net.sf.json.JSONException: There is a cycle in the hierarchy!
11-4-26 11:18:46 org.apache.catalina.core.StandardWrapperValve invoke严重: Servlet.service() for servlet action threw exceptionnet.sf.json.JSONException: There is a cycle in the hierarchy!at net.sf.json.util.CycleDetectionStrategy$StrictCycleDetectionStrategy.handleRepeatedReferenceAsObject(CycleDetectionStrategy.java:97)at net.sf.json.JSONObject._fromBean(JSONObject.java:657)at net.sf.json.JSONObject.fromObject(JSONObject.java:172)at net.sf.json.AbstractJSON._processValue(AbstractJSON.java:274)at net.sf.json.JSONObject._processValue(JSONObject.java:2655)at net.sf.json.JSONObject.processValue(JSONObject.java:2721)at net.sf.json.JSONObject.setInternal(JSONObject.java:2736)at net.sf.json.JSONObject.setValue(JSONObject.java:1424)at net.sf.json.JSONObject.defaultBeanProcessing(JSONObject.java:765)at net.sf.json.JSONObject._fromBean(JSONObject.java:699)at net.sf.json.JSONObject.fromObject(JSONObject.java:172)at net.sf.json.AbstractJSON._processValue(AbstractJSON.java:274)at net.sf.json.JSONArray._processValue(JSONArray.java:2513)at net.sf.json.JSONArray.processValue(JSONArray.java:2538)at net.sf.json.JSONArray.addValue(JSONArray.java:2525)at net.sf.json.JSONArray._fromCollection(JSONArray.java:1056)at net.sf.json.JSONArray.fromObject(JSONArray.java:123)at net.sf.json.AbstractJSON._processValue(AbstractJSON.java:240)at net.sf.json.JSONObject._processValue(JSONObject.java:2655)at net.sf.json.JSONObject.processValue(JSONObject.java:2721)at net.sf.json.JSONObject.setInternal(JSONObject.java:2736)at net.sf.json.JSONObject.setValue(JSONObject.java:1424)at net.sf.json.JSONObject.defaultBeanProcessing(JSONObject.java:765)at net.sf.json.JSONObject._fromBean(JSONObject.java:699)at net.sf.json.JSONObject.fromObject(JSONObject.java:172)at net.sf.json.AbstractJSON._processValue(AbstractJSON.java:274)at net.sf.json.JSONArray._processValue(JSONArray.java:2513)at net.sf.json.JSONArray.processValue(JSONArray.java:2538)at net.sf.json.JSONArray.addValue(JSONArray.java:2525)at net.sf.json.JSONArray._fromCollection(JSONArray.java:1056)at net.sf.json.JSONArray.fromObject(JSONArray.java:123)at net.sf.json.JSONArray.fromObject(JSONArray.java:105)at com.hbsi.struts.action.UserAction.UserList(UserAction.java:56)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 org.apache.struts.actions.DispatchAction.dispatchMethod(DispatchAction.java:270)at org.apache.struts.actions.DispatchAction.execute(DispatchAction.java:187)at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:431)at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:236)at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1196)at org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:432)at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298)at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:859)at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588)at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)at java.lang.Thread.run(Thread.java:619)
?
?
?错误原因：json中的
?
?
UserDaoImpl udi = new UserDaoImpl();List<User> list = new ArrayList<User>();list = udi.listUser();List<UserUtil> userUtil = new ArrayList<UserUtil>();JSONArray jsor = JSONArray.fromObject(list);response.setContentType("application/json;charset=UTF-8");response.getWriter().print(jsor);return null;?项目中使用了AJAX技术，JAR包为：json-lib.jar， 在开发过程中遇到了一个JSON-LIB和Hibernate有关的问题：
?主要是json中支持关联UserDaoImpl udi = new UserDaoImpl();List<User> list = new ArrayList<User>();list = udi.listUser();//兼容hibernate和jsonList<UserUtil> userUtil = new ArrayList<UserUtil>();for (User u : list) {UserUtil uu = new UserUtil();uu.setUsername(u.getUsername());uu.setId(u.getId());userUtil.add(uu);}JSONArray jsor = JSONArray.fromObject(userUtil);response.setContentType("application/json;charset=UTF-8");response.getWriter().print(jsor);return null;?
?
?