Question

I have a POJO that is used with GWT’s RequestFactory and an associated proxy. The POJO has both static methods (list()) and instance methods (persist()) which need access to my database. My database connection pool is set up to be injected as a singleton via Guice. What I am unsure of is how exactly can I perform the injection so that both of these types of methods can access it?

Furthermore, the instances of the POJO are created using an empty constructor, thus negating the ability to use constructor injection.

Here’s a sample POJO for reference’s sake:

public class Person {
    private Integer id;
    private String name;

    public Integer getId() { return this.id; }
    public void setId(Integer id) { this.id = id; }
    public String getName() { return this.name; }
    public void setName(String name) { this.name = name; }

    public void persist() {
        //TODO: save state to DB
    }
    public static List<Person> list() {
        //TODO: get all people from DB
        return null;
    }
}

Answer 1

Somehow, GWT’s style is still not very aware of the needs of dependency injection. This is – to some extent – excusable on the client side, but not so much on the server side (and to be honest, I’d really wish, that the GWT and Guice team will join forces to improve this situation.)

Now, fortunately, Guice provides a “legacy” mechanism for injecting static fields, see “Static injections” in http://code.google.com/docreader/#p=google-guice&s=google-guice&t=Injections). So you can inject your EntityManager/EntityManagerFactory (or whatever you’re using to perform persistence) into a static field.

You don’t have to do that directly, but you can use a Provider. Then choose the correct scope (e.g. @RequestScoped) to make the provider give you the correct instance.

Note: I haven’t tried that yet (though I’m planning to do so), because I’m not yet using RequestFactory in a real project. I hope that the legacy mechanism works in this case, but you may hit some roadblocks (?)