Java Spring AOP之PointCut案例詳解
一、PointCut接口
/* * 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; }
由源碼可知,PointCut接口就是定義了兩個(gè)元素,ClassFilter和MethodMatcher。PointCut接口就是為了獲得這兩個(gè)元素。換句話說,PointCut的功能,都包含在了這兩個(gè)元素里。下面看這 兩個(gè)元素源碼。
二、ClassFilter接口
/* * 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 */ @FunctionalInterface public 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; }
這個(gè)接口用來(lái)過濾要生成代理的類和給定的類是否匹配。
該接口的實(shí)現(xiàn)類應(yīng)該提供正確的equals()方法和hashCode()方法,以便于能在緩存中使用。例如通過cglib生成的代理對(duì)象。(這句話什么意思,不理解)。
matches方法就是判斷參數(shù)中的class類是否和切點(diǎn)定義的類相匹配。如果匹配,則生成代理對(duì)象,如果不匹配,則過濾掉。
三、MethodMatcher接口
/* * 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,用來(lái)判斷方法是否需要進(jìn)行增強(qiáng)。ClassFilter過濾需要生成代理的類。而這個(gè)類里,不是所有的方法都需要增強(qiáng)的,所以要通過MethodMatcher接口匹配出要增強(qiáng)的方法來(lái)。
MethodMatcher分為靜態(tài)匹配和動(dòng)態(tài)匹配。靜態(tài)匹配是根據(jù)方法名匹配。動(dòng)態(tài)匹配是根據(jù)參數(shù)進(jìn)行匹配(不知道這么理解對(duì)不對(duì))
MethodMatcher的實(shí)現(xiàn)類中,如果isRuntime()方法返回false,則使用靜態(tài)匹配,無(wú)論參數(shù)是什么,只要方法名匹配,則都會(huì)進(jìn)行增強(qiáng)。而且這個(gè)接口中帶有3個(gè)參數(shù)的matches方法,即matches(java.lang.reflect.Method, Class, Object[])就永遠(yuǎn)不會(huì)執(zhí)行。
實(shí)現(xiàn)類中,如果兩個(gè)參數(shù)的matches方法返回true,且isRuntime()也返回true。那么在執(zhí)行增強(qiáng)之前,會(huì)執(zhí)行三個(gè)參數(shù)的matches方法,來(lái)判斷這個(gè)增強(qiáng)是否要執(zhí)行。
下面來(lái)看接口三個(gè)方法的注釋:
boolean matches(Method method, Class<?> targetClass);
靜態(tài)核對(duì)給定的方法是否需要增強(qiáng)。如果返回false。則不再會(huì)執(zhí)行三個(gè)參數(shù)的matches方法。
boolean isRuntime();
當(dāng)兩個(gè)參數(shù)的matches方法返回true時(shí),是否要執(zhí)行三個(gè)參數(shù)的matches方法。該方法在AOP代理生成的時(shí)候執(zhí)行,而不是每次調(diào)用代理方法之前執(zhí)行。意思就是生成代理對(duì)象的時(shí)候,就已經(jīng)判斷好要不要執(zhí)行三個(gè)參數(shù)的matches方法了。
boolean matches(Method method, Class<?> targetClass, Object... args);
該方法執(zhí)行的時(shí)機(jī)是增強(qiáng)方法要執(zhí)行之前,判斷參數(shù)是否滿足要求,如果滿足,則執(zhí)行增強(qiáng)。注意isRuntime方法是創(chuàng)建代理對(duì)象時(shí)就決定好的,而是否執(zhí)行三個(gè)參數(shù)的matches方法是調(diào)用增強(qiáng)之前判斷的。
總結(jié)
從上面的源碼可以看出,PointCut就是起到過濾的作用,首先是過濾類,然后再過濾方法,篩選出需要加強(qiáng)的方法來(lái)。由接口可知,我們要將參數(shù)中的class或method進(jìn)行比較,然后過濾,那么,和誰(shuí)進(jìn)行比較呢?要過濾的類和方法的規(guī)則存在哪里了呢?請(qǐng)看下回分解。
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