java - Guice 只注入(inject)一些构造函数

Question

假设我有一些 Message 类，如下所示。 (为简单起见，这是一个虚构的类。)

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，并且可能想对这种发送能力进行单元测试，我认为我应该在 Message 中注入(inject) MessageSender > 的 send() 方法。但我该怎么做呢？

我所见过和理解的所有 Guice 示例似乎都是在构造函数中进行注入(inject):

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了一个 text 参数，我不想注入(inject)它。那么我应该怎么做呢？

(注意:我是一个完全的 Google Guice 菜鸟。我想我理解依赖注入(inject)，但我不明白如何用 Guice 实际实现它。)

Answer 1

您可以使用辅助注入(inject)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, MessageSender sender) {
    this.text = text;
    this.sender = sender;
  }

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

工厂:

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