Java关闭钩子
在Java程序中可以通过添加关闭钩子，，实现在程序退出时关闭资源的功能。 使用Runtime.addShutdownHook(Thread hook)向JVM添加关闭钩子
(Thread hook) {SecurityManager sm = System.getSecurityManager();if (sm != null) {sm.checkPermission(new RuntimePermission(“shutdownHooks”));}ApplicationShutdownHooks.add(hook);}
ShutdownHook(Thread hook)方法，可以注册一个JVM关闭的钩子，这个钩子可以在以下几种场景被调用： 1）程序正常退出 2）使用System.exit() 3）终端使用Ctrl+C触发的中断 4）系统关闭 5）使用Kill pid命令干掉进程
在Eclipse中使用关闭钩子
在Eclipse中直接点击Terminate关闭程序时不会触发关闭钩子的。在Linux下使用kill -9也是不会触发钩子的
如果想在Eclipse中实现关闭钩子的功能，需要另起一个线程监听控制台，在控制台输入Enter时关闭系统
/** * <p>类描述： 输入Enter键关闭系统 </p> * <p>创建人：王成委 </p> * <p>创建时间：2015年6月8日 下午5:23:31 </p> */{private Log logger = LogFactory.getLog(getClass());() {logger.info(“press ENTER to call System.exit(0) “);try {System.in.read();} catch (IOException e) {e.printStackTrace();}System.exit(0);}}Spring中关闭资源的配置
在使用Spring时，可以在Bean中配置destroy-method来实现系统关闭时对Bean的一些处理。
==> (){logger.info(“Stop socket handler.”);}Java+Spring实现在程序退出时关闭Spring/** * <p>类描述： 系统关闭钩子，用于关闭Spring资源 </p> * <p>创建人：王成委 </p> * <p>创建时间：2015年6月8日 下午5:06:46 </p> */{private Log logger = LogFactory.getLog(getClass());private ConfigurableApplicationContext applicationContext;public ShutDownHook(ConfigurableApplicationContext applicationContext ){super();this.applicationContext = applicationContext;}() {logger.info(“Start clean the login info.”);//在系统关闭时，清理所有用户的登录状态TbDxpUserLoginStatusRepository repository = applicationContext.getBean(TbDxpUserLoginStatusRepository.class);repository.deleteAll();applicationContext.close();logger.info(“Socket server shutdown”);}}
在ShutdownHook实例化时需要传入Spring上下文，在系统关闭时调用ApplicationContext的Close方法。
(String[] args) {ClassPathXmlApplicationContext ct =new ClassPathXmlApplicationContext(“applicationContext.xml”);Runtime.getRuntime().addShutdownHook(new ShutDownHook(ct));//在正式部署时不需要下面的代码，这段代码仅供调试时使用Thread thread = new ExitThread();thread.start();}
最终效果如下
::43:51 CST 2015]; root of context hierarchy2015-06-09 09:43:52,263 INFO XmlBeanDefinitionReader – Loading XML bean definitions from class path resource 2015-06-09 09:43:55,559 INFO XmlBeanDefinitionReader – Loading XML bean definitions from class path resource 2015-06-09 09:43:55,724 INFO XmlBeanDefinitionReader – Loading XML bean definitions from class path resource 2015-06-09 09:44:01,358 INFO PropertyPlaceholderConfigurer – Loading properties file from class path resource [jdbc.properties]2015-06-09 09:44:02,687 INFO MLog – MLog clients using slf4j logging.2015-06-09 09:44:06,563 INFO C3P0Registry – Initializing c3p0-0.9.5-pre9 :; debug2015-06-09 09:44:08,930 INFO LocalContainerEntityManagerFactoryBean – Building JPA container EntityManagerFactory for persistence unit ‘Oracle’2015-06-09 09:44:09,251 INFO LogHelper – HHH000204: Processing PersistenceUnitInfo [name: Oracle…]2015-06-09 09:44:13,400 INFO Version – HHH000412: Hibernate Core {4.3.7.Final}2015-06-09 09:44:13,404 INFO Environment – HHH000206: hibernate.properties not found2015-06-09 09:44:13,439 INFO Environment – HHH000021: Bytecode provider name : javassist2015-06-09 09:44:15,016 INFO Version – HCANN000001: Hibernate Commons Annotations {4.0.5.Final}2015-06-09 09:44:15,660 INFO Dialect – HHH000400: Using dialect: org.hibernate.dialect.Oracle10gDialect2015-06-09 09:44:15,739 INFO LobCreatorBuilder – HHH000422: Disabling contextual LOB creation as connection was null2015-06-09 09:44:16,056 INFO ASTQueryTranslatorFactory – HHH000397: Using ASTQueryTranslatorFactory2015-06-09 09:44:21,032 INFO EhCacheManagerFactoryBean – Initializing EhCache CacheManager2015-06-09 09:44:21,977 INFO ExitThread – press ENTER to call System.exit(0) 2015-06-09 09:54:23,694 INFO ShutDownHook – Start clean the login info.2015-06-09 09:54:23,787 INFO AbstractPoolBackedDataSource – Initializing c3p0 pool… com.mchange.v2.c3p0.ComboPooledDataSource , acquireRetryDelay , automaticTestTable , checkoutTimeout , connectionTesterClassName fff0, debugUnreturnedConnectionStackTraces , driverClass , forceUseNamedDriverClass hge7dt991ndh1jygiycad, initialPoolSize :, maxIdleTime , maxPoolSize , maxStatementsPerConnection , numHelperThreads , privilegeSpawnedThreads , statementCacheNumDeferredCloseThreads , testConnectionOnCheckout , userOverrides Hibernate: select tbdxpuserl0_.SESSION_ID as SESSION_ID1_1_, tbdxpuserl0_.CREATE_TIME as CREATE_TIME2_1_, tbdxpuserl0_.IP_ADDR as IP_ADDR3_1_, tbdxpuserl0_.LOGIN_TIME as LOGIN_TIME4_1_, tbdxpuserl0_.status as status5_1_, tbdxpuserl0_.USER_ID as USER_ID6_1_, tbdxpuserl0_.username as username7_1_ from TB_DXP_USER_LOGIN_STATUS tbdxpuserl0_2015-06-09 09:54:25,555 INFO ClassPathXmlApplicationContext – Closing org.springframework.context.support.ClassPathXmlApplicationContext@2e52cdcc: startup date ; root of context hierarchy2015-06-09 09:54:25,556 INFO EhCacheManagerFactoryBean – Shutting down EhCache CacheManager2015-06-09 09:54:25,574 INFO SimpleHanlder – Stop socket handler.2015-06-09 09:54:25,576 INFO LocalContainerEntityManagerFactoryBean – Closing JPA EntityManagerFactory for persistence unit ‘Oracle’2015-06-09 09:54:25,579 INFO ShutDownHook – Socket server shutdown
此方法可以实现在系统退出时对资源的关闭及缓存数据清理等功能，是一个非常使用的功能。
文中部分内容来自其他博文，代码是我项目中的代码。如有雷同，请勿见怪。 本文只介绍如何使用，至于原理请问度娘和谷歌
任何的限制，都是从自己的内心开始的。
