Hibernate Second Level Cache Example

To enable second level cache, here we will use EHCache.
Change mapping file category.hbm.xml, and one line


<cache usage="read-write"/>


<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping>
    <class name="net.tecbar.domain.Category" table="category">
        <cache usage="read-write"/>
        <id name="id" type="integer">
            <column name="id" />
            <generator class="native"></generator>
        </id>
        <property name="name" type="string">
            <column name="name" />
        </property>
        <property name="description" type="string">
            <column name="description" />
        </property>
    </class>
</hibernate-mapping>

<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"

"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping>

</id>

</property>

</property>

</class>

</hibernate-mapping>

add one ehcache.xml, a simple example


<ehcache>
    <diskStore path="java.io.tmpdir"/>

    <defaultCache
        maxElementsInMemory="10000"
        eternal="false"
        timeToIdleSeconds="120"
        timeToLiveSeconds="120"
        overflowToDisk="true"
        />
</ehcache>

<defaultCache

maxElementsInMemory="10000"

eternal="false"

timeToIdleSeconds="120"

timeToLiveSeconds="120"

overflowToDisk="true"

</ehcache>


<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping>
    <class name="net.tecbar.domain.Category" table="category">
        <cache usage="read-write"/>
        <id name="id" type="integer">
            <column name="id" />
            <generator class="native"></generator>
        </id>
        <property name="name" type="string">
            <column name="name" />
        </property>
        <property name="description" type="string">
            <column name="description" />
        </property>
    </class>
</hibernate-mapping>

<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"

"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping>

</id>

</property>

</property>

</class>

</hibernate-mapping>

Let’s use the same code as we used in the 1st level cache example


package net.tecbar.hibernate;

import net.tecbar.domain.Category;

public class HibernateSecondLevelCacheExample {

	// we enabled 2nd level cache
	public static void main(String[] args) throws InterruptedException {
		// query database and put the entity into the 1st level cache and second level cache
		final Category category = (Category)HibernateUtil.getSession().get(Category.class, 3);
		System.out.println(category);
		HibernateUtil.closeSession();	
		// The entity was removed after the previous session close. 
		// However, it is still available in second level cache
			
		// it will search the second level cache.
		// Once the record is found, it will be put it into the 1st level cache again
		final Category category2 = (Category)HibernateUtil.getSession().get(Category.class, 3);
		System.out.println(category2);
		
		HibernateUtil.closeSession(); 
	}
}

package net.tecbar.hibernate;

import net.tecbar.domain.Category;

public class HibernateSecondLevelCacheExample {

// we enabled 2nd level cache

public static void main(String[] args) throws InterruptedException {

// query database and put the entity into the 1st level cache and second level cache

final Category category = (Category)HibernateUtil.getSession().get(Category.class, 3);

System.out.println(category);

HibernateUtil.closeSession();

// The entity was removed after the previous session close.

// However, it is still available in second level cache

// it will search the second level cache.

// Once the record is found, it will be put it into the 1st level cache again

final Category category2 = (Category)HibernateUtil.getSession().get(Category.class, 3);

System.out.println(category2);

HibernateUtil.closeSession();

}

The output:


Hibernate: select category0_.id as id1_0_0_, category0_.name as name2_0_0_, category0_.description as descript3_0_0_ from category category0_ where category0_.id=?
PIAccount [id=3, name=car, description=2015 models]
PIAccount [id=3, name=car, description=2015 models]

Hibernate: select category0_.id as id1_0_0_, category0_.name as name2_0_0_, category0_.description as descript3_0_0_ from category category0_ where category0_.id=?

PIAccount [id=3, name=car, description=2015 models]

Part of Hibernate Debug level log


DEBUG [SQL]:109 - select category0_.id as id1_0_0_, category0_.name as name2_0_0_, category0_.description as descript3_0_0_ from category category0_ where category0_.id=?
DEBUG [LogicalConnectionImpl]:226 - Obtaining JDBC connection
DEBUG [LogicalConnectionImpl]:232 - Obtained JDBC connection
DEBUG [ResultSetProcessorImpl]:127 - Starting ResultSet row #0
DEBUG [EntityReferenceInitializerImpl]:142 - On call to EntityIdentifierReaderImpl#resolve, EntityKey was already known; should only happen on root returns with an optional identifier specified
DEBUG [TwoPhaseLoad]:160 - Resolving associations for [net.tecbar.domain.Category#3]
DEBUG [TwoPhaseLoad]:194 - Adding entity to second-level cache: [net.tecbar.domain.Category#3]
DEBUG [TwoPhaseLoad]:286 - Done materializing entity [net.tecbar.domain.Category#3]
DEBUG [AbstractLoadPlanBasedEntityLoader]:208 - Done entity load : net.tecbar.domain.Category#3
[LogicalConnectionImpl]:246 - Releasing JDBC connection
DEBUG [LogicalConnectionImpl]:264 - Released JDBC connection

DEBUG [SQL]:109 - select category0_.id as id1_0_0_, category0_.name as name2_0_0_, category0_.description as descript3_0_0_ from category category0_ where category0_.id=?

DEBUG [LogicalConnectionImpl]:226 - Obtaining JDBC connection

DEBUG [LogicalConnectionImpl]:232 - Obtained JDBC connection

DEBUG [ResultSetProcessorImpl]:127 - Starting ResultSet row #0

DEBUG [EntityReferenceInitializerImpl]:142 - On call to EntityIdentifierReaderImpl#resolve, EntityKey was already known; should only happen on root returns with an optional identifier specified