Friday, October 31, 2014

Spring Caching abstraction and Google Guava Cache

Spring provides a great out of the box support for caching expensive method calls. The caching abstraction is covered in a great detail here.

My objective here is to cover one of the newer cache implementations that Spring now provides with 4.0+ version of the framework - using Google Guava Cache

In brief, consider a service which has a few slow methods:

public class DummyBookService implements BookService {

 @Override
 public Book loadBook(String isbn) {
  // Slow method 1.

 }

 @Override
 public List<Book> loadBookByAuthor(String author) {
  // Slow method 2
 }

}

With Spring Caching abstraction, repeated calls with the same parameter can be sped up by an annotation on the method along these lines - here the result of loadBook is being cached in to a "book" cache and listing of books cached into another "books" cache:

public class DummyBookService implements BookService {

 @Override
 @Cacheable("book")
 public Book loadBook(String isbn) {
  // slow response time..

 }

 @Override
 @Cacheable("books")
 public List<Book> loadBookByAuthor(String author) {
  // Slow listing
 }
}

Now, Caching abstraction support requires a CacheManager to be available which is responsible for managing the underlying caches to store the cached results, with the new Guava Cache support the CacheManager is along these lines:

@Bean
public CacheManager cacheManager() {
 return new GuavaCacheManager("books", "book");
}

Google Guava Cache provides a rich API to be able to pre-load the cache, set eviction duration based on last access or created time, set the size of the cache etc, if the cache is to be customized then a guava CacheBuilder can be passed to the CacheManager for this customization:

@Bean
public CacheManager cacheManager() {
 GuavaCacheManager guavaCacheManager =  new GuavaCacheManager();
 guavaCacheManager.setCacheBuilder(CacheBuilder.newBuilder().expireAfterAccess(30, TimeUnit.MINUTES));
 return guavaCacheManager;
}

This works well if all the caches have a similar configuration, what if the caches need to be configured differently - for eg. in the sample above, I may want the "book" cache to never expire but the "books" cache to have an expiration of 30 mins, then the GuavaCacheManager abstraction does not work well, instead a better solution is actually to use a SimpleCacheManager which provides a more direct way to get to the cache and can be configured this way:

@Bean
public CacheManager cacheManager() {
 SimpleCacheManager simpleCacheManager = new SimpleCacheManager();
 GuavaCache cache1 = new GuavaCache("book", CacheBuilder.newBuilder().build());
 GuavaCache cache2 = new GuavaCache("books", CacheBuilder.newBuilder()
             .expireAfterAccess(30, TimeUnit.MINUTES)
             .build());
 simpleCacheManager.setCaches(Arrays.asList(cache1, cache2));
 return simpleCacheManager;
}

This approach works very nicely, if required certain caches can be configured to be backed by a different caching engines itself, say a simple hashmap, some by Guava or EhCache some by distributed caches like Gemfire.


2 comments:

  1. How can I implement a combination of both?, a general for any caches, and one for specific ones.

    ReplyDelete