Spring boot - 没有@component 注解的bean配置

Question

As part of my university project I was asked to implement a simple spring-boot app(backend only) which can communicate with Postman through HTTP requests.

The project built in controller-service-repository architecture and conatins only 1 Entity(Post object with string content) and 2 end-points(create new post, get all posts).

I know there is a few ways to configure beans in spring-boot:

1. with an external XML file.
2. With @Configuration annotation & @Bean annotation
3. With @Component annotation(@RestController,@Service, @JpaRepository)

The 3rd way working great but i was asked to implement the 2nd way and I'm really struggling to get this working.

Im getting:

ServletException: Circular view path [post]: would dispatch back to the current handler URL [/post] again. Check your ViewResolver setup!

Tried to explore about this exception and i did manage to "solve" it by adding this maven dependency:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-thymeleaf</artifactId>
    <version>2.5.2</version>
</dependency>

which led to:

"org.thymeleaf.exceptions.TemplateInputException: Error resolving template [post], template might not exist or might not be accessible by any of the configured Template Resolvers"

what am i doing wrong ?

Configuration class:

@Configuration
@EnableJpaRepositories(basePackages = {
        "com.example.microblog.post.domain.repository"
})
public class ApplicationBeans {

    @Bean
    public PostController postController(PostService postService){
        return new PostController(postService);
    }

    @Bean
    public PostService postService(){
        return new PostService();

    }

}

Controller class:

@AllArgsConstructor
@RequestMapping(path = "post")
public class PostController {

    @Autowired
    private PostService service;

    @CrossOrigin(origins = "http://localhost:4200")
    @PostMapping("")
    public PostEntity create(@RequestBody PostDto dto) {
        return service.create(dto);
    }

    @GetMapping("/all")
    @CrossOrigin(origins = "http://localhost:4200")
    public List<PostEntity> getAll() {
        return service.getAll();
    }

}

Service Class:

@Transactional
public class PostService {

    @Autowired
    private PostRepository PostRepository;


    public PostEntity create(PostDto dto){
        PostEntity newPost = new PostEntity(dto.getContent());
        return PostRepository.save(newPost);
    }

    public List<PostEntity> getAll(){
        return PostRepository.findAll();
    }

Repository class:

public interface PostRepository extends JpaRepository<PostEntity,Long> {}

Answer 1

For second approach, when you create a Bean, try not to have @Component/@Controller ... on the class for which you create the bean

@Configuration
public class AppConfig {
    @Bean
    public TransferService transferService() {
        return new TransferServiceImpl();
    }
}

You can continue to autowire them like in third approach, try not to keep beans of same name

Answer 2

Your error points in the direction, that your Controller has difficulties to resolve the answer of your Service to a valid JSON response.

Note that @RestController is just a convenient way to add @Controller and @ResponseBody annotation. When you just add a @Bean annotation you are not adding either @Controller or @ResponseBody. If you want to use the Controller class without using these Annotations you need to implement the functionality that these classes provide.

However I really see no way, why option 2 would be used for a Controller class. If you want to use it for a @Service class (which is doing the same as @Component) you can use the approach that Ravi suggested.