Spring - REST Controller

A REST Controller in Spring Boot is a class annotated with @RestController that processes incoming HTTP requests and returns data objects rather than views.

• It combines the functionality of @Controller and @ResponseBody.
• It is primarily used for building RESTful APIs.
• The response is automatically converted to JSON or XML using message converters.

@RestController Annotation

The @RestController annotation is used to define a class as a RESTful web controller in Spring.

• It marks the class as a controller where every method returns data instead of a view.
• It is a combination of @Controller and @ResponseBody.
• It automatically converts Java objects returned from methods into JSON or XML responses.

Example:

@RestController
public class HelloController {

    @GetMapping("/hello")
    public String sayHello() {
        return "Hello, Welcome to REST API!";
    }
}

Explanation

• @RestController tells Spring that this class will handle REST API requests.
• @GetMapping("/hello") maps the HTTP GET request to the method.
• The method returns a String, which Spring sends directly to the client as the response.

@Controller vs @ResponseBody.

Step-by-Step Implementation

Step 1: Create a Spring Boot Project

Use Spring Initializr to generate a new Spring Boot project.

Project Configuration:

• Project Type: Maven
• Language: Java
• Spring Boot Version: 3.x (Latest Version)
• Dependencies: Spring Web
• Java Version: 17+

Click on Generate, which will download the starter project.

Step 2: Import the Project in IDE

• Open IntelliJ IDEA (or Eclipse/STS).
• Go to File -> New -> Project from Existing Sources and select pom.xml.
• Wait for Maven to download dependencies.

Note:

In the Import Project for Maven window, make sure you choose the same version of JDK which you selected while creating the project.

Step 3: Create the Model Class

Go to src -> main -> java, create a java class with the name Details.

Details.java:

public class Details {
    
    private int id;
    private String name;

    // Constructor
    public Details(int id, String name) {
        this.id = id;
        this.name = name;
    }

    // Getters and Setters
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
}

Step 4: Create a REST Controller

Now create another Java class with the name Controller and add the annotation @RestController.

Controller.java:

import org.springframework.web.bind.annotation.*;
import java.util.*;

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

    private List<Details> detailsList = new ArrayList<>();

    // GET API → Fetch all details
    @GetMapping("/details")
    public List<Details> getAllDetails() {
        return detailsList;
    }

    // POST API → Add new detail
    @PostMapping("/details")
    public String addDetails(@RequestBody Details details) {
        detailsList.add(details);
        return "Data Inserted Successfully";
    }

    // PUT API → Update detail by ID
    @PutMapping("/details/{id}")
    public String updateDetails(@PathVariable int id, @RequestBody Details updatedDetails) {
        for (Details details : detailsList) {
            if (details.getId() == id) {
                details.setName(updatedDetails.getName());
                return "Data Updated Successfully";
            }
        }
        return "Detail not found!";
    }

    // DELETE API → Remove detail by ID
    @DeleteMapping("/details/{id}")
    public String deleteDetails(@PathVariable int id) {
        detailsList.removeIf(details -> details.getId() == id);
        return "Data Deleted Successfully";
    }
}

This application is now ready to run.

Step 5: Run the Application

Run the SpringBootApplication class to start the embedded Tomcat server.

Note: The default port of the Tomcat server is 8080 and can be changed in the application.properties file.

Step 6: Test APIs using Postman

1. Add a New Detail (POST Request)

Endpoint: POST http://localhost:8080/api/details

Request Body:

{

"id": 1,

"name": "John Doe"

}

Response:

"Data Inserted Successfully"

2. Fetch All Details (GET Request)

Endpoint: GET http://localhost:8080/api/details

Response:

[

{

"id": 1,

"name": "John Doe"

}

]

3. Delete a Detail (DELETE Request)

Endpoint: DELETE http://localhost:8080/api/details/1

Response:

"Data Deleted Successfully"

To know how to use Postman, refer: How to test Rest APIs in Postman