Reconstructing generic types at runtime with Guice via Types and TypeLiterals

Question

I have a few types that are like this

// a value that is aware of its key type (K)
Bar
// something that deals with such values and keys
Foo

        

Answer 1

From the JavaDoc for Binder:

Guice cannot currently bind or inject a generic type, such as Set all type parameters must be fully specified.

You can create bindings for Foo when K and V are bound. If you need to make bindings for Foo for more than one type of key, you can make a method that makes it easier to do these bindings. One way to do that is to create a method like this in your module:

> AnnotatedBindingBuilder> bind(Class keyType,
    Class barType) {
  ParameterizedType bType = Types.newParameterizedType(Bar.class, keyType);
  ParameterizedType fType = Types.newParameterizedType(Foo.class, barType,
      keyType);

  @SuppressWarnings("unchecked")
  TypeLiteral> typeLiteral =
      (TypeLiteral>) TypeLiteral.get(fType);

  return bind(typeLiteral);
}

Then if you have these classes:

class StringValue implements Bar {
  ...
}

class StringValueProcessor implements Foo {
  ...
}

You can create a binding like this:

bind(String.class, StringValue.class).to(StringValueProcessor.class);

...so that Guice could inject into a class like this:

static class Target {
  private final Foo foo;

  @Inject
  public Target(Foo foo) {
    this.foo = foo;
  }
}