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Hibernate Second Level Cache

Hibernate Second Level Cache

Explanation

  • Definition : The second-level cache in Hibernate is an optional cache that stores objects across sessions. Unlike the first-level cache, which is specific to a session, the second-level cache can be shared among different sessions and is typically used to cache frequently accessed data.
  • Scope : The second-level cache spans the entire SessionFactory, meaning it is shared across multiple sessions.
  • Configuration : Hibernate supports various caching providers, one of which is EHCache. EHCache is a widely-used, open-source caching library for Java that integrates well with Hibernate.

 Advantages

  • Improved Performance : By caching objects at the SessionFactory level, it reduces database access for frequently used data, thereby improving performance.
  • Reduced Load : It reduces the load on the database, especially for read-heavy applications.

Steps to Configure Hibernate Second Level Cache

  1. Add Dependencies : Include the necessary Hibernate and EHCache dependencies in your pom.xml or build.gradle file.
  2. Configure Hibernate : Update the Hibernate configuration file (hibernate.cfg.xml) to enable the second-level cache and specify EHCache as the provider.
  3. Configure EHCache : Create an ehcache.xml configuration file to define cache regions and settings.
  4.  Annotate Entities : Use Hibernate annotations to specify which entities and collections should be cached.

Hibernate Second Level Cache

Step 1: Add Dependencies (Maven Example)
 Step 1: Add Dependencies (Maven Example) 

xml
<dependency>
    <groupId>org.hibernate</groupId>
    <artifactId>hibernate-core</artifactId>
    <version>5.4.32.Final</version>
</dependency>
<dependency>
    <groupId>org.hibernate</groupId>
    <artifactId>hibernate-ehcache</artifactId>
    <version>5.4.32.Final</version>
</dependency>
<dependency>
    <groupId>net.sf.ehcache</groupId>
    <artifactId>ehcache</artifactId>
    <version>2.10.6</version>
</dependency>

Step 2: Configure Hibernate (hibernate.cfg.xml)
Step 2: Configure Hibernate (hibernate.cfg.xml) 

xml
<hibernate-configuration>
    <session-factory>
        <!-- Database connection settings -->
        <property name="hibernate.connection.driver_class">com.mysql.cj.jdbc.Driver</property>
        <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/your_database</property>
        <property name="hibernate.connection.username">your_username</property>
        <property name="hibernate.connection.password">your_password</property>

        <!-- Hibernate properties -->
        <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
        <property name="hibernate.hbm2ddl.auto">update</property>

        <!-- Enable second-level cache -->
        <property name="hibernate.cache.use_second_level_cache">true</property>
        <property name="hibernate.cache.region.factory_class">org.hibernate.cache.ehcache.EhCacheRegionFactory</property>
        <property name="hibernate.cache.use_query_cache">true</property>

        <!-- Entity classes -->
        <mapping class="com.example.Student"/>
    </session-factory>
</hibernate-configuration>

Step 3: Configure EHCache (ehcache.xml)
 Step 3: Configure EHCache (ehcache.xml) 

xml
<ehcache>
    <defaultCache
        maxEntriesLocalHeap="10000"
        eternal="false"
        timeToIdleSeconds="300"
        timeToLiveSeconds="600"
        overflowToDisk="true"
        diskPersistent="false"
        diskExpiryThreadIntervalSeconds="120"
        memoryStoreEvictionPolicy="LRU"/>
    
    <cache name="com.example.Student"
           maxEntriesLocalHeap="1000"
           eternal="false"
           timeToIdleSeconds="300"
           timeToLiveSeconds="600"
           overflowToDisk="true"
           diskPersistent="false"
           diskExpiryThreadIntervalSeconds="120"
           memoryStoreEvictionPolicy="LRU"/>
</ehcache>

Step 4: Annotate Entities
Step 4: Annotate Entities 

java
import javax.persistence.*;
import org.hibernate.annotations.Cache;
import org.hibernate.annotations.CacheConcurrencyStrategy;

@Entity
@Table(name = "student")
@Cacheable
@Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
public class Student {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private int id;

    @Column(name = "first_name")
    private String firstName;

    @Column(name = "last_name")
    private String lastName;

    @Column(name = "email")
    private String email;

    // Getters and setters
    // toString method
}

Example of Hibernate Second Level Cache

In this example, EHCache is configured as the second-level cache provider. The Student entity is marked as cacheable, meaning instances of Student will be stored in the second-level cache according to the settings defined in ehcache.xml.

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