Spring REST Controller (original) (raw)

Last Updated : 9 Mar, 2026

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:

Java `

@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.

Feature	@Controller	@ResponseBody
Purpose	Handles web requests and returns views	Sends data directly in response
Return Type	View name (HTML/JSP)	Raw data (JSON/XML/String)
View Resolver	Used	Not used
Usage	Web MVC applications	REST APIs

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.

Spring-Initializr

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:

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:

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.