笔记：分页

笔记：分页

核心工具类：PageBean

PageBean核心三件套，index：索引页；size：每一页的大小；totalCount：总共多少条记录。

package com.bjsxt.util;

import java.util.List;

/**
 * 分页的三个基本属性
 * 1.每页几条记录size  可以有默认值5
 * 2.当前页号  index    可以有默认值1
 * 3.记录总数totalCount：不可能有默认值，需要查询数据库获取真正的记录总数
 * 
 * 4.一共多少页 ：totalPageCount=totalCount/size+1    23/5
 * 		5  30  31 32 33 34 35  
 * 5.上一页    index-1  当前页1，上一页1
 * 6.下一页   index+1  当前页是最后一页  下一页：还是最后一页
 * 
 * 扩展
 * 分页Bean还可以放要查询的数据  protected List<T> list;
 * 分页Bean还可以放页码列表     [1]  2  3  4  5   private int[] numbers;
 * 
 * @author Administrator
 *
 * @param <T>
 */
public class PageBean<T> {
	private int size = 5;//每页显示记录  //
	private int index = 1;// 当前页号      
	private int totalCount = 0;// 记录总数      ok
	
	private int totalPageCount = 1;// 总页数   ok
	
	
	
	private int[] numbers;//展示页数集合  //ok
	protected List<T> list;//要显示到页面的数据集  

	/**
	 * 得到开始记录
	 * @return
	 */
	public int getStartRow() {

		return (index - 1) * size;
	}

	/**
	 * 得到结束记录
	 * @return
	 */
	public int getEndRow() {
		
		return index * size;
	}

	/**
	 * @return Returns the size.
	 */
	public int getSize() {		
		return size;
	}

	/**
	 * @param size
	 * The size to set.
	 */
	public void setSize(int size) {
		if (size > 0) {
			this.size = size;
		}
	}
	/**
	 * @return Returns the currentPageNo.
	 */
	public int getIndex() {
		if (totalPageCount == 0) {
			
			return 0;
		}
		
		return index;
	}

	/**
	 * @param currentPageNo
	 * The currentPageNo to set.
	 */
	public void setIndex(int index) {
		if (index > 0) {
			this.index = index;
		}
	}

	/**
	 * @return Returns the totalCount.
	 */
	public int getTotalCount() {
		return totalCount;
	}

	/**
	 * @param totalCount
	 *  The totalCount to set.
	 */
	public void setTotalCount(int totalCount) {
		if (totalCount >= 0) {
			this.totalCount = totalCount;
			setTotalPageCountByRs();//根据总记录数计算总页�?
		}
	}

	
	public int getTotalPageCount() {
		return this.totalPageCount;
	}

	/**
	 * 根据总记录数计算总页�?
	 * 5   
	 * 20    4
	 * 23    5
	 */
	private void setTotalPageCountByRs() {
		if (this.size > 0 && this.totalCount > 0 && this.totalCount % this.size == 0) {
			this.totalPageCount = this.totalCount / this.size;
		} else if (this.size > 0 && this.totalCount > 0 && this.totalCount % this.size > 0) {
			this.totalPageCount = (this.totalCount / this.size) + 1;
		} else {
			this.totalPageCount = 0;
		}
		setNumbers(totalPageCount);//获取展示页数集合
	}

	public int[] getNumbers() {
		return numbers;
	}
	
	/**
	 * 设置显示页数集合
	 * 
	 * 默认显示10个页码
	 * 41  42  43  44    [45 ]   46  47  48  49  50
	 * 
	 * 
	 *  [1] 2  3 4  5 6 7 8  9  10
	 *  
	 *  41  42  43  44    45    46  47  [48]  49  50
	 * @param totalPageCount
	 */
	public void setNumbers(int totalPageCount) {
		if(totalPageCount>0){
			//!.当前数组的长度
			int[] numbers = new int[totalPageCount>10?10:totalPageCount];//页面要显示的页数集合
			int k =0;
			//
			//1.总页数长度<10   1 2 3 4 ....   7
			//2.总页数长度>=10
			//     当前页<=6  1 2 3 4    10
			//     当前页>=总页数-5           ......12 13 14 15  
			//     其他                                5  6  7 8   9 当前页(10)  10  11 12  13
			for(int i = 0;i < totalPageCount;i++){
				//保证当前页为集合的中�?
				if((i>=index- (numbers.length/2+1) || i >= totalPageCount-numbers.length) && k<numbers.length){
					numbers[k] = i+1;
					k++;
				}else if(k>=numbers.length){
					break;
				}				
			}
			
			this.numbers = numbers;
		}
		
	}
	
	public void setNumbers(int[] numbers) {
		this.numbers = numbers;
	}

	public List<T> getList() {
		return list;
	}

	public void setList(List<T> list) {
		this.list = list;
	}


/*
	public static int getTotalPageCount(int iTotalRecordCount, int iPageSize) {
		if (iPageSize == 0) {
			return 0;
		} else {
			return (iTotalRecordCount % iPageSize) == 0 ? (iTotalRecordCount / iPageSize) : (iTotalRecordCount / iPageSize) + 1;
		}
	}*/
}

 

这里是一段JAVA代码分页的代码

package com.bjsxt.servlet;

import com.bjsxt.entity.Student;
import com.bjsxt.service.StudentService;
import com.bjsxt.service.impl.StudentServiceImpl;
import com.bjsxt.util.PageBean;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class ShowAllServlet extends HttpServlet {


    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        //解决post表单的中文乱码问题
        request.setCharacterEncoding("utf-8");

        //1.接收来自页面的请求页码、每页记录数、查询条件
        String sindex = request.getParameter("index");//null "aa"
        int index = 1;
        try {
            index = Integer.parseInt(sindex);
        } catch (NumberFormatException e) {
            e.printStackTrace();
        }
        String ssize = request.getParameter("size");//null "aa"
        int size = 5;
        try {
            size = Integer.parseInt(ssize);
        } catch (NumberFormatException e) {
            e.printStackTrace();
        }
        String name = request.getParameter("name");
        String sminScore = request.getParameter("minScore");
        double minScore = 0;
        try{
            if(sminScore != null){
                minScore = Double.parseDouble(sminScore);
            }
        }catch (NumberFormatException e){
            e.printStackTrace();
        }

        //2
        PageBean<Student> pageBean = new PageBean<Student>();
        pageBean.setIndex(index);
        pageBean.setSize(size);
        StudentService studentService = new StudentServiceImpl();
        // List <Student> stuList =studentService.findAll();
        studentService.find(pageBean,name,minScore);
        request.setAttribute("pageBean", pageBean);//!!!!!!!
        request.setAttribute("name",name);
        request.setAttribute("minScore",sminScore);//
        //3com.bjsxt

        request.getRequestDispatcher("/jsp/showAll.jsp").forward(request, response);
    }


    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        this.doGet(request, response);
    }

}

接下来的一段HTML代码。

<%--
  Created by IntelliJ IDEA.
  User: Administrator
  Date: 2019/05/29
  Time: 10:19
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
<head>
    <title>Title</title>

    <base href="http://localhost:8080/stumgr/">
    <script type="text/javascript">
        function changeSize(size){
            change(1,size);
        }

        function change (index,size) {
            document.form1.index.value=index;
            document.form1.size.value=size;
            document.form1.submit();
            // location.href="servlet/ShowAllServlet?index="+index+"&size="+size;
        }
    </script>

</head>
<body>
<hr>
<form action="servlet/ShowAllServlet" method="post" id="form1" name="form1">
    <table align="center">
        <tr>
            <td>姓名</td>
            <td>
                <input type="text" name="name" value="${name}">
                <input type="hidden" name="index" value="">
                <input type="hidden" name="size" value="">
            </td>
            <td>分数>=</td>
            <td><input type="text" name="minScore" value="${minScore}"></td>
            <td><input type="submit" value="提交"></td>
        </tr>
    </table>
</form>
<hr>

<!-- 显示所有学生   /stumanager/    -->
<table align="center" border="1" width="60%">
    <tr>
        <th>学生 编号</th>
        <th>学生姓名</th>
        <th>学生年龄</th>
        <th>学生成绩</th>
        <th>vs.index</th>
        <th>更新操作</th>
        <th>删除操作</th>
    </tr>
    <c:forEach items="${studentPageBean.list}" var="stu" varStatus="vs">
        <tr>
            <td>${stu.id }</td>
            <td>${stu.name }</td>
            <td>${stu.age }</td>
            <td>${stu.score }</td>
            <td>${vs.index }</td>
            <td><a href="/stumanager/servlet/StudentServlet?operate=preupdate&sid=${stu.id}">更新</a></td>
            <td><a href="/stumanager/servlet/StudentServlet?operate=delete&sid=${stu.id}">删除</a></td>
        </tr>
    </c:forEach>
    <tr>
        <td colspan="11">
            <c:if test="${studentPageBean.index==1}">
                上一页
            </c:if>
            <c:if test="${studentPageBean.index!=1}">
                <%--<a href="servlet/ShowAllServlet?index=${studentPageBean.index-1}">上一页</a>--%>
                <a href="javascript:change(${studentPageBean.index-1},${studentPageBean.size})">上一页</a>
            </c:if>


            <c:if test="${studentPageBean.index==studentPageBean.totalPageCount}">
                下一页
            </c:if>
            <c:if test="${studentPageBean.index!=studentPageBean.totalPageCount}">
                <%--<a href="servlet/ShowAllServlet?index=${studentPageBean.index+1}">下一页</a>--%>
                <a href="javascript:change(${studentPageBean.index+1},${studentPageBean.size})">下一页</a>
            </c:if>


            <c:forEach items="${studentPageBean.numbers}" var="i">
                <c:if test="${studentPageBean.index==i}">
                    <%--[<a href="servlet/ShowAllServlet?index=${i}">${i}</a>]--%>
                    [<a href="javascript:change(${i},${studentPageBean.size})">${i}</a>]
                </c:if>
                <c:if test="${studentPageBean.index!=i}">
                    <a href="javascript:change(${i},${studentPageBean.size})">${i}</a>
                </c:if>
            </c:forEach>

            <select onchange="changeSize(this.value)">
                <c:forEach begin="5" end="25" step="5" var="i">
                    <c:if test="${studentPageBean.size==i}">
                        <option value="${i}" selected>${i}</option>
                    </c:if>
                    <c:if test="${studentPageBean.size!=i}">
                        <option value="${i}">${i}</option>
                    </c:if>
                </c:forEach>
            </select>

            一共有${studentPageBean.totalPageCount}页
            共有${studentPageBean.totalCount}条记录
        </td>
    </tr>

</table>
</body>
</html>