bytecode_manip.java

import java.io.File;
import java.io.FileInputStream;
import java.util.Scanner;

import javassist.*;
import uk.co.agena.minerva.util.helpers.*;

class Injector
{

	private CtClass cc;

	public Injector() throws Exception {
		ClassPool pool = ClassPool.getDefault();
		pool.importPackage("uk.co.agena.minerva.util.io");
		pool.importPackage("javax.swing");
		pool.importPackage("java.util");
		pool.importPackage("java.io");
		pool.importPackage("uk.co.agena.minerva.util.helpers");
		cc = pool.get("uk.co.agena.minerva.util.helpers.ProbabilityCalculator");
		Scanner scanner = new Scanner(new File("randomiseProbabilities.java")).useDelimiter("\\Z");
		inject("randomiseProbabilities", scanner.next());
		inject("getType", "{ return \"Professional\"; }");
		scanner = new Scanner(new File("compileProperties.java")).useDelimiter("\\Z");
		inject("compileProperties", scanner.next());
		cc.writeFile();
	}

	private void inject(String method, String body) throws Exception {
		// Find the method we want to patch and rename it 
		// (we will be creating a new method with the original name).
		CtMethod m_old = cc.getDeclaredMethod(method);
		m_old.setName( method +  "$impl" );

		// Create a new method with the same name as the old one
		CtMethod m_new = CtNewMethod.copy(m_old, method, cc, null);

		// Provide the new method's implementation
		StringBuilder sb = new StringBuilder();
		sb.append(body);
		m_new.setBody( sb.toString() );

		// Add the new method to the class. Patch the .class file
		cc.addMethod( m_new );
	}

	public static void main(String[] argv) throws Exception
	{
		new Injector();
	}


}