Welcome to Hibernate Caching - First Level Cache Example Tutorial. Recently we looked into Hibernate architecture, hibernate mapping and how to use HQL for firing SQL queries in object oriented way. Today we will look into one of the important aspects of Hibernate - Hibernate Cache.
Hibernate Cache can be very useful in gaining fast application performance if used correctly. The idea behind cache is to reduce the number of database queries, hence reducing the throughput time of the application. Hibernate comes with different types of Cache:
For my hibernate first level cache example program, I am using same configuration as in HQL Example, you can check that out and configure the tables and populate it with dummy data. Let’s first look into the program, it’s output and then we will go through some of the important points related to Hibernate First Level Cache. HibernateCacheExample.java
package com.journaldev.hibernate.main;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import com.journaldev.hibernate.model.Employee;
import com.journaldev.hibernate.util.HibernateUtil;
public class HibernateCacheExample {
public static void main(String[] args) throws InterruptedException {
SessionFactory sessionFactory = HibernateUtil.getSessionFactory();
Session session = sessionFactory.getCurrentSession();
Transaction tx = session.beginTransaction();
//Get employee with id=1
Employee emp = (Employee) session.load(Employee.class, new Long(1));
printData(emp,1);
//waiting for sometime to change the data in backend
Thread.sleep(10000);
//Fetch same data again, check logs that no query fired
Employee emp1 = (Employee) session.load(Employee.class, new Long(1));
printData(emp1,2);
//Create new session
Session newSession = sessionFactory.openSession();
//Get employee with id=1, notice the logs for query
Employee emp2 = (Employee) newSession.load(Employee.class, new Long(1));
printData(emp2,3);
//START: evict example to remove specific object from hibernate first level cache
//Get employee with id=2, first time hence query in logs
Employee emp3 = (Employee) session.load(Employee.class, new Long(2));
printData(emp3,4);
//evict the employee object with id=1
session.evict(emp);
System.out.println("Session Contains Employee with id=1?"+session.contains(emp));
//since object is removed from first level cache, you will see query in logs
Employee emp4 = (Employee) session.load(Employee.class, new Long(1));
printData(emp4,5);
//this object is still present, so you won't see query in logs
Employee emp5 = (Employee) session.load(Employee.class, new Long(2));
printData(emp5,6);
//END: evict example
//START: clear example to remove everything from first level cache
session.clear();
Employee emp6 = (Employee) session.load(Employee.class, new Long(1));
printData(emp6,7);
Employee emp7 = (Employee) session.load(Employee.class, new Long(2));
printData(emp7,8);
System.out.println("Session Contains Employee with id=2?"+session.contains(emp7));
tx.commit();
sessionFactory.close();
}
private static void printData(Employee emp, int count) {
System.out.println(count+":: Name="+emp.getName()+", Zipcode="+emp.getAddress().getZipcode());
}
}
When we run above example, the output contains a lot of hibernate related information. But we are mostly interested in our code specific output and the queries fired by hibernate to load the data. The output snippet looks like below.
Hibernate Configuration loaded
Hibernate serviceRegistry created
Hibernate: select employee0_.emp_id as emp_id1_1_0_, employee0_.emp_name as emp_name2_1_0_, employee0_.emp_salary as emp_sala3_1_0_, address1_.emp_id as emp_id1_0_1_, address1_.address_line1 as address_2_0_1_, address1_.city as city3_0_1_, address1_.zipcode as zipcode4_0_1_ from EMPLOYEE employee0_ left outer join ADDRESS address1_ on employee0_.emp_id=address1_.emp_id where employee0_.emp_id=?
1:: Name=Pankaj, Zipcode=95129
2:: Name=Pankaj, Zipcode=95129
Hibernate: select employee0_.emp_id as emp_id1_1_0_, employee0_.emp_name as emp_name2_1_0_, employee0_.emp_salary as emp_sala3_1_0_, address1_.emp_id as emp_id1_0_1_, address1_.address_line1 as address_2_0_1_, address1_.city as city3_0_1_, address1_.zipcode as zipcode4_0_1_ from EMPLOYEE employee0_ left outer join ADDRESS address1_ on employee0_.emp_id=address1_.emp_id where employee0_.emp_id=?
3:: Name=PankajK, Zipcode=95129
Hibernate: select employee0_.emp_id as emp_id1_1_0_, employee0_.emp_name as emp_name2_1_0_, employee0_.emp_salary as emp_sala3_1_0_, address1_.emp_id as emp_id1_0_1_, address1_.address_line1 as address_2_0_1_, address1_.city as city3_0_1_, address1_.zipcode as zipcode4_0_1_ from EMPLOYEE employee0_ left outer join ADDRESS address1_ on employee0_.emp_id=address1_.emp_id where employee0_.emp_id=?
4:: Name=David, Zipcode=95051
Session Contains Employee with id=1?false
Hibernate: select employee0_.emp_id as emp_id1_1_0_, employee0_.emp_name as emp_name2_1_0_, employee0_.emp_salary as emp_sala3_1_0_, address1_.emp_id as emp_id1_0_1_, address1_.address_line1 as address_2_0_1_, address1_.city as city3_0_1_, address1_.zipcode as zipcode4_0_1_ from EMPLOYEE employee0_ left outer join ADDRESS address1_ on employee0_.emp_id=address1_.emp_id where employee0_.emp_id=?
5:: Name=Pankaj, Zipcode=95129
6:: Name=David, Zipcode=95051
Hibernate: select employee0_.emp_id as emp_id1_1_0_, employee0_.emp_name as emp_name2_1_0_, employee0_.emp_salary as emp_sala3_1_0_, address1_.emp_id as emp_id1_0_1_, address1_.address_line1 as address_2_0_1_, address1_.city as city3_0_1_, address1_.zipcode as zipcode4_0_1_ from EMPLOYEE employee0_ left outer join ADDRESS address1_ on employee0_.emp_id=address1_.emp_id where employee0_.emp_id=?
7:: Name=Pankaj, Zipcode=95129
Hibernate: select employee0_.emp_id as emp_id1_1_0_, employee0_.emp_name as emp_name2_1_0_, employee0_.emp_salary as emp_sala3_1_0_, address1_.emp_id as emp_id1_0_1_, address1_.address_line1 as address_2_0_1_, address1_.city as city3_0_1_, address1_.zipcode as zipcode4_0_1_ from EMPLOYEE employee0_ left outer join ADDRESS address1_ on employee0_.emp_id=address1_.emp_id where employee0_.emp_id=?
8:: Name=David, Zipcode=95051
Session Contains Employee with id=2?true
Important Points about First level cache in Hibernate that can be derived from above program are:
evict()
method to remove a single object from the hibernate first level cache.clear()
method to clear the cache i.e delete all the objects from the cache.contains()
method to check if an object is present in the hibernate cache or not, if the object is found in cache, it returns true or else it returns false.That’s all for hibernate caching and first level cache example, in future posts we will look into Hibernate Second Level Cache - EHCache implementation.
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It is very good explanation of first level cache. I am reading this first time and I got understood the concept. Thanks
- Saravanank
Do you think session cache can lead to data inconsistency with multiple threads working on same data or in case of multiple instance of the application running.
- veer
Loved the example, I can use it for my interviews…
- jagadish
Great example to explain the hibernate first level cache
- Muthu
You should use get method or add comment before print method that query is fired or not because load will never fire a query.And it can confuse new learners.
- Jaspreet Singh
Isn’t printData(emp4,5); supposed to show name as PankajK as it is hitting database where data was updated earlier during Thread.sleep(10000). Correct me if I am wrong.
- Rohit Roy
Very Clearly explaind, on the first read it was little bit confusing but eventually ended with a very good explanantion.
- Vijay Raj R
Is criteria uses the cache technique or only get() and load() with will use it.
- Aj
Nice explanation…
- Ram
I am getting following error when I try to runt the program. Can you please provide the solution? org.hibernate.AnnotationException: Unknown mappedBy in: com.test.model.Employee.address, referenced property unknown: com.test.model.Address.employee at org.hibernate.cfg.OneToOneSecondPass.doSecondPass(OneToOneSecondPass.java:153) at org.hibernate.cfg.Configuration.originalSecondPassCompile(Configuration.java:1697) at org.hibernate.cfg.Configuration.secondPassCompile(Configuration.java:1426) at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1846) at com.test.util.HibernateUtilities.buildAnnotationSessionFactory(HibernateUtilities.java:52) at com.test.util.HibernateUtilities.getSessionAnnotationFactory(HibernateUtilities.java:99) at com.test.HibernateCacheExample.main(HibernateCacheExample.java:14)
- Chintan