How CheerpJ Works

CheerpJ is a WebAssembly-based Java Virtual Machine for the browser. This means Java applications can be executed from the browser with no Java installations. Amazing, right? but… How does it work?

Full Java Runtime

CheerpJ comes with a full OpenJDK runtime, providing full compatibility with any Java application

Full JVM in WebAssembly

CheerpJ runs Java bytecode thanks to a WebAssembly Just-In-Time compiler

Secure by Design

CheerpJ operates within the browser sandbox, using safe and secure Web APIs for system access

CheerpJ runs in any modern browser using standard Web technologies, particularly WebAssembly, JavaScript, and HTML5. It can either be integrated into a web page like any JavaScript library, by simply adding a <script> tag, or via a browser extension.

CheerpJ is very simple to use as it exposes an API for executing standalone Java applications, applets, Java Web Starts, and Java libraries – entirely in the browser. One of the strengths of CheerpJ is that it works directly with Java byte code/JARs, meaning no need to modify or have access to the application’s source code.

CheerpJ assets are static, which makes it easily self-hostable, and we provide a cloud version under the CheerpJ Community Licence (free to use for personal projects and technical evaluations).

Find out more about the Architecture

Key Features

Java on the browser

CheerpJ is a Java Virtual Machine in WebAssembly, that enables modern browsers to run Java 8, Java 11, Java 17 (preview), client-side.

Full Runtime

CheerpJ comes with a full OpenJDK runtime environment, ensuring that existing applications ‘will just work’. This includes Java Swing, AWT, and any other runtime component.

Scalable JNI Architecture

CheerpJ has extensive native method compatibility, and allows developers to ship custom natives in JavaScript / WebAssembly, providing a viable path for running complex Java applications.

Networking and System

CheerpJ provides a full networking stack (HTTP(s), TCP/IP), as well as support for file access, clipboard, audio, printing, and more.

Java-JavaScript Interoperability

CheerpJ provides multiple mechanisms for Java and JavaScript to interoperate.

Full Classloader Support

CheerpJ gives full control to the appropriate Classloader for class resolution, including application-provided ones. This ensures full compatibility with the most complex applications.

Effortless Deployment

CheerpJ does not need access to the source code at all, operating at the level of Java bytecode. Third-party libraries, dependencies and obfuscated code pose no issue.

Legacy Modernization

With CheerpJ, you can modernize access to legacy Java Applets and Applications on modern browsers, removing the requirement for IE, Edge IE mode, and for a local Java installation.