package com.soa.entities;

    public class Client {

        private int id;
        private String name;
        private double savings;

        public Client() {

        }

        public Client(int id, String name, double savings) {
            this.id = id;
            this.name = name;
            this.savings = savings;
        }

        public int getId() {
            return id;
        }

        public void setId(int id) {
            this.id = id;
        }

        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }

        public double getSavings() {
            return savings;
        }

        public void setSavings(double savings) {
            this.savings = savings;
        }

    }

package com.soa.dao;

    import java.sql.Connection;
    import java.sql.DriverManager;
    import java.sql.SQLException;

    public class ConnectionStackOverflow {

        private final static String user = "root";
        private final static String password = "";

        public static Connection getConexion() throws SQLException, InstantiationException, IllegalAccessException, ClassNotFoundException {
            Class.forName("com.mysql.jdbc.Driver");
            Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/homebanking" , user, password);
            return connection;
        }

        public static void closeConnection() throws SQLException, InstantiationException, IllegalAccessException, ClassNotFoundException {
            getConexion().close();
        }
    }

package com.soa.controllers;

    import java.sql.Connection;
    import java.sql.PreparedStatement;
    import java.sql.ResultSet;
    import java.sql.Statement;

    import com.soa.dao.ConnectionStackOverflow;
    import com.soa.entities.Client;

    public class AccountController {

        /* Método para insertar un cliente a la DB */
        public static void insertClient(String name, String lastname, double savings) {
            Connection connection = null;
            /* Intentamos conectarnos */
            try {
                connection = ConnectionStackOverflow.getConexion();

                /* Si no es nula que entre al método que nos facilita realizar la insercción */
                if (connection != null) {
                    PreparedStatement ps;
                    String sql = "INSERT INTO accounts(name, lastname, savings) VALUES(?,?,?)";
                    ps = connection.prepareStatement(sql);
                    ps.setString(1, name);
                    ps.setString(2, lastname);
                    ps.setDouble(3, savings);
                    ps.executeUpdate();
                    ps.close();
                    System.out.println("Query executed");
                } else {
                    System.out.println("Connection appears to be null");
                }
            } catch (Exception error) {
                System.out.println("Cannot even connect");
                error.getMessage();
                error.printStackTrace();
            }
        }

        /*
         * Método para retornar un cliente por su id , este es que seguramente se usaría
         * en una app de Escritorio, llegando el id por un campo hidden
         */
        public static Client retriveClient(int id) {
            Connection connection = null;

            String name = null;
            double savings = 0;
            Client client = null;

            try {
                connection = ConnectionStackOverflow.getConexion();

                if (connection != null) {
                    Statement st;
                    String sql = "SELECT * FROM accounts WHERE id=" + id;
                    st = connection.createStatement();
                    ResultSet rs = st.executeQuery(sql);

                    /*
                     * Mientras haya un resultado en la tabla le decimos que nos lo traiga y que a
                     * su vez grabe las variables recuperadas en name y savings, y por último lo
                     * agregamos a un cliente nuevo
                     */
                    while (rs.next()) {
                        name = rs.getString("name");
                        savings = rs.getDouble("savings");
                        client = new Client(id, name, savings);
                    }
                    /* Lo probamos por consola para ver si funcionó */
                    System.out.println(client.getSavings());
                    System.out.println("Query executed");
                } else {
                    System.out.println("Connection appears to be null");
                }
            } catch (Exception error) {
                System.out.println("Cannot even connect");
                error.getMessage();
                error.printStackTrace();
            }
            return client;
        }

        /*
         * Esta consulta no es recomendada ya que lo ideal es realizar la consulta sobre
         * el id y en este caso lo estoy haciendo sobre el name y lastname, va a ser
         * untema tuyo como solucionarlo
         */
        public static double getPersistedSavings(String name, String lastname) {
            Connection connection = null;
            double savings = 0;
            Client client = null;
            try {
                connection = ConnectionStackOverflow.getConexion();
                /*  Si la conexión no es nula entonces que pase al métodos de averiguación de datos */
                if (connection != null) {
                    Statement st;
                    String sql = "SELECT savings FROM accounts WHERE name='" + name + "' AND lastname='" + lastname + "' ";
                    st = connection.createStatement();
                    ResultSet rs = st.executeQuery(sql);

                    /*  Sólo queremos los savings o saldo, usamos el constructor vacío y le seteamos el valor recuperado    */
                    while (rs.next()) {
                        savings = rs.getDouble("savings");
                        client = new Client();
                        client.setSavings(savings);
                    }
                    System.out.println(client.getSavings());
                    System.out.println("Query executed");
                } else {
                    System.out.println("Connection appears to be null");
                }
            } catch (Exception error) {
                System.out.println("Cannot even connect");
                error.getMessage();
                error.printStackTrace();
            }
            return savings;
        }

    }

package com.soa.servlets;

    import java.io.IOException;
    import java.io.PrintWriter;

    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import javax.servlet.http.HttpSession;

    import com.soa.controllers.AccountController;

    public class InsertClientServlet extends HttpServlet {
        private static final long serialVersionUID = 1L;

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

            try {

                /* Recuperamos los datos de los inputs del jsp */
                String name = request.getParameter("name");
                String lastname = request.getParameter("lastname");
                String savings = request.getParameter("savings");

                /* Parseamos el String y lo pasamos a double */
                double doubleSavings = Double.parseDouble(savings);

                /* LLamamos al método que inserta los datos a la DB */
                AccountController.insertClient(name, lastname, doubleSavings);

                /*
                 * Además de haberlo insertado creamos una session y le agremos los siguientes
                 * atributos, name, lastname, savings
                 */
                HttpSession session = request.getSession(false);
                session.setAttribute("name", name);
                session.setAttribute("lastname", lastname);
                session.setAttribute("savings", doubleSavings);

                /*
                 * Cuando todo termina que nos derive a otra web donde vamos a consultar los
                 * savings por datos persistidos y por pasamanos de sessiones
                 */
                getServletConfig().getServletContext().getRequestDispatcher("/querySavings.jsp").forward(request, response);

            } catch (Exception error) {
                error.getMessage();
                error.printStackTrace();
            }

        }

    }

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
        pageEncoding="ISO-8859-1"%>
    <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
    <html>
    <head>
    <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
    <title>Insert title here</title>
    </head>

    <script type="text/javascript">

        function send() {
            var frm = document.frmInsertClient;
            frm.submit();
        }
    </script>

    <body>
        <h1>Insertar Cliente</h1>

        <form action="InsertClientServlet" method="get" name="frmInsertClient">
            <table>
                <tr>
                    <td><label>Nombre: </label></td>
                    <td><input type="text" name="name" /></td>
                </tr>
                <tr>

                    <td><label>Apellido: </label></td>
                    <td><input type="text" name="lastname" /></td>
                </tr>
                <tr>
                    <td><label>Saldo: </label></td>
                    <td><input type="number" name="savings" /></td>
                </tr>
                <tr>
                    <td><input type="button" value="boton" onclick="send()" /></td>
                </tr>
            </table>
        </form>

    </body>
    </html>

package com.soa.servlets;

    import java.io.IOException;
    import java.io.PrintWriter;
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import javax.servlet.http.HttpSession;

    import com.soa.controllers.AccountController;

    public class QuerySavingsServlet extends HttpServlet {
        private static final long serialVersionUID = 1L;

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

            try {
                /* Grabados en session */
                HttpSession session = request.getSession(false);
                PrintWriter pw = response.getWriter();
                pw.println("Este saldo es que escribimos en la pantallas pasadas y que lo grabamos en memoria Session");
                pw.println("******************************   " + session.getAttribute("savings")
                        + "   **************************************");

                /* Consultados en la Base de Datos, información persistida */
                String name = (String) session.getAttribute("name");
                String lastname = (String) session.getAttribute("lastname");
                double persistedSavings = AccountController.getPersistedSavings(name, lastname);
                pw.println("Este saldo es el que está persistido en la DB y que consultamos por medio una consulta");
                pw.println("******************************   " + persistedSavings
                        + "   **************************************");

            } catch (Exception error) {
                error.printStackTrace();
            }
        }

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

        }

    }

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
        pageEncoding="ISO-8859-1"%>
    <%@ page import="com.soa.entities.Client"%>
    <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
    <html>
    <head>
    <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
    <title>Averiguar saldo</title>
    </head>

    <script type="text/javascript">

        function send() {
            var frm = document.frmSavings;
            frm.submit();
        }
    </script>
    <body>

        <h1>Averiguar saldo</h1>

        <%
            session.getAttribute("name");
            session.getAttribute("savings");
            session.getAttribute("lastname");
        %>
    Esta es la sessión de <% out.print(session.getAttribute("name")); %><br>

        <form action="QuerySavingsServlet" method="get" name="frmSavings">
            <input type="hidden" name="id" value=<% out.print(session.getAttribute("name")); %> /> <br>
            <input type="text" value=<% out.print(session.getAttribute("savings")); %>> <input type="button" value="Averiguar Saldo" onclick="send()" />
        </form>
    </body>
    </html>

<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xmlns="http://java.sun.com/xml/ns/javaee"
        xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
        id="WebApp_ID" version="3.0">
        <display-name>StackOverflowWeb</display-name>
        <welcome-file-list>
            <welcome-file>index.html</welcome-file>
            <welcome-file>index.htm</welcome-file>
            <welcome-file>index.jsp</welcome-file>
            <welcome-file>default.html</welcome-file>
            <welcome-file>default.htm</welcome-file>
            <welcome-file>default.jsp</welcome-file>
        </welcome-file-list>
        <servlet>
            <servlet-name>InsertClientServlet</servlet-name>
            <servlet-class>com.soa.servlets.InsertClientServlet</servlet-class>
        </servlet>
        <servlet-mapping>
            <servlet-name>InsertClientServlet</servlet-name>
            <url-pattern>/InsertClientServlet</url-pattern>
        </servlet-mapping>

        <servlet>
            <servlet-name>QuerySavingsServlet</servlet-name>
            <servlet-class>com.soa.servlets.QuerySavingsServlet</servlet-class>
        </servlet>
        <servlet-mapping>
            <servlet-name>QuerySavingsServlet</servlet-name>
            <url-pattern>/QuerySavingsServlet</url-pattern>
        </servlet-mapping>
    </web-app>