Spring Web Services

@Controller

Creates a Map of model objects and finds a View (html). So, it’s used to display HTML contents. Is a specialization of @Component.

@RequestBody

Maps the HttpRequest body to a domain object: deserializes the inbound HttpRequest body onto a Java object.

@ResponseBody

Tells a Controller that the object returned is automatically serialized into JSON and passed back into the HttpResponse object.

@RestController

Is a combination of @Controller and @ResponseBody. Automatically serializes return objects into HttpResponse.

@RequestMapping(method = RequestMethod.GET, path = “/my-rest-controller”)

Maps an HTTP Get request to a method. It can be replaced for the next Mapping annotations.

@GetMapping(path = “/my-path”)

@PostMapping(path = “/my-path”)

@PutMapping(path = “/my-path”)

@PathVariable

@Component and its variants

@Autowired

URI and ResponseEntity classes

    /**
     * 
     * @param user
     * @return a ResponseEntity with headers:
     *      HTTP 201 created code: HTTP/1.1 201 
     *      location of the new resource: Location: http://localhost:8080/users/4
     * of the new resource.
     */
    @PostMapping(path = "/users")
    public ResponseEntity<Object> createUser(@RequestBody  User user) {

        User createdUser = userDaoService.save(user);

        URI location = ServletUriComponentsBuilder
                .fromCurrentRequest()
                .path("/{id}")
                .buildAndExpand(createdUser.getId()).toUri();

        return ResponseEntity.created(location).build();
    }

@ResponseStatus(code = HttpStatus.NOT_FOUND)

Using @ResponseStatusCode in an Unchecked Exception (RunTime Exception) thrown in a Controller:

    @ResponseStatus(code = HttpStatus.NOT_FOUND)
    public class UserNotFoundException extends RuntimeException {
        public UserNotFoundException(String message) {
            super(message);
        }
    }

Response: Structure, fields, of the response are provided by Spring by default.

´´´ HTTP/1.1 404 Content-Type: application/json Transfer-Encoding: chunked Date: Tue, 03 Dec 2019 01:33:20 GMT

{ “timestamp”: “2019-12-03T01:33:20.234+0000”, “status”: 404, “error”: “Not Found”, “message”: “id = 5”, “trace”: “com.neojal.restfulwebservices.user”, “path”: “/users/5” } ´´´

ResponseEntityExceptionHandler abstract class (Spring)

It is possible to create a customized error response structure by extending and implementing the methods defined in such class, as well as using @ControllerAdvice and @RestController in such class, as follows:

´´´java @ControllerAdvice @RestController public class CustomizedResponseEntityExceptionHandler extends ResponseEntityExceptionHandler {

@ExceptionHandler(Exception.class)
public final ResponseEntity<Object> handleAllExceptions(Exception ex, WebRequest request) {

    ExceptionResponse exceptionResponse =
            new ExceptionResponse(
                    new Date(), ex.getMessage(), request.getDescription(false));

    return new ResponseEntity(exceptionResponse, HttpStatus.INTERNAL_SERVER_ERROR);
}

@ExceptionHandler(UserNotFoundException.class)
public final ResponseEntity<Object> handleUserNotFoundExceptions(Exception ex, WebRequest request) {

    ExceptionResponse exceptionResponse =
            new ExceptionResponse(
                    new Date(), ex.getMessage(), request.getDescription(false));

    return new ResponseEntity(exceptionResponse, HttpStatus.NOT_FOUND);
}

@Override
protected ResponseEntity<Object> handleMethodArgumentNotValid(MethodArgumentNotValidException ex, HttpHeaders headers, HttpStatus status, WebRequest request) {

    ExceptionResponse exceptionResponse =
            new ExceptionResponse(
                    new Date(), "Validation Failed.", request.getDescription(false));

    return new ResponseEntity(exceptionResponse, HttpStatus.BAD_REQUEST);
} } ´´´

@ControllerAdvice

@Valid (java Validation API) and Hibernate Validator implementation

Rest Clients

Spring RestTemplate

Synchronous client to perform HTTP requests, exposing a simple, template method API over underlying HTTP client libraries such as the JDK HttpURLConnection, Apache HttpComponents, and others.

The RestTemplate offers templates for common scenarios by HTTP method, in addition to the generalized exchange and execute methods that support of less frequent cases.