Spring cache @Cacheable method ignored when called from within the same class

I'm trying to call a @Cacheable method from within the same class:

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

public List<Person> findPersons(int[] ids) {
   List<Person> list = new ArrayList<Person>();
   for (int id : ids) {
      list.add(findPerson(id));
   }
   return list;
}

and hoping that the results from findPersons are cached as well, but the @Cacheable annotation is ignored, and findPerson method got executed everytime.

Am I doing something wrong here, or this is intended?

This is because of the way proxies are created for handling caching, transaction related functionality in Spring. This is a very good reference of how Spring handles it - Transactions, Caching and AOP: understanding proxy usage in Spring

In short, a self call bypasses the dynamic proxy and any cross cutting concern like caching, transaction etc which is part of the dynamic proxies logic is also bypassed.

The fix is to use AspectJ compile time or load time weaving.

Here is what I do for small projects with only marginal usage of method calls within the same class. In-code documentation is strongly advidsed, as it may look strage to colleagues. But its easy to test, simple, quick to achieve and spares me the full blown AspectJ instrumentation. However, for more heavy usage I'd advice the AspectJ solution.

@Service
@Scope(proxyMode = ScopedProxyMode.TARGET_CLASS)
class PersonDao {

    private final PersonDao _personDao;
    
    @Autowired
    public PersonDao(PersonDao personDao) {
        _personDao = personDao;
    }

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

    public List<Person> findPersons(int[] ids) {
        List<Person> list = new ArrayList<Person>();
        for (int id : ids) {
            list.add(_personDao.findPerson(id));
        }
        return list;
    }
}

For anyone using the Grails Spring Cache plugin, a workaround is described in the documentation. I had this issue on a grails app, but unfortunately the accepted answer seems to be unusable for Grails. The solution is ugly, IMHO, but it works.

The example code demonstrates it well:

class ExampleService {
    def grailsApplication

    def nonCachedMethod() {
        grailsApplication.mainContext.exampleService.cachedMethod()
    }

    @Cacheable('cachedMethodCache')
    def cachedMethod() {
        // do some expensive stuff
    }
}

Simply replace exampleService.cachedMethod() with your own service and method.