216 lines
9.2 KiB
Markdown
216 lines
9.2 KiB
Markdown
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## AdvisorChainFactory
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- [AdvisorChainFactory](#AdvisorChainFactory)
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- [一、基本信息](#一基本信息)
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- [二、基本描述](#二基本描述)
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- [三、主要功能](#三主要功能)
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- [四、接口源码](#四接口源码)
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- [五、主要实现](#五主要实现)
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- [六、最佳实践](#六最佳实践)
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- [七、源码分析](#七源码分析)
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- [八、常见问题](#八常见问题)
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### 一、基本信息
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✒️ **作者** - Lex 📝 **博客** - [掘金](https://juejin.cn/user/4251135018533068/posts) 📚 **源码地址** - [github](https://github.com/xuchengsheng/spring-reading)
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### 二、基本描述
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`AdvisorChainFactory`接口是Spring AOP中负责创建顾问链的工厂接口，通过`getInterceptorsAndDynamicInterceptionAdvice()`方法，它能够将一组顾问对象转换为拦截器数组，用于管理和执行切面逻辑，提供了灵活性和可扩展性来定制切面的执行方式。
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### 三、主要功能
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1. **创建顾问链（Advisor Chain）**
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+ 通过`getInterceptorsAndDynamicInterceptionAdvice()`方法，将一组顾问对象转换为拦截器数组，形成顾问链，用于在目标方法执行前后执行特定的操作。
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2. **动态顾问链的创建**
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+ 可以根据运行时的情况动态地创建顾问链，例如根据目标对象的类型或方法签名动态地决定哪些通知要被执行。
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### 四、接口源码
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`AdvisorChainFactory`接口 ，用于创建Advisor链的工厂接口。其中的方法 `getInterceptorsAndDynamicInterceptionAdvice()` 接受AOP配置（`Advised`对象）、被代理的方法以及目标类，并返回一个包含MethodInterceptors的列表，用于配置Advisor链。这个接口的目的是根据给定的配置，确定在代理方法执行时应该应用哪些拦截器，以及是否需要动态匹配方法。
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```java
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/**
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* Advisor链工厂的工厂接口。
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* Factory interface for advisor chains.
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*
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* @author Rod Johnson
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* @author Juergen Hoeller
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*/
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public interface AdvisorChainFactory {
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/**
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* 根据给定的Advisor链配置，确定一组MethodInterceptor对象。
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* Determine a list of {@link org.aopalliance.intercept.MethodInterceptor} objects
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* for the given advisor chain configuration.
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* @param config 表示AOP配置的Advised对象
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* @param method 被代理的方法
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* @param targetClass 目标类（可能为null，表示没有目标对象的代理，在这种情况下，方法的声明类是下一个最佳选择）
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* @return 一个MethodInterceptors的列表（也可能包括InterceptorAndDynamicMethodMatchers）
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*/
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List<Object> getInterceptorsAndDynamicInterceptionAdvice(Advised config, Method method, @Nullable Class<?> targetClass);
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}
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```
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### 五、主要实现
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1. **DefaultAdvisorChainFactory**
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+ 负责根据给定的AOP配置、被代理的方法和目标类，确定应该应用哪些拦截器，并支持动态方法匹配和缓存机制，以提供高效的顾问链创建功能
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### 六、最佳实践
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使用`DefaultAdvisorChainFactory`类来创建Advisor链。首先，创建了一个`AdvisedSupport`对象，配置了前置通知和后置返回通知。然后，指定了目标类和目标方法。接着，实例化了`DefaultAdvisorChainFactory`类，并调用其`getInterceptorsAndDynamicInterceptionAdvice()`方法获取Advisor链。最后，打印了Advisor链中的拦截器。
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```java
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public class AdvisorChainFactoryDemo {
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public static void main(String[] args) throws NoSuchMethodException {
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// 创建AOP配置对象
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AdvisedSupport config = new AdvisedSupport();
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// 添加前置通知
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config.addAdvice(new MyMethodBeforeAdvice());
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// 添加后置返回通知
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config.addAdvice(new MyAfterReturningAdvice());
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// 设置目标类
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Class<MyService> targetClass = MyService.class;
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// 获取目标方法
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Method method = targetClass.getDeclaredMethod("doSomething");
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// 创建默认的Advisor链工厂实例
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DefaultAdvisorChainFactory chainFactory = new DefaultAdvisorChainFactory();
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// 获取Advisor链
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List<Object> chain = chainFactory.getInterceptorsAndDynamicInterceptionAdvice(config, method, targetClass);
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// 打印Advisor链中的拦截器
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chain.forEach(System.out::println);
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}
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}
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```
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运行结果，显示了Advisor链中的两个拦截器，分别是`MethodBeforeAdviceInterceptor`和`AfterReturningAdviceInterceptor`。这些拦截器是根据配置的前置通知和后置返回通知生成的，用于在目标方法执行前后进行相应的操作。
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```java
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org.springframework.aop.framework.adapter.MethodBeforeAdviceInterceptor@215be6bb
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org.springframework.aop.framework.adapter.AfterReturningAdviceInterceptor@4439f31e
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```
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### 七、源码分析
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`DefaultAdvisorChainFactory`类。它提供了一种简单但确定的方法，根据给定的`Advised`对象，在方法级别确定通知链的构建顺序。通过遍历配置的Advisor数组，并根据Advisor的类型和Pointcut来确定应该应用哪些拦截器，最终返回一个拦截器列表。在此过程中，它支持动态方法匹配和引入拦截器的处理，并提供了一个缓存机制来提高性能。
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```java
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/**
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* 给定一个 {@link Advised} 对象，为一个方法确定一个通知链的简单但确定的方法。总是重新构建每个通知链；
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* 子类可以提供缓存功能。
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*
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* @author Juergen Hoeller
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* @author Rod Johnson
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* @author Adrian Colyer
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* @since 2.0.3
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*/
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@SuppressWarnings("serial")
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public class DefaultAdvisorChainFactory implements AdvisorChainFactory, Serializable {
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@Override
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public List<Object> getInterceptorsAndDynamicInterceptionAdvice(
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Advised config, Method method, @Nullable Class<?> targetClass) {
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// 获取Advisor适配器注册表
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AdvisorAdapterRegistry registry = GlobalAdvisorAdapterRegistry.getInstance();
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// 获取AOP配置中的所有Advisor
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Advisor[] advisors = config.getAdvisors();
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// 创建一个拦截器列表
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List<Object> interceptorList = new ArrayList<>(advisors.length);
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// 获取实际类
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Class<?> actualClass = (targetClass != null ? targetClass : method.getDeclaringClass());
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Boolean hasIntroductions = null;
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// 遍历所有Advisor
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for (Advisor advisor : advisors) {
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if (advisor instanceof PointcutAdvisor) {
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// 添加条件性地。
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PointcutAdvisor pointcutAdvisor = (PointcutAdvisor) advisor;
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if (config.isPreFiltered() || pointcutAdvisor.getPointcut().getClassFilter().matches(actualClass)) {
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// 获取Advisor的Pointcut和MethodMatcher
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MethodMatcher mm = pointcutAdvisor.getPointcut().getMethodMatcher();
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boolean match;
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if (mm instanceof IntroductionAwareMethodMatcher) {
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if (hasIntroductions == null) {
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// 检查是否存在匹配的IntroductionAdvisor
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hasIntroductions = hasMatchingIntroductions(advisors, actualClass);
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}
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match = ((IntroductionAwareMethodMatcher) mm).matches(method, actualClass, hasIntroductions);
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}
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else {
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match = mm.matches(method, actualClass);
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}
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// 如果匹配，则将Interceptor添加到拦截器列表中
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if (match) {
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MethodInterceptor[] interceptors = registry.getInterceptors(advisor);
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if (mm.isRuntime()) {
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// 如果是动态匹配，则创建一个新的InterceptorAndDynamicMethodMatcher对象
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for (MethodInterceptor interceptor : interceptors) {
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interceptorList.add(new InterceptorAndDynamicMethodMatcher(interceptor, mm));
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}
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}
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else {
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// 否则直接添加Interceptor
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interceptorList.addAll(Arrays.asList(interceptors));
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}
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}
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}
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}
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else if (advisor instanceof IntroductionAdvisor) {
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IntroductionAdvisor ia = (IntroductionAdvisor) advisor;
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if (config.isPreFiltered() || ia.getClassFilter().matches(actualClass)) {
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// 如果是IntroductionAdvisor，则直接获取Interceptor并添加到拦截器列表中
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Interceptor[] interceptors = registry.getInterceptors(advisor);
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interceptorList.addAll(Arrays.asList(interceptors));
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}
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}
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else {
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// 对于其他类型的Advisor，直接获取Interceptor并添加到拦截器列表中
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Interceptor[] interceptors = registry.getInterceptors(advisor);
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interceptorList.addAll(Arrays.asList(interceptors));
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}
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}
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// 返回拦截器列表
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return interceptorList;
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}
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/**
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* 判断Advisor中是否存在匹配的引入拦截器。
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*/
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private static boolean hasMatchingIntroductions(Advisor[] advisors, Class<?> actualClass) {
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for (Advisor advisor : advisors) {
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if (advisor instanceof IntroductionAdvisor) {
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IntroductionAdvisor ia = (IntroductionAdvisor) advisor;
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if (ia.getClassFilter().matches(actualClass)) {
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return true;
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}
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}
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}
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return false;
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}
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}
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```
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### 八、常见问题
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1. **拦截器未被正确应用**
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+ 如果`AdvisorChainFactory`未正确构建Advisor链，可能会导致拦截器未按预期应用于目标方法。
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2. **动态方法匹配错误**
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+ 如果动态方法匹配器（DynamicMethodMatcher）未正确配置或应用，可能会导致拦截器未在预期条件下执行。
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3. **引入拦截器未生效**
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+ 如果引入拦截器（IntroductionInterceptor）未被正确添加到Advisor链中，可能会导致引入功能无法正常工作。
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