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今天就跟大家聊聊有關(guān)基于spring @Cacheable 注解的spel表達(dá)式該如何解析執(zhí)行,可能很多人都不太了解,為了讓大家更加了解,小編給大家總結(jié)了以下內(nèi)容,希望大家根據(jù)這篇文章可以有所收獲。
日常使用中spring的 @Cacheable 大家一定不陌生,基于aop機(jī)制的緩存實(shí)現(xiàn),并且可以選擇cacheManager具體提供緩存的中間件或者進(jìn)程內(nèi)緩存,類似于 @Transactional 的transactionManager ,都是提供了一種多態(tài)的實(shí)現(xiàn),抽象出上層接口,實(shí)現(xiàn)則供客戶端選擇,或許這就是架構(gòu)吧,抽象的設(shè)計(jì),使用interface對(duì)外暴露可擴(kuò)展實(shí)現(xiàn)的機(jī)制,使用abstract 整合類似實(shí)現(xiàn)。
那么我們就看看 @Cacheable提供的一種方便的機(jī)制,spel表達(dá)式取方法 參數(shù)的邏輯,大家都寫過注解,但是注解邏輯需要的參數(shù)可以使用spel動(dòng)態(tài)取值是不是好爽~
@Target({ElementType.TYPE, ElementType.METHOD}) @Retention(RetentionPolicy.RUNTIME) @Inherited @Documented public @interface Cacheable { // spring的別名機(jī)制,這里不討論,和cacheNames作用一致 @AliasFor("cacheNames") String[] value() default {}; @AliasFor("value") String[] cacheNames() default {}; // 今天的主角,就從他入手 String key() default ""; // 拼接key的 抽象出來的接口 String keyGenerator() default ""; // 真正做緩存這件事的人,redis,caffine,還是其他的都可以,至于內(nèi)存還是進(jìn)程上層抽象的邏輯不關(guān)心,如果你使用caffine //就需要自己考慮 多服務(wù)實(shí)例的一致性了 String cacheManager() default ""; String cacheResolver() default ""; // 是否可以執(zhí)行緩存的條件 也是 spel 如果返回結(jié)果true 則進(jìn)行緩存 String condition() default ""; // 如果spel 返回true 則不進(jìn)行緩存 String unless() default ""; // 是否異步執(zhí)行 boolean sync() default false; }
SpringCacheAnnotationParser#parseCacheableAnnotation 解析注解,還好就一個(gè)地方
繼續(xù)跟蹤上述方法 SpringCacheAnnotationParser#parseCacheAnnotations 走到這里,
@Nullable private Collection<CacheOperation> parseCacheAnnotations( DefaultCacheConfig cachingConfig, AnnotatedElement ae, boolean localOnly) { Collection<? extends Annotation> anns = (localOnly ? AnnotatedElementUtils.getAllMergedAnnotations(ae, CACHE_OPERATION_ANNOTATIONS) : AnnotatedElementUtils.findAllMergedAnnotations(ae, CACHE_OPERATION_ANNOTATIONS)); if (anns.isEmpty()) { return null; } final Collection<CacheOperation> ops = new ArrayList<>(1); anns.stream().filter(ann -> ann instanceof Cacheable).forEach( ann -> ops.add(parseCacheableAnnotation(ae, cachingConfig, (Cacheable) ann))); anns.stream().filter(ann -> ann instanceof CacheEvict).forEach( ann -> ops.add(parseEvictAnnotation(ae, cachingConfig, (CacheEvict) ann))); anns.stream().filter(ann -> ann instanceof CachePut).forEach( ann -> ops.add(parsePutAnnotation(ae, cachingConfig, (CachePut) ann))); anns.stream().filter(ann -> ann instanceof Caching).forEach( ann -> parseCachingAnnotation(ae, cachingConfig, (Caching) ann, ops)); return ops; }
也沒有太多邏輯,將當(dāng)前攔截到的方法可能存在的多個(gè) SpringCache的注解解析為集合返回,那就是支持多個(gè)SpringCache注解同時(shí)放到一個(gè)方法嘍。
@Override @Nullable public Collection<CacheOperation> parseCacheAnnotations(Class<?> type) { // 到上邊發(fā)現(xiàn)這里入?yún)⑹且粋€(gè)類,那么可以推斷這里調(diào)用是啟動(dòng)或者類加載時(shí)進(jìn)行注解解析,然后緩存注解的寫死的參數(shù)返回 DefaultCacheConfig defaultConfig = new DefaultCacheConfig(type); return parseCacheAnnotations(defaultConfig, type); } //------------還有一個(gè)方法是對(duì)方法的解析也是對(duì)注解的解析返回------------------ @Override @Nullable public Collection<CacheOperation> parseCacheAnnotations(Method method) { DefaultCacheConfig defaultConfig = new DefaultCacheConfig(method.getDeclaringClass()); return parseCacheAnnotations(defaultConfig, method); }
再上邊 AnnotationCacheOperationSource#findCacheOperations ,兩個(gè)重載方法
@Override @Nullable protected Collection<CacheOperation> findCacheOperations(Class<?> clazz) { return determineCacheOperations(parser -> parser.parseCacheAnnotations(clazz)); } @Override @Nullable protected Collection<CacheOperation> findCacheOperations(Method method) { return determineCacheOperations(parser -> parser.parseCacheAnnotations(method)); }
AbstractFallbackCacheOperationSource#computeCacheOperations
這里有點(diǎn)看不懂暫時(shí)不細(xì)做追溯,目的就是spel
AbstractFallbackCacheOperationSource#getCacheOperations
還是處理解析注解返回
調(diào)用getCacheOperations方法的地方
如上圖直接查看第一個(gè)調(diào)用
CacheAspectSupport#execute 查看這個(gè)execute調(diào)用方是CacheInterceptor#invoke 實(shí)現(xiàn)的MethodInterceptor接口,那不用看其他的了,這里就是執(zhí)行方法攔截的地方,在這里會(huì)找到spel的動(dòng)態(tài)解析噢
順便看一下攔截方法中的執(zhí)行邏輯
@Override @Nullable public Object invoke(final MethodInvocation invocation) throws Throwable { Method method = invocation.getMethod(); // 這是個(gè)一個(gè) 函數(shù)式接口作為回調(diào),這里并沒有執(zhí)行,先執(zhí)行下面execute方法 即CacheAspectSupport#execute CacheOperationInvoker aopAllianceInvoker = () -> { try { return invocation.proceed(); } catch (Throwable ex) { throw new CacheOperationInvoker.ThrowableWrapper(ex); } }; try { return execute(aopAllianceInvoker, invocation.getThis(), method, invocation.getArguments()); } catch (CacheOperationInvoker.ThrowableWrapper th) { throw th.getOriginal(); } }
@Nullable 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); CacheOperationSource cacheOperationSource = getCacheOperationSource(); if (cacheOperationSource != null) { Collection<CacheOperation> operations = cacheOperationSource.getCacheOperations(method, targetClass); if (!CollectionUtils.isEmpty(operations)) { return execute(invoker, method, new CacheOperationContexts(operations, method, args, target, targetClass)); } } } // 方法邏輯是后執(zhí)行噢,先進(jìn)行緩存 return invoker.invoke(); }
@Nullable private Object execute(final CacheOperationInvoker invoker, Method method, CacheOperationContexts contexts) { // 注解上的是否異步的字段這里決定是否異步執(zhí)行 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, () -> unwrapReturnValue(invokeOperation(invoker)))); } catch (Cache.ValueRetrievalException ex) { // Directly propagate ThrowableWrapper from the invoker, // or potentially also an IllegalArgumentException etc. ReflectionUtils.rethrowRuntimeException(ex.getCause()); } } else { // No caching required, only call the underlying method return invokeOperation(invoker); } } // -------------同步執(zhí)行緩存邏輯-------------- // --------------------下面各種注解分別執(zhí)行,可以看出來springCache注解之間的順序 緩存刪除(目標(biāo)方法invoke前)并執(zhí)行、緩存增 //加(猜測(cè)是先命中一次緩存,如果沒有命中先存入空數(shù)據(jù)的緩存,提前占住緩存數(shù)據(jù),盡量減少并發(fā)緩存帶來的緩存沖洗問題)、 //緩存增加(帶有數(shù)據(jù)的)、上述兩個(gè)緩存增加的真正執(zhí)行 、緩存刪除(目標(biāo)方法invoke 后)并執(zhí)行 //當(dāng)然這個(gè) 是 invoke前執(zhí)行 或者后執(zhí)行 是取決于@CacheEvict 中的 beforeInvocation 配置,默認(rèn)false在后面執(zhí)行如果前面執(zhí)行unless就拿不到結(jié)果值了 // 那么spring cache 不是 延時(shí)雙刪噢,高并發(fā)可能存在數(shù)據(jù)過期數(shù)據(jù)重新灌入 // 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<>(); if (cacheHit == null) { collectPutRequests(contexts.get(CacheableOperation.class), CacheOperationExpressionEvaluator.NO_RESULT, cachePutRequests); } // 方法入?yún)⒔馕?nbsp;用于 key condition Object cacheValue; // 方法結(jié)果 解析 用于 unless Object returnValue; if (cacheHit != null && !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; }
不詳細(xì)探究執(zhí)行邏輯了,來看看生成key的邏輯,private 方法 generateKey
// 可以看出沒有生成key 會(huì)拋出異常,不允許null private Object generateKey(CacheOperationContext context, @Nullable Object result) { Object key = context.generateKey(result); if (key == null) { throw new IllegalArgumentException("Null key returned for cache operation (maybe you are " + "using named params on classes without debug info?) " + context.metadata.operation); } if (logger.isTraceEnabled()) { logger.trace("Computed cache key '" + key + "' for operation " + context.metadata.operation); } return key; } //------------------------繼續(xù)------------ /** * Compute the key for the given caching operation. */ @Nullable protected Object generateKey(@Nullable Object result) { if (StringUtils.hasText(this.metadata.operation.getKey())) { // 終于看到 spring核心包之一 org.springframework.expression 包里的類了。。。T.T EvaluationContext evaluationContext = createEvaluationContext(result); return evaluator.key(this.metadata.operation.getKey(), this.metadata.methodKey, evaluationContext); } return this.metadata.keyGenerator.generate(this.target, this.metadata.method, this.args); }
可以看到使用的 evaluator 是CacheOperationExpressionEvaluator類這個(gè)成員變量,類加載時(shí)便生成,里面有生成待解析實(shí)例的方法,有解析 key condition unless 的三個(gè)方法及ConcurrentMap 成員變量緩存到內(nèi)存中,將所有的Cache注解的 spel表達(dá)式緩存于此,默認(rèn) 64的大小,主要方法如下
public EvaluationContext createEvaluationContext(Collection<? extends Cache> caches, Method method, Object[] args, Object target, Class<?> targetClass, Method targetMethod, @Nullable Object result, @Nullable BeanFactory beanFactory) { CacheExpressionRootObject rootObject = new CacheExpressionRootObject( caches, method, args, target, targetClass); CacheEvaluationContext evaluationContext = new CacheEvaluationContext( rootObject, targetMethod, args, getParameterNameDiscoverer()); if (result == RESULT_UNAVAILABLE) { evaluationContext.addUnavailableVariable(RESULT_VARIABLE); } else if (result != NO_RESULT) { evaluationContext.setVariable(RESULT_VARIABLE, result); } if (beanFactory != null) { evaluationContext.setBeanResolver(new BeanFactoryResolver(beanFactory)); } return evaluationContext; } @Nullable public Object key(String keyExpression, AnnotatedElementKey methodKey, EvaluationContext evalContext) { return getExpression(this.keyCache, methodKey, keyExpression).getValue(evalContext); } public boolean condition(String conditionExpression, AnnotatedElementKey methodKey, EvaluationContext evalContext) { return (Boolean.TRUE.equals(getExpression(this.conditionCache, methodKey, conditionExpression).getValue( evalContext, Boolean.class))); } public boolean unless(String unlessExpression, AnnotatedElementKey methodKey, EvaluationContext evalContext) { return (Boolean.TRUE.equals(getExpression(this.unlessCache, methodKey, unlessExpression).getValue( evalContext, Boolean.class))); }
然后就返回想要的key了。
看完上述內(nèi)容,你們對(duì)基于spring @Cacheable 注解的spel表達(dá)式該如何解析執(zhí)行有進(jìn)一步的了解嗎?如果還想了解更多知識(shí)或者相關(guān)內(nèi)容,請(qǐng)關(guān)注億速云行業(yè)資訊頻道,感謝大家的支持。
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