Hibernate Second Level Cache

Hibernate second level cache uses a common cache for all the session object of a session factory. It is useful if you have multiple session objects from a session factory.

SessionFactory holds the second level cache data. It is global for all the session objects and not enabled by default.

Different vendors have provided the implementation of Second Level Cache.

EH Cache
OS Cache
Swarm Cache
JBoss Cache

Each implementation provides different cache usage functionality. There are four ways to use second level cache.

read-only: caching will work for read only operation.
nonstrict-read-write: caching will work for read and write but one at a time.
read-write: caching will work for read and write, can be used simultaneously.
transactional: caching will work for transaction.

The cache-usage property can be applied to class or collection level in hbm.xml file. The example to define cache usage is given below:

Let's see the second level cache implementation and cache usage.

Implementation	read-only	nonstrict-read-write	read-write	transactional
EH Cache	Yes	Yes	Yes	No
OS Cache	Yes	Yes	Yes	No
Swarm Cache	Yes	Yes	No	No
JBoss Cache	No	No	No	Yes

Hibernate Second Level Cache Example

To understand the second level cache through example, we need to follow the following steps:

Create the persistent class using Maven
Add project information and configuration in pom.xml file
Create the Configuration file
Create the class that retrieves the persistent object.

Here, we are assuming, there is emp1012 table in the oracle database containing some records.

1) Create the persistent class using Maven.

File: Employee.java

package com.javatpoint;  
import javax.persistence.*;
import org.hibernate.annotations.Cache;
import org.hibernate.annotations.CacheConcurrencyStrategy;
@Entity
@Table(name="emp1012")
@Cacheable
@Cache(usage=CacheConcurrencyStrategy.READ_ONLY)
public class Employee {  
	@Id
private int id;  
private String name;  
private float salary;  
  
public Employee() {}  
public Employee(String name, float salary) {  
    super();  
    this.name = name;  
    this.salary = salary;  
}
public int getId() {
	return id;
}
public void setId(int id) {
	this.id = id;
}
public String getName() {
	return name;
}
public void setName(String name) {
	this.name = name;
}
public float getSalary() {
	return salary;
}
public void setSalary(float salary) {
	this.salary = salary;
}  
}  

2) Add project information and configuration in pom.xml file.

Open pom.xml file and click source. Now, add the below dependencies between <dependencies>....</dependencies> tag.

  <dependency>
    <groupId>org.hibernate</groupId>
    <artifactId>hibernate-core</artifactId>
    <version>5.2.16.Final</version>
</dependency>
	
<dependency>
    <groupId>com.oracle</groupId>
    <artifactId>ojdbc14</artifactId>
    <version>10.2.0.4.0</version>
</dependency>
    
<dependency>
    <groupId>net.sf.ehcache</groupId>
    <artifactId>ehcache</artifactId>
    <version>2.10.3</version>
</dependency>
    
   
<dependency>
    <groupId>org.hibernate</groupId>
    <artifactId>hibernate-ehcache</artifactId>
    <version>5.2.16.Final</version>
</dependency>

3) Create the Configuration file

File: hibernate.cfg.xml

<?xml version='1.0' encoding='UTF-8'?>  
<!DOCTYPE hibernate-configuration PUBLIC  
          "-//Hibernate/Hibernate Configuration DTD 5.2.0//EN"  
          "http://hibernate.sourceforge.net/hibernate-configuration-5.2.0.dtd">  
  
<hibernate-configuration>  
  
    <session-factory>  
        <property name="show_sql">true</property>  
        <property name="hbm2ddl.auto">update</property>  
        <property name="dialect">org.hibernate.dialect.Oracle9Dialect</property>  
        <property name="connection.url">jdbc:oracle:thin:@localhost:1521:xe</property>  
        <property name="connection.username">system</property>  
        <property name="connection.password">jtp</property>  
        <property name="connection.driver_class">oracle.jdbc.driver.OracleDriver</property>  
       
         <property name="cache.use_second_level_cache">true</property> 
         <property name="cache.region.factory_class">org.hibernate.cache.ehcache.EhCacheRegionFactory</property>
         <mapping class="com.javatpoint.Employee"/>
    </session-factory>  
</hibernate-configuration>  

To implement second level cache, we need to define cache.provider_class property in the configuration file.

4) Create the class that retrieves the persistent object.

File: FetchTest.java

package com.javatpoint;  
  
import org.hibernate.Session;  
import org.hibernate.SessionFactory;
import org.hibernate.boot.Metadata;
import org.hibernate.boot.MetadataSources;
import org.hibernate.boot.registry.StandardServiceRegistry;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
  
public class FetchTest {  
public static void main(String[] args) {  
	StandardServiceRegistry ssr=new StandardServiceRegistryBuilder().configure("hibernate.cfg.xml").build();
	Metadata meta=new MetadataSources(ssr).getMetadataBuilder().build();
	
	SessionFactory factory=meta.getSessionFactoryBuilder().build();
      
    Session session1=factory.openSession();  
    Employee emp1=(Employee)session1.load(Employee.class,121);  
    System.out.println(emp1.getId()+" "+emp1.getName()+" "+emp1.getSalary());  
    session1.close();  
      
    Session session2=factory.openSession();  
    Employee emp2=(Employee)session2.load(Employee.class,121);  
    System.out.println(emp2.getId()+" "+emp2.getName()+" "+emp2.getSalary());  
    session2.close();  
      
}  
}  

Output:

As we can see here, hibernate does not fire query twice. If you don't use second level cache, hibernate will fire query twice because both query uses different session objects.

Download this hibernate example (Developed using Eclipse IDE)

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