JDK动态代理与CGLIB动态代理
JDK动态代理和CGLIB动态代理是SpringAOP非常重要的两个概念，SpringAOP是通过生成目标对象的代理类来实现对目标对象的增强，在说JDK的动态代理之前我们先来回顾一下静态代理：
一、静态代理：
首先定义一个业务接口
public interface ITestService {
void sayHello();
String getMsg();
}然后我们编写一个简单的实现类：
public class TestServiceImpl implements ITestService{
@Override
public void sayHello() {
System.out.println("TestServiceImpl sayHello");
}
@Override
public String getMsg() {
return "TestServiceImpl Msg";
}
}然后我们再编写一个代理类用来代理TestServiceImpl：
public class TestServiceProxy implements ITestService {
private ITestService target;
public TestServiceProxy(ITestService testService) {
this.target = testService;
}
@Override
public void sayHello() {
System.out.println("sayHello invoke before");
this.target.sayHello();
System.out.println("sayHello invoke after");
}
@Override
public String getMsg() {
System.out.println("getMsg invoke before");
String result = this.target.getMsg();
System.out.println("getMsg invoke after");
return result;
}
}最后我们编写一个场景类来模拟使用场景：
public class Client {
public static void main(String[] args) {
ITestService testService = new TestServiceProxy(new TestServiceImpl());
testService.sayHello();
String msg = testService.getMsg();
System.out.println(msg);
}
}最后输出：
结果很简单，我们通过TestServiceProxy对象实现了对TestServiceImpl的代理，并且这个代理对场景类Clinet是隐藏的，这个就是代理模式。
我们回头看一下这个静态代理的实现方式缺点，我们为了实现对ITestService的实现类的代理，写了一个代理类TestServiceProxy，这个代理类只能代理ITestService的子类，如果需要代理其他的对象，哪怕代理逻辑是一样的，也需要重新编写一个代理类，这样势必会导致类的数量大量增加，最终导致项目十分臃肿，JDK1.3中加入的代理模式就解决了这个问题，让代理类可以代理多个对象，不需要编写重复的代理逻辑。
二、JDK动态代理
JDK动态代理的核心是InvocationHandler接口，首先我们编写一个代理类，注意这个代理类的名字是MyProxy，说明它不再与任何具体的接口建立依赖关系。
public class MyProxy implements InvocationHandler {
private Object target;
public MyProxy(Object target) {
this.target = target;
}
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
System.out.println("invoke before");
Object result = method.invoke(target);
System.out.println("invoke after");
return result;
}
}接下来通过Proxy.newProxyInstance来生成一个代理对象，此时我们才需要传入被代理的接口，把与被代理对象建立依赖关系的步骤放到了场景类中。
public class Client {
public static void main(String[] args) {
// 将Proxy.newProxyInstance生成的代理对象输出到com\sun\proxy目录
System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles", true);
MyProxy proxy = new MyProxy(new TestServiceImpl());
ITestService service = (ITestService) Proxy.newProxyInstance(Client.class.getClassLoader(),
new Class[]{ITestService.class}, proxy);
service.sayHello();
String result = service.getMsg();
System.out.println(result);
}
}输出结果还是一样，JDK动态代理其实就是Proxy.newProxyInstance方法帮我们动态生成了一个代理对象，不需要我们手动去编写了，反编译查看一下生成的动态代理对象：
public final class $Proxy0 extends Proxy implements ITestService {
private static Method m1;
private static Method m3;
private static Method m2;
private static Method m0;
private static Method m4;
public $Proxy0(InvocationHandler var1) throws {
super(var1);
}
public final boolean equals(Object var1) throws {
try {
return (Boolean)super.h.invoke(this, m1, new Object[]{var1});
} catch (RuntimeException | Error var3) {
throw var3;
} catch (Throwable var4) {
throw new UndeclaredThrowableException(var4);
}
}
public final void sayHello() throws {
try {
super.h.invoke(this, m3, (Object[])null);
} catch (RuntimeException | Error var2) {
throw var2;
} catch (Throwable var3) {
throw new UndeclaredThrowableException(var3);
}
}
public final String toString() throws {
try {
return (String)super.h.invoke(this, m2, (Object[])null);
} catch (RuntimeException | Error var2) {
throw var2;
} catch (Throwable var3) {
throw new UndeclaredThrowableException(var3);
}
}
public final int hashCode() throws {
try {
return (Integer)super.h.invoke(this, m0, (Object[])null);
} catch (RuntimeException | Error var2) {
throw var2;
} catch (Throwable var3) {
throw new UndeclaredThrowableException(var3);
}
}
public final String getMsg() throws {
try {
return (String)super.h.invoke(this, m4, (Object[])null);
} catch (RuntimeException | Error var2) {
throw var2;
} catch (Throwable var3) {
throw new UndeclaredThrowableException(var3);
}
}
static {
try {
m1 = Class.forName("java.lang.Object").getMethod("equals", Class.forName("java.lang.Object"));
m3 = Class.forName("proxy.ITestService").getMethod("sayHello");
m2 = Class.forName("java.lang.Object").getMethod("toString");
m0 = Class.forName("java.lang.Object").getMethod("hashCode");
m4 = Class.forName("proxy.ITestService").getMethod("getMsg");
} catch (NoSuchMethodException var2) {
throw new NoSuchMethodError(var2.getMessage());
} catch (ClassNotFoundException var3) {
throw new NoClassDefFoundError(var3.getMessage());
}
}
}可以看到生成的$Proxy0通过继承Proxy接口来持有InvocationHandler，并且实现了传入的接口，实际调用method的时候其实是调用的InvocationHandler的invoker方法。通过这种方式实现了代理。并且$Proxy0不仅仅代理了getMsg和sayHello方法，还代理了toString，hasCode，equals等默认方法。
可以看到JDK动态代理的优点，MyProxy中实现的代理逻辑可以应用在任何想要代理的业务对象上，JDK的动态代理也是SpringAOP中默认的代理方式。
但是JDK动态代理是通过继承Proxy对象，并实现目标对象的父接口的方式来完成代理的，这种方式也有很大的局限性，如果一个类没有实现接口，那么就不能使用JDK动态代理了，就需要用到CGLIB动态代理了。
三、CGLIB动态代理
CGLIB全称是Code Generation Library，是一个高性能的code生成工具，能够在程序运行期间动态的扩展JAVA类与实现JAVA接口。
我们来看实现方式，首先编写一个业务对象，注意这个对象不再实现任何接口，并且将getMsg方法设置为final类型
public class TestService {
public void sayHello() {
System.out.println("TestService sayHello");
}
public final String getMsg() {
return "TestService Msg";
}
}CGLIB动态代理的核心是MethodInterceptor接口，我们需要自己编写一个类去实现MethodInterceptor，这个和InvocationHandler相同：
public class MyMethodInterceptor implements MethodInterceptor {
@Override
public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {
System.out.println("前置通知");
Object result = methodProxy.invokeSuper(o, objects);
System.out.println("后置通知");
return result;
}
}编写场景类，使用CGLIB生成代理对象：
public class Client {
public static void main(String[] args) {
// 将CGLIB生成的class对象存入磁盘
System.setProperty(DebuggingClassWriter.DEBUG_LOCATION_PROPERTY, ".\\");
// 创建Enhancer对象，用来生成代理类
Enhancer enhancer = new Enhancer();
// 设置被代理对象
enhancer.setSuperclass(TestService.class);
// 设置回调接口，就是的代理逻辑
enhancer.setCallback(new MyMethodInterceptor());
// 生成代理对象
TestService testService= (TestService)enhancer.create();
// 通过代理对象调用目标方法
testService.sayHello();
}
}结果如下：
生成的class类有三个，另外两个是为了生成代理对象服务的：
反编译出来看看：
package proxy;
import java.lang.reflect.Method;
import org.springframework.cglib.core.ReflectUtils;
import org.springframework.cglib.core.Signature;
import org.springframework.cglib.proxy.Callback;
import org.springframework.cglib.proxy.Factory;
import org.springframework.cglib.proxy.MethodInterceptor;
import org.springframework.cglib.proxy.MethodProxy;
public class TestService$$EnhancerByCGLIB$$6902e37c extends TestService 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;
static void CGLIB$STATICHOOK1() {
CGLIB$THREAD_CALLBACKS = new ThreadLocal();
CGLIB$emptyArgs = new Object[0];
Class var0 = Class.forName("proxy.TestService$$EnhancerByCGLIB$$6902e37c");
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$1$Method = var10000[0];
CGLIB$equals$1$Proxy = MethodProxy.create(var1, var0, "(Ljava/lang/Object;)Z", "equals", "CGLIB$equals$1");
CGLIB$toString$2$Method = var10000[1];
CGLIB$toString$2$Proxy = MethodProxy.create(var1, var0, "()Ljava/lang/String;", "toString", "CGLIB$toString$2");
CGLIB$hashCode$3$Method = var10000[2];
CGLIB$hashCode$3$Proxy = MethodProxy.create(var1, var0, "()I", "hashCode", "CGLIB$hashCode$3");
CGLIB$clone$4$Method = var10000[3];
CGLIB$clone$4$Proxy = MethodProxy.create(var1, var0, "()Ljava/lang/Object;", "clone", "CGLIB$clone$4");
CGLIB$sayHello$0$Method = ReflectUtils.findMethods(new String[]{"sayHello", "()V"}, (var1 = Class.forName("proxy.TestService")).getDeclaredMethods())[0];
CGLIB$sayHello$0$Proxy = MethodProxy.create(var1, var0, "()V", "sayHello", "CGLIB$sayHello$0");
}
final void CGLIB$sayHello$0() {
super.sayHello();
}
public final void sayHello() {
MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
if (this.CGLIB$CALLBACK_0 == null) {
CGLIB$BIND_CALLBACKS(this);
var10000 = this.CGLIB$CALLBACK_0;
}
if (var10000 != null) {
var10000.intercept(this, CGLIB$sayHello$0$Method, CGLIB$emptyArgs, CGLIB$sayHello$0$Proxy);
} else {
super.sayHello();
}
}
final boolean CGLIB$equals$1(Object var1) {
return super.equals(var1);
}
public final boolean equals(Object var1) {
MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
if (this.CGLIB$CALLBACK_0 == null) {
CGLIB$BIND_CALLBACKS(this);
var10000 = this.CGLIB$CALLBACK_0;
}
if (var10000 != null) {
Object var2 = var10000.intercept(this, CGLIB$equals$1$Method, new Object[]{var1}, CGLIB$equals$1$Proxy);
return var2 == null ? false : (Boolean)var2;
} else {
return super.equals(var1);
}
}
final String CGLIB$toString$2() {
return super.toString();
}
public final String toString() {
MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
if (this.CGLIB$CALLBACK_0 == null) {
CGLIB$BIND_CALLBACKS(this);
var10000 = this.CGLIB$CALLBACK_0;
}
return var10000 != null ? (String)var10000.intercept(this, CGLIB$toString$2$Method, CGLIB$emptyArgs, CGLIB$toString$2$Proxy) : super.toString();
}
final int CGLIB$hashCode$3() {
return super.hashCode();
}
public final int hashCode() {
MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
if (this.CGLIB$CALLBACK_0 == null) {
CGLIB$BIND_CALLBACKS(this);
var10000 = this.CGLIB$CALLBACK_0;
}
if (var10000 != null) {
Object var1 = var10000.intercept(this, CGLIB$hashCode$3$Method, CGLIB$emptyArgs, CGLIB$hashCode$3$Proxy);
return var1 == null ? 0 : ((Number)var1).intValue();
} else {
return super.hashCode();
}
}
final Object CGLIB$clone$4() throws CloneNotSupportedException {
return super.clone();
}
protected final Object clone() throws CloneNotSupportedException {
MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
if (this.CGLIB$CALLBACK_0 == null) {
CGLIB$BIND_CALLBACKS(this);
var10000 = this.CGLIB$CALLBACK_0;
}
return var10000 != null ? var10000.intercept(this, CGLIB$clone$4$Method, CGLIB$emptyArgs, CGLIB$clone$4$Proxy) : super.clone();
}
public static MethodProxy CGLIB$findMethodProxy(Signature var0) {
String var10000 = var0.toString();
switch(var10000.hashCode()) {
case -508378822:
if (var10000.equals("clone()Ljava/lang/Object;")) {
return CGLIB$clone$4$Proxy;
}
break;
case 1535311470:
if (var10000.equals("sayHello()V")) {
return CGLIB$sayHello$0$Proxy;
}
break;
case 1826985398:
if (var10000.equals("equals(Ljava/lang/Object;)Z")) {
return CGLIB$equals$1$Proxy;
}
break;
case 1913648695:
if (var10000.equals("toString()Ljava/lang/String;")) {
return CGLIB$toString$2$Proxy;
}
break;
case 1984935277:
if (var10000.equals("hashCode()I")) {
return CGLIB$hashCode$3$Proxy;
}
}
return null;
}
public TestService$$EnhancerByCGLIB$$6902e37c() {
CGLIB$BIND_CALLBACKS(this);
}
public static void CGLIB$SET_THREAD_CALLBACKS(Callback[] var0) {
CGLIB$THREAD_CALLBACKS.set(var0);
}
public static void CGLIB$SET_STATIC_CALLBACKS(Callback[] var0) {
CGLIB$STATIC_CALLBACKS = var0;
}
private static final void CGLIB$BIND_CALLBACKS(Object var0) {
TestService$$EnhancerByCGLIB$$6902e37c var1 = (TestService$$EnhancerByCGLIB$$6902e37c)var0;
if (!var1.CGLIB$BOUND) {
var1.CGLIB$BOUND = true;
Object var10000 = CGLIB$THREAD_CALLBACKS.get();
if (var10000 == null) {
var10000 = CGLIB$STATIC_CALLBACKS;
if (CGLIB$STATIC_CALLBACKS == null) {
return;
}
}
var1.CGLIB$CALLBACK_0 = (MethodInterceptor)((Callback[])var10000)[0];
}
}
public Object newInstance(Callback[] var1) {
CGLIB$SET_THREAD_CALLBACKS(var1);
TestService$$EnhancerByCGLIB$$6902e37c var10000 = new TestService$$EnhancerByCGLIB$$6902e37c();
CGLIB$SET_THREAD_CALLBACKS((Callback[])null);
return var10000;
}
public Object newInstance(Callback var1) {
CGLIB$SET_THREAD_CALLBACKS(new Callback[]{var1});
TestService$$EnhancerByCGLIB$$6902e37c var10000 = new TestService$$EnhancerByCGLIB$$6902e37c();
CGLIB$SET_THREAD_CALLBACKS((Callback[])null);
return var10000;
}
public Object newInstance(Class[] var1, Object[] var2, Callback[] var3) {
CGLIB$SET_THREAD_CALLBACKS(var3);
TestService$$EnhancerByCGLIB$$6902e37c var10000 = new TestService$$EnhancerByCGLIB$$6902e37c;
switch(var1.length) {
case 0:
var10000.();
CGLIB$SET_THREAD_CALLBACKS((Callback[])null);
return var10000;
default:
throw new IllegalArgumentException("Constructor not found");
}
}
public Callback getCallback(int var1) {
CGLIB$BIND_CALLBACKS(this);
MethodInterceptor var10000;
switch(var1) {
case 0:
var10000 = this.CGLIB$CALLBACK_0;
break;
default:
var10000 = null;
}
return var10000;
}
public void setCallback(int var1, Callback var2) {
switch(var1) {
case 0:
this.CGLIB$CALLBACK_0 = (MethodInterceptor)var2;
default:
}
}
public Callback[] getCallbacks() {
CGLIB$BIND_CALLBACKS(this);
return new Callback[]{this.CGLIB$CALLBACK_0};
}
public void setCallbacks(Callback[] var1) {
this.CGLIB$CALLBACK_0 = (MethodInterceptor)var1[0];
}
static {
CGLIB$STATICHOOK1();
}
}
生成的Class对象是TestService的子类，其中的核心是sayHello方法：
public final void sayHello() {
MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
if (this.CGLIB$CALLBACK_0 == null) {
CGLIB$BIND_CALLBACKS(this);
var10000 = this.CGLIB$CALLBACK_0;
}
if (var10000 != null) {
var10000.intercept(this, CGLIB$sayHello$0$Method, CGLIB$emptyArgs, CGLIB$sayHello$0$Proxy);
} else {
super.sayHello();
}
}可以看到是调用sayHello方法其实是通过MethodInterceptor的intercept方法来调用的，也就实现了代理逻辑。
以上就是JDK动态代理和CGLIB的动态代理，在SpringAOP中，默认是使用JDK动态代理，当一个类没有父接口时，会改用CBLIB动态代理。