java分页的写法

第一步：

      首先需要到如各部分岁对应的包，例如数据库驱动的包，实体类的包，c3p0的包，以及c3p0的配置文件

      创建数据库，创建数据库所对应的一个实体类，例如：student类，里边包含私有的属性，及set和get方法

第二步：

    创建另一个关于分页的实体类，里边只包含5项，如下可见

package com.qf.javabean;

import java.util.List;

public class PagStudent<T> {
    private int currentpage;//当前页
    private int pagsize;//每页的数据量
    private int totalpage;//总页数
    private int totalcount;//总数据量
    private List<T> list;

	public synchronized int getCurrentpage() {
		return currentpage;
	}
	public synchronized void setCurrentpage(int currentpage) {
		this.currentpage = currentpage;
	}
	public synchronized int getPagsize() {
		return pagsize;
	}
	public synchronized void setPagsize(int pagsize) {
		this.pagsize = pagsize;
	}
	public synchronized int getTotalpage() {
		return (int)Math.ceil(totalcount*1.0/pagsize);
	}
     //记住需要删除一个方法，是算出来的，不是被设置的
	public synchronized int getTotalcount() {
		return totalcount;
	}
	public synchronized void setTotalcount(int totalcount) {
		this.totalcount = totalcount;
	}
	public synchronized List<T> getList() {
		return list;
	}
	public synchronized void setList(List<T> list) {
		this.list = list;
	}
	public PagStudent(int currentpage, int pagsize, int totalcount, List<T> list) {
		super();
		this.currentpage = currentpage;
		this.pagsize = pagsize;
		this.totalcount = totalcount;
		this.list = list;
	}
	public PagStudent() {
		super();
	}  
}

第三步：创建JSP页面

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<%
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 'StudentPaging.jsp' starting page</title>
    <meta charset="UTF-8">
	<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>
<!-- Student [id=1, name=张无惧, sex=null, age=0, password=null, qq=null, phone=null, major=null, grade=null] -->
  <body>
      <table border="1px" align="center" width="90%" cellspacing="0px">
      <tr>
      <th colspan="9"><h1>学员信息展示平台</h1></th>
      </tr>
        <tr>
             <th >学员编号</th>
             <th >姓名</th>
             <th >性别</th>
             <th >年龄</th>
             <th >密码</th>
             <th >QQ号</th>
             <th >手机号</th>
             <th >专业</th>
             <th >班级</th>
          </tr>
        <c:forEach items="${page.list }" var="it">
 <!--      属性导航 -->
           <tr>
             <td>${it.id }</td>
             <td>${it.name }</td>
             <td>${it.sex }</td>
             <td>${it.age }</td>
             <td>${it.password }</td>
             <td>${it.qq }</td>
             <td>${it.phone }</td>
             <td>${it.major }</td>
             <td>${it.grade }</td>         
           </tr>
      </c:forEach>   
      </table>
   <center>     
           <c:if test="${page.currentpage != 1 }">           	
           	  <a href="${pageContext.request.contextPath }/servlet/PagStudent?currentpage=${page.currentpage-1 }">[上一页]</a>           	
           </c:if>
       
           <!-- 表里中间位置   ${page.totalpage }--> 
            <c:forEach var="i" begin="1" end="${page.totalpage}" step="1">
             <%--  <c:forEach var="i" begin="${i }" end="${(i+8)>page.totalpage?page.totalpage:(i+8) }" step="1">   --%>
              <!--  当页数过多时，显示部分页数，随着页数的增大，隐藏前边页数，显示后边的页数 -->
               <c:if test="${page.currentpage == i }">
                   ${i }    
               </c:if>          
               <c:if test="${page.currentpage !=i }">
                  <a href="${pageContext.request.contextPath }/servlet/PagStudent?currentpage=${i }">${i }</a>
               </c:if> 
               </c:forEach>

          <c:if test="${page.totalpage != page.currentpage }">
           	  <a href="${pageContext.request.contextPath }/servlet/PagStudent?currentpage=${page.currentpage+1 }">[下一页]</a>
           </c:if>
           
           <br/>
           
                       当前${page.currentpage }/总共${page.totalpage }
      </center>
  </body>
</html>

第四步：创建servlet，里边包含（获取数据，调用逻辑，转发或重定向）

package com.qf.web;

import java.io.IOException;
import java.sql.SQLException;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.qf.javabean.Student;
import com.qf.service.StudentService;

public class PagStudent extends HttpServlet {
	private static final long serialVersionUID = 1L;

	public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		request.setCharacterEncoding("UTF-8");
		int currentpage = Integer.parseInt(request.getParameter("currentpage"));
		// 当第一次访问的时候应该从请求中传递一个页数
		// System.out.println(currentpage+"获取了数据");
		int pagesize = 5;// 控制每页显示的数据量
		try {
			com.qf.javabean.PagStudent<Student> pagStudent = new StudentService().findPage(currentpage, pagesize);
			request.getSession().setAttribute("page", pagStudent);
			System.out.println("我又回到了这个界面");
			System.out.println(pagStudent.toString());
			List<Student> list = pagStudent.getList();
			for (Student student : list) {
				System.out.println(student);
			}
			System.out.println(pagStudent.getPagsize());
			System.out.println(pagStudent.getList());
			response.sendRedirect(request.getContextPath() + "/StudentPaging.jsp");

		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
			request.getSession().setAttribute("msg", "分页展示数据错误");
			response.sendRedirect(request.getContextPath() + "/msg.jsp");
		}
	}
	public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		doGet(request, response);
	}
}

第五步：创建一个Servlet包，里边包含两个方法

package com.qf.service;

import java.sql.SQLException;
import java.util.List;
import com.qf.dao.PagDao;
import com.qf.javabean.PagStudent;
import com.qf.javabean.Student;
public class StudentService {

	public com.qf.javabean.PagStudent<Student> findPage(int currentpage, int pagesize) throws SQLException {
		PagDao dao= new PagDao();
		int totalcount= dao.findcount();//调用两个方法
	    List<Student> list=dao.findListPage(currentpage,pagesize);	//
		return new PagStudent<Student>(currentpage,pagesize,totalcount,list);
	}

}

第六步：连接数据库的Dao，里边执行SQL语句

package com.qf.dao;

import java.sql.Connection;
import java.sql.SQLException;
import java.util.List;
import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.BeanListHandler;
import org.apache.commons.dbutils.handlers.ScalarHandler;
import com.qf.javabean.Student;
import com.qf.utils.DataSourceUtiles;
public class PagDao {

	public int findcount() throws SQLException {
		// TODO Auto-generated method stub
		QueryRunner runner= new QueryRunner();
		String sql = "select count(*) from student;";
		Connection conn = DataSourceUtiles.getConnection();
		Object query = runner.query(conn,sql,new ScalarHandler());
		//DataSourceUtiles.close(conn);
		System.out.println("数据库可以走到聚合函数");
		return ((Long)query).intValue();//此处的query为long型，转化
	}

	public List<Student> findListPage(int currentpage, int pagesize) throws SQLException {
		// TODO Auto-generated method stub
		QueryRunner runner= new QueryRunner();
		String sql="select *from student limit ?,?;";
		Connection connection = DataSourceUtiles.getConnection();
		
		List<Student> list = runner.query(connection, sql, new BeanListHandler<Student>(Student.class), (currentpage-1)*pagesize,pagesize);
		System.out.println("这一个数据也可以走到的");
		for (Student student : list) {
			System.out.println(student);
		}
		//DataSourceUtiles.close(connection);
		return list;
	}

}