session - 在有界/无界到 HTTP 会话时获取通知

Question

当我的对象有界/无界到 HTTP 的会话对象时，我如何得到通知。

Answer 1

让对象的类实现HttpSessionBindingListener。

public class YourObject implements HttpSessionBindingListener {

    @Override
    public void valueBound(HttpSessionBindingEvent event) {
        // The current instance has been bound to the HttpSession.
    }

    @Override
    public void valueUnbound(HttpSessionBindingEvent event) {
        // The current instance has been unbound from the HttpSession.
    }

}

如果您无法控制对象的类代码，因此您无法更改其代码，那么另一种方法是实现HttpSessionAttributeListener.

@WebListener
public class YourObjectSessionAttributeListener implements HttpSessionAttributeListener {

    @Override
    public void attributeAdded(HttpSessionBindingEvent event) {
        if (event.getValue() instanceof YourObject) {
            // An instance of YourObject has been bound to the session.
        }
    }

    @Override
    public void attributeRemoved(HttpSessionBindingEvent event) {
        if (event.getValue() instanceof YourObject) {
            // An instance of YourObject has been unbound from the session.
        }
    }

    @Override
    public void attributeReplaced(HttpSessionBindingEvent event) {
        if (event.getValue() instanceof YourObject) {
            // An instance of YourObject has been replaced in the session.
        }
    }

}

注意：当您仍在使用 Servlet 2.5 或更早版本时，请替换@WebListener为.<listener>web.xml