Spring caching implementation

Question

I am exploring spring caching facility. I have few queries regarding this.

First, should it be applied at service method level or DAO method level, where service method is calling DAO method.

Second, how should I avoid cache data getting stale?

Answer 1

IMO, The answer to both questions is "it depends".

Technically, Spring Wise, cache annotations applied on both Service and DAO will work, I don't think there is any difference, so it boils down to the concrete use case.

For example, if you "logically" plan to provide a cacheable abstraction of what should be calculated as a result of some computational process done on server, you better go with Caching at the service level.

If, on the other hand you have a DAO method that looks like Something getSomethingById(id) in the dao, and you would like to avoid relatively expensive calls to the underlying database, you can provide a cache at the level of the DAO. Having said that, it probably won't be useful to apply caching if you have methods like List<Something> fetchAll() or List<Something> fetchAllByFilter(). If you're working with JPA (implemented with Hibernate) they have their own abstraction of cache, but its kind of beyond the scope of the question, just something you should be aware of...

There are plenty of tutorials available on internet, some illustrate the service based approach, some go for DAO's methods annotations but again, these are only simple examples, in the real world you'll have to take a decision.

Now regarding the second question. In general caching makes sense if your data doesn't change much, so first off if it changes often, then probably caching is not appropriate/relevant for the use case.

Other than that, there are many techniques:

• Cache Data Eviction (usually time based). See this tutorial
• Some kind of messaging system that will send the message about the cache entry change. This one is especially useful if you have a distributed application and keep the cache in-memory only. When getting a message you might opt for "cache replication" or totally wiping out the cache, so that it will be "filled" with a new data eventually
• Using the Distributed cache technologies like Hazelcast or Redis as opposed to the in-memory caching. So that technically the cached data consistency will be guaranteed by caching provider.

I would like also to recommend you This tutorial - the speaker talks about different aspects of caching implementation and I think its really relevant to your question.