WatchService导致tomcat内存泄漏

Question

我有一个WatchService用于监视文件夹中的新文件和修改文件。

问题:应用程序在tomcat服务器上运行，当我关闭服务器时，记录以下错误消息(加上它需要很长时间直到服务器关闭):

01-Oct-2015 08:58:11.998 WARNING [localhost-startStop-2] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThreads The web application [myapp] appears to have started a thread named [Thread-5] but has failed to stop it. This is very likely to create a memory leak.
Stack trace of thread:
sun.nio.fs.WindowsNativeDispatcher.GetQueuedCompletionStatus0(Native Method)
sun.nio.fs.WindowsNativeDispatcher.GetQueuedCompletionStatus(Unknown Source)
sun.nio.fs.WindowsWatchService$Poller.run(Unknown Source)
java.lang.Thread.run(Unknown Source)
01-Oct-2015 08:58:11.998 WARNING [localhost-startStop-2] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThreads The web application [myapp] appears to have started a thread named [SimpleAsyncTaskExecutor-2] but has failed to stop it. This is very likely to create a memory leak.
Stack trace of thread:
sun.misc.Unsafe.park(Native Method)
java.util.concurrent.locks.LockSupport.park(Unknown Source)
java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(Unknown Source)
java.util.concurrent.LinkedBlockingDeque.takeFirst(Unknown Source)
java.util.concurrent.LinkedBlockingDeque.take(Unknown Source)
sun.nio.fs.AbstractWatchService.take(Unknown Source)

我该如何解决这个问题?我的值班和往常一样:

WatchService watchService = FileSystems.getDefault().newWatchService();
Path path = Paths.get(folder);
path.register(watchService, events);
WatchKey key = null;
while (true) {
    try {
        key = watchService.take();
        for (WatchEvent<?> event : key.pollEvents()) {
            //etc
        }
        key.reset();
    } catch (ClosedWatchServiceException e) {
        break;
    }
}

Answer 1

看起来好像你没有调用java.nio.file.WatchService.close()在你的代码的任何地方;java.nio.file.WatchService实现了java.io.Closeable，这意味着你可以很容易地确保你摆脱任何与不正确使用java.nio.file.WatchService相关的内存泄漏，通过使用一个尝试资源(自Java 7以来可用)块，如下所示:

try(WatchService watchService = FileSystems.getDefault().newWatchService()) {
    Path path = Paths.get(folder);
    path.register(watchService, events);
    WatchKey key = null;
    while (true) {
        try {
            key = watchService.take();
            for (WatchEvent<?> event : key.pollEvents()) {
                //etc
            }
            key.reset();
        } catch(InterruptedException | ClosedWatchServiceException e) { 
            Thread.currentThread().interrupt();            
        }
    }
}

还请看看WatchService java规范，阅读文档通常会有很大帮助。

The close method may be invoked at any time to close the service causing any threads waiting to retrieve keys, to throw ClosedWatchServiceException.