spring - 预计至少有 1 个有资格作为此依赖项的 Autowiring 候选者的 bean

Question

我对 Spring 非常陌生，正在尝试在 Spring Boot 中开发一个应用程序。我知道这是重复的问题，但我没有找到任何解决我的问题的方法。我有一个名为 UserController 的类，如下所示

    @RestController
    public class UserController {

        private static final Logger LOGGER = LoggerFactory.getLogger(UserController.class);
        private final UserService userService;

        DatabaseConnections dataconnections = new DatabaseConnections(); 
       @Autowired
       private DAO dao;      
        @Inject
        public UserController(final UserService userService) {
            this.userService = userService;  
        }

        @RequestMapping(value = "/user", method = RequestMethod.POST)
        public User createUser(@RequestBody @Valid final User user) {
            LOGGER.debug("Received request to create the {}", user);
            return userService.save(user);
        }
       @RequestMapping(value = "/getuser/{id}", method = RequestMethod.GET)
       public JSONObject getUser(@PathVariable String id) {

    return dao.getUsers(id);
    }
    }

我还有一个具有某些功能的类:

@Service("dao")
    public class DAO {    
      public JSONObject getUsers(@PathVariable String id) {
                Connection dbConnection = null;
                Statement statement = null;
                JSONObject userJSONObject = new JSONObject();
                String selectusers = "SELECT* from emp;
                try {
                    dbConnection = dataconnections.getPostgresConnection(hostname, port, dbname, username, password);
                    statement = dbConnection.createStatement();
                    ResultSet rs = statement.executeQuery(selectusers);
                    while (rs.next()) {
                           --
                        ---
                    }
                    return userJSONObject;
    } 

我想在usercontroler类中使用getUsers函数

当我尝试通过这种方式执行操作时，出现以下错误。

    Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'userController': Injection of autowired dependencies  
   failed; nested exception is   
org.springframework.beans.factory.BeanCreationException: Could not autowire  
 field: private com.emc.bdma.itaudemo.postgres.dao.DAO   
com.emc.bdma.itaudemo.restclient.controller.UserController.dao; nested   
exception is org.springframework.beans.factory.NoSuchBeanDefinitionException:   
No qualifying bean of type [com.emc.bdma.itaudemo.postgres.dao.DAO] found for  
 dependency: expected at least 1 bean which qualifies as autowire candidate for    
this dependency. Dependency annotations:   
{@org.springframework.beans.factory.annotation.Autowired(required=true)} 

Answer 1

似乎还没有找到你的 DAO 对象。我建议使用 @Service 注释来注释 DAO，如下所示:

@Service("dao")
public class DAO {
}

然后将其注入(inject)到您使用 @Autowired 注释的类中:

@Autowire
private DAO dao;

此外，您还可以以类似的方式 Autowiring 接口(interface)，然后指定如果有多个接口(interface)，将使用哪个实现。

如果不是这种情况，请发布调用 dao 函数的类的完整代码，以便我们可以看到全貌。