java - 谷歌指南 : use injected factory to instantiate multiple objects in a class?

Question

public class AppModule extends AbstractModule {
    @Override
    protected void configure() {
        install(new FactoryModuleBuilder().implement(BaseClass.class, ImplementingClass.class).build(FactoryClass.class));
    }
}

public class AnotherClass {
    @Inject
    private FactoryClass factoryClass;

    private BaseClass firstBaseObject = factoryClass.create("some_parameter");
    private BaseClass secondBaseObject = factoryClass.create("another_parameter");

    public void processSomething() {
        // ... do something that requires both firstBaseObject and secondBaseObject to already be initialized on each call
    }
}

有没有办法让我在每次调用 processSomething() 时都可以访问 firstBaseObject 和 secondBaseObject？ processSomething() 的每次调用都依赖于这两个已经实例化的对象，它们是具有大量元数据的巨大对象。即我能否以某种方式确保 factoryClass 在命中这两行时已经实例化？:

    private BaseClass firstBaseObject = factoryClass.create("some_parameter");
    private BaseClass secondBaseObject = factoryClass.create("another_parameter");

由于 factoryClass 为空，我在这两行中收到 NullPointerExceptions。

如果您需要更多信息，请告诉我，非常感谢!

Answer 1

使用下面的代码

public class AnotherClass {
    private final BaseClass firstBaseObject;
    private final BaseClass secondBaseObject;

    @Inject
    public AnotherClass(FactoryClass factoryClass) {
       firstBaseObject = factoryClass.create("some_parameter");
       secondBaseObject = factoryClass.create("another_parameter");
    }

    public void processSomething() {
        // ... do something that requires both firstBaseObject and secondBaseObject to already be initialized on each call
    }
}

不能使用字段或方法注入(inject)，因为 factoryClass 中的注入(inject)是在填充 firstBaseObject 和 secondBaseObject 之后进行的。

或

public class AppModule extends AbstractModule {
    @Override
    protected void configure() {
        ...
        bind(BaseClass.class)
        .annotatedWith(Names.named("firstBaseObject"))
        .toInstance(factoryClass.create("some_parameter"));

        bind(BaseClass.class)
        .annotatedWith(Names.named("secondBaseObject"))
        .toInstance(factoryClass.create("another_parameter"));
    }
}

public class AnotherClass {
    @Inject
    @Named("firstBaseObject")
    private BaseClass firstBaseObject;
    @Inject
    @Named("secondBaseObject")
    private BaseClass secondBaseObject;

    public void processSomething() {
        // ... do something that requires both firstBaseObject and secondBaseObject to already be initialized on each call
    }
}