一、PointCut接口
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/* * Copyright 2002-2012 the original author or authors. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * https://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */package org.springframework.aop;/** * Core Spring pointcut abstraction. * * <p>A pointcut is composed of a {@link ClassFilter} and a {@link MethodMatcher}. * Both these basic terms and a Pointcut itself can be combined to build up combinations * (e.g. through {@link org.springframework.aop.support.ComposablePointcut}). * * @author Rod Johnson * @see ClassFilter * @see MethodMatcher * @see org.springframework.aop.support.Pointcuts * @see org.springframework.aop.support.ClassFilters * @see org.springframework.aop.support.MethodMatchers */public interface Pointcut { /** * Return the ClassFilter for this pointcut. * @return the ClassFilter (never {@code null}) */ ClassFilter getClassFilter(); /** * Return the MethodMatcher for this pointcut. * @return the MethodMatcher (never {@code null}) */ MethodMatcher getMethodMatcher(); /** * Canonical Pointcut instance that always matches. */ Pointcut TRUE = TruePointcut.INSTANCE;} |
由源码可知，PointCut接口就是定义了两个元素，ClassFilter和MethodMatcher。PointCut接口就是为了获得这两个元素。换句话说,PointCut的功能，都包含在了这两个元素里。下面看这 两个元素源码。
二、ClassFilter接口
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/* * Copyright 2002-2019 the original author or authors. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * https://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */package org.springframework.aop;/** * Filter that restricts matching of a pointcut or introduction to * a given set of target classes. * * <p>Can be used as part of a {@link Pointcut} or for the entire * targeting of an {@link IntroductionAdvisor}. * * <p>Concrete implementations of this interface typically should provide proper * implementations of {@link Object#equals(Object)} and {@link Object#hashCode()} * in order to allow the filter to be used in caching scenarios — for * example, in proxies generated by CGLIB. * * @author Rod Johnson * @see Pointcut * @see MethodMatcher */@FunctionalInterfacepublic interface ClassFilter { /** * Should the pointcut apply to the given interface or target class? * @param clazz the candidate target class * @return whether the advice should apply to the given target class */ boolean matches(Class<?> clazz); /** * Canonical instance of a ClassFilter that matches all classes. */ ClassFilter TRUE = TrueClassFilter.INSTANCE;} |
这个接口用来过滤要生成代理的类和给定的类是否匹配。
该接口的实现类应该提供正确的equals()方法和hashCode()方法，以便于能在缓存中使用。例如通过cglib生成的代理对象。(这句话什么意思，不理解)。
matches方法就是判断参数中的class类是否和切点定义的类相匹配。如果匹配，则生成代理对象，如果不匹配，则过滤掉。
三、MethodMatcher接口
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/* * Copyright 2002-2019 the original author or authors. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * https://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */package org.springframework.aop;import java.lang.reflect.Method;/** * Part of a {@link Pointcut}: Checks whether the target method is eligible for advice. * * <p>A MethodMatcher may be evaluated <b>statically</b> or at <b>runtime</b> (dynamically). * Static matching involves method and (possibly) method attributes. Dynamic matching * also makes arguments for a particular call available, and any effects of running * previous advice applying to the joinpoint. * * <p>If an implementation returns {@code false} from its {@link #isRuntime()} * method, evaluation can be performed statically, and the result will be the same * for all invocations of this method, whatever their arguments. This means that * if the {@link #isRuntime()} method returns {@code false}, the 3-arg * {@link #matches(java.lang.reflect.Method, Class, Object[])} method will never be invoked. * * <p>If an implementation returns {@code true} from its 2-arg * {@link #matches(java.lang.reflect.Method, Class)} method and its {@link #isRuntime()} method * returns {@code true}, the 3-arg {@link #matches(java.lang.reflect.Method, Class, Object[])} * method will be invoked <i>immediately before each potential execution of the related advice</i>, * to decide whether the advice should run. All previous advice, such as earlier interceptors * in an interceptor chain, will have run, so any state changes they have produced in * parameters or ThreadLocal state will be available at the time of evaluation. * * <p>Concrete implementations of this interface typically should provide proper * implementations of {@link Object#equals(Object)} and {@link Object#hashCode()} * in order to allow the matcher to be used in caching scenarios — for * example, in proxies generated by CGLIB. * * @author Rod Johnson * @since 11.11.2003 * @see Pointcut * @see ClassFilter */public interface MethodMatcher { /** * Perform static checking whether the given method matches. * <p>If this returns {@code false} or if the {@link #isRuntime()} * method returns {@code false}, no runtime check (i.e. no * {@link #matches(java.lang.reflect.Method, Class, Object[])} call) * will be made. * @param method the candidate method * @param targetClass the target class * @return whether or not this method matches statically */ boolean matches(Method method, Class<?> targetClass); /** * Is this MethodMatcher dynamic, that is, must a final call be made on the * {@link #matches(java.lang.reflect.Method, Class, Object[])} method at * runtime even if the 2-arg matches method returns {@code true}? * <p>Can be invoked when an AOP proxy is created, and need not be invoked * again before each method invocation, * @return whether or not a runtime match via the 3-arg * {@link #matches(java.lang.reflect.Method, Class, Object[])} method * is required if static matching passed */ boolean isRuntime(); /** * Check whether there a runtime (dynamic) match for this method, * which must have matched statically. * <p>This method is invoked only if the 2-arg matches method returns * {@code true} for the given method and target class, and if the * {@link #isRuntime()} method returns {@code true}. Invoked * immediately before potential running of the advice, after any * advice earlier in the advice chain has run. * @param method the candidate method * @param targetClass the target class * @param args arguments to the method * @return whether there's a runtime match * @see MethodMatcher#matches(Method, Class) */ boolean matches(Method method, Class<?> targetClass, Object... args); /** * Canonical instance that matches all methods. */ MethodMatcher TRUE = TrueMethodMatcher.INSTANCE;} |
PointCut的一部分，用来判断方法是否需要进行增强。ClassFilter过滤需要生成代理的类。而这个类里，不是所有的方法都需要增强的，所以要通过MethodMatcher接口匹配出要增强的方法来。
MethodMatcher分为静态匹配和动态匹配。静态匹配是根据方法名匹配。动态匹配是根据参数进行匹配(不知道这么理解对不对)
MethodMatcher的实现类中，如果isRuntime()方法返回false，则使用静态匹配，无论参数是什么，只要方法名匹配，则都会进行增强。而且这个接口中带有3个参数的matches方法，即matches(java.lang.reflect.Method, Class, Object[])就永远不会执行。
实现类中，如果两个参数的matches方法返回true，且isRuntime()也返回true。那么在执行增强之前，会执行三个参数的matches方法，来判断这个增强是否要执行。
下面来看接口三个方法的注释:
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boolean matches(Method method, Class<?> targetClass); |
静态核对给定的方法是否需要增强。如果返回false。则不再会执行三个参数的matches方法。
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boolean isRuntime(); |
当两个参数的matches方法返回true时，是否要执行三个参数的matches方法。该方法在AOP代理生成的时候执行，而不是每次调用代理方法之前执行。意思就是生成代理对象的时候，就已经判断好要不要执行三个参数的matches方法了。
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boolean matches(Method method, Class<?> targetClass, Object... args); |
该方法执行的时机是增强方法要执行之前，判断参数是否满足要求，如果满足，则执行增强。注意isRuntime方法是创建代理对象时就决定好的，而是否执行三个参数的matches方法是调用增强之前判断的。
总结
从上面的源码可以看出，PointCut就是起到过滤的作用，首先是过滤类，然后再过滤方法，筛选出需要加强的方法来。由接口可知，我们要将参数中的class或method进行比较，然后过滤，那么，和谁进行比较呢？要过滤的类和方法的规则存在哪里了呢？请看下回分解。
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原文链接：https://blog.csdn.net/qq1309664161/article/details/120061132
