Hibernate Caching

Hibernate Cache Levels

Hibernate provides two levels of caching to improve performance by reducing database queries:

Cache Level	Scope	Default	Description
First-Level Cache (L1)	Session	Always enabled	Per-session cache. Entities loaded in a session are cached for the session's lifetime.
Second-Level Cache (L2)	SessionFactory	Disabled	Shared across sessions. Requires a cache provider (EHCache, Infinispan, etc.).
Query Cache	SessionFactory	Disabled	Caches query results. Works with L2 cache.

First-Level Cache Demo

Session session = sessionFactory.openSession();

// First get: hits the database
User user1 = session.get(User.class, 1L);
System.out.println("First get: " + user1.getUsername()); // SQL executed

// Second get: served from L1 cache (same session)
User user2 = session.get(User.class, 1L);
System.out.println("Second get: " + user2.getUsername()); // NO SQL - from cache

// Same object reference
System.out.println(user1 == user2); // true

// Clear L1 cache
session.evict(user1);  // Remove specific entity from cache
// session.clear();    // Clear entire L1 cache

// After evict: hits database again
User user3 = session.get(User.class, 1L);
System.out.println("After evict: " + user3.getUsername()); // SQL executed again

session.close();
// L1 cache is destroyed when session closes

Second-Level Cache with EHCache

L2 Cache Configuration

<!-- Enable L2 cache in hibernate.cfg.xml -->
<property name="hibernate.cache.use_second_level_cache">true</property>
<property name="hibernate.cache.use_query_cache">true</property>
<property name="hibernate.cache.region.factory_class">
    org.hibernate.cache.jcache.JCacheRegionFactory
</property>

<!-- pom.xml dependency -->
<!--
<dependency>
    <groupId>org.hibernate.orm</groupId>
    <artifactId>hibernate-jcache</artifactId>
    <version>6.4.0.Final</version>
</dependency>
<dependency>
    <groupId>org.ehcache</groupId>
    <artifactId>ehcache</artifactId>
    <version>3.10.8</version>
</dependency>
-->

import org.hibernate.annotations.Cache;
import org.hibernate.annotations.CacheConcurrencyStrategy;

// Cache strategies:
// READ_ONLY: For data that never changes (best performance)
// READ_WRITE: For data that changes occasionally (uses soft locks)
// NONSTRICT_READ_WRITE: No strict locking (slight risk of stale data)
// TRANSACTIONAL: Full transactional cache (JTA required)

@Entity
@Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
public class Product {
    @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private double price;
}

// Cache a collection
@Entity
public class User {
    @OneToMany(mappedBy = "user")
    @Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
    private List<Order> orders;
}

// Using query cache
Session session = sessionFactory.openSession();
List<Product> products = session.createQuery("FROM Product", Product.class)
        .setCacheable(true)           // Enable query cache
        .setCacheRegion("productCache") // Optional: named cache region
        .list();
session.close();

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Hibernate Caching

Hibernate Cache Levels

Second-Level Cache with EHCache

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