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REST APIs with Spring Boot

Spring Boot simplifies the process of building Java-based RESTful APIs with minimal configuration.

Create a Spring Boot Project in IntelliJ

Open IntelliJ IDEA and click on New Project.
Select Spring Initializr on the left panel. This option allows you to generate a Spring Boot project with necessary dependencies.
Choose Project SDK: Ensure that you have JDK 8 or higher installed.
Set Group and Artifact: This defines your project’s package and name. For example:
- Group: com.example
- Artifact: springboot-rest-api
In the Dependencies section, search for and add:
- Spring Web (for REST API development)
- Spring Boot DevTools (optional, for automatic restarts during development)
Click Next and then Finish. IntelliJ IDEA will automatically create and import the project.

Set Up REST Controller

Now that you have a Spring Boot project, let’s create a simple REST controller.

Navigate to the src/main/java directory of your project and create a package (e.g:com.example.springbootrestapi).

Inside the package, create a new class called HelloController.

package com.example.springbootrestapi;

import org.springframework.web.bind.annotation.GetMapping;

import org.springframework.web.bind.annotation.RestController;

@RestController

public class HelloController {

@GetMapping("/hello")

public String sayHello() {

return "Hello, World!";

}

@RestController: Tells Spring that this class will handle RESTful requests.
@GetMapping: Maps the /hello endpoint to the sayHello method, which returns a simple text message.

Run Your Application

Run the Application: In IntelliJ, find the class containing your main() method, typically named SpringbootRestApiApplication.java. This file is created automatically with the project.

package com.example.springbootrestapi;

import org.springframework.boot.SpringApplication;

import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication

public class SpringbootRestApiApplication {

public static void main(String[] args) {

SpringApplication.run(SpringbootRestApiApplication.class, args);

}

- @SpringBootApplication: This annotation marks the main class of the Spring Boot application and enables automatic configuration, component scanning, and more.
Right-click the file and select Run ‘SpringbootRestApiApplication’. IntelliJ will start your Spring Boot application.

Test Your REST API

Once your application is running, you can test it in several ways:

Browser: Open your browser and go to http://localhost:8080/hello. You should see “Hello, World!” as the response.
Postman: Use Postman or another API testing tool to send a GET request to http://localhost:8080/hello.

Handling Request Parameters

Spring Boot makes it easy to handle query parameters and path variables.

Request Parameter Example: Update your HelloController to accept a query parameter:

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@GetMapping("/greet")
public String greet(@RequestParam String name) {
return "Hello, " + name + "!";
}
- Test by navigating to http://localhost:8080/greet?name=John.
Path Variable Example: Modify the HelloController to handle path variables:

@GetMapping("/greet/{name}")

public String greetPathVariable(@PathVariable String name) {

return "Hello, " + name + "!";

}

- Test by navigating to http://localhost:8080/greet/John.

Returning JSON Responses

Spring Boot automatically converts Java objects into JSON. For example:

public class User {

private String name;

private int age;

// Getters and setters

}

@GetMapping("/user")

public User getUser() {

return new User("John", 30);

}

When you access http://localhost:8080/user, you’ll see a JSON response:

{

"name": "John",

"age": 30

}