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异常问题

当我们在处理 JSON 字符串时，我却遇到了下面这样的异常：

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: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.element(JSONArray.java:1724)
	at net.sf.json.JSONArray.add(JSONArray.java:1249)
	at net.sf.json.JSONArray.add(JSONArray.java:1245)
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