Spring AOP的实现原理（三）
本文共 15690 字，大约阅读时间需要 52 分钟。
生成SingleTon代理对象在getSingleTonInstance方法中完成，这个方法时ProxyFactoryBean生成AopProxy对象的入口。代理对象会封装对target目标对象的调用，也就是说针对target对象的方法调用行为会被这里生成的代理对象所拦截。具体的生成过程是首先读取ProxyFactoryBean配置，为生成代理对象做好准备。Spring通过AopProxy类来具体生成代理对象。对于getSingleTonInstance方法中生成代理对象的过程如下：
/** * Return the singleton instance of this class's proxy object, * lazily creating it if it hasn't been created already. * @return the shared singleton proxy */ private synchronized Object getSingletonInstance() { if (this.singletonInstance == null) { this.targetSource = freshTargetSource(); if (this.autodetectInterfaces && getProxiedInterfaces().length == 0 && !isProxyTargetClass()) { // Rely on AOP infrastructure to tell us what interfaces to proxy. // 根据AOP框架来判断需要代理的接口 Class targetClass = getTargetClass(); if (targetClass == null) { throw new FactoryBeanNotInitializedException("Cannot determine target class for proxy"); } // 这里设置代理对象的接口 setInterfaces(ClassUtils.getAllInterfacesForClass(targetClass, this.proxyClassLoader)); } // Initialize the shared singleton instance. super.setFrozen(this.freezeProxy); // 这里会使用ProxyFactoryBean来生成需要的proxy对象 this.singletonInstance = getProxy(createAopProxy()); } return this.singletonInstance; } - 1
- 2
- 3
- 4
- 5
- 6
- 7
- 8
- 9
- 10
- 11
- 12
- 13
- 14
- 15
- 16
- 17
- 18
- 19
- 20
- 21
- 22
- 23
- 24
- 25
/** * Return the proxy object to expose. *The default implementation uses a {@code getProxy} call with * the factory's bean class loader. Can be overridden to specify a * custom class loader. * @param aopProxy the prepared AopProxy instance to get the proxy from * @return the proxy object to expose * @see AopProxy#getProxy(ClassLoader) */ protected Object getProxy(AopProxy aopProxy) { return aopProxy.getProxy(this.proxyClassLoader); }
- 1
- 2
- 3
- 4
- 5
- 6
- 7
- 8
- 9
- 10
- 11
- 12
这里出现了AopProxy对象类型，Spring利用AOPProxy接口类把AOP代理对象的实现与框架其他部分有效隔离开来。AopProxy接口有两个子类实现，一个Cglib2AopProxy，另一个是JdkDynamicProxy。
具体代理对象的生成是在ProxyFactoryBean的基类AdvisedSupport中实现，借助AopProxyFactory完成，这个对象要么从JDK中生成，要么借助CGLIB获得。下面看看ProxyCreatorSupport中是如何生成代理对象的。/** * Subclasses should call this to get a new AOP proxy. They should not * create an AOP proxy with {@code this} as an argument. */ protected final synchronized AopProxy createAopProxy() { if (!this.active) { activate(); } // 通过AopProxyFactory取得AopProxy，这个AopProxyFactory是在初始化函数中定义的，使用的是DefaultAopProxyFactory return getAopProxyFactory().createAopProxy(this); } - 1
- 2
- 3
- 4
- 5
- 6
- 7
- 8
- 9
- 10
- 11
AopProxy代理对象的生成有两种方式，如果目标对象是接口类使用JDK来生成，否则Spring会使用CGLIB来生成目标的代理对象。下面看看在DefaultAopProxyFactory是如何生成AopProxy目标代理对象的：
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); } return CglibProxyFactory.createCglibProxy(config); } else { return new JdkDynamicAopProxy(config); } } - 1
- 2
- 3
- 4
- 5
- 6
- 7
- 8
- 9
- 10
- 11
- 12
- 13
- 14
- 15
- 16
在AopProxy代理对象的生成过程中，首先要从AdviseSupport对象中取得配置的目标对象，AOP完成的是切面应用对目标应用对象的增强。如果这里没有配置目标对象会直接抛出异常。一般而言，默认方式是使用JDK来产生AopProxy代理对象，但如果配置的目标对象不是接口类的实现，会使用CGLIB来产生AopProxy代理对象；在使用CGLIB来产生AopProxy代理对象时，因为CGLIB是第三方类库，本身不在JDK基类库中，所有需要在classPath中正确配置，以便能够加载和利用。在Spring中，使用JDK和CGLIB来生成AopProxy代理对象的工作，是由JdkDynamicAopProxy和CglibProxyFactory来完成。
4、JDK生成AopProxy对象（接口实现类） 通过上面我们已经知道生成AopProxy对象有两种方式，下面看下类图：
我们先看下JdkDynamicAopProxy是如何生成AopProxy对象的： public Object getProxy(ClassLoader classLoader) { if (logger.isDebugEnabled()) { logger.debug("Creating JDK dynamic proxy: target source is " + this.advised.getTargetSource()); } Class [] proxiedInterfaces = AopProxyUtils.completeProxiedInterfaces(this.advised); findDefinedEqualsAndHashCodeMethods(proxiedInterfaces); // 调用JDK生成Proxy return Proxy.newProxyInstance(classLoader, proxiedInterfaces, this); } - 1
- 2
- 3
- 4
- 5
- 6
- 7
- 8
- 9
5、CGLIB生成AopProxy对象（非接口实现类）
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); // Configure CGLIB Enhancer... // 来自advised的IOC配置，比如使用AOP的DynamicAdvisedInterceptor 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 MemorySafeUndeclaredThrowableStrategy(UndeclaredThrowableException.class)); enhancer.setInterceptDuringConstruction(false); // 通过设置DynamicAdvisedInterceptor拦截器来完成AOP功能，getCallBacks方法如下： // Callback aopInterceptor = new DynamicAdvisedInterceptor(this.advised) Callback[] callbacks = getCallbacks(rootClass); Class [] types = new Class [callbacks.length]; for (int x = 0; x < types.length; x++) { types[x] = callbacks[x].getClass(); } enhancer.setCallbackFilter(new ProxyCallbackFilter( this.advised.getConfigurationOnlyCopy(), this.fixedInterceptorMap, this.fixedInterceptorOffset)); enhancer.setCallbackTypes(types); enhancer.setCallbacks(callbacks); // Generate the proxy class and create a proxy instance. Object proxy; if (this.constructorArgs != null) { proxy = enhancer.create(this.constructorArgTypes, this.constructorArgs); } else { proxy = enhancer.create(); } return proxy; } 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 (Exception ex) { // TargetSource.getTarget() failed throw new AopConfigException("Unexpected AOP exception", ex); } } - 1
- 2
- 3
- 4
- 5
- 6
- 7
- 8
- 9
- 10
- 11
- 12
- 13
- 14
- 15
- 16
- 17
- 18
- 19
- 20
- 21
- 22
- 23
- 24
- 25
- 26
- 27
- 28
- 29
- 30
- 31
- 32
- 33
- 34
- 35
- 36
- 37
- 38
- 39
- 40
- 41
- 42
- 43
- 44
- 45
- 46
- 47
- 48
- 49
- 50
- 51
- 52
- 53
- 54
- 55
- 56
- 57
- 58
- 59
- 60
- 61
- 62
- 63
- 64
- 65
- 66
- 67
- 68
- 69
- 70
四、Spring AOP拦截器调用的实现 1、设计原理
在Spring AOP通过JDK的Proxy方式或CGLIB方式生成代理对象的时候，相关的拦截器已经配置到代理对象中去了，拦截器在代理对象中起作用是通过对这些方法的回调来完成的。 如果使用JDK的Proxy来生成代理对象，那么需要InvocationHandler来设置拦截器回调，而如果使用CGLIB来生成代理对象，通过DynamicAdvisedInterceptor来完成回调。 2、JdkDynamicAopProxy的invoke拦截 在JDKDynamicAopProxy生成代理对象时，他的AopProxy代理对象生成调用：Proxy.newProxyInstance(classLoader, proxiedInterfaces, this);
- 1
this指的是InvocationHandler对象，InvocationHandler是JDK定义反射类的一个接口，这个接口定义了invoke方法，此方法为回调方法。通过invoke的具体实现，来完成对目标对象方法调用的拦截器或者功能增强工作。在这个方法中，包含一个完整的拦截器链对目标对象的拦截过程，比如获取拦截器链中的拦截器进行配置，逐个运行拦截器链里的拦截器增强，知道最后的目标对象方法的运行。下面看下invoke的源码
/** * Implementation of {@code InvocationHandler.invoke}. * Callers will see exactly the exception thrown by the target, * unless a hook method throws an exception. */ public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { MethodInvocation invocation; Object oldProxy = null; boolean setProxyContext = false; TargetSource targetSource = this.advised.targetSource; Class
targetClass = null; Object target = null; try { if (!this.equalsDefined && AopUtils.isEqualsMethod(method)) { // The target does not implement the equals(Object) method itself. return equals(args[0]); } if (!this.hashCodeDefined && AopUtils.isHashCodeMethod(method)) { // The target does not implement the hashCode() method itself. return hashCode(); } if (!this.advised.opaque && method.getDeclaringClass().isInterface() && method.getDeclaringClass().isAssignableFrom(Advised.class)) { // Service invocations on ProxyConfig with the proxy config... return AopUtils.invokeJoinpointUsingReflection(this.advised, method, args); } Object retVal; 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 = targetSource.getTarget(); if (target != null) { targetClass = target.getClass(); } // Get the interception chain for this method. // 获得定义好的拦截器 List - 1
- 2
- 3
- 4
- 5
- 6
- 7
- 8
- 9
- 10
- 11
- 12
- 13
- 14
- 15
- 16
- 17
- 18
- 19
- 20
- 21
- 22
- 23
- 24
- 25
- 26
- 27
- 28
- 29
- 30
- 31
- 32
- 33
- 34
- 35
- 36
- 37
- 38
- 39
- 40
- 41
- 42
- 43
- 44
- 45
- 46
- 47
- 48
- 49
- 50
- 51
- 52
- 53
- 54
- 55
- 56
- 57
- 58
- 59
- 60
- 61
- 62
- 63
- 64
- 65
- 66
- 67
- 68
- 69
- 70
- 71
- 72
- 73
- 74
- 75
- 76
- 77
- 78
- 79
- 80
- 81
3、CglibAopProxy的intercept拦截器
使用CglibAopProxy生成AopProxy对象时候，对于AOP拦截器调用，回调的是DynamicAdvisedInterceptor对象生成的。回调的方法时intercept，下面看看回调方法的源码：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
你可能感兴趣的文章
博客文格式优化
查看>>
【托业】【新托业全真模拟】疑难语法题知识点总结（01~05）
查看>>
【SQL】group by 和order by 的区别。
查看>>
【F12】谷歌浏览器--前台效果可以在不访问服务器的前提下直接改样式看效果是否是预期值。...
查看>>
【Python】详解Python多线程Selenium跨浏览器测试
查看>>
Jmeter之参数化
查看>>
Shell 和Python的区别。
查看>>
Python 列表(list)、字典(dict)、字符串(string)常用基本操作小结
查看>>
Loadrunner之https协议录制回放报错如何解决？（九）
查看>>
python中xrange和range的异同
查看>>
列表、元组、集合、字典
查看>>
【Python】easygui小甲鱼
查看>>
【Python】关于Python多线程的一篇文章转载
查看>>
【Pyton】【小甲鱼】文件
查看>>
【Pyton】【小甲鱼】永久存储：腌制一缸美味的泡菜
查看>>
【Pyton】【小甲鱼】异常处理：你不可能总是对的
查看>>
APP性能测试工具
查看>>
【Pyton】【小甲鱼】类和对象
查看>>
压力测试工具JMeter入门教程
查看>>
作为一名软件测试工程师，需要具备哪些能力
查看>>