Java 动态生成类和实例, 并注入方法

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<String> 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();
}
}
}