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)
解決辦法：
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();