The functionality of OpenWebStart

Technical details

OpenWebStart is based on Iced-Tea-Web and the JNLP-specification defined in JSR-56. It will implement the most commonly used features of Java Web Start and it will be able to handle any typical JWS-based application. We plan to support all future versions of Java, starting with Java 11. In addition to Java 11, the first release of OpenWebStart will also support Java 8.

Read on for all the technical details:

How do I install and manage OpenWebStart?

OpenWebStart will come in two different versions:

  • An interactive installer with auto-update functionality
  • An unattended installer for automated roll-outs

If you use Web Start for several small customers or on your own, we recommend using the interactive installer. Our native installer will set up everything on your Windows, Mac, or Linux system so that OpenWebStart is immediately ready to use. OpenWebStart checks for updates automatically, and the Updater component keeps the tool current without the need for any user interaction.

If you or your customers are companies with IT departments of their own, we recommend an unattended installation to roll out OpenWebStart on multiple client machines. In this scenario, the auto-update functionality is inactive; your IT department is free to plan and handle rollouts of new versions based on your internal workflows.

For more information about available installers, see the Download page.


Which JNLP features will be supported?

Nothing will change from the point of view of your users. OpenWebStart will provide exactly the same JNLP-based workflow as Java Web Start:

  1. A user either clicks a link on a webpage, or an automated provisioning process downloads a JNLP file to the client. The JNLP file describes the application.
  2. OpenWebStart registers itself as default for the JNLP file extension and the MIME-type application/x-java-jnlp-file. From now on, OpenWebStart launches when users double-click any JNLP file.
  3. OpenWebStart parses the JNLP file, downloads all required resources (JARs, native libraries and images), and stores them in a cache.
  4. When all resources are downloaded, the application starts.

app manager

The included App Manager will manage all JNLP-based application that OpenWebStart has downloaded and started. The App Manager checks regularly whether updates are available for its managed applications, and downloads updates automatically.

Can I manage JDK/JRE versions?

OpenWebStart from Karakun will provide an integrated JVM Manager. The JVM Manager downloads Java versions from a dedicated server, and manages versions internally. With OpenWebStart, it will be easy for developers to specify the Java version to run JNLP-based applications.

JVM management

By default, OpenWebStart will download an OpenJDK-based Java version from a dedicated server. You can also configure servers manually in the OpenWebStart Control Panel.

download JVM

For further details see the JVM Manger detail description.

How do I configure OpenWebStart?

The well-known Java Control Panel that was installed together with Oracle Java was part of Web Start. When Web Start is removed from Oracle Java, we’ll also lose the Control Panel.

This is why OpenWebStart comes with its own Control Panel: The new Control Panel will, among other things, let you configure workflows to start JNLP-based applications by hand.

Under which license does OpenWebStart come?

OpenWebStart is released under the GPL with Classpath Exception. For more information, read the full license here.

Can I get a customer-specific build?

The free-to-use OpenWebStart builds use the default configuration described on this page.

If you want to evaluate OpenWebStart without registering the tool for the JNLP MIME-type, we can provide you with a build that is configured to use a custom “JNLPX” MIME-type instead. This allows for an easy migration from Oracle Web Start to OpenWebStart. Additionally, you can customise the server URL for JDK downloads, and provide JDKs for your clients and customers on a custom server. If you want to use a commercial JDK that is not publically available, you can even configure OpenWebStart to use authentication and download JDKs from a secure server.

These are custom configurations that we offer for our customers that have bought commercial support at Karakun. Just what you need? Contact us at!