版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/qq_26323323/article/details/81700626
前言：
缓存是我们常用的一种优化系统的方案。
无论是前端缓存还是应用层缓存或者数据库缓存，其本质都是将查询过的数据缓存下来，下次再次查询该数据的时候如果数据没有过期，则直接返回缓存中该数据即可，不再执行查询操作。
SpringCache是我们常用的一种应用层缓存方案，其一般应用在方法上，下面我们先来看下具体的使用方式，然后再从源码角度分析其实现方案
读者需要了解SpringCache的具体用法的话可以先参考其他文章。
1.SpringCache的使用
1）maven引入依赖
cache功能相关代码都在spring-context中，一般使用Spring的项目中都有该包，所以不用再单独引入
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2）Service（业务处理类，代码参考网上文章，非原创，有改动）
// 接口类
package cache;
public interface IService {
Account getAccountByName(String userName);
void updateAccount(Account account);
}
// 实现类
public class AccountService implements IService{
@Override
@Cacheable(value = "accountCache") // 使用了一个缓存名叫 accountCache
public Account getAccountByName(String userName) {
// 方法内部实现不考虑缓存逻辑，直接实现业务
System.out.println("real query account." + userName);
return getFromDB(userName);
}
@Override
@CacheEvict(value="accountCache",key="#account.getName()")
public void updateAccount(Account account) {
updateDB(account);
}
@CacheEvict(value = "accountCache", allEntries = true)
public void reload() {
}
private Account getFromDB(String acctName) {
System.out.println("real querying db..." + acctName);
return new Account(acctName);
}
private void updateDB(Account account) {
System.out.println("real update db..." + account.getName());
}
}如上所示：在方法上加上@cacheable等注解即可
3）Spring-cache-anno.xml文件（用于定义bean）
<?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:cache="http://www.springframework.org/schema/cache"
xmlns:p="http://www.springframework.org/schema/p"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/cache
http://www.springframework.org/schema/cache/spring-cache.xsd">
<!-- 添加driven -->
<cache:annotation-driven />
<bean id="accountServiceBean" class="cache.AccountService" />
<!-- generic cache manager -->
<bean id="cacheManager" class="org.springframework.cache.support.SimpleCacheManager">
<property name="caches">
<set>
<bean
class="org.springframework.cache.concurrent.ConcurrentMapCacheFactoryBean"
p:name="accountCache" />
</set>
</property>
</bean>
</beans>使用默认的SimpleCacheManager
4）测试（测试缓存是否生效）
public class Test {
public static void main(String[] args) {
ApplicationContext context = new ClassPathXmlApplicationContext("spring-cache-anno.xml");
IService s = context.getBean(IService.class);
// 第一次查询，应该走数据库
System.out.print("first query...");
s.getAccountByName("somebody");
// 第二次查询，应该不查数据库，直接返回缓存的值
System.out.print("second query...");
s.getAccountByName("somebody");
System.out.println();
}
}
//result：
first query...
real query account.somebody
real querying db...somebody
second query...
总结：根据结果可以看到，第二次查询的时候没有真正执行getFromDB()方法，而是从缓存中取的数据
2.写在源码分析之前
如果是我们来做的话，如何实现该功能？
基于我们对Spring的一贯理解，这应该是个代理，我们在获取IService的bean时候，应该获取的是个代理类，代理类执行业务方法，先去查询是否在缓存中有该数据，如果有则直接从缓存中获取，如果没有，则调用AccountService的方法
3.SpringCache源码结构分析
根据我们的示例可知，真正的内容都放在配置文件里了
配置文件中添加了一个driven（真正的功能应该在这里实现的）
<cache:annotation-driven />下面是两个bean（accountServiceBean是我们需要的，需要将AccountService注入到容器中。
至于SimpleCacheManager暂时不知道其作用，只知道其实现了CacheManage接口，我们先暂时放一下）
<bean id="accountServiceBean" class="cache.AccountService" />
<!-- generic cache manager -->
<bean id="cacheManager" class="org.springframework.cache.support.SimpleCacheManager">
<property name="caches">
<set>
<bean
class="org.springframework.cache.concurrent.ConcurrentMapCacheFactoryBean"
p:name="accountCache" />
</set>
</property>
</bean>1）<cache:annotation-driven/>的分析
但凡这种注解，都有对应的解析器，从之前分析AOP功能的源码可知，解析器都实现了NamespaceHandlerSupport类，我们来获取下NamespaceHandlerSupport的实现类都有哪些
里面有一个叫做CacheNamespaceHandler的类，看名字就像这个，我们来看下这个类
2）CacheNamespaceHandler
public class CacheNamespaceHandler extends NamespaceHandlerSupport {
static final String CACHE_MANAGER_ATTRIBUTE = "cache-manager";
static final String DEFAULT_CACHE_MANAGER_BEAN_NAME = "cacheManager";
...
@Override
public void init() {
// 主要是这句代码
registerBeanDefinitionParser("annotation-driven", new AnnotationDrivenCacheBeanDefinitionParser());
registerBeanDefinitionParser("advice", new CacheAdviceParser());
}
}Spring会默认调用其init()方法，annotation-driven对应的是AnnotationDrivenCacheBeanDefinitionParser解析器，我们来看下这个解析器的作用
3）AnnotationDrivenCacheBeanDefinitionParser
@Override
public BeanDefinition parse(Element element, ParserContext parserContext) {
String mode = element.getAttribute("mode");// mode默认为proxy
if ("aspectj".equals(mode)) {
// mode="aspectj"
registerCacheAspect(element, parserContext);
}
else {
// 直接调用该方法
registerCacheAdvisor(element, parserContext);
}
return null;
}
// registerCacheAdvisor()
private void registerCacheAdvisor(Element element, ParserContext parserContext) {
// 1.注册ProxyCreator类 在4）中详细分析
AopNamespaceUtils.registerAutoProxyCreatorIfNecessary(parserContext, element);
// 2.注册CacheAdvisor 在5）中详细分析
SpringCachingConfigurer.registerCacheAdvisor(element, parserContext);
if (jsr107Present && jcacheImplPresent) {
// 默认不会调用
JCacheCachingConfigurer.registerCacheAdvisor(element, parserContext);
}
}4）AopNamespaceUtils.registerAutoProxyCreatorIfNecessary(parserContext, element)
public static void registerAutoProxyCreatorIfNecessary(
ParserContext parserContext, Element sourceElement) {
// 重点在这里
BeanDefinition beanDefinition = AopConfigUtils.registerAutoProxyCreatorIfNecessary(
parserContext.getRegistry(), parserContext.extractSource(sourceElement));
useClassProxyingIfNecessary(parserContext.getRegistry(), sourceElement);
registerComponentIfNecessary(beanDefinition, parserContext);
}
// AopConfigUtils.registerAutoProxyCreatorIfNecessary()
public static BeanDefinition registerAutoProxyCreatorIfNecessary(BeanDefinitionRegistry registry, Object source) {
// 重点在这里
return registerOrEscalateApcAsRequired(InfrastructureAdvisorAutoProxyCreator.class, registry, source);
}可以看到，主要是为了将InfrastructureAdvisorAutoProxyCreator注册到容器中
5）SpringCachingConfigurer.registerCacheAdvisor(element, parserContext)
private static void registerCacheAdvisor(Element element, ParserContext parserContext) {
if (!parserContext.getRegistry().containsBeanDefinition(CacheManagementConfigUtils.CACHE_ADVISOR_BEAN_NAME)) {
Object eleSource = parserContext.extractSource(element);
// 1.注册AnnotationCacheOperationSource类到容器中
RootBeanDefinition sourceDef = new RootBeanDefinition("org.springframework.cache.annotation.AnnotationCacheOperationSource");
sourceDef.setSource(eleSource);
sourceDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
String sourceName = parserContext.getReaderContext().registerWithGeneratedName(sourceDef);
// 2.注册CacheInterceptor类到容器中
RootBeanDefinition interceptorDef = new RootBeanDefinition(CacheInterceptor.class);
interceptorDef.setSource(eleSource);
interceptorDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
parseCacheResolution(element, interceptorDef, false);
parseErrorHandler(element, interceptorDef);
CacheNamespaceHandler.parseKeyGenerator(element, interceptorDef);
interceptorDef.getPropertyValues().add("cacheOperationSources", new RuntimeBeanReference(sourceName));
String interceptorName = parserContext.getReaderContext().registerWithGeneratedName(interceptorDef);
// 3.注册BeanFactoryCacheOperationSourceAdvisor类到容器中，
RootBeanDefinition advisorDef = new RootBeanDefinition(BeanFactoryCacheOperationSourceAdvisor.class);
advisorDef.setSource(eleSource);
advisorDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
// 注意这里，将AnnotationCacheOperationSource和CacheInterceptor作为其属性注入进来
advisorDef.getPropertyValues().add("cacheOperationSource", new RuntimeBeanReference(sourceName));
advisorDef.getPropertyValues().add("adviceBeanName", interceptorName);
if (element.hasAttribute("order")) {
advisorDef.getPropertyValues().add("order", element.getAttribute("order"));
}
// 注意这句，将BeanFactoryCacheOperationSourceAdvisor类的注册名称设置为
// org.springframework.cache.config.internalCacheAdvisor
// 在下面会用到这个名称
parserContext.getRegistry().registerBeanDefinition(CacheManagementConfigUtils.CACHE_ADVISOR_BEAN_NAME, advisorDef);
...
}
}总结：由以上分析可知，我们添加<cache:annotation-driven />注解，主要是将以下类注入进Spring容器
* InfrastructureAdvisorAutoProxyCreator
* AnnotationCacheOperationSource
* CacheInterceptor（主要的拦截功能都实现在这里）
* BeanFactoryCacheOperationSourceAdvisor（重点关注这个，这个类在创建代理的时候被使用）
我们暂时只知道加载driven注解的时候，只是将这四个类注入到Spring容器中，而这些类具体在做什么，我们也不知道，更不知道与我们的AccountService类有什么关联。这些我们先暂时放一下，先看下CacheInterceptor和InfrastructureAdvisorAutoProxyCreator的功能简介
4.CacheInterceptor功能简单分析
其代码结构如下
可知：
* 其实现了InitializingBean接口，则CacheInterceptor创建的时候会默认调用afterPropertiesSet()方法；
* 其实现了SmartInitializingSingleton接口，则CacheInterceptor创建的时候会默认调用afterSingletonsInstantiated()方法
* 其实现了MethodInterceptor接口，则在被其拦截的方法上，默认会调用其invoke()方法
有关于这些接口的作用，不太明白的同学可以先看下对应的文章了解其大致作用
1）初始化afterPropertiesSet()方法
// 只是做了校验，没有其他功能
public void afterPropertiesSet() {
Assert.state(getCacheOperationSource() != null, "The 'cacheOperationSources' property is required: " +
"If there are no cacheable methods, then don't use a cache aspect.");
Assert.state(getErrorHandler() != null, "The 'errorHandler' property is required");
}2）初始化afterSingletonsInstantiated()方法
public void afterSingletonsInstantiated() {
if (getCacheResolver() == null) {
// Lazily initialize cache resolver via default cache manager...
try {
// 重点在这里
// 从工厂类中获取CacheManager的实现类
// 这里就与我们的Spring-cache-anno.xml配置文件中的创建的cacheManager
// bean关联起来了，在配置文件中创建的bean实现了接口CacheManager
// 则会在这里被使用
setCacheManager(this.beanFactory.getBean(CacheManager.class));
}
...
}
this.initialized = true;
}
// setCacheManager()
public void setCacheManager(CacheManager cacheManager) {
// private CacheResolver cacheResolver;
this.cacheResolver = new SimpleCacheResolver(cacheManager);
}3）invoke(）执行拦截方法（这个我们暂时先不分析，读者只需要知道这个拦截方法的存在即可）
public Object invoke(final MethodInvocation invocation) throws Throwable {
Method method = invocation.getMethod();
CacheOperationInvoker aopAllianceInvoker = new CacheOperationInvoker() {
@Override
public Object invoke() {
try {
return invocation.proceed();
}
catch (Throwable ex) {
throw new ThrowableWrapper(ex);
}
}
};
try {
return execute(aopAllianceInvoker, invocation.getThis(), method, invocation.getArguments());
}
catch (CacheOperationInvoker.ThrowableWrapper th) {
throw th.getOriginal();
}
}总结4：
CacheInterceptor主要是一个方法拦截器，在初始化的时候将CacheManager的实现类（由用户自定义实现）添加进来；
invoke()方法，真正执行拦截的方法
5.InfrastructureAdvisorAutoProxyCreator功能分析
其代码结构如下：
可以看到，其实现了BeanPostProcessor接口，则Spring在创建bean的时候，会默认调用InfrastructureAdvisorAutoProxyCreator的postProcessAfterInitialization()方法，就是在这个方法中创建代理类的，下面我们来看下这个方法
1）AbstractAutoProxyCreator.postProcessAfterInitialization()
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
if (bean != null) {
Object cacheKey = getCacheKey(bean.getClass(), beanName);
if (!this.earlyProxyReferences.contains(cacheKey)) {
// 重要方法
return wrapIfNecessary(bean, beanName, cacheKey);
}
}
return bean;
}
// wrapIfNecessary()
protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
...
// 1.获取当前类的所有切面拦截类，在2）中详细分析
Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
// 2.如果拦截类不为空，则需要创建当前类的代理类
if (specificInterceptors != DO_NOT_PROXY) {
this.advisedBeans.put(cacheKey, Boolean.TRUE);
// 3.创建代理类，在3）中详细分析
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;
}以上逻辑类似于之前分析的AOP源码，读者也可以先看下 https://blog.csdn.net/qq_26323323/article/details/81012855
2）getAdvicesAndAdvisorsForBean()获取当前类的所有切面拦截器
本方法为抽象方法，实现由子类AbstractAdvisorAutoProxyCreator实现
protected Object[] getAdvicesAndAdvisorsForBean(Class<?> beanClass, String beanName, TargetSource targetSource) {
List<Advisor> advisors = findEligibleAdvisors(beanClass, beanName);//重点在这里
if (advisors.isEmpty()) {
return DO_NOT_PROXY;
}
return advisors.toArray();
}
// findEligibleAdvisors()
protected List<Advisor> findEligibleAdvisors(Class<?> beanClass, String beanName) {
// 1.获取所有的Advisor
List<Advisor> candidateAdvisors = findCandidateAdvisors();
// 2.获取适合当前类的Advisor
List<Advisor> eligibleAdvisors = findAdvisorsThatCanApply(candidateAdvisors, beanClass, beanName);
extendAdvisors(eligibleAdvisors);
if (!eligibleAdvisors.isEmpty()) {
eligibleAdvisors = sortAdvisors(eligibleAdvisors);
}
return eligibleAdvisors;
}* findCandidateAdvisors()获取所有的Advisor
// findCandidateAdvisors()
protected List<Advisor> findCandidateAdvisors() {
return this.advisorRetrievalHelper.findAdvisorBeans();
}
//findAdvisorBeans()
public List<Advisor> findAdvisorBeans() {
// Determine list of advisor bean names, if not cached already.
String[] advisorNames = null;
synchronized (this) {
// 1.cachedAdvisorBeanNames=org.springframework.cache.config.internalCacheAdvisor
advisorNames = this.cachedAdvisorBeanNames;
if (advisorNames == null) {
// Do not initialize FactoryBeans here: We need to leave all regular beans
// uninitialized to let the auto-proxy creator apply to them!
advisorNames = BeanFactoryUtils.beanNamesForTypeIncludingAncestors(
this.beanFactory, Advisor.class, true, false);
this.cachedAdvisorBeanNames = advisorNames;
}
}
if (advisorNames.length == 0) {
return new LinkedList<Advisor>();
}
List<Advisor> advisors = new LinkedList<Advisor>();
for (String name : advisorNames) {
if (isEligibleBean(name)) {
if (this.beanFactory.isCurrentlyInCreation(name)) {
if (logger.isDebugEnabled()) {
logger.debug("Skipping currently created advisor '" + name + "'");
}
}
else {
try {
// 2.从工厂中获取CacheInterceptor对应的bean
// 在上述代码 3节5）中，可知，
// org.springframework.cache.config.internalCacheAdvisor这个名称对应bean为
// BeanFactoryCacheOperationSourceAdvisor类，
advisors.add(this.beanFactory.getBean(name, Advisor.class));
}
catch (BeanCreationException ex) {
Throwable rootCause = ex.getMostSpecificCause();
if (rootCause instanceof BeanCurrentlyInCreationException) {
BeanCreationException bce = (BeanCreationException) rootCause;
if (this.beanFactory.isCurrentlyInCreation(bce.getBeanName())) {
if (logger.isDebugEnabled()) {
logger.debug("Skipping advisor '" + name +
"' with dependency on currently created bean: " + ex.getMessage());
}
// Ignore: indicates a reference back to the bean we're trying to advise.
// We want to find advisors other than the currently created bean itself.
continue;
}
}
throw ex;
}
}
}
}
return advisors;
}总结2）：适合当前类的Advisor最终为BeanFactoryCacheOperationSourceAdvisor类，也就是我们之前在分析<cache:annotation-driven/>中注册的BeanFactoryCacheOperationSourceAdvisor bean
3）createProxy( Class<?> beanClass, String beanName, Object[] specificInterceptors, TargetSource targetSource)
创建代理类
这里笔者就不再继续分析了，具体读者可参考 https://blog.csdn.net/qq_26323323/article/details/81012855 博文中创建proxy过程分析一节
总结5：InfrastructureAdvisorAutoProxyCreator的主要作用就是实现了BeanPostProcessor接口，那么Spring的每个bean在创建的过程中，都需要调用其postProcessAfterInitialization()方法，在这个方法中查询出所有适合当前类的Advisor，然后创建当前类的代理类，并将Advisor封装进来，在以后调用当前类的方法时使用
6.代理类invoke()方法调用
通过以上分析可知，Spring为我们创建的AccountService bean实际是一个关于AccountService的代理类，在调用AccountService的相关方法时，实际调用的是代理类的invoke()方法，下面我们就来分析下，invoke()方法被调用的过程，具体了解下我们的缓存是如何工作的
由于本例是JDKProxy创建的方式，而非CGLIBProxy的创建方式，所以AccountService的代理类为JdkDynamicAopProxy，下面看下其invoke()方法
1）JdkDynamicAopProxy.invoke()
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
MethodInvocation invocation;
Object oldProxy = null;
boolean setProxyContext = false;
TargetSource targetSource = this.advised.targetSource;
Class<?> targetClass = null;
Object target = null;
try {
...
Object retVal;
if (this.advised.exposeProxy) {
// Make invocation available if necessary.
oldProxy = AopContext.setCurrentProxy(proxy);
setProxyContext = true;
}
target = targetSource.getTarget();
if (target != null) {
targetClass = target.getClass();
}
// 1.获取当前方法的拦截器链，也就是Advisor列表
// 最终返回的是当前Advisor的拦截器MethodInterceptor列表
// 在2）中详细分析
List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);
// 2.如果拦截器链为空，说明当前方法没有缓存注解，直接调用方法即可
if (chain.isEmpty()) {
Object[] argsToUse = AopProxyUtils.adaptArgumentsIfNecessary(method, args);
retVal = AopUtils.invokeJoinpointUsingReflection(target, method, argsToUse);
}
// 3.说明当前方法有缓存注解，则需要先调用拦截器链的方法
else {
invocation = new ReflectiveMethodInvocation(proxy, target, method, args, targetClass, chain);
// 真正的调用在这里
// 在3）中详细分析
retVal = invocation.proceed();
}
...
return retVal;
}
...
}2）AdvisedSupport.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);获取当前方法的拦截器链
public List<Object> getInterceptorsAndDynamicInterceptionAdvice(Method method, Class<?> targetClass) {
MethodCacheKey cacheKey = new MethodCacheKey(method);
List<Object> cached = this.methodCache.get(cacheKey);
if (cached == null) {
// 真正的实现在这里
cached = this.advisorChainFactory.getInterceptorsAndDynamicInterceptionAdvice(
this, method, targetClass);
this.methodCache.put(cacheKey, cached);
}
return cached;
}
//DefaultAdvisorChainFactory.getInterceptorsAndDynamicInterceptionAdvice()
public List<Object> getInterceptorsAndDynamicInterceptionAdvice(
Advised config, Method method, Class<?> targetClass) {
// This is somewhat tricky... We have to process introductions first,
// but we need to preserve order in the ultimate list.
List<Object> interceptorList = new ArrayList<Object>(config.getAdvisors().length);
Class<?> actualClass = (targetClass != null ? targetClass : method.getDeclaringClass());
boolean hasIntroductions = hasMatchingIntroductions(config, actualClass);
AdvisorAdapterRegistry registry = GlobalAdvisorAdapterRegistry.getInstance();
// 1.遍历当前bean的所有Advisor
// 就当前示例而言，只有一个Advisor，就是之前创建的BeanFactoryCacheOperationSourceAdvisor
for (Advisor advisor : config.getAdvisors()) {
if (advisor instanceof PointcutAdvisor) {
// Add it conditionally.
PointcutAdvisor pointcutAdvisor = (PointcutAdvisor) advisor;
if (config.isPreFiltered() || pointcutAdvisor.getPointcut().getClassFilter().matches(actualClass)) {
// 2.获取Advisor的Interceptor，也就是在分析<cache:annotation-driven />时
// 被添加到BeanFactoryCacheOperationSourceAdvisor类的CacheInterceptor类
MethodInterceptor[] interceptors = registry.getInterceptors(advisor);
MethodMatcher mm = pointcutAdvisor.getPointcut().getMethodMatcher();
if (MethodMatchers.matches(mm, method, actualClass, hasIntroductions)) {
if (mm.isRuntime()) {
// Creating a new object instance in the getInterceptors() method
// isn't a problem as we normally cache created chains.
for (MethodInterceptor interceptor : interceptors) {
interceptorList.add(new InterceptorAndDynamicMethodMatcher(interceptor, mm));
}
}
else {
interceptorList.addAll(Arrays.asList(interceptors));
}
}
}
}
else if (advisor instanceof IntroductionAdvisor) {
IntroductionAdvisor ia = (IntroductionAdvisor) advisor;
if (config.isPreFiltered() || ia.getClassFilter().matches(actualClass)) {
Interceptor[] interceptors = registry.getInterceptors(advisor);
interceptorList.addAll(Arrays.asList(interceptors));
}
}
else {
Interceptor[] interceptors = registry.getInterceptors(advisor);
interceptorList.addAll(Arrays.asList(interceptors));
}
}
return interceptorList;
}
所以，拦截器链最终返回的是我们之前分析的CacheInterceptor类
3）ReflectiveMethodInvocation.proceed()拦截器链的调用分析
// InterceptedMethodInvocation.proceed()
public Object proceed() throws Throwable {
try {
// 主要就是遍历调用Interceptor的invoke方法
return index == interceptors.length
? methodProxy.invokeSuper(proxy, arguments)
: interceptors[index].invoke(
new InterceptedMethodInvocation(proxy, methodProxy, arguments, index + 1));
} catch (Throwable t) {
pruneStacktrace(t);
throw t;
}
}那我们看下CacheInterceptor.invoke()方法
public Object invoke(final MethodInvocation invocation) throws Throwable {
Method method = invocation.getMethod();
CacheOperationInvoker aopAllianceInvoker = new CacheOperationInvoker() {
@Override
public Object invoke() {
try {
return invocation.proceed();
}
catch (Throwable ex) {
throw new ThrowableWrapper(ex);
}
}
};
try {
// 重点方法
return execute(aopAllianceInvoker, invocation.getThis(), method, invocation.getArguments());
}
catch (CacheOperationInvoker.ThrowableWrapper th) {
throw th.getOriginal();
}
}
//CacheAspectSupport.execute()
protected Object execute(CacheOperationInvoker invoker, Object target, Method method, Object[] args) {
// Check whether aspect is enabled (to cope with cases where the AJ is pulled in automatically)
if (this.initialized) {
Class<?> targetClass = getTargetClass(target);
// 1.获取当前方法的缓存操作
Collection<CacheOperation> operations = getCacheOperationSource().getCacheOperations(method, targetClass);
if (!CollectionUtils.isEmpty(operations)) {
// 2.执行缓存操作
return execute(invoker, method, new CacheOperationContexts(operations, method, args, target, targetClass));
}
}
return invoker.invoke();
}* getCacheOperationSource().getCacheOperations(method, targetClass)获取当前方法的缓存操作
默认实现类为AbstractFallbackCacheOperationSource
// AbstractFallbackCacheOperationSource.getCacheOperations(Method method, Class<?> targetClass)
public Collection<CacheOperation> getCacheOperations(Method method, Class<?> targetClass) {
if (method.getDeclaringClass() == Object.class) {
return null;
}
Object cacheKey = getCacheKey(method, targetClass);
Collection<CacheOperation> cached = this.attributeCache.get(cacheKey);
if (cached != null) {
return (cached != NULL_CACHING_ATTRIBUTE ? cached : null);
}
else {
Collection<CacheOperation> cacheOps = computeCacheOperations(method, targetClass);
if (cacheOps != null) {
if (logger.isDebugEnabled()) {
logger.debug("Adding cacheable method '" + method.getName() + "' with attribute: " + cacheOps);
}
this.attributeCache.put(cacheKey, cacheOps);
}
else {
this.attributeCache.put(cacheKey, NULL_CACHING_ATTRIBUTE);
}
return cacheOps;
}
}* 执行execute()方法（关于操作缓存细节笔者不再详细分析，读者可自行分析）
private Object execute(final CacheOperationInvoker invoker, Method method, CacheOperationContexts contexts) {
// Special handling of synchronized invocation
if (contexts.isSynchronized()) {
CacheOperationContext context = contexts.get(CacheableOperation.class).iterator().next();
if (isConditionPassing(context, CacheOperationExpressionEvaluator.NO_RESULT)) {
Object key = generateKey(context, CacheOperationExpressionEvaluator.NO_RESULT);
Cache cache = context.getCaches().iterator().next();
try {
return wrapCacheValue(method, cache.get(key, new Callable<Object>() {
@Override
public Object call() throws Exception {
return unwrapReturnValue(invokeOperation(invoker));
}
}));
}
catch (Cache.ValueRetrievalException ex) {
// The invoker wraps any Throwable in a ThrowableWrapper instance so we
// can just make sure that one bubbles up the stack.
throw (CacheOperationInvoker.ThrowableWrapper) ex.getCause();
}
}
else {
// No caching required, only call the underlying method
return invokeOperation(invoker);
}
}
// Process any early evictions
processCacheEvicts(contexts.get(CacheEvictOperation.class), true,
CacheOperationExpressionEvaluator.NO_RESULT);
// Check if we have a cached item matching the conditions
Cache.ValueWrapper cacheHit = findCachedItem(contexts.get(CacheableOperation.class));
// Collect puts from any @Cacheable miss, if no cached item is found
List<CachePutRequest> cachePutRequests = new LinkedList<CachePutRequest>();
if (cacheHit == null) {
collectPutRequests(contexts.get(CacheableOperation.class),
CacheOperationExpressionEvaluator.NO_RESULT, cachePutRequests);
}
Object cacheValue;
Object returnValue;
if (cacheHit != null && cachePutRequests.isEmpty() && !hasCachePut(contexts)) {
// If there are no put requests, just use the cache hit
cacheValue = cacheHit.get();
returnValue = wrapCacheValue(method, cacheValue);
}
else {
// Invoke the method if we don't have a cache hit
returnValue = invokeOperation(invoker);
cacheValue = unwrapReturnValue(returnValue);
}
// Collect any explicit @CachePuts
collectPutRequests(contexts.get(CachePutOperation.class), cacheValue, cachePutRequests);
// Process any collected put requests, either from @CachePut or a @Cacheable miss
for (CachePutRequest cachePutRequest : cachePutRequests) {
cachePutRequest.apply(cacheValue);
}
// Process any late evictions
processCacheEvicts(contexts.get(CacheEvictOperation.class), false, cacheValue);
return returnValue;
}总结：
缓存功能的实现实际也是通过Spring代理来实现的。生成当前类的代理类，调用代理类的invoke()方法，在invoke()方法中调用CacheInterceptor拦截器的execute()方法，拦截器会使用缓存器（本例中的SimpleCacheManager）来进行具体方法实现。
重要操作流程如下：
1）解析<cache:annotation-driven />，将InfrastructureAdvisorAutoProxyCreator注入到Spring容器中，该类的作用是在Spring创建bean实例的时候，会执行其postProcessAfterInitialization()方法，生成bean实例的代理类
2）解析<cache:annotation-driven />，将BeanFactoryCacheOperationSourceAdvisor类注入到Spring容器中，该类的主要作用是作为一个Advisor添加到上述代理类中
3）BeanFactoryCacheOperationSourceAdvisor类拥有对CacheInterceptor的依赖，CacheInterceptor作为一个方法拦截器，负责对缓存方法的拦截，
4）当前类方法调用被拦截到CacheInterceptor后，CacheInterceptor会调用我们在配置文件中配置的CacheManager实现（也就是本例中的SimpleCacheManager），来真正实现缓存功能