Creating REST API in Java

REST (Representational State Transfer) API is a web service communication protocol that allows for interaction with RESTful web services. In Java, creating REST APIs can be achieved using various frameworks, with Spring Boot being one of the most popular due to its ease of use, configuration, and flexibility.

Understanding REST API in Java

A REST API in Java typically involves:

HTTP Requests: Clients interact with the API over HTTP using methods such as GET, POST, PUT, and DELETE to retrieve, create, update, and delete resources, respectively.
Resource Identification: Resources (data or objects) are identified using URIs (Uniform Resource Identifiers).
Statelessness: Each request from the client to the server must contain all the information the server needs to understand and fulfill the request.
Data Exchange Format: REST APIs commonly use JSON (JavaScript Object Notation) or XML for data exchange due to their readability and compatibility with web technologies.

Creating a Simple REST API with Spring Boot

Spring Boot simplifies the process of developing RESTful services. It offers annotations and auto-configuration to swiftly create APIs.

Step 1: Set Up Spring Boot Project

Create a new Spring Boot project using Spring Initializr with the following dependencies:

Spring Web
Spring Boot DevTools

Step 2: Define a Resource Representation Class

Define a simple model class that represents the resource. For this example, consider a Book class.

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

    // Constructors, getters, and setters
    public Book(Long id, String title, String author) {
        this.id = id;
        this.title = title;
        this.author = author;
    }

    // Getters and setters
    // ...
}

public class Book {

private Long id;

private String title;

private String author;

// Constructors, getters, and setters

public Book(Long id, String title, String author) {

this.id = id;

this.title = title;

this.author = author;

}

// Getters and setters

// ...

}

Step 3: Create a REST Controller

Create a controller class annotated with @RestController to handle HTTP requests.

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;
import java.util.Arrays;
import java.util.List;

@RestController
public class BookController {

    private List<Book> books = Arrays.asList(
        new Book(1L, "Java Fundamentals", "John Doe"),
        new Book(2L, "Spring Boot in Action", "Jane Roe")
    );

    @GetMapping("/books")
    public List<Book> getAllBooks() {
        return books;
    }

    @GetMapping("/books/{id}")
    public Book getBookById(@PathVariable Long id) {
        return books.stream().filter(book -> book.getId().equals(id)).findFirst().orElse(null);
    }
}

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

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

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

import java.util.Arrays;

import java.util.List;

@RestController

public class BookController {

private List<Book> books = Arrays.asList(

new Book(1L, "Java Fundamentals", "John Doe"),

new Book(2L, "Spring Boot in Action", "Jane Roe")

);

@GetMapping("/books")

public List<Book> getAllBooks() {

return books;

}

@GetMapping("/books/{id}")

public Book getBookById(@PathVariable Long id) {

return books.stream().filter(book -> book.getId().equals(id)).findFirst().orElse(null);

}

Step 4: Run Your Application

Run your Spring Boot application. Spring Boot’s embedded Tomcat server will start, and your REST API will be accessible.

Testing the API

You can test your API using tools like Postman or CURL:

To get all books: GET http://localhost:8080/books
To get a book by ID: GET http://localhost:8080/books/1

Conclusion

REST APIs in Java enable developers to build scalable and flexible web services. Spring Boot, with its comprehensive ecosystem and ease of development, is an excellent choice for creating RESTful APIs. Through annotations like @RestController and @GetMapping, Spring Boot allows for the straightforward mapping of HTTP requests to handler methods, making the development of REST APIs in Java a more streamlined process.