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Spring Controllers

Mapping HTTP Requests

The @RequestMapping annotation can be used at the method level or the class level to map an HTTP request to the appropriate controller method. 

@RequestMapping("/sayhello")
public String sayHello() {
  return "Hello, world";
}

Base Path Mapping

When the @RequestMapping annotation is used at the class level, the specified path attribute becomes the base path for the class.

In the example code, getallRecipes is called for every GET request to the /foodierecipes endpoint.

@RequestMapping("/foodierecipes")
public class FoodieRecipesController {
  
  private final RecipeRepository recipeRepository;


  public FoodieRecipesController(RecipeRepository recipeRepo) {
    this.recipeRepository = recipeRepo;
  }


  @GetMapping()
  public Iterable<Recipe> getAllRecipes() {        
    return this.recipeRepository.findAll();
  }
}

Common Request Types

Spring provides annotations that map to common request types. These methods include @GetMapping, @PostMapping, @PutMapping, and @DeleteMapping.

// Method parameters and bodies omitted for brevity


@RestController
public class FlowerController {
  
  @GetMapping("/flowers")
  public Iterable<Flower> getAllFlowers() {}
  
  @PostMapping("/flowers")
  public Flower addFlower() {}
  
  @PutMapping("/flowers/{id}")
  public Flower editFlower() {}
  
  @DeleteMapping("/flowers/{id}")
  public Flower deleteFlower() {}
}

Accessing Parameters in Methods

The @RequestParam annotation can be used at the method parameter level to allow the HTTP request parameters to be accessed in the method. 

// Accepts GET requests to /fruit?fruitType=mango


@GetMapping("/fruit")
public fruit isFruitAvailable(@RequestParam String fruitType) {
  return fruit.find(fruitType);
}

REST Controllers

@RestController is a class level annotation used to combine the functionality of the @Controller and @ResponseBody annotations.

  • @Controller designates the annotated class as a controller
  • @ResponseBody allows returned objects to be automatically serialized into JSON and returned in the HTTP response body
@RestController
public class LocationController {
  
  @GetMapping("/{gpsCoordinates}")
  public City getByCoordinates(@PathVariable String gpsCoordinates) {
    return this.locations.findByCoordinates(gpsCoordinates);
  }
  
}

Response Exceptions

Spring controllers can return a custom HTTP status code by throwing an instance of ResponseStatusException, which accepts an argument of type HttpStatus.

@GetMapping("/{id}")
public Book isBookAvailable(@PathVariable string id) 
{
  if (id.isNumeric()) {
    int idAsInteger = Integer.parseInt(id)
    return book.findByID(idAsInteger)
  } 
  else {
    throw new ResponseStatusException(HttpStatus.BAD_REQUEST, "The ID contained a non-numerical value.");
  }
}

HttpStatus Type

In Spring, the HttpStatus type can be used to represent different HTTP status codes.

HttpStatus.OK // 200 code


HttpStatus.MOVED_PERMANENTLY // 301 code  


HttpStatus.NOT_FOUND // 404 code


HttpStatus.BAD_GATEWAY // 502 code

Spring Specifying HTTP Status Code

In Spring, we have the option of apply the @ResponseStatus annotation to a method to designate a specific HttpStatus. 

@PostMapping("/book")
@ResponseStatus(HttpStatus.CREATED)
public void addNewBook(@RequestParam string title) {
  this.library.add(title);
}

Deserializing to an Object

In Spring, applying the @RequestBody annotation to a controller’s method enables automatic deserialization of the HTTP request body to an object bound to the method’s argument. 

@GetMapping("/book")
public Book isBookAvailable(@RequestBody Book book) {
  return library.find(book);
}

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