Java利用ShutDownHook关闭系统资源

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

    public void addShutdownHook(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> */
public class ExitThread extends Thread {
    private Log logger = LogFactory.getLog(getClass());

    public void run() {
        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。

    <bean id="simpleHandler" class="com.tiamaes.gjds.socket.server.SimpleHanlder" destroy-method="destroy">
        <property name="annotationSocketServiceFactory" ref="annotationSocketServiceFactory" />
    </bean>

    //此方法需要声明void，并且没有任何参数
    public void destroy(){
        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> */
public class ShutDownHook extends Thread {

    private Log logger = LogFactory.getLog(getClass());

    private ConfigurableApplicationContext applicationContext;

    public ShutDownHook(ConfigurableApplicationContext applicationContext ){
        super();
        this.applicationContext = applicationContext;
    }

    @Override  
    public void run() {
        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。

    public static void main(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

2015-06-09 09:43:51,233 INFO ClassPathXmlApplicationContext  - Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@2e52cdcc: startup date [Tue Jun 09 09:43:51 CST 2015]; root of context hierarchy 2015-06-09 09:43:52,263 INFO XmlBeanDefinitionReader - Loading XML bean definitions from class path resource [applicationContext.xml] 2015-06-09 09:43:55,559 INFO XmlBeanDefinitionReader - Loading XML bean definitions from class path resource [applicationContext-service.xml] 2015-06-09 09:43:55,724 INFO XmlBeanDefinitionReader - Loading XML bean definitions from class path resource [applicationContext-db.xml] 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 [built 08-October-2014 03:06:08 -0700; debug? true; trace: 10] 2015-06-09 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 found 2015-06-09 09:44:13,439 INFO Environment - HHH000021: Bytecode provider name : javassist 2015-06-09 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.Oracle10gDialect 2015-06-09 09:44:15,739 INFO LobCreatorBuilder - HHH000422: Disabling contextual LOB creation as connection was null 2015-06-09 09:44:16,056 INFO ASTQueryTranslatorFactory - HHH000397: Using ASTQueryTranslatorFactory 2015-06-09 09:44:21,032 INFO EhCacheManagerFactoryBean - Initializing EhCache CacheManager 2015-06-09 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 [ acquireIncrement -> 5, acquireRetryAttempts -> 0, acquireRetryDelay -> 1000, autoCommitOnClose -> true, automaticTestTable -> null, breakAfterAcquireFailure -> false, checkoutTimeout -> 5000, connectionCustomizerClassName -> null, connectionTesterClassName -> com.mchange.v2.c3p0.impl.DefaultConnectionTester, contextClassLoaderSource -> caller, dataSourceName -> 1hge7dt991ndh1jygiycad|7402fff0, debugUnreturnedConnectionStackTraces -> false, description -> null, driverClass -> oracle.jdbc.OracleDriver, extensions -> {}, factoryClassLocation -> null, forceIgnoreUnresolvedTransactions -> false, forceUseNamedDriverClass -> false, identityToken -> 1hge7dt991ndh1jygiycad|7402fff0, idleConnectionTestPeriod -> 0, initialPoolSize -> 5, jdbcUrl -> jdbc:oracle:thin:@192.168.57.62:1521:orcl, maxAdministrativeTaskTime -> 0, maxConnectionAge -> 0, maxIdleTime -> 36000, maxIdleTimeExcessConnections -> 1800, maxPoolSize -> 20, maxStatements -> 0, maxStatementsPerConnection -> 0, minPoolSize -> 5, numHelperThreads -> 3, preferredTestQuery -> null, privilegeSpawnedThreads -> false, properties -> {user=******, password=******}, propertyCycle -> 0, statementCacheNumDeferredCloseThreads -> 0, testConnectionOnCheckin -> false, testConnectionOnCheckout -> false, unreturnedConnectionTimeout -> 0, userOverrides -> {}, usesTraditionalReflectiveProxies -> false ] 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 [Tue Jun 09 09:43:51 CST 2015]; root of context hierarchy 2015-06-09 09:54:25,556 INFO EhCacheManagerFactoryBean - Shutting down EhCache CacheManager 2015-06-09 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