The @Qualifier annotation

The @Qualifier annotation can be used to give a reference to a Spring bean. The reference can be used to qualify the dependency that needs to be autowired.

In the case of the following example, there are two sorting algorithms available: QuickSort and MergeSort. But since @Qualifier("mergesort") is used in the SomeService class, MergeSort, which also has a mergesort qualifier defined on it, becomes the candidate dependency selected for autowiring:

    @Component 
    @Qualifier("mergesort") 
    class MergeSort implements SortingAlgorithm { 
      // Class code here 
    } 
    @Component 
    class QuickSort implements SortingAlgorithm { 
     // Class code here 
    } 
    @Component 
    class SomeService { 
      @Autowired 
      @Qualifier("mergesort") 
      SortingAlgorithm algorithm; 
    }