spring 中 AOP是基于 “动态代理” 实现，其采用了两种方式：
- java代理：采用java内置的代理API实现
- cglib代理：采用第三方API实现
本文主要阐述这两种方式的区别
动态代理和静态代理
- 静态代理：编译时将增强代码植入class文件，因为是编译期进行的增强，所以代码运行时效率比动态代理高。使用Aspect可以实现静态代理。
- 动态代理：运行时生成代理类并加载，效率比静态代理要低，spring中使用了上文中的两种动态代理的方式来实现代理类的生成。
JDK 动态代理
cglib代理类的实现效率是比 jdk代理类实现效率要高，并且更强大的，但spring中更推荐使用java原生的代理方式，原因在于，第三方lib的实现有太多不确定性，使用java原生的代理方式更加有保障和稳定。
java代理类的实现主要靠Proxy类和InvocationHandler接口来实现。下面直接抛出示例代码demo：
/**
* jdk 代理的示例demo
*/
public class MyJdkProxy{
/**
* 接口
*/
public interface IHello{
void sayHello();
}
/**
* IHello接口实现类
*/
static class Hello implements IHello{
public void sayHello() {
System.out.println("Hello world!!");
}
}
/**
* 自定义InvocationHandler
*/
static class HWInvocationHandler implements InvocationHandler {
//目标对象
private Object target;
public HWInvocationHandler(Object target){
this.target = target;
}
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
System.out.println("------插入前置通知代码-------------");
//执行相应的目标方法
Object rs = method.invoke(target,args);
System.out.println("------插入后置处理代码-------------");
return rs;
}
}
public static void main(String[] args) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
//生成$Proxy0的class文件
System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles", "true");
/*
* 方式一：
*/
//获取动态代理类class并加载
Class proxyClazz = Proxy.getProxyClass(IHello.class.getClassLoader(),IHello.class);
//获得代理类的构造函数，并传入参数类型InvocationHandler.class
Constructor constructor = proxyClazz.getConstructor(InvocationHandler.class);
//通过构造函数来创建动态代理对象，将自定义的InvocationHandler实例传入
IHello iHello = (IHello) constructor.newInstance(new HWInvocationHandler(new Hello()));
/*
* 方式二：可看成方式一的语法糖
*/
// IHello iHello = (IHello) Proxy.newProxyInstance(IHello.class.getClassLoader(), //加载接口的类加载器
// new Class[]{IHello.class}, //一组接口
// new HWInvocationHandler(new Hello())); //自定义的InvocationHandler
//通过代理对象调用目标方法
iHello.sayHello();
}
}
代理类的class是在Proxy.getProxyClass(IHello.class.getClassLoader(),IHello.class)这个方法执行后被生成，class路径在项目根目录的com\sun\proxy中：
我们反编译下这个代理类class：
public final class $Proxy0
extends Proxy
implements MyJdkProxy.IHello
{
private static Method m1;
private static Method m3;
private static Method m2;
private static Method m0;
public $Proxy0(InvocationHandler paramInvocationHandler)
{
super(paramInvocationHandler);
}
public final boolean equals(Object paramObject)
{
try
{
return ((Boolean)this.h.invoke(this, m1, new Object[] { paramObject })).booleanValue();
}
catch (Error|RuntimeException localError)
{
throw localError;
}
catch (Throwable localThrowable)
{
throw new UndeclaredThrowableException(localThrowable);
}
}
public final void sayHello()
{
try
{
this.h.invoke(this, m3, null);
return;
}
catch (Error|RuntimeException localError)
{
throw localError;
}
catch (Throwable localThrowable)
{
throw new UndeclaredThrowableException(localThrowable);
}
}
public final String toString()
{
try
{
return (String)this.h.invoke(this, m2, null);
}
catch (Error|RuntimeException localError)
{
throw localError;
}
catch (Throwable localThrowable)
{
throw new UndeclaredThrowableException(localThrowable);
}
}
public final int hashCode()
{
try
{
return ((Integer)this.h.invoke(this, m0, null)).intValue();
}
catch (Error|RuntimeException localError)
{
throw localError;
}
catch (Throwable localThrowable)
{
throw new UndeclaredThrowableException(localThrowable);
}
}
static
{
try
{
m1 = Class.forName("java.lang.Object").getMethod("equals", new Class[] { Class.forName("java.lang.Object") });
m3 = Class.forName("test.wsz.spring.aop.MyJdkProxy$IHello").getMethod("sayHello", new Class[0]);
m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]);
m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[0]);
return;
}
catch (NoSuchMethodException localNoSuchMethodException)
{
throw new NoSuchMethodError(localNoSuchMethodException.getMessage());
}
catch (ClassNotFoundException localClassNotFoundException)
{
throw new NoClassDefFoundError(localClassNotFoundException.getMessage());
}
}
}
从代理类class可以看出，java生成的代理类实现了 被代理对象的接口IHello，同时继承了 Proxy。
这个地方解决了我们的一个疑惑：spring为什么要采用两种动态代理的实现方式？
原因就在于，JDK的动态代理只能针对被接口修饰的类，因为代理类$Proxy0必须继承Proxy，Java中的类又是单继承的，所以只能规定委托类Hello必须有实现接口IHello，从而使生成的代理类$Proxy0能够重写委托了中的方法sayHello()。
这里梳理下java中代理类的生成步骤：
- 通过
Proxy.getProxyClass()方法生成代理类的class文件并加载。（具体生成步骤见 源码中ProxyClassFactory.apply()） - 获取这个class的构造器，传入代理类的逻辑实现类
InvocationHandler作为构造函数参数，实例化class获得代理类对象。 - 调用代理类对象的对应方法
具体源码就不分析了，可看 深度剖析JDK动态代理机制
CGLIB 动态代理
不多说，直接上demo代码：
/**
* cglib 代理的示例demo
*/
public class MyCglibProxy {
/**
* Hello类
*/
static class Hello{
public void sayHello() {
System.out.println("Hello world!!");
}
}
static class HelloMethodInterceptor implements MethodInterceptor {
@Override
public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {
System.out.println("------插入前置通知代码-------------");
//执行相应的目标方法
Object rs = methodProxy.invokeSuper(o,objects);
System.out.println("------插入后置处理代码-------------");
return rs;
}
}
public static void main(String[] args) {
Enhancer enhancer = new Enhancer();
//代理类基础自 被代理类Hello
enhancer.setSuperclass(Hello.class);
//设置回调类，代理逻辑在回调类中
enhancer.setCallback(new HelloMethodInterceptor());
//生成代理类
Hello hello = (Hello) enhancer.create();
hello.sayHello();
}
}
生成的代理类class：
public class MyCglibProxy$Hello$$EnhancerByCGLIB$$1716bafc
extends MyCglibProxy.Hello
implements Factory
{
private boolean CGLIB$BOUND;
public static Object CGLIB$FACTORY_DATA;
private static final ThreadLocal CGLIB$THREAD_CALLBACKS;
private static final Callback[] CGLIB$STATIC_CALLBACKS;
private MethodInterceptor CGLIB$CALLBACK_0;
private static Object CGLIB$CALLBACK_FILTER;
private static final Method CGLIB$sayHello$0$Method;
private static final MethodProxy CGLIB$sayHello$0$Proxy;
private static final Object[] CGLIB$emptyArgs;
private static final Method CGLIB$equals$1$Method;
private static final MethodProxy CGLIB$equals$1$Proxy;
private static final Method CGLIB$toString$2$Method;
private static final MethodProxy CGLIB$toString$2$Proxy;
private static final Method CGLIB$hashCode$3$Method;
private static final MethodProxy CGLIB$hashCode$3$Proxy;
private static final Method CGLIB$clone$4$Method;
private static final MethodProxy CGLIB$clone$4$Proxy;
/* Error */
static void CGLIB$STATICHOOK1()
{
}
final void CGLIB$sayHello$0()
{
super.sayHello();
}
public final void sayHello()
{
MethodInterceptor tmp4_1 = this.CGLIB$CALLBACK_0;
if (tmp4_1 == null)
{
tmp4_1;
CGLIB$BIND_CALLBACKS(this);
}
if (this.CGLIB$CALLBACK_0 != null) {
return;
}
super.sayHello();
}
final boolean CGLIB$equals$1(Object paramObject)
{
return super.equals(paramObject);
}
public final boolean equals(Object paramObject)
{
MethodInterceptor tmp4_1 = this.CGLIB$CALLBACK_0;
if (tmp4_1 == null)
{
tmp4_1;
CGLIB$BIND_CALLBACKS(this);
}
MethodInterceptor tmp17_14 = this.CGLIB$CALLBACK_0;
if (tmp17_14 != null)
{
Object tmp41_36 = tmp17_14.intercept(this, CGLIB$equals$1$Method, new Object[] { paramObject }, CGLIB$equals$1$Proxy);
tmp41_36;
return tmp41_36 == null ? false : ((Boolean)tmp41_36).booleanValue();
}
return super.equals(paramObject);
}
final String CGLIB$toString$2()
{
return super.toString();
}
public final String toString()
{
MethodInterceptor tmp4_1 = this.CGLIB$CALLBACK_0;
if (tmp4_1 == null)
{
tmp4_1;
CGLIB$BIND_CALLBACKS(this);
}
MethodInterceptor tmp17_14 = this.CGLIB$CALLBACK_0;
if (tmp17_14 != null) {
return (String)tmp17_14.intercept(this, CGLIB$toString$2$Method, CGLIB$emptyArgs, CGLIB$toString$2$Proxy);
}
return super.toString();
}
final int CGLIB$hashCode$3()
{
return super.hashCode();
}
public final int hashCode()
{
MethodInterceptor tmp4_1 = this.CGLIB$CALLBACK_0;
if (tmp4_1 == null)
{
tmp4_1;
CGLIB$BIND_CALLBACKS(this);
}
MethodInterceptor tmp17_14 = this.CGLIB$CALLBACK_0;
if (tmp17_14 != null)
{
Object tmp36_31 = tmp17_14.intercept(this, CGLIB$hashCode$3$Method, CGLIB$emptyArgs, CGLIB$hashCode$3$Proxy);
tmp36_31;
return tmp36_31 == null ? 0 : ((Number)tmp36_31).intValue();
}
return super.hashCode();
}
final Object CGLIB$clone$4()
throws CloneNotSupportedException
{
return super.clone();
}
protected final Object clone()
throws CloneNotSupportedException
{
MethodInterceptor tmp4_1 = this.CGLIB$CALLBACK_0;
if (tmp4_1 == null)
{
tmp4_1;
CGLIB$BIND_CALLBACKS(this);
}
MethodInterceptor tmp17_14 = this.CGLIB$CALLBACK_0;
if (tmp17_14 != null) {
return tmp17_14.intercept(this, CGLIB$clone$4$Method, CGLIB$emptyArgs, CGLIB$clone$4$Proxy);
}
return super.clone();
}
/* Error */
public static MethodProxy CGLIB$findMethodProxy(net.sf.cglib.core.Signature arg0)
{
// Byte code:
// 0: aload_0
// 1: invokevirtual 119 java/lang/Object:toString ()Ljava/lang/String;
// 4: dup
// 5: invokevirtual 120 java/lang/Object:hashCode ()I
// 8: lookupswitch default:+112->120, -508378822:+52->60, 1535311470:+64->72, 1826985398:+76->84, 1913648695:+88->96, 1984935277:+100->108
// 60: ldc 122
// 62: invokevirtual 123 java/lang/Object:equals (Ljava/lang/Object;)Z
// 65: ifeq +56 -> 121
// 68: getstatic 116 test/wsz/spring/aop/MyCglibProxy$Hello$$EnhancerByCGLIB$$1716bafc:CGLIB$clone$4$Proxy Lnet/sf/cglib/proxy/MethodProxy;
// 71: areturn
// 72: ldc 125
// 74: invokevirtual 123 java/lang/Object:equals (Ljava/lang/Object;)Z
// 77: ifeq +44 -> 121
// 80: getstatic 49 test/wsz/spring/aop/MyCglibProxy$Hello$$EnhancerByCGLIB$$1716bafc:CGLIB$sayHello$0$Proxy Lnet/sf/cglib/proxy/MethodProxy;
// 83: areturn
// 84: ldc 127
// 86: invokevirtual 123 java/lang/Object:equals (Ljava/lang/Object;)Z
// 89: ifeq +32 -> 121
// 92: getstatic 68 test/wsz/spring/aop/MyCglibProxy$Hello$$EnhancerByCGLIB$$1716bafc:CGLIB$equals$1$Proxy Lnet/sf/cglib/proxy/MethodProxy;
// 95: areturn
// 96: ldc -127
// 98: invokevirtual 123 java/lang/Object:equals (Ljava/lang/Object;)Z
// 101: ifeq +20 -> 121
// 104: getstatic 85 test/wsz/spring/aop/MyCglibProxy$Hello$$EnhancerByCGLIB$$1716bafc:CGLIB$toString$2$Proxy Lnet/sf/cglib/proxy/MethodProxy;
// 107: areturn
// 108: ldc -125
// 110: invokevirtual 123 java/lang/Object:equals (Ljava/lang/Object;)Z
// 113: ifeq +8 -> 121
// 116: getstatic 98 test/wsz/spring/aop/MyCglibProxy$Hello$$EnhancerByCGLIB$$1716bafc:CGLIB$hashCode$3$Proxy Lnet/sf/cglib/proxy/MethodProxy;
// 119: areturn
// 120: pop
// 121: aconst_null
// 122: areturn
}
public MyCglibProxy$Hello$$EnhancerByCGLIB$$1716bafc()
{
CGLIB$BIND_CALLBACKS(this);
}
public static void CGLIB$SET_THREAD_CALLBACKS(Callback[] paramArrayOfCallback)
{
CGLIB$THREAD_CALLBACKS.set(paramArrayOfCallback);
}
public static void CGLIB$SET_STATIC_CALLBACKS(Callback[] paramArrayOfCallback)
{
CGLIB$STATIC_CALLBACKS = paramArrayOfCallback;
}
private static final void CGLIB$BIND_CALLBACKS(Object paramObject)
{
1716bafc local1716bafc = (1716bafc)paramObject;
if (!local1716bafc.CGLIB$BOUND)
{
local1716bafc.CGLIB$BOUND = true;
Object tmp23_20 = CGLIB$THREAD_CALLBACKS.get();
if (tmp23_20 == null)
{
tmp23_20;
CGLIB$STATIC_CALLBACKS;
}
local1716bafc.CGLIB$CALLBACK_0 = (tmp31_28 == null ? tmp31_28 : (MethodInterceptor)((Callback[])tmp23_20)[0]);
}
}
public Object newInstance(Callback[] paramArrayOfCallback)
{
CGLIB$SET_THREAD_CALLBACKS(paramArrayOfCallback);
CGLIB$SET_THREAD_CALLBACKS(null);
return new 1716bafc();
}
public Object newInstance(Callback paramCallback)
{
CGLIB$SET_THREAD_CALLBACKS(new Callback[] { paramCallback });
CGLIB$SET_THREAD_CALLBACKS(null);
return new 1716bafc();
}
/* Error */
public Object newInstance(Class[] arg1, Object[] arg2, Callback[] arg3)
{
// Byte code:
// 0: aload_3
// 1: invokestatic 195 test/wsz/spring/aop/MyCglibProxy$Hello$$EnhancerByCGLIB$$1716bafc:CGLIB$SET_THREAD_CALLBACKS ([Lnet/sf/cglib/proxy/Callback;)V
// 4: new 2 test/wsz/spring/aop/MyCglibProxy$Hello$$EnhancerByCGLIB$$1716bafc
// 7: dup
// 8: aload_1
// 9: dup
// 10: arraylength
// 11: tableswitch default:+24->35, 0:+17->28
// 28: pop
// 29: invokespecial 196 test/wsz/spring/aop/MyCglibProxy$Hello$$EnhancerByCGLIB$$1716bafc:<init> ()V
// 32: goto +17 -> 49
// 35: goto +3 -> 38
// 38: pop
// 39: new 202 java/lang/IllegalArgumentException
// 42: dup
// 43: ldc -52
// 45: invokespecial 207 java/lang/IllegalArgumentException:<init> (Ljava/lang/String;)V
// 48: athrow
// 49: aconst_null
// 50: invokestatic 195 test/wsz/spring/aop/MyCglibProxy$Hello$$EnhancerByCGLIB$$1716bafc:CGLIB$SET_THREAD_CALLBACKS ([Lnet/sf/cglib/proxy/Callback;)V
// 53: areturn
}
public Callback getCallback(int paramInt)
{
CGLIB$BIND_CALLBACKS(this);
switch (paramInt)
{
case 0:
break;
}
return null;
}
public void setCallback(int paramInt, Callback paramCallback)
{
switch (paramInt)
{
case 0:
this.CGLIB$CALLBACK_0 = ((MethodInterceptor)paramCallback);
break;
}
}
public Callback[] getCallbacks()
{
CGLIB$BIND_CALLBACKS(this);
return new Callback[] { this.CGLIB$CALLBACK_0 };
}
public void setCallbacks(Callback[] paramArrayOfCallback)
{
this.CGLIB$CALLBACK_0 = ((MethodInterceptor)paramArrayOfCallback[0]);
}
static {}
}
从反编译的class文件可看出，cglib生成的代理类是直接继承被代理类Hello，代理的具体逻辑是通过回调类HelloMethodInterceptor实现。
这里不详细分析cglib的源码，可看：深入理解CGLIB动态代理机制
两种动态代理方式的区别
- cglib底层运用了asm这个非常强大的Java字节码生成框架来生成class， 比jdk代理效率要高
- jdk代理只能代理被接口修饰的类，而cglib没有这个限制（原因上面已经分析，jdk是动态生成委托类的接口的实现类，cglib是动态生成委托类的子类）
最后补充下：spring中，如果bean实现了接口，则会使用jdk代理方式，否则采用cglib代理方式。也可通过<aop:aspectj-autoproxy proxy-target-class="true"/>配置来强制使用cglib代理方式
