类需要一个 bean，但找到了 2 个：

Question

我有以下界面：

 public interface MailSender {
    void sender(String to, String subject,String body);
}

通过 2 个实现：

 public class SmtpkMailSender implements MailSender   {

    static Log log=LogFactory.getLog(MailSender.class);

    public void sender(String to, String subject,String body){
        log.info("SMTP To: "+to);
        log.info("SMTP Subjecy: "+subject);
        log.info("SMTP body: "+body);
    }

}

第二个是：

 @Primary
public class MockMailSender implements MailSender   {

    static Log log=LogFactory.getLog(MailSender.class);

    public void sender(String to, String subject,String body){
        log.info("To: "+to);
        log.info("Subject: "+subject);
        log.info("body: "+body);
    }

}

我在控制器类中使用了依赖注入，如下所示：

 @RestController
public class MailController {

    @Autowired
    private MailSender smtpkMailSender;

    @RequestMapping("/send")
    public String send(){
        smtpkMailSender.sender("Person", "Important", "Take Care");
        return "mail is sent";
    }
}

最后我有一个包含我的 Bean 的配置类：

 @Configuration
public class MailConfig {

    @Bean
    public SmtpkMailSender getSmtpkMailSender(){
        return new SmtpkMailSender();
    }

    @Bean
    public MockMailSender getMockMailSender(){
        return new MockMailSender();
    }

}

不幸的是，当我运行我的应用程序时，它会抱怨：

 Description:

Field smtpkMailSender in com.example.demo.MailController required a single bean, but 2 were found:
    - getSmtpkMailSender: defined by method 'getSmtpkMailSender' in class path resource [com/example/mail/MailConfig.class]
    - getMockMailSender: defined by method 'getMockMailSender' in class path resource [com/example/mail/MailConfig.class]

Action:

Consider marking one of the beans as @Primary, updating the consumer to accept multiple beans, or using @Qualifier to identify the bean that should be consumed

如您所见，尽管我已将 MockMailSender 指定为 Primary，但 spring 仍然抱怨，并且无法识别它

原文由 Jeff 发布，翻译遵循 CC BY-SA 4.0 许可协议

Answer 1

由于您使用的是 java 配置，因此您应该使用 @Primary 注释标记配置方法，而不是类：

 @Configuration
public class MailConfig {
    @Bean
    public SmtpkMailSender getSmtpkMailSender(){
        return new SmtpkMailSender();
    }

    @Bean
    @Primary
    public MockMailSender getMockMailSender(){
        return new MockMailSender();
    }
}

原文由 Leffchik 发布，翻译遵循 CC BY-SA 3.0 许可协议

Answer 2

您可以使用 @Qualifier 注释来指定您想要自动装配的特定类型的实现。

 @RestController
public class MailController {

   @Autowired
   @Qualifier("smtpkMailSender")
   private MailSender smtpkMailSender;

   @RequestMapping("/send")
   public String send(){
      smtpkMailSender.sender("Person", "Important", "Take Care");
      return "mail is sent";
  }

}

原文由 Yogi 发布，翻译遵循 CC BY-SA 4.0 许可协议