Java 动态生成类和实例, 并注入方法

Java官方支持的, 必须要有接口才行

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.LinkedList;
import java.util.List;
import java.util.Random;


/**
 * @author David Ding
 *
 */
interface IJavaGen {
	int getRandomInt();

	void printClassInfo();
}

abstract class JavaGen implements IJavaGen {
	protected List calledMethods = new LinkedList<>(); // property

	public int getRandomInt() { // Get a random integer
		return new Random().nextInt(10000);
	}

	public abstract void printClassInfo();
}

class JavaGenHandler implements InvocationHandler {
	private JavaGen mTarget;

	public JavaGenHandler(JavaGen javaGen) {
		mTarget = javaGen;
	}

	// 动态注入
	@Override
	public Object invoke(Object obj, Method method, Object[] params) throws Throwable {
		Object ret = null;

		String name = method.getName();
		if (name.equals("getRandomInt")) { // intercept the getRandomInt
			ret = method.invoke(mTarget, params); // call the base method
			System.out.println("Print random int: " + ret);
		} else if (name.equals("printClassInfo")) { // print class info
			System.out.println("Class: " + obj.getClass());
			method.invoke(mTarget, params);
		}

		mTarget.calledMethods.add(name); // change the property

		return ret;
	}

}

public class JavaCodeGen {
	public static void main(String[] args) {
		try {
			Class genClass = Proxy.getProxyClass(IJavaGen.class.getClassLoader(), IJavaGen.class);
			Constructor cons = genClass.getConstructor(InvocationHandler.class);
			JavaGen target = new JavaGen() {

				@Override
				public void printClassInfo() {
					System.out.println("I have to implement this method! fuck!");
				}
			};
			IJavaGen javaGen = (IJavaGen) cons.newInstance(new JavaGenHandler(target));
			javaGen.getRandomInt();
			javaGen.printClassInfo();
			System.out.println(target.calledMethods);
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}