5. 删除数据
在删除数据的时候，需要指定删除条件，否则会把数据库表中的数据全部删除。在JSP页面中获得删除条件以后，调用JDBC的删除条件，把数据库表中的数据删除。删除操作的JSP页面代码如下：
delete.jsp
<%@ page language="java" import="java.util.*" pageEncoding="gb2312"%> <%@ page import="java.sql.*" %> <%@page import="java.sql.Connection"%> <%@page import="java.sql.PreparedStatement"%> <%@page import="java.sql.ResultSet"%> <%@page import="java.sql.DriverManager"%> <% 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 'delete.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"> <!-- <link rel="stylesheet" type="text/css" href="styles.css"> --> </head> <body> <form action="" method="post"> <label>请输入要删除的部门id：</label><br/><br/> <input type="text" name="d_id"/><br/><br/> <input type="submit" value="删除"/> </form> </body> <% Connection con = null; PreparedStatement ps = null; // ResultSet rs = null; try{ int d_id = 0; d_id = Integer.parseInt(request.getParameter("d_id")); Class.forName("com.mysql.jdbc.Driver"); System.out.println("数据库驱动创建成功！"); con = DriverManager.getConnection("jdbc:mysql://localhost:3306/bank","root","1234"); System.out.println("数据库连接成功！"); String sql = "delete from dept where d_id=?"; ps = con.prepareStatement(sql); ps.setInt(1,d_id); ps.executeUpdate(); out.println("删除成功！"); }catch (Exception e){ e.printStackTrace(); } %> </html>
程序运行界面如下：
6. 分页显示
当数据量很多的时候，一页显示不完，这个时候就需要用到分页显示。分页显示数据的时候，如果当前的页是第一页，【上一页】超链接是不可单击状态；如果当前页是最后一页，【下一页】超链接是不可单击状态。分页显示的所有代码都写在JSP文件中，代码如下：
showAllByPage.jsp
<%@ page language="java" import="java.util.*" pageEncoding="gb2312"%> <%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %> <%@ page import="com.cn.vo.*" %> <%@ page import="java.sql.*" %> <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <title>My JSP 'showAllByPage.jsp' starting page</title> </head> <% ResultSet rs = null; PreparedStatement pstmt =null; Connection conn = null; List<DeptVo> list = new ArrayList<DeptVo>(); try { String page1 = request.getParameter("page");//获得页面传递过来的page值赋值给page1 int page2 =1; if(page1 != null){ //如果页面传递过来的page值存在，则把该page1赋值给page2变量 page2 = Integer.parseInt(page1); } request.setAttribute("page2", page2); Class.forName("com.mysql.jdbc.Driver" );//创建数据库驱动 //连接数据库 conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/bank","root","1234"); //分页查询的SQL语句，每页显示5条记录 String sql = "select * from dept order by id desc limit ?,5"; pstmt = conn.prepareStatement(sql); pstmt.setInt(1, page2); rs = pstmt.executeQuery(); while(rs.next()){ DeptVo deptVo = new DeptVo(); // 把各属性放入CarsVo对象中 deptVo.setId(rs.getString("id")); deptVo.setAddress(rs.getString("address")); deptVo.setD_name(rs.getString("d_name")); deptVo.setEmpnumber(rs.getInt("empnumber")); deptVo.setD_id(rs.getInt("d_id")); list.add(deptVo);//把CarsVo对象放入集合中 request.setAttribute("list", list); } int count =0;//声明一个count变量，用于存储记录数 int maxpage = 0;//声明一个maxpage变量，原来表示最大页数 Statement stmt = conn.createStatement(); String sql1 ="select count(*) from dept";//查询总记录数的SQL语句 rs = stmt.executeQuery(sql1); while (rs.next()) { count = rs.getInt(1);//如果结果集存在，记录数初始化值为1 } maxpage = (count+4)/5;//最大页数等于总记录条数加上4，再除以5 request.setAttribute("maxpage", maxpage); } catch (SQLException e) { e.printStackTrace(); } %> <body> <table border="1" align="center" width="70%"> <tr> <td>部门编号</td> <td>部门地址</td> <td>部门人数</td> <td>部门名称</td> <td>部门id</td> </tr> <c:forEach items="${list}" var="list"> <tr> <td>${list.id }</td> <td>${list.address }</td> <td>${list.empnumber }</td> <td>${list.d_name }</td> <td>${list.d_id }</td> </tr> </c:forEach> </table> <div align="center"> <a href="?page=1">首页</a> <c:if test="${page2 ==1}">上一页</c:if> <c:if test="${page2 > 1}"><a href="?page=${page2 -1 }">上一页</a></c:if> <c:if test="${page2 == maxpage}">下一页</c:if> <c:if test="${page2 < maxpage}"><a href="?page=${page2 +1 }">下一页</a></c:if> <a href="?page=${maxpage }">末页</a> </div> </body> </html>
上述代码中，分页显示设置成每页显示5条记录，默认的页数为第一页，也就是说第一次访问时，看到的是第一页的数据，页面效果如下图所示：
