MVC-结合Servlet和JSP实现分页功能

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

首先准备 DAO

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);

4000
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;
}

}

只显示5条数据

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

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);

}
}

下一页

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

<a href="?start=${next}">[下一页]</a>

start=${next} 从服务器传递过来的next值

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);

}
}

<%@ 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>

上一页

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

<a href="?start=${pre}">[上一页]</a>

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);

}
}

<%@ 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>

第一页

只需要修改listHero.jsp即可

增加 

<a href="?start=0">[首  页]</a>

因为首页的start永远都是0

<%@ 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>

最后一页

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

<a href="?start=${last}">[末 页]</a>

start=${last} 从服务器传递过来的last值

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);

}
}

<%@ 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>
<
dde4
/td>
</tr>
</table>

边界处理

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

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);

}
}

套上Bootstrap

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