Preview:
//Update Table in the database

//index.html
<!DOCTYPE html>
<html>
<head>
    <meta charset="ISO-8859-1">
    <title>Updating User Details</title>
    <style>
        div {
            background-color: lightgreen;
            color: Red;
            padding: 20px;
            margin: 20px;
            border: 2px yellow;
        }
    </style>
</head>
<body>
    <div>
        <h1>Updating User Details</h1>
        <form action="UpdateDetails" method="post">
            <label>Username:</label>
            <input type="text" name="username" required>
            <br>
            <h3>Give updated details of the above user</h3>
            <label>Password:</label>
            <input type="password" name="password" required>
            <br>
            <label>Email:</label>
            <input type="email" name="email" required>
            <br>
            <input type="submit" name="submit" value="Update">
        </form>
    </div>
</body>
</html>


//UpdateServlet.java

import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.SQLException;

import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

@WebServlet("/UpdateDetails")
public class UpdateServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    public UpdateServlet() {
        super();
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        Connection con = null;
        PreparedStatement st = null;

        response.setContentType("text/html");
        PrintWriter pw = response.getWriter();

        try {
            // Load the Driver Class
            Class.forName("oracle.jdbc.OracleDriver");
            System.out.println("Driver loaded");

            // Create the connection
            con = DriverManager.getConnection("jdbc:oracle:thin:@//localhost:1521/XE", "system", "1234");
            System.out.println("Connection established");

            String user = request.getParameter("username");
            String pwd = request.getParameter("password");
            String email = request.getParameter("email");

            // Update statement (ensure the table and column names match your Oracle schema)
            st = con.prepareStatement("UPDATE studentdata SET password=?, email=? WHERE username=?");
            st.setString(1, pwd);
            st.setString(2, email);
            st.setString(3, user);

            int r = st.executeUpdate();
            if (r > 0) {
                pw.println("<h1>Hi " + user + ", your password and email have been updated successfully.</h1>");
            } else {
                pw.println("<h1>User not found or details are the same.</h1>");
            }
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
            pw.println("<h1>Error loading database driver: " + e.getMessage() + "</h1>");
        } catch (SQLException e) {
            e.printStackTrace();
            pw.println("<h1>Error updating details: " + e.getMessage() + "</h1>");
        } finally {
            try {
                if (st != null) {
                    st.close();
                }
                if (con != null) {
                    con.close();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }
}
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