CheerpJ Documentation

CheerpJ is a WebAssembly-based Java Virtual Machine (JVM) for the browser that provides a full runtime environment for Java 8, 11, and 17. It allows you to run Java applications, applets, and JNLP applications without browser plugins.

Key Capabilities:

• Run existing Java applications: Execute Java apps in the browser with no code changes.
• Java Applets: Include legacy applets in modern webpages without plugins.
• JNLP/Java Web Start: Migrate legacy Java Web Start applications to modern systems.
• Java-JavaScript Interoperability: Use Java libraries in JS/TS and call JavaScript/DOM from Java.
• Full Java SE Support: Includes support for Swing/AWT, Networking, a virtualized filesystem, Clipboard, Audio, and Printing.
• Multi-threading: Supports Java multi-threading and concurrent applications via Web Workers.

CheerpJ functions through the combination of two primary components:

1. Optimizing Java-to-JavaScript JIT compiler: Converts Java bytecode into highly optimized, garbage-collectible JavaScript.
2. Full Java SE Runtime: A complete runtime environment based on OpenJDK (supporting Java 8, 11, and 17).

Both components are written in C++ and compiled to WebAssembly and JavaScript using the Cheerp compiler.

This example demonstrates how to run two separate Java applications using CheerpJ that communicate with each other over a network.

To implement this pattern, follow the step-by-step tutorial provided in the official CheerpJ documentation to set up the server and client environments.

https://labs.leaningtech.com/cheerpj3/examples/serverclient

To use CheerpJ in your web application, you must include the loader script in your HTML. This script initializes the WebAssembly-based Java Virtual Machine environment in the browser.

Note: The version in the URL (e.g., 4.3) should match the version of CheerpJ you intend to use.

<script src="https://cjrtnc.leaningtech.com/4.3/loader.js"></script>

Use the Pitch Applet tutorial to learn how to execute JNLP (Java Network Launch Protocol) applets in the browser.

https://labs.leaningtech.com/cheerpj3/examples/jnlp#jnlp-applet-pitch

The Swing-Browser tutorial shows how to run a Java application in the browser that requires an active internet connection.

https://labs.leaningtech.com/cheerpj3/examples/java-browser

This example demonstrates how to use CheerpJ to execute a Java Swing application within a web browser while maintaining an active internet connection.

For a detailed, step-by-step guide on implementing this, refer to the official CheerpJ tutorial.

The SwingSet3 tutorial provides instructions on how to run applications built with the Java Swing toolkit in a browser environment.

https://labs.leaningtech.com/cheerpj3/examples/swingset3