无法实例化 PersistentEntityResourceAssembler

Question

我正在使用 spring 框架，在下面的代码中我想获取用户的会话但是当我调用 API 它给了我一个错误详细信息如下

控制器

@Controller()
public class SessionController {

    @Autowired UserRepository userRepo;

    @RequestMapping(value = "api/session", method = RequestMethod.GET)
    public @ResponseBody ResponseEntity<?> getUserSession(Authentication authentication,
            PersistentEntityResourceAssembler assembler){       
        User user = null;
        if(authentication != null && authentication.getPrincipal() !=null){
            GalaxUser principal = (GalaxUser) authentication.getPrincipal();
            user = userRepo.findByName(principal.getUsername());
        }
        if(user==null){
            return ResponseEntity.status(HttpStatus.UNAUTHORIZED).build();
        }
        return ResponseEntity.ok(assembler.toResource(user));
    }
    }

API : http://localhost:8080/api/session

错误：

org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.data.rest.webmvc.PersistentEntityResourceAssembler]: No default constructor found; nested exception is java.lang.NoSuchMethodException: org.springframework.data.rest.webmvc.PersistentEntityResourceAssembler.<init>()
    at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:105)
    at org.springframework.web.method.annotation.ModelAttributeMethodProcessor.createAttribute(ModelAttributeMethodProcessor.java:141)
    at org.springframework.web.servlet.mvc.method.annotation.ServletModelAttributeMethodProcessor.createAttribute(ServletModelAttributeMethodProcessor.java:81)
    at org.springframework.web.method.annotation.ModelAttributeMethodProcessor.resolveArgument(ModelAttributeMethodProcessor.java:101)
    at org.springframework.web.method.support.HandlerMethodArgumentResolverComposite.resolveArgument(HandlerMethodArgumentResolverComposite.java:121)
    at org.springframework.web.method.support.InvocableHandlerMethod.getMethodArgumentValues(InvocableHandlerMethod.java:158)
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:128)
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:97)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738)
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:967)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:901)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:635)

实际错误： 无法实例化 [org.springframework.data.rest.webmvc.PersistentEntityResourceAssembler]: No default constructor found; nested exception is java.lang.NoSuchMethodException: org.springframework.data.rest.webmvc.PersistentEntityResourceAssembler.<init>()

Answer 1

首先你必须使用 @RepositoryRestController 而不是 @Controller。
使用 @RepositoryRestController 时，@ResponseBody 不起作用，因此您需要 return 一个 @ResponseEntity，如下所示

@RequestMapping(value = "api/session", method = RequestMethod.GET) public ResponseEntity<PersistentEntityResource> getUserSession(Authentication authentication, PersistentEntityResourceAssembler assembler){

编辑：对于编辑后的错误堆栈，请自动装配它而不是将其作为参数传递

  @Autowired
    private PersistentEntityResourceAssembler assembler;

Answer 2

好的，现在通过将 return 语句替换为以下语句来解决问题 return new ResponseEntity<User>(user, HttpStatus.OK);

并从响应正文中删除 PersistentEntityResourceAssembler assembler

无法实例化 PersistentEntityResourceAssembler

Failed to instantiate PersistentEntityResourceAssembler

java

spring

session

spring-boot

instantiation