Java實現動態代理的兩種方式

一般而言，動態代理分為兩種，一種是JDK反射機制提供的代理，另一種是CGLIB代理。在JDK代理，必須提供接口，而CGLIB則不需要提供接口，在Mybatis里兩種動態代理技術都已經使用了，在Mybatis中通常在延遲加載的時候才會用到CGLIB動態代理。

1.JDK動態代理：

public interface Rent {
    public void rent();
}

public class Landlord implements Rent{

    @Override
    public void rent() {
        System.out.println("房東要出租房子了！");
    }
}

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;

public class Intermediary implements InvocationHandler{
    
    private Object post;
    
    Intermediary(Object post){
        this.post = post;
    }
    @Override
    public Object invoke(Object proxy, Method method, Object[] args)
            throws Throwable {
        Object invoke = method.invoke(post, args);
        System.out.println("中介：該房源已發布！");
        return invoke;
    }
}

import java.lang.reflect.Proxy;

public class Test {
    public static void main(String[] args) {
        Rent rent = new Landlord();
        Intermediary intermediary = new Intermediary(rent);
        Rent rentProxy = (Rent) Proxy.newProxyInstance(rent.getClass().getClassLoader(), rent.getClass().getInterfaces(), intermediary);
        rentProxy.rent();
    }
}

2.CGLIB動態代理：

public class Landlord {
    public void rent(){
        System.out.println("房東要出租房子了！");
    }
}

import java.lang.reflect.Method;

import net.sf.cglib.proxy.MethodInterceptor;
import net.sf.cglib.proxy.MethodProxy;

public class Intermediary implements MethodInterceptor {

    @Override
    public Object intercept(Object object, Method method, Object[] args,MethodProxy methodProxy) throws Throwable {
        Object intercept = methodProxy.invokeSuper(object, args);
        System.out.println("中介：該房源已發布！");
        return intercept;
    }
}

import net.sf.cglib.proxy.Enhancer;

public class Test {
    public static void main(String[] args) {
        Intermediary intermediary = new Intermediary();
        
        Enhancer enhancer = new Enhancer();  
        enhancer.setSuperclass(Landlord.class);
        enhancer.setCallback(intermediary);
        
        Landlord rentProxy = (Landlord) enhancer.create();
        rentProxy.rent();
    }
}