Delegates, Events and Pass by ref in Java using bytecode Manipulation

package csharp;

import java.io.IOException;
import java.lang.reflect.Method;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

import javassist.CannotCompileException;
import javassist.ClassPool;
import javassist.CtClass;
import javassist.CtMethod;
import javassist.CtNewMethod;
import javassist.CtPrimitiveType;
import javassist.Modifier;
import javassist.NotFoundException;

public abstract class Delegate {

	private static final Map<Integer, Class<? extends Delegate>> instanceDelegates = new ConcurrentHashMap<Integer, Class<? extends Delegate>>();
	private static final Map<Integer, Delegate> staticDelegates = new ConcurrentHashMap<Integer, Delegate>();

	protected Object object = null;

	protected Delegate() {

	}

	public static <T extends Delegate> T getInstance(
			Class<? extends Delegate> delClazz, Class clazz, String name) {
		try {
			int key = Math
					.abs((delClazz.getCanonicalName() + "_" + clazz.getCanonicalName() + "_static")
							.hashCode());
			Delegate delegate = staticDelegates.get(key);
			if (delegate == null) {
				Class<? extends Delegate> actualClazz = createClass(delClazz,
						name, key, clazz, true);
				delegate = actualClazz.newInstance();
				staticDelegates.put(key, delegate);
			}
			return (T) delegate;
		} catch (InstantiationException e) {
			throw new RuntimeException(e.getMessage(), e);
		} catch (IllegalAccessException e) {
			throw new RuntimeException(e.getMessage(), e);
		} catch (SecurityException e) {
			throw new RuntimeException(e.getMessage(), e);
		} catch (NoSuchMethodException e) {
			throw new RuntimeException(e.getMessage(), e);
		}
	}

	public static <T extends Delegate> T getInstance(
			Class<? extends Delegate> delClazz, Object object, String name) {
		try {
			int key = Math.abs((delClazz.getCanonicalName() + "_"
					+ object.getClass().getCanonicalName() + "_instance").hashCode());
			Class<? extends Delegate> actualClazz = instanceDelegates.get(key);
			if (actualClazz == null) {
				actualClazz = createClass(delClazz, name, key,
						object.getClass(), false);
				instanceDelegates.put(key, actualClazz);
			}
			Delegate delegate = actualClazz.newInstance();
			delegate.object = object;
			return (T) delegate;
		} catch (InstantiationException e) {
			throw new RuntimeException(e.getMessage(), e);
		} catch (IllegalAccessException e) {
			throw new RuntimeException(e.getMessage(), e);
		} catch (SecurityException e) {
			throw new RuntimeException(e.getMessage(), e);
		} catch (NoSuchMethodException e) {
			throw new RuntimeException(e.getMessage(), e);
		}
	}

	private static Class<? extends Delegate> createClass(
			Class<? extends Delegate> delClazz, String name, int key,
			Class clazz, boolean isStatic) throws SecurityException,
			NoSuchMethodException {
		try {
			Class<? extends Delegate> actualClazz;
			ClassPool pool = ClassPool.getDefault();
			CtClass newClass = pool.makeClass(clazz.getPackage().getName()
					+ ".D" + key);
			CtClass sup = pool.get(delClazz.getCanonicalName());
			newClass.setSuperclass(sup);
			Method[] methods = delClazz.getDeclaredMethods();

			Method method = null;
			for (Method m : methods) {
				if (m.getName().equals("invoke")) {
					if (method != null) {
						throw new IllegalStateException(delClazz.getCanonicalName()
								+ " contains two or more invoke methods.");
					}

					method = m;
					if (m.getModifiers() != 1025) {
						throw new IllegalStateException(
								delClazz.getCanonicalName()
										+ " required invoke method as 'public abstract ");
					}
				}
			}

			if (method == null) {
				throw new NullPointerException(delClazz.getCanonicalName()
						+ " does not have invoke method.");
			}

			StringBuilder params = new StringBuilder();
			StringBuilder values = new StringBuilder();
			StringBuilder paramTypes = new StringBuilder();

			Class[] parameterTypes = method.getParameterTypes();

			int i = 97;
			for (Class parameterType : parameterTypes) {
				if (params.length() != 0) {
					params.append(",");
					values.append(",");
					paramTypes.append(",");
				}
				params.append(parameterType.getCanonicalName() + " "
						+ new Character((char) i));
				values.append(new Character((char) i));
				paramTypes.append(parameterType.getCanonicalName() + ".class");
				i++;
			}

			Method objectMethod = clazz.getDeclaredMethod(name, parameterTypes);

			StringBuilder exceptions = new StringBuilder();
			if (!Modifier.isPrivate(objectMethod.getModifiers())) {
				Class[] exceptionTypes = method.getExceptionTypes();
				for (Class exceptionType : exceptionTypes) {
					if (exceptions.length() != 0) {
						exceptions.append(",");
					}
					exceptions.append(exceptionType.getCanonicalName());
				}
			} else {
				exceptions.append("java.lang.Exception");
			}

			String body = "public "
					+ method.getReturnType().getCanonicalName()
					+ " invoke("
					+ params.toString()
					+ ")"
					+ ((exceptions.length() != 0) ? " throws "
							+ exceptions.toString() : "") + " {";

			if (!Modifier.isPrivate(objectMethod.getModifiers())) {
				body += ((!method.getReturnType().getCanonicalName()
						.equals("void")) ? "return " : "")
						+ ((isStatic) ? clazz.getCanonicalName() : "(("
								+ clazz.getCanonicalName() + ")object)")
						+ "."
						+ name
						+ "(" + values.toString() + ");";
			} else {
				StringBuilder ps = new StringBuilder(
						"java.util.List ps = new java.util.ArrayList();");

				if (parameterTypes.length != 0) {
					for (String s : paramTypes.toString().split(",")) {
						ps.append("ps.add(" + s + ");");
					}
				}

				StringBuilder vs = new StringBuilder(
						"java.util.List vs = new java.util.ArrayList();");

				if (parameterTypes.length != 0) {
					i = 0;
					for (String s : values.toString().split(",")) {
						if (parameterTypes[i].isPrimitive()) {
							CtPrimitiveType primitiveType = (CtPrimitiveType) pool
									.get(parameterTypes[i].getCanonicalName());
							vs.append("vs.add("
									+ primitiveType.getWrapperName()
									+ ".valueOf(" + s + "));");
						} else {
							vs.append("vs.add(" + s + ");");
						}
						i++;
					}
				}

				body += "try {" + ps.toString() + vs.toString()
						+ "java.lang.reflect.Method method = "
						+ clazz.getCanonicalName() + ".class.getDeclaredMethod(\""
						+ name
						+ "\",(Class[])ps.toArray(new Class[ps.size()]));"
						+ "method.setAccessible(true);" + "method.invoke("
						+ ((isStatic) ? "null" : "object") + ",vs.toArray())"
						+ ";} catch (java.lang.Exception e) {throw e;}";
			}

			body += "}";

			CtMethod m = CtNewMethod.make(body, newClass);
			newClass.addMethod(m);
			actualClazz = newClass.toClass();
			return actualClazz;
		} catch (NotFoundException e) {
			throw new RuntimeException(e.getMessage(), e);
		} catch (CannotCompileException e) {
			throw new RuntimeException(e.getMessage(), e);
		}
	}
}