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4. Introduction to Hibernate

>> Saturday, March 19, 2011

Hibernate is an Object-Relational Mapping (ORM) solution for JAVA. It is a powerful, high performance object/relational persistence and query service. It allows us to develop persistent classes following object-oriented idiom – including association, inheritance and polymorphism.

Hibernate Architecture

Hibernate:

1) itself opens connection to database,
2) converts HQL (Hibernate Query Language) statements to database specific statement,
3) receives result set,
4) then performs mapping of these database specific data to Java objects which are directly used by Java application.

Hibernate uses the database specification from Hibernate Properties file. Automatic mapping is performed on the basis of the properties defined in hbm XML file defined for particular Java object.

3.Interaction with RDBMS

These are the General steps to follow while usingn JDBC.

1) Load the RDBMS specific JDBC driver because this driver actually communicates with the database.
2) Open the connection to database which is then used to send SQL statements and get results back.
3) Create JDBC Statement object. This object contains SQL query.
4) Execute statement which returns resultset(s). ResultSet contains the tuples of database table as a result of SQL query.
5) Process the result set.
6) Close the connection.

Example: Retrieve list of employees from Employee table using JDBC.

String url = “jdbc:odbc:” + dbName;

List employeeList = new ArrayList();

//load the jdbc-odbc driver 

class.forName(“sun.jdbc.odbc.JdbcOdbcDriver”);

//Open a connection to database

Connection con = DriverManager.getConnection(url);

//create Statement object

Statement stmt = con.createStatement();

//execute statement
ResultSet rs = stmt.executeQuery("SELECT * FROM Sells"); while ( rs.next() ){
  EmployeeBean eb = new Employeebean(); 
  eb.setName(rs.getString("name")); 
  eb.setSalary(rs.getFloat("salary")); 
  employeeList.add(eb);
}

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