Consider marking one of the beans as @Primary

Question

In my Java spring application, I have

public class BinarySearchImpl {

    @Autowired
    @Qualifier("Quick")
    SortAlgorithem sorter;

    Log log=LogFactory.getLog(BinarySearchImpl.class);

    public BinarySearchImpl(SortAlgorithem sorter) {
        log.info("Binary Search Bean is created");
        this.sorter=sorter;
    }

SortAlgorithem is an interface which makes my application loosely coupled:

public interface SortAlgorithem {

    public int[] sort(int[] arrayNumbers);

}

And then there are 2 implementations for this interface. One is BubbleSort:

@Component
@Qualifier("Bubble")
public class BubbleSort implements SortAlgorithem {

    Log log=LogFactory.getLog(BubbleSort.class);

    public int[] sort(int[] numbers) {
        log.info("Bubble sort is called");
        return numbers;
    }
}

and the other is QuickSort:

@Component
@Qualifier("Quick")
//@Primary
public class QuickSort implements SortAlgorithem{

    Log log= LogFactory.getLog(QuickSort.class);

    public int[] sort(int[] numbers) {
        log.info("Quick Sort is called");
        return numbers;
    }

}

At the end, when I call my app it complains with this message:

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

I am wondering... Why @Qualifier annotation does not work?

How does your `BinarySearchImpl` instance being created? Why do you need constructor param in it, since u r using field injection? — Leffchik, Nov 13 '17 at 10:41
There will be some more text before the "Consider..." you quote. Include that in the question too. — slim, Nov 13 '17 at 10:46

slim · Accepted Answer · 2017-11-13T13:57:24.947

You have annotated a field with @Autowired and @Qualifier, but you have also created a constructor which sets the field.

I think that Spring is using the constructor, but doesn't automatically know that the constructor parameter corresponds to the annotated field.

So move the annotations into the constructor declaration:

private SortAlgorithm sorter;

@Autowired 
public BinarySearchImpl(@Qualifier("quick") SortAlgorithm sorter) {
     this.sorter = sorter;
}

Alternatively, you could use a zero-arg constructor, keep your field annotation and let Spring inject using reflection. However in my opinion constructor-injection is better -- it allows you to unit test cleanly, without involving Spring or reflection.

As other answers point out, there are other ways to disambiguate autowired beans -- and the Spring docs explain them all -- but using qualifiers like this does work.

score 4 · Answer 2 · answered May 15 '19 at 11:20

The correct approach:

public interface SortAlgorithem {
    public int[] sort(int[] arrayNumbers);
}

@Component("Bubble")
public class BubbleSort implements SortAlgorithem {
    Log log = LogFactory.getLog(BubbleSort.class);

    public int[] sort(int[] numbers) {
        log.info("Bubble sort is called");
        return numbers;
   }
}

@Primary
@Component("Quick")
public class QuickSort implements SortAlgorithem {
    Log log = LogFactory.getLog(QuickSort.class);

    public int[] sort(int[] numbers) {
        log.info("Quick Sort is called");
        return numbers;
    }
}

and then you need to use your implementations like this:

@Autowired
@Qualifier(value = "Bubble")
private SortAlgorithem bubbleSort;

@Autowired
@Qualifier(value = "Quick")
private SortAlgorithem quickSort;

score 1 · Answer 3 · answered Nov 13 '17 at 10:42

1

try

@Component("qualifier_name")

answered Nov 13 '17 at 10:42

Sujal Mandal

923
1
13
27

score 1 · Answer 4 · answered Nov 13 '17 at 10:46

You have to declare your components like this:

@Component("Bubble")
public class BubbleSort implements SortAlgorithem {

    Log log=LogFactory.getLog(BubbleSort.class);

    public int[] sort(int[] numbers) {
        log.info("Bubble sort is called");
        return numbers;
    }
}

and

@Component("Quick")
public class QuickSort implements SortAlgorithem{

    Log log= LogFactory.getLog(QuickSort.class);

    public int[] sort(int[] numbers) {
        log.info("Quick Sort is called");
        return numbers;
    }

}

This should solve your issue.

Yes, but the question is "why doesn't `@Qualifier` work"? – slim Nov 13 '17 at 10:48 — slim, Nov 13 '17 at 10:48

score 1 · Answer 5 · answered Mar 12 '19 at 10:54

Hi Sorry for coming late to the party. I had 2 service class which were implementing a single interface like this,So I have done this with @Component("name") and it worked. though it is still a mystery why @Qualifier("name") did not worked?

Code:

@Service("signup")
//@Qualifier("signup")
public class SignUpGenerator implements ITestCaseGenerator {

}




@Component
public class SelUtil {

    @Autowired
    @Qualifier("login")
    ITestCaseGenerator login;

    @Autowired
    @Qualifier("signup")
    ITestCaseGenerator signUp;

}

score 0 · Answer 6 · answered Jun 30 '20 at 14:43

0

I had this problem when using @RequiredArgsConstructor annotation, and had to remove it (and use manual constructor with a @Qualifier annotation as per @slim answer).

answered Jun 30 '20 at 14:43

diman82

572
5
10

In my IntelliJ 2021.2.3 there is a helpful message for this: `Lombok does not copy the annotation 'org.springframework.beans.factory.annotation.Qualifier' into the constructor`. – lisymcaydnlb Dec 12 '21 at 20:12

Consider marking one of the beans as @Primary

6 Answers6

The correct approach:

Linked