在login.jsp里有

session.setAttribute("id",userid);

session.setAttribute("pvw",pvw);

session.setAttribute("name",name);

session.setAttribute("psw",psw);

在logout.jsp里设

session.setAttribute("id",null);

session.setAttribute("pvw",null);

session.setAttribute("name",null);

session.setAttribute("psw",null);

虽然结果是session值已经不存在了。但是logout.jsp提示出错：

java.lang.NullPointerException

at _0002flogout_0002ejsplogout_jsp_15._jspService(_0002flogout_0002ejsplogout_jsp_15.java:80)

at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:119)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)

at org.apache.jasper.servlet.JspServlet$JspCountedServlet.service(JspServlet.java:130)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)

at org.apache.jasper.servlet.JspServlet$JspServletWrapper.service(JspServlet.java:282)

at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:429)

at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:500)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)

at org.apache.tomcat.core.ServletWrapper.doService(ServletWrapper.java:405)

at org.apache.tomcat.core.Handler.service(Handler.java:287)

at org.apache.tomcat.core.ServletWrapper.service(ServletWrapper.java:372)

at org.apache.tomcat.core.ContextManager.internalService(ContextManager.java:812)

at org.apache.tomcat.core.ContextManager.service(ContextManager.java:758)

at org.apache.tomcat.service.http.HttpConnectionHandler.processConnection(HttpConnectionHandler.java:213)

at org.apache.tomcat.service.TcpWorkerThread.runIt(PoolTcpEndpoint.java:416)

at org.apache.tomcat.util.ThreadPool$ControlRunnable.run(ThreadPool.java:501)

at java.lang.Thread.run(Thread.java:484)

原因何在？？？？?

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先检查一下你的session是否还存在还是已经为null了,这个问题可能是session为null引起的.谢谢

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试试session.invalidate();

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session.removeAttribute("id");

session.removeAttribute("pvw");

session.removeAttribute("name");

session.removeAttribute("psw");

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用removeAttribute()

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当然不能放null了，一般都用removeAttribute()，不过最好的应该是用invalidate()