在做Hibernate 映射对象转换json 的时候，常常会遇到如下异常：

net.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:859)
	at net.sf.json.JSONObject.fromObject(JSONObject.java:194)
	at net.sf.json.JSONObject._processValue(JSONObject.java:2793)
	at net.sf.json.JSONObject._setInternal(JSONObject.java:2817)
	at net.sf.json.JSONObject.setValue(JSONObject.java:1527)
	at net.sf.json.JSONObject._fromBean(JSONObject.java:946)
	at net.sf.json.JSONObject.fromObject(JSONObject.java:194)

解决方法：

JsonConfig jsonConfig = new JsonConfig();
jsonConfig.setCycleDetectionStrategy(CycleDetectionStrategy.LENIENT); // 自动为我排除circle。

jsonConfig.setExcludes(new String[] { "user" }); // 设置转换中忽略的属性

JSONArray.fromObject(sourceList,jsonConfig)