using gson in a web service

This works well running it as a Java Application:

public class A {
    public String getString(){
        return "hey";
    }

    public String getString2(){
        Gson gs = new Gson();
        String a = gs.toJson("hello");
        String b = gs.fromJson(a, String.class);
        return b;
    }

    public static void main(String[] args) {
        A a = new A();
        System.out.println(a.getString());//returns "hey"
        System.out.println(a.getString2());//returns "hello"
    }
}

BUT when I publish it to tomcat and run the Client:

//client of A with AStub and ACallbackHandler au开发者_开发知识库togenerated by eclipse
public class AClient {
    public static void main(String[] args) {
        AStub s = new AStub();
        System.out.println(s.getString().get_return());
        //returns "hey"
        System.out.println(s.getString2().get_return());
        //fails with org.apache.axis2.AxisFault: com/google/gson/Gson
    }
}

Also sometimes when respublishing the tomcat server it shows a ClassNotFoundException

I'm using Eclipse EE Indigo, Axis2, GSON 1.7.1 and tomcat 6

What am I doing wrong?

I was not adding the external jar files! Putted them in the WebContent/WEB-INF/lib of the server.