相关疑难解决方法(0)

例

interface IA
{
  public void someFunction();
}

@Resource(name="b")
class B implements IA
{
  public void someFunction()
  {
    //busy code block
  }
  public void someBfunc()
  {
     //doing b things
  }
}

@Resource(name="c")
class C implements IA
{
  public void someFunction()
  {
    //busy code block
  }
  public void someCfunc()
  {
     //doing C things
  }
}

class MyRunner
{

  @Autowire
  @Qualifier("b") 
  IA worker;

  worker.someFunction();
}

谁可以给我解释一下这个.

• spring如何知道要使用哪种多态类型.
• 我需要@Qualifier还是@Resource？
• 为什么我们自动连接接口而不是实现的类？

代码中标题的问题:

@Transactional (readonly = true)
public interface FooService {
   void doSmth ();
}


public class FooServiceImpl implements FooService {
   ...
}

VS

public interface FooService {
   void doSmth ();
}

@Transactional (readonly = true)
public class FooServiceImpl implements FooService {
   ...
}

我是 Spring Boot 的新手，在编写文件上传 API 时出现以下错误：

Error:Description:
Field fileStorageService in com.primesolutions.fileupload.controller.FileController required a bean of type 'com.primesolutions.fileupload.service.FileStorageService' that could not be found.
The injection point has the following annotations:
    - @org.springframework.beans.factory.annotation.Autowired(required=true)
Action:
Consider defining a bean of type 'com.primesolutions.fileupload.service.FileStorageService' in your configuration.*

控制器类：

public class FileController 
{
    private static final Logger logger = LoggerFactory.getLogger(FileController.class);

    @Autowired
    private FileStorageService fileStorageService;

    @PostMapping("/uploadFile")
    public UploadFileResponse uploadFile(@RequestParam("file") MultipartFile file) {
        String fileName = fileStorageService.storeFile(file);

        String fileDownloadUri = ServletUriComponentsBuilder.fromCurrentContextPath()
                .path("/downloadFile/")
                .path(fileName)
                .toUriString();

        return new UploadFileResponse(fileName, fileDownloadUri, …