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();

（编辑：李大同）

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