Request Mapping with Spring REST

CRUD with REST

CRUD stands for Create/Read/Update/Delete regarding data storage and manipulation.

• On a blog, you Create a post, a user Reads a post, you can Update a post, and you can Delete a post.

Over the primary communications protocol of the web, HTTP, we use request methods that have meaning to the server:

CRUD Op.	HTTP Verb	URI	Request Body	Response Body
Read	GET	/api/v1/books		Collection of representations of all book resources
Read	GET	/api/v1/books/17		Representation of book 17
Create	POST	/api/v1/books	Representation of a new book resource	Description the result of the operation
Update	PUT	/api/v1/books/17	Representation of a new version of book 17
Update	PATCH	/api/v1/books/17	Description of changes to make to book 17
Delete	DELETE	/api/v1/books/17

@PathVariable, Why It's Important for REST

The presence of {} in a controller method's @RequestMapping always signifies the presence of a path variable.

• We use these to access a specific resource in an API.

The @PathVariable annotation accesses the variable from a request.

@RequestMapping("api/v1")
@RestController
public class BookController {
  @PutMapping("books/{bookId}")
  public Book replaceBook(@PathVariable Integer bookId, @RequestBody Book book) { ... }

Will pull a parameter value from a URL Path such as:

http://localhost:8080/api/v1/books/17

If the curly-braced path element doesn't match your parameter name, specify it in @PathVariable:

  @DeleteMapping("books/{bookId}")
  public void removeBook(@PathVariable("bookId") Integer id) { ... }

Implementation

In the controller route below we have created a method getEmployee mapped to api/employees/{id}.

@GetMapping("api/employees/{id}")
@ResponseBody
public Employee getEmployee(@PathVariable int id){
  return dao.findEmployeeById(id);
}

* This method will return a single Employee object, serialized as JSON. * Included in the route api/employees/{id} is a @PathVariable (id) represented by the {id} in the URL. * To access this value we annotate a method parameter with @PathVariable and give the variable the same name as indicated in the {}s * Path variables are String values. * Spring will attempt to convert the String value to the type of the annotated parameter. * If it cannot convert the value properly, it will throw an exception. * When a @PathVariable is present, this controller method cannot be called without the value provided in the URL.

Multilevel Resources

In the above example we only concerned ourselves with CRUD for the products themselves, but resources can have multiple levels of access to them.

If we create a BookReviewController, each review corresponds to a specific book.

Action	HTTP Method	Url Template
LIST	GET	/api/v1/books/{bookId}/reviews
READ	GET	/api/v1/books/{bookId}/reviews/{reviewId}
CREATE	POST	/api/v1/books/{bookId}/reviews
REPLACE	PUT	/api/v1/books/{bookId}/reviews/{reviewId}
UPDATE	PATCH	/api/v1/books/{bookId}/reviews/{reviewId}
DESTROY	DELETE	/api/v1/books/{bookId}/reviews/{reviewId}

@RequestMapping("api/v1")
@RestController
public class BookReviewController {
  @GetMapping("books/{bookId}/reviews/{reviewId}")
  public Review getReviewForBook(@PathVariable("bookId") Integer id,
                                 @PathVariable("reviewId") Integer rid) { ... }

@RequestParam

You can still use @RequestParam in a REST API, which retrieves named parameters from the request URL.

http://localhost:8080/api/v1/books?sortBy=author

We use @PathVariable to specify options and behaviors for our request.

• Don't use them to identify resources.

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