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How to start a Vaadin project with the build tool, Gradle.

Gradle is a popular build tool for Java, Groovy, Kotlin, and other projects. It’s an alternative to using Maven, and in many ways much simpler. It’s also more powerful. You can use it to build and run a Vaadin application and manage dependencies during development.

This page describes how to create, compile, and run a Vaadin application using the Vaadin Gradle plugin. The Gretty plugin is used to run an application in an embedded web server.

For information about using Gradle, see the Gradle User Manual.

Requirements

To use the Vaadin Gradle plugin, your environment needs to meet the following requirements:

  • Windows, Mac, or Linux operating system;

  • Java SDK 11 or later;

  • Gradle 5 or 6, which is optional because of the wrapper provided in the starter projects (see https://gradle.org/install on how to install directly); and

  • Node.js and npm, which is optional because they can also be installed locally to the project using the Vaadin Gradle plugin.

Note
Installing Gradle is Optional
If you plan to use Vaadin’s Gradle-based starter projects, there’s no need to install Gradle on your machine. A Gradle Wrapper script is included in starter projects. It manages locally the download and execution of Gradle for your project. For more information on using Gradle Wrapper, see the Official Gradle Documentation.

Creating a Vaadin Project

The easiest way to create a new project is to clone a starter repository containing an application skeleton.

You can also make a build.gradle file for any existing Vaadin project, as described in The Build File.

Cloning a Starter Repository

The following starter repositories are available. The default branch is for the latest Vaadin version. You can find older starters with long-term support in their respective branches:

  1. https://github.com/vaadin/base-starter-gradle

    A simple web application project to be deployed as a WAR package. This example can also be used for Java EE, by changing the servlet dependency to javax:javaee-api and perhaps also adding the dependency com.vaadin:vaadin-cdi for CDI integration.

    git clone https://github.com/vaadin/base-starter-gradle my-project

  2. https://github.com/vaadin/base-starter-spring-gradle

    A web application project skeleton that uses Spring Boot.

    git clone https://github.com/vaadin/base-starter-spring-gradle my-project

Starter Project Contents

When it’s been cloned, the project structure should look as follows:

base-starter-gradle
├── frontend                            // HTML templates and other front-end code
│   └──themes
│      └──my-theme                      // The application styles
│         └──styles.css
│         └──theme.json
│   └──index.html
├── gradle
│   └──wrapper
│      └──gradle-wrapper.jar            // Gradle wrapper sources
│      └──gradle-wrapper.properties
├── src/main
│   └──java
│      └──com.vaadin.starter.skeleton
│         └──AppShell.java              // Class for customising the Application Shell,
│                                       // also known as Bootstrap Page
│         └──GreetService.java          // Example data service
│         └──MainView.java              // The application skeleton
│   └──resources
│      └──simplelogger.properties       // Logging configuration
│   └──webapp
├── build.gradle                        // Gradle build configuration
├── gradle.properties                   // System properties and environment variables
├── gradlew                             // Gradle wrapper build scripts
├── gradlew.bat
├── LICENSE
├── README.md                           // Build and usage instructions
└── settings.gradle                     // Gradle build-related settings

Only the contents of base-starter-gradle — a simple web application starter without Spring Boot — are shown in the preceding figure. However, the Spring Boot-based starter project is a little different, except that it has an additional class annotated with @SpringBootApplication. If this is the first time you’ve tried Vaadin with Spring Boot, see Using Vaadin with Spring Boot for more information.

The most important files and folders are as follows:

src/main/java/<package>/MainView.java

The application view class for the root route, built from components.

src/main/java/<package>/GreetService.java

A trivial service object to separate business data and logic from the view.

frontend/src

Folder for HTML templates and JavaScript code. See the README file inside for more details.

frontend/styles/shared-styles.css

Application-specific style sheets to style the look of the application.

frontend/styles/vaadin-text-field-styles.css

An example of how to modify the style of the TextField component.

build.gradle

The Gradle build file, as described later in The Build File.

gradlew and gradlew.bat

Gradle Wrapper build scripts for Linux/Mac (gradlew) and Windows (gradlew.bat). The build scripts enable the project to be built without having Gradle preinstalled. Since the recommended way to execute any Gradle build is with the help of the Gradle Wrapper, gradlew is used instead of gradle throughout the documentation. However, the gradlew and gradle commands can be used interchangeably if you already have Gradle installed and you prefer to use your installed Gradle. You can learn more about the benefits of using Gradle Wrapper in the Official Gradle Documentation.

The Build File

At a minimum, the build.gradle file needs to enable the Vaadin Gradle Plugin:

plugins {
    id 'com.vaadin' version '20.0.0' (1)

    // Optional
    id 'org.gretty' version '3.0.3' (2)
    id 'war' (3)
    id 'groovy' (4)
}

  1. Use the plugin version that matches the Vaadin version. See github.com/vaadin/platform for the latest release. To try the pre-release version of the Vaadin Gradle plugin, see Using plugin pre-release version

  2. Use the Gretty embedded web server to run the application during development. See Running the Application for details.

  3. Build a WAR package to deploy to a traditional servlet container. You also need to define the Servlet API using providedCompile "javax.servlet:javax.servlet-api:3.1.0" in the dependencies section.

  4. By default, the plugin supports Java. You can include Groovy or Kotlin as an optional plugin.

Vaadin Plugin Configuration

Vaadin Gradle plugin options are configured in a vaadin block. For development, the block is usually like this:

vaadin {
    optimizeBundle = false
}

If the parameter is true, the front-end bundle is optimized for all supported browsers, but the compilation is much slower. For configuration options, see plugin configuration options

Configuring Repositories

The repositories section defines the locations to search for packages. The repository that contains the Vaadin libraries is required at a minimum:

repositories {
    mavenCentral()
    maven { url = "https://maven.vaadin.com/vaadin-addons" }
}

If you want to try the Vaadin platform pre-release versions, you can also add the following repository:

repositories {
    maven { url = "https://maven.vaadin.com/vaadin-prereleases" }
}
Note
Use Final Release Versions
To avoid any inconsistencies, don’t use pre-release versions in your production environment, especially snapshots. Vaadin recommends using the latest major version. See the https://vaadin.com/releases page for the latest releases.

You can use any Gradle repository definitions in the block. See Declaring Repositories in the Gradle documentation for more information.

Configuring Dependencies

You’ll need to add the vaadin-core or vaadin library as a Java dependency. You would do that like so:

dependencies {
    implementation "com.vaadin:vaadin-core:20.+"
}

When you specify a version of 20.+, you’re choosing to use the latest version of Vaadin. However, you can also specify the exact version. See Declaring Dependencies in the Gradle documentation for more details.

Other Configuration

In the starter project, default targets are defined for convenience, so that you can run gradle without specifying any tasks:

defaultTasks("clean", "vaadinBuildFrontend", "build")

Compiling

If you’ve defined the default tasks as described earlier in Other Configuration, you can run the following to compile:

./gradlew

On Windows, you would execute instead the following:

gradlew

To avoid unnecessary verbosity, only the Unix style of running ./gradlew is used for the rest of this document. You’ll need to replace it with gradlew if you’re using a Windows machine. Otherwise, the project builds with the standard build task. However, on the first build and also at other times when necessary, you’ll need to build the Vaadin frontend.

./gradlew vaadinBuildFrontend build

Vaadin Tasks

The Vaadin-related tasks handled by the plugin are as follows:

vaadinPrepareFrontend

This checks that Node.js and npm are installed, copies front-end resources, and creates or updates the package.json and Vite configuration files (i.e., vite.config.ts and vite.generated.ts). The front-end resources are inside .jar dependencies: they’re copied to node_modules.

vaadinBuildFrontend

This builds the front-end bundle with the Vite utility. Vaadin front-end resources (e.g., HTML, JavaScript, CSS, and images) are bundled to optimize loading the frontend. This task isn’t executed automatically on the build and other targets, so you’ll need to run it, explicitly.

vaadinClean

This cleans the project and removes node_modules, package-lock.json, vite.generated.ts, tsconfig.json, types.d.ts, pnpm-lock.yaml and pnpmfile.js. You’ll need to run this task if you upgrade the Vaadin version, and in other similar situations.

To get the complete list of tasks handled by the configured plugins, execute the following:

./gradlew tasks

Incremental Builds

Vaadin uses Gradle Incremental Builds feature for vaadinPrepareFrontend task to prevent it from running when the project’s configuration hasn’t been changed and the necessary front-end files have already been generated and haven’t changed since the previous build. This saves time when building and running applications in development mode.

If none of these items have been changed since the previous build, Gradle skips the prepare frontend task, giving an UP-TO-DATE state:

  • Inputs:

  • Outputs:

    • package.json, package-lock.json, vite.config.js and other front-end files generated by Vaadin.

The incremental build feature can be turned off with the following configuration parameter in the gradle.build file:

vaadin {
   alwaysExecutePrepareFrontend = true
}

This allows you to force the vaadinPrepareFrontend task execution as a fallback in case of issues in input or output definitions, while it’s being fixed.

Running the Application

You’d use a Spring Boot-based starter (i.e., Vaadin with Spring Boot) to run the application during development in a similar way to any normal Spring Boot application. This means you can run it either from the class containing the main() method — normally annotated with @SpringBootApplication — or by using Spring Boot’s Gradle plugin bootRun task:

./gradlew bootRun

If you’re using a simple web application (i.e., Vaadin without Spring Boot) to run the application during development, the Gradle plugin supports the Gretty plugin, which runs the application in an embedded web server. You can do this either in an IDE or from the command line.

One way to enable the Gretty plugin is in the plugin section of the gradle.build file, as in the starter project:

plugins {
    ...
    id 'org.gretty' version '3.0.3'
}

You can configure Gretty further in an optional gretty block:

gretty {
    contextPath = "/" (1)
    servletContainer = "jetty9.4" (2)
}

  1. Sets the context path to the root path. The default context path contains the project name, so the URL would be http://localhost:8080/myproject — adjusted for whatever your project is named.

  2. Use Jetty as the servlet container, with the specified version.

The application is started with the appRun task:

 ./gradlew appRun

The task compiles the application and starts the web server in http://localhost:8080/ — if the root context path is configured as described earlier.

You might need to add jcenter() to the list of repositories to be able to run Gretty tasks. Some artifacts from jcenter() haven’t yet been moved to mavenCentral(). In the future, this step becomes unnecessary:

repositories {
    // should be removed in the future as jcenter() is obsolete.
    jcenter()
}

See the Gretty documentation for a complete reference on using Gretty. For issues when running the application in development mode, see Known Issues for possible solutions.

Developing in Eclipse IDE

Gradle has first-class support in Eclipse, IDEA, NetBeans, and Android Studio, among others. The following section describes creating, importing, and developing a Vaadin Gradle project in the Eclipse IDE.

Importing a New Project

You can create a new Vaadin project by cloning the repository on the command line and importing it into Eclipse as a Gradle project. Below are the steps for this:

  • Clone the starter repository of your choice, as described earlier.

  • Select File › Import › Gradle › Existing Gradle Project.

  • Enter or select the Project root directory and then click Finish.

The project should appear in the Project Explorer.

You should now see the Gradle Tasks tab. You can browse the available tasks.

Gradle Tasks tab in eclipse
Gradle Tasks Tab in Eclipse

Running the Application

You can run the project using Gretty in an embedded web server. Below are the steps for this:

  • Open the Gradle Tasks tab.

  • Double-click the gretty → appRun task. The Gradle Executions tab then opens and shows the build progress.

  • When the :apprun task is running, open http://localhost:8080 in the browser.

  • To stop the server, go to the Console tab and press any key.

Production

To build a web application as a WAR package, you need the war plugin. You also need to enable it.

In build.gradle, include the plugin and enable WAR build:

plugins {
  ...
  id 'war'
}

war {
    enabled = true
}

When doing a production-ready build, the Vaadin Gradle plugin bundles and optimizes the client-side dependencies, as described in Deploying to Production. You enable this by either setting it in build.gradle or at the command line when invoking Gradle.

In build.gradle:

vaadin {
   productionMode = true
}

At the command-line, execute the following:

./gradlew -Pvaadin.productionMode=true war

If you’re using Vaadin with Spring Boot, the default packaging for production would normally be the jar. However, if you intend to package a Spring Boot application as a WAR to be deployed on a standalone container (e.g., tomcat), there are two additional steps you’ll need to perform.

First, your application class that’s annotated with @SpringBootApplication should extend SpringBootServletInitializer and override the configure() method:

@SpringBootApplication
public class DemoApplication extends SpringBootServletInitializer {
    @Override
    protected SpringApplicationBuilder configure(
	                     SpringApplicationBuilder application) {
        return application.sources(DemoApplication.class);
    }
}

Second, add the following dependency:

dependencies {
    providedRuntime 'org.springframework.boot:spring-boot-starter-tomcat'
}

Using Gradle Plugin Snapshot Versions

A snapshot version of the plugin is pushed to the pre-release repository. This section is about trying the pre-release and snapshot versions of the Vaadin Gradle plugin itself, not Vaadin.

To use the pre-release plugin, add the vaadin-prereleases repository to the project settings.gradle file. This file is mostly used within multi-module projects, but it’s useful for other configurations. Thus, if you don’t already have it in your project, create a plain text file called settings.gradle next to your build.gradle file, which is normally in the project root folder.

pluginManagement {
    repositories {
        maven { url = 'https://maven.vaadin.com/vaadin-prereleases' }
        gradlePluginPortal()
    }
}

The plugin then needs to be defined and applied in the build.gradle file.

buildscript {
    ...
    dependencies {
        classpath group: 'com.vaadin',
                name: 'vaadin-gradle-plugin',
                version: '20.0-SNAPSHOT'
    }
}

plugins {
    ...
}

apply plugin: 'com.vaadin'
Note
Remember to update the plugins block
Remove the part id 'com.vaadin' version 'xyz' from the plugins block. The plugin is applied by specifying apply plugin: 'com.vaadin' — as demonstrated in the preceding file extract.

Plugin Configuration Options

Here are all of the configuration options with their default values:

productionMode: Boolean = false

Indicates that the application is running in production mode. Defaults to false. For production, the frontend is bundled and optimized, as described in Deploying to Production. Running the vaadinBuildFrontend task automatically switches this to true, so there’s no need to configure anything.

forceProductionBuild: Boolean = false

Whether to generate a production bundle even if an existing pre-compiled bundle could be used. A value of 'true' forces bundle generation without validating if there is a usable production bundle already.

frontendOutputDirectory: File = null

The folder where Vite should output index.js and other generated files. Defaults to null, which uses the automatically detected value of the main SourceSet, usually build/resources/main/META-INF/VAADIN/webapp/.

npmFolder: File = project.projectDir

The folder where the package.json file is located. Defaults to the project root directory.

generatedFolder: File(project.projectDir, "target/frontend")

The target folder for generated files used by Vite.

frontendDirectory: File(project.projectDir, "frontend")

The directory with the front-end source files of the project.

generateBundle: Boolean = true

Set to true to generate a bundle from the project front-end sources.

runNpmInstall: Boolean = true

Run npm install after updating dependencies.

generateEmbeddableWebComponents: Boolean = true

Generate web components from WebComponentExporter inheritors.

frontendResourcesDirectory: File = File(project.projectDir, Constants.LOCAL_FRONTEND_RESOURCES_PATH)

Identifies the project front-end directory from where resources should be copied for use with Vite.

optimizeBundle: Boolean = true

Use byte code scanner strategy to discover front-end components.

pnpmEnable: Boolean = false

Use pnpm for installing npm front-end resources. Defaults to false.

useGlobalPnpm: Boolean = false

Use the globally installed pnpm tool or the default supported pnpm version. Defaults to false.

requireHomeNodeExec: Boolean = false

Force use of Vaadin home node executable. If it’s set to true, Vaadin home node is checked, and installed if absent. This is then be used instead of the globally or locally installed node.

useDeprecatedV14Bootstrapping: Boolean = false

Run the application in legacy V14 bootstrap mode. Defaults to false.

eagerServerLoad: Boolean = false

Add the initial User Interface Definition Language (UIDL) object to the bootstrap index.html. Defaults to false.

applicationProperties: File = File(project.projectDir, "src/main/resources/application.properties")

Application properties file in a Spring project.

openApiJsonFile: File = File(project.buildDir, "generated-resources/openapi.json")

Generated path of the OpenAPI JSON.

javaSourceFolder: File = File(project.projectDir, "src/main/java")

Java source folders for connect scanning.

generatedTsFolder: File = File(project.projectDir, "frontend/generated")

The folder where Flow puts TS API files for client projects.

nodeVersion: String = "v18.17.1"

The Node.js version to be used when Node.js is installed automatically by Vaadin, for example "v18.17.1". Defaults to [FrontendTools.DEFAULT_NODE_VERSION].

nodeDownloadRoot: String = "https://nodejs.org/dist/"

URL to download Node.js from. This can be needed in corporate environments where the Node.js download is provided from an intranet mirror. Defaults to [NodeInstaller.DEFAULT_NODEJS_DOWNLOAD_ROOT].

nodeAutoUpdate: Boolean = false

Flag to enable automatic update of the Node.js version installed in ~/.vaadin, if it’s older than the default or defined nodeVersion.

resourceOutputDirectory: File = File(project.buildDir, "vaadin-generated")

The output directory for generated non-served resources, such as the token file. Defaults to build/vaadin-generated.

Known Issues

When the list of dependencies causes the classpath to go over a set limit on Windows, the build automatically generates a JAR containing a manifest with the classpath. Sometimes, when running a Spring Boot application, the resource loader doesn’t load the classpath packages correctly from the manifest. The failed annotation scanning makes the required npm packages unavailable.

You can fix this in two ways: add the repository mavenLocal() to build file repositories; or specify the vaadin.whitelisted-packages property, see Vaadin Spring Configuration.

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