inserting data through a servlet using JDBC - mysql

Question

I am trying to make a Social network site where a user can log or register. Once logged in with correct credentials, the user could search in a friends list and invite him/her to be friend.
So far I have made 2 jsp files-
1 index.jsp [2] UserRegistration.jsp
[2]mySQl has SocialNetwork Schema with UserInfo and userRegistration tables.
[3] and in src folder my RegistrationServlet is like this:
// ********************************************************************
// JDBC driver name and database URL
final String JDBC_DRIVER = "com.mysql.jdbc.Driver";
final String DB_URL = "jdbc:mysql://localhost:3306/SocialNetwork";
// ***********************************************************************
// Database credentials
final String USER = "root";
final String PASS = "root";
Connection conn = null;
Statement stmt = null;
try {
// Register JDBC driver
Class.forName(JDBC_DRIVER);
// connection to mySQL server and Open a connection
System.out.println("Connecting to a selected database...");
conn = DriverManager.getConnection(DB_URL, USER, PASS);
System.out.println("Connected database successfully...");
// create a Statement object ()
System.out.println("Inserting records into the table...");
stmt = conn.createStatement();
// Execute a query
String sql = "INSERT INTO SocialNetwork.userInfo"
+ "(userName, userPW)" + "VALUES('" + nUser + "','" + nPW
+ "')";
int i = stmt.executeUpdate(sql);
out.println("Connection successfull.." + i);
//Update the Db
stmt.executeUpdate(sql);
// executeQuery () method and save it on ResultSet
sql = "SELECT * FROM SocialNetwork.userInfo";
ResultSet rs = stmt.executeQuery(sql);
// check inserted rows in the Db table
while (rs.next()) {
String Db_Name = rs.getString("userName");
String passwordFromDb = rs.getString("userPW");
// rs.getString(newPassW)
out.println("<br>DbName **" + Db_Name);
out.println("->DbPass **" + passwordFromDb);
}
} catch (Exception e) {
e.printStackTrace();
}
How could I connect the UserLogin servlet to the UserInfo table so that if the user’s name and password are found and matched in the DB , he could see his/her friends’ list.
If that username and password is not found in the UserInfo, a message should display that the user has to Register first.
Once the user is logged-in, he should see a list of all the Usernames and Age.
Later, the user could select a user from that list and invite that user to be his/her friend.