Follow these steps:

1) Import the following packages in your servlet file:

import java.sql.*;
import oracle.jdbc.driver.*;
import oracle.sql.*;

2) Load and Register the JDBC driver:

   DriverManager.registerDriver(new oracle.jdbc.driver.OracleDriver());

or you can use

Class.forName("oracle.jdbc.driver.OracleDriver");

3) Connect to database:

a) If you are using oracle oci driver,you have to use:

Connection conn = DriverManager.getConnection("jdbc:oracle:oci8:
@oracle.world", "root", "root");

where oracle.world is the TNSNAMES entry and root is the username and password.

b) If you are using oracle thin driver,you have to use:

Connection conn = DriverManager.getConnection ("jdbc:oracle:thin:@localhost:3306:roseindia",
"root", "root");

where localhost is the host,3306 is the port, roseindia is the database and root is the username and password.

4) Querying the database:

a)create statement:

Statement st = conn.createStatement();

b)write query and execute the query:

ResultSet rs = st.executeQuery("SELECT * from student");

5) Close the statement,resultset and connection:

rs.close();
st.close();
conn.close();

Try the following code:

import java.sql.*;
import oracle.sql.*;
import oracle.jdbc.driver.*;

public class Data { 
    public static void main(String[]args) {
        String msg=req.getParameter("msg");
        res.setContentType("text/html");
        PrintWriter out = res.getWriter();
        System.out.println(msg);
        try {
    DriverManager.registerDriver(new oracle.jdbc.driver.OracleDriver());
    Connection conn = DriverManager.getConnection("jdbc:oracle:thin: @localhost:3306:Oracle", "rose", "rose");
    Statement stmt=con.createStatement();
    ResultSet rs=stmt.executeQuery("select * from data");
    while(rs.next()){
        out.println(rs.getString("name")+"  "+rs.getString("address")+"<br>");
    }
        con.close();
        } 
        catch(Exception e){
        System.out.println(e);
        }
        }
        }