java GWT RPC XsrfToken序列化异常

Question

我正在开发一个gwt/app engine应用程序，升级到app engine 1.6.4/gwt 2.4.0后出现了一个问题。我使用Java作为应用程序引擎。我看到了序列化问题。我不确定升级是否导致了这个问题——它破坏了我的应用程序，我不得不重新创建Eclipse项目

我将GWT XsrfToken与GWT RPC一起使用。它在Eclipse的开发模式下运行良好，但当我将应用程序部署到app engine时，在app engine日志中出现以下异常：

javax.servlet.ServletContext log: Exception while dispatching incoming RPC call
com.google.gwt.user.client.rpc.SerializationException: Type 'com.google.gwt.user.client.rpc.XsrfToken' was not assignable to 'com.google.gwt.user.client.rpc.IsSerializable' and did not have a custom field serializer.For security purposes, this type will not be serialized.: instance = com.google.gwt.user.client.rpc.XsrfToken@1e80c87
    at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter.serialize(ServerSerializationStreamWriter.java:619)
    at com.google.gwt.user.client.rpc.impl.AbstractSerializationStreamWriter.writeObject(AbstractSerializationStreamWriter.java:126)
    at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter$ValueWriter$8.write(ServerSerializationStreamWriter.java:153)
    at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter.serializeValue(ServerSerializationStreamWriter.java:539)
    at com.google.gwt.user.server.rpc.RPC.encodeResponse(RPC.java:616)
    at com.google.gwt.user.server.rpc.RPC.encodeResponseForSuccess(RPC.java:474)
    at com.google.gwt.user.server.rpc.RPC.invokeAndEncodeResponse(RPC.java:571)
    at com.google.gwt.user.server.rpc.RemoteServiceServlet.processCall(RemoteServiceServlet.java:208)
    at com.google.gwt.user.server.rpc.RemoteServiceServlet.processPost(RemoteServiceServlet.java:248)
    at com.google.gwt.user.server.rpc.AbstractRemoteServiceServlet.doPost(AbstractRemoteServiceServlet.java:62)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:511)
...more 

任何帮助都将不胜感激