In this tutorial, we'll learn how to build a React application that consumes a Spring Boot REST API using the fetch() API. We'll also use Bootstrap 4 to style the UI.

The Fetch API is a web standard built into most modern browsers to let us make HTTP requests to the server.

Check out React JS Spring Boot REST API Tutorial at https://www.javaguides.net/2020/07/react-js-spring-boot-rest-api-example-tutorial.html

React is the most popular UI library for building user interfaces built and used internally by Facebook.

In the previous tutorial, we have used the Axios HTTP library to make a rest API call.

What we will build?

We will build a simple "single page application" using React as frontend and spring boot as backend.

We will create two projects:

1. Spring boot project - To develop simple REST API

2. React App - To consume REST API using fetch() function.

Prerequisites

You will need the following prerequisites to successfully complete the steps in this tutorial:

JavaScript fundamentals

Basic understanding of REST APIs

Node and NPM installed on your machine

Making an Ajax Calls in React

As we know, React is a JavaScript-based library that does not have the ability to make HTTP requests; thus, we need to use third-party libraries to achieve this.

There are plenty of libraries available to make HTTP calls into React apps. A few of them are listed below.

Axios
Fetch
Superagent
React-axios
Use-http
React-request

Fetch API Overview

The Fetch API is a web standard built into most modern browsers to let us make HTTP requests to the server.

The most important part is that fetch is asynchronous so it will run in the background and let you know when it finishes using promises.

The fetch API allows us to make HTTP requests with the standard HTTP verbs: GET, POST, PUT, PATCH, and DELETE.

The fetch function returns a promise which resolves when the request completes.

Develop Spring Boot Backend Application

Let's first create a simple /books rest endpoint using Spring boot.

1. Create Spring Boot Project in Eclipse STS IDE

Use below guide to create Spring boot project in Eclipse STS IDE:

Create Spring Boot Project in Spring Tool Suite [STS]

2. Add maven dependencies

<?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>2.3.1.RELEASE</version>
        <relativePath/>
        <!-- lookup parent from repository -->
    </parent>
    <groupId>net.javaguides</groupId>
    <artifactId>springboot-reactjs-example</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>springboot-reactjs-example</name>
    <description>Demo project for Spring Boot and React JS</description>
    <properties>
        <java.version>1.8</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-starter-test</artifactId>
            <scope>test</scope>
            <exclusions>
                <exclusion>
                    <groupId>org.junit.vintage</groupId>
                    <artifactId>junit-vintage-engine</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
    </dependencies>
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
</project>

3. Create Simple REST API - /books

Let's create a BookController class and add the following code to it:

package net.javaguides.springboot;

import java.util.Arrays;
import java.util.List;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.CrossOrigin;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class BookController {

    @CrossOrigin(origins = "http://localhost:3000")
    @GetMapping("/books")
    public List < Book > getBooks() {
        return Arrays.asList(new Book(1, "Core Java"), new Book(2, "Effective Java"), new Book(3, "Head First Java"));
    }
}

class Book {
    private int id;
    private String bookName;

    public Book(int id, String bookName) {
        super();
        this.id = id;
        this.bookName = bookName;
    }

    public int getId() {
        return id;
    }

    public String getBookName() {
        return bookName;
    }

    public void setId(int id) {
        this.id = id;
    }

    public void setBookName(String bookName) {
        this.bookName = bookName;
    }
}

4. Run Spring Boot Application and Test Rest API

Let's run this spring boot application from IDE -> Right-click -> Run As -> Java Application:

package net.javaguides.springboot;

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

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

Hit this "http://localhost:8080/books" link in a browser will display a list of books in JSON format.

Develop React JS Frontend Application

Let's go ahead and create a React application to consume below endpoint:

REST API - http://localhost:8080/books

We are going to use browser built-in fetch() function to make a REST API call in React App.

Let's start with creating a React App using create-react-app CLI.

1 - Create a React UI with Create React App

The Create React App CLI tool is an officially supported way to create single-page React applications. It offers a modern build setup with no configuration.

To create a new app, you may choose one of the following methods:

Using npx

npx create-react-app react-frontend

Using npm

npm init react-app react-frontend

npm init is available in npm 6+

Using Yarn

yarn create react-app react-frontend

Running any of these commands will create a directory called react-frontend inside the current folder. Inside that directory, it will generate the initial project structure and install the transitive dependencies:

my-app
├── README.md
├── node_modules
├── package.json
├── .gitignore
├── public
│   ├── favicon.ico
│   ├── index.html
│   ├── logo192.png
│   ├── logo512.png
│   ├── manifest.json
│   └── robots.txt
└── src
    ├── App.css
    ├── App.js
    ├── App.test.js
    ├── index.css
    ├── index.js
    ├── logo.svg
    └── serviceWorker.js

Let's explore important files and folders of the react project.

For the project to build, these files must exist with exact filenames:

public/index.html is the page template;
src/index.js is the JavaScript entry point.

You can delete or rename the other files.

Let's quickly explore the project structure.

package.json - The package.json file contains all the required dependencies for our React JS project. Most importantly, you can check the current version of the React that you are using. It has all the scripts to start, build, and eject our React app.

public folder - The public folder contains index.html. As react is used to build a single page application, we have this single HTML file to render all our components. Basically, it's an HTML template. It has a div element with id as root and all our components are rendered in this div with index.html as a single page for the complete react app.

src folder- In this folder, we have all the global javascript and CSS files. All the different components that we will be building, sit here.

index.js - This is the top renderer of your react app.

node_modules - All the packages installed by NPM or Yarn will reside inside the node_modules folder.

App.js - The App.js file contains the definition of our App component which actually gets rendered in the browser and this is the root component.

2. Adding Bootstrap in React Using NPM

Open a new terminal window, navigate to your project's folder, and run the following command:

$ npm install bootstrap --save

After installing the bootstrap package, you will need to import it in your React app entry file.

Open the src/index.js file and add the following code:

import 'bootstrap/dist/css/bootstrap.min.css';

src/index.js

Here is the complete code for index.js file:

import React from 'react';
import ReactDOM from 'react-dom';
import './index.css';
import App from './App';
import * as serviceWorker from './serviceWorker';
import 'bootstrap/dist/css/bootstrap.min.css';

ReactDOM.render(
  <React.StrictMode>
    <App />
  </React.StrictMode>,
  document.getElementById('root')
);

// If you want your app to work offline and load faster, you can change
// unregister() to register() below. Note this comes with some pitfalls.
// Learn more about service workers: https://bit.ly/CRA-PWA
serviceWorker.unregister();

3. Fetching and Displaying the REST API

Let's discuss how to use the browser fetch API to consume JSON data from the /books API endpoint.

Let's create APIService.js service implementation to make our HTTP REST call using fetch() API. Our backend Book endpoint is available at http://localhost:8080/books.

Let's create APIService.js file and add the following content to it:

const BOOKS_REST_API = 'http://localhost:8080/books';
class APIService {    
    getBooks(){
        return fetch(BOOKS_REST_API,{ 
            method: 'get',
                headers: {
                'Accept': 'application/json, text/plain, */*',
                'Content-Type': 'application/json',
                },
                'credentials': 'same-origin'
        })
        .then(res => res.json());        
    }

}

export default new APIService();

Make sure that you create an object of APIService class export it as:

export default new APIService();

4. Develop a React Component

Let's create a BookComponent.js file and add the following code to it.

import React from 'react'
import APIService from '../service/APIService'

export default class BookComponent extends React.Component {

    constructor(props) {
        super(props)
    
        this.state = {
             books: []
        }
    }
    
    componentDidMount(){
        APIService.getBooks().then((data) => {
            this.setState({ books: data })
            console.log(this.state.data)
          })
          .catch(function (ex) {
              console.log('Response parsing failed. Error: ', ex);
          });;
    }

    render() {
        return (
            <div>
                <h2 className="text-center">Book Details</h2>
                <table className="table table-striped">
                    <thead>
                        <tr>
                            <th>Book Id</th>
                            <th>Book Name</th>
                            <th>Book Author</th>
                        </tr>
                    </thead>
                    <tbody>
                        {
                            this.state.books.map(book =>
                                    <tr key={book.id}>
                                        <td>{book.id}</td>
                                        <td>{book.bookName}</td>
                                        <td>{book.author}</td>
                                    </tr>
                            )
                        }
                    </tbody>
                </table>
            </div>
        )
    }
}

Let's understand the above code step by step.

constructor() - The constructor() is invoked before the component is mounted. In the constructor, we have declared our book state variable:

 constructor(props) {
        super(props)
    
        this.state = {
             books: []
        }
    }

componentDidMount() - The componentDidMount() is called as soon as the component is mounted and ready. This is a good place to initiate API calls if you need to load data from a remote endpoint. Note that we are calling the loadBooks() method of APIService from componentDidMount() method:

 componentDidMount(){
        APIService.getBooks().then((data) => {
            this.setState({ books: data })
            console.log(this.state.data)
          })
          .catch(function (ex) {
              console.log('Response parsing failed. Error: ', ex);
          });;
    }

render() - The render() method is the most used lifecycle method. You will see it in all React classes. This is because render() is the only required method within a class component in React. The render() method that actually outputs HTML to the DOM.
APIService - We are using APIService class to getBooks() method which interns make an API call.

We are using the map operator to loop over our book list and create the view like:

{
 this.state.books.map(book =>
   <tr key={book.id}>
    <td>{book.id}</td>
    <td>{book.bookName}</td>
                                <td>{book.author}</td>
   </tr>
 )
}

5. App.js

In the previous step, we have created BookComponent so let's go ahead add BookComponent to App component:

import React from 'react';
import logo from './logo.svg';
import './App.css';
import BookComponent from './components/BookComponent';

function App() {
  return (
    <div>
      <header className="container">
         <BookComponent />
      </header>
    </div>
  );
}

export default App;

6. Run React App

Use below command to start the project:

npm start

Use yarn to start the project:

yarn start

Runs the app in development mode. Open http://localhost:3000 to view it in the browser.

Conclusion

In this tutorial, we have developed a simple React application to consume the Spring Boot REST API using fetch() API.

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