JDK动态代理和cglib代理

写一个简单的测试用例，Pig实现了Shout接口

public class MyInvocation implements InvocationHandler {

    Object k;

    public MyInvocation(Object k) {
        this.k = k;
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        //System.out.println(proxy);

        System.out.println("----- before -----");
        Object result = method.invoke(k, args);
        System.out.println("----- after -----");
        return result;
    }

    public Object getProxy() {
        return Proxy.newProxyInstance(Thread.currentThread()
                        .getContextClassLoader(), k.getClass().getInterfaces(),
                this);
    }

    public static void main(String[] args) {
        Shout p = (Shout) new MyInvocation(new Pig()).getProxy(); //接口
        p.f();
    }
}

//进入Proxy
public static Object newProxyInstance(ClassLoader loader,
                                          Class<?>[] interfaces,
                                          InvocationHandler h)
        throws IllegalArgumentException
    {
        if (h == null) {
            throw new NullPointerException();
        }

        final Class<?>[] intfs = interfaces.clone();
        ...

        Class<?> cl = getProxyClass0(loader, intfs);//获得代理类

        final Constructor<?> cons = cl.getConstructor(constructorParams);
        final InvocationHandler ih = h;
        return newInstance(cons, ih);  //反射生成实例
    }

    private static Class<?> getProxyClass0(ClassLoader loader,
                                           Class<?>... interfaces) {
        ...

        return proxyClassCache.get(loader, interfaces); //如果有实现了这些接口的代理类存在就直接返回了，否则创建一个新的
    }

    //proxyClassCache是一个弱引用
    private static final WeakCache<ClassLoader, Class<?>[], Class<?>>
        proxyClassCache = new WeakCache<>(new KeyFactory(), new ProxyClassFactory()); //泛型分别代表K键,P参数,V值

    public WeakCache(BiFunction<K, P, ?> subKeyFactory,
                     BiFunction<K, P, V> valueFactory) {
        this.subKeyFactory = Objects.requireNonNull(subKeyFactory); //为空抛异常
        this.valueFactory = Objects.requireNonNull(valueFactory);
    }

    public V get(K key, P parameter) {
        ...

        while (true) {
            if (supplier != null) {
                V value = supplier.get(); //获得生成的Class对象
                if (value != null) {
                    return value;
                }
            }
            ...
        }
    }

中间是WeakCache的代码，好长，省略掉

//进入Proxy的静态内部类ProxyClassFactory
public Class<?> apply(ClassLoader loader, Class<?>[] interfaces) {

            Map<Class<?>, Boolean> interfaceSet = new IdentityHashMap<>(interfaces.length);
            for (Class<?> intf : interfaces) { //对代理接口做检验
                Class<?> interfaceClass = null;
                interfaceClass = Class.forName(intf.getName(), false, loader);
                if (!interfaceClass.isInterface()) {
                    throw new IllegalArgumentException(
                        interfaceClass.getName() + " is not an interface");
                }
                ...
            }

            String proxyPkg = null;     // package to define proxy class in

            ....

            if (proxyPkg == null) {
                proxyPkg = ReflectUtil.PROXY_PACKAGE + ".";
            }
            long num = nextUniqueNumber.getAndIncrement();
            String proxyName = proxyPkg + proxyClassNamePrefix + num; //形如com.sun.proxy.$Proxy0

            byte[] proxyClassFile = ProxyGenerator.generateProxyClass(
                proxyName, interfaces); //生成字节码

            return defineClass0(loader, proxyName,
                                    proxyClassFile, 0, proxyClassFile.length); //生成Class对象
        }
    }

我们看一下生成的字节码

byte[] c = ProxyGenerator.generateProxyClass("com.sun.proxy.$Proxy0", Pig.class.getInterfaces());
FileUtil.appendBytes(new File("/Users/ws/Desktop/ttt.class"), c);

idea反编译打开看看

package com.sun.proxy;

...
public final class $Proxy0 extends Proxy implements Shout {
    private static Method m1;
    private static Method m3;
    private static Method m0;
    private static Method m2;

    public $Proxy0(InvocationHandler var1) throws  {
        super(var1);
    }

    public final boolean equals(Object var1) throws  {
        try {
            return ((Boolean)super.h.invoke(this, m1, new Object[]{var1})).booleanValue();
        } catch (RuntimeException | Error var3) {
            throw var3;
        } catch (Throwable var4) {
            throw new UndeclaredThrowableException(var4);
        }
    }

    public final void f() throws  {
        super.h.invoke(this, m3, (Object[])null);
    }

    ...
    static {
        m1 = Class.forName("java.lang.Object").getMethod("equals", new Class[]{Class.forName("java.lang.Object")});
        m3 = Class.forName("dynamic.Shout").getMethod("f", new Class[0]);
        m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[0]);
        m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]);
    }
}

//cglib输出代理类字节码只需要如下设置
System.setProperty(DebuggingClassWriter.DEBUG_LOCATION_PROPERTY, "/Users/ws/Desktop/xxx");

Waiter target = new NaiveWaiter();
BeforeAdvice advice = new GreetingBeforeAdvice();
//spring提供的代理工厂
ProxyFactory pf = new ProxyFactory();
//设置代理目标
pf.setTarget(target);
//为代理目标添加增强
pf.addAdvice(advice);
//生成代理实例
Waiter proxy = (Waiter) pf.getProxy();
proxy.greetTo("Brian");

于是会在指定目录下生成代理类，打开看看

package com.brianway.learning.spring.aop.advice;

public class NaiveWaiter$$EnhancerBySpringCGLIB$$ef901900 extends NaiveWaiter implements SpringProxy, Advised, Factory {
    private boolean CGLIB$BOUND;
    private static final ThreadLocal CGLIB$THREAD_CALLBACKS;
    private static final Callback[] CGLIB$STATIC_CALLBACKS;
    private MethodInterceptor CGLIB$CALLBACK_0;
    private MethodInterceptor CGLIB$CALLBACK_1;
    private NoOp CGLIB$CALLBACK_2;
    private Dispatcher CGLIB$CALLBACK_3;
    private Dispatcher CGLIB$CALLBACK_4;
    private MethodInterceptor CGLIB$CALLBACK_5;
    private MethodInterceptor CGLIB$CALLBACK_6;
    private static final Method CGLIB$greetTo$0$Method;
    private static final MethodProxy CGLIB$greetTo$0$Proxy;
    private static final Object[] CGLIB$emptyArgs;
    private static final Method CGLIB$serveTo$1$Method;
    private static final MethodProxy CGLIB$serveTo$1$Proxy;
    private static final Method CGLIB$equals$3$Method;
    private static final MethodProxy CGLIB$equals$3$Proxy;
    private static final Method CGLIB$toString$4$Method;
    private static final MethodProxy CGLIB$toString$4$Proxy;
    private static final Method CGLIB$hashCode$5$Method;
    private static final MethodProxy CGLIB$hashCode$5$Proxy;
    private static final Method CGLIB$clone$6$Method;
    private static final MethodProxy CGLIB$clone$6$Proxy;

static {
        ...
        CGLIB$STATICHOOK1();
    }

    static void CGLIB$STATICHOOK1() {
        CGLIB$THREAD_CALLBACKS = new ThreadLocal();
        CGLIB$emptyArgs = new Object[0];
        Class var0 = Class.forName("com.brianway.learning.spring.aop.advice.NaiveWaiter$$EnhancerBySpringCGLIB$$ef901900");
        Class var1;
        Method[] var10000 = ReflectUtils.findMethods(new String[]{"equals", "(Ljava/lang/Object;)Z", "toString", "()Ljava/lang/String;", "hashCode", "()I", "clone", "()Ljava/lang/Object;"}, (var1 = Class.forName("java.lang.Object")).getDeclaredMethods());
        CGLIB$equals$3$Method = var10000[0];
        CGLIB$equals$3$Proxy = MethodProxy.create(var1, var0, "(Ljava/lang/Object;)Z", "equals", "CGLIB$equals$3");
        CGLIB$toString$4$Method = var10000[1];
        CGLIB$toString$4$Proxy = MethodProxy.create(var1, var0, "()Ljava/lang/String;", "toString", "CGLIB$toString$4");
        CGLIB$hashCode$5$Method = var10000[2];
        CGLIB$hashCode$5$Proxy = MethodProxy.create(var1, var0, "()I", "hashCode", "CGLIB$hashCode$5");
        CGLIB$clone$6$Method = var10000[3];
        CGLIB$clone$6$Proxy = MethodProxy.create(var1, var0, "()Ljava/lang/Object;", "clone", "CGLIB$clone$6");
        var10000 = ReflectUtils.findMethods(new String[]{"greetTo", "(Ljava/lang/String;)V", "serveTo", "(Ljava/lang/String;)V"}, (var1 = Class.forName("com.brianway.learning.spring.aop.advice.NaiveWaiter")).getDeclaredMethods());
        CGLIB$greetTo$0$Method = var10000[0];
        CGLIB$greetTo$0$Proxy = MethodProxy.create(var1, var0, "(Ljava/lang/String;)V", "greetTo", "CGLIB$greetTo$0");
        CGLIB$serveTo$1$Method = var10000[1];
        CGLIB$serveTo$1$Proxy = MethodProxy.create(var1, var0, "(Ljava/lang/String;)V", "serveTo", "CGLIB$serveTo$1");
    }

    //被代理的方法
    public final void greetTo(String var1) {
            MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
            if(this.CGLIB$CALLBACK_0 == null) {
                CGLIB$BIND_CALLBACKS(this);
                var10000 = this.CGLIB$CALLBACK_0;
            }

            if(var10000 != null) {
                //进入拦截器
                var10000.intercept(this, CGLIB$greetTo$0$Method, new Object[]{var1}, CGLIB$greetTo$0$Proxy);
            } else {
                super.greetTo(var1);
            }
    }

原文地址：https://www.cnblogs.com/wangsong/p/10274850.html