筆者簡單看了一下《Spring實戰》中的demo，然後就應用到業務代碼中了，本以爲如此簡單的事情，竟然在代碼提交後的1個周，被同事發現。selectByTaskId()方法查出來的數據總是過時的。
代碼如下：
@Cacheable("taskParamsCache")
List<TaskParams> selectByTaskId(Long taskId);
// ...
// ...
@CacheEvict("taskParamsCache")
int deleteByTaskId(Long taskId);
想要的效果是當程序調用selectByTaskId()方法時，把結果緩存下來，然後在調用deleteByTaskId()方法時，將緩存清空。
經過數據庫數據對比之後，把問題排查的方向定位在@CacheEvict註解失效了。
下面是筆者通過源碼跟蹤排查問題的過程：
- 在deleteByTaskId()方法的調用出打斷點，跟進代碼到spring生成的代理層。
@Override
@Nullable
public Object intercept(Object proxy, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {
Object oldProxy = null;
boolean setProxyContext = false;
Object target = null;
TargetSource targetSource = this.advised.getTargetSource();
try {
if (this.advised.exposeProxy) {
// Make invocation available if necessary.
oldProxy = AopContext.setCurrentProxy(proxy);
setProxyContext = true;
}
// Get as late as possible to minimize the time we "own" the target, in case it comes from a pool...
target = targetSource.getTarget();
Class<?> targetClass = (target != null ? target.getClass() : null);
List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);
Object retVal;
// Check whether we only have one InvokerInterceptor: that is,
// no real advice, but just reflective invocation of the target.
if (chain.isEmpty() && Modifier.isPublic(method.getModifiers())) {
// We can skip creating a MethodInvocation: just invoke the target directly.
// Note that the final invoker must be an InvokerInterceptor, so we know
// it does nothing but a reflective operation on the target, and no hot
// swapping or fancy proxying.
Object[] argsToUse = AopProxyUtils.adaptArgumentsIfNecessary(method, args);
retVal = methodProxy.invoke(target, argsToUse);
}
else {
// We need to create a method invocation...
retVal = new CglibMethodInvocation(proxy, target, method, args, targetClass, chain, methodProxy).proceed();
}
retVal = processReturnType(proxy, target, method, retVal);
return retVal;
}
finally {
if (target != null && !targetSource.isStatic()) {
targetSource.releaseTarget(target);
}
if (setProxyContext) {
// Restore old proxy.
AopContext.setCurrentProxy(oldProxy);
}
}
}
通過getInterceptorsAndDynamicInterceptionAdvice獲取到當前方法的攔截器，裏面包含了CacheIneterceptor，說明註解被spring檢測到了。
進入CglibMethodInvocation(proxy, target, method, args, targetClass, chain, methodProxy).proceed()方法內部
- org.springframework.aop.framework.ReflectiveMethodInvocation#proceed
@Override
@Nullable
public Object proceed() throws Throwable {
// We start with an index of -1 and increment early.
if (this.currentInterceptorIndex == this.interceptorsAndDynamicMethodMatchers.size() - 1) {
return invokeJoinpoint();
}
Object interceptorOrInterceptionAdvice =
this.interceptorsAndDynamicMethodMatchers.get(++this.currentInterceptorIndex);
if (interceptorOrInterceptionAdvice instanceof InterceptorAndDynamicMethodMatcher) {
// Evaluate dynamic method matcher here: static part will already have
// been evaluated and found to match.
InterceptorAndDynamicMethodMatcher dm =
(InterceptorAndDynamicMethodMatcher) interceptorOrInterceptionAdvice;
if (dm.methodMatcher.matches(this.method, this.targetClass, this.arguments)) {
return dm.interceptor.invoke(this);
}
else {
// Dynamic matching failed.
// Skip this interceptor and invoke the next in the chain.
return proceed();
}
}
else {
// It's an interceptor, so we just invoke it: The pointcut will have
// been evaluated statically before this object was constructed.
return ((MethodInterceptor) interceptorOrInterceptionAdvice).invoke(this);
}
}
this.interceptorsAndDynamicMethodMatchers.get(++this.currentInterceptorIndex)方法取第一個攔截器，正是我們要關注的CacheIneterceptor，然後調用((MethodInterceptor) interceptorOrInterceptionAdvice).invoke(this)方法，繼續跟進
- org.springframework.cache.interceptor.CacheInterceptor#invoke
@Override
@Nullable
public Object invoke(final MethodInvocation invocation) throws Throwable {
Method method = invocation.getMethod();
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();
}
}
進入execute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);
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));
}
}
}
return invoker.invoke();
}
cacheOperationSource記錄系統中所有使用了緩存的方法，cacheOperationSource.getCacheOperations(method, targetClass)能獲取deleteByTaskId()方法緩存元數據，然後執行execute()方法
@Nullable
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, () -> 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<>();
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;
}
這裏大致過程是：
先執行beforInvokeEvict ---- 執行數據庫delete操作 --- 執行CachePut操作 ---- 執行afterInvokeEvict
我們的註解是方法調用後再使緩存失效，直接所以有效的操作應在倒數第2行
private void performCacheEvict(
CacheOperationContext context, CacheEvictOperation operation, @Nullable Object result) {
Object key = null;
for (Cache cache : context.getCaches()) {
if (operation.isCacheWide()) {
logInvalidating(context, operation, null);
doClear(cache);
}
else {
if (key == null) {
key = generateKey(context, result);
}
logInvalidating(context, operation, key);
doEvict(cache, key);
}
}
}
這裏通過context.getCaches()獲取到name爲taskParamsCache的緩存
然後generateKey生成key，注意這裏，發現生成的key是com.xxx.xxx.atomic.impl.xxxxdeleteByTaskId982，但是緩存中的key卻是com.xxx.xxx.atomic.impl.xxxxselectByTaskId982，下面調用的doEvict(cache, key)方法不再跟進了，就是從cache中移除key對應值。明顯這裏key對應不上的，這也是導致@CacheEvict沒有生效的原因。
總結：
筆者還是太大意了，當時看了註解@CacheEvict的對key的註釋：
大意就是如果沒有指定key，那就會使用方法所有參數生成一個key，明顯com.xxx.xxx.atomic.impl.xxxxselectByTaskId982是方法名 + 參數，可是你沒說把方法名還加上了啊，說好的只用參數呢，哈哈，這個bug是筆者使用不當引出的，很多人不會犯這種低級錯誤。
解決辦法就是使用SpEL明確定義key
@Cacheable(value = "taskParamsCache", key = "#taskId")
List<TaskParams> selectByTaskId(Long taskId);
// ...
// ...
@CacheEvict(value = "taskParamsCache", key = "#taskId")
int deleteByTaskId(Long taskId);