一个关于清空session属性的问题

Question

我想要清空session里的部分属性,但要留住我的登陆信息！代码如下:

Enumeration attNames = session.getAttributeNames();
while ( attNames.hasMoreElements() ) {
String attName = (String) attNames.nextElement();
if ( !attName.equalsIgnoreCase( "loginInfo" )
&& !attName.equalsIgnoreCase( "VerifyCode" )
&& !attName.startsWith( "org.apache" ) ) {
session.removeAttribute( attName );
}
}执行的时候老是报以下错误:javax.servlet.ServletException: java.util.ConcurrentModificationException
at org.apache.struts.action.RequestProcessor.processException(RequestProcessor.java:520)
at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:427)
at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:228)
at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1913)
at com.common.baseclass.ActionServletUTF8Encoding.process(ActionServletUTF8Encoding.java:45)
at org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:449)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:114)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:91)
at com.caucho.server.dispatch.ServletFilterChain.doFilter(ServletFilterChain.java:103)
at com.caucho.server.cache.CacheFilterChain.doFilter(CacheFilterChain.java:192)
at com.caucho.server.webapp.WebAppFilterChain.doFilter(WebAppFilterChain.java:187)
at com.caucho.server.dispatch.ServletInvocation.service(ServletInvocation.java:266)
at com.caucho.server.http.HttpRequest.handleRequest(HttpRequest.java:280)
at com.caucho.server.port.TcpConnection.handleConnection(TcpConnection.java:563)
at com.caucho.server.port.TcpConnection$AcceptTask.doAccept(TcpConnection.java:1122)
at com.caucho.server.port.TcpConnection$AcceptTask.run(TcpConnection.java:1069)
at com.caucho.util.ThreadPool$Item.runTasks(ThreadPool.java:759)
at com.caucho.util.ThreadPool$Item.run(ThreadPool.java:681)
at java.lang.Thread.run(Thread.java:619)
Caused by: java.util.ConcurrentModificationException
at java.util.Hashtable$Enumerator.next(Hashtable.java:1031)
at java.util.Collections$1.nextElement(Collections.java:3389)
at com.rmdkt.user.advice.SessionAdvice.cleanSessionAttribute(SessionAdvice.java:38)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethodWithGivenArgs(AbstractAspectJAdvice.java:597)
at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethod(AbstractAspectJAdvice.java:576)
at org.springframework.aop.aspectj.AspectJMethodBeforeAdvice.before(AspectJMethodBeforeAdvice.java:39)
at org.springframework.aop.framework.adapter.MethodBeforeAdviceInterceptor.invoke(MethodBeforeAdviceInterceptor.java:49)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
at org.springframework.aop.aspectj.MethodInvocationProceedingJoinPoint.proceed(MethodInvocationProceedingJoinPoint.java:77)
at com.rmdkt.user.advice.LoginValidateAdvice.actionLoginValidate(LoginValidateAdvice.java:68)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethodWithGivenArgs(AbstractAspectJAdvice.java:597)
at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethod(AbstractAspectJAdvice.java:583)
at org.springframework.aop.aspectj.AspectJAroundAdvice.invoke(AspectJAroundAdvice.java:60)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:89)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
at org.springframework.aop.framework.Cglib2AopProxy$DynamicAdvisedInterceptor.intercept(Cglib2AopProxy.java:629)
at com.rmdkt.user.company.struts.action.UserMgrShowMyselfEstateBusinessListAction$$EnhancerByCGLIB$$6ac69521.execute(<generated>)
at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:425)
at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:228)
at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1913)
at com.common.baseclass.ActionServletUTF8Encoding.process(ActionServletUTF8Encoding.java:45)
at org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:449)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:114)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:91)
at com.caucho.server.dispatch.ServletFilterChain.doFilter(ServletFilterChain.java:103)
at com.caucho.server.cache.CacheFilterChain.doFilter(CacheFilterChain.java:192)
at com.caucho.server.webapp.WebAppFilterChain.doFilter(WebAppFilterChain.java:187)
at com.caucho.server.dispatch.ServletInvocation.service(ServletInvocation.java:266)
at com.caucho.server.http.HttpRequest.handleRequest(HttpRequest.java:280)
at com.caucho.server.port.TcpConnection.handleConnection(TcpConnection.java:563)
at com.caucho.server.port.TcpConnection$AcceptTask.doAccept(TcpConnection.java:1122)
at com.caucho.server.port.TcpConnection$AcceptTask.run(TcpConnection.java:1069)
at com.caucho.util.ThreadPool$Item.runTasks(ThreadPool.java:759)
at com.caucho.util.ThreadPool$Item.run(ThreadPool.java:681)
at java.lang.Thread.run(Thread.java:619)循环到最后一个属性时，attNames.hasMoreElements()为真，可以进入到循环体内。但是执行attNames.nextElement()就报以上错误了。郁闷至极，网上查了半天也没有查到为什么！只有人说过关于Iterator报以上错误的解决办法。
有谁碰到过以上的问题吗？

Answer 1

会不会是你remove后，改变了session的attributeMap内的元素呢 ?试试这样:Enumeration attNames = session.getAttributeNames();
        while ( attNames.hasMoreElements() ) {
            String attName = (String) attNames.nextElement();
            if ( !attName.equalsIgnoreCase( "loginInfo" )
                    && !attName.equalsIgnoreCase( "VerifyCode" )
                    && !attName.startsWith( "org.apache" ) ) {
                session.removeAttribute( attName );
            }
            attNames = session.getAttributeNames(); //加上这句，重新get一次，保证attNames是最新的.
        }

Answer 2

sorry, 上面的代码会死循环,修改一下,放在if内就应该可以了。Enumeration attNames = session.getAttributeNames(); 
        while ( attNames.hasMoreElements() ) { 
            String attName = (String) attNames.nextElement(); 
            if ( !attName.equalsIgnoreCase( "loginInfo" ) 
                    && !attName.equalsIgnoreCase( "VerifyCode" ) 
                    && !attName.startsWith( "org.apache" ) ) { 
                session.removeAttribute( attName ); 
                attNames = session.getAttributeNames(); //加上这句，重新get一次，保证attNames是最新的.             } 
           }