JSP - 更改 SQL 数据库中的值答案

【问题标题】：JSP - Changing values in SQL databaseJSP - 更改 SQL 数据库中的值
【发布时间】：2014-09-05 00:40:02
【问题描述】：

我有一个表格，用于显示数据库中的项目。在第一个 ResultSet 中，我创建了一个下拉菜单，让您选择是否希望项目可用。但是，因为我在第一个 ResultSet rs 中创建了它，所以我不能在第二个 ResultSet rs1 中使用它。问题出在这一行：

if (request.getParameter(rs1.getString("naziv") + "polje").equals("Nedostupno"))

这是完整的代码：

<%@page import="java.sql.DriverManager"%>
<%@page import="java.sql.ResultSet"%>
<%@page import="java.sql.Statement"%>
<%@page import="java.sql.Connection"%>

<%@page contentType="text/html" pageEncoding="UTF-8"%>

<html>
<head>
    <link rel="stylesheet" type="text/css" href="Stil/cssstil.css">
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    <title>Prikaz oružja</title>
</head>
<body>
    <h1>Prikaz oruzja</h1>
    <%
        out.print("<p align = \"center\">Administrator <a style=\"color:red;\">" +     session.getAttribute("user") + "</a></p>");
    %>
    <table align = "center" bgcolor = "darkgrey" border = "1" cellpadding="3" cellspacing="1">
        <tr>
            <td>
                <p style = "color: black;">Naziv</p>
            </td>
            <td>
                <p style = "color: black;">Opis</p>
            </td>
            <td>
                <p style = "color: black;">Cena</p>
            </td>
            <td>
                <p style = "color: black;">Dostupnost</p>
            </td>
            <td>

            </td>
        </tr>
        <%
            try {
                Class.forName("com.mysql.jdbc.Driver");
                Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/CS230-Projekat", "root", "123");
                Statement statement = connection.createStatement();
                String sql = "SELECT * FROM oruzje";
                ResultSet rs = statement.executeQuery(sql);
                while (rs.next()) {
        %>
        <tr bgcolor="grey">

            <td><%=rs.getString("naziv")%></td>
            <td><%=rs.getString("opis")%></td>
            <td><%=rs.getString("cena")%></td>
            <%
                if (rs.getString("dostupnost").equals("1")) {
                    out.print("<td><p style = \"color: green; font-size: 20px\">Dostupno</p></td>");

                } else {
                    out.print("<td><p style = \"color: red; font-size: 20px\">Nedostupno</p></td>");
                }
            %>
            <%
                    int a = rs.getInt("dostupnost");
                    if (a == 1) {
                        out.print("<td><select name=\"" + rs.getString("naziv") + "polje\"><option value = \"Dostupno\">Dostupno</option><option value = \"Nedostupno\">Nedostupno</option></select></td>");
                    } else {
                        out.print("<td><select name=\"" + rs.getString("naziv") + "polje\"><option value = \"Dostupno\">Dostupno</option><option value = \"Nedostupno\">Nedostupno</option></select></td>");
                    }
                }


            %>
        </tr>
        <tr><td></td><td></td><td></td><td></td>
            <td align=center>
                <form method="post">
                    <%      Statement statement1 = connection.createStatement();
                            int bre;
                            ResultSet rs1 = statement.executeQuery(sql);
                            while (rs1.next()) {
                                if (request.getParameter(rs1.getString("naziv") + "polje").equals("Nedostupno")) {
                                    bre = statement1.executeUpdate("UPDATE oruzje SET dostupnost = 0 WHERE  naziv='" + rs1.getString("naziv") + "'");
                                } else {
                                    bre = statement1.executeUpdate("UPDATE oruzje SET dostupnost = 0 WHERE  naziv='" + rs1.getString("naziv") + "'");
                                }

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

                    %>
                    <input type="submit" value="Apply" name="Apply" />
                </form>
            </td>
        </tr>
    </table>

    <p style=" position: absolute; bottom: 0; left: 0; width: 100%; text-align: center;"><a href ="index.jsp"><img src = "Slike/home.png" alt = "home"/></a></p>
</body>

【问题讨论】：

我建议不要为您的 HTML 组件使用 dynamic 名称。另外，避免在代码中使用 scriptlet。
我知道我的代码很糟糕，但这是学校作业，我必须尽快完成它，所以我没有太多时间做研究，如您所见。不完全改代码能解决这个问题吗？
再次重申：我建议不要为您的 HTML 组件使用动态名称。没有必要这样做。为您的<select> 使用固定名称，以便在调用request.getParameter("nameOfYourHtmlSelectComponent") 时更容易检索所选值。
我明白，但是，如果我在数据库中添加额外的条目会怎样？然后
<select> 的内容，即<option>s 是动态的。组件的名称不需要。

标签： java jsp jdbc

【解决方案1】：

首先，我将在 Servlet 和 JSP 中拆分您的代码，并向您展示为什么这是一种更好的方法。

您的视图（假设称为“foo.jsp”）：

<%@page contentType="text/html" pageEncoding="UTF-8"%>
<!-- adding JSTL to your project -->
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>

<!DOCTYPE html>
<html>
<head>
    <link rel="stylesheet" type="text/css" href="Stil/cssstil.css">
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    <title>Prikaz oružja</title>
</head>
<body>
    <h1>Prikaz oruzja</h1>
    <p align="center">
        Administrator <span style="color:red"><c:out value="${user}" /></span>
    </p>
    <!--
        In this case, the form should wrap all your table
        since you want to process all the input elements
        inside it. Otherwise, you will update the entire data
        rather than update per entity.
    -->
    <form method="post">
        <table align="center" bgcolor="darkgrey" border="1" cellpadding="3" cellspacing="1">
            <th>
                <td>
                    <p style = "color: black;">Naziv</p>
                </td>
                <td>
                    <p style = "color: black;">Opis</p>
                </td>
                <td>
                    <p style = "color: black;">Cena</p>
                </td>
                <td>
                    <p style = "color: black;">Dostupnost</p>
                </td>
                <td>

                </td>
            </th>
            <c:forEach items="${oruzjeList}" var="oruzje">
            <tr bgcolor="grey">
                <td>${oruzje.naziv}</td>
                <td>${oruzje.opis}</td>
                <td>${oruzje.cena}</td>
                <td>
                    <p style="color: green; font-size: 20px">
                        <!-- printing the value dynamically in view -->
                        <c:out value="${oruzje.dostupnost == '1' ? 'Dostupno' : 'Nedostupno'}" />
                    </p>
                </td>
                <td>
                    <!--
                        oruzje.naziv should be an ID, not the "unique name"
                        because a name could contain empty spaces which
                        will break the name of the component
                        here I use id but you will replace it with your ID
                    -->
                    <select name="polje_${oruzje.id}">
                        <option value="1" ${oruzje.dostupnost == '1' ? 'selected' : ''}>Dostupno</option>
                        <option value="0" ${oruzje.dostupnost == '0' ? 'selected' : ''}>Nedostupno</option>
                    </select>
                    <!--
                        Additionally, we need to obtain the respective id for
                        the row to be updated.
                        We will use a hidden input field which uses the ID
                    -->
                    <input type="hidden" name="hidId_${oruzje.id}" value="${oruzje.id}" />
                </td>
            </tr>
            </c:forEach>
            <tr>
                <td></td><td></td><td></td><td></td>
                <td>
                    <input type="submit" value="Apply" />
                </td>
            </tr>
        </table>
    </form>
        <p style="position: absolute; bottom: 0; left: 0; width: 100%; text-align: center;">
            <a href="index.jsp"><img src="Slike/home.png" alt="home"/></a>
        </p>
</body>
</html>

这假设您有一个支持映射到您的数据库表的实体：

public class Oruzje {
    private int id;
    private String naziv;
    private String opis;
    private String cena;
    private String dostupnost;
    //propers getters and setters for your fields
}

现在，你的 Servlet：

//yes, a Servlet can map directly to your JSP
//there's no problem using this approach
@WebServlet("/foo.jsp")
public class OruzjeServlet extends HttpServlet {
    //I won't go far with more classes
    //nor with other improvements to the code
    //I'll write the basic stuff here in Servlet

    //this method should be in an utility class
    //to provide reusability
    private void closeResource(Closeable resource) {
        try {
            if (resource != null) {
                resource.close();
            }
        } catch (IOException e) {
            //silent exception
        }
    }

    //this method should also be in an utility class
    //and should recover the connection from a DataSource
    //instead of creating the physical connection everytime
    private Connection getConnection() {
        try {
            Class.forName("com.mysql.jdbc.Driver");
            Connection connection = DriverManager
                .getConnection("jdbc:mysql://localhost:3306/CS230-Projekat", "root", "123");
        } catch (Exception e) {
            //this should be splitted for better handling
            //but I leave this up to you
            //handle the exception
            //very basic handling
            e.printStacktrace();
        }
    }

    //this method should be in a proper DAO class
    //reusing a connection for execution of multiple statements
    private List<Oruzje> getOruzjeList(Connection con) {
        List<Oruzje> oruzjeList = new ArrayList<Oruzje>();
        Statement statement = null;
        ResultSet rs = null;
        try {
            statement = connection.createStatement();
            String sql = "SELECT * FROM oruzje";
            ResultSet rs = statement.executeQuery(sql);
            while (rs.next()) {
                Oruzje oruzje = new Oruzje();
                oruzje.setId(rs.getInt("id")); //use the real column
                oruzje.setNaziv(rs.getString("naziv"));
                oruzje.setOpis(rs.getString("opis"));
                oruzje.setCena(rs.getString("cena"));
                oruzje.setDostupnost(rs.getString("dostupnost"));
                oruzjeList.add(oruzje);
            }
        } catch (SQLException e) {
            //again, handle the exception
            e.printStacktrace();
        } finally {
            closeResource(rs);
            closeResource(statement);
        }
        return oruzjeList;
    }

    //this method will be executed when a client (browser)
    //tries to enter to your foo.jsp page
    public void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
        Connection con = getConnection();
        List<Oruzje> oruzjeList = getOruzjeList(con);
        closeResource(con);
        //setting the oruzjeList variable as attribute
        //this will feed the ${oruzjeList} used in the
        //<c:forEach>
        request.setAttribute("oruzjeList", oruzjeList);
        //now, forward the view to the right view (JSP)
        //it is not a redirect
        request.getRequestDispatcher("/foo.jsp").forward(request, response);
    }

    //this method will be executed when user selects "Apply"
    //option in the view (the JSP)
    //because you stated that the method to submit the <form>
    //is POST
    public void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
        //now, we just retrieve the necessary parameters and process the data
        //sent from the form
        Connection con = getConnection();
        List<Oruzje> oruzjeList = getOruzjeList(con);

        //each ? is a parameter in the query
        //starting at index 1
        String updateSql = "UPDATE oruzje SET dostupnost = ? WHERE id = ?";
        PreparedStatement pstmt = con.prepareStatement();
        for(Oruzje oruzje : oruzjeList) {
            //this is where the static part of the name becomes handy
            String theId = request.getParameter("hidId_" + oruzje.getId());
            String theDostupnost = request.getParameter("polje_" + oruzje.getId());
            //I'll avoid basic validation like
            //if (theId == null || "".equals(theId))
            //right to the update!

            //setting the first parameter: dostupnost = ?
            pstmt.setString(1, theDostupnost);
            //setting the second parameter: ID = ?
            //since it's an int, parsing the String to int
            pstmt.setInt(2, Integer.parseInt(theId));
            //perform the update for the current ID and Dostupnost
            pstmt.execute();
        }
        //at the end, closing the resources
        closeResource(pstmt);

        //this is cumbersome but just to make sure
        //the data was updated successfully
        oruzjeList = getOruzjeList(con);
        closeResource(con);
        //similar to the doGet, we will forward to the view
        request.getRequestDispatcher("/foo.jsp").forward(request, response);
    }
}

更多信息：

【讨论】：

如果您需要别的东西，请告诉我。