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Lesson 5: @GetMapping

Overview

Starting from this lesson, we will build a REST service that provides basic CRUD functionality. The flow of request is shown below:

In this lesson, we create an endpoint for retrieving the list of players from the database. The REST client will send a request to /players. The REST service will respond with a JSON array of all players.

In order to retrieve the list of players from the database, we will write a method getAllPlayers in the PlayerService class. This method will call a repository method and return a list of objects.

public List<Player> getAllPlayers() {
    //call repository method
}

To be able to use methods from the PlayerRepository, we have autowired it in the PlayerService class.

@Service
public class PlayerService {
 
    @Autowired
    PlayerRepository repo;
 
    //...
}

Demonstrated Concepts

findAll()

Since we have used the JpaRepository interface for our PlayerRepository which provides all the basic methods for CRUD operations, there is no need to write any implementation for the methods.

We can simply call methods provided by the JpaRepository from the service layer. The JpaRepository provides the findAll() method that returns a List of objects.

public List<Player> getAllPlayers() {
    return repo.findAll();
}

Back to the controller, we create a method on which the /players request will be mapped. Since /players is a GET request, we use the @GetMapping annotation on the method as follows:

@GetMapping("/players")
public List<Player> getAllPlayers() {
    //call service layer method
}

The @GetMapping annotation maps HTTP GET requests to controller methods. It is a shortcut for:

@RequestMapping(method = RequestMethod.GET)

The controller method calls the service layer method, getAllPlayers. To be able to use the PlayerService methods, we autowire PlayerService in the PlayerController class.

@RestController
public class PlayerController {

    @Autowired
    PlayerService service;

}

The getAllPlayers method returns a List of Player objects. The REST API will convert that list of POJOs to JSON and return it to the client.

@GetMapping("/players")
public List<Player> getAllPlayers() {
    return service.getAllPlayers();
}

We can test the REST endpoint with a web browser as well as Postman. You can run the code on your local machine and access the results by typing the URL localhost:8080/players in the web browser and it will return the response.

We can test the same URL with Postman as well. For this, we will send a GET request to the URL as we did in the last lesson.