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CheerpJ runs Java bytecode in modern browsers using a WebAssembly- and JavaScript-based runtime, so supported Java applications can work without a traditional browser plugin. It can run existing JAR-based applications, applets, libraries and Java Web Start/JNLP applications, but compatibility depends on the app’s Java version and its reliance on operating-system features, native code, hardware or browser-restricted networking.
What CheerpJ is—and what it is not
CheerpJ is a browser-delivered Java virtual machine and runtime from Leaning Technologies. Its documentation describes an OpenJDK-based runtime and a Java-to-JavaScript just-in-time compiler that use WebAssembly and JavaScript to run Java bytecode in the browser. The application’s source code is not required. CheerpJ’s overview describes it as “a WebAssembly-based Java Virtual Machine for the browser.”
That makes CheerpJ different from the discontinued style of browser Java plug-in: it runs within the browser’s modern web platform rather than installing a Java plug-in. The runtime includes support for Swing and AWT, a virtualized filesystem, networking features, clipboard, audio, printing, and Java/JavaScript interoperability, subject to browser capabilities and security rules. These are vendor-documented capabilities, not a guarantee that every application using those features will work unchanged.
Which Java versions and application types are supported?
CheerpJ’s overview lists Java 8, 11 and 17. Its more detailed compatibility specification gives an important qualification: Java 8 and Java 11 are marked full and production supported, while Java 17 is marked partial and described as preview. The same matrix lists Java 6 and 7 as available through their respective LTS versions. Check the current matrix before choosing a runtime for a deployment.
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Documented application categories include standard Java applications, including Swing apps; Java applets; Java libraries; and Java Web Start/JNLP applications. The vendor also cites Oracle Forms and EBS frontends as enterprise use cases. These categories indicate intended support, not certification of every app in that category.
Applet version constraint
For applets, CheerpJ’s applet quickstart says Java 8 is the default when no version is specified and that applets will not work if the runtime is changed to Java 11 or higher. Do not assume that an applet will behave like a standalone application with the same Java-version options.
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- 5-in-1 USB-C Hub: Experience comprehensive connectivity featuring a Power Delivery input, two USB-A 2.0 ports, a USB-A 3.0 port, and an HDMI port. (Note: The USB-C power delivery input port is only for connecting an external wall charger to power your laptop and cannot power peripheral devices.)
- 90W Pass-Through Charging: Achieve optimal charging with 90W pass-through power to your laptop, supported by a total input of 100W, with the hub reserving 10W for operational efficiency. (Note: Wall charger not included.)
- Quick Data Transfers: Accelerate your productivity with rapid data transfers using a high-speed 5Gbps USB 3.0 port and two 480Mbps USB 2.0 ports.
- 4K HDMI Display: Enhance your visual experience with a hub capable of delivering 4K resolution at 30Hz in both mirror and extend modes. Please note that this hub is compatible with MacBook (macOS 12 and newer), Windows 10 and 11, ChromeOS, and laptops equipped with DP Alt Mode and Power Delivery. Note: This device is not compatible with Linux.
- What You Get: Anker USB-C Hub (5-in-1, 4K HDMI), welcome guide, 18-month warranty, and our friendly customer service.
Run a Java application from a JAR
The documented quickstart needs the existing Java application archive or archives, an HTML page, and an HTTP server. The page loads CheerpJ’s versioned runtime loader, initializes it with cheerpjInit(), creates a display, and launches the app. Use cheerpjRunJar() for a JAR or cheerpjRunMain() when launching through a main class. See the exact configuration and current loader example in Run a Java Application.
- Prepare the application files. Have the application JARs and any supporting files required by the app.
- Create an HTML launch page. Add the versioned CheerpJ loader, initialize the runtime, and call the appropriate launch API for the JAR or main class. Follow the quickstart’s current example for the required arguments.
- Serve the page over HTTP. The quickstart says opening the HTML file directly from disk is unsupported. Use a simple local HTTP server during setup rather than a
file://URL. - Test the actual application. Check the app’s UI, files, network access and any integrations it needs; a successful launch alone does not establish that every workflow works.
Run a Java applet
The applet workflow likewise loads the runtime in an HTML page, calls cheerpjInit(), and uses an applet tag. Serve the page through an HTTP server. If the page could also encounter a native Java plug-in, the applet guide documents CheerpJ-prefixed tags such as <cheerpj-applet>. Follow the applet quickstart for the page markup and observe its Java 8 constraint.
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- Double Up on Efficiency: The two USB-A 3.0 ports and a USB-C port support a fast 5Gbps data rate, significantly boosting your transfer speeds and improving productivity.
- Fast and Reliable 85W Charging: Offers high-capacity, speedy charging for laptops up to 85W, so you spend less time tethered to an outlet and more time being productive.
- What You Get: Anker USB-C Hub (7-in-1), welcome guide, 18-month warranty, and our friendly customer service.
CheerpJ’s FoilSim tutorial shows a NASA aerodynamics applet integrated into a modern browser page. It is an example of the approach, not evidence that unrelated applets have the same compatibility.
Compatibility checks before migration
CheerpJ operates inside the browser security model. The compatibility specification says cross-origin restrictions apply; direct operating-system access is unavailable; and filesystem access depends on browser APIs. HTTP(S) networking is supported subject to browser security, while TCP requires an additional proxy component. Review the application’s dependencies before planning a migration.
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- Next-Level 10Gbps & 3A Charging: No more slow 480Mbps, this usb to usb c adapter has a transfer speed of up to 10Gbps, allowing you to do more transferring in less time. This usb adapter fits both USB A and USB C charger, supporting up to 3A fast charging
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- Broad Compatible: The usb c to usb adapter widely supports all USB C/ USB A devices like laptops, tablets, cellphones, car chargers, and phone chargers. Such as compatible with MacBook Pro/Air 2023/2022, Thunderbolt 4/3 Devices,Apple MagSafe Watch 9/8/7/SE/Ultra, iPad Pro 2022/2021, Samsung Galaxy S23/S20/S10, and iPhone 17/16/15 Pro. Plug and play
- Please Note: To reach 10Gbps speed, keep the cable under 3.3 ft. For USB A Male to USB C adapters, try flipping the USB C connector. USB C Male to USB A adapters support bidirectional 10Gbps transfer within 3.3 ft
- JavaFX: The compatibility matrix marks JavaFX as partial. Apps with extensive or advanced JavaFX use need particular scrutiny.
- Native code and JNI: Native binaries cannot execute inside the browser runtime. An app that depends on platform-specific native libraries may need changes or may not fit this approach.
- Operating-system integration: Direct process execution, OS-level hooks and similar functions are not available as they would be in a desktop environment.
- Hardware: Direct USB, serial, smart-card or proprietary hardware access can be a blocker or require redesign; do not assume browser runtime access to a device.
- Networking: Check custom protocols and low-level networking. Browser-origin rules constrain requests, and the vendor identifies TCP as requiring an additional proxy component.
- Browser and endpoint controls: The vendor lists Chrome, Edge, Chromium-based browsers, Firefox and Safari, including mobile counterparts, when they support modern WebAssembly. The cited material does not specify minimum browser versions or guarantee compatibility with every managed-device policy.
Is CheerpJ a fit for your project?
Use the application’s dependencies—not just its Java version—to decide whether a compatibility assessment is needed. A useful first-pass checklist is:
- Identify the Java version and whether the program is a standalone app, applet, library or JNLP application.
- Inventory its UI toolkit, especially JavaFX alongside Swing or AWT.
- Find native/JNI dependencies, operating-system calls, direct hardware access and process execution.
- Map its network protocols, cross-origin requirements and any TCP use.
- Confirm the target browsers, mobile needs and endpoint security policies.
- Test important end-to-end workflows, not only whether the application starts.
Leaning Technologies positions CheerpJ for cases such as replacing Java applets or Java Web Start and modernizing Oracle Forms/EBS frontends. Those are vendor-described use cases. Applications with OS integration, hardware, native code, substantial JavaFX or custom networking deserve technical review against the compatibility specification rather than an assumption of drop-in operation.
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- 5-in-1 Connectivity: Equipped with a 4K HDMI port, a 5 Gbps USB-C data port, two 5 Gbps USB-A ports, and a USB C 100W PD-IN port. Note: The USB C 100W PD-IN port supports only charging and does not support data transfer devices such as headphones or speakers.
- Powerful Pass-Through Charging: Supports up to 85W pass-through charging so you can power up your laptop while you use the hub. Note: Pass-through charging requires a charger (not included). Note: To achieve full power for iPad, we recommend using a 45W wall charger.
- Transfer Files in Seconds: Move files to and from your laptop at speeds of up to 5 Gbps via the USB-C and USB-A data ports. Note: The USB C 5Gbps Data port does not support video output.
- HD Display: Connect to the HDMI port to stream or mirror content to an external monitor in resolutions of up to 4K@30Hz. Note: The USB-C ports do not support video output.
- What You Get: Anker 332 USB-C Hub (5-in-1), welcome guide, our worry-free 18-month warranty, and friendly customer service.
Personal use and commercial licensing
The overview says CheerpJ is free for personal use and technical evaluation. It does not establish commercial pricing, production rights or organizational licensing conditions. Review the current CheerpJ licensing page directly before using it for commercial deployment.
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