re2j.Re2jHack

// TODO try to remove javassist dependency with this class
public class Re2jHack
{
	private static final AtomicBoolean PATCHED = new AtomicBoolean();

	private static void addMethodUnicodeIsLetter(final ClassPool cp) throws CannotCompileException, NotFoundException
	{
		final CtClass cc = cp.get("com.google.re2j.Unicode");
		cc.addMethod(
				CtMethod.make("static boolean isLetter(int r) { return is(com.google.re2j.UnicodeTables.L, r); }", cc));
		cc.toClass();
	}

	public static void patch()
	{
		patch(Arrays.asList());
	}

	/**
	 * Override of the patch() method working with classloaders of Tomcat/war
	 * 
	 * @param classes
	 *            some Class instances loaded by eventual other classloaders
	 */
	public static void patch(final Iterable<Class<? extends Object>> classes)
	{
		if (PATCHED.compareAndSet(false, true))
		{
			try
			{
				final ClassPool cp = ClassPool.getDefault();
				for (final Class<? extends Object> clazz : classes)
					cp.insertClassPath(new ClassClassPath(clazz));
				patchPR100(cp);
			}
			catch (final CannotCompileException | NotFoundException e)
			{
				throw new RuntimeException(e);
			}
		}
	}

	private static void patchPR100(final ClassPool cp) throws CannotCompileException, NotFoundException
	{
		// @see https://github.com/google/re2j/pull/100
		addMethodUnicodeIsLetter(cp);
		patchUtilsIsWordRune(cp);
	}

	private static void patchUtilsIsWordRune(final ClassPool cp) throws CannotCompileException, NotFoundException
	{
		final CtClass cc = cp.get("com.google.re2j.Utils");
		cc.getDeclaredMethod("isWordRune")
				.setBody("return (com.google.re2j.Unicode.isLetter($1) || ('0' <= $1 && $1 <= '9') || $1 == '_');");
		cc.toClass();
	}

	private Re2jHack()
	{
		// avoid instances
	}
}