为什么在Java servlet中设置会话中的属性有时会失败？

>可能会有两个不同的会话.
>可能会有一些代码从会话中删除配置对象.
>其他人？

这是一种可以测试以确定究竟发生了什么的方法.

您可以实现两个单独的侦听器接口来侦听特定的会话事件：javax.servlet.http.HttpSessionListener和javax.servlet.http.HttpSessionAttributeListener

我将使用一个类来实现这两个接口,该类将记录每个事件期间发生的事情以及事件来自哪个会话.

您应该能够轻松地将侦听器添加到web.xml文件中,以便它们实际上可以通过tomcat设置为会话的侦听器.

编辑

这是一个可以作为会话监听器放入web.xml的类. BalusC和我都建议您尝试这种方法来调试问题.如果您在设置“配置”属性的方式中看到任何有趣的内容,请只是幽默我们并告诉我们？

import javax.servlet.http.HttpSessionActivationListener;
import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionBindingEvent;
import javax.servlet.http.HttpSessionBindingListener;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

public class SessionListener implements HttpSessionListener,HttpSessionAttributeListener,HttpSessionBindingListener,HttpSessionActivationListener {

public void valueBound(HttpSessionBindingEvent event) {
    System.out.println("valueBound: " + event.getName() + " : " + event.getValue());
    System.out.println("  session: " + event.getSession().getId());
    this.printstacktrace();
}

public void valueUnbound(HttpSessionBindingEvent event) {
    System.out.println("valueUnbound: " + event.getName() + " : " + event.getValue());
    System.out.println("  session: " + event.getSession().getId());
    this.printstacktrace();
}

public void attributeAdded(HttpSessionBindingEvent event) {
    System.out.println("attributeAdded: " + event.getName() + " : " + event.getValue());
    System.out.println("  session: " + event.getSession().getId());
    this.printstacktrace();
}

public void attributeRemoved(HttpSessionBindingEvent event) {
    System.out.println("attributeRemoved: " + event.getName() + " : " + event.getValue());
    System.out.println("  session: " + event.getSession().getId());
    this.printstacktrace();
}

public void attributeReplaced(HttpSessionBindingEvent event) {
    System.out.println("attributeReplaced: " + event.getName() + " : " + event.getValue());
    System.out.println("  session: " + event.getSession().getId());
    this.printstacktrace();
}

public void sessionCreated(HttpSessionEvent event) {
    System.out.println("sessionCreated: " + event.getSession().getId());
    this.printstacktrace();
}

public void sessionDestroyed(HttpSessionEvent event) {
    System.out.println("sessionDestroyed: " + event.getSession().getId());
    this.printstacktrace();
}

public void sessionDidActivate(HttpSessionEvent event) {
    System.out.println("sessionDidActivate: " + event.getSession().getId());
    this.printstacktrace();
}

@Override
public void sessionWillPassivate(HttpSessionEvent event) {
    System.out.println("sessionWillPassivate: " + event.getSession().getId());
    this.printstacktrace();
}

private void printstacktrace() {
    try {
        if (true) {
            throw new Exception();
        }
    } catch (Exception e) {
        e.printstacktrace();
    }
}
}

请将上面的类添加到代码中,然后将以下内容添加到过滤器映射和servlet映射之间的web.xml文件中：

<listener>
    <listener-class><your.package.name>SessionListener</listener-class>
</listener>