From the spring documentation :
Jun 11, 2019 The ID of the student is, therefore, the cache key. The cache entry is the return value of the method, the student in our example. The method now creates a student object and stores it in the studentCache at the end. The next time this object is requested, it can be retrieved directly from the cache. JSR 107 Annotations vs. Spring Cache. 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.
How can I specify @Cachable to use isbn and checkWarehouse as key?
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.
Aug 23, 2018 We are also going to cover the option to create a custom key generator with Spring Cache. Spring Cache API uses a simple KeyGenerator for generating a key to store caching data. The default key generators for Spring Cache SimpleKeyGenerator.This default implementation uses the method parameters to generate the key. Here is the high-level overview for the default key generation algorithm. 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. Sep 15, 2015 We have earlier written few interesting articles on caching in spring and another good article on @Cacheable and @CacheEvict annotations for caching in spring. This is another comprehensive tutorial for spring caching using Spring 4.Spring caching is available since 3.1, but spring 4.1 has added lot of cool features with the existing spring caching framework.
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.
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.)
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:
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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: Cs6 master collection serial number.
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())”)