tomcat - struts2中的ClearCacheInterceptor

Question

在我的 web 应用程序中，我想包含 ClearCacheInterceptor，以便在执行注销操作后清除捕获，这样如果用户单击后退按钮，它就不会显示上一页。当我运行代码时它工作正常我可以登录执行其他操作但是当我单击注销时它显示错误。这是我的代码

public class ClearCacheInterceptor  extends AbstractInterceptor{

/**
 *
 */
private static final long serialVersionUID = 1L;

@Override

public String intercept(ActionInvocation invocation) throws Exception {

    ActionContext context=(ActionContext)invocation.getInvocationContext();

    HttpServletResponse response=(HttpServletResponse)context.get(StrutsStatics.HTTP_RESPONSE);

    response.setHeader("Cache-Control", "no-cache");

    response.setHeader("Pragma", "no-cache");

    response.setDateHeader("Expires", 0);

    String result=invocation.invoke();

    System.out.println("check result="+result);

    return result;

}

注销代码

  public String logOut() {
    String status = "";
     if (true) {
        session.clear();
        session = null;
        if (session instanceof org.apache.struts2.dispatcher.SessionMap) {
            try {
                ((org.apache.struts2.dispatcher.SessionMap) session).invalidate();
            } catch (IllegalStateException e) {
            }
        }
        status = "success";
    } else {
        addActionError(getText("system.ERROR"));
        status = "error";
    }

    return status;
}  

我的 struts.xml Action 文件

       <struts>
<!-- Configuration for the default package. -->
<constant name="struts.Devmode" value="false"></constant>
<constant name="struts.enable.DynamicMethodInvocation" value="false" />
<constant name="struts.custom.i18n.resources" value="ApplicationResources" />
<package name="default" extends="struts-default">
    <interceptors>
        <interceptor-stack name="defaultStack">
            <interceptor-ref name="exception" />
            <interceptor-ref name="alias" />
            <interceptor-ref name="servletConfig" />
            <interceptor-ref name="prepare" />
            <interceptor-ref name="i18n" />
            <interceptor-ref name="chain" />
            <interceptor-ref name="debugging" />
            <interceptor-ref name="profiling" />
            <interceptor-ref name="scopedModelDriven" />
            <interceptor-ref name="modelDriven" />
            <interceptor-ref name="fileUpload" />
            <interceptor-ref name="checkbox" />
            <interceptor-ref name="staticParams" />
            <interceptor-ref name="params">
                <param name="excludeParams">dojo..*,d-..*,6..*</param>
            </interceptor-ref>
            <interceptor-ref name="conversionError" />
            <interceptor-ref name="validation">
                <param name="excludeMethods">input,back,cancel,browse</param>
            </interceptor-ref>
            <interceptor-ref name="workflow">
                <param name="excludeMethods">input,back,cancel,browse</param>
            </interceptor-ref>
        </interceptor-stack>
        <interceptor name="clear-cache"  class="com.java.session.ClearCacheInterceptor" />
    </interceptors>
    <default-interceptor-ref name="defaultStack"/>

    <action name="users">
        <result>home.jsp </result>
    </action>
    <action name="UserAction" class="com.java.action.RegisterAction">
        <result name="input">/signup.jsp</result>
        <result name="success">/home.jsp</result>
        <result name="error">/error.jsp</result>
    </action>
    <action name="trialregister">
        <result>signup.jsp</result>
    </action>
    <action name="Activate" class="com.java.action.ActivationAction">
        <result name="input">/error.jsp</result>
        <result name="success">/home.jsp</result>
        <result name="error">/test1.jsp</result>
    </action>
    <action name="verifyLogin" class="com.java.action.LoginAction" method="verifyLogin">
         <result name="input">/home.jsp</result>
        <result name="success">/test1.jsp</result>
    </action>

    <action name="logOut" class="com.java.action.LoginAction" method="logOut">
        <interceptor-ref name="clear-cache"/>
        <result name="error">/error.jsp</result>
        <result name="success">/logout.jsp</result>
    </action>

    <action name="Back">
    <result>/index.jsp</result>    
    </action>

    <action name="Reroot">
    <result>/index.jsp</result>    
    </action>

</package>

日志中的错误信息是

    SEVERE: Servlet.service() for servlet default threw exception
          java.lang.NullPointerException
at com.java.action.LoginAction.logOut(LoginAction.java:103)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:601)
at com.opensymphony.xwork2.DefaultActionInvocation.invokeAction(DefaultActionInvocation.java:404)
at com.opensymphony.xwork2.DefaultActionInvocation.invokeActionOnly(DefaultActionInvocation.java:267)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:229)
at com.java.session.ClearCacheInterceptor.intercept(ClearCacheInterceptor.java:37)
at com.opensymphony.xwork2.DefaultActionInvocation$2.doProfiling(DefaultActionInvocation.java:224)
at com.opensymphony.xwork2.DefaultActionInvocation$2.doProfiling(DefaultActionInvocation.java:223)
at com.opensymphony.xwork2.util.profiling.UtilTimerStack.profile(UtilTimerStack.java:455)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:221)
at org.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:50)
at org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:504)
at org.apache.struts2.dispatcher.FilterDispatcher.doFilter(FilterDispatcher.java:419)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298)
at org.apache.coyote.http11.Http11AprProcessor.process(Http11AprProcessor.java:864)
at org.apache.coyote.http11.Http11AprProtocol$Http11ConnectionHandler.process(Http11AprProtocol.java:579)
at org.apache.tomcat.util.net.AprEndpoint$Worker.run(AprEndpoint.java:1665)
at java.lang.Thread.run(Thread.java:722)

Answer 1

请更改注销方法中的实现。你正在调用

session.clear();

然后设置为空。如果抛出异常在

session.clear(); 

那么这意味着当代码到达这里时，某些地方会调用 clear 或未创建 session 。还有一件事，您正在验证 instanceof 在 session= null 之后检查；始终为空。