expected at least 1 bean which qualifies as autowire candidate for this dependency

Question

I am very new to spring and trying to developing one application in spring boot.I know this is duplicate question but I didnt find any solution to my problem.. I have a class called UserController which is like below

    @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);
    }
    }

I have one more class which is having some function :

@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;
    } 

I want to use the getUsers function in usercontroler class

I am getting error below when I try to do by this way.

    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

I just solved the issue...

@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);
    }
    }  

There is a databaseConnection class is instantiating...We have to mark the class as @Component

@Component
public class DatabaseConnections {

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

And also declare DAo as @Component or service

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

Answer 2

It seems that it has not found yur DAO object. I suggest annotating the DAO with @Service annotation like this:

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

and then injecting it into the class where you are using it with @Autowired annotation:

@Autowire
private DAO dao;

Moreover, you can also autowire an interface in a similar way and then specify which implementation will be used if there are more than one.

If this is not the case, post the full code of the class calling the dao function, so we can see the whole picture.