上篇中讲到spring将所有的标签解析完成并封装成为RootBeanDefinition之后，并将RootBeanDefinition存储在BeanFactory工厂类的Map<String, BeanDefinition> beanDefinitionMap变量中，这篇接着分析spring使用aop面向切面编程，来实现对事物的控制，spring容器是如何创建目标类的代理类。
BeanPostProcessor创建和注册
从上文中提到的测试用例来看，
public class AuthUserServiceImplTest {
private static Logger logger = Logger.getLogger(AuthUserServiceImplTest.class);
public static void main(String[] args){
ApplicationContext ctx = new ClassPathXmlApplicationContext("bean.xml");
IAuthUserService authUserServiceImpl = ctx.getBean(AuthUserServiceImpl.class);
Map<String,Object> params = new HashMap<>();
params.put("userAccount","user002");
int ret = authUserServiceImpl.delete("user002");
}
}执行new ClassPathXmlApplicationContext("bean.xml")，创建ApplicationContext容器，此过程会解析bean.xml配置文件，完成所有的标签解析。refresh()方法主要完成spring 容器的创建过程，此处主要分析registerBeanPostProcessors()方法和finishBeanFactoryInitialization()方法。
public void refresh() throws BeansException, IllegalStateException {
Object var1 = this.startupShutdownMonitor;
synchronized(this.startupShutdownMonitor) {
this.prepareRefresh();
//创建工厂，解析标签并将bean封装成为RootBeanDefinition注册到工厂中
ConfigurableListableBeanFactory beanFactory = this.obtainFreshBeanFactory();
this.prepareBeanFactory(beanFactory);
try {
this.postProcessBeanFactory(beanFactory);
this.invokeBeanFactoryPostProcessors(beanFactory);
//注册后置处理器
this.registerBeanPostProcessors(beanFactory);
this.initMessageSource();
this.initApplicationEventMulticaster();
this.onRefresh();
this.registerListeners();
//创建bean等
this.finishBeanFactoryInitialization(beanFactory);
this.finishRefresh();
} catch (BeansException var9) {
this.logger.warn("Exception encountered during context initialization - cancelling refresh attempt", var9);
this.destroyBeans();
this.cancelRefresh(var9);
throw var9;
} finally {
this.resetCommonCaches();
}
}
}refresh()方法的调用过程：
后置处理器的注册在registerBeanPostProcessors()方法中完成。方法大概内容如下：
public static void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {
//在beanFactory工厂类中，根据类型BeanPostProcessor，查找所有的BeanPostProcessor的实现类名字
String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);
//存放PriorityOrdered接口的实现类
List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList();
List<BeanPostProcessor> internalPostProcessors = new ArrayList();
//存放Ordered接口的实现类
List<String> orderedPostProcessorNames = new ArrayList();
//存放未实现PriorityOrdered和Ordered接口的后置处理器
List<String> nonOrderedPostProcessorNames = new ArrayList();
String[] var8 = postProcessorNames;
int var9 = postProcessorNames.length;
String ppName;
BeanPostProcessor pp;
for(int var10 = 0; var10 < var9; ++var10) {
ppName = var8[var10];
if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
pp = (BeanPostProcessor)beanFactory.getBean(ppName, BeanPostProcessor.class);
priorityOrderedPostProcessors.add(pp);
if (pp instanceof MergedBeanDefinitionPostProcessor) {
internalPostProcessors.add(pp);
}
} else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
orderedPostProcessorNames.add(ppName);
} else {
nonOrderedPostProcessorNames.add(ppName);
}
}
//根据优先级进行排序后置处理器
sortPostProcessors(beanFactory, priorityOrderedPostProcessors);
//注册priorityOrdered后置处理器到工厂类中
registerBeanPostProcessors(beanFactory, (List)priorityOrderedPostProcessors);
List<BeanPostProcessor> orderedPostProcessors = new ArrayList();
Iterator var14 = orderedPostProcessorNames.iterator();
while(var14.hasNext()) {
String ppName = (String)var14.next();
BeanPostProcessor pp = (BeanPostProcessor)beanFactory.getBean(ppName, BeanPostProcessor.class);
orderedPostProcessors.add(pp);
if (pp instanceof MergedBeanDefinitionPostProcessor) {
internalPostProcessors.add(pp);
}
}
//根据优先级进行排序后置处理器
sortPostProcessors(beanFactory, orderedPostProcessors);
//注册ordered后置处理器到工厂类中
registerBeanPostProcessors(beanFactory, (List)orderedPostProcessors);
List<BeanPostProcessor> nonOrderedPostProcessors = new ArrayList();
Iterator var17 = nonOrderedPostProcessorNames.iterator();
while(var17.hasNext()) {
ppName = (String)var17.next();
pp = (BeanPostProcessor)beanFactory.getBean(ppName, BeanPostProcessor.class);
nonOrderedPostProcessors.add(pp);
if (pp instanceof MergedBeanDefinitionPostProcessor) {
internalPostProcessors.add(pp);
}
}
//根据未排序的后置处理器
registerBeanPostProcessors(beanFactory, (List)nonOrderedPostProcessors);
sortPostProcessors(beanFactory, internalPostProcessors);
registerBeanPostProcessors(beanFactory, (List)internalPostProcessors);
beanFactory.addBeanPostProcessor(new PostProcessorRegistrationDelegate.ApplicationListenerDetector(applicationContext));
}看看 registerBeanPostProcessors()方法的内容：
private static void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory, List<BeanPostProcessor> postProcessors) {
Iterator var2 = postProcessors.iterator();
while(var2.hasNext()) {
BeanPostProcessor postProcessor = (BeanPostProcessor)var2.next();
beanFactory.addBeanPostProcessor(postProcessor);
}
}方法接受一个后置处理器的列表，内部逐个处理器完成注册。看看addBeanPostProcessor()方法的内容：
public void addBeanPostProcessor(BeanPostProcessor beanPostProcessor) {
Assert.notNull(beanPostProcessor, "BeanPostProcessor must not be null");
this.beanPostProcessors.remove(beanPostProcessor);
this.beanPostProcessors.add(beanPostProcessor);
if (beanPostProcessor instanceof InstantiationAwareBeanPostProcessor) {
this.hasInstantiationAwareBeanPostProcessors = true;
}
if (beanPostProcessor instanceof DestructionAwareBeanPostProcessor) {
this.hasDestructionAwareBeanPostProcessors = true;
}
}首先删除集合中的BeanPostProcessor，在进行添加，beanPostProcessors集合是工厂类中一个list类型的私有变量private final List<BeanPostProcessor> beanPostProcessors = new ArrayList()。这样就完成了后置处理器BeanPostProcessor的注册。
看看工厂中注册的所有的处理器：
此文不是关注所有的BeanPostProcessor处理器，我们只重点关注和事务代理类相关的处理器AnnotationAwareAspectJAutoProxyCreator
创建代理类
完成后置处理器BeanPostProcessor的注册之后，容器会进行bean对象的创建工作，创建工作主要在finishBeanFactoryInitialization()方法中进行：
protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
.....
beanFactory.setTempClassLoader((ClassLoader)null);
beanFactory.freezeConfiguration();
beanFactory.preInstantiateSingletons();
}从方法中看出，直接调用了beanFactory.preInstantiateSingletons()，创建工作还是交给了工厂类来完成，这个beanFactory类的实现类就是DefaultListableBeanFactory。
preInstantiateSingletons方法中遍历集合变量beanDefinitionNames，此变量中存储了容器所有的标签定义。变量内容如下：
@Override
public void preInstantiateSingletons() throws BeansException {
List<String> beanNames = new ArrayList<String>(this.beanDefinitionNames);
for (String beanName : beanNames) {
RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
if (isFactoryBean(beanName)) {
final FactoryBean<?> factory = (FactoryBean<?>) getBean(FACTORY_BEAN_PREFIX + beanName);
boolean isEagerInit;
if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
isEagerInit = AccessController.doPrivileged(new PrivilegedAction<Boolean>() {
@Override
public Boolean run() {
return ((SmartFactoryBean<?>) factory).isEagerInit();
}
}, getAccessControlContext());
}
else {
isEagerInit = (factory instanceof SmartFactoryBean &&
((SmartFactoryBean<?>) factory).isEagerInit());
}
if (isEagerInit) {
getBean(beanName);
}
}
else {
getBean(beanName);
}
}
}
}然后根据beanName调用this.getBean(beanName)方法创建bean。
在实例化之前，beanFactory会遍历所有的后置处理器BeanPostProcessor的postProcessBeforeInstantiation(beanClass, beanName)方法，postProcessBeforeInstantiation方法的具体内容不是此处的重点，忽略，此处我们以authUserServiceImpl实例化为例，分析代理类的创建过程，在创建authUserServiceImpl的过程中会调用后置处理器AnnotationAwareAspectJAutoProxyCreator，在前文中提到过这个处理器，他是<aop:aspectj-autoproxy>标签对应的classbean类，在执行处理器的postProcessBeforeInstantiation方法的过程中会先实例化DefaultBeanFactoryPointcutAdvisor，我们在bean.xml中配置了<aop:advisor>标签，这个标签对应的beanClass类就是DefaultBeanFactoryPointcutAdvisor，这个是Advisor的实现类。spring会解析这个标签并将其封装成为RootBeanDefinition注册到工厂类中。为什么会实例化这个类呢，因为AnnotationAwareAspectJAutoProxyCreator的postProcessBeforeInstantiation这个方法中会遍历所有的Advisor配置器，为什么遍历所有的Advisor，此处不是分析的重点，忽略。
调用完处理器的postProcessBeforeInstantiation方法之后，接下来就是工厂类调用AuthUserServiceImpl的构造函数，进行authUserServiceImpl的实例化，实例化完成之后，调用工厂类的populateBean(beanName, mbd, instanceWrapper)方法，进行对象属性的赋值，赋值的过程又是一个遍历处理器BeanPostProcessor的过程，此处的处理器是InstantiationAwareBeanPostProcessor，完成实例化之后的属性赋值，赋值的过程中如果依赖其他对象，则会先实例化依赖的对象并进行赋值，之后才能完成authUserServiceImpl的赋值操作。authUserServiceImpl依赖于AuthUserMapper，AuthUserMapper依赖sqlSessionFacory，sqlSessionFacory依赖DataSource。
调用populateBean赋值完成之后，调用initializeBean(beanName, exposedObject, mbd)方法，进行对象的初始化。初始化首先调用处理器BeanPostProcessor的postProcessBeforeInitialization()方法，再调用InitializingBean实现类的afterPropertiesSet方法，再调用InitMethod方法，最后调用处理器BeanPostProcessor的postProcessAfterInitialization方法。
其他的处理器的postProcessAfterInitialization方法不做重点分析，重点分析处理器AnnotationAwareAspectJAutoProxyCreator的postProcessAfterInitialization方法，因为创建代理类的逻辑，在这个处理器中来完成的。
@Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
if (bean != null) {
Object cacheKey = getCacheKey(bean.getClass(), beanName);
if (!this.earlyProxyReferences.contains(cacheKey)) {
return wrapIfNecessary(bean, beanName, cacheKey);
}
}
return bean;
}处理器首先从beanFactory中根据Advisor.class类型查找出所有Advisor的实现类DefaultBeanFactoryPointcutAdvisor，目前容器中只有一个Advisor的实现类。DefaultBeanFactoryPointcutAdvisor包含两个成员，一个是pointcut，一个是Advice，
而这个Advisor中直接持有pointcut切入点的表达式expression="execution(* com.test.service.*.*(..))"，
当前创建的com.test.service.impl.AuthUserServiceImpl对象又符合表达式的要求，知道了pointcut切入点，还需要有advice，而这个advice并没有被实例化，所以此时又会先实例化advice，
@Override
public Advice getAdvice() {
synchronized (this.adviceMonitor) {
if (this.advice == null && this.adviceBeanName != null) {
Assert.state(this.beanFactory != null, "BeanFactory must be set to resolve 'adviceBeanName'");
this.advice = this.beanFactory.getBean(this.adviceBeanName, Advice.class);
}
return this.advice;
}
}adviceBeanName变量的值就是interceptorAdvice，这是我们在bean.xml中配置的advice-ref的值
<aop:config>
<aop:pointcut id="transactionPointcut" expression="execution(* com.test.service.*.*(..))"/>
<aop:advisor pointcut-ref="transactionPointcut" advice-ref="interceptorAdvice"/>
</aop:config>实例化advice之后，它引用的就是TransactionInterceptor，它是一个advice也是一个interceptor。为什么是TransactionInterceptor呢？
interceptorAdvice所指向的标签就是tx:advice，spring将tx:advice标签封装成为RootBeanDefinition存储在工厂类中，RootBeanDefinition的classbean就是指向的是TransactionInterceptor，
<!-- 配置通知 -->
<tx:advice id="interceptorAdvice" transaction-manager="transactionManager">
<tx:attributes>
<tx:method name="delete*" propagation="REQUIRED" read-only="false" rollback-for="Exception"/>
</tx:attributes>
</tx:advice>看看tx标签处理器：
public class TxNamespaceHandler extends NamespaceHandlerSupport {
@Override
public void init() {
registerBeanDefinitionParser("advice", new TxAdviceBeanDefinitionParser());
registerBeanDefinitionParser("annotation-driven", new AnnotationDrivenBeanDefinitionParser());
registerBeanDefinitionParser("jta-transaction-manager", new JtaTransactionManagerBeanDefinitionParser());
}
}advice所对应的解析器就是TxAdviceBeanDefinitionParser，解析器的getBeanClass()方法返回值就是TransactionInterceptor.class
回到处理器BeanPostProcessor的postProcessAfterInitialization()方法，调用wrapIfNecessary()方法，
protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
if (specificInterceptors != DO_NOT_PROXY) {
this.advisedBeans.put(cacheKey, Boolean.TRUE);
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;
}调用getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null)方法的目的就是，找到正在创建的AuthUserServiceImpl类，是否符合切入点的要求，如果符合就返回拦截器，就是上面我们找到的TransactionInterceptor。这个拦截器会在以后调用AuthUserServiceImpl的方法的时候起到拦截事物的作用。
既然拦截器是存在的，那就需要创建代理类，调用createProxy()来完成代理类的创建。
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);
}
return proxyFactory.getProxy(getProxyClassLoader());
}首先创建一个ProxyFactory工厂，这个工厂类来完成代理类的创建工作。spring aop在创建代理类的选择上，可以有两种方式创建代理类，一种是jdk的动态代理JdkDynamicAopProxy，另外一种是cglib方式ObjenesisCglibAopProxy。具体怎么选择，看如下代码：
public AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException {
if (config.isOptimize() || config.isProxyTargetClass() || hasNoUserSuppliedProxyInterfaces(config)) {
Class<?> targetClass = config.getTargetClass();
if (targetClass == null) {
throw new AopConfigException("TargetSource cannot determine target class: " +
"Either an interface or a target is required for proxy creation.");
}
if (targetClass.isInterface() || Proxy.isProxyClass(targetClass)) {
return new JdkDynamicAopProxy(config);
}
return new ObjenesisCglibAopProxy(config);
}
else {
return new JdkDynamicAopProxy(config);
}
}config.isOptimize()没找到在哪儿设置，默认是false，先不管。
config.isProxyTargetClass()的值就是<aop:aspectj-autoproxy proxy-target-class="true"/>标签中proxy-target-class属性的值，
hasNoUserSuppliedProxyInterfaces(config)判断当前目标类是否实现了某个接口，也就是判断是不是面向接口编程，并且实现了org.springframework.aop.SpringProxy接口，proxy-target-class等于false的时候才会判断是否面向接口编程。
private boolean hasNoUserSuppliedProxyInterfaces(AdvisedSupport config) {
Class<?>[] ifcs = config.getProxiedInterfaces();
return (ifcs.length == 0 || (ifcs.length == 1 && SpringProxy.class.isAssignableFrom(ifcs[0])));
}targetClass.isInterface()表示如果目标类是一个接口，使用jdk的动态代理JdkDynamicAopProxy创建代理类，
Proxy.isProxyClass(targetClass)表示目标类继承了java.lang.reflect.Proxy类，同样也会使用jdk的动态代理JdkDynamicAopProxy创建代理类，
确定采用cglib还是jdk动态代理方式策略之后，就调用getProxy()创建代理类。
代理类创建出来之后，spring将其注册到工厂类中的局部变量中
private final Map<String, Object> singletonObjects = new ConcurrentHashMap(64);
private final Set<String> registeredSingletons = new LinkedHashSet(64);
protected void addSingleton(String beanName, Object singletonObject) {
Map var3 = this.singletonObjects;
synchronized(this.singletonObjects) {
this.singletonObjects.put(beanName, singletonObject != null ? singletonObject : NULL_OBJECT);
this.singletonFactories.remove(beanName);
this.earlySingletonObjects.remove(beanName);
this.registeredSingletons.add(beanName);
}
}ok，这就完成了代理类的创建。
从上图中可以看得出来，这个authUserServiceImpl所引用的实例是用cglib的方式创建出来的。
最后附上一张时序图，这张时序图并不代表实际的过程，省略了一些过程，和简化了一些内容。
