Running Java from Node.js

Christian Dittrich

creatale GmbH

WebDev BBQ, 15.09.2015

Use Case

node-dv

• image manipulation: Leptonica and OpenCV
• OCR: Tesseract
• OMR: custom
• barcode reader: ZXing

ZXing in Node.js

• native module using official C++ port
• discontinued since 2013

What now?

DIY?

Requirements

• easy to keep up to date (automatically?)
• platform "independent" (at least Windows and Linux)
• easy to use API (has to work with buffers, not just files)
• performant

1. Execute Java

• childProcess.spawn
• node-jvm
• client + server (aka service)
not capable of working directly with buffers (only public static void main(String[] args) entry points)
usually extra processes

2. Java to C/C++

j2c

• https://bitbucket.org/arnetheduck/j2c
• Eclipse Plugin by Google
• supports Java 1.6
errors when compiling ZXing
no Java class library implementation provided

XMLVM

• http://xmlvm.org/overview/
• cross platform mobile development
problems with some java.nio classes ZXing uses (Paths, Files, DirectoryStream)

Tangible

• http://www.tangiblesoftwaresolutions.com/Product_Details/CPlusPlus_to_Java_Converter_Details.html
• costs money
• free version limited to 100 lines of code at once

Java2C

• http://sourceforge.net/projects/java2c/
• Java to C for embedded projects
only limited subset of Java supported (no generics, ZXing needs generics)
last updated in 2011

JCGO

• http://www.ivmaisoft.com/jcgo/
• supports only Java 1.4 (ZXing needs generics)

GCJ

• http://gcc.gnu.org/java/
• GNU
supports only Java 1.4 + some 1.5 features
last updated in 2009
java.nio missing (ZXing uses nio)

Toba

• http://www.cs.arizona.edu/projects/sumatra/toba/
• supports only Java 1.2
• last updated in 1999

XES

• http://www.euclideanspace.com/software/language/xes/userGuide/convert/javaToCpp/index.htm
• manual translation of symbol table necessary (e.g. java.io to System)

3. JNI

• 'java' node module
• ok-ish API

  var list = java.newInstanceSync("java.util.ArrayList");

has problems with memory management (frequent out of memory exceptions), waiting for GC kills performance

4. Java to JavaScript

XMLVM

• http://xmlvm.org/overview/
• cross platform mobile development
• uses Qooxdoo, client side only module

Java2Script

• https://code.google.com/p/java2script/
• Eclipse Plugin
compiled code contains errors
when compiling ZXing, some java.nio stuff missing

GWT

• http://www.gwtproject.org
• by Google
• for Web Applications
needs explicit support by project (has to be packaged into a GWT module)

GWT Exporter

• https://code.google.com/p/gwt-exporter/
• built on GWT, does not need an GWT Application to work
needs annotation of source code with @Export() and implements Exportable

Kotlin

• http://kotlinlang.org
• a JVM language by JetBrains
• compiles to JavaScript
• Java can be automatically translated to Kotlin
errors when compiling ZXing to JavaScript

Recap

1. Execute Java
2. Java to C/C++
3. JNI
4. Java to JavaScript

5. Java to C# + 'edge' node module

What is edge?

• https://github.com/tjanczuk/edge
• in process .NET code execution for Node.js and vice versa

var edge = require('edge');

var helloWorld = edge.func(function () {/*
	async (input) => { 
		return ".NET Welcomes " + input.ToString(); 
	}
*/});

helloWorld('JavaScript', function (error, result) {
	if (error) throw error;
	console.log(result);
});

sharpen

• https://github.com/mono/sharpen
• does not support multi dimensional arrays

Tangible

• http://www.tangiblesoftwaresolutions.com/Product_Details/Java_to_CSharp_Converter.html
• costs money
• free version limited to 100 lines of code at once

XES

• http://www.euclideanspace.com/software/language/xes/userGuide/convert/javaToCSharp/index.htm
• manual translation of symbol table necessary (e.g. java.io to stdio.h)

Octopus

• http://www.remotesoft.com/octopus/
• costs money
• online demo does not compile ZXing file

Java Language Conversion Assistant 2.0

• http://www.microsoft.com/en-us/download/details.aspx?id=14349
• by Microsoft
• no longer available :(

VaryCode

• https://www.varycode.com
• costs money
• free version limited to 2048 characters at once

Finally: The Solution

XMLVM

http://xmlvm.org/overview/

1. build JAR
2. compile to .NET-DLL via XMLVM
3. use 'edge' node module and IKVM to run in-process on Node.js

• easy to keep up to date
• platform independent (Mono)
• usable API (same classes and methods for every object in C# + litte JavaScript boilerplate)
• about 10% performance loss for ZXing, compared to original Java code

Example

Coming soon to GitHub

'zxing-edge' node module