How to Deploy a Java App (Spring Boot and Plain Java)

This guide shows how to run a Java web application on OpenPanel - a Spring Boot (or Quarkus, Micronaut, Javalin) JAR, or a simple single-file Java server. The app runs in its own container with an official Eclipse Temurin JDK, and OpenPanel's web server forwards your domain to it with free SSL.

Option 1: Spring Boot (or Any Executable JAR)​

Build the JAR​

Build the application on your computer or in CI:

./mvnw clean package -DskipTests     # Maven
# or
./gradlew bootJar                    # Gradle

This produces a file such as target/myapp-1.0.0.jar. The container image contains the JDK only - not Maven or Gradle - so upload the built JAR rather than building on the server.

Configure the port​

Spring Boot listens on port 8080 by default and on all interfaces. Keep that, or set it in application.properties:

server.port=8080
server.forward-headers-strategy=framework

forward-headers-strategy makes Spring generate correct https:// links behind OpenPanel's proxy.

Upload and create the app​

1. Add the domain in OpenPanel → Domains and upload the JAR to the domain folder, e.g. /var/www/html/example.com/app.jar, with the File Manager or FTP.
2. Go to OpenPanel → Websites → Install App → Setup Java Application:

Set -Xmx (maximum Java heap) to about half to two-thirds of the container's memory limit - the JVM also needs memory outside the heap.

To deploy a new version, upload the new JAR over the old one and Restart the app.

Option 2: Single-File Java Server​

Since Java 11, java Main.java compiles and runs a single source file directly - no build tool needed. This is the default when you set the Startup File to Main.java:

import com.sun.net.httpserver.HttpServer;
import java.net.InetSocketAddress;

public class Main {
    public static void main(String[] args) throws Exception {
        HttpServer server = HttpServer.create(new InetSocketAddress(3000), 0);
        server.createContext("/", exchange -> {
            byte[] body = "Hello from Java on OpenPanel!".getBytes();
            exchange.sendResponseHeaders(200, body.length);
            exchange.getResponseBody().write(body);
            exchange.close();
        });
        server.start();
    }
}

Use port 3000 in the app form and leave Run Install off.

Databases​

Inside OpenPanel, databases are reached by service name - never localhost:

spring.datasource.url=jdbc:mysql://mysql:3306/user_myapp
spring.datasource.username=user_myapp
spring.datasource.password=${DB_PASSWORD}

Use mariadb for MariaDB, or jdbc:postgresql://postgres:5432/dbname for PostgreSQL.

Managing the App​

In OpenPanel → Websites → Sites, click Manage to start, stop or restart the app, view Logs (stdout and stack traces), and change the JDK version, startup command and CPU/memory limits under Overview.

More: Java applications.

Troubleshooting​

Related​

• Deploy a Node.js app
• Deploy a Ruby app
• Deploy a Laravel app