Spring Framework 3.1 has a generic cache abstraction for transparently applying caching to Spring applications. It has caching support for classes and methods using two annotations: @Cacheable. Cache a method call. In the following example, the value is the return type, a Manual. The key is extracted from the ISBN argument using the id. Jun 29, 2017 Spring Boot cache with. Spring.cache.type=redis spring.redis.host=192. @CacheConfig — Class level annotation allows to specify global values for annotations like cache name or key generator.
License Key Generator
From the spring documentation :
How can I specify @Cachable to use isbn and checkWarehouse as key?
Mar 20, 2018 Spring Cache is nothing but a store of key-value pairs, where values are the ones returned from @Cacheable methods, whereas, for keys there has to be some strategy to generate them. By default Spring uses a simple key generation based on the following algorithm: If @Cacheable method has no arguments then SimpleKey.EMPTY is used as key. If you first call #getModel1 with 1 and then call #getModel2 with 1 then Spring Cache will return the value that #getModel1 returned because all the method arguments are equal. This is almost certainly not what you want. The following key generator solves this issue. Dec 18, 2014 Caching Data in Spring Using Redis. Implementing a Custom Key Generator. For basic purposes, the default key generation system for cached data works. The parameters to your method become the key in your cache store. For example, in the following method.
Update: Current Spring cache implementation uses all method parameters as the cache key if not specified otherwise. If you want to use selected keys, refer to Arjan’s answer which uses SpEL list {#isbn, #includeUsed} which is the simplest way to create unique keys.
From Spring Documentation
The default key generation strategy changed with the release of Spring
4.0. Earlier versions of Spring used a key generation strategy that, for multiple key parameters, only considered the hashCode() of
parameters and not equals(); this could cause unexpected key
collisions (see SPR-10237 for background). The new
‘SimpleKeyGenerator’ uses a compound key for such scenarios.
Before Spring 4.0
I suggest you to concat the values of the parameters in Spel expression with something like key='#checkWarehouse.toString() + #isbn.toString()'), I believe this should work as org.springframework.cache.interceptor.ExpressionEvaluator returns Object, which is later used as the key so you don’t have to provide an int in your SPEL expression.
As for the hash code with a high collision probability – you can’t use it as the key.
Someone in this thread has suggested to use T(java.util.Objects).hash(#p0,#p1, #p2) but it WILL NOT WORK and this approach is easy to break, for example I’ve used the data from SPR-9377 :
Both lines print -636517714 on my environment.
P.S. Actually in the reference documentation we have
I think that this example is WRONG and misleading and should be removed from the documentation, as the keys should be unique.
P.P.S. also see https://jira.springsource.org/browse/SPR-9036 for some interesting ideas regarding the default key generation. /steam-key-generator-media-file.html.
I’d like to add for the sake of correctness and as an entertaining fact that using a secure cryptographic hash function like SHA256, due to the properties of such function IS possible for this task, but to compute it every time may be too expensive.
After some limited testing with Spring 3.2, it seems one can use a SpEL list: {.., .., ..}. This can also include null values. Spring passes the list as the key to the actual cache implementation. When using Ehcache, such will at some point invoke List#hashCode(), which takes all its items into account. (I am not sure if Ehcache only relies on the hash code.)
Spring Cacheable Keygenerator Example
I use this for a shared cache, in which I include the method name in the key as well, which the Spring default key generator does not include. This way I can easily wipe the (single) cache, without (too much…) risking matching keys for different methods. Like:
Of course, if many methods need this and you’re always using all parameters for your key, then one can also define a custom key generator that includes the class and method name:
…with:
You can use a Spring-EL expression, for eg on JDK 1.7:
This will work
@Cacheable(value=”bookCache”, key=”#checkwarehouse.toString().append(#isbn.toString())”)