@Bean 注释在 Spring Boot 中不起作用

Question

I created the Model

@Repository
public class Model {
    String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Model(String name) {
        super();
        this.name = name;
    }

    public Model() {
        super();
        // TODO Auto-generated constructor stub
    }
}

Then I created the configuration class with a bean

@Component
public class Config {

    @Bean
    public Model beanB() {
        Model a=new Model();
        a.setName("Daniel3");
        return a;
    }   
}

Then I created the Controller class

@RestController
public class TestController {

    @Autowired
    Model model;

    @GetMapping("/test")
    @ResponseBody
    public Model test() {
        return model;
    }

}

When I hit the controller url, I am getting the below response

{"name":null}

But if I modify configuration class as

    @Bean
    @Primary
    public Model beanB() {
        Model a=new Model();
        a.setName("test");
        return a;
    }   

I get the output as {"name":"test"} . And I am observing the same behaviour when using Autowired Model instead of new Model()

Can anyone explain this behavior?

Answer 1

Right now, you are registering two different beans of type Model as you use @Repository on your Model class which you shouldn't do as this is used for database repositories. If you remove @Repository from your Model you'll only have one bean definition and hence get the correct one injected to your controller:

// @Repository remove this, should not be used here
public class Model {
    String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Model(String name) {
        super();
        this.name = name;
    }

    public Model() {
        super();
        // TODO Auto-generated constructor stub
    }
}

The reason it works with @Primary is that you then define are order hof importance among all beans of the type Model .

Answer 2

@Repository意味着您在 bean 工厂中注入了一个类型为 repository 的 bean，此外，当您还添加@Bean注释时，它将成为第二个 bean，因此它在这两个 bean 之间创建了一个重要的问题，当您添加@Primary它赋予了重要性到你的@Bean注释 bean。