Setting up Javalin with Maven

IDE Guides

- Instructions for IntelliJ IDEA
- Instructions for Eclipse
- Instructions for VS Code

About Maven

Maven is a build automation tool used primarily for Java projects. It addresses two aspects of building software: First, it describes how software is built, and second, it describes its dependencies.

Maven projects are configured using a Project Object Model, which is stored in a pom.xml-file.

Here’s a minimal example:

<project>
    <!-- model version - always 4.0.0 for Maven 2.x POMs -->
    <modelVersion>4.0.0</modelVersion>

    <!-- project coordinates - values which uniquely identify this project -->
    <groupId>com.mygroup</groupId>
    <artifactId>my-javalin-project</artifactId>
    <version>1.0.0-SNAPSHOT</version>

    <!-- library dependencies -->
    <dependencies>
        <dependency>
            <groupId>io.javalin</groupId>
            <artifactId>javalin</artifactId>
            <version>6.7.0</version>
        </dependency>
    </dependencies>
</project>

Instructions for IntelliJ IDEA

Click File and select New project...
Select Maven on the left hand menu and click Next
Enter GroupId, ArtifactId and Version, and click Next
Give your project a name and click Finish:
Paste the Javalin dependency into the generated pom.xml. If prompted, tell IntelliJ to enable auto-import.

<dependencies>
    <dependency>
        <groupId>io.javalin</groupId>
        <artifactId>javalin</artifactId>
        <version>6.7.0</version>
    </dependency>
</dependencies>

Finally, paste the Javalin “Hello World” snippet into a new file, HelloWorld.java:

Java
Kotlin

import io.javalin.Javalin;

void main() {
    var app = Javalin.create(/*config*/)
        .get("/", ctx -> ctx.result("Hello World"))
        .start(7070);
}

import io.javalin.Javalin

fun main() {
    val app = Javalin.create(/*config*/)
        .get("/") { ctx -> ctx.result("Hello World") }
        .start(7070)
}

Depending on your setup, you might need to explicitly set the language level to Java 11. This can be done in the in the pom.xml. Add the following snippet:

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.10.1</version>
            <configuration>
                <source>11</source>
                <target>11</target>
            </configuration>
        </plugin>
    </plugins>
</build>

Now everything should be ready for you to run your application. Enjoy!

⚠ Note: Due to a bug in the IntelliJ integration with Maven there is a known issue where intelliJ will show an error in the code editor, if this happens, refreshing the project and running the goal mvn clean package should fix the issue.

Instructions for Eclipse

Click File and select New then Other...
Expand Maven and select Maven Project, then click Next
Check the Create a simple project checkbox and click Next
Enter GroupId, ArtifactId, Verison, and Name, and click Finish
Open the pom.xml file and click the pom.xml tab. Paste the Javalin dependency

<dependencies>
    <dependency>
        <groupId>io.javalin</groupId>
        <artifactId>javalin</artifactId>
        <version>6.7.0</version>
    </dependency>
</dependencies>

Finally, paste the Javalin “Hello World” snippet into a new file, HelloWorld.java:

Java
Kotlin

import io.javalin.Javalin;

void main() {
    var app = Javalin.create(/*config*/)
        .get("/", ctx -> ctx.result("Hello World"))
        .start(7070);
}

import io.javalin.Javalin

fun main() {
    val app = Javalin.create(/*config*/)
        .get("/") { ctx -> ctx.result("Hello World") }
        .start(7070)
}

Depending on your setup, you might need to explicitly set the language level to Java 11. This can be done in the in the pom.xml. Add the following snippet:

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.10.1</version>
            <configuration>
                <source>11</source>
                <target>11</target>
            </configuration>
        </plugin>
    </plugins>
</build>

Depending on your version of eclipse, you might have to

Right click on your project select Maven then Update Project

Now everything should be ready for you to run your application. Enjoy!

Instructions for VS Code

Prerequisites

Before creating a Maven project, ensure you have the Extension Pack for Java installed. This extension pack includes essential Java development tools and Maven support. Install it from the VS Code Marketplace or by searching for “Extension Pack for Java” in the Extensions view (Ctrl+Shift+X / Cmd+Shift+X).

Creating a New Maven Project

Open the Command Palette (Ctrl+Shift+P / Cmd+Shift+P)
Type Java: Create Java Project and select it
Select Maven as the project type
Select maven-archetype-quickstart as the archetype
Select the latest version of the archetype
Enter the GroupId (e.g., com.mygroup)
Enter the ArtifactId (e.g., my-javalin-project)
Select a folder to create the project in
When prompted in the terminal:
- Press Enter to accept the default version (1.0-SNAPSHOT)
- Type Y and press Enter to confirm the properties configuration

⚠ macOS/Linux Users: If you encounter errors with the Maven wrapper (mvnw), ensure Maven is installed on your system (see Prerequisites above). The Java extension will automatically detect and use the system-installed Maven.

Adding Javalin Dependency

Open the generated pom.xml file and add the Javalin dependency inside the <dependencies> section:

<dependency>
    <groupId>io.javalin</groupId>
    <artifactId>javalin</artifactId>
    <version>6.7.0</version>
</dependency>

Your <dependencies> section should now include both JUnit (added by the archetype) and Javalin.

Configuring Java Version

Update the maven-compiler-plugin configuration in your pom.xml to use Java 11 (or higher):

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.13.0</version>
            <configuration>
                <source>11</source>
                <target>11</target>
            </configuration>
        </plugin>
    </plugins>
</build>

Creating the Application

The archetype creates a package structure (e.g., com.example) based on your GroupId. You can either modify the generated App.java or create a new HelloWorld.java in the same package directory (e.g., src/main/java/com/example/):

package com.example; // use your GroupId as the package name

import io.javalin.Javalin;

public class HelloWorld {
    public static void main(String[] args) {
        var app = Javalin.create(/*config*/)
            .get("/", ctx -> ctx.result("Hello World"))
            .start(7070);
    }
}

💡 Note: We use the traditional public static void main(String[] args) syntax for better compatibility with VS Code’s debugger. Java 21’s implicit class syntax (void main()) may cause issues with debugging.

Running the Application

There are several ways to run your Javalin application:

Using the Run button: Open HelloWorld.java and click the Run button (▶) above the main method. This CodeLens feature is provided by the Java extension and works out of the box.

Using Debug Configuration (F5): For a more configurable debugging setup, create .vscode/launch.json:

{
    "version": "0.2.0",
    "configurations": [
        {
            "type": "java",
            "name": "Run HelloWorld",
            "request": "launch",
            "mainClass": "com.example.HelloWorld",
            "projectName": "my-javalin-project"
        }
    ]
}

💡 Note: Update mainClass to match your package and class name (e.g., com.mygroup.HelloWorld), and projectName to match your project’s ArtifactId from pom.xml.

Then press F5 or go to Run → Start Debugging. VS Code’s Java extension handles compilation automatically.

💡 Tip: If VS Code doesn’t recognize the Javalin imports, try:

Right-click on pom.xml → select Maven → Reload project

Or run Maven: Reload Projects from the Command Palette (Ctrl+Shift+P / Cmd+Shift+P)

If issues persist, run Java: Clean Java Language Server Workspace from the Command Palette

⚠ Troubleshooting “ClassNotFoundException”: If you see Error: Could not find or load main class HelloWorld:

Right-click on pom.xml → select Maven → Reload project to ensure dependencies are resolved

Run Java: Clean Java Language Server Workspace from the Command Palette

Reload VS Code window: Ctrl+Shift+P / Cmd+Shift+P → Developer: Reload Window

Now everything should be ready for you to run your application. Enjoy!

IDE Guides

About Maven

Instructions for IntelliJ IDEA

Instructions for Eclipse

Instructions for VS Code

Prerequisites

Creating a New Maven Project

Adding Javalin Dependency

Configuring Java Version

Creating the Application

Running the Application

Thanks for reading