java 如何在 Cacheable 注释中的条件下使用密钥
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How do I use the key, in a condition in Cacheable annotation
提问by Nandita Rao
I'm caching the results of a function using the @cacheable annotation. I have 3 different caches and the key for each one is the user id of the currently logged in user concatenated with an argument in the method . On a certain event I want to evict all the cache entries which have the key that starts with that particular user id. For example :
我正在使用 @cacheable 注释缓存函数的结果。我有 3 个不同的缓存，每个缓存的键是当前登录用户的用户 ID 与方法中的参数连接。在某个事件中，我想驱逐所有具有以该特定用户 ID 开头的键的缓存条目。例如 ：
@Cacheable(value = "testCache1", key = "'abcdef'")
I want the cache evict annotation to be something like :
我希望缓存驱逐注释是这样的：
@CacheEvict(value = "getSimilarVendors", condition = "key.startsWith('abc')")
But when I try to implement this it gives me an error :
但是当我尝试实现它时，它给了我一个错误：
Property or field 'key' cannot be found on object of type'org.springframework.cache.interceptor.CacheExpressionRootObject' - maybe not public?
What is the correct way to implement this?
实现这一点的正确方法是什么？
回答by John Blum
All of the Spring Cache annotations (i.e. @Cacheable, @CacheEvict, etc) work on 1 cache entry per operation. @CacheEvictdoes support clearing the entire cache (with the allEntriesattribute, however ignores the key in this case), but it is not selective (capable) in clearing a partial set of entries based on a key pattern in a single operation as you have described.
所有 Spring Cache 注释（即@Cacheable、@CacheEvict等）针对每个操作处理 1 个缓存条目。 @CacheEvict确实支持清除整个缓存（使用allEntries属性，但在这种情况下会忽略键），但在您描述的单个操作中基于键模式清除部分条目集时没有选择性（能够）。
The main reason behind this is the Spring Cacheinterface abstraction itself, where the evict(key:Object)method takes a single key argument. But technically, it actually depends on the underlying Cache implementation (e.g. GemfireCache), which would need to support eviction on all entries who's keys match a particular pattern, which is typically, not the case for most caches (e.g. certainly not for GemFire, and not for Google Guava Cache either; see hereand here.)
这背后的主要原因是 Spring Cache接口抽象本身，其中evict(key:Object)方法采用单个键参数。但从技术上讲，它实际上取决于底层 Cache 实现（例如GemfireCache），它需要支持对所有键匹配特定模式的条目进行驱逐，这通常不是大多数缓存的情况（例如，GemFire 肯定不是，并且也不适用于 Google Guava Cache；请参阅此处和此处。）
That is not to say you absolutely cannot achieve your goal. It's just not something supported out-of-the-box.
这并不是说您绝对无法实现目标。它只是不支持开箱即用的东西。
The interesting thing, minus some technical issues with your approach, is that your condition achieves sort of what you want... a cache eviction only occurs if the key satisfies the condition. However, you @CacheEvict annotated method is just missing the "key", hence the error. So, something like the following would satisfy the SpEL in your condition...
有趣的是，减去你的方法的一些技术问题，你的条件达到了你想要的......只有当键满足条件时才会发生缓存驱逐。但是，您 @CacheEvict 注释的方法只是缺少“键”，因此出现错误。因此，类似以下内容将满足您条件下的 SpEL ...
@CacheEvict(condition = "#key.startsWith('abc')")
public void someMethod(String key) {
...
}
However, you have to specify the key as an argument in this case. But, you don't want a specific key, you want a pattern matching several keys. So, forgo the condition and just use...
但是，在这种情况下，您必须将键指定为参数。但是，您不需要特定的键，而是需要匹配多个键的模式。所以，放弃条件，只使用......
@CacheEvict
public void someMethod(String keyPattern) {
...
}
By way of example, using Guava as the caching provider, you would now need to provide a "custom" implementation extending GuavaCache.
例如，使用 Guava 作为缓存提供者，您现在需要提供一个扩展GuavaCache的“自定义”实现。
public class CustomGuavaCache extends org.springframework.cache.guava.GuavaCache {
protected boolean isMatch(String key, String pattern) {
...
}
protected boolean isPattern(String key) {
...
}
@Override
public void evict(Object key) {
if (key instanceof String && isPattern(key.toString()))) {
Map<String, Object> entries = this.cache.asMap();
Set<String> matchingKeys = new HashSet<>(entries.size());
for (String actualKey : entries.keySet()) {
if (isMatch(actualKey, key.toString()) {
matchingKeys.add(actualKey);
}
}
this.cache.invalidateAll(matchingKeys);
}
else {
this.cache.invalidate(key);
}
}
}
Now just extend the GuavaCacheManagerto plugin your "custom" GuavaCache(CustomGuavaCache)...
现在只需扩展GuavaCacheManager以插入您的“自定义” GuavaCache（CustomGuavaCache）...
public class CustomGuavaCacheManager extends org.springframework.cache.guava.GuavaCacheManager {
@Override
protected Cache createGuavaCache(String name) {
return new CustomGuavaCache(name, createNativeGuavaCache(name), isAllowNullValues());
}
}
This approach takes advantage of Guava's Cache'sinvalidateAll(keys:Iterable)method. And, of course, you could use Java's Regex support to perform the "matching" on the desired keys to be evicted inside the isMatch(key, pattern)method.
这种方法利用了 Guava 的Cache 的invalidateAll(keys:Iterable)方法。而且，当然，您可以使用 Java 的 Regex 支持对要在isMatch(key, pattern)方法内驱逐的所需键执行“匹配” 。
So, I have not tested this, but this (or something similar) should achieve (almost) what you want (fingers crossed ;-)
所以，我没有测试过这个，但是这个（或类似的东西）应该（几乎）达到你想要的（手指交叉；-）
Hope this helps!
希望这可以帮助！
Cheers, John
干杯，约翰
