Question

I have a List<Foo> foos which I can send to a GWT RPC service without problems.
But if I wrap that list into a new object, I’m getting an exception on startup.

subtype MyDTO is not assignable to 'com.google.gwt.user.client.rpc.IsSerializable' or 'java.io.Serializable' nor does it have a custom field serializer (reached via MyDTO)

Why can I send the list itself, but not a wrapper object?

with:

class MyDTO {
    List<Foo> foos; //containing Rectanlges (see below)
    public MyDTO() {}

    List<Foo> getFoos() { return foos; }
    void setFoos(List<Foo> foots) { this.foos = foos; }
}

with Foo beeing an interface like:

interface Foo {
    abstract int getX();
    abstract void setX(int x);
}

class Rectangle implements Foo {
    private int x;
    public Rectangle() {};

    //impl of foo methods
}

Of course this structure does not make much sence, but it describes my problem.
If I just send the List foos via RPC everything works fine.

If I send the MyDTO wrapper holding the list of foos, mentioned Exception is thrown.
What is wrong here?

Answer 1

Make MyDTO implement Serializable. List is Serializable by default.