Friday, 1 July 2016

Caching in JavaEE with Couchbase

One of Couchbase Server's typical use cases is caching. As you might know it is a KV store. The value of a KV pair can be JSON document. Not only the fact that Couchbase Server can store JSON documents makes it a document database, more the fact that you can index and query on JSON data defines it's characteristic as a JSON document database. Back to the KV store: If you you configure the built-in managed cache in a way that all your data is fitting into memory then Couchbase Server is used as a highly available distributed cache.

If you are a Java developer, then one of your questions might be if it makes sense to use Couchbase as a cache for your applications. I had several projects, where EhCache was replaced by Couchbase because of the Garbage Collection implications. The performance was often quite better with a centralized, low-latency (sub-milliseconds) cache than with one which was colocated with the application instances. This indeed depends on several factors (size of the cache entries, number of cache entries, access throughput). The next questions might be how to best integrate such a cache into your application. A typical pattern is:
  • Try to read the data from the cache
  • If it is there, then use it
  • If is not there then get the data from the source system (e.g. relational DBMS)
  • Put it into the cache
  • The next time when you try to access the same data, then it will be most probably in the cache
Couchbase's Java SDK is quite simple for CRUD operations:
  • C: Insert
  • R: Get
  • U: Update, Replace
  • D: Remove
So as soon as you established a Bucket (a data container) connection, you can use it as a cache. However, this is involving implementation work on your side. 

I just looked at the Java standard JCache and also used the chance to play a bit around with CDI (Dependency Injection). JCache is implemented by several providers and look at that there is already a Developer Preview of a Couchbase implementation available (http://blog.couchbase.com/jcache-dp2).

Side note: The Couchbase JCache implementation is not yet officially released. Couchbase has also a good Spring Data integration which also comes with cashing support.

So let's get started. First we need to have a cache instance which we can use for caching purposes.


As you can see, we are creating a CacheProvider, then a Config and finally a CacheManager in order to access the Cache. Our cache is an object cache, whereby objects are stored by a string key. The Factory ensures that we have only a single instance of our ObjectCache. It's not using CDI and so can be also used with JavaSE. In a real world you would probably not use constants for the factory configuration, but it seemed to be sufficient for this example.

Now let's use the factory. Actually we misuse it a bit here because we use it in a Producer. In a pure CDI world, you would just use the code for initializing the cache in the producer method. So the producer is actually your factory, whereby the producer method acts as a source of objects to be injected. The annotation 'CBObjectCache' was bound to the producer.



Now that we have a producer, we can just inject CBObjectCache somewhere else. Let's do this in an Interceptor. We will use this interceptor later in order to cache objects automatically when a method is called. The annotation 'Cached' is bound to our interceptor.



Now in order to use our interceptor, we just have to annotate a method which should cache the passed data. The example below shows that the 'createHelloMessage' is annotated with 'Cached'. So before the actual method code is executed, the value of the variable 'name' will be cached in Couchbase. In order proof this, the value is fetched in the method body again to be printed out by the 'HelloWorldServlet'.



Before I forget it, here how it is looking like in Couchbase:


Hope this small introduction to JCache and CDI was interesting for you. :-)

The full source code can be found here: https://github.com/dmaier-couchbase/cb-jboss/tree/master/hello-jcache-cdi .


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