Running a Java Program from a Browser without Plugins

The easiest and highest-performance option is TeaVM, a transpiler that converts Java classes into JavaScript. Your code then runs in the browser natively without any plugin.

Read an introductory article here: https://blogs.oracle.com/javamagazine/java-in-the-browser-with-teavm

TeaVM's main site is here: http://teavm.org/

Thinking on its eventual deployment as a Mobile App, a Web Server chart or simply as a PC as a program, being Java a perfect selection for me.
(..)
Hence, which is the way to go with a Java program like this? Which is the proper sustainable Java way to do this (and not subject to something like what happened to Java Web Start)?

Two lines of Java

What happened is that our old friend, the Java Standard Edition, split into two lines:

1. Oracle Java SE ("commercial Java"): needs paid license for commercial use for releases since April 16th, 2019
2. OpenJDK ("open source Java"): open source (GPLv2 with linking exception), does not contain Oracle's Java Web Start implementation

The Oracle Java SE version keeps Java Web Start and Java FX available and supported only for Java SE 8. Newer Java versions, esp. Java SE 11 do not carry these anymore.

It is not a complete client / desktop technology removal, because Oracle, according to the Java Client Roadmap Update 2018, continues to support AWT and Swing for at least 5 more years on both Java SE 8 and Java SE 11.

You can continue deployment via Java Web Start

Open source Java got a decent implementation of Java Web Start, which is free and available for Java SE 8 and newer Java versions like Java SE 11.

This is Karakun's OpenWebStart based on Red Hat's IcedTea-Web, now beyond version 1.0, which you already found.

Continued support is not guaranteed but seems likely. So you might continue on this track.

Or you might deploy via an app store

Oracle's explanation for dropping Java Web Start was, that they want to change the deployment model to applications with bundled runtime:

As client application development continues to shift from the old “plugin” world to modern deployment, the need for a standalone Java Runtime Environment (JRE) that is installed centrally, separately from Java applications has diminished. Using the ‘jlink’ tool introduced with JDK 9 will make it even easier for application developers to package and deploy dedicated runtimes rather than relying on a pre-installed system JRE.

(Source: Faster and Easier Use and Redistribution of Java SE)

Deployment, according to Oracle, would occur via some app store like the iTunes Store:

No doubt this was true, but the OSes have shifted hard and fast away from this model. The "app store" model is now it. macOS has been ratcheting this down hard for several years now. MSFT -- even in the enterprise market -- has signaled this direction as well. For sure we need to find options to support the legacy, but the future here is limited.

(Source: OpenJDK discussion mailing list)

Note that Java Start Web Start handled the updating of available new versions of applications on the client machines, and so do typical app stores.

Of course you can serve a version of your app with bundled runtime on your web site, but then you usually have to implement some mechanism to handle updates of your application on the machines of your users yourself.

What to choose?

It is true that the separate JRE installation has disadvantages, e.g. I changed my JRE recently and suddenly the IDE for Java did not work anymore. :-)

Moving deployment from a web site you control to an app store controled by the OS vendor or mighty players like Valve, has its own challenges. E.g. access restrictions, fees, release delays because of the review process, or they might not like your app for some reason and will not publish it.

Then adoption: Personally I have seen private use of app stores mostly on mobile devices and macs, but no use in companies yet. This might be a factor in your decision which road to pursue.

I've missed the Java on browser too. Because of curiosity I just developed an "JVM-Server", which precompiles the Java-Classes to native JavaScript and serves them to a WebBrowser. Look here is a Hello World example application which is running on Browser: https://github.com/neo-expert/jsjvm_helloworld

There is also a Library which implements WebGL bindings. In the above Example is a WebGL demo included, where a 3D cube will be rendered. The code is written in pure Java.

Is it a swing app? Will have to map that to a web (html) app to make it work on a browser nowadays.

You cannot run any of those programs from a browser directly.

Java used to java applets and java web start - where the browser helped you install a java app on local system but user had to seperately have installed JRE (Java run time) to run it locally.

Now all we have are web apps. basically apps that might have a a session, login, authenticaiton and authorition but in the end the app outputs HTML, Javascript, images and text data (JSON. XML etc) that is rendered on the web page.

Look at J2EE. I'm a java fan. but it takes longer to develop, but i think it runs better. Especially with a good framework like Spring Boot (it includes MVC see https://dzone.com/articles/7-best-java-frameworks-for-2016)

But learning curve is there. Buy a book or do a course online like udemy or similar.youtube has free videos. but not sure of the order/ quality.

If you choose php - many free and cheap servers like x10hosting to start with and learning curve is less too. Good framework - packages like drupal and wordpress.

On the browser HTML, Javacript run. There are frameworks for this too. Like gogole's angular https://angular.io/ this too needs a book/seperate study. Old days we used to use simple Javascript ...

For mobiles - sometimes can get away with using a URL OR there are frameworks that wrap a web page in an 'app' for android, iphone etc OR make a native app - but then will have different code bases.

I know someone who used a game engine to make a mostly single code base (some classes are specific to each platform like android, iphone) but used to render business graphs and a few interaction use cases (about 40). He used https://libgdx.badlogicgames.com/

As your research already revealed, Java is not a relevant web frontend technology anymore. Prefer Javascript and CSS for browser frontends, instead. Feed the frontend code with data served by Java backend services. The Java Servlet Specification is still the base for server-side Java. Many frameworks (like Spring or Jersey, to name a few) are build on top of it. Either chose one of these frameworks, or - for really simple use-cases - build an application only with plain servlets. Any servlet needs to be deployed in a servlet container (e.g. Apache Tomcat).

Your Java code needs probably some refactoring in order to provide an API for the web. As you are asking for near-realtime communication, you should have a look at the WebSockets standard which is designed for bidirectional and fast client-server-communication on the Internet and supported by all modern browsers (nice intro explaining the difference to WebRTC and arguing why WebSockets are often the better choice). To plot your data in a browser with Javascript and SVG, have a look on the D3.js library. A quick search brings you to demos like this one: D3 Real Time Chart. Also, there are other libraries that are built on top of D3, for example plotly.js.

Summary:

• Java is fine for web backend services.
• Your code needs refactoring to serve a backend API, preferably WebSockets. (introduction on how to start in Java at https://www.baeldung.com/java-websockets)
• Get familiar with a Javascript browser plot library, such as D3.js.