Question

It’s been a while since I’ve been doing GWT and I needed something small done quickly. I set things up and now I have a RPC I need, but it fails.

The RPC is supposed to give me a ArrayList, and Vacancy is located in #projectname#.client.model.
The call is made in #projectname#.client.model.

The interfaces for my Services are in #project#name.client.Service.

Finally, the calls of course go to #projectname#.server.

Vacancy implements IsSerializable. The Exception I get from running my RPC is the following:

Starting Jetty on port 8888
[WARN] Exception while dispatching incoming RPC call
com.google.gwt.user.client.rpc.SerializationException: Type 'firsteight.client.model.Vacancy' was not included in the set of types which can be serialized by this SerializationPolicy or its Class object could not be loaded. For security purposes, this type will not be serialized.: instance = firsteight.client.model.Vacancy@15fdd2f
    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.client.rpc.core.java.util.Collection_CustomFieldSerializerBase.serialize(Collection_CustomFieldSerializerBase.java:44)
    at com.google.gwt.user.client.rpc.core.java.util.ArrayList_CustomFieldSerializer.serialize(ArrayList_CustomFieldSerializer.java:39)
    at com.google.gwt.user.client.rpc.core.java.util.ArrayList_CustomFieldSerializer.serializeInstance(ArrayList_CustomFieldSerializer.java:51)
    at com.google.gwt.user.client.rpc.core.java.util.ArrayList_CustomFieldSerializer.serializeInstance(ArrayList_CustomFieldSerializer.java:28)
    at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter.serializeImpl(ServerSerializationStreamWriter.java:740)
    at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter.serialize(ServerSerializationStreamWriter.java:621)
    at com.google.gwt.user.client.rpc.impl.AbstractSerializationStreamWriter.writeObject(AbstractSerializationStreamWriter.java:126)
    at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter$ValueWriter$8.write(ServerSerializationStreamWriter.java:153)
    at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter.serializeValue(ServerSerializationStreamWriter.java:539)
    at com.google.gwt.user.server.rpc.RPC.encodeResponse(RPC.java:616)
    at com.google.gwt.user.server.rpc.RPC.encodeResponseForSuccess(RPC.java:474)
    at com.google.gwt.user.server.rpc.RPC.invokeAndEncodeResponse(RPC.java:571)
    at com.google.gwt.user.server.rpc.RemoteServiceServlet.processCall(RemoteServiceServlet.java:208)
    at com.google.gwt.user.server.rpc.RemoteServiceServlet.processPost(RemoteServiceServlet.java:248)
    at com.google.gwt.user.server.rpc.AbstractRemoteServiceServlet.doPost(AbstractRemoteServiceServlet.java:62)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:487)
    at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:362)
    at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
    at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:181)
    at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:729)
    at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:405)
    at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
    at org.mortbay.jetty.handler.RequestLogHandler.handle(RequestLogHandler.java:49)
    at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
    at org.mortbay.jetty.Server.handle(Server.java:324)
    at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:505)
    at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:843)
    at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:647)
    at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:211)
    at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:380)
    at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:395)
    at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:488)

The RPC I make is the following:

void getVacs() {
    try {
        homeService.getVacancies(new AsyncCallback<ArrayList<Vacancy>>() {
            public void onFailure(Throwable caught)
            {
                RootPanel.get("grayblock").add(new HTML("Failed:" + caught.getMessage()));
            }

            public void onSuccess(ArrayList<Vacancy> result)
            {
                RootPanel.get("grayblock").add(new HTML(result.get(0).getTitle()));
            }
        });
    } catch (IllegalArgumentException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

I thought I had done all I needed to make Vacancy Serializable, and an ArrayList of Vacancy as returntype for the RPC counts as having Vacancy as return type.. right? What am I doing wrong?

Thanks in advance!

Answer 1

This is normally caused by using a non-serializable class, which can occur if your class does not implement com.google.gwt.user.client.rpc.IsSerializable or if you have forgotten to add an empty constructor.

To pass a bean you have to fulfill the following requirements (from GWT site):

1. It implements either Java Serializable or GWT IsSerializable
   interface, either directly, or because it derives from a superclass
   that does.
2. Its non-final, non-transient instance fields are themselves
   serializable
3. It has a default (zero argument) constructor with any access
   modifier (e.g. private Foo(){} will work)

Even if you fulfill these requirements may happen that GWT compiler say:

was not included in the set of types which can be
serialized by this SerializationPolicy or its Class object could not
be loaded. For security purposes, this type will not be serialized.:
instance = @

The problem may have different causes. Here his a complete check list to use for solving the problem:

1. Verify that the class has a default constructor (without arguments)
2. Verify that the class implements Serializable or IsSerializable or
   implements an Interface that extends Serializable or extends a class
   that implement Serializable
3. Verify that the class is in a client.* package or …
4. Verify, if the class is not in client.* package, that is compiled in
   your GWT xml module definition. By default
   is present. If your class is in another package you have to add it
   to source. For example if your class is under domain.* you should
   add it to xml as . Be aware that the class
   cannot belong to server package! More details on GWT page:
   http://code.google.com/webtoolkit/doc/latest/DevGuideOrganizingProjects.html#DevGuideModuleXml
5. If you are including the class from another GWT project you have to
   add the inherits to your xml module definition. For example if your
   class Foo is in the package com.dummy.domain you have to add
   to the module definition.
   More details here:
   http://code.google.com/webtoolkit/doc/latest/DevGuideOrganizingProjects.html#DevGuideInheritingModules
6. If you are including the class from another GWT project released as
   a jar verify that the jar contains also the source code because GWT
   recompile also the Java source for the classes passed to the Client.

PS:copied from http://isolasoftware.it/2011/03/22/gwt-serialization-policy-error/ because the site is unavailable currently. If you want to read the original article search it from google using the above URL and read it from google web cache.