Raymond Yang

Introduction:

In previous post I talked about what is dependency injection and why use Guice. Today I would like to share my experience of using Guice injector.

Module

Before create injector, we should define module. Module specify where to find all the dependencies required.

public class TestModule extends AbstractModule {
    @Override
    protected void configure() {
        bind(SomeClassA.class).toInstance(Singleton.class);
        bind(SomeClassB.class).toInstance(SomeInstanceA);
        install(new SomeModule());
        requireBinding(SomeClassC.class);
    }
}

In Above I list four usage of configure. Each one has different meaning. In short, bind is type, instance is real object. It tells the program when meet the type, where to find the real object.

Override configure is required for each Module. It tells Guice how to get the dependencies.

bind(SomeClassA.class).toInstance(Singleton.class);

This statement is most usual. It means make ‘SomeClassA’ to Singleton, SomeClassA is a dependency. Make it to singleton makes it easy to get the instance when other places use this.

bind(SomeClassB.class).toInstance(SomeInstanceA);

When the object is not complicate to create, and don’t have other dependency. We can directly bind a specific instance to a type.

requireBind();

Require bind is always used when a module is already binded (in Singleton), and here it will be used again.

install(Module);

install is always used for bind another module.