Today, we are going to explore a little bit one of the cache options have available when working with Java projects. This option is Caffeine.

Caffeine is a high performance, near optimal caching library based on Java 8. For more details, see our user’s guide and browse the API docs for the latest release.

— Caffeine wiki —

Let’s do it.

As a base project we are going to use a similar code to the one written for the previous article “Cache: Spring Boot + Ehcache“.

The only thing we are going to change is we are going to duplicate the existing endpoint to allow be able to try two different ways of working with Caffeine.

Once we have our new endpoint ready to go, it is time to start configuring Caffeine. We are going to take two different approaches:

1. Make use of Spring injection capabilities.
2. More manual approach.

Leveraging Spring injection capabilities

First, we are going to create our configuration class. To activate the cache capabilities on Spring we can use the configuration and enable configuration annotations:

• @Configuration
• @EnableCaching

With this, we can add now the beans to create our cache and configure appropriately Caffeine.

@Bean
@SuppressWarnings("all")
public Caffeine caffeineConfig() {
    return Caffeine.newBuilder()
        .maximumSize(50)
        .expireAfterWrite(10, TimeUnit.SECONDS)
        .removalListener(CacheEventLogger.removalListener());
}

@Bean
@SuppressWarnings("all")
public CacheManager cacheManager(final Caffeine caffeine) {
    final CaffeineCacheManager caffeineCacheManager = new CaffeineCacheManager();

    caffeineCacheManager.setCaffeine(caffeine);

    return caffeineCacheManager;
}

As you can see, something pretty simple. I have tried to mimic the configuration set for the Ehcache example on the previous article. If you have not done it, you can check it now. A summary of this configuration is:

• Cache size: 50 entries.
• And the expiration policy: Expiration after the write of 10 seconds.

Now on the service, we just need to add the appropriate annotation to indicate we want to use the cache.

@Cacheable(cacheNames = MD5_CACHE_ID)
@Override
public String generateMd5SpringCache(final String text) {
    log.info("The value was not cached by Spring");
    return generateMd5(text);
}

That simple.

Manual approach

We have the possibility of creating the cache manually. This can be desired for multiple reasons like: not having Spring available, wanting component isolation, not dealing with the cache manages an multiple caches or, whatever reason, us, as a developers decide that it fits the best our use case.

To do this manual configuration we just need to exclude the configuration class and the beans’ creation, create the cache in our service class and invoke it when a request arrives.

final LoadingCache<String, String> md5Cache = Caffeine.newBuilder()
    .maximumSize(50)
    .expireAfterWrite(10, TimeUnit.SECONDS)
    .removalListener(CacheEventLogger.removalListener())
    .build(this::generateMd5Wrapper);

@Override
public String generateMd5ManualCache(final String text) {
    return md5Cache.get(text);
}

Nothing too fancy. It is worth it a note about the method ‘generateMd5Wrapper‘. It is completely unnecessary, the only reason it has been created is to be able to write an extra log line to run the demo and to have visible effects of the cache working.

The last thing we have defined is a removal listener to log when an object is removed from the cache. Again, this is just for demo purposes and, it is not necessary.

public static RemovalListener<String, String> removalListener() {
    return (String key, String graph, RemovalCause cause) ->
        log.info("Key {} was removed ({})", key, cause);
}

And, with this, everything should be in place to test it. We just need to run our application and invoke our endpoints, for example, using ‘curl’.

curl http://localhost:8080/api/hashes/spring/hola
curl http://localhost:8080/api/hashes/manual/hola

The result should be something like this:

2020-10-31 08:15:19.610 : The value was not cached by Spring
2020-10-31 08:15:35.316 : The value was not cached by Spring
2020-10-31 08:15:35.317 : Key hola was removed (EXPIRED)
2020-10-31 08:15:39.717 : The value was not cached manually
2020-10-31 08:15:55.443 : The value was not cached manually
2020-10-31 08:15:55.443 : Key hola was removed (EXPIRED)

As we can see, invoking multiple times the endpoint only created the first log line and, it is just after waiting for some time (more than 10 seconds) when the cache entry gets expired and re-created.

Obviously, this is a pretty simple example but, this can help us to increase the performance of our system for more complex operations.

As usual, you can find the code here.