java – Guice只注册一些构造函数

假设我有一些Message类,如下所示. (这是一个简单的组合课.)

public class Message {
  private String text;

  public Message(String text) {
    this.text = text;
  }

  public void send(Person recipient) {
    // I think I should be Guice-injecting the sender.
    MessageSender sender = new EmailBasedMessageSender();
    sender.send(recipient,this.text);
  }
}

由于我有不同的MessageSender实现,并且可能希望单元测试这种发送能力,我想我应该在Message的send()方法中注入MessageSender.但是我该怎么办？

我看到的所有的Guice示例,我明白,在构造函数中似乎注入了：

public class Message {
  private String text;
  private MessageSender sender;

  // ??? I don't kNow what to do here,since the `text` argument shouldn't be injected.
  @Inject
  public Message(String text,MessageSender sender) {
    this.text = text;
    this.sender = sender;
  }

  public void send(Person recipient) {
    this.sender.send(recipient,this.text);
  }
}

public class MessageSenderModule extends AbstractModule {
  @Override 
  protected void configure() {
    bind(MessageSender.class).to(EmailBasedMessageSender.class);
  }
}

但是我的Message类在其构造函数中接受一个文本参数,我不想注入它.那我该怎么办呢？

(注意：我是一个完整的Google Guice noob,我认为我了解依赖注入,但我不明白如何用Guice实际实现它.)

解决方法

您可以使用辅助注射通过工厂提供文本,以及由Guice实例化的消息发送者：

public class Message {
  private String text;
  private MessageSender sender;

  @Inject
  public Message(@Assisted String text,this.text);
  }
}

厂：

public interface MessageFactory{
    Message buildMessage(String text);
}

模块：

public class MessageSenderModule extends AbstractModule {
  @Override 
  protected void configure() {
    bind(MessageSender.class).to(EmailBasedMessageSender.class);
    FactoryModuleBuilder factoryModuleBuilder = new FactoryModuleBuilder();
    install(factoryModuleBuilder.build(MessageFactory.class));
  }
}

用法：

@Inject MessageFactory messageFactory;

void test(Recipient recipient){
  Message message = messageFactory.buildMessage("hey there");
  message.send(recipient);
}

Assisted Injection Wiki