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  • SpringAOP[4]代理工厂

    序：代理对象的创建

    无论是AspecJProxyFactory、ProxyFactoryBean、ProxyFactory大体逻辑都是：

    1. 填充ProxyCreatorSupport，实际上它是Advised子类，即填充代理配置类（添加Advisor、添加Advice）
    2. 得到JDK或者CGLIB的AopProxy；
    3. Proxy Bean被调用时，被invoke或intercept方法拦截，并且会调用ProxyCreatorSupport（AdvisedSupport）的getInterceptorsAndDynamicInterceptionAdvice方法去初始化advice和各个方法上的拦截器链并缓存。

    上述三个类本身并没有什么关系，但是都继承自ProxyCreatorSupport，创建代理对象的核心就是在ProxyCreatorSupport中实现的。

    一、通过ProxyFactoryBean配置

    FactoryBean目的是构建复杂的Bean对象，而ProxyFactoryBean的getObject()最终产生的便是Proxy Bean。

    配置类：

    @Configuration
public class MyConfig {
    @Bean
    public LogMethodBeforeAdvice logMethodBeforeAdvice() {
        return new LogMethodBeforeAdvice();
    }

    @Bean("tService")
    public TService tService() {
        return new TService();
    }

    @Bean("proxyFactoryBean")
    public ProxyFactoryBean proxyFactoryBean(TService tService) {
        ProxyFactoryBean proxyFactoryBean = new ProxyFactoryBean();
        //代理的目标对象，效果等效于setTargetSource()
        proxyFactoryBean.setTarget(tService);
        //设置`String[] interceptorNames`，以便后续初始化"拦截器链"。
        proxyFactoryBean.setInterceptorNames("logMethodBeforeAdvice");
        return proxyFactoryBean;
    }
}

    拦截器类：

    public class LogMethodBeforeAdvice implements MethodBeforeAdvice {
    @Override
    public void before(Method method, Object[] args, Object target) throws Throwable {
        System.out.println("this is logMethodBeforeAdvice!");
    }
}

    目标类：

    public class TService {
    public void run1(){
        System.out.println("This is a run1() Method!");
    }
}

    测试类：

    public class TestProxy {
    public static void main(String[] args) {
        AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(MyConfig.class);
        //可以使用@Primary指定元素，或直接使用name名获取。
        //Exception in thread "main" org.springframework.beans.factory.NoUniqueBeanDefinitionException:
        // No qualifying bean of type 'com.tellme.Impl.proxy.TService' available:
        // expected single matching bean but found 2: tService,proxyFactoryBean。（或生成两个Bean名字）
        //TService bean = applicationContext.getBean(TService.class);
        //若使用Class获取Bean，会获取到两个Bean对象。
        TService bean = (TService)applicationContext.getBean("proxyFactoryBean");
        bean.run1();
        System.out.println(bean.getClass());
    }
}

    结果：

    this is logMethodBeforeAdvice!
This is a run1() Method!
class com.tellme.Impl.proxy.TService$$EnhancerBySpringCGLIB$$6ac1bfc1

     

    如测试案例所示，构建ProxyFactoryBean的过程实际上是完成的是代理配置。即填充Advised对象。而Advised对象实际上是由多个Advisor组成。

    而ProxyFactoryBean便是借助于控制反转，只是传入Interceptors类名便完成拦截对象的填充。

    ProxyFactoryBean实际上实现的是FactoryBean接口，那么产生的Bean是getObject方法返回的。而getObject便完成代理对象的创建过程。


    1.1 初始化AdvisorChain

    代理对象的创建，首先要创建配置对象，即实现Advised接口，Spring实现了该接口。我们最终通过ProxyCreatorSupport提供的API便可以完成配置

     配置Advised，实际上执行的是initializeAdvisorChain()。

    1. 在IOC容器中通过BeanName获取到Advice对象，（当然这种情况属于单例，而Spring作为一个框架，实际上会考虑原型模式以及通配符的情况）。
    2. 借助AdvisorAdapterRegistry将Advice转换为Advisor（当然pointcut是Pointcut.TRUE，拦截所有的方法）。
    3. 将Advisor加入到AdvicedSupport维护的列表中。该代理对象会持有所有的Advisor。
    public class ProxyFactoryBean extends ProxyCreatorSupport
        implements FactoryBean<Object>, BeanClassLoaderAware, BeanFactoryAware {

    /** Whether the advisor chain has already been initialized. */
    private boolean advisorChainInitialized = false;

    //（步骤1：获取代理对象）
    @Override
    @Nullable
    public Object getObject() throws BeansException {
        //初始化AdvisorChain。
        initializeAdvisorChain();
        if (isSingleton()) {
            return getSingletonInstance();
        }
        else {
            if (this.targetName == null) {
                logger.info("Using non-singleton proxies with singleton targets is often undesirable. " +
                        "Enable prototype proxies by setting the 'targetName' property.");
            }
            return newPrototypeInstance();
        }
    }
    //（步骤2：初始化过滤器链）
    private synchronized void initializeAdvisorChain() throws AopConfigException, BeansException {
        //若拦截器链已经初始化，直接跳出。
        if (this.advisorChainInitialized) {
            return;
        }
        //该变量实际上是由proxyFactoryBean.setInterceptorNames("logMethodBeforeAdvice");设置的
        if (!ObjectUtils.isEmpty(this.interceptorNames)) {
            if (this.beanFactory == null) {
                throw new IllegalStateException("No BeanFactory available anymore (probably due to serialization) " +
                        "- cannot resolve interceptor names " + Arrays.asList(this.interceptorNames));
            }

            // Globals can't be last unless we specified a targetSource using the property...
            if (this.interceptorNames[this.interceptorNames.length - 1].endsWith(GLOBAL_SUFFIX) &&
                    this.targetName == null && this.targetSource == EMPTY_TARGET_SOURCE) {
                throw new AopConfigException("Target required after globals");
            }

            // Materialize interceptor chain from bean names.
            for (String name : this.interceptorNames) {
                if (logger.isTraceEnabled()) {
                    logger.trace("Configuring advisor or advice '" + name + "'");
                }
              //若是拦截器名字以*结尾，要全局搜索出来（相当于一个批量处理）
              //最终依旧会调用addAdvisorOnChainCreation加入到单例池中。
                if (name.endsWith(GLOBAL_SUFFIX)) {
                    if (!(this.beanFactory instanceof ListableBeanFactory)) {
                        throw new AopConfigException(
                                "Can only use global advisors or interceptors with a ListableBeanFactory");
                    }
                    addGlobalAdvisor((ListableBeanFactory) this.beanFactory,
                            name.substring(0, name.length() - GLOBAL_SUFFIX.length()));
                }

                else {
                    // If we get here, we need to add a named interceptor.
                    // We must check if it's a singleton or prototype.
                    Object advice;
                    if (this.singleton || this.beanFactory.isSingleton(name)) {
                        // Add the real Advisor/Advice to the chain.
                        //若是拦截器为单例，那么在单例池中获取单例对象
                        advice = this.beanFactory.getBean(name);
                    }
                    else {
                        // It's a prototype Advice or Advisor: replace with a prototype.
                        // Avoid unnecessary creation of prototype bean just for advisor chain initialization.
                        //若是多例，每次均产生一个拦截器对象
                        advice = new PrototypePlaceholderAdvisor(name);
                    }
                    //将获取到的拦截器对象加入到拦截器链中。
                    addAdvisorOnChainCreation(advice, name);
                }
            }
        }
        //设置标识为true。
        this.advisorChainInitialized = true;
    }
    //（步骤3：将advice转转化为Advisor）
    private void addAdvisorOnChainCreation(Object next, String name) {
        // We need to convert to an Advisor if necessary so that our source reference
        // matches what we find from superclass interceptors.
        Advisor advisor = namedBeanToAdvisor(next);
        if (logger.isTraceEnabled()) {
            logger.trace("Adding advisor with name '" + name + "'");
        }
      //将Advisor加入到Advised的配置列表中
        addAdvisor(advisor);
    }
    //（步骤4：转换为Advisor）
    private Advisor namedBeanToAdvisor(Object next) {
        try {
            return this.advisorAdapterRegistry.wrap(next);
        }
        catch (UnknownAdviceTypeException ex) {
            throw new AopConfigException("Unknown advisor type " + next.getClass() +
                    "; Can only include Advisor or Advice type beans in interceptorNames chain except for last entry," +
                    "which may also be target or TargetSource", ex);
        }
    }

}

     

    实际上执行的是wrap()方法

    上述是实际上是通过DefaultPointcutAdvisor(advice)将advice转换为了增强器即Advisor。Pointcut使用的是Pointcut.TRUE，即拦截target中所有的Method。

    public class DefaultAdvisorAdapterRegistry implements AdvisorAdapterRegistry, Serializable {

    private final List<AdvisorAdapter> adapters = new ArrayList<>(3);
    public DefaultAdvisorAdapterRegistry() {
        registerAdvisorAdapter(new MethodBeforeAdviceAdapter());
        registerAdvisorAdapter(new AfterReturningAdviceAdapter());
        registerAdvisorAdapter(new ThrowsAdviceAdapter());
    }
    @Override
    public Advisor wrap(Object adviceObject) throws UnknownAdviceTypeException {
        if (adviceObject instanceof Advisor) {
            return (Advisor) adviceObject;
        }
        if (!(adviceObject instanceof Advice)) {
            throw new UnknownAdviceTypeException(adviceObject);
        }
        Advice advice = (Advice) adviceObject;
        if (advice instanceof MethodInterceptor) {
            // So well-known it doesn't even need an adapter.
            return new DefaultPointcutAdvisor(advice);
        }
        for (AdvisorAdapter adapter : this.adapters) {
            // Check that it is supported.
            if (adapter.supportsAdvice(advice)) {
                return new DefaultPointcutAdvisor(advice);
            }
        }
        throw new UnknownAdviceTypeException(advice);
    }
}

    调用addAdvisor(advisor);是将Advisor加入到AdvisedSupport维护的List<Advisor>中。创建出的代理对象会包含Advised的配置。

    2 获取代理对象

    源码：org.springframework.aop.framework.ProxyFactoryBean#getObject

    public Object getObject() throws BeansException {  
    //初始化AdvisorChain（此时我们在这...）
    initializeAdvisorChain();  
    if (isSingleton()) {  
        //返回单例对象。
        return getSingletonInstance();  
    }  
    else {  
        if (this.targetName == null) {  
            logger.info("Using non-singleton proxies with singleton targets is often undesirable. " +  
                    "Enable prototype proxies by setting the 'targetName' property.");  
        }  
        return newPrototypeInstance();  
    }  
}  
    private synchronized Object getSingletonInstance() {  
    if (this.singletonInstance == null) {  
    //根据设置的targetName，去单例池中获取bean对象
        this.targetSource = freshTargetSource();  
        //这一步是如果你手动没有去设置需要被代理的接口，Spring还是会去帮你找看你有没有实现啥接口，然后全部给你代理上。可见Spring的容错性是很强的
        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");  
            }  
            //Spring自动寻找接口，并且设置接口
            setInterfaces(ClassUtils.getAllInterfacesForClass(targetClass, this.proxyClassLoader));  
        }  
        // Initialize the shared singleton instance.  
        super.setFrozen(this.freezeProxy);  
        //创建代理对象。
        this.singletonInstance = getProxy(createAopProxy());  
    }  
    return this.singletonInstance;  
}  
    //返回代理对象
protected Object getProxy(AopProxy aopProxy) {  
    //实际上是调用的AopProxy对象创建的代理对象。
    return aopProxy.getProxy(this.proxyClassLoader);  
}

    1. 2. 脱离IOC容器使用

    public class ProxyFactoryBeanDemo {
    public static void main(String[] args) {
        String pointcutExpression = "execution (void com.tellme.Impl.proxy.TService.run1())";
        ProxyFactoryBean proxyFactoryBean = new ProxyFactoryBean();
        proxyFactoryBean.setTarget(new TService());
        //设置切点
        AspectJExpressionPointcut pointcut = new AspectJExpressionPointcut();
        pointcut.setExpression(pointcutExpression);
        Advice advice=(MethodInterceptor) invocation -> {
            System.out.println("请求before...");
            Object obj = invocation.proceed();
            System.out.println("请求after...");
            return obj;
        };
        //创建Advisor
        Advisor advisor=new DefaultPointcutAdvisor(pointcut,advice);
        //加入到Advised过滤器链中
        proxyFactoryBean.addAdvisor(advisor);
        //获取代理对象
        TService service = (TService)proxyFactoryBean.getObject();
        service.run1();
        System.out.println(service.toString());
    }
}

    借助IOC容器，实际上做两件事情：

    • 初始化AdvisorChain，根据传入的proxyFactoryBean.setInterceptorNames("");去IOC容器中获取Advice对象。
    • 根据Advised配置，创建Proxy对象。

    最后都借助于getProxy(createAopProxy())产生代理对象。所以PoxyFactoryBean可以不借助于IOC执行。


    二、 通过AspectJProxyFactory配置

    @Aspect
public class MyAspect {
    @Pointcut("execution (void com.tellme.Impl.proxy.TService.run1())")
    private void beforeAdd(){
    }
    @Before("beforeAdd()")
    public void before1(){
        System.out.println("---------before----------");
    }
}
    public class Demo {
    public static void main(String[] args) {
        AspectJProxyFactory proxyFactory=new AspectJProxyFactory(new TService());
        proxyFactory.addAspect(MyAspect.class);
        TService bean =proxyFactory.getProxy();
        bean.run1();
    }
}

    我们传入MyAspect类，便自动完成了代理。

    • 需要注意的是：使用AspectjProxyFactory基于切面类创建代理对象时，我们指定的切面类必须包含@Aspect注解。

    • 虽然我们自己可以通过编程的方式可以通过AspectjProxyFactory创建基于@Aspect切面类的代理类，但是通过<aop:aspectj-autoproxy/>（@EnableAspectJAutoProxy）使用基于注解的AspectJ风格的AOP时，Spring内部不是通过AspectjProxyFactory创建的代理对象，而是通过ProxyFactory。

    【小家Spring】面向切面编程Spring AOP创建代理的方式：ProxyFactoryBean、ProxyFactory、AspectJProxyFactory（JDK Proxy和CGLIB）_Java方向盘-CSDN博客
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  • 原文地址：https://www.cnblogs.com/chenxingyang/p/15559345.html
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