Spring中的destroy-method方法

转载：http://technoboy.iteye.com/blog/970293。destroy-method 欠缺，补上。

1. Bean标签的destroy-method方法

配置数据源的时候，会有一个destroy-method方法

Java代码

1. <bean id = "dataSource" class = "org.apache.commons.dbcp.BasicDataSource" destroy-method="close">
2. <property name="driverClassName" value="${jdbc.driver}"></property>
3. <property name="url" value="${jdbc.url}"></property>
4. <property name="username" value="${jdbc.username}"></property>
5. <property name="password" value="${jdbc.password}"></property>
6. <property name="maxActive" value="${maxActive}"></property>
7. <property name="maxWait" value="${maxWait}"></property>
8. <property name="maxIdle" value="30"></property>
9. <property name="initialSize" value="2"></property>
10. </bean>

<bean id = "dataSource" class = "org.apache.commons.dbcp.BasicDataSource" destroy-method="close">
	<property name="driverClassName" value="${jdbc.driver}"></property>
		<property name="url" value="${jdbc.url}"></property>
		<property name="username" value="${jdbc.username}"></property>
		<property name="password" value="${jdbc.password}"></property>
		<property name="maxActive" value="${maxActive}"></property>
		<property name="maxWait" value="${maxWait}"></property>
		<property name="maxIdle" value="30"></property>
		<property name="initialSize" value="2"></property>
</bean>

这个destroy-method属性是干什么用的。什么时候调用呢?
Spring中的doc上是这么说destroy-method方法的---

Java代码

1. The name of the custom destroy method to invoke on bean factory shutdown. The method must have no arguments, but may throw any exception. Note: Only invoked on beans whose lifecycle is under the full control of the factory - which is always the case for singletons, but not guaranteed for any other scope.

The name of the custom destroy method to invoke on bean factory shutdown. The method must have no arguments, but may throw any exception. Note: Only invoked on beans whose lifecycle is under the full control of the factory - which is always the case for singletons, but not guaranteed for any other scope.

其实，这是依赖在Servlet容器或者EJB容器中，它才会被自动给调用的。比如我们用Servlet容器，经常在web.xml文件中配置这样的监听器

Java代码

1. <listener>
2. <listener-class>
3. org.springframework.web.context.ContextLoaderListener
4. </listener-class>
5. </listener>

<listener>
   <listener-class>
	org.springframework.web.context.ContextLoaderListener
   </listener-class>
</listener>

我们按层次包，看一下ContextLoaderListener这个类。

Java代码

1. public class ContextLoaderListener extends ContextLoader implements ServletContextListener {
2. //这个是web容器初始化调用的方法。
3. public void contextInitialized(ServletContextEvent event) {
4. this.contextLoader = createContextLoader();
5. if (this.contextLoader == null) {
6. this.contextLoader = this;
7. }
8. this.contextLoader.initWebApplicationContext(event.getServletContext());
9. }
11. //这个是web容器销毁时调用的方法。
12. public void contextDestroyed(ServletContextEvent event) {
13. if (this.contextLoader != null) {
14. this.contextLoader.closeWebApplicationContext(event.getServletContext());
15. }
16. ContextCleanupListener.cleanupAttributes(event.getServletContext());
17. }

public class ContextLoaderListener extends ContextLoader implements ServletContextListener {
  //这个是web容器初始化调用的方法。
  public void contextInitialized(ServletContextEvent event) {
		this.contextLoader = createContextLoader();
		if (this.contextLoader == null) {
			this.contextLoader = this;
		}
		this.contextLoader.initWebApplicationContext(event.getServletContext());
	}
  
  //这个是web容器销毁时调用的方法。
  public void contextDestroyed(ServletContextEvent event) {
		if (this.contextLoader != null) {
			this.contextLoader.closeWebApplicationContext(event.getServletContext());
		}
		ContextCleanupListener.cleanupAttributes(event.getServletContext());
	}

ContextLoaderListener实现了javax.servlet.ServletContextListener，它是servlet容器的监听器接口。
ServletContextListener接口中定义了两个方法。

Java代码

1. public void contextInitialized(ServletContextEvent event)；
2. public void contextDestroyed(ServletContextEvent event)；

public void contextInitialized(ServletContextEvent event)；
public void contextDestroyed(ServletContextEvent event)；

分别在容器初始化或者销毁的时候调用。
那么当我们销毁容器的时候，其实就是调用的contextDestroyed方法里面的内容。
这里面执行了ContextLoader的closeWebApplicationContext方法。

Java代码

1. public void closeWebApplicationContext(ServletContext servletContext) {
2. servletContext.log("Closing Spring root WebApplicationContext");
3. try {
4. if (this.context instanceof ConfigurableWebApplicationContext) {
5. ((ConfigurableWebApplicationContext) this.context).close();
6. }
7. }
8. finally {
9. ClassLoader ccl = Thread.currentThread().getContextClassLoader();
10. if (ccl == ContextLoader.class.getClassLoader()) {
11. currentContext = null;
12. }
13. else if (ccl != null) {
14. currentContextPerThread.remove(ccl);
15. }
16. servletContext.removeAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE);
17. if (this.parentContextRef != null) {
18. this.parentContextRef.release();
19. }
20. }
21. }

public void closeWebApplicationContext(ServletContext servletContext) {
		servletContext.log("Closing Spring root WebApplicationContext");
		try {
			if (this.context instanceof ConfigurableWebApplicationContext) {
				((ConfigurableWebApplicationContext) this.context).close();
			}
		}
		finally {
			ClassLoader ccl = Thread.currentThread().getContextClassLoader();
			if (ccl == ContextLoader.class.getClassLoader()) {
				currentContext = null;
			}
			else if (ccl != null) {
				currentContextPerThread.remove(ccl);
			}
			servletContext.removeAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE);
			if (this.parentContextRef != null) {
				this.parentContextRef.release();
			}
		}
	}

这里面，将context转型为ConfigurableWebApplicationContext，而
ConfigurableWebApplicationContext继承自ConfigurableApplicationContext，在ConfigurableApplicationContext(ConfigurableApplicationContext实现了Lifecycle,正是前文提到的lifecycle)里有
close()方法的定义。在AbstractApplicationContext实现了close()方法。真正执行的是

Java代码

1. protected void destroyBeans() {
2. getBeanFactory().destroySingletons();
3. }

protected void destroyBeans() {
    getBeanFactory().destroySingletons();
}

方法(spring容器在启动的时候,会创建org.apache.commons.dbcp.BasicDataSource的对象，放入singleton缓存中。那么在容器销毁的时候，会清空缓存并调用BasicDataSourc中的close()方法。
)
BasicDataSourc类中的close()方法

Java代码

1. public synchronized void close() throws SQLException {
2. GenericObjectPool oldpool = connectionPool;
3. connectionPool = null;
4. dataSource = null;
5. try {
6. if (oldpool != null) {
7. oldpool.close();
8. }
9. } catch(SQLException e) {
10. throw e;
11. } catch(RuntimeException e) {
12. throw e;
13. } catch(Exception e) {
14. throw new SQLNestedException("Cannot close connection pool", e);
15. }
16. }

public synchronized void close() throws SQLException {
        GenericObjectPool oldpool = connectionPool;
        connectionPool = null;
        dataSource = null;
        try {
            if (oldpool != null) {
                oldpool.close();
            }
        } catch(SQLException e) {
            throw e;
        } catch(RuntimeException e) {
            throw e;
        } catch(Exception e) {
            throw new SQLNestedException("Cannot close connection pool", e);
        }
    }

那么，如果spring不在Servlet或者EJB容器中,我们就需要手动的调用AbstractApplicationContext类中的close()方法，去实现相应关闭的功能。