客户端使用Ajax访问struts2 ， struts2如何返回一个json数据！json-lib与flexjson

错误提示：

21:21:25,316 ERROR runtime:96 - Template processing error: "Method public java.lang.String org.apache.commons.lang.exception.NestableRuntimeException.getMessage(int) threw an exception when invoked on net.sf.json.JSONException: There is a cycle in the hierarchy!"21:21:25,316 ERROR runtime:96 - Temp