[Spring] 스프링에서의 Restful web Service

Restful web service를 스프링에서 어떻게 구현할 수 있을까?

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기존의 Spring 방식은 밑의 방식과 같다.

 

request를 받으면 Dispatcher Servlet이 받고, Handler Mapping을 통해 어떤 컨트롤러로 보낼지 결정해서 Service, DAO를 거쳐 View를 만들어 다시 Response로 Client로 보내주는 방식이였다.

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Controller는 단순히 object(객체)를 return한다.

이 object data(객체데이터)가 json/xml 형태로 HTTP response 메시지에 담겨서 전달이 된다. 

 

@RestController, @RequestBody, ResponseEntity class, @PathVariable을 통해 REST API를 구현하게 된다.

 

1) @ResonseBody 어노테이션

@Controller
@RequestMapping("/rest/cart")
public class CartResources {

   @RequestMapping("/{cartId}")
   public @ResponseBody  Cart getCartById (@PathVariable(value = "cartId") int cartId) {
        return cartService.getCartById(cartId);
   }
}

 

- return되는 Cart가 ResponseBody에 담아서 넣어주게 된다. 

- spring 3 부터 지원이됨.

- return 하는 객체는 json 형태로 serialize해준다.

 

2) @RestController 어노테이션

@RestController
@RequestMapping("/rest/cart")
public class CartResources {

   @RequestMapping("/{cartId}")
   public Cart getCartById (@PathVariable(value = "cartId") int cartId) {
        return cartService.getCartById(cartId);
   }
}

- spring 4.0 에서 추가됨.

- @Controller + @ResponseBody 라고 보면된다. -> @ResponseBody안써두되고, @RestController만 달아주면 된다.

 

3) @PathVariable 어노테이션

@RestController
@RequestMapping("/rest/cart")
public class CartResources {

   @RequestMapping("/{cartId}")
   public Cart getCartById (@PathVariable(value = "cartId") int cartId) {
        return cartService.getCartById(cartId);
   }
}

- @RequestMapping("/{cartId}") 에 cartId에 넣어줌

 

4) ResponseEntity <T> class

- status code, headers, body 이렇게 3가지의 내용을 Response에 담아야하는데 그걸 담아주는 객체가 ResponseEntity 이다. 

- 밑의 표처럼 몇가지 생성자가 있다.

Constructor	Description
ResponseEntity (HttpStatus status)	Create a new ResponseEntity with the given status code, and no body nor headers.
ResponseEntity (MultiValueMap<String,String> headers, HttpStatus status)	Create a new ResponseEntity with the given headers and status code, and no body.
ResponseEntity (T body,  HttpStatus status)	Create a new ResponseEntity with the given body and status code, and no headers.
ResponseEntity (T body,  MultiValueMap<String,String> headers,  HttpStatus status)	Create a new ResponseEntity with the given body, headers, and status code.

@RestController
@RequestMapping("/api")
public class RestApiController {

  @Autowired
  private UserService userService; 

  @RequestMapping(value = "/users", method = RequestMethod.GET)
  public ResponseEntity<List<User>> listAllUsers() {

     List<User> users = userService.findAllUsers();
     if (users.isEmpty()) {
       return new ResponseEntity<>(HttpStatus.NO_CONTENT);
     }
     return new ResponseEntity<List<User>>(users, HttpStatus.OK);
  }
}

5) @RequestBody 어노테이션

- client가 정보를 보낼때 json형태로 보내는데 이것을 받아서 Deserialization해서 필드에 넣어주기를 원함. 

=> 그렇게 스프링에게 하도록 해주는 것이 @RequestBody 어노테이션이라고 보면된다.

 

@RequestMapping(value = "/users", method = RequestMethod.POST)
public ResponseEntity<Void> createUser(@RequestBody User user, UriComponentsBuilder ucBuilder) {

      if (userService.isUserExist(user)) {
          throw new UserDuplicateException(user);
      }

      userService.saveUser(user);

      HttpHeaders headers = new HttpHeaders();
      headers.setLocation(ucBuilder.path("/api/users/{id}").
                buildAndExpand(user.getId()).toUri());

      return new ResponseEntity<Void>(headers, HttpStatus.CREATED);
}

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1) REST API 정의 

HTTP Method	URI	Operation
GET	/api/users	returns a list of users
GET	/api/users/1	returns the user with ID 1
POST	/api/users	creates a new user
PUT	/api/users/3	updates the user with ID 3
DELETE	/api/users/4	deletes the user with ID 4
DELETE	/api/users	deletes all the users

 

2) Dependencies 추가

<!-- jackson-databind -->
<dependency>
   <groupId>com.fasterxml.jackson.core</groupId>
   <artifactId>jackson-databind</artifactId>
   <version>2.10.0</version>
</dependency>

 

3) Rest Client (Postman)

Rest Client

 

4) CRUD 과정

@RestController // @Controller + @ResponseBody
@RequestMapping("/api")
public class RestApiController {

	@Autowired
	UserService userService;
	
	//Retrieve All Users 
	@GetMapping(value ="/users")
	public ResponseEntity<List <User>> listAllUsers(){//status, header, body
		
		List<User> users = userService.findAllUsers();
		
		if(users.isEmpty()) {
			return new ResponseEntity<>(HttpStatus.NO_CONTENT);
		}
		return new ResponseEntity<List<User>>(users, HttpStatus.OK);
		//body(json), status
	}
	
	@GetMapping(value ="/users/{id}")
	public ResponseEntity<User> getUser(@PathVariable("id") long id){
		User user = userService.findById(id);
		if(user == null) {
			//to do list: custom exception
			throw new UserNotFoundException(id);
		}
		return new ResponseEntity<User>(user, HttpStatus.OK);
	}
	
	//Create a User
	@PostMapping(value="/users")
	public ResponseEntity<Void> createUser(@RequestBody User user, UriComponentsBuilder ucBuilder){
		
		//중복확인
		if(userService.doesUserExist(user)) {
			//to do list: exception
			throw new UserDuplicatedException(user.getName());
		}
		userService.saveUser(user);
		
		HttpHeaders headers = new HttpHeaders();
		headers.setLocation(ucBuilder.path("/api/users/{id}").buildAndExpand(user.getId()).toUri());
		//헤더에 location을 준다.
		return new ResponseEntity<>(headers, HttpStatus.CREATED);
	}
	
	//Update a User
	@PutMapping(value="/users/{id}")
	public ResponseEntity<User> updateUser(@PathVariable("id") long id, @RequestBody User user){
		User currentUser = userService.findById(id);
		
		if(currentUser == null) {
			//to do list: custom exception
			throw new UserNotFoundException(id);
		}
		
		currentUser.setName(user.getName());
		currentUser.setAge(user.getAge());
		currentUser.setSalary(user.getSalary());
		
		userService.updateUser(currentUser);
		
		return new ResponseEntity<User> (currentUser, HttpStatus.OK);
	}
	
	@DeleteMapping(value="/users/{id}")
	public ResponseEntity<Void> deleteUser(@PathVariable("id") long id){
		User user = userService.findById(id);
		if(user == null) {
			//to do list: custom exception
			throw new UserNotFoundException(id);
		}
		userService.deleteUserById(id);
		return new ResponseEntity<>(HttpStatus.NO_CONTENT);
	}
	
	@DeleteMapping(value="/users")
	public ResponseEntity<Void> deleteAllUser(){
		userService.deleteAllUsers();
		return new ResponseEntity<>(HttpStatus.NO_CONTENT);
	}
}