知识回顾
在文章初识AOP中，了解到为什么要用代理，静态代理和动态代理的区别，在JDK的动态代理中讲到JDK的动态代理是如何实现的，有什么优缺点，CGLIB中动态代理中我们又说明了CGLIB如何实现动态代理，和JDK动态代理有什么区别，同时我们在spring aop & jdk的动态代理中讲到了spring aop如何利用JDK的动态代理的，本篇将继续聊下Spring中的AOP是如何结合CGLIB的动态代理的
Spring AOP 示例
前提：先引入spring-context的jar包
同样的例子 定义一个IHello的接口和一个Hello的实现类如下
package seven.com.seven.aop;
public interface IHello {
void say();
}
package seven.com.seven.aop;
public class Hello implements IHello {
@Override
public void say() {
System.out.println("hello word");
}
}
定义一个前置通知，一个后置通知，一个环绕通知，如下
package seven.com.seven.aop;
import org.springframework.aop.MethodBeforeAdvice;
import java.lang.reflect.Method;
public class BeforeAdvice implements MethodBeforeAdvice {
@Override
public void before(Method method, Object[] args, Object target) throws Throwable {
System.out.println("------------------before------------------");
}
}
package seven.com.seven.aop;
import org.springframework.aop.AfterReturningAdvice;
import java.lang.reflect.Method;
public class AfterAdvice implements AfterReturningAdvice {
@Override
public void afterReturning(Object returnValue, Method method, Object[] args, Object target) throws Throwable {
System.out.println("------------------after------------------");
}
}package seven.com.seven.aop;
import org.aopalliance.intercept.MethodInterceptor;
import org.aopalliance.intercept.MethodInvocation;
public class SurroundAdvice implements MethodInterceptor {
@Override
public Object invoke(MethodInvocation invocation) throws Throwable {
System.out.println("------------------surround before---------------------");
Object result = invocation.proceed();
System.out.println("------------------surround after----------------------");
return result;
}
}
spring aop 实现动态代理
package seven.com.seven.aop;
import net.sf.cglib.core.DebuggingClassWriter;
import org.springframework.aop.framework.ProxyFactory;
public class DynamicSpringProxy {
private Object target;
public Object getProxy(Object target) {
/**
* 通过此语句可以把JDK动态代理 生成的class文件保存到磁盘，然后通过 反编译工具得到代码
*/
//System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles", "true");
/**
* 通过此语句可以把CGLIB动态代理 生成的class文件保存到磁盘，然后通过 反编译工具得到代码
*/
System.setProperty(DebuggingClassWriter.DEBUG_LOCATION_PROPERTY, "D:\\code");
this.target = target;
ProxyFactory factory = new ProxyFactory();
factory.setTarget(target);//让spring 走cglib的动态代理
factory.addAdvice(new BeforeAdvice());
factory.addAdvice(new AfterAdvice());
factory.addAdvice(new SurroundAdvice());
return factory.getProxy();
}
}
package seven.com;
import seven.com.seven.aop.*;
public class App {
public static void main(String[] args) {
Hello hello = new Hello();
IHello proxy = (IHello) new DynamicSpringProxy().getProxy(hello);
proxy.say();
}
}运行结果
------------------before------------------
------------------surround before------------------
hello word
------------------surround after------------------
------------------after------------------分析
前面的过程基本一样，根据选项选择使用JDK的动态代理还是CGLIB的动态代理，上一篇都讲过了，我们直接看下ObjenesisCglibAopProxy的getProxy方法
public Object getProxy(ClassLoader classLoader) {
if (logger.isDebugEnabled()) {
logger.debug("Creating CGLIB proxy: target source is " + this.advised.getTargetSource());
}
try {
Class<?> rootClass = this.advised.getTargetClass();
Assert.state(rootClass != null, "Target class must be available for creating a CGLIB proxy");
Class<?> proxySuperClass = rootClass;
if (ClassUtils.isCglibProxyClass(rootClass)) {
proxySuperClass = rootClass.getSuperclass();
Class<?>[] additionalInterfaces = rootClass.getInterfaces();
for (Class<?> additionalInterface : additionalInterfaces) {
this.advised.addInterface(additionalInterface);
}
}
// Validate the class, writing log messages as necessary.
validateClassIfNecessary(proxySuperClass, classLoader);
// 和之前讲到的CGLib一样，开始使用Enhancer 对象创建动态代理，有一点不一样就是CallBack是动态获取的，因为CallBack其实也就是MethodInterceptor，最终会执行MethodInterceptor的intercept方法
Enhancer enhancer = createEnhancer();
if (classLoader != null) {
enhancer.setClassLoader(classLoader);
if (classLoader instanceof SmartClassLoader &&
((SmartClassLoader) classLoader).isClassReloadable(proxySuperClass)) {
enhancer.setUseCache(false);
}
}
enhancer.setSuperclass(proxySuperClass);
enhancer.setInterfaces(AopProxyUtils.completeProxiedInterfaces(this.advised));
enhancer.setNamingPolicy(SpringNamingPolicy.INSTANCE);
enhancer.setStrategy(new ClassLoaderAwareUndeclaredThrowableStrategy(classLoader));
Callback[] callbacks = getCallbacks(rootClass);
Class<?>[] types = new Class<?>[callbacks.length];
for (int x = 0; x < types.length; x++) {
types[x] = callbacks[x].getClass();
}
// fixedInterceptorMap only populated at this point, after getCallbacks call above
enhancer.setCallbackFilter(new ProxyCallbackFilter(
this.advised.getConfigurationOnlyCopy(), this.fixedInterceptorMap, this.fixedInterceptorOffset));
enhancer.setCallbackTypes(types);
// Generate the proxy class and create a proxy instance.
return createProxyClassAndInstance(enhancer, callbacks);
}
catch (CodeGenerationException ex) {
throw new AopConfigException("Could not generate CGLIB subclass of class [" +
this.advised.getTargetClass() + "]: " +
"Common causes of this problem include using a final class or a non-visible class",
ex);
}
catch (IllegalArgumentException ex) {
throw new AopConfigException("Could not generate CGLIB subclass of class [" +
this.advised.getTargetClass() + "]: " +
"Common causes of this problem include using a final class or a non-visible class",
ex);
}
catch (Throwable ex) {
// TargetSource.getTarget() failed
throw new AopConfigException("Unexpected AOP exception", ex);
}
}
和之前讲到的CGLIB一样，使用Enhancer 对象创建动态代理，有一点不一样就是CallBack是动态获取的，因为CallBack其实也就是MethodInterceptor，最终会执行MethodInterceptor的intercept方法，看下获取callback的方法,在CglibAopProxy中有个getCallbacks：
private Callback[] getCallbacks(Class<?> rootClass) throws Exception {
// Parameters used for optimization choices...
boolean exposeProxy = this.advised.isExposeProxy();
boolean isFrozen = this.advised.isFrozen();
boolean isStatic = this.advised.getTargetSource().isStatic();
// Choose an "aop" interceptor (used for AOP calls).
Callback aopInterceptor = new DynamicAdvisedInterceptor(this.advised);
// Choose a "straight to target" interceptor. (used for calls that are
// unadvised but can return this). May be required to expose the proxy.
Callback targetInterceptor;
if (exposeProxy) {
targetInterceptor = isStatic ?
new StaticUnadvisedExposedInterceptor(this.advised.getTargetSource().getTarget()) :
new DynamicUnadvisedExposedInterceptor(this.advised.getTargetSource());
}
else {
targetInterceptor = isStatic ?
new StaticUnadvisedInterceptor(this.advised.getTargetSource().getTarget()) :
new DynamicUnadvisedInterceptor(this.advised.getTargetSource());
}
// Choose a "direct to target" dispatcher (used for
// unadvised calls to static targets that cannot return this).
Callback targetDispatcher = isStatic ?
new StaticDispatcher(this.advised.getTargetSource().getTarget()) : new SerializableNoOp();
Callback[] mainCallbacks = new Callback[] {
aopInterceptor, // for normal advice
targetInterceptor, // invoke target without considering advice, if optimized
new SerializableNoOp(), // no override for methods mapped to this
targetDispatcher, this.advisedDispatcher,
new EqualsInterceptor(this.advised),
new HashCodeInterceptor(this.advised)
};
Callback[] callbacks;
// If the target is a static one and the advice chain is frozen,
// then we can make some optimizations by sending the AOP calls
// direct to the target using the fixed chain for that method.
if (isStatic && isFrozen) {
Method[] methods = rootClass.getMethods();
Callback[] fixedCallbacks = new Callback[methods.length];
this.fixedInterceptorMap = new HashMap<String, Integer>(methods.length);
// TODO: small memory optimization here (can skip creation for methods with no advice)
for (int x = 0; x < methods.length; x++) {
List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(methods[x], rootClass);
fixedCallbacks[x] = new FixedChainStaticTargetInterceptor(
chain, this.advised.getTargetSource().getTarget(), this.advised.getTargetClass());
this.fixedInterceptorMap.put(methods[x].toString(), x);
}
// Now copy both the callbacks from mainCallbacks
// and fixedCallbacks into the callbacks array.
callbacks = new Callback[mainCallbacks.length + fixedCallbacks.length];
System.arraycopy(mainCallbacks, 0, callbacks, 0, mainCallbacks.length);
System.arraycopy(fixedCallbacks, 0, callbacks, mainCallbacks.length, fixedCallbacks.length);
this.fixedInterceptorOffset = mainCallbacks.length;
}
else {
callbacks = mainCallbacks;
}
return callbacks;
}最终要的就是 Callback aopInterceptor = new DynamicAdvisedInterceptor(this.advised);了，这个MethodInterceptor就是后续代理类会执行的方法，看下其intercept如下,其实也是根据上面添加的Advice，生成对应的拦截器，然后使用责任链模式，循环调用拦截器而已，就连最终创建的MethodInvocation，其实创建的CglibMethodInvocation也是继承自ReflectiveMethodInvocation（我们上篇文章spring aop 使用jdk动态代理就是用到这个对象）
@Override
public Object intercept(Object proxy, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {
Object oldProxy = null;
boolean setProxyContext = false;
Class<?> targetClass = null;
Object target = null;
try {
if (this.advised.exposeProxy) {
// Make invocation available if necessary.
oldProxy = AopContext.setCurrentProxy(proxy);
setProxyContext = true;
}
// May be null. Get as late as possible to minimize the time we
// "own" the target, in case it comes from a pool...
target = getTarget();
if (target != null) {
targetClass = target.getClass();
}
List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);
Object retVal;
// Check whether we only have one InvokerInterceptor: that is,
// no real advice, but just reflective invocation of the target.
if (chain.isEmpty() && Modifier.isPublic(method.getModifiers())) {
// We can skip creating a MethodInvocation: just invoke the target directly.
// Note that the final invoker must be an InvokerInterceptor, so we know
// it does nothing but a reflective operation on the target, and no hot
// swapping or fancy proxying.
Object[] argsToUse = AopProxyUtils.adaptArgumentsIfNecessary(method, args);
retVal = methodProxy.invoke(target, argsToUse);
}
else {
// We need to create a method invocation...
retVal = new CglibMethodInvocation(proxy, target, method, args, targetClass, chain, methodProxy).proceed();
}
retVal = processReturnType(proxy, target, method, retVal);
return retVal;
}
finally {
if (target != null) {
releaseTarget(target);
}
if (setProxyContext) {
// Restore old proxy.
AopContext.setCurrentProxy(oldProxy);
}
}
}总结
Spring AOP 不论选择使用JDK动态代理还是使用CGLIB做动态代理，最终都是根据我们之前添加的通知（Advice），来创建拦截器，然后根据连接器集合创建MethodInvocation，最终按照责任链模式，执行所有拦截器
