jimp example with J2V8.java

package com.eclipsesource.j2v8.tutorial;

import java.io.File;
import java.io.IOException;
import java.io.PrintWriter;
import java.nio.ByteBuffer;

import com.eclipsesource.v8.NodeJS;
import com.eclipsesource.v8.Releasable;
import com.eclipsesource.v8.V8Array;
import com.eclipsesource.v8.V8Object;
import com.eclipsesource.v8.V8TypedArray;

public class Exercise1 {
	
	private static String JIMP_SCRIPT = "var Jimp = require('/Users/irbull/node_modules/jimp');\n"
			+ "  Jimp.read('/Users/irbull/Downloads/IMG_20160706_175824.jpg', (err, image) => {\n"
			+ "    if (err) throw err;\n"
			+ "    process_in_java(image.bitmap.data);\n"
			+ "    image.write('/Users/irbull/Downloads/output.jpg');\n"
			+ "  });\n";

	public static void main(String[] args) throws IOException {
		final NodeJS nodeJS = NodeJS.createNodeJS();
		nodeJS.getRuntime().registerJavaMethod((V8Object receiver, V8Array parameters) -> {
			V8TypedArray typedArray = (V8TypedArray) parameters.get(0);
			ByteBuffer buffer = typedArray.getByteBuffer();
			try {
				for(int i = 0; i < buffer.limit(); i+=4) {
					int gray = createGrayscale(buffer, i);
					buffer.put(i, (byte) gray);
					buffer.put(i+1, (byte) gray);
					buffer.put(i+2, (byte) gray);
				};
					
			} finally {
				typedArray.release();		
			}
			return null;
		}, "process_in_java");

		File script = createTemporaryScriptFile(JIMP_SCRIPT, "jimpscript.js");
		nodeJS.exec(script);
		
		while(nodeJS.isRunning()) {
			nodeJS.handleMessage();
		}		
		nodeJS.release();
	}
	
	private static int createGrayscale(ByteBuffer buffer, int i) {
		int red = 0xFF & buffer.get(i);
		int green = 0xFF & buffer.get(i+1);
		int blue = 0xFF & buffer.get(i+2);
		int gray = (int) (red + green + blue ) / 3;
		return gray;
	}

	public static void executeJSFunction(V8Object object, String name) {
		Object result = object.executeFunction(name, null);
		if (result instanceof Releasable) {
			((Releasable) result).release();
		}
	}

	public static void executeJSFunction(V8Object object, String name, Object... params) {
		Object result = object.executeJSFunction(name, params);
		if (result instanceof Releasable) {
			((Releasable) result).release();
		}
	}
	
	private static File createTemporaryScriptFile(final String script, final String name) throws IOException {
		File tempFile = File.createTempFile(name, ".js");
		PrintWriter writer = new PrintWriter(tempFile, "UTF-8");
		try {
			writer.print(script);
		} finally {
			writer.close();
		}
		return tempFile;
		
	}
}