How to force library class to use your bean in autowiring

Question

I have encountered a scenario in my application where I am calling a library class method which uses autowiring with @Qualifier annotation. In my case, the behavior is exact same but the autowired bean should be different. This autowired bean simply calls a REST service.

I have tried to show the scenario with few simple classes:

public interface IMessage {
    public String getMessage();
}

public class HelloMessage implements IMessage {
    public String getMessage() {
        return "Hello";
    }
}

public class HiMessage implements IMessage  {
    public String getMessage() {
        return "Hi";
    }
}

public class PrintMessage { 
    @Qualifier("helloMessage")
    @Autowired
    private IMessage message;

    public void service() {
        System.out.println(message.getMessage());
    }
}

Suppose all these classes belong to library. The only thing I am trying to achieve is HiMessage bean to be autowired in PrintMessage class. Overriding this class would be simple solution but since the service() method behavior is exact same so I don't want to override it just for using different autowired bean.

answer would be here: https://stackoverflow.com/questions/40830548/spring-autowired-and-qualifier — tharanga-dinesh, Sep 23 '18 at 16:59
@M.Deinum How can you declare two beans with same id? Alias option is there but that would also require redefining the behavior in a different bean. — Sumit Srivastava, Sep 23 '18 at 17:03
Why would you need to change the behavior? When creating a bean with the same name it will override the other one, hence the `HiMessage` bean is availabel and will be injected. — M. Deinum, Sep 23 '18 at 17:24

score 0 · Answer 1 · answered Sep 23 '18 at 17:02

In your @Configuration class, create a @Bean("helloMessage")-annotated method which just returns the desired bean:

@Bean("helloMessage)"
public IMessage republishHiMessage() {
    return new HiMessage();
}

or by using parameter injection, if your desired object is already known as hiMessage:

@Bean("helloMessage)"
public IMessage republishHiMessage(@Qualifier("hiMessage") IMessage hiMessage) {
    return hiMessage;
}

score 0 · Answer 2 · answered Sep 23 '18 at 17:02

For Example in following case it is necessary provide a qualifer.

@Component
@Qualifier("helloMessage")
public class HelloMessage implements IMessage {
    public String getMessage() {
        return "Hello";
    }
}

Hope this will be help for you. cheers!

How to force library class to use your bean in autowiring

2 Answers2