Running Swing Applications with JetBrains Projector in a browser

Java Swing is part of the Java Runtime since version 1.2. Swing is also part of the Java Foundation Classes, which are the library for creating component bases, modular, portable, and cross-platform graphical user interfaces. Being part of the core runtime, Java Swing is a valid choice for a lot of projects running in a different environment, starting from tiny calculator applications to humongous insurance or tax administration systems.

Time has changed. Nowadays the Internet is almost everywhere. Writing HTML, CSS and JavaScript is a convenient way to implement and distribute the user interface. Uploading these assets is a lot simpler than installing a Java Runtime, and some libraries on a client machine. Also, we do not need a lot of resources to render an HTML page. The Java Runtime on the other hand needs more resources and also has some startup lag before we can even start to use the application.

The mentioned humongous applications don’t go away. At least, they need time and a lot of money to be rewritten into some kind of "newer" technology. This also introduces financial and organizational risk. Risk no one wants to take without benefit.

Given the need to reduce distribution overhead for existing Java Swing applications, the need to make them usable on low end and SoC devices, and the strategy to migrate them to a newer technology stack without a big bang rewrite, what might be an option to do so? A well-known software company from Prague might have an answer to this question.

JetBrains Projector is a self-hosted technology that runs Swing-based applications on the server, allowing you access to them from anywhere using Web-browsers and native apps.

The following use cases come to mind for Projector:

Internally, Projector replaces the Swing rendering pipeline with some kind of remote rendering. The new rendering pipeline generates drawing command lists, which are sent to a client that is implements rendering of such commands. This client can be HTML and JavaScript, using WebSockets as the communication protocols. A client can also be implemented as a native application using Java or any other frontend technology, even native Android or iOS apps are possible. The whole setup is very similar to the X Window System.

JetBrains is using Projector to make IntelliJ available to the web, which is pretty cool. But Projector can also be used for any Java Swing-based app!

I tried to use ERDesignerNG with Projector. ERDesignerNG is a Swing-based database modeling tool. Here is a screenshot running it as a desktop app:

With minor changes to the startup script and including Projector in the classpath as described here, it runs in a browser:

This is awesome. Now I can deploy this application as a SaaS application by running it in the cloud. A new opportunity to make money :-).

There are also other possibilities. Projector comes with a module called Projector Server. I used this module for ERDesignerNG to make it available as a webpage. There is also a module called Projector Agent. Projector Agents starts the application and renders the regular Swing frontend, but it also starts a Projector Server to make the running application available over HTTP. This is quite neat for presentation and training purposes. In terms of a web-based IDE this can be also used for pair programming, which IntelliJ already does!

Projector is a drop-in replacement for all kinds of Swing-based applications. But there are some things we have to be aware of:

All in all, Projector is an awesome solution and a migration path enabler for existing Java Swing-based applications. Of course, there needs some more work to be done in the real world for many projects. Projectors part is presentation technology replacement, which it does very well.