Getting null value for @Value with @AllArgsConstructor

Question

I am getting null as a value when I use @Value with @AllArgsConstructor combination.

@Service
@Slf4j
@AllArgsConstructor
public class ReconService{
    
    private ReconRepo reconRepo;
    private InService inService;
    @Value("${threshold.count}")
    private Integer threshold;
    
    public void doSomething(List<Record> records) {
       if(threshold < records.size()) {
         throw new RuntimeException("threshold exceeded");
       }
    }
}

In the doSomething() , I am getting threshold variable value as null Could you please help me on this.

Answer 1

When you create a constructor, you're telling spring boot container that class dependencies will be injected using it. In that case, dependency specifications like @Qualified or @Value need to be declared on constructor parameter. Because your constructor is being generated by lombok, it doesn't includes annotations on parameters.

Using @Value directly on the field works for field injection, but in your case you are using constructor injection.

For your code to work you'll need to do the following:

@Service
@Slf4j
public class ReconService{

    private ReconRepo reconRepo;
    private InService inService;
    private Integer threshold;

    public ReconService(
        ReconRepo reconRepo,
        InService inService,
        @Value("${threshold.count}") Integer threshold
    ) {
        this.reconRepo = reconRepo;
        this.inService = inService;
        this.threshold = threshold; 
    }

    public void doSomething(List<Record> records) {
        if(threshold < records.size()) {
            throw new RuntimeException("threshold exceeded");
        }
    }
}

Answer 2

When I used both @NoArgsConstructor and @AllArgsConstructor it worked.

@Service
@Slf4j
@AllArgsConstructor
@NoArgsConstructor
public class ReconService{
    
    private ReconRepo reconRepo;
    private InService inService;
    @Value("${threshold.count}")
    private Integer threshold;
    
    public void doSomething(List<Record> records) {
       if(threshold < records.size()) {
         throw new RuntimeException("threshold exceeded");
       }
    }
}

Answer 3

You can use @RequiredArgsConstructor to inject your beans via constructor and your threshold value to be injected with field injection. For that you have to make your beans final

@Service
@Slf4j
@RequiredArgsConstructor
public class ReconService{
    
    private final ReconRepo reconRepo;
    private final InService inService;
    @Value("${threshold.count}")
    private Integer threshold;
    
    public void doSomething(List<Record> records) {
       if(threshold < records.size()) {
         throw new RuntimeException("threshold exceeded");
       }
    }
}

Answer 4

您应该使用@RequiredArgsConstructor ，它只会初始化标有@NonNull或final关键字的字段。