Ok.Here are the details:
In the installdir/conf/server.xml file following additions have been
made:-
Under GlobalNamingResources I have added the line,
<Resource name="jdbc/MyDSN" auth="Container"
type="javax.sql.DataSource" description="Sample Database"/>

In the installdir/webapps/myapp/META-INF/context.xml I have added,
<Resource name="jdbc/MyDSN" auth="Container"
type="javax.sql.DataSource" username="" password=""
driverClassName="sun.java.jdbc.JdbcOdbcDriver" url="JdbcOdbcDriver"
maxActive="20" maxIdle="4"/>

In the Java file i have wriiten the following code,
import java.sql.*;
public static Connection connect() throws java.sql.SQLException
{
 Context initCtx = new InitialContext();
 Context envCtx = (Context) initCtx.lookup("java:comp/env");
 DataSource ds = (DataSource)
 envCtx.lookup("jdbc/MyDSN");
}