使用"横切"技术，AOP把软件系统分为两个部分：核心关注点和横切关注点。业务处理的主要流程是核心关注点，与之关系不大的部分是横切关注点。横切关注点的一个特点是，他们经常发生在核心关注点的多处，而各处基本相似，比如权限认证、日志、事务。AOP的作用在于分离系统中的各种关注点，将核心关注点和横切关注点分离开来。
AOP核心概念
1、横切关注点
对哪些方法进行拦截，拦截后怎么处理，这些关注点称之为横切关注点
2、切面（aspect）
类是对物体特征的抽象，切面就是对横切关注点的抽象
3、连接点（joinpoint）
被拦截到的点，因为Spring只支持方法类型的连接点，所以在Spring中连接点指的就是被拦截到的方法，实际上连接点还可以是字段或者构造器
4、切入点（pointcut）
对连接点进行拦截的定义
5、通知（advice）
所谓通知指的就是指拦截到连接点之后要执行的代码，通知分为前置、后置、异常、最终、环绕通知五类
6、目标对象
代理的目标对象
7、织入（weave）
将切面应用到目标对象并导致代理对象创建的过程
8、引入（introduction）
在不修改代码的前提下，引入可以在运行期为类动态地添加一些方法或字段
使用ProxyFactoryBean实现AOP
Spring自己的AOP实现在于ProxyFactoryBean。
接口
package com.shoudongdaili; public interface IPerson { void say(); }
实现类
package com.shoudongdaili; public class Person3 implements IPerson { private String name3; private int age3; public String getName3() { return name3; } public void setName3(String name3) { this.name3 = name3; } public int getAge3() { return age3; } public void setAge3(int age3) { this.age3 = age3; } @Override public String toString() { return "Person3 [name3=" + name3 + ", age3=" + age3 + "]"; } @Override public void say() { System.out.println(toString()); } }
通知类
package com.shoudongdaili; import java.lang.reflect.Method; import org.aopalliance.intercept.MethodInterceptor; import org.springframework.aop.MethodBeforeAdvice; import org.springframework.aop.framework.autoproxy.DefaultAdvisorAutoProxyCreator; public class MyAdvice3 implements MethodBeforeAdvice { @Override public void before(Method method, Object[] args, Object target) throws Throwable { //arg0 是 目标类的方法 arg1是目标类的入参数 arg2是目标类实例 发生异常则抛给Throwable System.out.println("before my advice3..."); } }
bean.xml
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p" xmlns:aop="http://www.springframework.org/schema/aop" xmlns:tx="http://www.springframework.org/schema/tx" xmlns:context="http://www.springframework.org/schema/context" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.2.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.2.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.2.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop.xsd"> <!-- 代理前原对象 --> <bean id="person3" class="com.shoudongdaili.Person3"></bean>
<!-- 通知类 --> <bean id="myAdvice3" class="com.shoudongdaili.MyAdvice3"></bean>
<!-- 代理对象 --> <bean id="proxyPerson3" class="org.springframework.aop.framework.ProxyFactoryBean"> <property name="proxyInterfaces" value="com.shoudongdaili.IPerson"></property> <property name="target" ref="person3"></property> <property name="interceptorNames"> <list> <value>myAdvice3</value> </list> </property> </bean> </beans>
测试类
package com.shoudongdaili; import org.springframework.context.support.ClassPathXmlApplicationContext; public class BeanTest3 { public static void main(String[] args) { ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("zidongdaili/shoudongdaili-bean.xml"); // IPerson的实现类有Person3和proxyPerson3代理类这两个，注意这里是使用proxyPerson3 IPerson person3 = (IPerson) context.getBean("proxyPerson3"); person3.say(); } }
源代码解读
然后我们就要源码分析下这一过程，先看下是如何产生代理对象的，在ProxyFactoryBean的getObject方法中：
public class ProxyFactoryBean extends ProxyCreatorSupport
implements FactoryBean<Object>, BeanClassLoaderAware, BeanFactoryAware {
@Override
public Object getObject() throws BeansException {
//重点一
initializeAdvisorChain();
if (isSingleton()) {
//重点二
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.");
}
return newPrototypeInstance();
}
}
}
重点1：就是根据我们配置的interceptorNames来获取对应的bean，并却转化成Advisor。
this.advisorChainInitialized：标示是否已进行过初始化，若以初始化则不再进行初始化。然后就是将interceptorNames转化成Advisor。根据interceptorNames所包含的字符串到容器中进行查找，如果含有*则，则表示进行一定的匹配，符合的都会纳入。
如下：
private synchronized void initializeAdvisorChain() throws AopConfigException, BeansException {
if (this.advisorChainInitialized) {
return;
}
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 + "'");
}
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.
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.
advice = new PrototypePlaceholderAdvisor(name);
}
addAdvisorOnChainCreation(advice, name);
}
}
}
this.advisorChainInitialized = true;
}
这中间页经过了Advice到Advisor的转换，如下：
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 + "'");
}
addAdvisor(advisor);
}
private Advisor namedBeanToAdvisor(Object next) {
try {
return this.advisorAdapterRegistry.wrap(next);
}
catch (UnknownAdviceTypeException ex) {
// We expected this to be an Advisor or Advice,
// but it wasn't. This is a configuration error.
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);
}
}
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);
}
public class DefaultPointcutAdvisor extends AbstractGenericPointcutAdvisor implements Serializable {
public DefaultPointcutAdvisor(Advice advice) {
this(Pointcut.TRUE, advice);
}
}
这个包裹过程已经见过很多遍了，采用了适配器的模式。
之后又是和其他的AOP方式接轨了，设置一些列要实现的接口和参数，使用DefaultAopProxyFactory先创建出AopProxy，要么是JdkDynamicAopProxy，要么是CglibAopProxy，然后就可以调用AopProxy的getProxy方法来获取代理对象。
具体JdkDynamicAopProxy和CglibAopProxy的区别联系，参阅java中代理，静态代理，动态代理以及spring aop代理方式，实现原理统一汇总
这种方式实现的AOP还是比较麻烦的，同时配置一个ProxyFactoryBean仅能实现对一个目标对象的拦截，要想拦截多个目标对象，需要配置多个ProxyFactoryBean。所以大部分还是使用Spring引进的aspectj的AOP方式来进行AOP编程。
使用DefaultAdvisorAutoProxyCreator实现自动代理完成AOP
接口
package com.zidongdaili; public interface IPerson4 { void sayhi(); }
实现类
package com.zidongdaili; public class Person4 implements IPerson4 { private String name4; private int age4; public String getName4() { return name4; } public void setName4(String name4) { this.name4 = name4; } public int getAge4() { return age4; } public void setAge4(int age4) { this.age4 = age4; } @Override public String toString() { return "Person4 [name4=" + name4 + ", age4=" + age4 + "]"; } @Override public void sayhi() { System.out.println(toString()); } }
通知类
package com.zidongdaili; import java.lang.reflect.Method; import org.springframework.aop.MethodBeforeAdvice; public class MyAdvice4 implements MethodBeforeAdvice { @Override public void before(Method method, Object[] args, Object target) throws Throwable { //arg0 是 目标类的方法 arg1是目标类的入参数 arg2是目标类实例 发生异常则抛给Throwable System.out.println("before my advice4..."); } }
bean.xml
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p" xmlns:aop="http://www.springframework.org/schema/aop" xmlns:tx="http://www.springframework.org/schema/tx" xmlns:context="http://www.springframework.org/schema/context" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.2.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.2.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.2.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop.xsd"> <bean id="person4" class="com.zidongdaili.Person4"></bean> <bean id="myAdvice4" class="com.zidongdaili.MyAdvice4"></bean> <bean class="org.springframework.aop.support.RegexpMethodPointcutAdvisor"> <!-- id="advisor" 可以不写 --> <property name="pattern"> <value>.*say.+</value> <!-- 业务实现方法名匹配 --> </property> <property name="advice"> <ref bean="myAdvice4" /> </property> </bean>
<!-- 自动代理 --> <bean id="autoProxyCreator" class="org.springframework.aop.framework.autoproxy.DefaultAdvisorAutoProxyCreator"> </bean> </beans>
测试类
package com.zidongdaili; import org.springframework.context.support.ClassPathXmlApplicationContext; public class BeanTest4 { public static void main(String[] args) { ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("zidongdaili/zidongdaili-bean.xml"); IPerson4 person4 = (IPerson4) context.getBean("person4"); person4.sayhi(); } }
使用BeanNameAutoProxyCreator实现自动代理完成AOP
BeanNameAutoProxyCreator是自动代理创建器的三种(BeanNameAutoProxyCreator,DefaultAdvisorAutoProxyCreator,AbstractAdvisorAutoProxyCreator)之一.它是根据拦截器和设置的Bean的名称表达式做匹配来创建代理.下面是个例子
1.主要依赖(略)
2.声明一个环绕通知(拦截器)
public class MyMethodInterceptor implements MethodInterceptor { @Override public Object invoke(MethodInvocation invocation) throws Throwable { System.out.println(getClass()+"调用方法前"); Object ret=invocation.proceed(); System.out.println(getClass()+"调用方法后"); return ret; } }
3.要创建代理的目标类与接口
public interface UserService { void print(); } public class UserServiceImpl implements UserService { public void print(){ System.out.println(getClass()+"#print"); } }
4.配置
@Configuration public class AppConfig { //要创建代理的目标Bean @Bean public UserService userService(){ return new UserServiceImpl(); } //创建Advice或Advisor @Bean public Advice myMethodInterceptor(){ return new MyMethodInterceptor(); } //使用BeanNameAutoProxyCreator来创建代理 @Bean public BeanNameAutoProxyCreator beanNameAutoProxyCreator(){ BeanNameAutoProxyCreator beanNameAutoProxyCreator=new BeanNameAutoProxyCreator(); //设置要创建代理的那些Bean的名字 beanNameAutoProxyCreator.setBeanNames("userSer*"); //设置拦截链名字(这些拦截器是有先后顺序的) beanNameAutoProxyCreator.setInterceptorNames("myMethodInterceptor"); return beanNameAutoProxyCreator; } }
5.测试
public class Main { public static void main(String[] args) { ApplicationContext applicationContext=new AnnotationConfigApplicationContext(AppConfig.class); UserService userService= applicationContext.getBean(UserService.class); userService.print(); } }
源码分析
BeanNameAutoProxyCreator是一个BeanPostProcessor.它在Bean实例化随后,调用回调org.springframework.aop.framework.autoproxy.AbstractAutoProxyCreator#postProcessAfterInitialization进行后期处理来完成代理的创建.
其中AbstractAutoProxyCreator是BeanNameAutoProxyCreator的超类,BeanNameAutoProxyCreator没有重写postProcessAfterInitialization方法.下面看看这个方法:
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException { if (bean != null) { Object cacheKey = getCacheKey(bean.getClass(), beanName); if (!this.earlyProxyReferences.contains(cacheKey)) { //关键代码在这里 return wrapIfNecessary(bean, beanName, cacheKey); } } return bean; }
再看看wrapIfNecessary方法:
protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) { if (beanName != null && this.targetSourcedBeans.contains(beanName)) { return bean; } if (Boolean.FALSE.equals(this.advisedBeans.get(cacheKey))) { return bean; } if (isInfrastructureClass(bean.getClass()) || shouldSkip(bean.getClass(), beanName)) { this.advisedBeans.put(cacheKey, Boolean.FALSE); return bean; } //这个bean是否匹配要创建代理也是在这个方法. Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null); if (specificInterceptors != DO_NOT_PROXY) { this.advisedBeans.put(cacheKey, Boolean.TRUE); //关键代码在这里 Object proxy = createProxy(bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(bean)); this.proxyTypes.put(cacheKey, proxy.getClass()); return proxy; } this.advisedBeans.put(cacheKey, Boolean.FALSE); return bean; }
再看看createProxy方法:
protected Object createProxy( Class<?> beanClass, String beanName, Object[] specificInterceptors, TargetSource targetSource) { ProxyFactory proxyFactory = new ProxyFactory(); proxyFactory.copyFrom(this); if (!proxyFactory.isProxyTargetClass()) { if (shouldProxyTargetClass(beanClass, beanName)) { proxyFactory.setProxyTargetClass(true); } else { evaluateProxyInterfaces(beanClass, proxyFactory); } } Advisor[] advisors = buildAdvisors(beanName, specificInterceptors); for (Advisor advisor : advisors) { proxyFactory.addAdvisor(advisor); } proxyFactory.setTargetSource(targetSource); customizeProxyFactory(proxyFactory); proxyFactory.setFrozen(this.freezeProxy); if (advisorsPreFiltered()) { proxyFactory.setPreFiltered(true); } //关键代码看这里 return proxyFactory.getProxy(getProxyClassLoader()); }
再看看org.springframework.aop.framework.ProxyFactory#getProxy(java.lang.ClassLoader)如下:
public Object getProxy(ClassLoader classLoader) { return createAopProxy().getProxy(classLoader); }
再看看org.springframework.aop.framework.ProxyCreatorSupport#createAopProxy
public Object getProxy(ClassLoader classLoader) { return createAopProxy().getProxy(classLoader); }
再看看createAopProxy方法
protected final synchronized AopProxy createAopProxy() { if (!this.active) { activate(); } return getAopProxyFactory().createAopProxy(this); }
剩下的就与ProxyFactoryBean创建代理类似了.
手动实现自动代理实现AOP
我们也可以写一个类，来实现DefaultAdvisorAutoProxyCreator自动代理的功能！
首先，我们需要实现一个接口，也就是BeanPostProcessor接口。
BeanPostProcessor接口作用是：如果我们需要在Spring容器完成Bean的实例化、配置和其他的初始化前后添加一些自己的逻辑处理，我们就可以定义一个或者多个BeanPostProcessor接口的实现，然后注册到容器中。
而我们想要在原型对象bean被创建之后就代理了，就必须在原来的容器中拿到原来的原型对象，需要拿到原来spring容器中的切面对象，这个时候，我们就需要原来的容器，这个时候就需要另一个接口，也就是ApplicationContextAware接口！
通过这2个接口，我们就可以实现自动代理了。
package cn.hncu.xmlImpl; import org.springframework.aop.Advisor; import org.springframework.aop.framework.ProxyFactoryBean; import org.springframework.beans.BeansException; import org.springframework.beans.factory.config.BeanPostProcessor; import org.springframework.context.ApplicationContext; import org.springframework.context.ApplicationContextAware; public class MyAutoProxy implements BeanPostProcessor,ApplicationContextAware{ private ApplicationContext applicationContext=null; //bean创建之前调用 @Override public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException { return bean;//在这里，我们直接放行 } //bean创建之后调用 @Override public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException { ProxyFactoryBean factory = new ProxyFactoryBean(); //把原型对象放入代理工厂 factory.setTarget(bean); //在这里 Advisor adv = applicationContext.getBean(Advisor.class); factory.addAdvisor(adv); //返回被代理后的对象 return factory.getObject(); } //拿到原来的spring中的容器 @Override public void setApplicationContext(ApplicationContext applicationContext) throws BeansException { this.applicationContext=applicationContext; } }
bean.xml
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p" xmlns:aop="http://www.springframework.org/schema/aop" xmlns:tx="http://www.springframework.org/schema/tx" xmlns:context="http://www.springframework.org/schema/context" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.2.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.2.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.2.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop.xsd"> <bean id="person4" class="com.zidongdaili.Person4"></bean> <bean id="myAdvice4" class="com.zidongdaili.MyAdvice4"></bean> <bean class="org.springframework.aop.support.RegexpMethodPointcutAdvisor"> <!-- id="advisor" 可以不写 --> <property name="pattern"> <value>.*say.+</value> <!-- 业务实现方法名匹配 --> </property> <property name="advice"> <ref bean="myAdvice4" /> </property> </bean> <!-- 自己写的自动代理 -->
<bean class="cn.hncu.xmlImpl.MyAutoProxy"></bean> </beans>
