Spring Boot Constructor Based Dependency Injection not working

Question

I've used Spring Boot to develop a REST Service. In one of the REST controllers I have a field based dependency injection that I like to change to a constructor based dependency injection. My setup of the dependency injections currently looks like this:

@RestController
public class ParameterDateController {

    private ParameterDateController() {
    }

    private ParameterDate parameterDate;

    private ParameterDateController(ParameterDate parameterDate) {
        this.parameterDate = parameterDate;
    }

    @Autowired
    private ParameterDateService parameterDateService;

// here are the metods of the endpoints
}

With this setup everything works fine. I would likt to change ParameterDateService to constructor based and I tried with this:

@RestController
public class ParameterDateController {

    private ParameterDateController() {
    }

    private ParameterDate parameterDate;

    private ParameterDateController(ParameterDate parameterDate) {
        this.parameterDate = parameterDate;
    }

    private ParameterDateService parameterDateService;

    private ParameterDateController(ParameterDateService parameterDateService) {
        this.parameterDateService = parameterDateService;
    }

// here are the metods of the endpoints
}

After the change to constructor based dependency injection I get a NullPointerException when I try to inject the dependency like this parameterDateService.postParameterDate(parameterDate);. I inject the same way when I have it setup as field based dependency injection and that gives no NullPointerException. The constructor based dependency injection for ParameterDate works as expected.

What is it I'm doing wrong?

You must add Autowired on the second constructor. Or remove the first one. You should also make it public: what's the point of a constructor you can't call without reflection? If you're happy with that, field injection is also fine. — JB Nizet, Jun 10 '17 at 09:29

ledniov · Accepted Answer · 2017-06-10T09:39:19.470

0

If you want to have two dependencies wired via constructor - you have to declare them as constructor parameters, so here you have to declare:

public ParameterDateController(ParameterDate parameterDate, ParameterDateService parameterDateService) {
    this.parameterDate = parameterDate;
    this.parameterDateService = parameterDateService;
}

Here's a good answer about constructor injection.

edited Jun 10 '17 at 09:39

answered Jun 10 '17 at 09:33

ledniov

2,302
3
21
27

Spring Boot Constructor Based Dependency Injection not working

1 Answers1