Leaning Technologies has released CheerpJ 5, which it describes as the first full OpenJDK distribution to bring Java 21 and Java 25 (in preview) to the browser. The release extends the company's WebAssembly-based Java support — which previously covered Java 8, 11 and 17 — by shipping the complete JDK rather than only a runtime, so Java can be compiled in the browser itself.

Full JDK in the browser, no local install

CheerpJ runs Java applications, libraries and applets in a browser tab without requiring a local Java installation or any plugins, targeting desktop and mobile browsers. CheerpJ 5 moves the tool beyond a runtime: it ships the full OpenJDK JDK, so Java can be compiled in the browser. The company points to browser-based IDEs, coding courses and interactive tutorials as use cases for in-browser compilation, letting developers build on the latest Java and deploy to both native and browser from a single code base.

WasmGC backend and an LTS commitment

CheerpJ 5 currently compiles Java bytecode to JavaScript, and ships an opt-in execution backend based on WasmGC that is described as a technology preview, with a production-ready version planned for CheerpJ 6. That backend runs in and generates WebAssembly. Leaning Technologies, based in Leeds, UK, said CheerpJ has been in development for more than eight years and is used by organisations including NASA, Ticketmaster and Moody's. The company committed to supporting each future long-term support (LTS) Java release within six months.

Stefano De Rossi, CEO and co-founder of Leaning Technologies, framed the release as Java gaining a first-class web target: "Today, Java has joined Rust, C++ and Go as a language with a best-in-class browser target. Developers can build on the latest Java and deploy to native and browser from a single code base, and their users can run the result in a browser tab without installing a Java runtime."

Availability

CheerpJ 5 is available now. The company says it is free for open-source projects, personal projects and one-person companies, with paid licenses for other businesses.

Sources

  • Full Java 21/25 in-browser distribution (WasmGC preview backend), 8+ years in development, NASA/Ticketmaster/Moody's usage, LTS support, pricing, CEO statement: CheerpJ 5 press release