Hibernate - Part 2

Java Hibernate Training
Hibernate - Part 2

Classification: Restricted
Agenda
• Generator Class in Hibernate
• SQL Dialects
• Collection Mapping
• One-to-one Mapping
• Cascade Types
• Many to one / One to many
• Hibernate Lazy Loading
• Transaction Management
• HQL – Hibernate Query Language
• HCQL – Hibernate Criteria Query Language
• Hibernate Caching

Hibernate
• Hibernate framework simplifies the development of java application to
interact with the database.
• Hibernate is an open source, lightweight, ORM (Object Relational
Mapping) tool.
• An ORM tool simplifies the data creation, data manipulation and data
access. It is a programming technique that maps the object to the data
stored in the relational database.

Advantages of Hibernate
• Open-source and Lightweight: Hibernate framework is open-source and
lightweight.
• Fast performance: The performance of hibernate framework is fast because cache
is internally used in hibernate framework. There are two types of cache in hibernate
framework first level cache and second level cache. First level cache is enabled by
default.
• Database Independent query: HQL (Hibernate Query Language) is the object-
oriented version of SQL. It generates the database independent queries. So you
don't need to write database specific queries. Before Hibernate, If database is
changed for the project, we need to change the SQL query as well that leads to the
maintenance problem.
• Automatic table creation: Hibernate framework provides the facility to create the
tables of the database automatically. So there is no need to create tables in the
database manually.
• Simplifies complex join: To fetch data form multiple tables is easy in hibernate
framework.
• Provides query statistics and database status: Hibernate supports Query cache and
provide statistics about query and database status.

Hibernate Architecture – High Level

Hibernate – Detailed Architecture

Hibernate Architecture – Important Elements
• SessionFactory
The SessionFactory is a factory of session and client of ConnectionProvider. It holds second
level cache (optional) of data. The org.hibernate.SessionFactory interface provides factory
method to get the object of Session.
• Session
The session object provides an interface between the application and data stored in the
database. It is a short-lived object and wraps the JDBC connection. It is factory of
Transaction, Query and Criteria. It holds a first-level cache (mandatory) of data. The
org.hibernate.Session interface provides methods to insert, update and delete the object. It
also provides factory methods for Transaction, Query and Criteria.
• Transaction
The transaction object specifies the atomic unit of work. It is optional. The
org.hibernate.Transaction interface provides methods for transaction management.
• ConnectionProvider
It is a factory of JDBC connections. It abstracts the application from DriverManager or
DataSource. It is optional.
• TransactionFactory
It is a factory of Transaction. It is optional.

Hibernate jar files…
• Download from Hibernate official site
http://hibernate.org/orm/downloads/

Hibernate tools download
• http://tools.jboss.org/downloads/

Your first Hibernate project
• Create the java project
• Add jar files for hibernate
• Create the Persistent class
• Create the mapping file for Persistent class
• Create the Configuration file
• Create the class that retrieves or stores the persistent object
• Run the application

Your first Hibernate project – Steps in detail
• Create the java project by File Menu - New - project - java project . Now
specify the project name e.g. firsthb then next - finish
• To add the jar files Right click on your project - Build path - Add external
archives. In this example, we are connecting the application with oracle
database. So you must add the ojdbc14.jar file as well.

//Create the POJO class
public class Employee {
private int id;
private String firstName,lastName;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
}

• Mapping file for POJO - employee.hbm.xml
<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="Employee" table="emp1000">
<id name="id">
<generator class="assigned"></generator>
</id>
<property name="firstName"></property>
<property name="lastName"></property>
</class>
</hibernate-mapping>
** INSTEAD OF WRITING A SEPARATE MAPPING FILE, GIVE MAPPING INFO IN THE POJO ITSELF

• Create entry in configuration file: hibernate.cfg.xml
<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory>
<property name="dialect">org.hibernate.dialect.Oracle9Dialect</property>
<property name="connection.url">jdbc:oracle:thin:@localhost:1521:xe</property>
<property name="connection.username">system</property>
<property name="connection.password">oracle</property>
<property name="connection.driver_class">oracle.jdbc.driver.OracleDriver</property>
<mapping resource="employee.hbm.xml"/>
<mapping resource=“department.hbm.xml"/>
</session-factory>
</hibernate-configuration>

Your first Hibernate project – Steps – HibernateUtil
import org.hibernate.SessionFactory;
import org.hibernate.cfg.AnnotationConfiguration;
public class HibernateUtil
{
private static final SessionFactory sessionFactory;
static{
try{
sessionFactory = new AnnotationConfiguration().configure().buildSessionFactory();
}
catch(Throwable th){
System.err.println("Initial SessionFactory creation failed"+th);
throw new ExceptionInInitializerError(th);
}
}
public static SessionFactory getSessionFactory(){
return sessionFactory;
}
}

CRUD operations: Create
//Create student entity object
Student student = new Student();
student.setStudentName(“Bill Clinton");
student.setRollNumber(01);
student.setCourse("MCA");
//Create session factory object
SessionFactory sessionFactory = HibernateUtil.getSessionFactory();
//getting session object from session factory
Session session = sessionFactory.openSession();
//getting transaction object from session object
session.beginTransaction();
session.save(student);
System.out.println("Inserted Successfully");
session.getTransaction().commit();
session.close();
sessionFactory.close();

CRUD operations: Read
Query query = session.createQuery("from Student");
List students = query.list();
for(Student student : students) {
System.out.println("Roll Number: "+student.getRollNumber()+", Student
Name: "+student.getStudentName()+", Course: "+student.getCourse());
}

CRUD operations: Update
Student student = (Student)session.get(Student.class, 2);
student.setStudentName(“Pawan Kumar");
System.out.println("Updated Successfully");

CRUD operations: Delete
Student student = (Student)session.load(Student.class, 4);
session.delete(student);
System.out.println("Deleted Successfully");

Hibernate Session API methods
• save()
• update()
• delete()
• get()
• saveOrUpdate()
• persist()
• load()
• merge() – Exercise…

save() vs persist()
• persist() is well defined. It makes a transient instance persistent. However,
it doesn't guarantee that the identifier value will be assigned to the
persistent instance immediately, the assignment might happen at flush
time.
• persist() also guarantees that it will not execute an INSERT statement if it is
called outside of transaction boundaries. This is useful in long-running
conversations with an extended Session/persistence context.
• save() does not guarantee the same, it returns an identifier, and if an
INSERT has to be executed to get the identifier (e.g. "identity" generator,
not "sequence"), this INSERT happens immediately, no matter if you are
inside or outside of a transaction. This is not good in a long-running
conversation with an extended Session/persistence context.

load() vs get()
Session.load():
• It will always return a “proxy” (Hibernate term) without hitting the
database. In Hibernate, proxy is an object with the given identifier value,
its properties are not initialized yet, it just look like a temporary fake
object.
• If no row found , it will throws an ObjectNotFoundException.
Session.get():
• It always hit the database and return the real object, an object that
represent the database row, not proxy.
• If no row found , it return null.

merge()
• Exercise:
• What is the use of Session.merge() method?
• Hint: Refer to the API.

Demo of all CRUD operations…

Hibernate with Annotations
• The hibernate application can be created with annotation. There are many
annotations that can be used to create hibernate application such as
@Entity, @Id, @Table etc.
• Hibernate Annotations are based on the JPA 2 specification and supports all
the features.
• All the JPA annotations are defined in the javax.persistence.* package.
Hibernate EntityManager implements the interfaces and life cycle defined
by the JPA specification.
• The core advantage of using hibernate annotation is that you don't need
to create mapping (hbm) file. Here, hibernate annotations are used to
provide the meta data.

• Add the jar file for oracle (if your database is oracle) and annotation
o hibernate-commons-annotations.jar
o ejb3-persistence.jar
o hibernate-annotations.jar
• Create the Persistent class
• Annotations used:
o @Entity annotation marks this class as an entity.
o @Table annotation specifies the table name where data of this entity is to be
persisted. If you don't use @Table annotation, hibernate will use the class name as
the table name by default.
o @Id annotation marks the identifier for this entity.
o @Column annotation specifies the details of the column for this property or field. If
@Column annotation is not specified, property name will be used as the column
name by default.
• Add mapping of Persistent class in configuration file
• Create the class that retrieves or stores the persistent object

@Entity
@Table(name= "emp500")
public class Employee {
@Id
private int id;
private String firstName,lastName;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
}

Exercise of Web application using Hibernate…
• Replace JDBC DAO class in the web app for Student registration information
with Hibernate code.

Generator classes in Hibernate
• The <generator> subelement of id used to generate the unique identifier for the objects of persistent class.
There are many generator classes defined in the Hibernate Framework.
• assigned: It is the default generator strategy if there is no <generator> element . In this case, application
assigns the id.
<id ...>
<generator class="assigned"></generator>
</id>
• increment: It generates the unique id only if no other process is inserting data into this table. It
generates short, int or long type identifier. The first generated identifier is 1 normally and incremented as 1.
<id ...>
<generator class="increment"></generator>
</id>
• sequence: It uses the sequence of the database. if there is no sequence defined, it creates a sequence
automatically e.g. in case of Oracle database, it creates a sequence named HIBERNATE_SEQUENCE.
<id ...>
<generator class="sequence"></generator>
</id>

Generator classes in Hibernate
• Some other generator classes:
• hilo
• native
• identity
• seqhilo
• uuid
• guid
• select
• foreign
• sequence-identity

SQL Dialects in Hibernate
RDBMS Dialect
Oracle (any version) org.hibernate.dialect.OracleDialect
Oracle9i org.hibernate.dialect.Oracle9iDialect
Oracle10g org.hibernate.dialect.Oracle10gDialect
MySQL org.hibernate.dialect.MySQLDialect
MySQL with InnoDB org.hibernate.dialect.MySQLInnoDBDialect
MySQL with MyISAM org.hibernate.dialect.MySQLMyISAMDialect
DB2 org.hibernate.dialect.DB2Dialect
DB2 AS/400 org.hibernate.dialect.DB2400Dialect
DB2 OS390 org.hibernate.dialect.DB2390Dialect
Microsoft SQL Server org.hibernate.dialect.SQLServerDialect
Sybase org.hibernate.dialect.SybaseDialect
Sybase Anywhere org.hibernate.dialect.SybaseAnywhereDialect

Collection Mapping in Hibernate
• One-to-one mapping
• Many-to-one mapping/One-to-many mapping
• Many-to-many mapping

One-to-one mapping (Employee to Address)

Cascade Types
• CascadeType.PERSIST : means that save() or persist() operations cascade to related
entities.
• CascadeType.MERGE : means that related entities are merged when the owning
entity is merged.
• CascadeType.REFRESH : does the same thing for the refresh() operation.
• CascadeType.REMOVE : removes all related entities association with this setting
when the owning entity is deleted.
• CascadeType.DETACH : detaches all related entities if a “manual detach” occurs.
• CascadeType.ALL : is shorthand for all of the above cascade operations.
Example:
@OneToMany(cascade={CascadeType.REFRESH, CascadeType.MERGE}, fetch =
FetchType.LAZY)
@JoinColumn(name="EMPLOYEE_ID")
private Set<AccountEntity> accounts;
Above cascading will cause accounts collection to be only merged and refreshed.

Many to one / One to Many

One-to-many demo..
• Using List
• Using Bag
• Using Set
• Using Map

Many-to-many demo
• Exercise: Will give you an exercise to try it out.

Hibernate Lazy Loading
• Lazy collection loads the child objects on demand, it is used to improve
performance. Since Hibernate 3.0, lazy collection is enabled by default.
• To use lazy collection, you may optionally use lazy="true" attribute in your
collection. It is by default true, so you don't need to do this. If you set it to
false, all the child objects will be loaded initially which will decrease
performance in case of big data.
<list name="answers" lazy="true">
<key column="qid"></key>
<index column="type"></index>
<one-to-many class="Answer"/>
</list>

Hibernate Transaction Management
• Using Transaction interface
Session session = null;
Transaction tx = null;
try {
session = sessionFactory.openSession();
tx = session.beginTransaction();
//some actions
tx.commit();
}catch (Exception ex) {
ex.printStackTrace();
tx.rollback();
}
finally {
session.close();
}

HQL – Hibernate Query Language
• public int executeUpdate() is used to execute the update or delete query.
• public List list() returns the result of the query as a list.
• public Query setFirstResult(int rowno) specifies the row number from
where record will be retrieved.
• public Query setMaxResult(int rowno) specifies the no. of records to be
retrieved from the relation (table).
• public Query setParameter(int position, Object value) it sets the value to
the JDBC style query parameter.
• public Query setParameter(String name, Object value) it sets the value to
a named query parameter.

HQL examples
//Get all records from Emp
Query query=session.createQuery("from Emp");//here persistent class name
is Emp
List list=query.list();
//Pagination example
Query query=session.createQuery("from Emp");
query.setFirstResult(5);
query.setMaxResult(10);
List list=query.list();//will return the records from 5 to 10th number

HQL Examples
//HQL Update Query
Transaction tx=session.beginTransaction();
Query q=session.createQuery("update User set name=:n where id=:i");
q.setParameter("n","Udit Kumar");
q.setParameter("i",111);
int status=q.executeUpdate();
System.out.println(status);
tx.commit();
//HQL Delete Query
Query query=session.createQuery("delete from Emp where id=100");
//specifying class name (Emp) not tablename
query.executeUpdate();

HQL Examples – Aggregate functions
//Total salary of all employees
Query q=session.createQuery("select sum(salary) from Emp");
List<Emp> list=q.list();
Iterator<Emp> itr=list.iterator();
while(itr.hasNext()){
System.out.println(itr.next());
}
Other examples: max(salary), min(salary), count(id), avg(salary)…

Hibernate Criteria Query Language
• Fetch records based on specific criteria
• Advantage: The HCQL provides methods to add criteria, so it is easy for the
java programmer to add criteria. The java programmer is able to add many
criteria on a query.
• Uses:
• Criteria interface
• Order class
• Restrictions class

HCQL Examples
//Get all records
Crietria c=session.createCriteria(Emp.class);//passing Class class argument
List list=c.list();
//Pagination
• Criteria c=session.createCriteria(Emp.class);
• c.setFirstResult(10);
• c.setMaxResult(20);
• List list=c.list();
//Records whose salary is greater than 10000
Criteria c=session.createCriteria(Emp.class);
c.add(Restrictions.gt("salary",10000));//salary is the propertyname
List list=c.list();

HCQL Examples
//Records in asc order of salary
Crietria c=session.createCriteria(Emp.class);
c.addOrder(Order.asc("salary"));
List list=c.list();
//HCQL with Projection (i.e. specific columns of a table
Criteria c=session.createCriteria(Emp.class);
c.setProjection(Projections.property("name"));
List list=c.list();

Java & JEE Training
Advanced Concepts – Performance improvement using
Caching and Connection Pooling

Hibernate Caching
• Hibernate caching improves the performance of the application by pooling
the object in the cache.
• There are mainly two types of caching: first level cache and second level
cache.
• First Level Cache
Session object holds the first level cache data. It is enabled by default. The
first level cache data will not be available to entire application. An
application can use many session object.
• Second Level Cache
SessionFactory object holds the second level cache data. The data stored
in the second level cache will be available to entire application. But we
need to enable it explicitely.

Hibernate Caching using EHCache Example
• In hibernate.cfg.xml
<property name="cache.provider_class">org.hibernate.cache.EhCacheProvider</property>
<property name="hibernate.cache.use_second_level_cache">true</property>
• Cache usage setting in hbm file
<cache usage="read-only" />
• ehcache.xml
<?xml version="1.0"?>
<ehcache>
<defaultCache
maxElementsInMemory="100"
eternal="false"
timeToIdleSeconds="120"
timeToLiveSeconds="200" />
<cache name="Employee"
maxElementsInMemory="100"
eternal="false"
timeToIdleSeconds="5"
timeToLiveSeconds="200" />
</ehcache>

Hibernate caching.. Exercise.
• Use EHCache or any 3rd party caching for Hibernate
• To test if it is working, create and destroy to sessions back to back and
perform the same query operation on Employee table. The second query
should not hit the database.
• What is evict?

Hibernate Exercise: Questions
• What is the difference between get() and load() methods?
• What is the difference between save() and persist() methods?

Hibernate – Connection Pooling
• Hibernate comes with internal connection pooling, not suitable for
production though.
• So we need to use a third party tool like C3P0.
• Exercise: Configure Hibernate connection pooling using C3P0.
• Download c3p0 dependencies/jars.
• Configure various pooling parameters:
• Min and max number of JDBC connections in the pool.
• Timeout of an idle connection
• Max number of prepared statements that will be cached.

Topics to be covered in next session
• Introduction to Struts Framework
• Features
• Evolution
• Struts Demo
• Declarative validation
• Architecture
• Validators
• Interceptors

Thank you!

Hibernate - Part 2

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