各位大神，我要异步通过省加载城市，可是转json的时候就报错了
public String getCitys(){
List<City> citys = cityService.find("from City where province.pid=?", new Object[]{pid});
JSONObject jo = new JSONObject();
jo.put("citys", citys);
HttpServletResponse response = ServletActionContext.getResponse();
ResponseUtils.renderJson(response, jo.toString());
return null;
}
java.lang.reflect.InvocationTargetException
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 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.DeprecationInterceptor.intercept(DeprecationInterceptor.java:41)
at org.apache.struts2.interceptor.DeprecationInterceptor$$FastClassBySpringCGLIB$$418f35cf.invoke()
at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204)
at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:711)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:157)
at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:98)
at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:262)
at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:95)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:92)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:644)
at org.apache.struts2.interceptor.DeprecationInterceptor$$EnhancerBySpringCGLIB$$52e7eb5c.intercept()
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:246)
at org.apache.struts2.interceptor.debugging.DebuggingInterceptor.intercept(DebuggingInterceptor.java:256)
at org.apache.struts2.interceptor.debugging.DebuggingInterceptor$$FastClassBySpringCGLIB$$30837115.invoke()
at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204)
at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:711)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:157)
