Java Servlet Form validation

Design a form and perform server side validation
INDEX CODE:
<html>
<head>
<title>Login Form</title>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
</head>
<body style="margin-left: 25px;">
<h1>
            Form Validation Login Page
</h1>
<form action="demoServlet">
<br/><h3>Enter Username:<input type="text" name="username" style="margin-left: 20px;"></h3><br>
<h3>Enter Password:<input type="password" name="pass" style="margin-left: 20px;"></h3><br><br>
<input type="submit" value="Login" style="margin-left: 80px;">
</form>

</body>

</html>

SERVELET CODE:
importjava.io.IOException;
importjava.io.PrintWriter;
importjava.sql.Connection;
importjava.sql.DriverManager;
importjava.sql.ResultSet;
importjava.sql.Statement;
importjavax.servlet.ServletException;
importjavax.servlet.http.HttpServlet;
importjavax.servlet.http.HttpServletRequest;
importjavax.servlet.http.HttpServletResponse;

public class demoServlet extends HttpServlet {
    Connection conn;

protected void processRequest(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
        Connection conn = null;

try {
            String username = request.getParameter("username");
            String pass = request.getParameter("pass");
            String userName = "scse";
            String password = "scse";
            String url = "jdbc:mysql://localhost/scse";
Class.forName("com.mysql.jdbc.Driver").newInstance();
conn = DriverManager.getConnection(url, userName, password);
            Statement s = conn.createStatement();
s.executeQuery("SELECT * FROM register where username = '" + username + "' && pass = '" + pass +"' " );
ResultSetrs = s.getResultSet();
while (rs.next()) {
out.println(username+" is successfully logged in and you have validated your username and password.");

}
rs.close();
s.close();

} catch (Exception e) {
out.println(e.toString());
}
finally {
out.close();
if (conn != null) {
try {
conn.close();
out.println("Database connection terminated");
                } catch (Exception e) {
                }
            }

        }
    }

    @Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throwsServletException, IOException {
processRequest(request, response);
    }

    @Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throwsServletException, IOException {
processRequest(request, response);
    }
}