HTTP & Web

Single Page Application development with React and Vert.x

This document will show you how to develop a Single Page Application (SPA) with React and Vert.x.

What you will build

You will create a React frontend communicating over HTTP with a Vert.x backend.

When developing an SPA, it is very convenient to get instant feedback after updating a Javascript, HTML or CSS file. With React, this requires you start a development server with npm that handles requests for frontend resources:

But what about requests that must be processed by Vert.x? You will configure the project so that the frontend development server proxies API requests to the backend:

What you need

A text editor or IDE
Java 11 or higher
Maven or Gradle
Node
npm
npx, an NPM package runner

Create a project

The code of this project contains Maven and Gradle build files that are functionally equivalent.

Using Maven

Add the vertx-web dependency in your Maven POM file:

Maven pom.xml

  <dependencies>
    <dependency>
      <groupId>io.vertx</groupId>
      <artifactId>vertx-web</artifactId>
      <version>${vertx.version}</version>
    </dependency>
  </dependencies>

Then add the exec-maven-plugin:

Maven pom.xml

      <plugin>
        <groupId>org.codehaus.mojo</groupId>
        <artifactId>exec-maven-plugin</artifactId>
        <version>3.5.0</version>
        <configuration>
          <mainClass>io.vertx.howtos.react.BackendVerticle</mainClass>
        </configuration>
      </plugin>

Using Gradle

Assuming you use Gradle with the Kotlin DSL, add the vertx-web dependency:

Gradle build.gradle.kts

dependencies {
  val vertxVersion = "5.0.0.CR2"
  implementation("io.vertx:vertx-web:${vertxVersion}")
}

Then configure the application main class:

Gradle build.gradle.kts

application {
  mainClass = "io.vertx.howtos.react.BackendVerticle"
}

Expose a message service over HTTP

Let’s start with the backend service. It shall handle requests on the /api/message path by retuning a greeting message:

Java src/main/java/io/vertx/howtos/react/BackendVerticle.java

    Router router = Router.router(vertx);
    Route messageRoute = router.get("/api/message"); (1)
    messageRoute.handler(rc -> {
      rc.response().end("Hello React from Vert.x!"); (2)
    });

    router.get().handler(StaticHandler.create()); (3)

    return vertx.createHttpServer()
      .requestHandler(router)
      .listen(8080);

1	A Vert.x Web `Route` is defined to match HTTP requests on the `/api/message` path
2	The `Route` handler replies to requests with a greeting message
3	The `StaticHandler` is required to handle requests for static resources

You may wonder why we need a StaticHandler if the frontend development server handles static resources? Keep in mind that when the whole application is built and put to production, the frontend will be bundled with and served by the backend HTTP server.

Before we can test the implementation, the BackendVerticle needs a main method:

Java src/main/java/io/vertx/howtos/react/BackendVerticle.java

  public static void main(String[] args) {
    Vertx vertx = Vertx.vertx(); (1)
    vertx.deployVerticle(new BackendVerticle()).await(); (2)
    System.out.println("Verticle started!");
  }

1	Create a `Vertx` context
2	Deploy `BackendVerticle`

You can run the application:

straight from your IDE or,
with Maven: mvn compile exec:java, or
with Gradle: ./gradlew run (Linux, macOS) or gradlew run (Windows).

The following example uses the HTTPie command line HTTP client. Please refer to the installation documentation if you don’t have it installed on your system yet.

To receive a greeting, open your terminal and execute this:

http :8080/api/message

You should see:

HTTP/1.1 200 OK
content-length: 24

Hello React from Vert.x!

Displaying the message in the browser

We have a fully operational backend, we can create the frontend. To do so, run the create-react-app package with npx:

cd src/main
npx create-react-app frontend

This will:

create a package.json file that defines dependencies as well as build and run scripts
install the dependencies
generate a skeleton application

In this how-to, the frontend code lives as part of the backend project, inside the src directory. This is easier to get started, in particular if your team includes more backend-oriented developers. However, as you project grows, you might prefer to split the frontend and the backend into separate modules.

The skeleton application is not of great interest here so let’s remove it:

rm -rf frontend/src/*

Then open your favorite editor and implement the React frontend:

Javascript src/main/frontend/src/index.js

import React from 'react';
import ReactDOM from 'react-dom';

class Greeter extends React.Component { (1)

  constructor(props) {
    super(props);
    this.state = { (2)
      message: "Default message"
    }
  }

  componentDidMount() { (5)
    fetch("/api/message")
      .then(response => response.text())
      .then(text => this.setState({message: text}));
  }

  render() { (3)
    return (
      <div>
        <span>{this.state.message}</span>
      </div>
    );
  }
}

ReactDOM.render( (4)
  <Greeter/>,
  document.getElementById('root')
);

1	Our frontend consists in a single React `Greeter` component
2	The `Greeter` component holds state, which is a message to display in the browser
3	The message is displayed within a simple HTML `span`
4	The `Greeter` component is rendered in the web page
5	After initial rendering, an HTTP request is sent to the backend; the result is used to udpate the component state

Last but not least, you must configure the frontend development server to proxy API requests to the backend. Open the package.json file in you editor and add:

Javascript src/main/frontend/package.json

"proxy": "http://localhost:8080"

That’s it, open a terminal and start the frontend development server:

cd src/main/frontend
npm start

A browser tab should automatically be opened and pointing to http://localhost:3000.

You should see:

Hello React from Vert.x!

Putting it all together

In production of course you will not start a frontend development server. So the Maven POM (or Gradle build) file shall be configured to:

run a frontend build
copy the static files to the src/main/resources/webroot folder

Do you remember the StaticHandler from the first section? It looks for static files in the webroot folder by default. This is why you must copy static files to src/main/resources/webroot.

Add these plugins to your Maven POM file:

Maven pom.xml

      <plugin>
        <groupId>com.github.eirslett</groupId>
        <artifactId>frontend-maven-plugin</artifactId>
        <version>1.7.6</version>
        <configuration>
          <nodeVersion>v22.12.0</nodeVersion>
          <npmVersion>10.9.0</npmVersion>
          <workingDirectory>src/main/frontend</workingDirectory>
          <installDirectory>target</installDirectory>
        </configuration>
        <executions>
          <execution>
            <id>install-node-and-npm</id>
            <phase>generate-resources</phase>
            <goals>
              <goal>install-node-and-npm</goal> (1)
            </goals>
          </execution>
          <execution>
            <phase>generate-resources</phase>
            <id>npm-install</id>
            <goals>
              <goal>npm</goal>
            </goals>
            <configuration>
              <arguments>install</arguments> (2)
            </configuration>
          </execution>
          <execution>
            <id>npm-run-build</id>
            <phase>generate-resources</phase>
            <goals>
              <goal>npm</goal> (3)
            </goals>
            <configuration>
              <arguments>run build</arguments>
            </configuration>
          </execution>
        </executions>
      </plugin>
      <plugin>
        <artifactId>maven-resources-plugin</artifactId>
        <version>3.1.0</version>
        <executions>
          <execution>
            <id>copy-to-webroot</id>
            <phase>process-resources</phase>
            <goals>
              <goal>copy-resources</goal> (4)
            </goals>
            <configuration>
              <outputDirectory>${project.build.outputDirectory}/webroot</outputDirectory>
              <resources>
                <resource>
                  <directory>${basedir}/src/main/frontend/build</directory>
                  <filtering>false</filtering>
                </resource>
              </resources>
            </configuration>
          </execution>
        </executions>
      </plugin>

1	Downloading Node and `npm` in the build directory allows to run the frontend build on CI where they might not be present
2	Download frontend dependencies with `npm install`
3	Create a production-ready build of the frontend
4	Copy static files to `src/main/resources/webroot`

If you use Gradle, first add the Gradle NPM plugin:

Gradle build.gradle.kts

import com.github.gradle.node.npm.task.NpmTask

plugins {
  java
  application
  id("com.github.node-gradle.node") version "7.0.2"
}

Then the configuration is similar to what we did with Maven:

Gradle build.gradle.kts

node {
  version = "22.12.0"
  npmVersion = "10.9.0"
  download = true
  nodeProjectDir = File("src/main/frontend")
}

val buildFrontend by tasks.creating(NpmTask::class) {
  args = listOf("run", "build")
  dependsOn("npm_install")
}

val copyToWebRoot by tasks.creating(Copy::class) {
  from("src/main/frontend/build")
  destinationDir = File("build/classes/java/main/webroot")
  dependsOn(buildFrontend)
}

val processResources by tasks.getting(ProcessResources::class) {
  dependsOn(copyToWebRoot)
}

Make sure all previous npm, mvn or gradlew executions are terminated and start the Vert.x server:

with Maven: mvn compile exec:java, or
with Gradle: ./gradlew run (Linux, macOS) or gradlew run (Windows).

Browse to http://localhost:8080 and you should see:

Hello React from Vert.x!

Summary

This document covered:

the creation of a new React application with create-react-app
running a frontend development server (for live-reload) that delegates API requests to the Vert.x backend
bundling the frontend static files together with the Vert.x classes when going to production

Single Page Application development with React and Vert.x

What you will build

Development workflow

What you need

Create a project

Using Maven

Using Gradle

Expose a message service over HTTP

Displaying the message in the browser

Putting it all together

Summary

See also