JPA second level cache

JPA second level cache

JPA 2.0 standardized the Hibernate second level cache and introduced a new cache API.

There are 3 built-in cache implementation shipped with Hibernate 4, HashTable, Ehcache, Infinispan. HashTable is a in-memory solution, it is useful to test purpose. Ehcache is one of the most popular cache solutions,
Hibernate provides integration with Ehcache. Infinispan is also from JBoss.org community, it is the base of JBoss's next-generation cache and datagrid solution, infinispan is the recommended cache solution if you are using Hibernate/JPA in JBoss application servers.

Enable Cache

By default, JPA 2nd level cache is disabled.

You must specify the value of javax.persistence.sharedCache.mode property or shared-cache-mode element in persistence.xml file.

javax.persistence.sharedCache.mode=ENABLE_SELECTIVE

or

 
  
 
  
 ENABLE_SELECTIVE

 

 

There are four optional values, ALL, ENABLE_SELECTIVE, DISABLE_SELECTIVE, NONE.

ALL will enable cache for all entities, ENABLE_SELECTIVE and DISABLE_SELECTIVE should be used with the JPA specific @Cacheable annotation. The former will enable cache for the entities annotated with @Cacheable or @Cacheable(true). The later will DISABLE cache for the entities annotated with @Cacheable(false) and enable cache for other entities. NONE will disable cache for all entities.

Configure Hibernate cache provider

Now you need configure some properties for Hibernate specific cache provider.

An example of using Ehcache as backend cache provider.

hibernate.cache.use_second_level_cache=true
hibernate.cache.use_query_cache=true
hibernate.cache.region.factory_class = org.hibernate.cache.ehcache.EhCacheRegionFactory

hibernate.cache.use_query_cache is use for enable cache for JPA query result.

It also require you add extra dependency in your pom.xml file.

 
    
 
  
 
  
    org.hibernate 
  
    
 
  
 
  
    hibernate-ehcache 
  


 

 

Test codes

Add @Cacheable(true) to the entity class, we are using the ENABLE_SELECTIVE cache strategy and must apply this annotation to enable cache.

@Entity
@Cacheable(true)
//@Cache(usage=CacheConcurrencyStrategy.READ_ONLY, region="conf_region")
public class Conference {
}

Hibernate also provides specific @Cache annotation to tune the cache settings. Please read the official Hibernate Document for more detailed info.

Write some codes for test purpose and enable the logging info.

@Test
@Transactional
public void retrieveConference() {

    log.debug("============beginning of calling retrieveConference===========");
    final Long id = 1L;

    Conference conference = conferenceDao.findById(id);

    assertTrue(conference != null);

    assertTrue("JUD2013".equals(conference.getName()));

    Conference conference2 = conferenceDao.findById(id);

    assertTrue(conference == conference2);

    log.debug("============end of calling retrieveConference===========");
}

You will find the entity object is cached after it is persisted, and the later queries will not hint database at all.

Sample codes

The codes are hosted on my Github account.

https://github.com/hantsy/spring-sandbox

I also tried to add sample settings and codes for Infinispan, but failed to make it worked in the standalone test.