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https://github.com/jtulach/bck2brwsr

Bck2Brwsr VM to transpile Java bytecode to JavaScript
https://github.com/jtulach/bck2brwsr

bytecode gradle-plugins java javascript jvm maven-plugin transpiler

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Bck2Brwsr VM to transpile Java bytecode to JavaScript

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# Bring Java Back to Browser!



[Bck2Brwsr](http://bck2brwsr.apidesign.org) VM is a Java virtual machine which is capable to take bytecode 

and transpile it

(either ahead-of-time - e.g. during compilation on desktop - or just-in-time, e.g. in a browser) 

into appropriate JavaScript code which does the same thing. As a result one can write in Java, 

compile with JavaC, run it with [Bck2Brwsr](http://bck2brwsr.apidesign.org) in any modern browser. 



# Getting Started



If you have a **Maven** or **Gradle** project it is as easy as adding one plugin

to get your Java application into browser. Imagine you have a simple hello world

application in `src/main/java` structure of your project:

```java

public class Hello {

    public static void main(String... args) {

        System.err.println("Hello from Java in JS!");

    }

}

```

then it is just about adding following plugin into your `pom.xml`:

```xml

    

        

            

                org.apidesign.bck2brwsr

                bck2brwsr-maven-plugin

                0.51

            

        

    

```

and executing `mvn clean install bck2brwsr:aot bck2brwsr:show` -

more info in a [dedicated page](docs/MAVEN.md).



It is similarly easy with **Gradle**. Just by adding (the same)

single plugin and configuring your script to use it:

```groovy

buildscript {

    repositories {

        mavenCentral()

    }

    dependencies {

        classpath "org.apidesign.bck2brwsr:bck2brwsr-maven-plugin:0.51"

    }

}



repositories {

    mavenCentral()

}



apply plugin: 'bck2brwsr'

```

you'll be able to invoke `./gradlew bck2brwsrShow` and see your Java 

application greetings from the browser. 

An in-depth [tutorial is available](docs/GRADLE.md) as well.



## How do I deploy?



Just copy the generated files to any web hosting service! No application

server needed, no code needs to be executed on the server. The whole application is 

*just* a set of pages that can be copied anywhere. In case of **Gradle** it consists of:

```bash

$ find build/web/

build/web/

build/web/index.html

build/web/lib

build/web/lib/emul-0.51-rt.js

build/web/main.js

build/web/bck2brwsr.js

```

The structure of pages generated by **Maven** is similar with the primary HTML file being `target/index.html`.



## Talking to Your Java Code



Once your application is running in the browser, you can interact with it

from a console. Btw. output of `System.out` and `System.err` is primarily 

printed into the console. Open the console and try:

```js

var System = vm.loadClass("java.lang.System")

System.exit(0)

```

and voilá! your browser is closed. Obviously the above snippet is more useful for 

other methods in your application than `System.exit`. You can use it to 

locate any `public class` and invoke any of its `public static` methods.



## Launching



Browsers download scripts asynchronously, as such the `vm.loadClass` may not be

immediatelly ready, but it may get loaded with a delay. To accomodate such restriction

one can use a callback style of the above:

```js

vm.loadClass("java.lang.System", function(System) {

  System.exit(0)

});

```

Usage of callback is recommended when executing the first Java method (as that usually means

loading of new scripts) and is exactly what the default content of `index.html` does:

```html



var vm = bck2brwsr('main.js');

vm.loadClass('Hello', function(mainClass) {

  mainClass.invoke('main');

});



```

The first line loads the [Bck2Brwsr](http://bck2brwsr.apidesign.org) virtual machine. 

Then one fills it with transpiled code of one's application `var vm = bck2brwsr('main.js');`

together with required libraries. At the end one invokes `main` method of the `Hello` class

using the callback syntax.



# More?



More info at [project home page](http://bck2brwsr.apidesign.org). Questions to [bck2brwsr group](https://groups.google.com/forum/#!forum/bck2brwsr).