EclipseLink/Examples/JPA/Caching

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How to use EclispeLink Caching

EclipseLink offers the following caching strategies to maintain identity:

Option (Identity Map)	Caching	Guaranteed Identity	Memory Use
Full Identity Map	Yes	Yes	Very High
Weak Identity Map	Yes	Yes	Low
Soft Identity Map	Yes	Yes	High
Soft Cache Weak Identity Map Hard Cache Weak Identity Map	Yes	Yes	Medium-high
No Identity Map	No	No	None

See the documentation for details on these types.

Using the @Cache Annonation

You may define the @Cache annotation on the following:

• @Entity
• @MappedSuperclass;
• the root of the inheritance hierarchy (if applicable).
  

If you define the @Cache annotation on an inheritance subclass, the annotation will be ignored. If you define the @Cache annotation on @Embeddable EclipseLink will throw an exception.

Example of @Cache Annoatation

 @Target({TYPE})
 @Retention(RUNTIME)
 public @interface Cache {
   CacheType type() default SOFT_WEAK;
   int size() default 100;
   boolean shared() default true;
   int expiry() default -1;
   TimeOfDay expiryTimeOfDay() default @TimeOfDay(specified=false);
   boolean alwaysRefresh() default false;
   boolean refreshOnlyIfNewer() default false;
   boolean disableHits() default false; 
   CacheCoordinationType coordinationType() default SEND_OBJECT_CHANGES;
 }

Attributes of the @Cache Annotation

Attribute	Description	Default	Required or Optional	Override with Persistence Unit Property
type	Set this attribute to the type (org.eclipse.persistence.annotations.CacheType enumerated type) of the cache that you will be using: FULL WEAK SOFT SOFT_WEAK HARD_WEAK CACHE NONE	CacheType.SOFT_WEAK	optional	eclipselink.cache.type.<ENTITY> eclipselink.cache.type.default
size	Set this attribute to an int value to define the size of cache to use (number of objects).	100
shared	Indicate whether cached instances should be in the shared cache or in a client isolated cache (see Isolated Client Session Cache). true - use shared cache for cached instances; false - use client isolated cache for cached instances.	true	optional
expiry	The int value to enable the expiration of the cached instance after a fixed period of time (milliseconds). Queries executed against the cache after this will be forced back to the database for a refreshed copy.	-1 (no expiry)	optional
expiryTimeOfDay	Specific time of day (org.eclipse.persistence.annotations.TimeOfDay) when the cached instance will expire. Queries executed against the cache after this will be forced back to the database for a refreshed copy.	@TimeOfDay(specified=false)	optional
alwaysRefresh	Set to a boolean value of true to force all queries that go to the database to always refresh the cache.	false	optional
refreshOnlyIfNewer	Set to a boolean value of true to force all queries that go to the database to refresh the cache only if the data received from the database by a query is newer than the data in the cache (as determined by the optimistic locking field). Note: This option only applies if one of the other refreshing options, such as alwaysRefresh, is already enabled. Note: A version field is necessary to apply this feature.	false	optional
disableHits	Set to a boolean value of true to force all queries to bypass the cache for hits, but still resolve against the cache for identity. This forces all queries to hit the database.	false	optional
coordinationType	Set this attribute to the cache coordination mode (org.eclipse.persistence.annotations.CacheCoordinationType enumerated type).	CacheCoordinationType.SEND_OBJECT_CHANGES	optional