日常使用中spring的 @Cacheable 大家一定不陌生沟堡，基于aop機(jī)制的緩存實現(xiàn)油吭，并且可以選擇cacheManager具體提供緩存的中間件或者進(jìn)程內(nèi)緩存弱恒，類似于 @Transactional 的transactionManager 射亏，都是提供了一種多態(tài)的實現(xiàn)虫腋，抽象出上層接口莽红，實現(xiàn)則供客戶端選擇妥畏，或許這就是架構(gòu)吧，抽象的設(shè)計安吁，使用interface對外暴露可擴(kuò)展實現(xiàn)的機(jī)制醉蚁，使用abstract 整合類似實現(xiàn)。
那么我們就看看 @Cacheable提供的一種方便的機(jī)制鬼店，spel表達(dá)式取方法 參數(shù)的邏輯网棍，大家都寫過注解，但是注解邏輯需要的參數(shù)可以使用spel動態(tài)取值是不是好爽~

直接進(jìn)入主題 跟隨spring的調(diào)用鏈

直接看 @Cacheable 注解就可以了

@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Inherited
@Documented
public @interface Cacheable {
        // spring的別名機(jī)制妇智，這里不討論滥玷，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俘陷，redis罗捎，caffine，還是其他的都可以拉盾，至于內(nèi)存還是進(jìn)程上層抽象的邏輯不關(guān)心桨菜，如果你使用caffine
//就需要自己考慮 多服務(wù)實例的一致性了
    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;
}

接下來看 key獲取是在哪里 SpringCacheAnnotationParser#parseCacheableAnnotation 解析注解，還好就一個地方
沒有任何邏輯就是一個組裝，繼續(xù)跟蹤上述方法 SpringCacheAnnotationParser#parseCacheAnnotations 走到這里倒得，

    @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;
    }

也沒有太多邏輯泻红，將當(dāng)前攔截到的方法可能存在的多個 SpringCache的注解解析為集合返回，那就是支持多個SpringCache注解同時放到一個方法嘍霞掺。

    @Override
    @Nullable
    public Collection<CacheOperation> parseCacheAnnotations(Class<?> type) {
// 到上邊發(fā)現(xiàn)這里入?yún)⑹且粋€類谊路，那么可以推斷這里調(diào)用是啟動或者類加載時進(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);
    }
//------------還有一個方法是對方法的解析也是對注解的解析返回------------------
    @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 這里有點看不懂暫時不細(xì)做追溯菩彬，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調(diào)用

CacheAspectSupport#execute 查看這個execute調(diào)用方是CacheInterceptor#invoke 實現(xiàn)的MethodInterceptor接口缠劝，那不用看其他的了，這里就是執(zhí)行方法攔截的地方骗灶，在這里會找到spel的動態(tài)解析噢
順便看一下攔截方法中的執(zhí)行邏輯惨恭，了解一下@Cacheable的攔截順序

    @Override
    @Nullable
    public Object invoke(final MethodInvocation invocation) throws Throwable {
        Method method = invocation.getMethod();
// 這是個一個 函數(shù)式接口作為回調(diào)，這里并沒有執(zhí)行耙旦，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();
        }
    }

接下來看 execute方法

    @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)行噢脱羡，先進(jìn)行緩存
        return invoker.invoke();
    }

再看 重載方法execute

    @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)行免都、緩存增
//加(猜測是先命中一次緩存锉罐，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)绕娘，盡量減少并發(fā)緩存帶來的緩存沖洗問題)脓规、
//緩存增加(帶有數(shù)據(jù)的)、上述兩個緩存增加的真正執(zhí)行 业舍、緩存刪除(目標(biāo)方法invoke 后)并執(zhí)行
//當(dāng)然這個 是 invoke前執(zhí)行 或者后執(zhí)行 是取決于@CacheEvict 中的 beforeInvocation 配置抖拦，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?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)行邏輯了舷暮，來看看生成key的邏輯态罪，private 方法 generateKey

// 可以看出沒有生成key  會拋出異常，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 包里的類了下面。复颈。。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類這個成員變量沥割，類加載時便生成耗啦，里面有生成待解析實例的方法，有解析 key condition unless 的三個方法及ConcurrentMap 成員變量緩存到內(nèi)存中机杜，將所有的Cache注解的 spel表達(dá)式緩存于此帜讲，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