自定義攔截器中的NullPointerException

Question

我是新的struts framework。在這里我試圖創建自定義攔截器，我只是將給定的用戶名轉換為大寫並在jsp中顯示它。

我的index.jsp代碼是：

<s:form action="login"> <s:textfield name="name" label="UserName"></s:textfield> <s:submit value="Submit"></s:submit> </s:form>

攔截器代碼為：

    public class CustomInterceptorExample implements Interceptor
{

    @Override
    public void destroy() 
    {
        // TODO Auto-generated method stub

    }

    @Override
    public void init() 
    {
        // TODO Auto-generated method stub
        System.out.println("Custom Interceptor called.....");
    }

    @Override
    public String intercept(ActionInvocation ai) throws Exception
    {
        // TODO Auto-generated method stub

        ValueStack vs=ai.getStack();
        String name=vs.findString("name"); //here i am getting exception
        System.out.println(name);
        vs.set("name", name.toUpperCase());
        System.out.println("intercept() called..."+ai.invoke());
        return ai.invoke();
    }

}

Struts.xml代碼是：

<struts>
 <package name="default" extends="struts-default">

<interceptors>
<interceptor name="logerName" class="com.strutsLearner.CustomInterceptorExample"></interceptor>
</interceptors>    

<action name="product" class="com.strutsLearner.Product">
<result name="success">welcome.jsp</result>
</action>

<action name="login" class="com.strutsLearner.Login">
<interceptor-ref name="defaultStack"></interceptor-ref>  
<interceptor-ref name="logerName"></interceptor-ref>
<result>LogResult.jsp</result>  
</action>
</package>
</struts>    

堆棧跟蹤為：

java.lang.NullPointerException
    com.strutsLearner.CustomInterceptorExample.intercept(CustomInterceptorExample.java:31)
    com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)
    org.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:52)
    org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:488)
    org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:77)
    org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:91)

誰能告訴我我在哪里弄錯了。

Answer 1

您需要在stuts.xml文件中編寫defaultStack攔截器

<interceptor-ref name="defaultStack"></interceptor-ref>