Hibernate Caching

I found some useful information on internet about hibernate caching.I thought of sharing with everyone.
High-volume database traffic is a frequent cause of performance problems in Web applications. Hibernate is a high-performance, object/relational persistence and query service. In many cases, second-level caching can be just what Hibernate needs to realize its full performance-handling potential.

What is caching – Anything you can do to minimize traffic between a database and an application server is probably a good thing. In theory, an application ought to be able to maintain a cache containing data already loaded from the database, and only hit the database when information has to be updated. When the database is hit, the changes may invalidate the cache.

There are two different cache used in hibernate-
1. First Level cache – This is associated with session. This is default implemented in hibernate on a per-transaction basis. Hibernate uses this cache mainly to reduce the number of SQL queries it needs to generate within a given transaction. For example, if an object is modified several times within the same transaction, Hibernate will generate only one SQL UPDATE statement at the end of the transaction, containing all the modifications
2. Second level cache – This is associated with Session Factory object. It will survive Sessions and can be reused in new Session by same SessionFactory (which usually is one per application). By default the 2nd level cache is not enabled. This ’second-level’ cache exists as long as the session factory is alive. The second-level cache holds on to the ‘data’ for all properties and associations for individual entities that are marked to be cached. The second level cache is responsible for caching objects across sessions.

Cache Type
EHCache (Easy Hibernate Cache) — http://ehcache.sourceforge.net/
OSCache (Open Symphony) — http://www.opensymphony.com/oscache/
SwarmCache — http://swarmcache.sourceforge.net/
JBoss TreeCache — http://jboss.org/wiki/Wiki.jsp?page=JBossCache

• EHCache -s an open source widely used java distributed cache for general purpose caching, Java EE and light-weight containers. It features memory and disk stores, replicate by copy and invalidate, listeners, cache loaders, cache extensions, cache exception handlers, a gzip caching servlet filter, RESTful and SOAP APIs and much more. Ehcache is available under an Apache open source license and is actively developed, maintained and supported.It support read only, Non strict Read/write,Read/write caching.It does not support transactional caching architecture.
• OSCache – is “a Java framework” developed by OpenSymphony that makes it easy to cache content in Web applications.It is a caching solution that includes a JSP tag library and set of classes to perform fine grained dynamic caching of JSP content, servlet responses or arbitrary objects.It provides both in memory and persistent on disk caches.They can allow your site to have graceful error tolerance .It support read only, Non strict Read/write,Read/write caching.It does not support transactional schema caching architecture.
• SwarmCache is a simple cluster-based caching solution based on JavaGroups. It supports read-only or nonstrict read/write caching. This type of cache is appropriate for applications that typically have many more read operations than write operations.It support read only, Non strict Read/write caching.It does not support ,Read/write and transactional caching architecture.It is is a cluster-based caching.
• JBoss TreeCache – is a powerful replicated (synchronous or asynchronous) and transactional cache. Use this solution if you really need a true transaction-capable caching architecture.

Hibernate Mapping Cheat Sheet

http://ndpsoftware.com/HibernateMappingCheatSheet.html

what Hibernate is and will show some examples

Main features
Hibernate is a solution for object relational mapping and a persistence management
solution or persistent layer. This is probably not understandable for anybody learning
Hibernate.
What you can imagine is probably that you have your application with some functions
(business logic) and you want to save data in a database. When you use Java all the
business logic normally works with objects of different class types. Your database tables
are not at all objects.
Hibernate provides a solution to map database tables to a class. It copies the database
data to a class. In the other direction it supports to save objects to the database. In this
process the object is transformed to one or more tables.
Saving data to a storage is called persistence. And the copying of tables to objects and
vice versa is called object relational mapping.
Why using Object Relational Mapping?
Better system architecture
When you include all functionality of your application and the access to the database
within your dialogs, you will have some severe disadvantages.
It is really difficult to reuse code. You will repeat code at many places. If you change
anything it is quite hard to find out all places where you have to add changes.
When you separate your dialogs from your logic and the logic from the persistence
mechanism you can more easily apply changes to one part without influencing the other
parts.
Reduce time for standard DB actions
Most queries in database development are simple “insert, update, delete” statements.
There is no need to develop all these tedious statements. Hibernate helps you save time.
Loading classes from the database looks like
Query query = session.createQuery("select b from Bug as b");
for (Iterator iter = query.iterate(); iter.hasNext();) {
bugs.add((Bug) iter.next());
}
return bugs;
saving a class “bug” to the database looks like
session.update(bug);
Advanced features difficult to develop yourself
Caching solutions, transactions and other features Hibernate provides are not so easy to
implement. It is actually non sense to develop something which allready exist.
Using Hibernate everything is there. You just have to use it.
How Hibernate works
What is nice and in my opinion an advantage over entity beans, hibernate starts from simple java
classes (Pojo = Plain Old Java Objects).
To use hibernate you will create a simple java class:
public class Bug
implements Serializable
{
private int hashValue = 0;
private java.lang.Integer id;
private java.lang.String title;
public Bug()
{
}
public Bug(java.lang.Integer fid)
{
this.setId(fid);
}
public java.lang.Integer getId() {
return id;
}
public void setId(java.lang.Integer id) {
this.id = id;
}
public java.lang.String getTitle() {
return title;
}
public void setTitle(java.lang.String title) {
this.title = title;
}
.............
Than you create a mapping file. The mapping file explains Hibernate which field in the class is
mapped to which field in the database.




public.bug_fid_seq





And you start using your hibernate class.
Example to create a new entry in the database:
try {
Bug bug = new Bug();
bug.setTitle("Title");
bug.setTuserFk(tuser);
Transaction tx = session.beginTransaction();
session.save(bug);
tx.commit();
} catch (HibernateException e) {
e.printStackTrace();
}
The creation of the description file can be done with tools like MyEclipse. MyEclipse provides
functionality to create classes and description files directly from database tables.
Hibernate includes tools to
• generate Java classes from description files
• description files from existing database tables
• database tables from description files.