Free Hibernate Tutorial | VirtualNuggets

Global IT Corporate Online Training Services
Hibernate
URL: www.VirtualNuggets.com
Email ID: Info@VirtualNuggets.Com
Phone: India: +91-888 556 0202
USA: +1-707 666 8949

Hibernate Tutorial
Hibernate is a high-performance Object/Relational persistence and query service which is
licensed under the open source GNU Lesser General Public License (LGPL) and is free to
download. Hibernate not only takes care of the mapping from Java classes to database tables
(and from Java data types to SQL data types), but also provides data query and retrieval
facilities.
This tutorial will teach you how to use Hibernate to develop your database based web
applications in simple and easy steps.
Audience
This tutorial is designed for Java programmers with a need to understand the Hibernate
framework and API. After completing this tutorial you will find yourself at a moderate level of
expertise in using Hibernate from where you can take yourself to next levels.
Prerequisites
We assume you have good understanding of the Java programming language. A basic
understanding of relational databases, JDBC and SQL is very helpful.

ORM Overview
What is JDBC?
JDBC stands for Java Database Connectivity and provides a set of Java API for accessing the
relational databases from Java program. These Java APIs enables Java programs to execute SQL
statements and interact with any SQL compliant database.
JDBC provides a flexible architecture to write a database independent application that can run on
different platforms and interact with different DBMS without any modification.
Pros and Cons of JDBC
Pros of JDBC Cons of JDBC
 Clean and simple SQL processing
 Good performance with large data
 Very good for small applications
 Simple syntax so easy to learn
 Complex if it is used in large projects
 Large programming overhead
 No encapsulation
 Hard to implement MVC concept
 Query is DBMS specific
Why Object Relational Mapping (ORM)?
When we work with an object-oriented systems, there's a mismatch between the object model
and the relational database. RDBMSs represent data in a tabular format whereas object-oriented
languages, such as Java or C# represent it as an interconnected graph of objects. Consider the
following Java Class with proper constructors and associated public function:
public class Employee {
private int id;
private String first_name;
private String last_name;
private int salary;
public Employee() {}
public Employee(String fname, String lname, int salary) {
this.first_name = fname;
this.last_name = lname;
this.salary = salary;
}

public int getId() {
return id;
}
public String getFirstName() {
return first_name;
}
public String getLastName() {
return last_name;
}
public int getSalary() {
return salary;
}
}
Consider above objects need to be stored and retrieved into the following RDBMS table:
create table EMPLOYEE (
id INT NOT NULL auto_increment,
first_name VARCHAR(20) default NULL,
last_name VARCHAR(20) default NULL,
salary INT default NULL,
PRIMARY KEY (id)
);
First problem, what if we need to modify the design of our database after having developed few
pages or our application? Second, Loading and storing objects in a relational database exposes us
to the following five mismatch problems.
Mismatch Description
Granularity
Sometimes you will have an object model which has more classes than
the number of corresponding tables in the database.
Inheritance
RDBMSs do not define anything similar to Inheritance which is a
natural paradigm in object-oriented programming languages.
Identity
A RDBMS defines exactly one notion of 'sameness': the primary key.
Java, however, defines both object identity (a==b) and object equality
(a.equals(b)).
Associations Object-oriented languages represent associations using object
references where as am RDBMS represents an association as a foreign

key column.
Navigation
The ways you access objects in Java and in a RDBMS are
fundamentally different.
The Object-Relational Mapping (ORM) is the solution to handle all the above impedance
mismatches.
What is ORM?
ORM stands for Object-Relational Mapping (ORM) is a programming technique for converting
data between relational databases and object oriented programming languages such as Java, C#
etc. An ORM system has following advantages over plain JDBC
S.N. Advantages
1 Lets business code access objects rather than DB tables.
2 Hides details of SQL queries from OO logic.
3 Based on JDBC 'under the hood'
4 No need to deal with the database implementation.
5 Entities based on business concepts rather than database structure.
6 Transaction management and automatic key generation.
7 Fast development of application.
An ORM solution consists of the following four entities:
S.N. Solutions
1 An API to perform basic CRUD operations on objects of persistent classes.
2
A language or API to specify queries that refer to classes and properties of
classes.

3 A configurable facility for specifying mapping metadata.
4
A technique to interact with transactional objects to perform dirty checking,
lazy association fetching, and other optimization functions.
Java ORM Frameworks:
There are several persistent frameworks and ORM options in Java. A persistent framework is an
ORM service that stores and retrieves objects into a relational database.
 Enterprise JavaBeans Entity Beans
 Java Data Objects
 Castor
 TopLink
 Spring DAO
 Hibernate
 And many more

Hibernate Overview
Hibernate is an Object-Relational Mapping(ORM) solution for JAVA and it raised as an open
source persistent framework created by Gavin King in 2001. It is a powerful, high performance
Object-Relational Persistence and Query service for any Java Application.
Hibernate maps Java classes to database tables and from Java data types to SQL data types and
relieve the developer from 95% of common data persistence related programming tasks.
Hibernate sits between traditional Java objects and database server to handle all the work in
persisting those objects based on the appropriate O/R mechanisms and patterns.
Hibernate Advantages:
 Hibernate takes care of mapping Java classes to database tables using XML files and without
writing any line of code.
 Provides simple APIs for storing and retrieving Java objects directly to and from the database.
 If there is change in Database or in any table then the only need to change XML file properties.
 Abstract away the unfamiliar SQL types and provide us to work around familiar Java Objects.
 Hibernate does not require an application server to operate.
 Manipulates Complex associations of objects of your database.
 Minimize database access with smart fetching strategies.
 Provides Simple querying of data.
Supported Databases:
Hibernate supports almost all the major RDBMS. Following is list of few of the database engines
supported by Hibernate.
 HSQL Database Engine
 DB2/NT
 MySQL

 PostgreSQL
 FrontBase
 Oracle
 Microsoft SQL Server Database
 Sybase SQL Server
 Informix Dynamic Server
Supported Technologies:
 Hibernate supports a variety of other technologies, including the following:
 XDoclet Spring
 J2EE
 Eclipse plug-ins
 Maven

Hibernate Architecture
The Hibernate architecture is layered to keep you isolated from having to know the underlying
APIs. Hibernate makes use of the database and configuration data to provide persistence services
(and persistent objects) to the application.
Following is a very high level view of the Hibernate Application Architecture.
Following is a detailed view of the Hibernate Application Architecture with few important core .

Hibernate uses various existing Java APIs, like JDBC, Java Transaction API(JTA), and Java
Naming and Directory Interface (JNDI). JDBC provides a rudimentary level of abstraction of
functionality common to relational databases, allowing almost any database with a JDBC driver
to be supported by Hibernate. JNDI and JTA allow Hibernate to be integrated with J2EE
application servers.
Following section gives brief description of each of the class objects involved in Hibernate
Application Architecture.
Configuration Object:
The Configuration object is the first Hibernate object you create in any Hibernate application and
usually created only once during application initialization. It represents a configuration or
properties file required by the Hibernate. The Configuration object provides two keys
components:
 Database Connection: This is handled through one or more configuration files supported by
Hibernate. These files are hibernate.properties and hibernate.cfg.xml.
 Class Mapping Setup
This component creates the connection between the Java classes and database tables..
SessionFactory Object:
Configuration object is used to create a SessionFactory object which inturn configures Hibernate
for the application using the supplied configuration file and allows for a Session object to be
instantiated. The SessionFactory is a thread safe object and used by all the threads of an
application.
The SessionFactory is heavyweight object so usually it is created during application start up and
kept for later use. You would need one SessionFactory object per database using a separate
configuration file. So if you are using multiple databases then you would have to create multiple
SessionFactory objects.
Session Object:
A Session is used to get a physical connection with a database. The Session object is lightweight
and designed to be instantiated each time an interaction is needed with the database. Persistent
objects are saved and retrieved through a Session object.
The session objects should not be kept open for a long time because they are not usually thread
safe and they should be created and destroyed them as needed.
Transaction Object:
A Transaction represents a unit of work with the database and most of the RDBMS supports
transaction functionality. Transactions in Hibernate are handled by an underlying transaction
manager and transaction (from JDBC or JTA).

This is an optional object and Hibernate applications may choose not to use this interface, instead
managing transactions in their own application code.
Query Object:
Query objects use SQL or Hibernate Query Language (HQL) string to retrieve data from the
database and create objects. A Query instance is used to bind query parameters, limit the number
of results returned by the query, and finally to execute the query.
Criteria Object:
Criteria object are used to create and execute object oriented criteria queries to retrieve objects.

Hibernate Environment Setup
This chapter will explain how to install Hibernate and other associated packages to prepare a
develop environment for the Hibernate applications. We will work with MySQL database to
experiment with Hibernate examples, so make sure you already have setup for MySQL database.
For a more detail on MySQL you can check our MySQL Tutorial.
Downloading Hibernate:
It is assumed that you already have latest version of Java is installed on your machine. Following
are the simple steps to download and install Hibernate on your machine.
 Make a choice whether you want to install Hibernate on Windows, or Unix and then proceed to
the next step to download .zip file for windows and .tz file for Unix.
 Download the latest version of Hibernate from http://www.hibernate.org/downloads.
 At the time of writing this tutorial I downloaded hibernate-distribution-3.6.4.Final and when
you unzip the downloaded file it will give you directory structure as follows.
Installing Hibernate:
Once you downloaded and unzipped the latest version of the Hibernate Installation file, you need
to perform following two simple steps. Make sure you are setting your CLASSPATH variable
properly otherwise you will face problem while compiling your application.
 Now copy all the library files from /lib into your CLASSPATH, and change your classpath
variable to include all the JARs:
 Finally copy hibernate3.jar file into your CLASSPATH. This file lies in the root directory of
the installation and is the primary JAR that Hibernate needs to do its work.
Hibernate Prerequisites:
Following is the list of the packages/libraries required by Hibernate and you should install them
before starting with Hibernate. To install these packages you would have to copy library files
from /lib into your CLASSPATH, and change your CLASSPATH variable accordingly.

S.N. Packages/Libraries
1 dom4j - XML parsing www.dom4j.org/
2 Xalan - XSLT Processor http://xml.apache.org/xalan-j/
3 Xerces - The Xerces Java Parser http://xml.apache.org/xerces-j/
4
cglib - Appropriate changes to Java classes at
runtime http://cglib.sourceforge.net/
5 log4j - Logging Faremwork http://logging.apache.org/log4j
6 Commons - Logging, Email etc. http://jakarta.apache.org/commons
7 SLF4J - Logging Facade for Java http://www.slf4j.org

Hibernate Configuration
Hibernate requires to know in advance where to find the mapping information that defines how
your Java classes relate to the database tables. Hibernate also requires a set of configuration
settings related to database and other related parameters. All such information is usually supplied
as a standard Java properties file called hibernate.properties, or as an XML file
named hibernate.cfg.xml.
I will consider XML formatted file hibernate.cfg.xml to specify required Hibernate properties in
my examples. Most of the properties take their default values and it is not required to specify
them in the property file unless it is really required. This file is kept in the root directory of your
application's classpath.
Hibernate Properties:
Following is the list of important properties you would require to configure for a databases in a
standalone situation:
S.N. Properties and Description
1
hibernate.dialect
This property makes Hibernate generate the appropriate SQL for the chosen
database.
2
hibernate.connection.driver_class
The JDBC driver class.
3
hibernate.connection.url
The JDBC URL to the database instance.
4
hibernate.connection.username
The database username.
5
hibernate.connection.password
The database password.
6
hibernate.connection.pool_size
Limits the number of connections waiting in the Hibernate database connection
pool.
7 hibernate.connection.autocommit

Allows autocommit mode to be used for the JDBC connection.
If you are using a database along with an application server and JNDI then you would have to
configure the following properties:
S.N. Properties and Description
1
hibernate.connection.datasource
The JNDI name defined in the application server context you are using for the
application.
2
hibernate.jndi.class
The InitialContext class for JNDI.
3
hibernate.jndi.<JNDIpropertyname>
Passes any JNDI property you like to the JNDI InitialContext.
4
hibernate.jndi.url
Provides the URL for JNDI.
5
hibernate.connection.username
The database username.
6
hibernate.connection.password
The database password.
Hibernate with MySQL Database:
MySQL is one of the most popular open-source database systems available today. Let us
createhibernate.cfg.xml configuration file and place it in the root of your application's classpath.
You would have to make sure that you have testdb database available in your MySQL database
and you have a user test available to access the database.
The XML configuration file must conform to the Hibernate 3 Configuration DTD, which is
available from http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd.
<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-configuration SYSTEM
"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">

<hibernate-configuration>
<session-factory>
<property name="hibernate.dialect">
org.hibernate.dialect.MySQLDialect
</property>
<property name="hibernate.connection.driver_class">
com.mysql.jdbc.Driver
</property>

<property name="hibernate.connection.url">
jdbc:mysql://localhost/test
</property>
<property name="hibernate.connection.username">
root
</property>
<property name="hibernate.connection.password">
root123
</property>

<mapping resource="Employee.hbm.xml"/>
</session-factory>
</hibernate-configuration>
The above configuration file includes <mapping> tags which are related to hibernate-mapping
file and we will see in next chapter what exactly is a hibernate mapping file and how and why do
we use it. Following is the list of various important databases dialect property type:
Database Dialect Property
DB2 org.hibernate.dialect.DB2Dialect
HSQLDB org.hibernate.dialect.HSQLDialect
HypersonicSQL org.hibernate.dialect.HSQLDialect
Informix org.hibernate.dialect.InformixDialect
Ingres org.hibernate.dialect.IngresDialect

Interbase org.hibernate.dialect.InterbaseDialect
Microsoft SQL Server 2000 org.hibernate.dialect.SQLServerDialect
Microsoft SQL Server 2005 org.hibernate.dialect.SQLServer2005Dialect
Microsoft SQL Server 2008 org.hibernate.dialect.SQLServer2008Dialect
MySQL org.hibernate.dialect.MySQLDialect
Oracle (any version) org.hibernate.dialect.OracleDialect
Oracle 11g org.hibernate.dialect.Oracle10gDialect
Oracle 10g org.hibernate.dialect.Oracle10gDialect
Oracle 9i org.hibernate.dialect.Oracle9iDialect
PostgreSQL org.hibernate.dialect.PostgreSQLDialect
Progress org.hibernate.dialect.ProgressDialect
SAP DB org.hibernate.dialect.SAPDBDialect
Sybase org.hibernate.dialect.SybaseDialect
Sybase Anywhere org.hibernate.dialect.SybaseAnywhereDialect

Free Hibernate Tutorial | VirtualNuggets

Hibernate Sessions
A Session is used to get a physical connection with a database. The Session object is
lightweight and designed to be instantiated each time an interaction is needed with the database.
Persistent objects are saved and retrieved through a Session object.The session objects should not
be kept open for a long time because they are not usually thread safe and they should be created
and destroyed them as needed. The main function of the Session is to offer create, read and
delete operations for instances of mapped entity classes. Instances may exist in one of the
following three states at a given point in time:
 transient: A new instance of a a persistent class which is not associated with a Session and has
no representation in the database and no identifier value is considered transient by Hibernate.
 persistent: You can make a transient instance persistent by associating it with a Session. A
persistent instance has a representation in the database, an identifier value and is associated with
a Session.
 detached: Once we close the Hibernate Session, the persistent instance will become a detached
instance.
A Session instance is serializable if its persistent classes are serializable. A typical transaction
should use the following idiom:
Session session = factory.openSession();
Transaction tx = null;
try {
tx = session.beginTransaction();
// do some work
...
tx.commit();
}
catch (Exception e) {
if (tx!=null) tx.rollback();
e.printStackTrace();
}finally {
session.close();
}
If the Session throws an exception, the transaction must be rolled back and the session must be
discarded.
Session Interface Methods:
There are number of methods provided by the Session interface but I'm going to list down few
important methods only, which we will use in this tutorial. You can check Hibernate
documentation for a complete list of methods associated with Session and SessionFactory.

S.N. Session Methods and Description
1
Transaction beginTransaction()
Begin a unit of work and return the associated Transaction object.
2
void cancelQuery()
Cancel the execution of the current query.
3
void clear()
Completely clear the session.
4
Connection close()
End the session by releasing the JDBC connection and cleaning up.
5
Criteria createCriteria(Class persistentClass)
Create a new Criteria instance, for the given entity class, or a superclass of an
entity class.
6
Criteria createCriteria(String entityName)
Create a new Criteria instance, for the given entity name.
7
Serializable getIdentifier(Object object)
Return the identifier value of the given entity as associated with this session.
8
Query createFilter(Object collection, String queryString)
Create a new instance of Query for the given collection and filter string.
9
Query createQuery(String queryString)
Create a new instance of Query for the given HQL query string.
10
SQLQuery createSQLQuery(String queryString)
Create a new instance of SQLQuery for the given SQL query string.
11
void delete(Object object)
Remove a persistent instance from the datastore.
12 void delete(String entityName, Object object)

Remove a persistent instance from the datastore.
13
Session get(String entityName, Serializable id)
Return the persistent instance of the given named entity with the given
identifier, or null if there is no such persistent instance.
14
SessionFactory getSessionFactory()
Get the session factory which created this session.
15
void refresh(Object object)
Re-read the state of the given instance from the underlying database.
16
Transaction getTransaction()
Get the Transaction instance associated with this session.
17
boolean isConnected()
Check if the session is currently connected.
18
boolean isDirty()
Does this session contain any changes which must be synchronized with the
database?
19
boolean isOpen()
Check if the session is still open.
20
Serializable save(Object object)
Persist the given transient instance, first assigning a generated identifier.
21
void saveOrUpdate(Object object)
Either save(Object) or update(Object) the given instance.
22
void update(Object object)
Update the persistent instance with the identifier of the given detached
instance.
23 void update(String entityName, Object object)
Update the persistent instance with the identifier of the given detached

Hibernate Persistent Class
The entire concept of Hibernate is to take the values from Java class attributes and persist them
to a database table. A mapping document helps Hibernate in determining how to pull the values
from the classes and map them with table and associated fields.
Java classes whose objects or instances will be stored in database tables are called persistent
classes in Hibernate. Hibernate works best if these classes follow some simple rules, also known
as the Plain Old Java Object (POJO) programming model. There are following main rules of
persistent classes, however, none of these rules are hard requirements.
 All Java classes that will be persisted need a default constructor.
 All classes should contain an ID in order to allow easy identification of your objects within
Hibernate and the database. This property maps to the primary key column of a database table.
 All attributes that will be persisted should be declared private and
have getXXX and setXXXmethods defined in the JavaBean style.
 A central feature of Hibernate, proxies, depends upon the persistent class being either non-final,
or the implementation of an interface that declares all public methods.
 All classes that do not extend or implement some specialized classes and interfaces required by
the EJB framework.
The POJO name is used to emphasize that a given object is an ordinary Java Object, not a special
object, and in particular not an Enterprise JavaBean.
A simple POJO example:
Based on the few rules mentioned above we can define a POJO class as follows:
private int id;
private String firstName;
private String lastName;
private int salary;
this.firstName = fname;
this.lastName = lname;
}
return id;

}
public void setId( int id ) {
this.id = id;
}
return firstName;
}
public void setFirstName( String first_name ) {
this.firstName = first_name;
}
return lastName;
}
public void setLastName( String last_name ) {
this.lastName = last_name;
}
return salary;
}
public void setSalary( int salary ) {
}
}
Hibernate Mapping Files

An Object/relational mappings are usually defined in an XML document. This mapping file
instructs Hibernate how to map the defined class or classes to the database tables.
Though many Hibernate users choose to write the XML by hand, a number of tools exist to
generate the mapping document. These include XDoclet, Middlegen and AndroMDA for
advanced Hibernate users.
Let us consider our previously defined POJO class whose objects will persist in the table defined
in next section.
private int id;
private int salary;
}
return id;
}
this.id = id;
}
return firstName;
}
}
return lastName;
}
}
return salary;
}
}

}
There would be one table corresponding to each object you are willing to provide persistence.
Consider above objects need to be stored and retrieved into the following RDBMS table:
PRIMARY KEY (id)
);
Based on the two above entities we can define following mapping file which instructs Hibernate
how to map the defined class or classes to the database tables.
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="Employee" table="EMPLOYEE">
<meta attribute="class-description">
This class contains the employee detail.
</meta>
<id name="id" type="int" column="id">
<generator class="native"/>
</id>
<property name="firstName" column="first_name" type="string"/>
<property name="lastName" column="last_name" type="string"/>
<property name="salary" column="salary" type="int"/>
</class>
</hibernate-mapping>
You should save the mapping document in a file with the format <classname>.hbm.xml. We
saved our mapping document in the file Employee.hbm.xml. Let us see little detail about the
mapping elements used in the mapping file:
 The mapping document is an XML document having <hibernate-mapping> as the root element
which contains all the <class> elements.
 The <class> elements are used to define specific mappings from a Java classes to the database
tables. The Java class name is specified using the name attribute of the class element and the
database table name is specified using the table attribute.
 The <meta> element is optional element and can be used to create the class description.

 The <id> element maps the unique ID attribute in class to the primary key of the database table.
The name attribute of the id element refers to the property in the class and the column attribute
refers to the column in the database table. The type attribute holds the hibernate mapping type,
this mapping types will convert from Java to SQL data type.
 The <generator> element within the id element is used to automatically generate the primary
key values. Set the class attribute of the generator element is set to native to let hibernate pick up
either identity, sequence or hilo algorithm to create primary key depending upon the capabilities
of the underlying database.
 The <property> element is used to map a Java class property to a column in the database table.
The name attribute of the element refers to the property in the class and the column attribute
There are other attributes and elements available which will be used in a mapping document and
I would try to cover as many as possible while discussing other Hibernate related topics.
Hibernate Mapping Types
When you prepare a Hibernate mapping document, we have seen that you map Java data types
into RDBMS data types. The types declared and used in the mapping files are not Java data
types; they are not SQL database types either. These types are called Hibernate mapping types,
which can translate from Java to SQL data types and vice versa.
This chapter lists down all the basic, date and time, large object, and various other builtin
mapping types.
Primitive types:

Mapping type Java type ANSI SQL Type
integer int or java.lang.Integer INTEGER
long long or java.lang.Long BIGINT
short short or java.lang.Short SMALLINT
float float or java.lang.Float FLOAT
double double or java.lang.Double DOUBLE
big_decimal java.math.BigDecimal NUMERIC
character java.lang.String CHAR(1)
string java.lang.String VARCHAR
byte byte or java.lang.Byte TINYINT
boolean boolean or java.lang.Boolean BIT
yes/no boolean or java.lang.Boolean CHAR(1) ('Y' or 'N')
true/false boolean or java.lang.Boolean CHAR(1) ('T' or 'F')
Date and time types:
date java.util.Date or java.sql.Date DATE
time java.util.Date or java.sql.Time TIME
timestamp java.util.Date or java.sql.Timestamp TIMESTAMP

calendar java.util.Calendar TIMESTAMP
calendar_date java.util.Calendar DATE
Binary and large object types:
binary byte[] VARBINARY (or BLOB)
text java.lang.String CLOB
serializable
any Java class that implements
java.io.Serializable
VARBINARY (or BLOB)
clob java.sql.Clob CLOB
blob java.sql.Blob BLOB
JDK-related types:
class java.lang.Class VARCHAR
locale java.util.Locale VARCHAR
timezone java.util.TimeZone VARCHAR
currency java.util.Currency VARCHAR

Hibernate Examples
Let us try an example of using Hibernate to provide Java persistence in a standalone application.
We will go through different steps involved in creating Java Application using Hibernate
technology.
Create POJO Classes:
The first step in creating an application is to build the Java POJO class or classes, depending on
the application that will be persisted to the database. Let us consider our Employee class
with getXXX andsetXXX methods to make it JavaBeans compliant class.
A POJO (Plain Old Java Object) is a Java object that doesn't extend or implement some
specialized classes and interfaces respectively required by the EJB framework. All normal Java
objects are POJO.

When you design a classs to be persisted by Hibernate, it's important to provide JavaBeans
compliant code as well as one attribute which would work as index like id attribute in the
Employee class.
private int id;
private int salary;
}
return id;
}
this.id = id;
}
return firstName;
}
}
return lastName;
}
}
return salary;
}
}
}

Create Database Tables:
Second step would be creating tables in your database. There would be one table corresponding
to each object you are willing to provide persistence. Consider above objects need to be stored
and retrieved into the following RDBMS table:
PRIMARY KEY (id)
);
Create Mapping Configuration File:
This step is to create a mapping file that instructs Hibernate how to map the defined class or
classes to the database tables.
<hibernate-mapping>
</meta>
</id>
</class>
You should save the mapping document in a file with the format <classname>.hbm.xml. We
saved our mapping document in the file Employee.hbm.xml. Let us see little detail about the
mapping document:
 The mapping document is an XML document having <hibernate-mapping> as the root element
which contains all the <class> elements.

 The <class> elements are used to define specific mappings from a Java classes to the database
tables. The Java class name is specified using the name attribute of the class element and the
database table name is specified using the table attribute.
 The <meta> element is optional element and can be used to create the class description.
 The <id> element maps the unique ID attribute in class to the primary key of the database table.
The name attribute of the id element refers to the property in the class and the column attribute
 The <generator> element within the id element is used to automatically generate the primary
key values. Set the class attribute of the generator element is set to native to let hibernate pick up
either identity, sequence or hilo algorithm to create primary key depending upon the capabilities
of the underlying database.
 The <property> element is used to map a Java class property to a column in the database table.
The name attribute of the element refers to the property in the class and the column attribute
There are other attributes and elements available which will be used in a mapping document and
I would try to cover as many as possible while discussing other Hibernate related topics.
Create Application Class:
Finally, we will create our application class with the main() method to run the application. We
will use this application to save few Employee's records and then we will apply CRUD
operations on those records.
import java.util.List;
import java.util.Date;
import java.util.Iterator;
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
public class ManageEmployee {
private static SessionFactory factory;
public static void main(String[] args) {
try{
factory = new Configuration().configure().buildSessionFactory();
}catch (Throwable ex) {
System.err.println("Failed to create sessionFactory object." + ex);
throw new ExceptionInInitializerError(ex);
}
ManageEmployee ME = new ManageEmployee();

/* Add few employee records in database */
Integer empID1 = ME.addEmployee("Zara", "Ali", 1000);
Integer empID2 = ME.addEmployee("Daisy", "Das", 5000);
Integer empID3 = ME.addEmployee("John", "Paul", 10000);
/* List down all the employees */
ME.listEmployees();
/* Update employee's records */
ME.updateEmployee(empID1, 5000);
/* Delete an employee from the database */
ME.deleteEmployee(empID2);
/* List down new list of the employees */
ME.listEmployees();
}
/* Method to CREATE an employee in the database */
public Integer addEmployee(String fname, String lname, int salary){
Integer employeeID = null;
try{
Employee employee = new Employee(fname, lname, salary);
employeeID = (Integer) session.save(employee);
tx.commit();
}catch (HibernateException e) {
}finally {
session.close();
}
return employeeID;
}
/* Method to READ all the employees */
public void listEmployees( ){
try{
List employees = session.createQuery("FROM Employee").list();
for (Iterator iterator =
employees.iterator(); iterator.hasNext();){
Employee employee = (Employee) iterator.next();
System.out.print("First Name: " + employee.getFirstName());

System.out.print(" Last Name: " + employee.getLastName());
System.out.println(" Salary: " + employee.getSalary());
}
tx.commit();
}finally {
session.close();
}
}
/* Method to UPDATE salary for an employee */
public void updateEmployee(Integer EmployeeID, int salary ){
try{
Employee employee =
(Employee)session.get(Employee.class, EmployeeID);
employee.setSalary( salary );
session.update(employee);
tx.commit();
}finally {
session.close();
}
}
/* Method to DELETE an employee from the records */
public void deleteEmployee(Integer EmployeeID){
try{
Employee employee =
session.delete(employee);
tx.commit();
}finally {
session.close();
}
}

}
Compilation and Execution:
Here are the steps to compile and run the above mentioned application. Make sure you have set
PATH and CLASSPATH appropriately before proceeding for the compilation and execution.
 Create hibernate.cfg.xml configuration file as explained in configuration chapter.
 Create Employee.hbm.xml mapping file as shown above.
 Create Employee.java source file as shown above and compile it.
 Create ManageEmployee.java source file as shown above and compile it.
 Execute ManageEmployee binary to run the program.
You would get following result, and records would be created in EMPLOYEE table.
$java ManageEmployee
.......VARIOUS LOG MESSAGES WILL DISPLAY HERE........
First Name: Zara Last Name: Ali Salary: 1000
First Name: Daisy Last Name: Das Salary: 5000
First Name: John Last Name: Paul Salary: 10000
If you check your EMPLOYEE table, it should have following records:
mysql> select * from EMPLOYEE;
+----+------------+-----------+--------+
| id | first_name | last_name | salary |
+----+------------+-----------+--------+
| 29 | Zara | Ali | 5000 |
| 31 | John | Paul | 10000 |
+----+------------+-----------+--------+
2 rows in set (0.00 sec
mysql>

Hibernate O/R Mappings
So far we have seen very basic O/R mapping using hibernate but there are three most important
mapping topics which we have to learn in detail. These are the mapping of collections, the
mapping of associations between entity classes and Component Mappings.
Collections Mappings:
If an entity or class has collection of values for a particular variable, then we can map those
values using any one of the collection interfaces available in java. Hibernate can persist instances
ofjava.util.Map, java.util.Set, java.util.SortedMap, java.util.SortedSet, java.util.List, and
any array of persistent entities or values.
Collection type Mapping and Description
java.util.Set
This is mapped with a <set> element and initialized with
java.util.HashSet
java.util.SortedSet
This is mapped with a <set> element and initialized with
java.util.TreeSet. The sort attribute can be set to either a
comparator or natural ordering.
java.util.List
This is mapped with a <list> element and initialized with
java.util.ArrayList
java.util.Collection
This is mapped with a <bag> or <ibag> element and initialized
with java.util.ArrayList
java.util.Map
This is mapped with a <map> element and initialized with
java.util.HashMap
java.util.SortedMap
This is mapped with a <map> element and initialized with
java.util.TreeMap. The sort attribute can be set to either a
comparator or natural ordering.
Arrays are supported by Hibernate with <primitive-array> for Java primitive value types and
<array> for everything else. However, they are rarely used so I'm not going to discuss them in
this tutorial.

If you want to map a user defined collection interfaces which is not directly supported by
Hibernate, you need to tell Hibernate about the semantics of your custom collections which is not
very easy and not recommend to be used.
Association Mappings:
The mapping of associations between entity classes and the relationships between tables is the
soul of ORM. Following are the four ways in which the cardinality of the relationship between
the objects can be expressed. An association mapping can be unidirectional as well as
bidirectional.
Mapping type Description
Many-to-One Mapping many-to-one relationship using Hibernate
One-to-One Mapping one-to-one relationship using Hibernate
One-to-Many Mapping one-to-many relationship using Hibernate
Many-to-Many Mapping many-to-many relationship using Hibernate
Component Mappings:
It is very much possible that an Entity class can have a reference to another class as a member
variable. If the referred class does not have it's own life cycle and completely depends on the life
cycle of the owning entity class, then the referred class hence therefore is called as the
Component class.
The mapping of Collection of Components is also possible in a similar way just as the mapping
of regular Collections with minor configuration differences. We will see these two mappings in
detail with examples.
Mapping type Description
Component Mappings
Mapping for a class having a reference to another class as a
member variable.

Hibernate Annotations
So far you have seen how Hibernate uses XML mapping file for the transformation of data from
POJO to database tables and vice versa. Hibernate annotations is the newest way to define
mappings without a use of XML file. You can use annotations in addition to or as a replacement
of XML mapping metadata.
Hibernate Annotations is the powerful way to provide the metadata for the Object and Relational
Table mapping. All the metadata is clubbed into the POJO java file along with the code this
helps the user to understand the table structure and POJO simultaneously during the
development.
If you going to make your application portable to other EJB 3 compliant ORM applications, you
must use annotations to represent the mapping information but still if you want greater flexibility
then you should go with XML-based mappings.
Environment Setup for Hibernate Annotation
First of all you would have to make sure that you are using JDK 5.0 otherwise you need to
upgrade your JDK to JDK 5.0 to take advantage of the native support for annotations.
Second, you will need to install the Hibernate 3.x annotations distribution package, available
from the sourceforge: (Download Hibernate Annotation) and copy hibernate-annotations.jar,
lib/hibernate-comons-annotations.jar and lib/ejb3-persistence.jar from the Hibernate
Annotations distribution to your CLASSPATH
Annotated Class Example:
As I mentioned above while working with Hibernate Annotation all the metadata is clubbed into
the POJO java file along with the code this helps the user to understand the table structure and
POJO simultaneously during the development.
Consider we are going to use following EMPLOYEE table to store our objects:
PRIMARY KEY (id)
);
Following is the mapping of Employee class with annotations to map objects with the defined
EMPLOYEE table:
import javax.persistence.*;

@Entity
@Table(name = "EMPLOYEE")
@Id @GeneratedValue
@Column(name = "id")
private int id;
@Column(name = "first_name")
@Column(name = "last_name")
@Column(name = "salary")
private int salary;
return id;
}
this.id = id;
}
return firstName;
}
}
return lastName;
}
}
return salary;
}
}
}
Hibernate detects that the @Id annotation is on a field and assumes that it should access
properties on an object directly through fields at runtime. If you placed the @Id annotation on

the getId() method, you would enable access to properties through getter and setter methods by
default. Hence, all other annotations are also placed on either fields or getter methods, following
the selected strategy. Following section will explain the annotations used in the above class.
@Entity Annotation:
The EJB 3 standard annotations are contained in the javax.persistence package, so we import
this package as the first step. Second we used the @Entity annotation to the Employee class
which marks this class as an entity bean, so it must have a no-argument constructor that is visible
with at least protected scope.
@Table Annotation:
The @Table annotation allows you to specify the details of the table that will be used to persist
the entity in the database.
The @Table annotation provides four attributes, allowing you to override the name of the table,
its catalogue, and its schema, and enforce unique constraints on columns in the table. For now
we are using just table name which is EMPLOYEE.
@Id and @GeneratedValue Annotations:
Each entity bean will have a primary key, which you annotate on the class with
the @Id annotation. The primary key can be a single field or a combination of multiple fields
depending on your table structure.
By default, the @Id annotation will automatically determine the most appropriate primary key
generation strategy to be used but you can override this by applying
the @GeneratedValue annotation which takes two parameters strategy and generator which
I'm not going to discuss here, so let us use only default the default key generation strategy.
Letting Hibernate determine which generator type to use makes your code portable between
different databases.
@Column Annotation:
The @Column annotation is used to specify the details of the column to which a field or property
will be mapped. You can use column annotation with the following most commonly used
attributes:
 name attribute permits the name of the column to be explicitly specified.
 length attribute permits the size of the column used to map a value particularly for a String
value.
 nullable attribute permits the column to be marked NOT NULL when the schema is generated.
 unique attribute permits the column to be marked as containing only unique values.
Finally, we will create our application class with the main() method to run the application. We
will use this application to save few Employee's records and then we will apply CRUD
operations on those records.

import org.hibernate.cfg.AnnotationConfiguration;
try{
factory = new AnnotationConfiguration().
configure().
//addPackage("com.xyz") //add package if used.
addAnnotatedClass(Employee.class).
buildSessionFactory();
}
ME.listEmployees();
ME.listEmployees();
}

try{
Employee employee = new Employee();
employee.setFirstName(fname);
employee.setLastName(lname);
employee.setSalary(salary);
tx.commit();
}finally {
session.close();
}
return employeeID;
}
try{
}
tx.commit();
}finally {
session.close();
}
}
try{

Employee employee =
tx.commit();
}finally {
session.close();
}
}
try{
Employee employee =
tx.commit();
}finally {
session.close();
}
}
}
Database Configuration:
Now let us create hibernate.cfg.xml configuration file to define database related parameters.
This time we are not going
<session-factory>
</property>

</property>

</property>
root
</property>
cohondob
</property>
</session-factory>
 Delete Employee.hbm.xml mapping file from the path.
+----+------------+-----------+--------+

+----+------------+-----------+--------+
| 29 | Zara | Ali | 5000 |
| 31 | John | Paul | 10000 |
+----+------------+-----------+--------+
2 rows in set (0.00 sec
mysql>
Hibernate Query Language
Hibernate Query Language (HQL) is an object-oriented query language, similar to SQL, but
instead of operating on tables and columns, HQL works with persistent objects and their
properties. HQL queries are translated by Hibernate into conventional SQL queries which in
turns perform action on database.
Although you can use SQL statements directly with Hibernate using Native SQL but I would
recommend to use HQL whenever possible to avoid database portability hassles, and to take
advantage of Hibernate's SQL generation and caching strategies.
Keywords like SELECT , FROM and WHERE etc. are not case sensitive but properties like table
and column names are case sensitive in HQL.
FROM Clause
You will use FROM clause if you want to load a complete persistent objects into memory.
Following is the simple syntax of using FROM clause:
String hql = "FROM Employee";
Query query = session.createQuery(hql);
List results = query.list();
If you need to fully qualify a class name in HQL, just specify the package and class name as
follows:
String hql = "FROM com.hibernatebook.criteria.Employee";

AS Clause
The AS clause can be used to assign aliases to the classes in your HQL queries, specially when
you have long queries. For instance, our previous simple example would be the following:
String hql = "FROM Employee AS E";
The AS keyword is optional and you can also specify the alias directly after the class name, as
follows:
String hql = "FROM Employee E";
SELECT Clause
The SELECT clause provides more control over the result set than the from clause. If you want
to obtain few properties of objects instead of the complete object, use the SELECT clause.
Following is the simple syntax of using SELECT clause to get just first_name field of the
Employee object:
String hql = "SELECT E.firstName FROM Employee E";
It is notable here that Employee.firstName is a property of Employee object rather than a field
of the EMPLOYEE table.
WHERE Clause
If you want to narrow the specific objects that are returned from storage, you use the WHERE
clause. Following is the simple syntax of using WHERE clause:
String hql = "FROM Employee E WHERE E.id = 10";

ORDER BY Clause
To sort your HQL query's results, you will need to use the ORDER BY clause. You can order
the results by any property on the objects in the result set either ascending (ASC) or descending
(DESC). Following is the simple syntax of using ORDER BY clause:
String hql = "FROM Employee E WHERE E.id > 10 ORDER BY E.salary DESC";
If you wanted to sort by more than one property, you would just add the additional properties to
the end of the order by clause, separated by commas as follows:
String hql = "FROM Employee E WHERE E.id > 10 " +
"ORDER BY E.firstName DESC, E.salary DESC ";
GROUP BY Clause
This clause lets Hibernate pull information from the database and group it based on a value of an
attribute and, typically, use the result to include an aggregate value. Following is the simple
syntax of using GROUP BY clause:
String hql = "SELECT SUM(E.salary), E.firtName FROM Employee E " +
"GROUP BY E.firstName";
Using Named Paramters
Hibernate supports named parameters in its HQL queries. This makes writing HQL queries that
accept input from the user easy and you do not have to defend against SQL injection attacks.
Following is the simple syntax of using named parameters:
String hql = "FROM Employee E WHERE E.id = :employee_id";
query.setParameter("employee_id",10);

UPDATE Clause
Bulk updates are new to HQL with Hibernate 3, and deletes work differently in Hibernate 3 than
they did in Hibernate 2. The Query interface now contains a method called executeUpdate() for
executing HQL UPDATE or DELETE statements.
The UPDATE clause can be used to update one or more properties of an one or more objects.
Following is the simple syntax of using UPDATE clause:
String hql = "UPDATE Employee set salary = :salary " +
"WHERE id = :employee_id";
query.setParameter("salary", 1000);
query.setParameter("employee_id", 10);
int result = query.executeUpdate();
System.out.println("Rows affected: " + result);
DELETE Clause
The DELETE clause can be used to delete one or more objects. Following is the simple syntax
of using DELETE clause:
String hql = "DELETE FROM Employee " +
"WHERE id = :employee_id";
INSERT Clause
HQL supports INSERT INTO clause only where records can be inserted from one object to
another object. Following is the simple syntax of using INSERT INTO clause:
String hql = "INSERT INTO Employee(firstName, lastName, salary)" +
"SELECT firstName, lastName, salary FROM old_employee";

Aggregate Methods
HQL supports a range of aggregate methods, similar to SQL. They work the same way in HQL
as in SQL and following is the list of the available functions:
S.N. Functions Description
1 avg(property name) The average of a property's value
2
count(property name or
*)
The number of times a property occurs in the
results
3 max(property name) The maximum value of the property values
4 min(property name) The minimum value of the property values
5 sum(property name) The sum total of the property values
The distinct keyword only counts the unique values in the row set. The following query will
return only unique count:
String hql = "SELECT count(distinct E.firstName) FROM Employee E";
Pagination using Query
There are two methods of the Query interface for pagination.
S.N. Method & Description
1
Query setFirstResult(int startPosition)
This method takes an integer that represents the first row in your result set,
starting with row 0.
2
Query setMaxResults(int maxResult)
This method tells Hibernate to retrieve a fixed number maxResults of objects.

Using above two methods together, we can construct a paging component in our web or Swing
application. Following is the example which you can extend to fetch 10 rows at a time:
String hql = "FROM Employee";
query.setFirstResult(1);
query.setMaxResults(10);
List results = query.list(
Hibernate Criteria Queries
Hibernate provides alternate ways of manipulating objects and in turn data available in RDBMS
tables. One of the methods is Criteria API which allows you to build up a criteria query object
programmatically where you can apply filtration rules and logical conditions.
The Hibernate Session interface provides createCriteria() method which can be used to create
aCriteria object that returns instances of the persistence object's class when your application
executes a criteria query.

Following is the simplest example of a criteria query is one which will simply return every object
that corresponds to the Employee class.
Criteria cr = session.createCriteria(Employee.class);
List results = cr.list();
Restrictions with Criteria:
You can use add() method available for Criteria object to add restriction for a criteria query.
Following is the example to add a restriction to return the records with salary is equal to 2000:
cr.add(Restrictions.eq("salary", 2000));
Following are the few more examples covering different scenarios and can be used as per
requirement:
// To get records having salary more than 2000
cr.add(Restrictions.gt("salary", 2000));
// To get records having salary less than 2000
cr.add(Restrictions.lt("salary", 2000));
// To get records having fistName starting with zara
cr.add(Restrictions.like("firstName", "zara%"));
// Case sensitive form of the above restriction.
cr.add(Restrictions.ilike("firstName", "zara%"));
// To get records having salary in between 1000 and 2000
cr.add(Restrictions.between("salary", 1000, 2000));
// To check if the given property is null
cr.add(Restrictions.isNull("salary"));
// To check if the given property is not null
cr.add(Restrictions.isNotNull("salary"));
// To check if the given property is empty
cr.add(Restrictions.isEmpty("salary"));
// To check if the given property is not empty
cr.add(Restrictions.isNotEmpty("salary"));
You can create AND or OR conditions using LogicalExpression restrictions as follows:

Criterion salary = Restrictions.gt("salary", 2000);
Criterion name = Restrictions.ilike("firstNname","zara%");
// To get records matching with OR condistions
LogicalExpression orExp = Restrictions.or(salary, name);
cr.add( orExp );
// To get records matching with AND condistions
LogicalExpression andExp = Restrictions.and(salary, name);
cr.add( andExp );
Though all the above conditions can be used directly with HQL as explained in previous tutorial.
Pagination using Criteria:
There are two methods of the Criteria interface for pagination.
S.N. Method & Description
1
public Criteria setFirstResult(int firstResult)
This method takes an integer that represents the first row in your result set,
starting with row 0.
2
public Criteria setMaxResults(int maxResults)
This method tells Hibernate to retrieve a fixed number maxResults of objects.
Using above two methods together, we can construct a paging component in our web or Swing
application. Following is the example which you can extend to fetch 10 rows at a time:
cr.setFirstResult(1);
cr.setMaxResults(10);
Sorting the Results:

The Criteria API provides the org.hibernate.criterion.Order class to sort your result set in
either ascending or descending order, according to one of your object's properties. This example
demonstrates how you would use the Order class to sort the result set:
// To get records having salary more than 2000
// To sort records in descening order
crit.addOrder(Order.desc("salary"));
// To sort records in ascending order
crit.addOrder(Order.asc("salary"));
Projections & Aggregations:
The Criteria API provides the org.hibernate.criterion.Projections class which can be used to
get average, maximum or minimum of the property values. The Projections class is similar to the
Restrictions class in that it provides several static factory methods for
obtaining Projection instances.
Following are the few examples covering different scenarios and can be used as per requirement:
// To get total row count.
cr.setProjection(Projections.rowCount());
// To get average of a property.
cr.setProjection(Projections.avg("salary"));
// To get distinct count of a property.
cr.setProjection(Projections.countDistinct("firstName"));
// To get maximum of a property.
cr.setProjection(Projections.max("salary"));
// To get minimum of a property.
cr.setProjection(Projections.min("salary"));
// To get sum of a property.

cr.setProjection(Projections.sum("salary"));
Criteria Queries Example:
Consider the following POJO class:
private int id;
private int salary;
}
return id;
}
this.id = id;
}
return firstName;
}
}
return lastName;
}
}
return salary;
}
}
}
Let us create the following EMPLOYEE table to store Employee objects:

PRIMARY KEY (id)
);
Following will be mapping file.
<hibernate-mapping>
</meta>
</id>
</class>
Finally, we will create our application class with the main() method to run the application where
we will use Criteria queries:
import org.hibernate.Criteria;
import org.hibernate.criterion.Restrictions;
import org.hibernate.criterion.Projections;

try{
}
Integer empID4 = ME.addEmployee("Mohd", "Yasee", 3000);
ME.listEmployees();
/* Print Total employee's count */
ME.countEmployee();
/* Print Toatl salary */
ME.totalSalary();
}
try{
tx.commit();
}finally {
session.close();
}
return employeeID;
}
/* Method to READ all the employees having salary more than 2000 */

try{
// Add restriction.
List employees = cr.list();
}
tx.commit();
}finally {
session.close();
}
}
/* Method to print total number of records */
public void countEmployee(){
try{
// To get total row count.
cr.setProjection(Projections.rowCount());
List rowCount = cr.list();
System.out.println("Total Coint: " + rowCount.get(0) );
tx.commit();
}finally {
session.close();
}
}
/* Method to print sum of salaries */

public void totalSalary(){
try{
// To get total salary.
cr.setProjection(Projections.sum("salary"));
List totalSalary = cr.list();
System.out.println("Total Salary: " + totalSalary.get(0) );
tx.commit();
}finally {
session.close();
}
}
}
First Name: Mohd Last Name: Yasee Salary: 3000
Total Coint: 4
Total Salary: 15000

+----+------------+-----------+--------+
+----+------------+-----------+--------+
| 14 | Zara | Ali | 2000 |
| 15 | Daisy | Das | 5000 |
| 16 | John | Paul | 5000 |
| 17 | Mohd | Yasee | 3000 |
+----+------------+-----------+--------+
4 rows in set (0.00 sec)
mysql>

Hibernate Native SQL
You can use native SQL to express database queries if you want to utilize database-specific
features such as query hints or the CONNECT keyword in Oracle. Hibernate 3.x allows you to
specify handwritten SQL, including stored procedures, for all create, update, delete, and load
operations.
Your application will create a native SQL query from the session with
the createSQLQuery() method on the Session interface.:
public SQLQuery createSQLQuery(String sqlString) throws HibernateException
After you pass a string containing the SQL query to the createSQLQuery() method, you can
associate the SQL result with either an existing Hibernate entity, a join, or a scalar result using
addEntity(), addJoin(), and addScalar() methods respectively.
Scalar queries:
The most basic SQL query is to get a list of scalars (values) from one or more tables. Following
is the syntax for using native SQL for scalar values:
String sql = "SELECT first_name, salary FROM EMPLOYEE";
SQLQuery query = session.createSQLQuery(sql);
query.setResultTransformer(Criteria.ALIAS_TO_ENTITY_MAP);
Entity queries:
The above queries were all about returning scalar values, basically returning the "raw" values
from the resultset. The following is the syntax to get entity objects as a whole from a native sql
query via addEntity().
String sql = "SELECT * FROM EMPLOYEE";
query.addEntity(Employee.class);

Named SQL queries:
The following is the syntax to get entity objects from a native sql query via addEntity() and using
named SQL query.
String sql = "SELECT * FROM EMPLOYEE WHERE id = :employee_id";
Native SQL Example:
Consider the following POJO class:
private int id;
private int salary;
}
return id;
}
this.id = id;
}
return firstName;
}
}
return lastName;
}

}
return salary;
}
}
}
PRIMARY KEY (id)
);
Following will be mapping file.
<hibernate-mapping>
</meta>
</id>
</class>
we will use Native SQL queries:
import java.util.*;

import org.hibernate.SQLQuery;
import org.hibernate.Criteria;
import org.hibernate.Hibernate;
try{
}
Integer empID4 = ME.addEmployee("Mohd", "Yasee", 3000);
/* List down employees and their salary using Scalar Query */
ME.listEmployeesScalar();
/* List down complete employees information using Entity Query */
ME.listEmployeesEntity();
}
try{
tx.commit();
}finally {

session.close();
}
return employeeID;
}
/* Method to READ all the employees using Scalar Query */
public void listEmployeesScalar( ){
try{
String sql = "SELECT first_name, salary FROM EMPLOYEE";
query.setResultTransformer(Criteria.ALIAS_TO_ENTITY_MAP);
List data = query.list();
for(Object object : data)
{
Map row = (Map)object;
System.out.print("First Name: " + row.get("first_name"));
System.out.println(", Salary: " + row.get("salary"));
}
tx.commit();
}finally {
session.close();
}
}
/* Method to READ all the employees using Entity Query */
public void listEmployeesEntity( ){
try{
String sql = "SELECT * FROM EMPLOYEE";
List employees = query.list();

}
tx.commit();
}finally {
session.close();
}
}
}
First Name: Zara, Salary: 2000
First Name: Daisy, Salary: 5000
First Name: John, Salary: 5000
First Name: Mohd, Salary: 3000
First Name: Mohd Last Name: Yasee Salary: 3000
+----+------------+-----------+--------+

+----+------------+-----------+--------+
| 26 | Zara | Ali | 2000 |
| 27 | Daisy | Das | 5000 |
| 28 | John | Paul | 5000 |
| 29 | Mohd | Yasee | 3000 |
+----+------------+-----------+--------+
4 rows in set (0.00 sec)
mysql>
Hibernate Caching
Caching is all about application performance optimization and it sits between your application
and the database to avoid the number of database hits as many as possible to give a better
performance for performance critical applications.

Caching is important to Hibernate as well which utilizes a multilevel caching schemes as
explained below:
First-level cache:
The first-level cache is the Session cache and is a mandatory cache through which all requests
must pass. The Session object keeps an object under its own power before committing it to the
database.
If you issue multiple updates to an object, Hibernate tries to delay doing the update as long as
possible to reduce the number of update SQL statements issued. If you close the session, all the
objects being cached are lost and either persisted or updated in the database.
Second-level cache:
Second level cache is an optional cache and first-level cache will always be consulted before any
attempt is made to locate an object in the second-level cache. The second-level cache can be
configured on a per-class and per-collection basis and mainly responsible for caching objects
across sessions.
Any third-party cache can be used with Hibernate.
An org.hibernate.cache.CacheProvider interface is provided, which must be implemented to
provide Hibernate with a handle to the cache implementation.
Query-level cache:
Hibernate also implements a cache for query resultsets that integrates closely with the second-level
cache.

This is an optional feature and requires two additional physical cache regions that hold the
cached query results and the timestamps when a table was last updated. This is only useful for
queries that are run frequently with the same parameters.
The Second Level Cache:
Hibernate uses first-level cache by default and you have nothing to do to use first-level cache.
Let's go straight to the optional second-level cache. Not all classes benefit from caching, so it's
important to be able to disable the second-level cache
The Hibernate second-level cache is set up in two steps. First, you have to decide which
concurrency strategy to use. After that, you configure cache expiration and physical cache
attributes using the cache provider.
Concurrency strategies:
A concurrency strategy is a mediator which responsible for storing items of data in the cache and
retrieving them from the cache. If you are going to enable a second-level cache, you will have to
decide, for each persistent class and collection, which cache concurrency strategy to use.
 Transactional: Use this strategy for read-mostly data where it is critical to prevent stale data in
concurrent transactions,in the rare case of an update.
 Read-write: Again use this strategy for read-mostly data where it is critical to prevent stale data
in concurrent transactions,in the rare case of an update.
 Nonstrict-read-write: This strategy makes no guarantee of consistency between the cache and
the database. Use this strategy if data hardly ever changes and a small likelihood of stale data is
not of critical concern.
 Read-only: A concurrency strategy suitable for data which never changes. Use it for reference
data only.
If we are going to use second-level caching for our Employee class, let us add the mapping
element required to tell Hibernate to cache Employee instances using read-write strategy.
<hibernate-mapping>
</meta>
<cache usage="read-write"/>
</id>

</class>
The usage="read-write" attribute tells Hibernate to use a read-write concurrency strategy for the
defined cache.
Cache provider:
Your next step after considering the concurrency strategies you will use for your cache candidate
classes is to pick a cache provider. Hibernate forces you to choose a single cache provider for the
whole application.
S.N. Cache Name Description
1 EHCache
It can cache in memory or on disk and clustered caching and it
supports the optional Hibernate query result cache.
2 OSCache
Supports caching to memory and disk in a single JVM, with a
rich set of expiration policies and query cache support.
3 warmCache
A cluster cache based on JGroups. It uses clustered invalidation
but doesn't support the Hibernate query cache
4 JBoss Cache
A fully transactional replicated clustered cache also based on
the JGroups multicast library. It supports replication or
invalidation, synchronous or asynchronous communication, and
optimistic and pessimistic locking. The Hibernate query cache
is supported
Every cache provider is not compatible with every concurrency strategy. The following
compatibility matrix will help you choose an appropriate combination.
Strategy/Provider Read-only Nonstrictread-write Read-write Transactional
EHCache X X X

OSCache X X X
SwarmCache X X
JBoss Cache X X
You will specify a cache provider in hibernate.cfg.xml configuration file. We choose EHCache
as our second-level cache provider:
<session-factory>
</property>
</property>
</property>
root
</property>
root123
</property>
<property name="hibernate.cache.provider_class">
org.hibernate.cache.EhCacheProvider
</property>
</session-factory>

Now, you need to specify the properties of the cache regions. EHCache has its own configuration
file,ehcache.xml, which should be in the CLASSPATH of the application. A cache configuration
in ehcache.xml for the Employee class may look like this:
<diskStore path="java.io.tmpdir"/>
<defaultCache
maxElementsInMemory="1000"
eternal="false"
timeToIdleSeconds="120"
timeToLiveSeconds="120"
overflowToDisk="true"
/>
<cache name="Employee"
maxElementsInMemory="500"
eternal="true"
timeToIdleSeconds="0"
timeToLiveSeconds="0"
overflowToDisk="false"
/>
That's it, now we have second-level caching enabled for the Employee class and Hibernate now
hits the second-level cache whenever you navigate to a Employee or when you load a Employee
by identifier.
You should analyze your all the classes and choose appropriate caching strategy for each of the
classes. Sometime, second-level caching may downgrade the performance of the application. So
it is recommended to benchmark your application first without enabling caching and later on
enable your well suited caching and check the performance. If caching is not improving system
performance then there is no point in enabling any type of caching.
The Query-level Cache:
To use the query cache, you must first activate it using
the hibernate.cache.use_query_cache="true"property in the configuration file. By setting this
property to true, you make Hibernate create the necessary caches in memory to hold the query
and identifier sets.
Next, to use the query cache, you use the setCacheable(Boolean) method of the Query class. For
example:
Session session = SessionFactory.openSession();
Query query = session.createQuery("FROM EMPLOYEE");
query.setCacheable(true);
List users = query.list();
SessionFactory.closeSession();

Hibernate also supports very fine-grained cache support through the concept of a cache region. A
cache region is part of the cache that's given a name.
Query query = session.createQuery("FROM EMPLOYEE");
query.setCacheable(true);
query.setCacheRegion("employee");
List users = query.list();
SessionFactory.closeSession();
This code uses the method to tell Hibernate to store and look for the query in the employee area
of the cache.
Hibernate Batch Processing
Consider a situation when you need to upload a large number of records into your database using
Hibernate. Following is the code snippet to achieve this using Hibernate:
Transaction tx = session.beginTransaction();
for ( int i=0; i<100000; i++ ) {
Employee employee = new Employee(.....);
session.save(employee);
}
tx.commit();
session.close();
Because by default, Hibernate will cache all the persisted objects in the session-level cache and
ultimately your application would fall over with an OutOfMemoryException somewhere
around the 50,000th row. You can resolve this problem if you are using batch processing with
Hibernate.
To use the batch processing feature, first set hibernate.jdbc.batch_size as batch size to a
number either at 20 or 50 depending on object size. This will tell the hibernate container that
every X rows to be inserted as batch. To implement this in your code we would need to do little
modification as follows:
for ( int i=0; i<100000; i++ ) {
Employee employee = new Employee(.....);

if( i % 50 == 0 ) { // Same as the JDBC batch size
//flush a batch of inserts and release memory:
session.flush();
session.clear();
}
}
tx.commit();
session.close();
Above code will work fine for the INSERT operation, but if you are willing to make UPDATE
operation then you can achieve using the following code:
Session session = sessionFactory.openSession();
ScrollableResults employeeCursor = session.createQuery("FROM EMPLOYEE")
.scroll();
int count = 0;
while ( employeeCursor.next() ) {
Employee employee = (Employee) employeeCursor.get(0);
employee.updateEmployee();
seession.update(employee);
if ( ++count % 50 == 0 ) {
session.flush();
session.clear();
}
}
tx.commit();
session.close();
Batch Processing Example:
Let us modify configuration file as to add hibernate.jdbc.batch_size property:
<session-factory>
</property>

</property>
</property>
root
</property>
root123
</property>
<property name="hibernate.jdbc.batch_size">
50
</property>
</session-factory>
Consider the following POJO Employee class:
private int id;
private int salary;
}
return id;
}
this.id = id;
}
return firstName;
}

}
return lastName;
}
}
return salary;
}
}
}
PRIMARY KEY (id)
);
Following will be mapping file to map Employee objects with EMPLOYEE table.
<hibernate-mapping>
</meta>
</id>
</class>

we will use flush() and clear() methods available with Session object so that Hibernate keep
writing these records into the database instead of caching them in the memory.
import java.util.*;
try{
}
/* Add employee records in batches */
ME.addEmployees( );
}
/* Method to create employee records in batches */
public void addEmployees( ){
try{
for ( int i=0; i<100000; i++ ) {
String fname = "First Name " + i;
String lname = "Last Name " + i;
Integer salary = i;
if( i % 50 == 0 ) {
session.flush();

session.clear();
}
}
tx.commit();
}finally {
session.close();
}
return ;
}
}
 Create hibernate.cfg.xml configuration file as explained above.
 Execute ManageEmployee binary to run the program which will create 100000 records in
EMPLOYEE table.

Hibernate Interceptors
As you have learnt that in Hibernate, an object will be created and persisted. Once the object has
been changed, it must be saved back to the database. This process continues until the next time
the object is needed, and it will be loaded from the persistent store.
Thus an object passes through different stages in its life cycle and Interceptor
Interface provides methods which can be called at different stages to perform some required
tasks. These methods are callbacks from the session to the application, allowing the application
to inspect and/or manipulate properties of a persistent object before it is saved, updated, deleted
or loaded. Following is the list of all the methods available within the Interceptor interface:
S.N. Method and Description
1
findDirty()
This method is be called when the flush() method is called on a Session object.
2
instantiate()
This method is called when a persisted class is instantiated.

3
isUnsaved()
This method is called when an object is passed to the saveOrUpdate() method/
4
onDelete()
This method is called before an object is deleted.
5
onFlushDirty()
This method is called when Hibernate detects that an object is dirty (ie. have
been changed) during a flush i.e. update operation.
6
onLoad()
This method is called before an object is initialized.
7
onSave()
This method is called before an object is saved.
8
postFlush()
This method is called after a flush has occurred and an object has been updated
in memory.
9
preFlush()
This method is called before a flush.
Hibernate Interceptor gives us total control over how an object will look to both the application
and the database.
How to use Interceptors?
To build an interceptor you can either implement Interceptor class directly or
extend EmptyInterceptorclass. Following will be the simple steps to use Hibernate Interceptor
functionality.
Create Interceptors:
We will extend EmptyInterceptor in our example where Interceptor's method will be called
automatically when Employee object is created and updated. You can implement more methods
as per your requirements.
import java.io.Serializable;

import org.hibernate.EmptyInterceptor;
import org.hibernate.type.Type;
public class MyInterceptor extends EmptyInterceptor {
private int updates;
private int creates;
private int loads;
public void onDelete(Object entity,
Serializable id,
Object[] state,
String[] propertyNames,
Type[] types) {
// do nothing
}
// This method is called when Employee object gets updated.
public boolean onFlushDirty(Object entity,
Serializable id,
Object[] currentState,
Object[] previousState,
Type[] types) {
if ( entity instanceof Employee ) {
System.out.println("Update Operation");
return true;
}
return false;
}
public boolean onLoad(Object entity,
Serializable id,
Object[] state,
Type[] types) {
// do nothing
return true;
}
// This method is called when Employee object gets created.
public boolean onSave(Object entity,
Serializable id,
Object[] state,
Type[] types) {
if ( entity instanceof Employee ) {
System.out.println("Create Operation");

return true;
}
return false;
}
//called before commit into database
public void preFlush(Iterator iterator) {
System.out.println("preFlush");
}
//called after committed into database
public void postFlush(Iterator iterator) {
System.out.println("postFlush");
}
Create POJO Classes:
Now let us modify a little bit our first example where we used EMPLOYEE table and Employee
class to play with:
private int id;
private int salary;
}
return id;
}
this.id = id;
}
return firstName;
}
}
return lastName;

}
}
return salary;
}
}
}
Create Database Tables:
Second step would be creating tables in your database. There would be one table corresponding
to each object you are willing to provide persistence. Consider above objects need to be stored
and retrieved into the following RDBMS table:
salary INT default NULL, PRIMARY KEY (id)
)
Create Mapping Configuration File:
This step is to create a mapping file that instructs Hibernate how to map the defined class or
classes to the database tables.
<hibernate-mapping>
</meta>
</id>

</class>
Finally, we will create our application class with the main() method to run the application. Here
it should be noted that while creating session object we used our Interceptor class as an
argument.
try{
}
ME.listEmployees();

ME.listEmployees();
}
Session session = factory.openSession( new MyInterceptor() );
try{
tx.commit();
}finally {
session.close();
}
return employeeID;
}
try{
}
tx.commit();
}finally {
session.close();
}
}

try{
Employee employee =
tx.commit();
}finally {
session.close();
}
}
try{
Employee employee =
tx.commit();
}finally {
session.close();
}
}
}

 Create MyInterceptor.java source file as shown above and compile it.
Create Operation
preFlush
postFlush
Create Operation
preFlush
postFlush
Create Operation
preFlush
postFlush
preFlush
postFlush
preFlush
Update Operation
postFlush
preFlush
postFlush
preFlush
postFlush
+----+------------+-----------+--------+
+----+------------+-----------+--------+
| 29 | Zara | Ali | 5000 |
| 31 | John | Paul | 10000 |
+----+------------+-----------+--------+

2 rows in set (0.00 secmysql>
Hibernate Quick Guide
Hibernate is an Object-Relational Mapping(ORM) solution for JAVA and it raised as an open
source persistent framework created by Gavin King in 2001. It is a powerful, high performance
Object-Relational Persistence and Query service for any Java Application.
Hibernate maps Java classes to database tables and from Java data types to SQL data types and
relieve the developer from 95% of common data persistence related programming tasks.
Hibernate sits between traditional Java objects and database server to handle all the work in
persisting those objects based on the appropriate O/R mechanisms and patterns.
Hibernate Advantages:
 Hibernate takes care of mapping Java classes to database tables using XML files and without
writing any line of code.
 Provides simple APIs for storing and retrieving Java objects directly to and from the database.
 If there is change in Database or in any table then the only need to change XML file properties.
 Abstract away the unfamiliar SQL types and provide us to work around familiar Java Objects.
 Hibernate does not require an application server to operate.
 Manipulates Complex associations of objects of your database.
 Minimize database access with smart fetching strategies.
 Provides Simple querying of data.
Supported Databases:
Hibernate supports almost all the major RDBMS. Following is list of few of the database engines
supported by Hibernate.

 HSQL Database Engine
 DB2/NT
 MySQL
 PostgreSQL
 FrontBase
 Oracle
 Microsoft SQL Server Database
 Sybase SQL Server
 Informix Dynamic Server

Hibernate Architecture
The Hibernate architecture is layered to keep you isolated from having to know the underlying
APIs. Hibernate makes use of the database and configuration data to provide persistence services
(and persistent objects) to the application.
Following is a very high level view of the Hibernate Application Architecture.
Following is a detailed view of the Hibernate Application Architecture with few important core
classes.

Hibernate uses various existing Java APIs, like JDBC, Java Transaction API(JTA), and Java
Naming and Directory Interface (JNDI). JDBC provides a rudimentary level of abstraction of
functionality common to relational databases, allowing almost any database with a JDBC driver
to be supported by Hibernate. JNDI and JTA allow Hibernate to be integrated with J2EE
application servers.
Following section gives brief description of each of the class objects involved in Hibernate
Application Architecture.
Configuration Object:
The Configuration object is the first Hibernate object you create in any Hibernate application and
usually created only once during application initialization. It represents a configuration or
properties file required by the Hibernate. The Configuration object provides two keys
components:
 Database Connection: This is handled through one or more configuration files supported by
Hibernate. These files are hibernate.properties and hibernate.cfg.xml.
 Class Mapping Setup
 This component creates the connection between the Java classes and database tables..
SessionFactory Object:
Configuration object is used to create a SessionFactory object which inturn configures Hibernate
for the application using the supplied configuration file and allows for a Session object to be
instantiated. The SessionFactory is a thread safe object and used by all the threads of an
application.
The SessionFactory is heavyweight object so usually it is created during application start up and
kept for later use. You would need one SessionFactory object per database using a separate
configuration file. So if you are using multiple databases then you would have to create multiple
SessionFactory objects.
Session Object:
A Session is used to get a physical connection with a database. The Session object is lightweight
and designed to be instantiated each time an interaction is needed with the database. Persistent
objects are saved and retrieved through a Session object.
The session objects should not be kept open for a long time because they are not usually thread
safe and they should be created and destroyed them as needed.
Transaction Object:
A Transaction represents a unit of work with the database and most of the RDBMS supports
transaction functionality. Transactions in Hibernate are handled by an underlying transaction
manager and transaction (from JDBC or JTA).

Free Hibernate Tutorial | VirtualNuggets

More Related Content

What's hot (20)

Similar to Free Hibernate Tutorial | VirtualNuggets (20)

More from Virtual Nuggets (20)

Recently uploaded (20)

Free Hibernate Tutorial | VirtualNuggets