問題：getInputStream() has already been called for this request

問題描述：

2012-4-6 22:25:42 org.apache.catalina.core.StandardWrapperValve invoke

嚴重: Servlet.service() for servlet default threw exception
java.lang.IllegalStateException: getInputStream() has already been called for this request
at org.apache.catalina.connector.Request.getReader(Request.java:1187)
at org.apache.catalina.connector.RequestFacade.getReader(RequestFacade.java:470)
at javax.servlet.ServletRequestWrapper.getReader(ServletRequestWrapper.java:248)
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)
...

問題原因及解決方案：

將對象轉換爲JSON格式時出錯，解決方法保證轉換成JSON數據的每個java對象可序列化，而Serializable就是java提供的通用數據保存和讀取的接口。