在Spring MVC中，@ ResponseBody在添加自定义注释时返回null

Question

例如，

@Authority
@RequestMapping(value="/list",method = RequestMethod.POST)
public @ResponseBody String listNewEnterprises(HttpServletRequest request) {    
    JSONObject json = new JSONObject();
    //do something
    Object o;
    try {
        json.put("result", "success");
        json.put("value", o);
    } catch (JSONException e) {
        e.printStackTrace();
    }
    System.out.println(json);// can print the json value
    return json.toString();
}

在添加@Authority之前一切正常，但一旦添加@Authority，ajax就会变为空。

我的@Authority用于授权用户访问该方法的权利，该方法通过扩展HandlerInterceptorAdapter来拦截。

spring-mvc.xml配置为：

<bean class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping"/>
<mvc:annotation-driven />
<mvc:interceptors>      
     <bean class="com.sjd.annotation.AuthorityAnnotationInterceptor"></bean>
</mvc:interceptors>

========================================

我的AuthorityAnnotationInterceptor类实现如下：

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

import org.apache.log4j.Logger;
import org.springframework.web.method.HandlerMethod;
import org.springframework.web.servlet.handler.HandlerInterceptorAdapter;

public class AuthorityAnnotationInterceptor extends HandlerInterceptorAdapter {
private final Logger logger = Logger.getLogger(getClass());

@Override
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
    HandlerMethod handler2 = (HandlerMethod) handler;
    Authority auth = handler2.getMethodAnnotation(Authority.class);
    if (null == auth) {
        return true;
    }
    String url = request.getRequestURL().toString();
    logger.debug(url);
    if (null == url) {
        return false;
    }
    HttpSession session  = request.getSession();
    String userAuthority = (String) session.getAttribute("authority");
    //boolean hasAuthority = AuthorityHelper.hasAuthority(userAuthority,url, auth.type());
    boolean hasAuthority = true;
    if (hasAuthority) {
        logger.debug("pass");
        return true;
    }
    else {
        logger.debug("fail");
        return false;
    }
}

}