Spring Boot JPA不起作用

Question

I have a controller class which is below. I have a TagRepository interface which extends JPA repository which I am using to save TagReader instance to my DB and it works fine when I use it in my controller class. However, when I try to use tagRepository in another class and try to save my TagReader object from there it throws a null pointer exception.

The following logic works fine.

@RestController
public class Controller {

@Autowired
TagRepository tagRepository;

@Autowired
Rfid6204Connection rfid6204Connection;

@RequestMapping(value = "/test")
public void testRepoController(){

    String tagid = "0x3504ACE6E0040E5147D516A6";
    String serial ="00333478";
    String departure ="2017-12-22T12:16:58.857";
    String type = "ISOC";


    TagReader tagReader = new TagReader(tagid,serial,departure,type,"5");


    tagRepository.save(tagReader);
  }
}

The following logic throws a null pointer exception.

@component
public class Rfid6204Connection{

    @Autowired
    static TagRepository tagRepository;

    public static void test(TagReader tag){
        tagRepository.save(tag);
    }

}

Can someone please tell me what the issue is?

Answer 1

I think you are using Rfid6204Connection.test as a static method. Spring doesn't work with Static methods. It works with Objects instantiated by the Spring Container. So change your Rfid6204Connection as below;

@Component
public class Rfid6204Connection{

    @Autowired
    private TagRepository tagRepository;

    public void test(TagReader tag){
        tagRepository.save(tag);
    }

}

And use it wherever you want as below;

@Autowired 
Rfid6204Connection rfid6204Connection;

// Within a method or constructor
rfid6204Connection.test(tag);

Answer 2

You made the Autowired field static and when the class loader loads the static values, the Spring context is not yet loaded and your object is not correctly initialized; remove the static keyword:

@Autowired
private TagRepository tagRepository;

Answer 3

you couldn't autowired static variables directly

then, you have some options. first, autowired instance of TagRepository and after dependency injection set a instance to static variable

@Component
public class Rfid6204Connection {
private static TagRepository sTagRepository;

@Autowired
private TagRepository tagRepository;

@PostConstruct
public void init() {
    Rfid6204Connection.sTagRepository = tagRepository;
}
}

second prepare setter method of TagRepository and put a autowired

public class Rfid6204Connection {

    private static TagRepository tagRepository;

    @Autowired
    public void setTagRepository(TagRepository tagRepository) {
        Rfid6204Connection.tagRepository = tagRepository;
    }

}

but originally ... you shoudn't autowire to static variables.