net.sf.json.JSONException: There is a cycle in the hierarchy!

net.sf.json.JSONException: There is a cycle in the hierarchy!
    atnet.sf.json.util.CycleDetectionStrategy$StrictCycleDetectionStrategy.handleRepeatedReferenceAsObject(CycleDetectionStrategy.java:97)
    atnet.sf.json.JSONObject._fromBean(JSONObject.java:833)
    atnet.sf.json.JSONObject.fromObject(JSONObject.java:168)
    atnet.sf.json.AbstractJSON._processValue(AbstractJSON.java:265)
    atnet.sf.json.JSONObject._processValue(JSONObject.java:2808)
    atnet.sf.json.JSONObject.processValue(JSONObject.java:2874)
    atnet.sf.json.JSONObject.setInternal(JSONObject.java:2889)
    atnet.sf.json.JSONObject.setValue(JSONObject.java:1577)
    atnet.sf.json.JSONObject._fromBean(JSONObject.java:934)
    atnet.sf.json.JSONObject.fromObject(JSONObject.java:168)
    atnet.sf.json.AbstractJSON._processValue(AbstractJSON.java:265)
    atnet.sf.json.JSONArray._processValue(JSONArray.java:2514)
    atnet.sf.json.JSONArray.processValue(JSONArray.java:2539)
    atnet.sf.json.JSONArray.addValue(JSONArray.java:2526)
    atnet.sf.json.JSONArray._fromCollection(JSONArray.java:1057)
    atnet.sf.json.JSONArray.fromObject(JSONArray.java:123)
    atnet.sf.json.AbstractJSON._processValue(AbstractJSON.java:237)
    atnet.sf.json.JSONObject._processValue(JSONObject.java:2808)
    atnet.sf.json.JSONObject.processValue(JSONObject.java:2874)
    atnet.sf.json.JSONObject.setInternal(JSONObject.java:2889)
    atnet.sf.json.JSONObject.setValue(JSONObject.java:1577)
    atnet.sf.json.JSONObject._fromBean(JSONObject.java:934)
    atnet.sf.json.JSONObject.fromObject(JSONObject.java:168)
    atnet.sf.json.AbstractJSON._processValue(AbstractJSON.java:265)
    atnet.sf.json.JSONArray._processValue(JSONArray.java:2514)
    atnet.sf.json.JSONArray.processValue(JSONArray.java:2539)
    atnet.sf.json.JSONArray.addValue(JSONArray.java:2526)
    atnet.sf.json.JSONArray._fromCollection(JSONArray.java:1057)
    atnet.sf.json.JSONArray.fromObject(JSONArray.java:123)
    atnet.sf.json.JSONArray.fromObject(JSONArray.java:105)
    atcn.csdn.city.servlet.CityJsonServlet.doGet(CityJsonServlet.java:34)
    atjavax.servlet.http.HttpServlet.service(HttpServlet.java:617)
    atjavax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    atorg.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
    atorg.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    atorg.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
    atorg.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
    atorg.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
    atorg.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
    atorg.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
    atorg.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:291)
    atorg.apache.coyote.http11.Http11Processor.process(Http11Processor.java:859)
    atorg.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:602)
    atorg.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
    atjava.lang.Thread.run(Thread.java:619)
 

 解决办法：

 

ProvinceService pService = new ProvinceServiceImpl();
       List<Province> province = pService.getObjects();
 
       JsonConfig config = new JsonConfig();
       config.setJsonPropertyFilter(new PropertyFilter() {
          
           public boolean apply(Object source, String name, Object value) {
              if(name.equals("city")){
                  return true;
              }else{
                 
                  return false;
              }
           }
       });
      
       PrintWriter out = response.getWriter();
       out.println(JSONArray.fromObject(province,config).toString());
       out.flush();
       out.close();