Spring源码分析 AOP设计实现过程

Spring源码分析 AOP设计实现过程

设计理念

将分散在程序各处的横切关注点剥离出来，并已集中的方式进行表达 AOP和继承有些类似，前者重点考虑程序横切逻辑，后者重点考虑纵向职责分派

AOP核心概念

Advice（通知） -定义在连接点处的行为，围绕方法调用而进行注入

-Pointcut（切点） -确定在哪些连接点处应用通知

Advisor()通知器 -组合Advice与Pointcut

AOP 代理

未使用代理如下

已使用代理如下

如图所示

AOP代理可以 执行目标对象之前后都可以先执行指定好的通知器（切点和通知）

SpringAOP目标代理对象创建如下

JDK动态代理 （代理接口）CGLIB（代理实现类）

AOP代理源码分析

public class ProxyFactoryBean extends ProxyCreatorSupport implements FactoryBean, BeanClassLoaderAware, BeanFactoryAware public Object getObject() throws BeansException { //步骤1 initializeAdvisorChain(); //步骤2 if (isSingleton()) return getSingletonInstance(); if (targetName == null) logger.warn("Using non-singleton proxies with singleton targets is often undesirable. Enable prototype proxies by setting the 'targetName' property."); return newPrototypeInstance(); } }

ProxyFactoryBean是springAop底层实现源头，构建其AOP代理 如上 步骤1 配置通知事件会调用getObject()方法，initializeAdvisorChain（）会把配置的Adviser通知器方法加载到集合中，以便后续目标方法执行前后去集合中匹配，根据每个Adviser的pointcut去执行 步骤2 根据配置的 scope属性，默认是single

紧接着分析 getSingletonInstance()方法获取代理对象

private synchronized Object getSingletonInstance() { if (singletonInstance == null) { targetSource = freshTargetSource(); if (autodetectInterfaces && getProxiedInterfaces().length == 0 && !isProxyTargetClass()) { Class targetClass = getTargetClass(); if (targetClass == null) throw new FactoryBeanNotInitializedException( "Cannot determine target class for proxy"); //1 setInterfaces(ClassUtils.getAllInterfacesForClass(targetClass, proxyClassLoader)); } super.setFrozen(freezeProxy); //2 singletonInstance = getProxy(createAopProxy()); } return singletonInstance; } public interface AopProxy { public abstract Object getProxy(); public abstract Object getProxy(ClassLoader classloader); }

如上 //1 表示创建出来代理对象要实现代理接口 //2 通过工厂代理创建AopProxy接口，调用其getProxy,生成代理实例

AOP选择动态代理和CGLIB 源码如下

public class DefaultAopProxyFactory implements AopProxyFactory, Serializable { public AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException { if (config.isOptimize() || config.isProxyTargetClass() || hasNoUserSuppliedProxyInterfaces(config)) { Class targetClass = config.getTargetClass(); if (targetClass == null) throw new AopConfigException( "TargetSource cannot determine target class: Either an interface or a target is required for proxy creation."); if (targetClass.isInterface()) return new JdkDynamicAopProxy(config); else return CglibProxyFactory.createCglibProxy(config); } else { return new JdkDynamicAopProxy(config); } } |

源码分析

如果目标对象实现了接口，那么Spring就会通过动态代理为目标对象生成代理对象，否则通过CGLIB代理 代理模式作用是：为其它对象提供一种代理以控制对这个对象的访问

接着分析JDK动态代理源码如下

final class JdkDynamicAopProxy implements AopProxy, InvocationHandler, Serializable { public Object getProxy(ClassLoader classLoader) { if (logger.isDebugEnabled()) logger.debug((new StringBuilder()) .append("Creating JDK dynamic proxy: target source is ") .append(advised.getTargetSource()).toString()); Class proxiedInterfaces[] = AopProxyUtils .completeProxiedInterfaces(advised); findDefinedEqualsAndHashCodeMethods(proxiedInterfaces); //rs Proxy return Proxy.newProxyInstance(classLoader, proxiedInterfaces, this); } } public interface InvocationHandler extends Callback { public abstract Object invoke(Object obj, Method method, Object aobj[]) throws Throwable; }

通过其源码发现 如上rs Proxy真正使用JDK动态代理获得代理实例，代理类需要继承InvocationHandler接口， InvocationHandler内部只有一个抽象方法invoke（参数1指代理类，参数2指代理方法，参数3指方法参数值） Proxy.newProxyInstance(参数1 类加载器，参数2 动态代理对象实现了接口，参数3 指InvocationHandler 实例通过反射生成对象的实例) 由此可得 JDK动态代理 实现步骤 1.创建一个实现接口InvocationHandler的类吗，它必须实现invoke方法 2.创建被代理类以及接口 3.通过proxy的静态方法创建代理 4.通过代理调用方法

CGLIB 源码如下

final class CglibAopProxy implements AopProxy, Serializable { public Object getProxy(ClassLoader classLoader) { if (logger.isDebugEnabled()) logger.debug((new StringBuilder()) .append("Creating CGLIB proxy: target source is ") .append(advised.getTargetSource()).toString()); try { Class rootClass = 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(); Class arr$[] = additionalInterfaces; int len$ = arr$.length; for (int i$ = 0; i$ < len$; i$++) { Class additionalInterface = arr$[i$]; advised.addInterface(additionalInterface); } } validateClassIfNecessary(proxySuperClass); Enhancer enhancer = createEnhancer(); if (classLoader != null) { enhancer.setClassLoader(classLoader); if ((classLoader instanceof SmartClassLoader) && ((SmartClassLoader) classLoader) .isClassReloadable(proxySuperClass)) enhancer.setUseCache(false); } enhancer.setSuperclass(proxySuperClass); enhancer.setStrategy(new UndeclaredThrowableStrategy(java / lang / reflect / UndeclaredThrowableException)); enhancer.setInterfaces(AopProxyUtils .completeProxiedInterfaces(advised)); enhancer.setInterceptDuringConstruction(false); Callback callbacks[] = getCallbacks(rootClass); enhancer.setCallbacks(callbacks); enhancer.setCallbackFilter(new ProxyCallbackFilter(advised .getConfigurationOnlyCopy(), fixedInterceptorMap, fixedInterceptorOffset)); Class types[] = new Class[callbacks.length]; for (int x = 0; x < types.length; x++) types[x] = callbacks[x].getClass(); enhancer.setCallbackTypes(types); Object proxy; //结果 if (constructorArgs != null) proxy = enhancer.create(constructorArgTypes, constructorArgs); else proxy = enhancer.create(); return proxy; } catch (CodeGenerationException ex) { throw new AopConfigException( (new StringBuilder()) .append("Could not generate CGLIB subclass of class [") .append(advised.getTargetClass()) .append("]: ") .append("Common causes of this problem include using a final class or a non-visible class") .toString(), ex); } catch (IllegalArgumentException ex) { throw new AopConfigException( (new StringBuilder()) .append("Could not generate CGLIB subclass of class [") .append(advised.getTargetClass()) .append("]: ") .append("Common causes of this problem include using a final class or a non-visible class") .toString(), ex); } catch (Exception ex) { throw new AopConfigException("Unexpected AOP exception", ex); } } }

如上结果 通过 Enhancer.create生成代理实例，其通过Enhancer 字节码类构建类的接口、类型、类回调等参数 最终会的代理实例对象

总结：

本篇文章主要阐述 AOP拦截触发器执行过程、AOP代理实现的两种方式

作者简介：张程 技术研究

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