-jsse-nio2-8081-exec-6] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThreads The web application [wfmserver] appears to have started a thread named [Smack-Ping 0 (0)] but has failed to stop it. This is very likely to create a memory leak. Stack trace of thread:
sun.misc.Unsafe.park(Native Method)
java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:215)
java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:2078)
java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1093)
java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:809)
java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
java.lang.Thread.run(Thread.java:748)
10-Oct-2017 17:44:06.952 WARNING [https-jsse-nio2-8081-exec-6] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThreads The web application [wfmserver] appears to have started a thread named [Smack-Incoming Processor 0 (0)] but has failed to stop it. This is very likely to create a memory leak. Stack trace of thread:
sun.misc.Unsafe.park(Native Method)
java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
java.util.concurrent.ArrayBlockingQueue.take(ArrayBlockingQueue.java:403)
java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
java.lang.Thread.run(Thread.java:748)
10-Oct-2017 17:44:06.953 WARNING [https-jsse-nio2-8081-exec-6] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThreads The web application [wfmserver] appears to have started a thread named [Smack-Single Threaded Executor 0 (0)] but has failed to stop it. This is very likely to create a memory leak. Stack trace of thread:
sun.misc.Unsafe.park(Native Method)
java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
java.lang.Thread.run(Thread.java:748)
10-Oct-2017 17:44:06.953 WARNING [https-jsse-nio2-8081-exec-6] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThreads The web application [wfmserver] appears to have started a thread named [MappedByteBufferSource Async Flush Thread] but has failed to stop it. This is very likely to create a memory leak. Stack trace of thread:
sun.misc.Unsafe.park(Native Method)
java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1081)
java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:809)
java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
java.lang.Thread.run(Thread.java:748)
10-Oct-2017 17:44:06.953 WARNING [https-jsse-nio2-8081-exec-6] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThreads The web application [wfmserver] appears to have started a thread named [Smack-Cached Executor 0 (0)] but has failed to stop it. This is very likely to create a memory leak. Stack trace of thread:
sun.misc.Unsafe.park(Native Method)
java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:215)
java.util.concurrent.SynchronousQueue$TransferStack.awaitFulfill(SynchronousQueue.java:460)
java.util.concurrent.SynchronousQueue$TransferStack.transfer(SynchronousQueue.java:362)
java.util.concurrent.SynchronousQueue.poll(SynchronousQueue.java:941)
java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1073)
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
java.lang.Thread.run(Thread.java:748)
所以，我的问题是我应该如何关闭smack？我如何防止内存泄漏？