GWT客户端和服务器的不同接口实现

Question

Assume that we've some interface my.gwt.shared.Facade in shared package of our GWT project (exists both server and client) and two implementation of it: class my.gwt.client.ClientFacadeImpl (exists only client) and class my.gwt.server.ServerFacadeImpl (exists only server).

Is there any way to write a piece of code or annotation that substitute ClientFacadeImpl in client side and ServerFacadeImpl in server side?

Answer 1

Thanks all for the answers and discussion. I've found simple and elegant solution for my needs.

So, I've interface my.gwt.shared.Facade and two classes: class my.gwt.client.ClientFacadeImpl and class my.gwt.server.ServerFacadeImpl .

interface Facade {
    Map<Boolean, Facade> FACADES = new HashMap<Boolean, Facade>();
}

Now, we should fill you FACADES interface. This is done like that:

public class MyEntry implements EntryPoint {
static {
    Facade.FACADES.put(true, ClientFacadeImpl.INSTANCE); // client side
}

And

@Startup
@Singleton
public class Initializer {
    @PostConstruct
    private void init() {
        Facade.FACADES.put(false, ServerFacadeImpl.INSTANCE); // server side
        // other things
    }
}

Now, when I need to get appropriate Facade, I just write

 Facade facade = Facade.FACADES.get(GWT.isClient());

Also in this case in map is only corresponding to server or client side implementation.

PS Goal of this question was to allow handling of some GwtEvents fired on client direclty on server and vice-versa. This solution removed large set of DTO (data transfer objects) and simplified code a lot.

Answer 2

There's no answer to your question other than "it depends". Or rather, of course there are ways of doing what you ask, but would you accept the tradeoffs?

Given that you tagged the question with dependency-injection, let's start with that. If you use a DI tool with GWT, it's likely GIN (Dagger 2 would work, but it's still under development). In that case, just use distinct modules for GIN client-side and Guice server-side that bind() the appropriate implementation.

For a few releases, GWT.create() can be made to work outside a GWT (client) environment (ie on the server side). You have to register a ClassInstantiator on the ServerGwtBridge as an alternative to the rebind rules from gwt;xml files. So you could have a <replace-with class="my.gwt.client.ClientFacadeImpl"> rule in your gwt.xml , and a ClassInstantiator returning a ServerFacadeImpl on the server side.

Finally, you can also use a static factory and replace it with a client-side specific version by way of <super-source> .

A last one, but I'm unsure whether it'd work: you could use an if / else using GWT.isClient() , and annotate your ServerFacadeImpl with @GwtIncompatible to tell the GWT compiler that you know it's not client-compatible.