struts2种配置json
很简单的代码

setMessage(MESSAGE);
String str = request.getParameter("username");


JSONObject jsonResult = new JSONObject();

JSONArray jsonArray = new JSONArray();

JSONObject jsonObject  = new JSONObject();
jsonObject.put("param1", str + "1");
jsonObject.put("param2", str + "2");
jsonObject.put("param3", str + "3");
System.out.println("asdfasdfa");
jsonArray.add(jsonObject);

jsonResult.put("result1", str);

jsonResult.put("result2", jsonArray);
// response.setCharacterEncoding("UTF-8");
// response.setContentType("text/plain;charset=UTF-8");
// response.getWriter().print(jsonResult.toString());

response.setContentType("text/html; charset=utf-8");
response.getWriter().print(jsonResult.toString());

return SUCCESS;

异常如下，不知道哪里的问题

13-10-18 17:04:22.843:INFO::Started SelectChannelConnector@0.0.0.0:8080
十月 18, 2013 5:04:25 下午 com.opensymphony.xwork2.util.logging.commons.CommonsLogger error
SEVERE: Exception occurred during processing request: null
java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at com.opensymphony.xwork2.DefaultActionInvocation.invokeAction(DefaultActionInvocation.java:450)
at com.opensymphony.xwork2.DefaultActionInvocation.invokeActionOnly(DefaultActionInvocation.java:289)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:252)
at org.apache.struts2.interceptor.debugging.DebuggingInterceptor.intercept(DebuggingInterceptor.java:256)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
at com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor.doIntercept(DefaultWorkflowInterceptor.java:167)
at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
at com.opensymphony.xwork2.validator.ValidationInterceptor.doIntercept(ValidationInterceptor.java:265)
at org.apache.struts2.interceptor.validation.AnnotationValidationInterceptor.doIntercept(AnnotationValidationInterceptor.java:68)
at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
at com.opensymphony.xwork2.interceptor.ConversionErrorInterceptor.intercept(ConversionErrorInterceptor.java:138)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
at com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:239)
at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
at com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:239)
at com.opensy