Spring Boot – REST Example

In modern web development, most applications follow the Client-Server Architecture. The Client (frontend) interacts with the server (backend) to fetch or save data. This communication happens using the HTTP protocol. On the server, we expose a bunch of services that are accessible via the HTTP protocol. The client can then directly call the services by sending the HTTP request. 

Now, this is where REST comes into the picture.  Rest stands for Representation State Transfer. It is a convention to build these HTTP services. So we use a simple HTTP protocol principle to provide support to CREATE, READ, UPDATE, & DELETE data, commonly referred to as CRUD operations. In short, it is a set of rules that developers follow when they create their API. One of these rules states that you should be able to get a piece of data (called a resource) when you link to a specific URL.

Let’s implement a REST application and understand the REST approach by creating an example where we simply return the Book data in the form of JSON. 

Step-by-Step Guide to Build a RESTful API using SpringBoot

Step 1: Setting up the Spring Boot Project

So first, we will set up the spring project in STS IDE. The steps are outlined below:

• Click File -> New -> Project -> Select Spring Starter Project  -> Click Next.
• A New Dialog box will open where you will provide the project-related information like project name, Java version, Maven version, and so on.
• After that, select required maven dependencies like Spring Web, and Spring Boot DevTools (which provide fast application restarts, LiveReload, and configurations for an enhanced development experience).
• Click Finish to generate the project.

Step 2: Project Structure

Once the project is created, we will see the following structure

pom.xml:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>3.4.3</version>
		<relativePath/> <!-- lookup parent from repository -->
	</parent>
	<groupId>com.example</groupId>
	<artifactId>book-api</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>book-api</name>
	<description>Demo project for Spring Boot</description>
	<url/>
	<licenses>
		<license/>
	</licenses>
	<developers>
		<developer/>
	</developers>
	<scm>
		<connection/>
		<developerConnection/>
		<tag/>
		<url/>
	</scm>
	<properties>
		<java.version>17</java.version>
	</properties>
	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>

		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-devtools</artifactId>
			<scope>runtime</scope>
			<optional>true</optional>
		</dependency>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-test</artifactId>
			<scope>test</scope>
		</dependency>
	</dependencies>

	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
			</plugin>
		</plugins>
	</build>

</project>

Note: Since we are not using a database in this example, no configuration is needed in application.properties.

Step 3: Create the POJO Class

A POJO class represents the data model. In this case, we’ll create a Book class.

Book.java:

package com.example.demo.model;

public class Book {
    private int id;
    private String title;
    private String author;

    public Book(int id, String title, String author)
    {
        this.id = id;
        this.title = title;
        this.author = author;
    }
    // Getters and Setters
    public int getId() { return id; }
    public void setId(int id) { this.id = id; }

    public String getTitle() { return title; }
    public void setTitle(String title)
    {
        this.title = title;
    }

    public String getAuthor() { return author; }
    public void setAuthor(String author)
    {
        this.author = author;
    }
}

Step 4: Create the Service Interface and Service Implementation Class

Here, we have created an interface called BookService which contains all the service methods that our application is going to provide to the user. And BookServiceImpl class that implements the BookService interface. 

package com.example.demo.service;
import com.example.demo.model.Book;

import java.util.List;

public interface BookService {
    List<Book> findAllBooks();
    Book findBookById(int id);
    void deleteAllBooks();

}

package com.example.demo.service;

import com.example.demo.model.Book;
import org.springframework.stereotype.Service;
import java.util.ArrayList;
import java.util.List;

@Service
public class BookServiceImpl implements BookService {
    private List<Book> books = new ArrayList<>();

    public BookServiceImpl() {
        // Sample data for books
        books.add(new Book(1, "The Great Gatsby", "F. Scott Fitzgerald"));
        books.add(new Book(2, "1984", "George Orwell"));
        books.add(new Book(3, "To Kill a Mockingbird", "Harper Lee"));
    }

    @Override
    public List<Book> findAllBooks() {
        return books;
    }

    @Override
    public Book findBookById(int id) {
        return books.stream().filter(book -> book.getId() == id).findFirst().orElse(null);
    }

    @Override
    public void deleteAllBooks() {
        books.clear();
    }

}

Step 5: Create the REST Controller

The Controller layer exposes the APIs to the client. Create a RestController class to handle HTTP requests.

ExController.java:

package com.example.demo.controller;

import com.example.demo.model.Book;
import com.example.demo.service.BookService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;

import java.util.List;

@RestController
@RequestMapping("/api")
public class ExController {
	 @Autowired
	    private BookService bookService;

	    @GetMapping("/")
	    public String home() {
	        return "Welcome to the Book API!";
	    }

	    @GetMapping("/findbyid/{id}")
	    public Book findBookById(@PathVariable int id) {
	        return bookService.findBookById(id);
	    }

	    @GetMapping("/findall")
	    public List<Book> findAllBooks() {
	        return bookService.findAllBooks();
	    }

	    @DeleteMapping("/delete")
	    public String deleteAllBooks() {
	        bookService.deleteAllBooks();
	        return "All books have been deleted.";
	    }

}

Note: Here is the ExController class where we are exposing all the APIs which we have created. 

API’s list

• http://localhost:8080/: To save the data
• http://localhost:8080/findbyid/2: Find Book by id
• http://localhost:8080/findall: Find all books
• http://localhost:8080/delete: Delete all books

Step 6: Run the Application

The main application class, BookApiApplication, is automatically generated by Spring Boot. It contains the main method to run the application.

BookApiApplication.java:

package com.example.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class BookApiApplication {

	public static void main(String[] args) {
		SpringApplication.run(BookApiApplication.class, args);
	}
}

Step 7: Test the APIs

Test the APIs using Postman to verify they work as expected

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Article Tags :

• Advance Java
• Java-Spring-Boot