19.3. Managing the caches

Whenever you pass an object to save(), update() or saveOrUpdate() and whenever you retrieve an object using load(), get(), list(), iterate() or scroll(), that object is added to the internal cache of the Session.
When flush() is subsequently called, the state of that object will be synchronized with the database. If you do not want this synchronization to occur or if you are processing a huge number of objects and need to manage memory efficiently, the evict() method may be used to remove the object and its collections from the first-level cache.
ScrollableResult cats = sess.createQuery("from Cat as cat").scroll(); //a huge result set
while ( cats.next() ) {
    Cat cat = (Cat) cats.get(0);
    doSomethingWithACat(cat);
    sess.evict(cat);
}
The Session also provides a contains() method to determine if an instance belongs to the session cache.
To completely evict all objects from the session cache, call Session.clear()
For the second-level cache, there are methods defined on SessionFactory for evicting the cached state of an instance, entire class, collection instance or entire collection role.
sessionFactory.evict(Cat.class, catId); //evict a particular Cat
sessionFactory.evict(Cat.class);  //evict all Cats
sessionFactory.evictCollection("Cat.kittens", catId); //evict a particular collection of kittens
sessionFactory.evictCollection("Cat.kittens"); //evict all kitten collections
The CacheMode controls how a particular session interacts with the second-level cache.
  • CacheMode.NORMAL - read items from and write items to the second-level cache
  • CacheMode.GET - read items from the second-level cache, but don't write to the second-level cache except when updating data
  • CacheMode.PUT - write items to the second-level cache, but don't read from the second-level cache
  • CacheMode.REFRESH - write items to the second-level cache, but don't read from the second-level cache, bypass the effect of hibernate.cache.use_minimal_puts, forcing a refresh of the second-level cache for all items read from the database
To browse the contents of a second-level or query cache region, use the Statistics API:
Map cacheEntries = sessionFactory.getStatistics()
        .getSecondLevelCacheStatistics(regionName)
        .getEntries();
You'll need to enable statistics, and, optionally, force Hibernate to keep the cache entries in a more human-understandable format:
hibernate.generate_statistics true
hibernate.cache.use_structured_entries true