美学原理Spring AOP –JDK动态代理方

咱俩领悟Spring是通过JDK或者CGLib实现动态代理的,前天我们商量一下JDK实现动态代理的规律。

一、简述

Spring在解析Bean的定义之后会拿Bean的定义生成一个BeanDefinition对象又鉴于BeanDefinitionHolder对象拥有。在是历程遭到,假诺Bean需要给通切入,BeanDefinition会叫再一次换成一个proxyDefinition(其实为是一个BeanDefinition对象,只然则描述的是一个ProxyFactoryBean)。ProxyFactoryBean是一个实现了FactoryBean的接口,用来扭转于受切入的目的。Spring
AOP的贯彻多是通过ProxyFactoryBean实现之。大家前几天议论的紧要为是是近乎。
  于谈论ProxyFactoryBean在此之前,我们事先看一下一个BeanDefinition转换成proxyDefintion的经过。

public final BeanDefinitionHolder decorate(Node node, BeanDefinitionHolder definitionHolder, ParserContext parserContext) {
        BeanDefinitionRegistry registry = parserContext.getRegistry();

        // get the root bean name - will be the name of the generated proxy factory bean
        String existingBeanName = definitionHolder.getBeanName();
        BeanDefinition targetDefinition = definitionHolder.getBeanDefinition();
        BeanDefinitionHolder targetHolder = new BeanDefinitionHolder(targetDefinition, existingBeanName + ".TARGET");

        // delegate to subclass for interceptor definition
        BeanDefinition interceptorDefinition = createInterceptorDefinition(node);

        // generate name and register the interceptor
        String interceptorName = existingBeanName + "." + getInterceptorNameSuffix(interceptorDefinition);
        BeanDefinitionReaderUtils.registerBeanDefinition(
                new BeanDefinitionHolder(interceptorDefinition, interceptorName), registry);

        BeanDefinitionHolder result = definitionHolder;

        if (!isProxyFactoryBeanDefinition(targetDefinition)) {
            // create the proxy definition 这里创建proxyDefinition对象,并且从原来的BeanDefinition对象中复制属性
            RootBeanDefinition proxyDefinition = new RootBeanDefinition();
            // create proxy factory bean definition
            proxyDefinition.setBeanClass(ProxyFactoryBean.class);
            proxyDefinition.setScope(targetDefinition.getScope());
            proxyDefinition.setLazyInit(targetDefinition.isLazyInit());
            // set the target
            proxyDefinition.setDecoratedDefinition(targetHolder);
            proxyDefinition.getPropertyValues().add("target", targetHolder);
            // create the interceptor names list
            proxyDefinition.getPropertyValues().add("interceptorNames", new ManagedList<String>());
            // copy autowire settings from original bean definition.
            proxyDefinition.setAutowireCandidate(targetDefinition.isAutowireCandidate());
            proxyDefinition.setPrimary(targetDefinition.isPrimary());
            if (targetDefinition instanceof AbstractBeanDefinition) {
                proxyDefinition.copyQualifiersFrom((AbstractBeanDefinition) targetDefinition);
            }
            // wrap it in a BeanDefinitionHolder with bean name
            result = new BeanDefinitionHolder(proxyDefinition, existingBeanName);
        }

        addInterceptorNameToList(interceptorName, result.getBeanDefinition());
        return result;
    }

二、ProxyFactoryBean的原理
咱俩事先来拘禁一下ProxyFactoryBean的继续关系:

ProxyFactoryBean类图

ProxyFactoryBean实现了FactoryBean、BeanClassLoaderAware、BeanFactoryAware接口,那里就不多说了。ProxyCreatorSupport这多少个仿佛则是成立代理对象的关键所在。  我们先行来看望暴发代理对象的法:

public Object getObject() throws BeansException {
        initializeAdvisorChain();
        if (isSingleton()) {
                        //单例
            return getSingletonInstance();
        }
        else {
            if (this.targetName == null) {
                logger.warn("Using non-singleton proxies with singleton targets is often undesirable. " +

                        "Enable prototype proxies by setting the 'targetName' property.");
            }
                        //非单例
            return newPrototypeInstance();
        }
    }

initializeAdvisorChain()方法是将通告链实例化。然后判断目的是否要杀成单例而挑选调用不同的模式,这里我们才看生成单例对象的方法。

private synchronized Object getSingletonInstance() {
        if (this.singletonInstance == null) {
            this.targetSource = freshTargetSource();
                        //如果以接口的方式代理对象
            if (this.autodetectInterfaces && getProxiedInterfaces().length == 0 && !isProxyTargetClass()) {
                // Rely on AOP infrastructure to tell us what interfaces to proxy.
                Class<?> targetClass = getTargetClass();
                if (targetClass == null) {
                    throw new FactoryBeanNotInitializedException("Cannot determine target class for proxy");
                }
                      //获取目标类实现的所有接口,并注册给父类的interfaces属性,为jdk动态代理做准备
                setInterfaces(ClassUtils.getAllInterfacesForClass(targetClass, this.proxyClassLoader));
            }
            // Initialize the shared singleton instance.
            super.setFrozen(this.freezeProxy);
                   //这里产生代理对象
            this.singletonInstance = getProxy(createAopProxy());
        }
        return this.singletonInstance;
    }

俺们雅观看,发生代理对象是因而getProxy()方法实现的,这些办法大家看一下:

protected Object getProxy(AopProxy aopProxy) {
        return aopProxy.getProxy(this.proxyClassLoader);
    }

AopProxy对象的getProxy()方法暴发我们需要的代理对象,究竟AopProxy那多少个类似是呀,大家连下先押一下暴发这目的的格局createAopProxy():

protected final synchronized AopProxy createAopProxy() {
        if (!this.active) {
            activate();
        }
        return getAopProxyFactory().createAopProxy(this);
    }

createAopProxy方法:
    public AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException {
                //目标对象不是接口类的实现或者没有提供代理接口
        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.");
            }  
            //代理对象自身是接口
            if (targetClass.isInterface()) {
                return new JdkDynamicAopProxy(config);
            }
            return new ObjenesisCglibAopProxy(config);
        }
        else {
            return new JdkDynamicAopProxy(config);
        }
    }

以此间大家无非看JdkDynamicAopProxy这些类似的贯彻,大家眼前提到,真正代理对象的转是由于AopProxy的getProxy方法成功的,这里大家看一下JdkDynamicAopProxy的getProxy方法,这也是本文探究的要:

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);
        return Proxy.newProxyInstance(classLoader, proxiedInterfaces, this);
    }

咱看可以老懂的观,代理对象的变动间接以了jdk动态代理:Proxy.newProxyInstance(classLoader, proxiedInterfaces, this);要是代理逻辑是因而兑现了InvocationHandler接口的invoke方法实现的。而此运用的落实了InvocationHandler接口的类似即是JdkDynamicAopProxy自身。JdkDynamicAopProxy自身实现了InvocationHandler接口,完成了Spring
AOP拦截器链拦截等一律文山会海逻辑,大家看一下JdkDynamicAopProxy的invoke方法的现实贯彻:

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 {
            //没有重写equals方法
            if (!this.equalsDefined && AopUtils.isEqualsMethod(method)) {
                // The target does not implement the equals(Object) method itself.
                return equals(args[0]);
            }
            //没有重写hashCode方法
            if (!this.hashCodeDefined && AopUtils.isHashCodeMethod(method)) {
                // The target does not implement the hashCode() method itself.
                return hashCode();
            }
          //代理的类是Advised,这里直接执行,不做任何代理
            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.
            //获得代理对象
            target = targetSource.getTarget();
            if (target != null) {
                targetClass = target.getClass();
            }

            // Get the interception chain for this method.
            //获得已经定义的拦截器链
            List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);

            // Check whether we have any advice. If we don't, we can fallback on direct
            // reflective invocation of the target, and avoid creating a MethodInvocation.
            if (chain.isEmpty()) {
                // 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.
                //拦截器链是空的,直接执行需要代理的方法
                retVal = AopUtils.invokeJoinpointUsingReflection(target, method, args);
            }
            else {
                // We need to create a method invocation...
                //这里是调用拦截器链的地方,先创建一个MethodInvocation对象,然后调用该对象的proceed方法完成拦截器链调用
                invocation = new ReflectiveMethodInvocation(proxy, target, method, args, targetClass, chain);
                // Proceed to the joinpoint through the interceptor chain.
                retVal = invocation.proceed();
            }

            // Massage return value if necessary.
            Class<?> returnType = method.getReturnType();
            //这里处理返回值,判断返回值和方法需要的返回是否一致
            if (retVal != null && retVal == target && returnType.isInstance(proxy) &&
                    !RawTargetAccess.class.isAssignableFrom(method.getDeclaringClass())) {
                // Special case: it returned "this" and the return type of the method
                // is type-compatible. Note that we can't help if the target sets
                // a reference to itself in another returned object.
                retVal = proxy;
            } else if (retVal == null && returnType != Void.TYPE && returnType.isPrimitive()) {
                throw new AopInvocationException("Null return value from advice does not match primitive return type for: " + method);
            }
            return retVal;
        }
        finally {
            if (target != null && !targetSource.isStatic()) {
                // Must have come from TargetSource.
                targetSource.releaseTarget(target);
            }
            if (setProxyContext) {
                // Restore old proxy.
                AopContext.setCurrentProxy(oldProxy);
            }
        }
    }

掣肘器链的调用

自从下边的代码和注释中我们得以视spring实现aop的最紧要流程,具体什么调用拦截器链,我们来拘禁一下MethodInvocation的proceed方法

public Object proceed() throws Throwable {
        //  We start with an index of -1 and increment early.
        //   currentInterceptorIndex是从-1开始的,所以拦截器链调用结束的时候index是 this.interceptorsAndDynamicMethodMatchers.size() - 1
        //  调用链结束后执行目标方法
        if (this.currentInterceptorIndex == this.interceptorsAndDynamicMethodMatchers.size() - 1) {
            return invokeJoinpoint();
        }
        //  获得当前处理到的拦截器
        Object interceptorOrInterceptionAdvice =
                this.interceptorsAndDynamicMethodMatchers.get(++this.currentInterceptorIndex);
        //  这里判断是否是InterceptorAndDynamicMethodMatcher,如果是,这要判断是否匹配methodMatcher,不匹配则此拦截器不生效
        if (interceptorOrInterceptionAdvice instanceof InterceptorAndDynamicMethodMatcher) {
            // Evaluate dynamic method matcher here: static part will already have
            // been evaluated and found to match.
            InterceptorAndDynamicMethodMatcher dm =
                    (InterceptorAndDynamicMethodMatcher) interceptorOrInterceptionAdvice;
            if (dm.methodMatcher.matches(this.method, this.targetClass, this.arguments)) {
                return dm.interceptor.invoke(this);
            }
            else {
                // Dynamic matching failed.
                // Skip this interceptor and invoke the next in the chain.
                return proceed();
            }
        }
        else {
            // It's an interceptor, so we just invoke it: The pointcut will have
            // been evaluated statically before this object was constructed.
            return ((MethodInterceptor) interceptorOrInterceptionAdvice).invoke(this);
        }
    }

proceed()方法是一个递归方法,我们可依照代码的声明知道大致逻辑,InterceptorAndDynamicMethodMatcher的代码如下,我们得以视,InterceptorAndDynamicMethodMatcher
持有一个MethodInterceptor 对象与一个MethodMatcher
对象,在阻止器链调用过程中,即使拦截器是InterceptorAndDynamicMethodMatcher
,则会优先依据MethodMatcher 判断是否配合,匹配MethodInterceptor 才会生效。

class InterceptorAndDynamicMethodMatcher {

    final MethodInterceptor interceptor;

    final MethodMatcher methodMatcher;

    public InterceptorAndDynamicMethodMatcher(MethodInterceptor interceptor, MethodMatcher methodMatcher) {
        this.interceptor = interceptor;
        this.methodMatcher = methodMatcher;
    }

}

关于MethodInterceptor 是什么,MethodInterceptor
的逻辑是怎么样的,大家可以拘留一下MethodInterceptor
的一个子类AfterReturningAdviceInterceptor的兑现:

public class AfterReturningAdviceInterceptor implements MethodInterceptor, AfterAdvice, Serializable {    private final AfterReturningAdvice advice;    /**     * Create a new AfterReturningAdviceInterceptor for the given advice.     * @param advice the AfterReturningAdvice to wrap     */    public AfterReturningAdviceInterceptor(AfterReturningAdvice advice) {        Assert.notNull(advice, "Advice must not be null");        this.advice = advice;    }    @Override    public Object invoke(MethodInvocation mi) throws Throwable {        Object retVal = mi.proceed();        this.advice.afterReturning(retVal, mi.getMethod(), mi.getArguments(), mi.getThis());        return retVal;    }}

AfterReturningAdviceInterceptor的打算是在吃摄的计再次来到结果以后上加我们用的拍卖逻辑,其促成格局大家得看来,先调用MethodInvocation
的proceed,也就是是事先连续处理拦截器链,等调用完成后执行我们要的逻辑:this.advice.afterReturning(retVal, mi.getMethod(), mi.getArguments(), mi.getThis());
暨此处,spring使用jdk动态代理实现aop的剖析多截止,其中拦截器链的调用比较难知晓而且于首要,需要的同班可以多看就同块。
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