如何在会话对象被销毁之前调用方法？ [英] How to call a method before the session object is destroyed?

问题描述

开发JSP应用程序时，可以定义会话超时值，比如30分钟。

超时后，会话对象被销毁。
此外，我可以通过编程方式使会话调用session.invalidate（）无效。

由于我在HTTP会话中保存了一个复杂的Java对象，因此无效之前会话或让tomcat app服务器过期，我需要调用一个保存的对象方法来释放一些内存。当然，当用户单击注销按钮时，我可以通过编程方式执行此操作。

我想要做的是拦截Tomcat应用服务器什么时候会破坏所有过期的会话（30分钟或自定义），这样我就可以预先处理会话中保存的Java对象，调用特定方法来释放内存。

是否可以？

解决方案

是的，这是可能的。您可以使用 HttpSessionListener 并在 sessionDestroyed（）方法中完成工作，

  @WebListener 
公共类MyHttpSessionListener实现HttpSessionListener {
 
 @Override 
 public void sessionDestroyed（HttpSessionEvent event）{
 //这里的工作。 
} 
 
 // ... 
} 
  

或你可以让作为会话属性存储的复杂对象实现 HttpSessionBindingListener 并在 valueUnbound（）方法。

 公共类YourComplexObject实现HttpSessionBindingListener {
 
 @Override 
 public void valueUnbound（HttpSessionBindingEvent事件）{
 //在这里完成工作。 
} 
 
 // ... 
} 
  

每当要从会话中删除对象时（通过 HttpSession＃removeAttribute（）或通过会话的无效/过期）将调用它。 / p>


When developing a JSP application it's possible to define a session timeout value, say 30 minutes.

After that timeout, the session object is destroyed. Moreover I can programmatically invalidate a session calling session.invalidate() .

Since I'm saving a complex Java object inside the HTTP session, before invalidate the session or let it expire by the tomcat app server, I need to call a saved object method to release some memory. Of course I can do it programmatically when the user click a logout button.

What I would like to do is intercepting the Tomcat app server when it is going to destroy all expired sessions (30 minutes or custom), so that I can pre-process Java objects saved in the session calling a specific method to release memory.

Is it possible?

解决方案

Yes, that's possible. You could use HttpSessionListener and do the job in sessionDestroyed() method,

@WebListener
public class MyHttpSessionListener implements HttpSessionListener {

    @Override
    public void sessionDestroyed(HttpSessionEvent event) {
        // Do here the job.
    }

    // ...
}

Or you could let the complex object which is been stored as a session attribute implement the HttpSessionBindingListener and do the job in valueUnbound() method.

public class YourComplexObject implements HttpSessionBindingListener {

    @Override
    public void valueUnbound(HttpSessionBindingEvent event) {
        // Do here the job.
    }

    // ...
}

It will be called whenever the object is to be removed from the session (either explicitly by HttpSession#removeAttribute() or by an invalidation/expire of the session).

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