Servlets-Session属性变为NULL

Question

我是servlet和jsp的新手。 在我的程序中，流程如下：

loginpage.html > controller （ loginpage.html在这里我创建了这样的会话）

HttpSession session = request.getSession(true);
session.setAttribute("uid", uname);
System.out.println("session:"+session.getAttribute("uid"));// shows the value of uid

-> create_user.html > conroller （现在将uid值显示为null）-> view_customers.jsp （此处需要uid值，但为null ）。

如何避免会话属性变为空？ 提前致谢！

Answer 1

如何避免会话属性变为空？

您可以使用HttpSessionAttributeListener监视session scope的属性状态（添加/删除/替换）。

样例代码：

public class MySessionAttributeListener implements HttpSessionAttributeListener {

    public MySessionAttributeListener() {
    }

    public void attributeAdded(HttpSessionBindingEvent sessionBindingEvent) {

        // Get the session
        HttpSession session = sessionBindingEvent.getSession();

        // Log some information
        System.out.println("[SessionAttr] " + new java.util.Date()
                + " Attribute added, session " + session + ": " + sessionBindingEvent.getName()
                + "=" + sessionBindingEvent.getValue());
    }

    public void attributeRemoved(HttpSessionBindingEvent sessionBindingEvent) {

        // Get the session
        HttpSession session = sessionBindingEvent.getSession();

        // Log some information
        System.out.println("[SessionAttr] " + new java.util.Date()
                + " Attribute removed, session " + session + ": "
                + sessionBindingEvent.getName());
    }

    public void attributeReplaced(HttpSessionBindingEvent sessionBindingEvent) {

        // Get the session
        HttpSession session = sessionBindingEvent.getSession();

        // Log some information
        System.out.println("[SessionAttr] " + new java.util.Date()
                + " Attribute replaced, session " + session + ": "
                + sessionBindingEvent.getName() + "=" + sessionBindingEvent.getValue());
    }
}

web.xml ：（在web.xml中的行下方添加）

<listener>
    <listener-class>com.x.y.z.MySessionAttributeListener</listener-class>
</listener>