Spring Boot缓存源码分析
前言
项目里面要增加一个应用缓存，原本想着要怎么怎么来整合ehcache和springboot，做好准备配置这个配置那个，结果只需要做三件事：
- pom依赖
- 写好一个ehcache的配置文件
- 在boot的application上加上注解@EnableCaching.
这就完事了，是不是很魔幻。
pom依赖
<dependency>
<groupId>net.sf.ehcache</groupId>
<artifactId>ehcache</artifactId>
<version>2.10.5</version>
</dependency>
配置文件
<?xml version="1.0" encoding="UTF-8"?>
<ehcache>
<!-- 设定缓存的默认数据过期策略 -->
<defaultCache
maxElementsInMemory="500"
maxElementsOnDisk="2000"
eternal="false"
overflowToDisk="true"
timeToIdleSeconds="90"
timeToLiveSeconds="300"
diskPersistent="false"
diskExpiryThreadIntervalSeconds="300"/>
</ehcache>
应用上加上EnableCaching注解
@SpringBootApplication
@EnableCaching
public class EhCacheApplication {
public static void main(String[] args) {
SpringApplication.run(EhCacheApplication.class, args);
}
}
然后就可以在代码里面使用cache注解了，像这样。
@CachePut(value = "fish-ehcache", key = "#person.id")
public Person save(Person person) {
System.out.println("为id、key为:" + person.getId() + "数据做了缓存");
return person;
}
@CacheEvict(value = "fish-ehcache")
public void remove(Long id) {
System.out.println("删除了id、key为" + id + "的数据缓存");
}
@Cacheable(value = "fish-ehcache", key = "#person.id")
public Person findOne(Person person) {
findCount.incrementAndGet();
System.out.println("为id、key为:" + person.getId() + "数据做了缓存");
return person;
}
很方便对不对。下面，我们就来挖一挖，看看spring是怎么来做到的。主要分成两部分，一是启动的时候做了什么，二是运行的时候做了什么，三是和第三方缓存组件的适配
启动的时候做了什么、
这个得从@EnableCaching标签开始，在使用缓存功能时，在springboot的Application启动类上需要添加注解@EnableCaching，这个标签引入了
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import({CachingConfigurationSelector.class})
public @interface EnableCaching {
boolean proxyTargetClass() default false;
AdviceMode mode() default AdviceMode.PROXY;
int order() default 2147483647;
}
引入了CachingConfigurationSelector类，这个类便开启了缓存功能的配置。这个类添加了AutoProxyRegistrar.java,ProxyCachingConfiguration.java两个类。
- AutoProxyRegistrar : 实现了ImportBeanDefinitionRegistrar接口。这里看不懂，还需要继续学习。
- ProxyCachingConfiguration : 是一个配置类，生成了BeanFactoryCacheOperationSourceAdvisor，CacheOperationSource，和CacheInterceptor这三个bean。
CacheOperationSource封装了cache方法签名注解的解析工作，形成CacheOperation的集合。CacheInterceptor使用该集合过滤执行缓存处理。解析缓存注解的类是SpringCacheAnnotationParser，其主要方法如下
/**
由CacheOperationSourcePointcut作为注解切面，会解析
SpringCacheAnnotationParser.java
扫描方法签名，解析被缓存注解修饰的方法，将生成一个CacheOperation的子类并将其保存到一个数组中去
**/
protected Collection<CacheOperation> parseCacheAnnotations(SpringCacheAnnotationParser.DefaultCacheConfig cachingConfig, AnnotatedElement ae) {
Collection<CacheOperation> ops = null;
//找@cacheable注解方法
Collection<Cacheable> cacheables = AnnotatedElementUtils.getAllMergedAnnotations(ae, Cacheable.class);
if (!cacheables.isEmpty()) {
ops = this.lazyInit(ops);
Iterator var5 = cacheables.iterator();
while(var5.hasNext()) {
Cacheable cacheable = (Cacheable)var5.next();
ops.add(this.parseCacheableAnnotation(ae, cachingConfig, cacheable));
}
}
//找@cacheEvict注解的方法
Collection<CacheEvict> evicts = AnnotatedElementUtils.getAllMergedAnnotations(ae, CacheEvict.class);
if (!evicts.isEmpty()) {
ops = this.lazyInit(ops);
Iterator var12 = evicts.iterator();
while(var12.hasNext()) {
CacheEvict evict = (CacheEvict)var12.next();
ops.add(this.parseEvictAnnotation(ae, cachingConfig, evict));
}
}
//找@cachePut注解的方法
Collection<CachePut> puts = AnnotatedElementUtils.getAllMergedAnnotations(ae, CachePut.class);
if (!puts.isEmpty()) {
ops = this.lazyInit(ops);
Iterator var14 = puts.iterator();
while(var14.hasNext()) {
CachePut put = (CachePut)var14.next();
ops.add(this.parsePutAnnotation(ae, cachingConfig, put));
}
}
Collection<Caching> cachings = AnnotatedElementUtils.getAllMergedAnnotations(ae, Caching.class);
if (!cachings.isEmpty()) {
ops = this.lazyInit(ops);
Iterator var16 = cachings.iterator();
while(var16.hasNext()) {
Caching caching = (Caching)var16.next();
Collection<CacheOperation> cachingOps = this.parseCachingAnnotation(ae, cachingConfig, caching);
if (cachingOps != null) {
ops.addAll(cachingOps);
}
}
}
return ops;
}
解析Cachable,Caching,CachePut,CachEevict 这四个注解对应的方法都保存到了Collection<CacheOperation> 集合中。
执行方法时做了什么
执行的时候，主要使用了CacheInterceptor类。
public class CacheInterceptor extends CacheAspectSupport implements MethodInterceptor, Serializable {
public CacheInterceptor() {
}
public Object invoke(final MethodInvocation invocation) throws Throwable {
Method method = invocation.getMethod();
CacheOperationInvoker aopAllianceInvoker = new CacheOperationInvoker() {
public Object invoke() {
try {
return invocation.proceed();
} catch (Throwable var2) {
throw new ThrowableWrapper(var2);
}
}
};
try {
return this.execute(aopAllianceInvoker, invocation.getThis(), method, invocation.getArguments());
} catch (ThrowableWrapper var5) {
throw var5.getOriginal();
}
}
}
这个拦截器继承了CacheAspectSupport类和MethodInterceptor接口。其中CacheAspectSupport封装了主要的逻辑。比如下面这段。
/**
CacheAspectSupport.java
执行@CachaEvict @CachePut @Cacheable的主要逻辑代码
**/
private Object execute(final CacheOperationInvoker invoker, Method method, CacheAspectSupport.CacheOperationContexts contexts) {
if (contexts.isSynchronized()) {
CacheAspectSupport.CacheOperationContext context = (CacheAspectSupport.CacheOperationContext)contexts.get(CacheableOperation.class).iterator().next();
if (this.isConditionPassing(context, CacheOperationExpressionEvaluator.NO_RESULT)) {
Object key = this.generateKey(context, CacheOperationExpressionEvaluator.NO_RESULT);
Cache cache = (Cache)context.getCaches().iterator().next();
try {
return this.wrapCacheValue(method, cache.get(key, new Callable<Object>() {
public Object call() throws Exception {
return CacheAspectSupport.this.unwrapReturnValue(CacheAspectSupport.this.invokeOperation(invoker));
}
}));
} catch (ValueRetrievalException var10) {
throw (ThrowableWrapper)var10.getCause();
}
} else {
return this.invokeOperation(invoker);
}
} else {
/**
执行@CacheEvict的逻辑，这里是当beforeInvocation为true时清缓存
**/
this.processCacheEvicts(contexts.get(CacheEvictOperation.class), true, CacheOperationExpressionEvaluator.NO_RESULT);
//获取命中的缓存对象
ValueWrapper cacheHit = this.findCachedItem(contexts.get(CacheableOperation.class));
List<CacheAspectSupport.CachePutRequest> cachePutRequests = new LinkedList();
if (cacheHit == null) {
//如果没有命中，则生成一个put的请求
this.collectPutRequests(contexts.get(CacheableOperation.class), CacheOperationExpressionEvaluator.NO_RESULT, cachePutRequests);
}
Object cacheValue;
Object returnValue;
/**
如果没有获得缓存对象，则调用业务方法获得返回对象，hasCachePut会检查exclude的情况
**/
if (cacheHit != null && cachePutRequests.isEmpty() && !this.hasCachePut(contexts)) {
cacheValue = cacheHit.get();
returnValue = this.wrapCacheValue(method, cacheValue);
} else {
returnValue = this.invokeOperation(invoker);
cacheValue = this.unwrapReturnValue(returnValue);
}
this.collectPutRequests(contexts.get(CachePutOperation.class), cacheValue, cachePutRequests);
Iterator var8 = cachePutRequests.iterator();
while(var8.hasNext()) {
CacheAspectSupport.CachePutRequest cachePutRequest = (CacheAspectSupport.CachePutRequest)var8.next();
/**
执行cachePut请求，将返回对象放到缓存中
**/
cachePutRequest.apply(cacheValue);
}
/**
执行@CacheEvict的逻辑，这里是当beforeInvocation为false时清缓存
**/
this.processCacheEvicts(contexts.get(CacheEvictOperation.class), false, cacheValue);
return returnValue;
}
}
上面的代码片段比较核心，均是cache的内容，对于aop的源码，这里不详细展开，应该单起一篇文章进行研究。主要的类和接口都在spring的context中，org.springframework.cache包中。
和第三方缓存组件的适配
通过以上的分析，知道了spring cache功能的来龙去脉，下面需要分析的是，为什么只需要maven声明一下依赖，spring boot 就可以自动就适配了.
在上面的执行方法中，我们看到了cachePutRequest.apply(cacheValue) ,这里会操作缓存，CachePutRequest是CacheAspectSupport的内部类。
private class CachePutRequest {
private final CacheAspectSupport.CacheOperationContext context;
private final Object key;
public CachePutRequest(CacheAspectSupport.CacheOperationContext context, Object key) {
this.context = context;
this.key = key;
}
public void apply(Object result) {
if (this.context.canPutToCache(result)) {
//从context中获取cache实例，然后执行放入缓存的操作
Iterator var2 = this.context.getCaches().iterator();
while(var2.hasNext()) {
Cache cache = (Cache)var2.next();
CacheAspectSupport.this.doPut(cache, this.key, result);
}
}
}
}
Cache是一个标准接口，其中EhCacheCache就是EhCache的实现类。这里就是SpringBoot和Ehcache之间关联的部分，那么context中的cache列表是什么时候生成的呢。答案是CacheAspectSupport的getCaches方法
protected Collection<? extends Cache> getCaches(CacheOperationInvocationContext<CacheOperation> context, CacheResolver cacheResolver) {
Collection<? extends Cache> caches = cacheResolver.resolveCaches(context);
if (caches.isEmpty()) {
throw new IllegalStateException("No cache could be resolved for '" + context.getOperation() + "' using resolver '" + cacheResolver + "'. At least one cache should be provided per cache operation.");
} else {
return caches;
}
}
而获取cache是在每一次进行进行缓存操作的时候执行。可以看一下调用栈
貌似有点跑题，拉回来... 在spring-boot-autoconfigure包里，有所有自动装配相关的类。这里有个EhcacheCacheConfiguration类 ，如下
@Configuration
@ConditionalOnClass({Cache.class, EhCacheCacheManager.class})
@ConditionalOnMissingBean({CacheManager.class})
@Conditional({CacheCondition.class, EhCacheCacheConfiguration.ConfigAvailableCondition.class})
class EhCacheCacheConfiguration {
......
static class ConfigAvailableCondition extends ResourceCondition {
ConfigAvailableCondition() {
super("EhCache", "spring.cache.ehcache", "config", new String[]{"classpath:/ehcache.xml"});
}
}
}
这里会直接判断类路径下是否有ehcache.xml文件
