Run Java Applets with CheerpJ

CheerpJ lets you easily access Java Applets in the browser without installing Java, relying on cloud virtual machines or using legacy browsers.

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What you probably already know

  1. Modern browsers can't run Java applets

    Chrome removed the Java plug-in in 2015, and Firefox and Safari followed by 2018. Internet Explorer 11, the last browser that ran applets, was retired in June 2022.

  2. Many critical business applications still run as applets

    Oracle Forms and E-Business Suite, banking and trading systems, government services and internal tools built years ago still depend on them.

  3. Today they're kept running with workarounds

    IE mode in Microsoft Edge, a virtual desktop such as Citrix, VDI or RDS that streams an old browser to the user, or a VNC connection to a machine that still has Java and an old browser installed.

Why workarounds for Java applets won’t work forever

IE mode has an end date

Microsoft supports IE mode through at least the end of 2029, and it relies on Windows components. Windows 10 reached the end of support on 14 October 2025.

Virtual desktops are expensive to run for one application

Users need a remote session on a server, sized for the number of people working at the same time. The session hosts need their own maintenance and licensing, and clicks and keystrokes travel over the network to the server and back.

Desktop Java has to be patched and licensed

Java 8 has to be kept up to date on users' computers, commercial Java 8 updates need an Oracle subscription, and security teams are increasingly restricting desktop Java on managed computers.

Why CheerpJ for Java applets

The applet runs in the browser tab

CheerpJ is a Java runtime built from OpenJDK and compiled to WebAssembly, so applets run in current versions of Chrome, Edge, Firefox and Safari.

Your applet stays as it is

CheerpJ runs the existing JAR files from their bytecode, so you need neither the source code nor a rebuild.

Java comes off users' computers

CheerpJ delivers the runtime to the browser along with the application, and you update it centrally.

Applets run on Java 8

CheerpJ runs applets on Java 8, the release they were built for.

How CheerpJ works in an enterprise environment

There are two ways to deploy it.

1 Script tag

On your own page, with the CheerpJ script tag

Add CheerpJ’s loader to the page that hosts the applet, and the page provides the Java runtime. You can host the runtime and the application files on a web server inside your network, and users sign in through your usual access controls.

2 Browser extension

Through the browser extension

The CheerpJ Applet Runner runs applets on the pages they’re already on, with the page and server left as they are. IT deploys it to managed Chrome and Edge browsers through Group Policy, like any other managed extension.

A self-hosted version is available for organisations that can’t use the Chrome Web Store or Edge Add-ons, including air-gapped networks.

index.html 
<script src="https://cjrtnc.leaningtech.com/4.3/loader.js"></script>
<applet
  archive="Example.jar"
  code="ExamplePath.ExampleApplet"
  height="900"
  width="900"
></applet>
<script>
  cheerpjInit();
</script>

Security

The applet runs inside the browser’s sandbox, under the same security model as your other web applications. Files, clipboard, printing and audio go through browser APIs and their permissions.

Networking

The applet connects to its back-end services and databases over your network, governed by the browser’s security policies and your own network controls. For connections a browser doesn’t normally allow, such as direct database access, CheerpJ uses a Tailscale VPN that you can host on your own network.

Licensing

Technical evaluation is free and unlimited. Business use needs a licence. See licensing and pricing.

Organisations running applets with CheerpJ

Global financial institution

A global financial institution wanted the internal users of its configuration management database, a Java applet, to stop needing Java installed on their desktops. With CheerpJ hosted on its own server, the applet runs in Chrome and Edge without a local Java installation. The project took two months, against a projected two years.

PhET

PhET, the simulation library from the University of Colorado Boulder, began as Java applets. PhET brought its free educational Java simulations to the web with CheerpJ.

CF Fertilisers

As part of a wider IT and cybersecurity initiative, CF Fertilisers removed Java 8 from every user computer at its sites in the UK and the US, while continuing to use Oracle E-Business Suite. Removing it reduced the company's Java-related vulnerabilities by around 75%, as reflected in its updated Rapid7 scores.

Rated 4.6 out of 5 on the Chrome Web Store

4.6
★★★★★★★★★★ 286 ratings
Read the reviews on the Chrome Web Store
A superb extension with great customer support! We have an large, extensive applet that displays automated weather reports from commercial aircraft-- that is used by weather services world-wide. You can see it at https://amdar.noaa.gov/demo_java/. Thanks to CheerpJ we can now run it again in a browser (chrome). The CheerpJ version is FAST -- able to display 800,000+ wind barbs in just a couple of seconds. In addition, the developers were able to quickly update the app to allow some obscure…
Bill M.
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