Question

我很新兴春天并尝试在spring boot中开发一个应用程序。我知道这是重复的问题，但我没有找到解决问题的方法.. 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课程：

@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

当我尝试这样做时，我收到错误。

    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 {
}

然后将其注入到使用@Autowired注释的类中：

@Autowire
private DAO dao;

此外，您还可以以类似的方式自动装配接口，然后指定在有多个实现时将使用哪个实现。

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

Answer 2

我刚刚解决了这个问题...

@RestController
    public class UserController {

        private static final Logger LOGGER = LoggerFactory.getLogger(UserController.class);
        private final UserService userService;
   @Autowired
        DatabaseConnections dataconnections 
       @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);
    }
    }

有一个databaseConnection类正在实例化......我们必须将该类标记为@Component

@Component
public class DatabaseConnections {

  public Connection getPostgresConnection(String hostname, String port, String dbname, String username, String password)

并将DAo声明为@Component或服务

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

预计至少有1个bean可以作为此依赖项的autowire候选者

2 个答案: