代理的三种方式，静态，动态，cglib

代理是一种常见的设计模式，它允许一个对象（代理对象）控制另一个对象（真实对象）的访问。在Java中，代理主要分为静态代理和动态代理两种方式，而CGLIB代理是动态代理的一种变体。

1. 静态代理

静态代理是在编译时期就已经确定好代理类，并固定代理关系。下面是一个简单的示例：

// 接口
interface Subject {
    void request();
}

// 真实对象
class RealSubject implements Subject {
    @Override
    public void request() {
        System.out.println("RealSubject: Handling request.");
    }
}

// 代理对象
class ProxySubject implements Subject {
    private RealSubject realSubject;

    public ProxySubject(RealSubject realSubject) {
        this.realSubject = realSubject;
    }

    @Override
    public void request() {
        System.out.println("ProxySubject: Before handling request.");
        realSubject.request();
        System.out.println("ProxySubject: After handling request.");
    }
}

// 客户端
public class StaticProxyExample {
    public static void main(String[] args) {
        RealSubject realSubject = new RealSubject();
        ProxySubject proxySubject = new ProxySubject(realSubject);

        proxySubject.request();
    }
}

2. 动态代理

动态代理是在运行时期生成代理类，无需在编译时期确定代理关系。Java中的动态代理通常使用java.lang.reflect.Proxy类和java.lang.reflect.InvocationHandler接口来实现。下面是一个简单的动态代理示例：

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

// 接口
interface Subject {
    void request();
}

// 真实对象
class RealSubject implements Subject {
    @Override
    public void request() {
        System.out.println("RealSubject: Handling request.");
    }
}

// 动态代理处理器
class DynamicProxyHandler implements InvocationHandler {
    private Object target;

    public DynamicProxyHandler(Object target) {
        this.target = target;
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        System.out.println("DynamicProxy: Before handling request.");
        Object result = method.invoke(target, args);
        System.out.println("DynamicProxy: After handling request.");
        return result;
    }
}

// 客户端
public class DynamicProxyExample {
    public static void main(String[] args) {
        RealSubject realSubject = new RealSubject();
        InvocationHandler handler = new DynamicProxyHandler(realSubject);

        Subject proxySubject = (Subject) Proxy.newProxyInstance(
                Subject.class.getClassLoader(),
                new Class[]{Subject.class},
                handler);

        proxySubject.request();
    }
}

3. CGLIB代理

CGLIB代理是一种基于字节码的代理方式，它不需要接口支持。下面是一个简单的CGLIB代理示例：

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

// 真实对象
class RealSubject {
    public void request() {
        System.out.println("RealSubject: Handling request.");
    }
}

// CGLIB代理处理器
class CglibProxy implements MethodInterceptor {
    @Override
    public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
        System.out.println("CglibProxy: Before handling request.");
        Object result = proxy.invokeSuper(obj, args);
        System.out.println("CglibProxy: After handling request.");
        return result;
    }
}

// 客户端
public class CglibProxyExample {
    public static void main(String[] args) {
        Enhancer enhancer = new Enhancer();
        enhancer.setSuperclass(RealSubject.class);
        enhancer.setCallback(new CglibProxy());

        RealSubject cglibProxy = (RealSubject) enhancer.create();
        cglibProxy.request();
    }
}