Spring cache源码深度解析

Spring cache源码深度解析

Spring cache是一个缓存API层，封装了对多种缓存的通用操作，可以借助注解方便地为程序添加缓存功能。常见的注解有@Cacheable、@CachePut、@CacheEvict，有没有想过背后的原理是什么？楼主带着疑问，阅读完Spring cache的源码后，做一个简要总结。先说结论，核心逻辑在CacheAspectSupport类，封装了所有的缓存操作的主体http://逻辑，下面详细介绍。

题外话：如何阅读开源代码？

有2种方法，可以结合起来使用：

静态代码阅读：查找关键类、方法的usage之处，熟练使用find usages功能，找到所有相关的类、方法，静态分析核心逻辑的执行过程，一步步追根问底，直至建立全貌运行时debug：在关键方法上加上断点，并且写一个单元测试调用类库/框架，熟练使用step into/step over/resume来动态分析代码的执行过程

核心类图

如图所示，可以分成以下几类class：

Cache、CacheManager：Cache抽象了缓存的通用操作，如get、put，而CacheManager是Cache的集合，之所以需要多个Cache对象，是因为需要多种缓存失效时间、缓存条目上限等CacheInterceptor、CacheAspectSupport、AbstractCacheInvoker：CacheInterceptor是一个AOP方法拦截器，在方法前后做额外的逻辑，也即查询缓存、写入缓存等，它继承了CacheAspectSupport（缓存操作的主体逻辑）、AbstractCacheInvoker（封装了对Cache的读写）CacheOperation、AnnotationCacheOperationSource、SpringCacheAnnotationParser：CacheOperation定义了缓存操作的缓存名字、缓存key、缓存条件condition、CacheManager等，AnnotationCacheOperationSource是一个获取缓存注解对应CacheOperation的类，而SpringCachehttp://AnnotationParser是真正解析注解的类，解析后会封装成CacheOperation集合供AnnotationCacheOperationSource查找

源码分析（带注释解释）

下面对Spring cache源码做分析，带注释解释，只摘录核心代码片段。

1、解析注解

首先看看注解是如何解析的。注解只是一个标记，要让它真正工作起来，需要对注解做解析操作，并且还要有对应的实际逻辑。

SpringCacheAnnotationParser：负责解析注解，返回CacheOperation集合

public class SpringCacheAnnotationParser implements CacheAnnotationParser, Serializable {

// 解析类级别的缓存注解

@Override

public Collection<CacheOperation> parseCacheAnnotations(Class<?> type) {

DefaultCacheConfig defaultConfig = getDefaultCacheConfig(type);

return parseCacheAnnotations(defaultConfig, type);

}

// 解析方法级别的缓存注解

@Override

public Collection<CacheOperation> parseCacheAnnotations(Method method) {

DefaultCacheConfig defaultConfig = getDefaultCacheConfig(method.getDeclaringClass());

return parseCacheAnnotations(defaultConfig, method);

}

// 解析缓存注解

private Collection<CacheOperation> parseCacheAnnotations(DefaultCacheConfig cachingConfig, AnnotatedElement ae) {

Collection<CacheOperation> ops = null;

// 解析@Cacheable注解

Collection<Cacheable> cacheables = AnnotatedElementUtils.getAllMergedAnnotations(ae, Cacheable.class);

if (!cacheables.isEmpty()) {

ops = lazyInit(ops);

for (Cacheable cacheable : cacheables) {

ops.add(parseCacheableAnnotation(ae, cachingConfig, cacheable));

}

}

// 解析@CacheEvict注解

Collection<CacheEvict> evicts = AnnotatedElementUtils.getAllMergedAnnotations(ae, CacheEvict.class);

if (!evicts.isEmpty()) {

ops = lazyInit(ops);

for (CacheEvict evict : evicts) {

ops.add(parseEvictAnnotation(ae, cachingConfig, evict));

}

}

// 解析@CachePut注解

Collection<CachePut> puts = AnnotatedElementUtils.getAllMergedAnnotations(ae, CachePut.class);

if (!puts.isEmpty()) {

ops = lazyInit(ops);

for (CachePut put : puts) {

ops.add(parsePutAnnotation(ae, cachingConfig, put));

}

}

// 解析@Caching注解

Collection<Caching> cachings = AnnotatedElementUtils.getAllMergedAnnotations(ae, Caching.class);

if (!cachings.isEmpty()) {

ops = lazyInit(ops);

for (Caching caching : cachings) {

Collection<CacheOperation> cachingOps = parseCachingAnnotation(ae, cachingConfig, caching);

if (cachingOps != null) {

ops.addAll(cachingOps);

}

}

}

return ops;

}

AnnotationCacheOperationSource：调用SpringCacheAnnotationParser获取注解对应CacheOperation

public class AnnotationCacheOperationSource extends AbstractFallbackCacheOperationSource implements Serializable {

// 查找类级别的CacheOperation列表

@Override

protected Collection<CacheOperation> findCacheOperations(final Class<?> clazz) {

return determineCacheOperations(new CacheOperationProvider() {

@Override

public Collection<CacheOperation> getCacheOperations(CacheAnnotationParser parser) {

return parser.parseCacheAnnotations(clazz);

}

});

}

// 查找方法级别的CacheOperation列表

@Override

protected Collection<CacheOperation> findCacheOperations(final Method method) {

return determineCacheOperations(new CacheOperationProvider() {

@Override

public Collection<CacheOperation> getCacheOperations(CacheAnnotationParser parser) {

return parser.parseCacheAnnotations(method);

}

});

}

}

AbstractFallbackCacheOperationSource：AnnotationCacheOperationSource的父类，实现了获取CacheOperation的通用逻辑

public abstract class AbstractFallbackCacheOperationSource implements CacheOperationSource {

/**

* Cache of CacheOperations, keyed by method on a specific target class.

* <p>As this base class is not marked Serializable, the cache will be recreated

* after serialization - provided that the concrete subclass is Serializable.

*/

private final Map<Object, Collection<CacheOperation>> attributeCache =

new ConcurrentHashMap<Object, Collection<CacheOperation>>(1024);

// 根据Method、Class反射信息，获取对应的CacheOperation列表

@Override

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);

// 因解析反射信息较耗时，所以用map缓存，避免重复计算

// 如在map里已记录，直接返回

if (cached != null) {

return (cached != NULL_CACHING_ATTRIBUTE ? cached : null);

}

// 否则做一次计算，然后写入map

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;

}

}

// 计算缓存操作列表，优先用target代理类的方法上的注解，如果不存在则其次用target代理类，再次用原始类的方法，最后用原始类

private Collection<CacheOperation> computeCacheOperations(Method method, Class<?> targetClass) {

// Don't allow no-public methods as required.

if (allowPublicMethodsOnly() && !Modifier.isPublic(method.getModifiers())) {

return null;

}

// The method may be on an interface, but we need attributes from the target class.

// If the target class is null, the method will be unchanged.

Method specificMethod = ClassUtils.getMostSpecificMethod(method, targetClass);

// If we are dealing with method with generic parameters, find the original method.

specificMethod = BridgeMethodResolver.findBridgedMethod(specificMethod);

// 调用findCacheOperations（由子类AnnotationCacheOperationSource实现），最终通过SpringCacheAnnotationParser来解析

// First try is the method in the target class.

Collection<CacheOperation> opDef = findCacheOperations(specificMethod);

if (opDef != null) {

return opDef;

}

// Second try is the caching operation on the target class.

opDef = findCacheOperations(specificMethod.getDeclaringClass());

if (opDef != null && ClassUtils.isUserLevelMethod(method)) {

return opDef;

}

if (specificMethod != method) {

// Fallback is to look at the original method.

opDef = findCacheOperations(method);

if (opDef != null) {

return opDef;

}

// Last fallback is the class of the original method.

opDef = findCacheOperations(method.getDeclaringClass());

if (opDef != null && ClassUtils.isUserLevelMethod(method)) {

return opDef;

}

}

return null;

}

2、逻辑执行

以@Cacheable背后的逻辑为例。预期是先查缓存，如果缓存命中了就直接使用缓存值，否则执行业务逻辑，并把结果写入缓存。

ProxyCachingConfiguration：是一个配置类，用于生成CacheInterceptor类和CacheOperationSource类的Spring bean

CacheInterceptor：是一个AOP方法拦截器，它通过CacheOperationSource获取第1步解析注解的CacheOperation结果（如缓存名字、缓存key、condition条件），本质上是拦截原始方法的执行，在之前、之后增加逻辑

// 核心类，缓存拦截器

public class CacheInterceptor extends CacheAspectSupport implements MethodInterceptor, Serializable {

// 拦截原始方法的执行，在之前、之后增加逻辑

@Override

public Object invoke(final MethodInvocation invocation) throws Throwable {

Method method = invocation.getMethod();

// 封装原始方法的执行到一个回调接口，便于后续调用

CacheOperationInvoker aopAllianceInvoker = new CacheOperationInvoker() {

@Override

public Object invoke() {

try {

// 原始方法的执行

return invocation.proceed();

}

catch (Throwable ex) {

throw new ThrowableWrapper(ex);

}

}

};

try {

// 调用父类CacheAspectSupport的方法

return execute(aopAllianceInvoker, invocation.getThis(), method, invocation.getArguments());

}

catch (CacheOperationInvoker.ThrowableWrapper th) {

throw th.getOriginal();

}

}

}

CacheAspectSupport：缓存切面支持类，是CacheInterceptor的父类，封装了所有的缓存操作的主体逻辑

主要流程如下：

通过CacheOperationSource，获取所有的CacheOperation列表如果有@CacheEvict注解、并且标记为在调用前执行，则做删除/清空缓存的操作如果有@Cacheable注解，查询缓存如果缓存未命中（查询结果为null），则新增到cachePutRequests，后续执行原始方法后会写入缓存缓存命中时，使用缓存值作为结果；缓存未命中、或有@CachePut注解时，需要调用原始方法，使用原始方法的返回值作为结果如果有@CachePut注解，则新增到cachePutRequests如果缓存未命中，则把查询结果值写入缓存；如果有@CachePut注解，也把方法执行结果写入缓存如果有@CacheEvict注解、并且标记为在调用后执行，则做删除/清空缓存的操作

// 核心类，缓存切面支持类，封装了所有的缓存操作的主体逻辑

public abstract class CacheAspectSupport extends AbstractCacheInvoker

implements BeanFactoryAware, InitializingBean, SmartInitializingSingleton {

// CacheInterceptor调父类的该方法

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);

// 通过CacheOperationSource，获取所有的CacheOperation列表

Collection<CacheOperation> operations = getCacheOperationSource().getCacheOperations(method, targetClass);

if (!CollectionUtils.isEmpty(operations)) {

// 继续调一个private的execute方法执行

return execute(invoker, method, new CacheOperationContexts(operations, method, args, target, targetClass));

}

}

// 如果spring bean未初始化完成，则直接调用原始方法。相当于原始方法没有缓存功能。

return invoker.invoke();

}

private的execute方法

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);

}

}

// 如果有@CacheEvict注解、并且标记为在调用前执行，则做删除/清空缓存的操作

// Process any early evictions

processCacheEvicts(contexts.get(CacheEvictOperation.class), true,

CacheOperationExpressionEvaluator.NO_RESULT);

// 如果有@Cacheable注解，查询缓存

// Check if we have a cached item matching the conditions

Cache.ValueWrapper cacheHit = findCachedItem(contexts.get(CacheableOperation.class));

// 如果缓存未命中（查询结果为null），则新增到cachePutRequests，后续执行原始方法后会写入缓存

// 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)) {

// 缓存命中的情况，使用缓存值作为结果

// If there are no put requests, just use the cache hit

cacheValue = cacheHit.get();

returnValue = wrapCacheValue(method, cacheValue);

}

else {

// 缓存未命中、或有@CachePut注解的情况，需要调用原始方法

// Invoke the method if we don't have a cache hit

// 调用原始方法，得到结果值

returnValue = invokeOperation(invoker);

cacheValue = unwrapReturnValue(returnValue);

}

// 如果有@CachePut注解，则新增到cachePutRequests

// Collect any explicit @CachePuts

collectPutRequests(contexts.get(CachePutOperation.class), cacheValue, cachePutRequests);

// 如果缓存未命中，则把查询结果值写入缓存；如果有@CachePut注解，也把方法执行结果写入缓存

// Process any collected put requests, either from @CachePut or a @Cacheable miss

for (CachePutRequest cachePutRequest : cachePutRequests) {

cachePutRequest.apply(cacheValue);

}

// 如果有@CacheEvict注解、并且标记为在调用后执行，则做删除/清空缓存的操作

// Process any late evictions

processCacheEvicts(contexts.get(CacheEvictOperation.class), false, cacheValue);

return returnValue;

}

private Cache.ValueWrapper findCachedItem(Collection<CacheOperationContext> contexts) {

Object result = CacheOperationExpressionEvaluator.NO_RESULT;

for (CacheOperationContext context : contexts) {

// 如果满足condition条件，才查询缓存

if (isConditionPassing(context, result)) {

// 生成缓存key，如果注解中指定了key，则按照Spring表达式解析，否则使用KeyGenerator类生成

Object key = generateKey(context, result);

// 根据缓存key，查询缓存值

Cache.ValueWrapper cached = findInCaches(context, key);

if (cached != null) {

return cached;

}

else {

if (logger.isTraceEnabled()) {

logger.trace("No cache entry for key '" + key + "' in cache(s) " + context.getCacheNames());

}

}

}

}

return null;

}

private Cache.ValueWrapper findInCaches(CacheOperationContext context, Object key) {

for (Cache cache : context.getCaches()) {

// 调用父类AbstractCacheInvoker的doGet方法，查询缓存

Cache.ValueWrapper wrapper = doGet(cache, key);

if (wrapper != null) {

if (logger.isTraceEnabled()) {

logger.trace("Cache entry for key '" + key + "' found in cache '" + cache.getName() + "'");

}

return wrapper;

}

}

return null;

}

AbstractCacheInvoker：CacheAspectSupport的父类，封装了最终查询Cache接口的逻辑

public abstract class AbstractCacheInvoker {

// 最终查询缓存的方法

protected Cache.ValueWrapper doGet(Cache cache, Object key) {

try {

// 调用Spring Cache接口的查询方法

return cache.get(key);

}

catch (RuntimeException ex) {

getErrorHandler().handleCacheGetError(ex, cache, key);

return null; // If the exception is handled, return a cache miss

}

}

}

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