First Hibernate Example First Hibernate Example

First Hibernate Example without IDE

we will be  creating the first hibernate application without IDE. For creating it we need to follow following steps:

1. Create the Persistent class
2. Create the mapping file for Persistent class
3. Create the Configuration file
4. Create the class that retrieves or stores the persistent object
5. Load the jar file
6. Run the first hibernate application without IDE..

1) Create Your  Persistent class

A simple Persistent class should follow some rules:

• A no-arg constructor: It is recommended that you have a default constructor at least package visibility so that hibernate can create the instance of the Persistent class by newInstance() method.
• Provide an identifier property (optional): It is mapped to the primary key column of the database.
• Declare getter and setter methods (optional): The Hibernate recognizes the method by getter and setter method names by default.
• Prefer non-final class: Hibernate uses the concept of proxies, that depends on the persistent class. The application programmer will not be able to use proxies for lazy association fetching.

Let’s create the simple Persistent class:

Employee.java

1. package com.clickatme.mypackage;
2. 
   
3. public class Employee {
4. private int id;
5. private String firstName,lastName;
6. 
   
7. public int getId() {
8.     return id;
9. }
10. public void setId(int id) {
11.     this.id = id;
12. }
13. public String getFirstName() {
14.     return firstName;
15. }
16. public void setFirstName(String firstName) {
17.     this.firstName = firstName;
18. }
19. public String getLastName() {
20.     return lastName;
21. }
22. public void setLastName(String lastName) {
23.     this.lastName = lastName;
24. }
25. 
    
26. 
    
27. }

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2) Create the mapping file for Persistent class

The mapping file name conventionally, should be class_name.hbm.xml. There are many elements of the mapping file.

• hibernate-mapping is the root element in the mapping file.
• class It is the sub-element of the hibernate-mapping element. It specifies the Persistent class.
• id It is the subelement of class. It specifies the primary key attribute in the class.
• generator It is the subelement of id. It is used to generate the primary key. There are many generator classes such as assigned (It is used if id is specified by the user), increment, hilo, sequence, native etc. We will learn all the generator classes later.
• property It is the subelement of class that specifies the property name of the Persistent class.

Let’s see the mapping file for the Employee class:

employee.hbm.xml

1. <?xml version=‘1.0’ encoding=‘UTF-8’?>
2. <!DOCTYPE hibernate-mapping PUBLIC
3.  “-//Hibernate/Hibernate Mapping DTD 3.0//EN”
4.  “http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd”>
5. 
   
6.  <hibernate-mapping>
7.   <class name=“com.clickatme.mypackage.Employee” table=“emp1000”>
8.     <id name=“id”>
9.      <generator class=“assigned”></generator>
10.     </id>
11. 
    
12.     <property name=“firstName”></property>
13.     <property name=“lastName”></property>
14. 
    
15.   </class>
16. 
    
17.  </hibernate-mapping>

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3) Create the Configuration file

The configuration file contains informations about the database and mapping file. Conventionally, its name should be hibernate.cfg.xml .

hibernate.cfg.xml

1. <?xml version=‘1.0’ encoding=‘UTF-8’?>
2. <!DOCTYPE hibernate-configuration PUBLIC
3.           “-//Hibernate/Hibernate Configuration DTD 3.0//EN”
4.           “http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd”>
5. 
   
6. <hibernate-configuration>
7. 
   
8.     <session-factory>
9.         <property name=“hbm2ddl.auto”>update</property>
10.         <property name=“dialect”>org.hibernate.dialect.Oracle9Dialect</property>
11.         <property name=“connection.url”>jdbc:oracle:thin:@localhost:1521:xe</property>
12.         <property name=“connection.username”>system</property>
13.         <property name=“connection.password”>oracle</property>
14.         <property name=“connection.driver_class”>oracle.jdbc.driver.OracleDriver</property>
15.     <mapping resource=“employee.hbm.xml”/>
16.     </session-factory>
17. 
    
18. </hibernate-configuration>

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4) Create the class that retrieves or stores the object

In this class, we are simply storing the employee object to the database.

1. package com.clickatme.mypackage;
2. 
   
3. import org.hibernate.Session;
4. import org.hibernate.SessionFactory;
5. import org.hibernate.Transaction;
6. import org.hibernate.cfg.Configuration;
7. 
   
8. public class DataStore {
9. public static void main(String[] args) {
10. 
    
11.     //creating configuration object
12.     Configuration cfg=new Configuration();
13.     cfg.configure(“hibernate.cfg.xml”);//populates the data of the configuration file
14. 
    
15.     //creating seession factory object
16.     SessionFactory factory=cfg.buildSessionFactory();
17. 
    
18.     //creating session object
19.     Session session=factory.openSession();
20. 
    
21.     //creating transaction object
22.     Transaction t=session.beginTransaction();
23. 
    
24.     Employee e1=new Employee();
25.     e1.setId(115);
26.     e1.setFirstName(“sonoo”);
27.     e1.setLastName(“jaiswal”);
28. 
    
29.     session.persist(e1);//persisting the object
30. 
    
31.     t.commit();//transaction is commited
32.     session.close();
33. 
    
34.     System.out.println(“successfully saved”);
35. 
    
36. }
37. }

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5) Load the jar file

For successfully running the hibernate application, you should have the hibernate4.jar file.
Some other jar files or packages are required such as

• cglib
• log4j
• commons
• SLF4J
• dom4j
• xalan
• xerces

How to run the first hibernate application without IDE
We may run this hibernate application by IDE (e.g. Eclipse, Myeclipse, Netbeans etc.) or without IDE. We will learn about creating hibernate application in Eclipse IDE in next chapter.
To run the hibernate application without IDE:

• install the oracle10g for this example.
• load the jar files for hibernate. (One of the way to load the jar file is copy all the jar files under the JRE/lib/ext folder). It is better to put these jar files inside the public and private JRE both.
• Now Run the DataStore class by java com.clickatme.mypackage.DataStore

Note: You need to connect with the internet to run this example.

Introduction To Hibernate

               Hibernate Architecture

The Hibernate architecture includes many objects persistent object, session factory, transaction factory, connection factory, session, transaction etc.

There are 4 layers in hibernate architecture java application layer, hibernate framework layer, backhand api layer and database layer.Let's see the diagram of hibernate architecture:
This is the high level architecture of Hibernate with mapping file and configuration file.

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Hibernate framework uses many objects session factory, session, transaction etc. alongwith existing Java API such as JDBC (Java Database Connectivity), JTA (Java Transaction API) and JNDI (Java Naming Directory Interface).

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Elements of Hibernate Architecture

For creating the first hibernate application, we must know the elements of Hibernate architecture. They are as follows:

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.