<% String code = request.getParameter("YYM"); if (code == null || code.isEmpty()) { %> <a href="Admin.jsp">请输入预约码，点击返回签到</a> <% } else { Connection conn = SQLConn.openDB(); final String SELECT_SQL = "SELECT ACode FROM User_ZC JOIN YuYue ON User_ZC.UserId = YuYue.UserId WHERE Login = 1 AND State = 1 AND Arrive IS NULL"; final String UPDATE_SQL = "UPDATE YuYue SET Arrive =1 WHERE ACode = ?"; PreparedStatement pstmtSelect = conn.prepareStatement(SELECT_SQL); ResultSet rs = pstmtSelect.executeQuery(); int count = 0; while (rs.next()) { String Acode = rs.getString("ACode"); if (Acode.equals(code)) { try { PreparedStatement pstmtUpdate = conn.prepareStatement(UPDATE_SQL); pstmtUpdate.setString(1, code); count = pstmtUpdate.executeUpdate(); pstmtUpdate.close(); } catch (SQLException e) { e.printStackTrace(); } break; }else{ System.out.print("预约码不匹配"); } } if (count > 0){ %> <a href="Admin.jsp">签到成功</a> <% } else { %> <a href="Admin.jsp">签到失败</a> <% } rs.close(); pstmtSelect.close(); conn.close(); } %>其中，输入的“YYM”值为003004，并且数据库中有该字段，为什么会跳到“签到失败”页面？

request.getParameter()取值为null的解决方法

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基于request.getAttribute与request.getParameter的区别详解

在Java Servlet和JSP开发中，HttpServletRequest接口提供了两种主要的方法来获取客户端发送到服务器的数据：getAttribute()和getParameter()。它们虽然都用于获取请求中的数据，但有着本质的区别，下面将详细...

<% String code = String.valueOf(request.getParameter("YYM")); System.out.print(code); if (code == null || code.isEmpty()) { %> 请输入预约码，点击返回签到 <% } else { Connection conn = SQLConn.openDB(); final String SELECT_SQL = "SELECT ACode FROM User_ZC JOIN YuYue ON User_ZC.UserId = YuYue.UserId WHERE Login = 1 AND State = 1 AND Arrive IS NULL"; final String UPDATE_SQL = "UPDATE YuYue SET Arrive =1 WHERE ACode = ?"; PreparedStatement pstmtSelect = conn.prepareStatement(SELECT_SQL); ResultSet rs = pstmtSelect.executeQuery(); int count = 0; while (rs.next()) { String Acode = rs.getString("ACode"); if (code==Acode) { try { PreparedStatement pstmtUpdate = conn.prepareStatement(UPDATE_SQL); pstmtUpdate.setString(1, code); count = pstmtUpdate.executeUpdate(); pstmtUpdate.close(); } catch (SQLException e) { e.printStackTrace(); } break; }else{ System.out.print("预约码不匹配"); } } if (count > 0){ %> 签到成功 <% } else { %> 签到失败 <% } rs.close(); pstmtSelect.close(); conn.close(); } %>为什么输入正确的YYM，也会提示“预约码不匹配”

在Java中，当比较两个字符串对象时，应该使用equals()方法，而不是"=="运算符。...if (code==Acode) { 改为 if (code.equals(Acode)) { 这样就可以正确地比较code和Acode的内容是否相同了。

<% String code = request.getParameter("YYM"); if (code == null || code.isEmpty()) { %> 请输入预约码，点击返回签到 <% } else { Connection conn = SQLConn.openDB(); final String SELECT_SQL = "SELECT ACode FROM User_ZC JOIN YuYue ON User_ZC.UserId = YuYue.UserId WHERE Login = 1 AND State = 1 AND Arrive IS NULL"; final String UPDATE_SQL = "UPDATE YuYue SET Arrive =1 WHERE ACode = ?"; PreparedStatement pstmtSelect = conn.prepareStatement(SELECT_SQL); ResultSet rs = pstmtSelect.executeQuery(); int count = 0; while (rs.next()) { String Acode = rs.getString("ACode"); if (Acode.equals(code)) { try { PreparedStatement pstmtUpdate = conn.prepareStatement(UPDATE_SQL); pstmtUpdate.setString(1, code); count = pstmtUpdate.executeUpdate(); pstmtUpdate.close(); } catch (SQLException e) { e.printStackTrace(); } break; } } if (count > 0){ %> 签到成功 <% } else { %> 签到失败 <% } rs.close(); pstmtSelect.close(); conn.close(); } %>为什么总是跳转到“签到失败”页面，请找出bug

因此，建议在打开连接之后添加一个if语句来检查连接是否成功打开。另外，还需要检查是否有与该预约码相匹配的记录。如果没有，则也会导致跳转到“签到失败”页面。因此，建议添加一个else语句，在其中输出“该预约码...

解释一下这段代码<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%> <% String path = request.getContextPath();%> <% String itemId = request.getParameter("itemId"); %> <% String parentId = request.getParameter("parentId"); %> <% boolean parent=true; %> <% if(itemId==null){ itemId="";} if(parentId==null){ parent=false;}%>

- 第二个 <% %> 标签中的代码使用 request.getParameter("itemId") 方法获取名为 "itemId" 的请求参数的值，并将结果赋值给 itemId 变量。 - 第三个 <% %> 标签中的代码使用 request.getParameter(...

解释这段代码： <% if("yes".equals(request.getParameter("passwordRemember")) && request.getParameter("userId") != "" && request.getParameter("userId") != null && request.getParameter("passwordKey") != "" && request.getParameter("passwordKey") != null ){ %> <c:redirect url="/sweb/PCSMenu/PCSF905W022Page/open" > <c:param name="userId" value='<%=(String)request.getParameter("userId") %>'/> <c:param name="passwordKey" value='<%=(String)request.getParameter("passwordKey") %>'/> <c:param name="passwordRemember" value='<%=(String)request.getParameter("passwordRemember") %>'/> </c:redirect> <%-- リダイレクトしなかった場合用 --%> <c:param name="passwordKey" value='<%=(String)request.getParameter("passwordKey") %>'/></c:url>">F3JavaSample トップ画面へ <% }else{%> <c:redirect url="/sweb/auth/PCSF905W016Page/open" /> <%-- リダイレクトしなかった場合用 --%> F3JavaSample トップ画面へ <% }%>

首先，通过 request.getParameter("passwordRemember") 获取名为 "passwordRemember" 的请求参数的值。然后，通过 equals() 方法与字符串 "yes" 比较，判断是否为 "yes"。如果满足条件： - 使用 <c:redirect>...

详细解读一下这段代码：<%@ page language="java" import="java.text.,java.util." contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> <title>使用application内置对象--checkMessage.jsp</title> </head> <body bgcolor="#abcdef"> <%!Vector<String> v = new Vector<String>(); int i = 0;%> <% String datetime = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss").format(Calendar.getInstance().getTime()); //获取系统时间 %> <% request.setCharacterEncoding("utf-8"); String name = request.getParameter("name"); String title = request.getParameter("title"); String message = request.getParameter("message"); %> <% if (name == null || "".equals(name.trim())) { //trim()主要解决里面只有空格的问题 name = " 网友" + (int) (Math.random() * 100000 + 10000); } if (title == null || "".equals(title.trim())) { title = " 无"; } if (message == null || "".equals(message.trim())) { message = " 无"; } %> <% i++; String str = "第" + "" + i + " " + "楼 " + ".留言人: " + name + ".标题: " + title + ".内容:
" + message + ".时间: " + datetime + ".
"; v.add(str); application.setAttribute("message", v); %> 留言成功. 返回留言板 </body> </html>

5. 在 <% %> 中获取了系统时间和用户提交的留言信息（姓名、标题和内容），并对用户提交的信息进行了检查和处理，比如如果用户没有输入姓名，则随机生成一个姓名。 6. 在 <% %> 中构造了一个字符串 str，表示一条...

<% request.setCharacterEncoding("utf-8");%> <% String name= request.getParameter("name"); String submit= request.getParameter("submit"); %> <% if(submit!=null){ session.setAttribute("sessionname",name);} %> <%= session.getAttribute("sessionname")%>欢迎您的登录 [退出]

2. 通过 request.getParameter() 方法获取用户在登录页面中输入的姓名。 3. 如果用户点击了提交按钮，则将用户的姓名存储在 Session 中。 4. 在页面中通过 session.getAttribute() 方法获取存储在 Session 中的...

<%@ page language="java" import="java.util." pageEncoding="utf-8"%> <%@page import="com.util.SQLConn"%> <%@page import="java.sql." %> <%@page import="java.sql.Statement" %> <%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %> <%@ taglib prefix="fmt" uri="http://java.sun.com/jsp/jstl/fmt" %> <html> <body> <% // 获取前端数据 String username = request.getParameter("username"); String usernum = request.getParameter("usernum"); String userpwd = request.getParameter("userpwd"); // 执行数据库操作 Connection conn = null; PreparedStatement pstmt = null; ResultSet rs = null; int count = 0; try { conn = SQLConn.openDB(); String sql = "INSERT INTO User_ZC(UserID, Name, Code, Power) VALUES (?, ?, ?, ?)"; pstmt = conn.prepareStatement(sql); pstmt.setString(1, usernum); pstmt.setString(2, username); pstmt.setString(3, userpwd); pstmt.setInt(4, 1); count = pstmt.executeUpdate(); } catch (SQLException e) { e.printStackTrace(); } finally { SQLConn.closeDB(conn, pstmt, rs); } // 根据执行结果进行相应的操作 if (count > 0) { request.getRequestDispatcher("ZCS.jsp").forward(request,response); } else { request.getRequestDispatcher("ZCB.jsp").forward(request,response); } %> </body> </html>,优化代码

String username = request.getParameter("username"); String usernum = request.getParameter("usernum"); String userpwd = request.getParameter("userpwd"); %> <%-- 执行数据库操作 --%> <% int count = ...

<%@ page language="java" import="java.util." pageEncoding="utf-8"%> <%@page import="com.util.SQLConn"%> <%@page import="java.sql." %> <%@page import="java.sql.Statement" %> <%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %> <%@ taglib prefix="fmt" uri="http://java.sun.com/jsp/jstl/fmt" %> <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <title>登陆跳转servlet</title> </head> <body> <%-- 获取前端数据 --%> <% String usernum = request.getParameter("usernum"); String userpwd = request.getParameter("userpwd"); %> <%-- 定义SQLConn类和INSERT_SQL常量 --%> <% SQLConn sqlConn = new SQLConn(); //final String INSERT_SQL = "INSERT INTO User_ZC(UserID, Name, Code, Power) VALUES (?, ?, ?, ?)"; sqlConn.openDB();//打开数据库 String sql = "select UserId,Code from User_ZC"; ResultSet rs = sqlConn.execQuery(sql); boolean v = false; while(rs.next()){ if(rs.getString("usernum").equals(usernum)&&rs.getString("userpwd").compareTo(userpwd)==0){ v = true; } } rs.close(); sqlConn.closeDB(); if(v){ request.getRequestDispatcher("ZCS.jsp").forward(request, response); }else{ request.getRequestDispatcher("ZCB.jsp").forward(request, response); } %> </body> </html> 找bug

String usernum = request.getParameter("usernum"); String userpwd = request.getParameter("userpwd"); 2. 在比较密码时，应该使用 equals() 方法而不是 compareTo() 方法。 if(rs.getString(...

<%-- 作者：GGG166 --%> <%@page contentType="text/html;charset=gb2312" %> <%@page import="java.util."%> <html> <body> <%! Vector v=new Vector();//动态数组 int i=0; ServletContext application; synchronized void leaveWord(String s){//方法声明，用于在添加评论 application=getServletContext(); i++; v.add("No"+i+","+s); application.setAttribute("Mess",v); } %> <% request.setCharacterEncoding("gb2312");//乱码处理 String name=request.getParameter("name");//接收姓名 String title=request.getParameter("title");//接收标题 String message=request.getParameter("message");//接收评论 if(name==null){ name="guest"+(int)(Math.random()10000); } if(title==null){ title="无标题"; } if(message==null){ message="无信息"; } String s=name+"#"+title+"#"+message; leaveWord(s); out.print("你的评论已提交！"); %> 返回留言页面 </body> </html>

这段代码是一个 JSP 页面，用于添加留言功能。其中使用了一个 Vector 动态数组来存储留言信息，并使用 ServletContext 对象来共享数据。在 leaveWord 方法中，将新的留言信息添加到 Vector 中，并将其存储在 ...

<%@ page language="java" import="java.util." pageEncoding="utf-8"%> <%@page import="com.util.SQLConn"%> <%@page import="java.sql." %> <%@page import="java.sql.Statement" %> <% String path = request.getContextPath(); String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/"; %> <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <base href="<%=basePath%>"> <title>My JSP 'ZC.jsp' starting page</title> <meta http-equiv="pragma" content="no-cache"> <meta http-equiv="cache-control" content="no-cache"> <meta http-equiv="expires" content="0"> <meta http-equiv="keywords" content="keyword1,keyword2,keyword3"> <meta http-equiv="description" content="This is my page"> </head> <body> <% //获取前端数据 String usr = request.getParameter("username"); String num = request.getParameter("usernum"); String pwd = request.getParameter("userpwd"); //创建数据库类的对象 SQLConn.openDB(); //insert into User_ZC(Name,Code,Number,Power) values('usr的变量','num的变量','pwd的变量','1'); String sql = "insert into User_ZC(UserID,Name,Code,Power) values('"+num+"','"+usr+"','"+pwd+"','"+1+"')"; System.out.print("sql:"+sql); //执行SQL语句 if(SQLConn.execUpdate(sql) != 0 &&!"".equals(SQLConn.execUpdate(sql))){ int n = SQLConn.execUpdate(sql); System.out.print("n:"+n); if(n != 0 ){ request.getRequestDispatcher("ZCS.jsp").forward(request,response); }else{ request.getRequestDispatcher("ZCB.jsp").forward(request,response); } }else{System.out.print("执行SQL语句失败");} //关闭数据库 SQLConn.closeDB(); %> </body> </html>，优化代码

String username = request.getParameter("username"); String usernum = request.getParameter("usernum"); String userpwd = request.getParameter("userpwd"); // 执行数据库操作 Connection conn = null; ...

<%@ page language="java" import="java.util., java.sql." pageEncoding="utf-8"%> <%@page import="com.util.SQLConn"%> <%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %> <%@ taglib prefix="fmt" uri="http://java.sun.com/jsp/jstl/fmt" %> <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <title>登陆跳转servlet</title> </head> <body> <% String usernum = request.getParameter("usernum"); String userpwd = request.getParameter("userpwd"); Connection conn = SQLConn.openDB(); // 使用PreparedStatment进行预编译 PreparedStatement pstmt = conn.prepareStatement("select UserId, Code,Login from User_ZC where UserId=? and Code=? and Login=0"); pstmt.setString(1, usernum); pstmt.setString(2, userpwd); ResultSet rs = pstmt.executeQuery(); boolean v = rs.next(); if(v){ final String UPDATE_SQL = "update User_ZC set Login=? where UserId=?"; int count = 0; try { Connection connn = SQLConn.openDB(); PreparedStatement pstmte = conn.prepareStatement(UPDATE_SQL); { pstmt.setInt(1, 1); pstmt.setString(2, usernum); count = pstmt.executeUpdate(); } } catch (SQLException e) { e.printStackTrace(); } if (count > 0){ request.getRequestDispatcher("ZCS.jsp").forward(request, response); }else{System.out.print("登陆失败");} } else{ request.getRequestDispatcher("ZCB.jsp").forward(request, response); } %> </body> </html>找bug

在第24行，应该使用已经预编译好的 PreparedStatement 对象 pstmte 而不是重新使用 conn.prepareStatement() 方法创建一个新的 PreparedStatement 对象。正确的代码应该是： pstmte.setInt(1, 1);...

<% String name=request.getParameter("name"); name=new String(name.getBytes("iso-8859-1"),"UTF-8"); session.setAttribute("name",name); String sex=request.getParameter("gender"); String[] hobby=request.getParameterValues("hobby"); String mes=""; if(name.equals("")){ mes="昵称不能为空，请输入昵称"; mes = URLEncoder.encode(mes); session.setAttribute("mes",mes); RequestDispatcher rd = request.getRequestDispatcher("input.jsp"); rd.forward(request,response); } else{ RequestDispatcher rd = request.getRequestDispatcher("infromation.jsp"); rd.forward(request,response); } session.setAttribute("sex",sex); session.setAttribute("hobby",hobby); %>哪里错了

if (name == null || name.equals("")) { mes = "昵称不能为空，请输入昵称"; mes = URLEncoder.encode(mes, "UTF-8"); session.setAttribute("mes", mes); RequestDispatcher rd = request....

request.setCharacterEncoding("utf-8"); response.setContentType("text/html;charset=utf-8"); int id = Integer.parseInt(request.getParameter("id")); String name = request.getParameter("name"); String description = request.getParameter("description"); String price = request.getParameter("price"); String category = request.getParameter("category"); String manufacturer = request.getParameter("manufacturer"); String stockQuantity = request.getParameter("stockQuantity"); String isAvailable = request.getParameter("isAvailable"); Product product = new Product(id, name, description, Double.parseDouble(price), category, manufacturer, Integer.parseInt(stockQuantity), null, LocalDateTime.now(), isAvailable); ProductDao productDao = new ProductDao(); int update = productDao.update(product); if(update > 0){ request.getRequestDispatcher("productListServlet").forward(request,response);添加注释

这段代码是一个Servlet中的doPost方法的代码片段，主要作用是根据请求中的参数更新商品信息，并将请求转发...if(update > 0){ request.getRequestDispatcher("productListServlet").forward(request,response); }

// 先连接数据库 Class.forName("com.mysql.jdbc.Driver"); String url = "jdbc:mysql://localhost:3306/javaweb?useUnicode=true&characterEncoding=UTF-8"; String username="root"; String password=""; Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/environment?charaterEncoding=utf-8","root","123456"); request.setCharacterEncoding("UTF-8");//设置字符编码，避免出现乱码 double time1 = Double.parseDouble(request.getParameter("time1")); double time2 = Double.parseDouble(request.getParameter("time2")); String sql = "select * from cx where time>=? and time<=?"; PreparedStatement preparedStatement = conn.prepareStatement(sql); preparedStatement.setDouble(1,time1); preparedStatement.setDouble(2,time2); ResultSet resultSet = preparedStatement.executeQuery();//执行sql语句用来返回单个 ResultSet 对象 resultSet.last();//移动到最后一条记录 %> 在此段时间内共有 <%=resultSet.getRow()%>条记录温度湿度光照时间 <% resultSet.beforeFirst(); while (resultSet.next()){ %> <%=resultSet.getString("temperature")%> <%=resultSet.getString("humidity")%> <%=resultSet.getString("guangzhao")%> <%=resultSet.getString("time")%> <%}%> <% if (resultSet!=null){ resultSet.close(); } if (preparedStatement!=null){ preparedStatement.close(); } if (conn!=null){ conn.close(); } %> 找出这段代码的错误

request.setCharacterEncoding("UTF-8"); 3. 在执行 SQL 语句时，应该先使用 resultSet.next() 方法将指针移动到第一行，再进行数据的读取，例如： resultSet.beforeFirst(); while (resultSet.next()){...

public void update() { String forwardurl = request.getParameter("forwardurl"); String id = request.getParameter("id"); if (id == null) return; Album album = (Album) DALBase.load(Album.class, new Integer(id)); if (album == null) return; String name = request.getParameter("name"); String des = request.getParameter("des"); String xtype = request.getParameter("xtype"); String privilege = request.getParameter("privilege"); String pubren = request.getParameter("pubren"); String pubtime = request.getParameter("pubtime"); String tupian = request.getParameter("tupian"); SimpleDateFormat sdfalbum = new SimpleDateFormat("yyyy-MM-dd"); album.setName(name); album.setDes(des); album.setXtype(xtype); album.setPrivilege(privilege); album.setPubren(pubren); if (pubtime != null) { try { album.setPubtime(sdfalbum.parse(pubtime)); } catch (ParseException e) { e.printStackTrace(); } } album.setTupian(tupian); DALBase.update(album); // attachments(new Integer(album.getId()).toString()); if (forwardurl == null) { forwardurl = "/admin/albummanager.do?actiontype=get"; } try { response.sendRedirect(SystemParam.getSiteRoot() + forwardurl); } catch (Exception e) { e.printStackTrace(); } }翻译这段代码

这段代码是Java语言编写的，其作用是更新相册信息。...接着，将获取的参数设置到相册对象的属性中。如果有发布时间参数，将其转换为日期格式并设置到相册对象的属性中。最后，将更新后的相册对象保存到数据库中，并将...

private void query(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //查询用户列表 String queryUserName = request.getParameter("queryname"); String temp = request.getParameter("queryUserRole"); String pageIndex = request.getParameter("pageIndex"); int queryUserRole = 0; UserService userService = new UserServiceImpl(); List<User> userList = null;

这段代码是一个私有方法query的实现。在这个方法中，首先通过request...接下来，声明一个名为userList的List<User>类型的变量，并赋初值为null。这段代码的作用是查询用户列表，具体的查询逻辑可能在后续代码中实现。

将下列代码补全<%@ page import="java.sql.*" %> <% String studentId = request.getParameter("studentId"); String studentName = request.getParameter("studentName"); String phoneNumber = request.getParameter("phoneNumber"); Connection connection = null; PreparedStatement statement = null; try { // 建立数据库连接 Class.forName("com.mysql.jdbc.Driver"); connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/student_db", "username", "password"); // 执行插入学生数据的SQL语句 String insertQuery = "INSERT INTO students (student_id, student_name, phone_number) VALUES (?, ?, ?)"; statement = connection.prepareStatement(insertQuery); statement.setString(1, studentId); statement.setString(2, studentName); statement.setString(3, phoneNumber); statement.executeUpdate(); // 提示添加成功 out.println("添加学生成功"); out.println("学号: " + studentId + ""); out.println("姓名: " + studentName + ""); out.println("电话: " + phoneNumber + ""); } catch (Exception e) { // 处理数据库异常 out.println("添加学生失败"); out.println("Error: " + e.getMessage() + ""); e.printStackTrace(); } finally { // 关闭数据库连接和语句 if (statement != null) { statement.close(); } if (connection != null) { connection.close(); } } %>

String studentId = request.getParameter("studentId"); String studentName = request.getParameter("studentName"); String phoneNumber = request.getParameter("phoneNumber"); Connection connection = ...

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