Create a DSL to describe a consumer chain

[cstroe]

Currently, to create a consumer chain that operates on an SVN Dump stream you must write Java code, compile it into your JAR and then run it on your SVN dump file. It is a tedious process.

To make this easier, we can create a DSL that describes a consumer chain. The file that describes the consumer chain can be read at runtime and the consumer chain be generated dynamically, requiring no recompilation.

This will make running the program from the CLI much easier.

The DSL should be implemented in JavaCC.

[cstroe]

Commit b77596a adds a CliConsumer. The CliConsumer should have an option to read a DSL file to describe the consumer chain.

[cstroe]

Alternatively, we can use JSR 233: Scripting for the Java Platform, with any of the supported languages (there are many) to parse some dynamic scripting language. I'm thinking either Javascript or Ruby (or both).

http://www.drdobbs.com/jvm/jsr-223-scripting-for-the-java-platform/215801163

[cstroe]

Looks like Javascript support is distributed with Java:

The following 1 scripting engines were found

Engine name: Oracle Nashorn
    Version: 1.8.0_60
    Language: ECMAScript
    Engine supports the following extensions:
        js
    Engine has the following short names:
        nashorn
        Nashorn
        js
        JS
        JavaScript
        javascript
        ECMAScript
        ecmascript
=========================

[cstroe]

So adding support for any scripting language is as easy as making the ScriptEngine implementation available.

JRuby docs: https://github.com/jruby/jruby/wiki/Embedding-with-JSR-223

[cstroe]

This article (http://zeroturnaround.com/rebellabs/why-you-should-tap-into-the-power-of-ruby-from-the-comfort-of-the-jvm/) recommends using JRuby Embed (originally called RedBridge) instead of JSR 223, however, we should probably stick to JSR 223 to make adding other languages easy.

RedBridge explained: https://github.com/jruby/jruby/wiki/RedBridge
JRuby Java Integration: https://github.com/jruby/jruby/wiki/JavaIntegration

[cstroe]

Adding this to pom.xml:

<dependency>
    <groupId>org.jruby</groupId>
    <artifactId>jruby-complete</artifactId>
    <version>1.7.9</version>
</dependency>

Yields:

The following 2 scripting engines were found

Engine name: JSR 223 JRuby Engine
    Version: 1.7.9
    Language: ruby
    Engine supports the following extensions:
        rb
    Engine has the following short names:
        ruby
        jruby
=========================
Engine name: Oracle Nashorn
    Version: 1.8.0_60
    Language: ECMAScript
    Engine supports the following extensions:
        js
    Engine has the following short names:
        nashorn
        Nashorn
        js
        JS
        JavaScript
        javascript
        ECMAScript
        ecmascript
=========================

Very nice.

[cstroe]

https://github.com/jruby/jruby/wiki/AccessingJRubyObjectInJava