Guice

Question

假设有一个 class 构造函数看起来像这样：

public A(@Assited long id, @Assisten String name, ServiceA serviceA, ServiceB serviceB)

还有一个工厂：

public interface AFactory{

    A create(long id, String name);
}

所以要创建 A 的实例，我显然需要做类似的事情：

injector = Guice.createInjector(new MyModule());
AFactory af = injector.getInstance(AFactory .class);
A a = AFactory.create(100, "mike");

但是，假设我有其他 classes: Class B, Class C 和 Class D 有一个类型为 A 的成员，例如（使用字段注入但可以是 ctor还有）：

    public class B{
       @Inject
       A a;
    }

并且我希望将 A 的 相同实例 注入那些 classes。但仍然可以选择将 A 的另一个实例注入其他 classes（假设 Class E 和 F）。

正确的做法是什么？我只是想不出一个干净的方法来做到这一点。

Answer 1

您可以构造您的模块以使用 Providers（我正在使用 @Provides methods below, but you can use full Provider classes or instances if you'd like), and mark the consistent A as @Singleton. If you want two bindings of A (consistent and inconsistent), at least one of them should be marked with a binding annotation; I'm using @Named here out of convenience, but you can use any binding annotation as listed in the docs。

public class AModule extends AbstractModule {
  @Override public void configure() {
    // Install your AFactory module. Here, injections for AFactory should succeed.
    install(new FactoryModuleBuilder().build(AFactory.class));
  }

  /**
   * Provides a singleton @Named("consistent") A.
   * Inject @Named("consistent") A into B, C, and D; Guice will cache the instance.
   */
  @Provides @Singleton @Named("consistent")
      A provideConsistentA(AFactory factory) {
    return factory.create(100, "mike");
  }

  /**
   * Provides an unscoped A.
   * Inject A without an annotation into E and F; each instance will be separate.
   */
  @Provides @Singleton A provideUnscopedA(AFactory factory) {
    return factory.create(200, "jeff");
  }
}

Guice - 绑定由辅助注入工厂创建的实例

Guice - Binding an instance created by assisted injection factory

java

dependency-injection

guice-3

assisted-inject