MVC系列教材（三）- 结合Servlet和JSP 实现分页功能

MVC系列教材（二）- 结合Servlet和JSP 实现查询功能

MVC系列教材（四）- 使用Servlet 验证用户是否登陆

工具版本兼容问题

随着数据中记录的增多，网页上显示的数据会越来越多。

当多到一定程度的时候，就会影响用户的体验。

解决办法是通过分页技术，一次只显示数据库中的部分数据，如果要看其他数据，可以通过"下一页" "最后一页" 等翻页操作实现

纠

步骤 1 : 首先准备 DAO
步骤 2 : 只显示5条数据
步骤 3 : 下一页
步骤 4 : 上一页
步骤 5 : 第一页
步骤 6 : 最后一页
步骤 7 : 边界处理
步骤 8 : 套上Bootstrap

步骤 1 :

首先准备 DAO

edit 顶折

纠问

在DAO中提供方法

public List<Hero> list(int start, int count)

start表示开始的个数，count表示取多少条
比如 list(0, 5) ，即表示第一页，每页有5条数据
比如 list(5, 5) ，即表示第二页，每页有5条数据

package dao; import java.sql.Connection; import java.sql.DriverManager; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.SQLException; import java.sql.Statement; import java.util.ArrayList; import java.util.List; import bean.Hero; public class HeroDAO { public int getTotal() { int total = 0; try { Class.forName("com.mysql.jdbc.Driver"); Connection c = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/how2java?characterEncoding=UTF-8", "root", "admin"); Statement s = c.createStatement(); String sql = "select count(*) from hero"; ResultSet rs = s.executeQuery(sql); while (rs.next()) { total = rs.getInt(1); } System.out.println("total:" + total); s.close(); c.close(); } catch (ClassNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); } return total; } public void add(Hero hero) { try { Class.forName("com.mysql.jdbc.Driver"); Connection c = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/how2java?characterEncoding=UTF-8", "root", "admin"); String sql = "insert into hero values(null,?,?,?)"; PreparedStatement ps = c.prepareStatement(sql); ps.setString(1, hero.name); ps.setFloat(2, hero.hp); ps.setInt(3, hero.damage); ps.execute(); ResultSet rs = ps.getGeneratedKeys(); if (rs.next()) { int id = rs.getInt(1); hero.id = id; } ps.close(); c.close(); } catch (ClassNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); } } public void update(Hero hero) { try { Class.forName("com.mysql.jdbc.Driver"); Connection c = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/how2java?characterEncoding=UTF-8", "root", "admin"); String sql = "update hero set name= ?, hp = ? , damage = ? where id = ?"; PreparedStatement ps = c.prepareStatement(sql); ps.setString(1, hero.name); ps.setFloat(2, hero.hp); ps.setInt(3, hero.damage); ps.setInt(4, hero.id); ps.execute(); ps.close(); c.close(); } catch (ClassNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); } } public void delete(int id) { try { Class.forName("com.mysql.jdbc.Driver"); Connection c = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/how2java?characterEncoding=UTF-8", "root", "admin"); Statement s = c.createStatement(); String sql = "delete from hero where id = " + id; s.execute(sql); s.close(); c.close(); } catch (ClassNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); } } public Hero get(int id) { Hero hero = null; try { Class.forName("com.mysql.jdbc.Driver"); Connection c = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/how2java?characterEncoding=UTF-8", "root", "admin"); Statement s = c.createStatement(); String sql = "select * from hero where id = " + id; ResultSet rs = s.executeQuery(sql); if (rs.next()) { hero = new Hero(); String name = rs.getString(2); float hp = rs.getFloat("hp"); int damage = rs.getInt(4); hero.name = name; hero.hp = hp; hero.damage = damage; hero.id = id; } s.close(); c.close(); } catch (ClassNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); } return hero; } public List<Hero> list() { return list(0, Short.MAX_VALUE); } public List<Hero> list(int start, int count) { List<Hero> heros = new ArrayList<Hero>(); try { Class.forName("com.mysql.jdbc.Driver"); Connection c = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/how2java?characterEncoding=UTF-8", "root", "admin"); String sql = "select * from hero order by id desc limit ?,? "; PreparedStatement ps = c.prepareStatement(sql); ps.setInt(1, start); ps.setInt(2, count); ResultSet rs = ps.executeQuery(); while (rs.next()) { Hero hero = new Hero(); int id = rs.getInt(1); String name = rs.getString(2); float hp = rs.getFloat("hp"); int damage = rs.getInt(4); hero.id = id; hero.name = name; hero.hp = hp; hero.damage = damage; heros.add(hero); } ps.close(); c.close(); } catch (ClassNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); } return heros; } }

代码行数较多，请点击查看

package dao;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;

import bean.Hero;

public class HeroDAO {

	public int getTotal() {
		int total = 0;
		try {
			Class.forName("com.mysql.jdbc.Driver");

			Connection c = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/how2java?characterEncoding=UTF-8",
					"root", "admin");

			Statement s = c.createStatement();

			String sql = "select count(*) from hero";

			ResultSet rs = s.executeQuery(sql);
			while (rs.next()) {
				total = rs.getInt(1);
			}

			System.out.println("total:" + total);

			s.close();

			c.close();

		} catch (ClassNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return total;
	}

	public void add(Hero hero) {

		try {
			Class.forName("com.mysql.jdbc.Driver");

			Connection c = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/how2java?characterEncoding=UTF-8",
					"root", "admin");

			String sql = "insert into hero values(null,?,?,?)";
			PreparedStatement ps = c.prepareStatement(sql);
			ps.setString(1, hero.name);
			ps.setFloat(2, hero.hp);
			ps.setInt(3, hero.damage);

			ps.execute();

			ResultSet rs = ps.getGeneratedKeys();
			if (rs.next()) {
				int id = rs.getInt(1);
				hero.id = id;
			}

			ps.close();

			c.close();

		} catch (ClassNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}

	public void update(Hero hero) {
		try {
			Class.forName("com.mysql.jdbc.Driver");

			Connection c = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/how2java?characterEncoding=UTF-8",
					"root", "admin");

			String sql = "update hero set name= ?, hp = ? , damage = ? where id = ?";
			PreparedStatement ps = c.prepareStatement(sql);
			ps.setString(1, hero.name);
			ps.setFloat(2, hero.hp);
			ps.setInt(3, hero.damage);
			ps.setInt(4, hero.id);

			ps.execute();

			ps.close();

			c.close();

		} catch (ClassNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}

	}

	public void delete(int id) {
		try {
			Class.forName("com.mysql.jdbc.Driver");

			Connection c = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/how2java?characterEncoding=UTF-8",
					"root", "admin");

			Statement s = c.createStatement();

			String sql = "delete from hero where id = " + id;

			s.execute(sql);

			s.close();

			c.close();

		} catch (ClassNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}

	public Hero get(int id) {
		Hero hero = null;
		try {
			Class.forName("com.mysql.jdbc.Driver");

			Connection c = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/how2java?characterEncoding=UTF-8",
					"root", "admin");

			Statement s = c.createStatement();

			String sql = "select * from hero where id = " + id;

			ResultSet rs = s.executeQuery(sql);

			if (rs.next()) {
				hero = new Hero();
				String name = rs.getString(2);
				float hp = rs.getFloat("hp");
				int damage = rs.getInt(4);
				hero.name = name;
				hero.hp = hp;
				hero.damage = damage;
				hero.id = id;
			}

			s.close();

			c.close();

		} catch (ClassNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return hero;
	}

	public List<Hero> list() {
		return list(0, Short.MAX_VALUE);
	}

	public List<Hero> list(int start, int count) {
		List<Hero> heros = new ArrayList<Hero>();

		try {
			Class.forName("com.mysql.jdbc.Driver");

			Connection c = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/how2java?characterEncoding=UTF-8",
					"root", "admin");

			String sql = "select * from hero order by id desc limit ?,? ";

			PreparedStatement ps = c.prepareStatement(sql);
			ps.setInt(1, start);
			ps.setInt(2, count);

			ResultSet rs = ps.executeQuery();

			while (rs.next()) {
				Hero hero = new Hero();
				int id = rs.getInt(1);
				String name = rs.getString(2);
				float hp = rs.getFloat("hp");
				int damage = rs.getInt(4);
				hero.id = id;
				hero.name = name;
				hero.hp = hp;
				hero.damage = damage;
				heros.add(hero);
			}

			ps.close();

			c.close();

		} catch (ClassNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return heros;
	}

}

步骤 2 :

只显示5条数据

edit 顶折

纠问

修改HeroListServlet

int start = 0;
int count = 5;
List<Hero> heros = new HeroDAO().list(start, count);

即表示只获取5条数据

代码行数较多，请点击查看

package servlet;

import java.io.IOException;
import java.util.List;

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

import bean.Hero;
import dao.HeroDAO;

public class HeroListServlet extends HttpServlet {

	protected void service(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		response.setContentType("text/html; charset=UTF-8");

		int start = 0;
		int count = 5;
		List<Hero> heros = new HeroDAO().list(start, count);

		request.setAttribute("heros", heros);

		request.getRequestDispatcher("listHero.jsp").forward(request, response);

	}
}

步骤 3 :

edit 顶折

纠问

HeroListServlet :
通过参数获取start，如果浏览器没有传递参数，就设置为0。
根据start，计算next. next的值就是start+count.
然后把next传递给listHero.jsp

listHero.jsp
在最后面增加一个超链

start=${next} 从服务器传递过来的next值

HeroListServlet.java
listHero.jsp

代码行数较多，请点击查看

package servlet;

import java.io.IOException;
import java.util.List;

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

import bean.Hero;
import dao.HeroDAO;

public class HeroListServlet extends HttpServlet {

	protected void service(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		response.setContentType("text/html; charset=UTF-8");

		int start = 0;
		int count = 5;

		try {
			start = Integer.parseInt(request.getParameter("start"));
		} catch (NumberFormatException e) {
			// 当浏览器没有传参数start时
		}

		int next = start + count;

		List<Hero> heros = new HeroDAO().list(start, count);

		request.setAttribute("next", next);

		request.setAttribute("heros", heros);

		request.getRequestDispatcher("listHero.jsp").forward(request, response);

	}
}

代码行数较多，请点击查看


<%@ page language="java" contentType="text/html; charset=UTF-8"
	pageEncoding="UTF-8" import="java.util.*"%>

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>

<table align='center' border='1' cellspacing='0'>
	<tr>
		<td>id</td>
		<td>name</td>
		<td>hp</td>
		<td>damage</td>
		<td>edit</td>
		<td>delete</td>
	</tr>
	<c:forEach items="${heros}" var="hero" varStatus="st">
		<tr>
			<td>${hero.id}</td>
			<td>${hero.name}</td>
			<td>${hero.hp}</td>
			<td>${hero.damage}</td>
			<td><a href="editHero?id=${hero.id}">edit</a></td>
			<td><a href="deleteHero?id=${hero.id}">delete</a></td>
		</tr>
	</c:forEach>
	<tr>
		<td colspan="6" align="center">
			<a href="?start=${next}">[下一页]</a>
		</td>
	</tr>
</table>

步骤 4 :

edit 顶折

纠问

HeroListServlet:
根据start，计算pre. pre的值就是start-count.
然后把pre传递给listHero.jsp

listHero.jsp
在下一页前增加一个超链

start=${pre} 从服务器传递过来的pre值

HeroListServlet.java
listHero.jsp

代码行数较多，请点击查看

package servlet;

import java.io.IOException;
import java.util.List;

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

import bean.Hero;
import dao.HeroDAO;

public class HeroListServlet extends HttpServlet {

	protected void service(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		response.setContentType("text/html; charset=UTF-8");

		int start = 0;
		int count = 5;

		try {
			start = Integer.parseInt(request.getParameter("start"));
		} catch (NumberFormatException e) {
			// 当浏览器没有传参数start时
		}

		int next = start + count;
		int pre = start - count;

		request.setAttribute("next", next);
		request.setAttribute("pre", pre);

		List<Hero> heros = new HeroDAO().list(start, count);
		request.setAttribute("heros", heros);

		request.getRequestDispatcher("listHero.jsp").forward(request, response);

	}
}

代码行数较多，请点击查看


<%@ page language="java" contentType="text/html; charset=UTF-8"
	pageEncoding="UTF-8" import="java.util.*"%>

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>

<table align='center' border='1' cellspacing='0'>
	<tr>
		<td>id</td>
		<td>name</td>
		<td>hp</td>
		<td>damage</td>
		<td>edit</td>
		<td>delete</td>
	</tr>
	<c:forEach items="${heros}" var="hero" varStatus="st">
		<tr>
			<td>${hero.id}</td>
			<td>${hero.name}</td>
			<td>${hero.hp}</td>
			<td>${hero.damage}</td>
			<td><a href="editHero?id=${hero.id}">edit</a></td>
			<td><a href="deleteHero?id=${hero.id}">delete</a></td>
		</tr>
	</c:forEach>
	<tr>
		<td colspan="6" align="center">
			<a href="?start=${pre}">[上一页]</a>
			<a href="?start=${next}">[下一页]</a>
		</td>
	</tr>
</table>

步骤 5 :

第一页

edit 顶折

纠问

只需要修改listHero.jsp即可

增加

因为首页的start永远都是0

代码行数较多，请点击查看

<%@ page language="java" contentType="text/html; charset=UTF-8"
	pageEncoding="UTF-8" import="java.util.*"%>

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>

<table align='center' border='1' cellspacing='0'>
	<tr>
		<td>id</td>
		<td>name</td>
		<td>hp</td>
		<td>damage</td>
		<td>edit</td>
		<td>delete</td>
	</tr>
	<c:forEach items="${heros}" var="hero" varStatus="st">
		<tr>
			<td>${hero.id}</td>
			<td>${hero.name}</td>
			<td>${hero.hp}</td>
			<td>${hero.damage}</td>
			<td><a href="editHero?id=${hero.id}">edit</a></td>
			<td><a href="deleteHero?id=${hero.id}">delete</a></td>
		</tr>
	</c:forEach>
	<tr>
		<td colspan="6" align="center">
			<a href="?start=0">[首  页]</a>
			<a href="?start=${pre}">[上一页]</a>
			<a href="?start=${next}">[下一页]</a>
		</td>
	</tr>
</table>

步骤 6 :

最后一页

edit 顶折

纠问

HeroListServlet:
在HeroListServlet中计算last
last需要根据总数total和每页有多少条数据count来计算得出。

同时，还要看total是否能够整除count
假设总数是50，是能够被5整除的，那么最后一页的开始就是45

if (0 == total % count)
last = total - count;

假设总数是51，不能够被5整除的，那么最后一页的开始就是50

last = total - total % count;

listHero.jsp
在下一页后增加一个超链

start=${last} 从服务器传递过来的last值

HeroListServlet.java
listHero.jsp

代码行数较多，请点击查看

package servlet;

import java.io.IOException;
import java.util.List;

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

import bean.Hero;
import dao.HeroDAO;

public class HeroListServlet extends HttpServlet {

	protected void service(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		response.setContentType("text/html; charset=UTF-8");

		int start = 0;
		int count = 5;

		try {
			start = Integer.parseInt(request.getParameter("start"));
		} catch (NumberFormatException e) {
			// 当浏览器没有传参数start时
		}

		int next = start + count;
		int pre = start - count;

		int total = new HeroDAO().getTotal();

		int last;
		// 假设总数是50，是能够被5整除的，那么最后一页的开始就是45
		if (0 == total % count)
			last = total - count;
		// 假设总数是51，不能够被5整除的，那么最后一页的开始就是50
		else
			last = total - total % count;

		request.setAttribute("next", next);
		request.setAttribute("pre", pre);
		request.setAttribute("last", last);

		List<Hero> heros = new HeroDAO().list(start, count);
		request.setAttribute("heros", heros);

		request.getRequestDispatcher("listHero.jsp").forward(request, response);

	}
}

代码行数较多，请点击查看


<%@ page language="java" contentType="text/html; charset=UTF-8"
	pageEncoding="UTF-8" import="java.util.*"%>

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>

<table align='center' border='1' cellspacing='0'>
	<tr>
		<td>id</td>
		<td>name</td>
		<td>hp</td>
		<td>damage</td>
		<td>edit</td>
		<td>delete</td>
	</tr>
	<c:forEach items="${heros}" var="hero" varStatus="st">
		<tr>
			<td>${hero.id}</td>
			<td>${hero.name}</td>
			<td>${hero.hp}</td>
			<td>${hero.damage}</td>
			<td><a href="editHero?id=${hero.id}">edit</a></td>
			<td><a href="deleteHero?id=${hero.id}">delete</a></td>
		</tr>
	</c:forEach>
	<tr>
		<td colspan="6" align="center">
			<a href="?start=0">[首  页]</a>
			<a href="?start=${pre}">[上一页]</a>
			<a href="?start=${next}">[下一页]</a>
			<a href="?start=${last}">[末  页]</a>
		</td>
	</tr>
</table>

步骤 7 :

边界处理

edit 顶折

纠问

上一页，下一页有一个问题，
如果在第一页点击上一页，就会看不到数据了，因为在第一页的时候，pre=-5,也就导致传递到serlvet的start=-5;
同样的在最后一页的时候，点击下一页，也有类似的问题。

解决办法是进行边界处理：

pre = pre < 0 ? 0 : pre;

如果pre是负数了，就使用0

next = next > last ? last : next;

如果next大于last，就使用last

代码行数较多，请点击查看

package servlet;

import java.io.IOException;
import java.util.List;

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

import bean.Hero;
import dao.HeroDAO;

public class HeroListServlet extends HttpServlet {

	protected void service(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		response.setContentType("text/html; charset=UTF-8");

		int start = 0;
		int count = 5;

		try {
			start = Integer.parseInt(request.getParameter("start"));
		} catch (NumberFormatException e) {
			// 当浏览器没有传参数start时
		}

		int next = start + count;
		int pre = start - count;

		int total = new HeroDAO().getTotal();

		int last;
		if (0 == total % count)
			last = total - count;
		else
			last = total - total % count;

		pre = pre < 0 ? 0 : pre;
		next = next > last ? last : next;

		request.setAttribute("next", next);
		request.setAttribute("pre", pre);
		request.setAttribute("last", last);

		List<Hero> heros = new HeroDAO().list(start, count);
		request.setAttribute("heros", heros);

		request.getRequestDispatcher("listHero.jsp").forward(request, response);

	}
}

步骤 8 :

套上Bootstrap

edit 顶折

纠问

代码行数较多，请点击查看

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8" import="java.util.*"%>
<!DOCTYPE html>
<script src="https://how2j.cn/study/js/jquery/2.0.0/jquery.min.js"></script>
<link href="https://how2j.cn/study/css/bootstrap/3.3.6/bootstrap.min.css" rel="stylesheet">
<script src="https://how2j.cn/study/js/bootstrap/3.3.6/bootstrap.min.js"></script>
    
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>

<script>
$(function(){
	$("a").addClass("btn btn-default btn-xs");
	
});

</script> 
<table style="width:500px; margin:44px auto" class="table table-striped table-bordered table-hover  table-condensed" align='center' border='1' cellspacing='0'>
    <tr>
        <td>id</td>
        <td>name</td>
        <td>hp</td>
        <td>damage</td>
        <td>edit</td>
        <td>delete</td>
    </tr>
    <c:forEach items="${heros}" var="hero" varStatus="st">
        <tr>
            <td>${hero.id}</td>
            <td>${hero.name}</td>
            <td>${hero.hp}</td>
            <td>${hero.damage}</td>
            <td><a href="editHero?id=${hero.id}">编辑</a></td>
            <td><a href="deleteHero?id=${hero.id}">删除</a></td>
        </tr>
    </c:forEach>

</table>
		<nav>
		  <ul class="pager">

            <li><a href="?start=0">首  页</a></li>
            <li><a href="?start=${pre}">上一页</a></li>
            <li><a href="?start=${next}">下一页</a></li>
            <li><a href="?start=${last}">末  页</a></li>
		  </ul>            
        </nav>

MVC系列教材（二）- 结合Servlet和JSP 实现查询功能

MVC系列教材（四）- 使用Servlet 验证用户是否登陆

HOW2J公众号，关注后实时获知最新的教程和优惠活动，谢谢。

问答区域

2022-05-13 点击上下首尾页没反应是怎么回事呢

lusir_666

关于 J2EE-MVC-分页的提问

点击分页无反应

package servlet;
 
import java.io.IOException;
import java.util.List;
 
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
 
import bean.Hero;
import dao.HeroDAO;
 
public class HeroListServlet extends HttpServlet {
 
    protected void service(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("text/html; charset=UTF-8");
         int start=0;
         int count=5;
         //start=Integer.parseInt(request.getParameter("start"));
        
        int next=start+count;
        int pre=start-count;
        int total=new HeroDAO().getTotal();
        int last;
        if(0==total%count){
        	last=total-count;
        }else{
        	last=total-total%count;
        }
        pre = pre < 0 ? 0 : pre;
        next = next > last ? last : next;
       /* StringBuffer sb = new StringBuffer();
        sb.append("<table align='center' border='1' cellspacing='0'>\r\n");
        sb.append("<tr><td>id</td><td>name</td><td>hp</td><td>damage</td><td>edit</td><td>delete</td></tr>\r\n");
 
        String trFormat = "<tr><td>%d</td><td>%s</td><td>%f</td><td>%d</td><td><a href='editHero?id=%d'>edit</a></td><td><a href='deleteHero?id=%d'>delete</a></td></tr>\r\n";
 
        for (Hero hero : heros) {
            String tr = String.format(trFormat, hero.getId(), hero.getName(), hero.getHp(), hero.getDamage(),hero.getId(),hero.getId());
             
            sb.append(tr);
        }
 
        sb.append("</table>");
 
        response.getWriter().write(sb.toString());*/
       
        request.setAttribute("last", last);
        request.setAttribute("pre", pre);
        request.setAttribute("next", next);
        List<Hero> heros = new HeroDAO().list(start,count);
        request.setAttribute("heros", heros);
        
        request.getRequestDispatcher("listHero.jsp").forward(request, response);
    }
}

1 个答案

2bconfident
答案时间：2022-07-06

因为第21行被屏蔽了，start的值取不到，一直是默认值0

回答已经提交成功，正在审核。请于我的回答处查看回答记录，谢谢

2021-09-08 处理尾页时，边界设置 next下一页有bug，用next>total判断更理想

Nihili

关于 J2EE-MVC-分页的提问

处理尾页时，边界设置 next下一页有bug，用next>total判断更理想

回答已经提交成功，正在审核。请于我的回答处查看回答记录，谢谢

2021-04-07 优化一体性增加

2020-10-13 上面的边界处理可以不使用三目运算符,使用Math类中的max()和min()函数

2020-05-31 点上一页或下一页的时候，a标签

提问太多，页面渲染太慢，为了加快渲染速度，本页最多只显示几条提问。还有 21 条以前的提问，请点击查看

提问之前请登陆

提问已经提交成功，正在审核。请于我的提问处查看提问记录，谢谢

关于 J2EE-MVC-分页的提问

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