Overload GWT Date_CustomFieldSerializer - date

Question

I'm trying to overload the GWT "Date_CustomFieldSerializer" ( GWT 2.5.1 with maven2 and java1.6 ).
I've read that it is possible to overload a serializer by creating the same package structure inside your own project.
In my case I reproduce the package com.google.gwt.user.client.rpc.core.java.util to overload the class Date_CustomFieldSerializer but it does not seem to work well.
When serializing the Date, GWT Date_CustomSerializer is used but when the Date is deserialized my own "Date_CustomSerializer" is used.
If I delete the compiled Date_CustomFieldSerializer.class off gwt-user.jar and gwt-servlet.jar then my own Date_CustomFieldSerializer is always used but this is a bad solution, I am after a clean way to say to GWT that uses my own serializer always.
For delvelopment I use jetty and maven with the gwt-maven-plugin and in production mode I use weblogic.
I try to compile my own version of GWT but it fails when I try to run it, the server says:
[ERROR] Unable to initialize static dispatcher
java.lang.UnsupportedClassVersionError: com/google/gwt/core/client/JavaScriptObject$ : Unsupported major.minor version 51.0
How can I set it up to use my own serializer without GWT custom compilation?

Answer 1

Is your version first on the classpath?

Answer 2

It'a the version of Java.
You must compile the GWT Jar and your class with the same version of java.
The version 51 is the Java 7 version. (How to fix java.lang.UnsupportedClassVersionError: Unsupported major.minor version)
But the GWT must be compiled with java 6.
You must set your java source to 1.6