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Getting Things Done with Hibernate
Robert Greiner
CSE7330
Southern Methodist University
Introduction – A quick Quiz.

How many of you are proficient in:
Quiz Results: How did you do?

Did you answer “Yes” to all of the databases?
 If
not, this presentation is for You!
Hibernate’s Most Important Features

Object to Relational Mapping Tool.
Relational databases do not map well to the real world
 Takes Java Objects and maps them to relational tables




Not easy!
Works with any relational database
Handles Database Transactions Automatically
Possible through mapping files
 Programmers don’t need to worry about writing SQL



FACT: Programmers are not typically proficient in SQL but still
need to interact with databases on a regular basis.
Another tool to help you get things done.

Because that’s what gets you hired and keeps you employed
What Hibernate Isn’t?

The answer to all of your database problems.
No amount of awesome code will substitute for good design.
 At the end of the day, data is stored in a relational model

Example

Suppose you have a system that needs to keep
track of students and courses (easy)
 Students
Table
 Courses Table

How do we express the m:n relationship for students
that need to enroll in several courses? (not as easy)
 Enrolled

Table (This does not map well to an object)
Can Hibernate help with this?
 Yes!
Let’s see some code
The Anatomy of a Hibernate Project

Java Classes
Student.java
 Course.java


Hibernate Mapping File
Student.hbm.xml
 Course.hbm.xml


Hibernate Files
hibernate.cfg.xml
 HibernateUtil.java
 StudentManager.java


main()
Regular Java Objects
Student.java
public class Student {
private
private
private
private
Just a regular everyday Java class
long sid;
String firstName;
String lastName;
double gpa;
Student() {} //Default constructor
public Student(String firstName, String lastName, double gpa) {
this.firstName = firstName;
this.lastName = lastName;
this.gpa = gpa;
}
public void setSid(long sid) {
this.sid = sid;
}
public long getSid() {
return this.sid;
}
public String getFirstName() {
return firstName;
}
Need a getter/setter for each database value
public void setFirstName(String firstName) {
this.firstName = firstName;
}
...
...
}
Course.java
public class Course {
long cid;
String name;
Set students = new HashSet();
public Course() {}
Each course object holds a
collection of the Students
enrolled in it.
public Course(String name) {
this.name = name;
}
...
...
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Set getStudents() {
return students;
}
public void setStudents(Set students) {
this.students = students;
}
public void addStudent(Student student) {
this.students.add(student);
}
}
Student.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="CSE7330.greiner.hibernate.Student" table="students">
<id name="sid" column="sid">
<generator class="increment" />
</id>
<property name="firstName" column="first_name" />
<property name="lastName" column="last_name" />
<property name="gpa" column="gpa" />
</class>
</hibernate-mapping>
Teach Hibernate how to map objects to the database
Course.hbm.xml
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="CSE7330.greiner.hibernate.Course" table="courses">
<id name="cid" column="cid">
<generator class="increment" />
</id>
<property name="name" column="course_name" />
<set name="students" table="list" lazy="true">
<key column="cid"/>
<many-to-many column="sid" class="Student"/>
</set>
</class>
</hibernate-mapping>
Hibernate.cfg.xml
<!DOCTYPE hibernate-configuration SYSTEM
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory>
<property name="hibernate.connection.driver_class">org.hsqldb.jdbcDriver</property>
<property name="hibernate.connection.url“>jdbc:hsqldb:hsql://localhost</property>
<property name="hibernate.connection.username“>sa</property>
<property name="hibernate.dialect“>org.hibernate.dialect.HSQLDialect</property>
<property
<property
<property
<property
<property
name="hibernate.c3p0.min_size">5</property>
name="hibernate.c3p0.max_size">20</property>
name="hibernate.c3p0.timeout">300</property>
name="hibernate.c3p0.max_statements">50</property>
name="hibernate.c3p0.idle_test_period">3000</property>
<property name="show_sql">false</property>
<property name="format_sql">true</property>
<mapping resource="CSE7330/greiner/hibernate/Student.hbm.xml" />
<mapping resource="CSE7330/greiner/hibernate/Course.hbm.xml" />
</session-factory>
</hibernate-configuration>
HibernateUtil.java – The Setup
public class HibernateUtil {
private static final SessionFactory sessionFactory = buildSessionFactory();
private static Session session = HibernateUtil.getSessionFactory().openSession();
private static SessionFactory buildSessionFactory() {
try {
return new Configuration().configure().buildSessionFactory();
}
catch (Throwable ex) {
System.out.println("Exception!!!!");
throw new ExceptionInInitializerError(ex);
}
}
public static SessionFactory getSessionFactory() {
return sessionFactory;
}
...
HibernateUtil.java – Insert Students/Courses
public static void insertStudents(List<Student> students) {
//Inserts a list of students into the database
Session session = HibernateUtil.getSessionFactory().openSession();
Transaction tx = session.beginTransaction();
for (Student s : students) {
Long sid = (Long) session.save(s);
}
tx.commit();
session.close();
}
public static void insertCourses(List<Course> courses) {
Session session = HibernateUtil.getSessionFactory().openSession();
Transaction tx = session.beginTransaction();
for (Course c : courses) {
Long sid = (Long) session.save(c);
}
tx.commit();
session.close();
}
HibernateUtil.java – Read Students/Courses
private static List<Student> getStudents() {
List<Student> students = new ArrayList<Student>();
students = session.createCriteria(Student.class).list();
return students;
}
private static List<Course> getCourses() {
List<Course> courses = new ArrayList<Course>();
courses = session.createCriteria(Course.class).list();
return courses;
}
HibernateUtil.java – Print Collections
public static void printDatabaseState() {
List<Student> students = getStudents();
List<Course> courses = getCourses();
Set studentsInCourse = new HashSet();
for (Student s : students) {
System.out.println(s.getSid() + " - " + s.getFirstName() + " " + s.getLastName());
}
for (Course c : courses) {
studentsInCourse = c.getStudents();
System.out.println(c.getName());
for (Object s : studentsInCourse) {
System.out.println("
" + ((Student)s).getFirstName() + " " + ((Student)s).getLastName());
}
}
}
StudentManager.java
public class StudentManager {
List<Student> students = new ArrayList<Student>();
List<Course> courses = new ArrayList<Course>();
public static void main(String[] args) {
//Initialize and call each method
}
public void addStudents() {
this.students.add(new Student("Albert", "Einstein", 4.0));
this.students.add(new Student("Carl", "Sagan", 2.5));
this.students.add(new Student("Alan", "Turing", 4.0));
this.students.add(new Student("Ken", "Thompson", 4.0));
this.students.add(new Student("Bill", "Gates", 0.0));
this.students.add(new Student("Steve", "Jobs", 3.5));
HibernateUtil.insertStudents(this.students);
}
public void addCourses() {
this.courses.add(new Course("CSE7330"));
this.courses.add(new Course("CSE5330"));
this.courses.add(new Course("CSE7314"));
this.courses.add(new Course("CSE8313"));
this.courses.get(0).addStudent(this.students.get(0));
this.courses.get(0).addStudent(this.students.get(1));
this.courses.get(0).addStudent(this.students.get(2));
this.courses.get(1).addStudent(this.students.get(3));
this.courses.get(1).addStudent(this.students.get(5));
this.courses.get(2).addStudent(this.students.get(0));
this.courses.get(2).addStudent(this.students.get(1));
this.courses.get(3).addStudent(this.students.get(2));
this.courses.get(3).addStudent(this.students.get(3));
this.courses.get(3).addStudent(this.students.get(5));
HibernateUtil.insertCourses(this.courses);
}
}
Results
Program Output
1 - Albert Einstein
2 - Carl Sagan
3 - Alan Turing
4 - Ken Thompson
5 - Bill Gates
6 - Steve Jobs
CSE7330
Alan Turing
Albert Einstein
Carl Sagan
CSE5330
Steve Jobs
Ken Thompson
CSE7314
Albert Einstein
Carl Sagan
CSE8313
Alan Turing
Steve Jobs
Ken Thompson
Summary


It can be difficult to express real life objects as
relations
Hibernate is an Object to Relational mapping tool
 Example:
 Allows

No 3rd Enrolled object needed
for a more Object Oriented approach
Hibernate allows you to interact with a database
without having to know platform-specific SQL
 Did
you see one line of SQL in this presentation?
Future Applications

Web frameworks are moving towards ORM.
 Rails
(Ruby)
 Django (Python)

Hibernate for other languages
 nHibernate
(.NET)
The 5 W’s of Hibernate





Who: Hibernate is maintained by Red Hat
What: Object to Relational Mapping Tool
When: Your next project that uses a database
Where: Project Homepage: http://hibernate.org
Why: Get things done!
References





Harnessing Hibernate

Dr. James Elliot

O'Reilly Media (April 1, 2008)

Amazon Link
Java Persistence with Hibernate

Christian Bauer

Manning Publications; Revised edition (November 24, 2006)

Amazon Link
https://www.hibernate.org/

Official Hibernate Project Site

Red Hat

11/11/2009
http://www.allapplabs.com/hibernate/hibernate_tutorials.htm

Hibernate Tutorials

Bushan Dongare

Good intro tutorial to hibernate

11/11/2009
http://stackoverflow.com/questions/tagged/hibernate

Stack Overflow Tag for Hibernate Questions

Great community resource for getting your questions answered

Community Authored and Licensed

2008-2009