CODEWITHSUNDEEP
javadependency-injectionguice
Chry Cheng
Chry Cheng

Reputation: 3468

How can I have Guice manage a class in a jar (if at all possible)?

Let's say I have a class A in a jar in my class-path (i.e., I have no control over its source and thus cannot simply annotate it with @Inject). A has the following constructor definition:

A(B b, C c) {
    this.b = b;
    this.c = c;
}

In my code base, I have classes:

BImpl implements B

and

CImpl implements C

My question is: How do I configure Guice to manage instances of A to be injected with BImpl and CImpl (if it is even within the scope of the framework)?

Upvotes: 1

Views: 536

Answers (1)

A.H.
A.H.

Reputation: 66263

When you say "a class A in a jar file" I assume you have no control over the source of that class - you cannot simply add @Inject to the constructor.

If that is the case, then you can define a Module like this:

class MyModule extends AbstractModule {
    @Override
    protected void configure() {
        bind(B.class).to(BImpl.class);
        bind(C.class).to(CImpl.class);

        try {
            bind(A.class).toConstructor(A.class.getConstructor(B.class, C.class));
        } catch (NoSuchMethodException e) {
            throw new RuntimeException(e);
        }
    }
}

The first two bindings are standard - you bind the interface types to the implementation types.

The last binding uses toConstructor (since Guice 3.0), which allows you to "glue" foreign components more easily - just as in your case.

Upvotes: 1

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