The Java EE 7 Tutorial

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44.2 Specifying the Cache Mode Settings to Improve Performance

To adjust the cache mode settings for a persistence unit, specify one of the cache modes as the value of the shared-cache-mode element in the persistence.xml deployment descriptor (shown in bold):

<persistence-unit name="examplePU" transaction-type="JTA">
    <provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
    <jta-data-source>java:comp/DefaultDataSource</jta-data-source>
    <shared-cache-mode>DISABLE_SELECTIVE</shared-cache-mode>
</persistence-unit>

Note:

Because support for a second-level cache is not required by the Java Persistence API specification, setting the second-level cache mode in persistence.xml will have no effect when you use a persistence provider that does not implement a second-level cache.

Alternatively, you can specify the shared cache mode by setting the javax.persistence.sharedCache.mode property to one of the shared cache mode settings:

EntityManagerFactory emf = 
    Persistence.createEntityManagerFactory(
        "myExamplePU", new Properties().add(
            "javax.persistence.sharedCache.mode", "ENABLE_SELECTIVE"));

44.2.1 Setting the Cache Retrieval and Store Modes

If you have enabled the second-level cache for a persistence unit by setting the shared cache mode, you can further modify the behavior of the second-level cache by setting the javax.persistence.cache.retrieveMode and javax.persistence.cache.storeMode properties. You can set these properties at the persistence context level by passing the property name and value to the EntityManager.setProperty method, or you can set them on a per-EntityManager operation (EntityManager.find or EntityManager.refresh) or on a per-query level.

44.2.1.1 Cache Retrieval Mode

The cache retrieval mode, set by the javax.persistence.retrieveMode property, controls how data is read from the cache for calls to the EntityManager.find method and from queries.

You can set the retrieveMode property to one of the constants defined by the javax.persistence.CacheRetrieveMode enumerated type, either USE (the default) or BYPASS.

When the property is set to USE, data is retrieved from the second-level cache, if available. If the data is not in the cache, the persistence provider will read it from the database.

When the property is set to BYPASS, the second-level cache is bypassed and a call to the database is made to retrieve the data.

44.2.1.2 Cache Store Mode

The cache store mode, set by the javax.persistence.storeMode property, controls how data is stored in the cache.

The storeMode property can be set to one of the constants defined by the javax.persistence.CacheStoreMode enumerated type: either USE (the default), BYPASS, or REFRESH.

When the property is set to USE, the cache data is created or updated when data is read from or committed to the database. If data is already in the cache, setting the store mode to USE will not force a refresh when data is read from the database.

When the property is set to BYPASS, data read from or committed to the database is not inserted or updated in the cache. That is, the cache is unchanged.

When the property is set to REFRESH, the cache data is created or updated when data is read from or committed to the database, and a refresh is forced on data in the cache upon database reads.

44.2.1.3 Setting the Cache Retrieval or Store Mode

To set the cache retrieval or store mode for the persistence context, call the EntityManager.setProperty method with the property name and value pair:

EntityManager em = ...;
em.setProperty("javax.persistence.cache.storeMode", "BYPASS");

To set the cache retrieval or store mode when calling the EntityManager.find or EntityManager.refresh methods, first create a Map<String, Object> instance and add a name/value pair as follows:

EntityManager em = ...;
Map<String, Object> props = new HashMap<String, Object>();
props.put("javax.persistence.cache.retrieveMode", "BYPASS");
String personPK = ...;
Person person = em.find(Person.class, personPK, props);

Note:

The cache retrieval mode is ignored when calling the EntityManager.refresh method, as calls to refresh always result in data being read from the database, not the cache.

To set the retrieval or store mode when using queries, call the Query.setHint or TypedQuery.setHint methods, depending on the type of query:

EntityManager em = ...;
CriteriaQuery<Person> cq = ...;
TypedQuery<Person> q = em.createQuery(cq);
q.setHint("javax.persistence.cache.storeMode", "REFRESH");
...

Setting the store or retrieve mode in a query or when calling the EntityManager.find or EntityManager.refresh method overrides the setting of the entity manager.

44.2.2 Controlling the Second-Level Cache Programmatically

The javax.persistence.Cache interface defines methods for interacting with the second-level cache programmatically. The Cache interface defines methods to do the following:

  • Check whether a particular entity has cached data

  • Remove a particular entity from the cache

  • Remove all instances (and instances of subclasses) of an entity class from the cache

  • Clear the cache of all entity data


Note:

If the second-level cache has been disabled, calls to the Cache interface's methods have no effect, except for contains, which will always return false.

44.2.2.1 Checking whether an Entity's Data Is Cached

Call the Cache.contains method to find out whether a given entity is currently in the second-level cache. The contains method returns true if the entity's data is cached, and false if the data is not in the cache:

EntityManager em = ...;
Cache cache = em.getEntityManagerFactory().getCache();
String personPK = ...;
if (cache.contains(Person.class, personPK)) {
  // the data is cached
} else {
  // the data is NOT cached
}

44.2.2.2 Removing an Entity from the Cache

Call one of the Cache.evict methods to remove a particular entity or all entities of a given type from the second-level cache. To remove a particular entity from the cache, call the evict method and pass in the entity class and the primary key of the entity:

EntityManager em = ...;
Cache cache = em.getEntityManagerFactory().getCache();
String personPK = ...;
cache.evict(Person.class, personPK);

To remove all instances of a particular entity class, including subclasses, call the evict method and specify the entity class:

EntityManager em = ...;
Cache cache = em.getEntityManagerFactory().getCache();
cache.evict(Person.class);

All instances of the Person entity class will be removed from the cache. If the Person entity has a subclass, Student, calls to the above method will remove all instances of Student from the cache as well.

44.2.2.3 Removing All Data from the Cache

Call the Cache.evictAll method to completely clear the second-level cache:

EntityManager em = ...;
Cache cache = em.getEntityManagerFactory().getCache();
cache.evictAll();
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