struts2 <debug>标签报错:Caught an exception while getting the property values of null

java.lang.NullPointerException

at com.opensymphony.xwork2.ognl.OgnlUtil.getBeanInfo(OgnlUtil.java:398)

at com.opensymphony.xwork2.ognl.OgnlUtil.getPropertyDescriptors(OgnlUtil.java:344)

at com.opensymphony.xwork2.ognl.OgnlUtil.getBeanMap(OgnlUtil.java:375)

at com.opensymphony.xwork2.ognl.OgnlReflectionProvider.getBeanMap(OgnlReflectionProvider.java:97)

at org.apache.struts2.components.Debug.start(Debug.java:71)

at org.apache.struts2.views.jsp.ComponentTagSupport.doStartTag(ComponentTagSupport.java:53)

at org.apache.jsp.WEB_002dINF.jsp.member2Restaurant.searchPartner_jsp._jspx_meth_s_005fdebug_005f0(searchPartner_jsp.java:272)

at org.apache.jsp.WEB_002dINF.jsp.member2Restaurant.searchPartner_jsp._jspService(searchPartner_jsp.java:183)

at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)

at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)

at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)

at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)

at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:749)

at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:487)

at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:412)

at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:339)

at org.apache.struts2.dispatcher.ServletDispatcherResult.doExecute(ServletDispatcherResult.java:164)

at org.apache.struts2.dispatcher.StrutsResultSupport.execute(StrutsResultSupport.java:186)

at com.opensymphony.xwork2.DefaultActionInvocation.executeResult(DefaultActionInvocation.java:374)

at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:278)

at com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:236)

at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)

at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:249)

at com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor.intercept(ExceptionMappingInterceptor.java:187)

at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:249)

at cn.com.eatlab.web.AuthInterceptor.intercept(AuthInterceptor.java:74)

...........

ERROR ExceptionMappingInterceptor:38 - Caught an exception while getting the property values of null- Class: com.opensymphony.xwork2.ognl.OgnlUtil

File: OgnlUtil.java

Method: getBeanInfo

Line: 398 - com/opensymphony/xwork2/ognl/OgnlUtil.java:398:-1

org.apache.jasper.JasperException: Caught an exception while getting the property values of null - Class: com.opensymphony.xwork2.ognl.OgnlUtil

File: OgnlUtil.java

Method: getBeanInfo

Line: 398 - com/opensymphony/xwork2/ognl/OgnlUtil.java:398:-1

at org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:549)

at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:470)

at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)

at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)

debug进去到Debug.class文件发现这样一段代码：

public boolean start(Writer writer) {
        boolean result = super.start(writer);

        ValueStack stack = getStack();
        Iterator iter = stack.getRoot().iterator();
        List stackValues = new ArrayList(stack.getRoot().size());
        while (iter.hasNext()) {
            Object o = iter.next();
            Map values;
            try {
                values = reflectionProvider.getBeanMap(o);
            } catch (Exception e) {
                throw new StrutsException("<span style="color:#ff0000;">Caught an exception while getting the property values of</span> " + o, e);
            }
            stackValues.add(new DebugMapEntry(o.getClass().getName(), values));
        }

        addParameter("stackValues", stackValues);

        return result;
  }

图片


发现root中一个对象为null，此为发出异常的的原因，

接着发现jsp页面有一个<s:debug></s:debug>标签，去掉此标签后就正常了。

但是又产生了一个新的问题，debug标签就是debug用的，却因为debug标签产生bug......

搞清楚为什么就要知道为什么 valueStack.getRoot() 中会有一个 为null的 对象，

也就是要搞清楚valueStack到底是放的什么东西...然后...求分析...

续：

在论坛问了一下，没有结果，冷静分析了一下，其他的页面都可以正常，唯独这一个页面不可以，由此断定出问题的地方在action里面，

然后发现这么一段代码：ActionContext.getContext().getValueStack().push(member);

这就是问题所在，可想而知当时的root里面的null从何而来，于是加一个if(member != null){}，问题也算是解决了。

具体不知道是谁添加的，用来干什么的，所以加一个if判断一下，估计是页面上用到，只是有点不符合我们代码的一贯风格。

就是这么个问题，还debug来debug去的...