How do I tell Spring cache not to cache null value in @Cacheable annotation

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Hooray, as of Spring 3.2 the framework allows for this using Spring SPEL and unless. Note from the java doc surrounding Cacheable:

http://static.springsource.org/spring/docs/3.2.x/javadoc-api/org/springframework/cache/annotation/Cacheable.html

public abstract String unless

Spring Expression Language (SpEL) attribute used to veto method caching.

Unlike condition(), this expression is evaluated after the method has been called and can therefore refer to the result. Default is “”, meaning that caching is never vetoed.

The important aspect is that unless is evaluated after the method has been called. This makes perfect sense because the method will never get executed if the key is already in the cache.

So in the above example you would simply annotate as follows (#result is available to test the return value of a method):

@Cacheable(value="defaultCache", key="#pk", unless="#result == null")
public Person findPerson(int pk) {
   return getSession.getPerson(pk);
}

I would imagine this condition arises from the use of pluggable cache implementations such as Ehcache which allows caching of nulls. Depending on your use case scenario this may or may not be desirable.

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