干净的停止tomcat/java应用程序

通常在使用了jdbc或者netty的应用程序中，当shutdown tomcat或java应用程序时，会出现无法停止的情况，报类似如下错误：

严重: The web application [] registered the JDBC driver [com.mysql.jdbc.Driver] but failed to unregister it when the web application was stopped. To prevent a memory leak, the JDBC Driver has been forcibly unregistered.
2014-12-11 17:57:37 org.apache.catalina.loader.WebappClassLoader clearReferencesThreads
严重: The web application [] appears to have started a thread named [FileWatchdog] but has failed to stop it. This is very likely to create a memory leak.
2014-12-11 17:57:37 org.apache.catalina.loader.WebappClassLoader clearReferencesThreads
严重: The web application [] appears to have started a thread named [DefaultQuartzScheduler_Worker-1] but has failed to stop it. This is very likely to create a memory leak.
2014-12-11 17:57:37 org.apache.catalina.loader.WebappClassLoader clearReferencesThreads
严重: The web application [] appears to have started a thread named [DefaultQuartzScheduler_Worker-2] but has failed to stop it. This is very likely to create a memory leak.
2014-12-11 17:57:37 org.apache.catalina.loader.WebappClassLoader clearReferencesThreads
严重: The web application [] appears to have started a thread named [DefaultQuartzScheduler_Worker-3] but has failed to stop it. This is very likely to create a memory leak.
2014-12-11 17:57:37 org.apache.catalina.loader.WebappClassLoader clearReferencesThreads
严重: The web application [] appears to have started a thread named [DefaultQuartzScheduler_Worker-4] but has failed to stop it. This is very likely to create a memory leak.

应该来说，在至少95%的应用中，这个时候采用kill -9杀掉tomcat或java进程的方式并没有什么问题，因为通常业务进行了检测，亦或是互联网应用可以容忍少量的数据不一致性。所以这个时候无需强行介入或者关心，但是如果应用中缓存了相关需要持久化的数据，这个时候就不能直接这么粗暴的停止应用程序了，这会导致数据的不一致性。

在我们公司开发的通信应用框架中，其中支持一种可信的模式，所有请求接收到必须被执行，因此为了最大化性能，我们使用了进程内缓存，同时为了确保尽可能最小化不必要的异常检测和客户体验，我们需要干净的关闭相关线程池和连接。

在运行于servlet容器的模式下，可通过实现ServletContextListener接口或者继承spring的ContextLoaderListener类的contextDestroyed方法来释放相关资源，如下所示：

    public void contextDestroyed(ServletContextEvent event) {
        SpiderShutdownCleaner.shutdown();
        super.contextDestroyed(event);
    }

当所有的非daemon线程均停止后，对于活动线程而言，其实就是调用Thread.interupt（正常停止）或者stop（强杀，已经deprecated），jvm就会退出。

干净的停止tomcat/java应用程序

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