通用分页(二)

通用分页核心思路：
将上一次查询请求再发一次，只是当前页变了而已。

首页 1 2 3 4 … 100 末页跳转

MySQL分页：select * from 表 limit 3,3

每页显示记录数　　　　自己设置
当前页　　　　　　　　来自前端
总页数　　　　　　　　总记录数%每页显示记录数==0?总记录数/每页显示记录数:总记录数/每页显示记录数+1
总记录数　　　　　　　数据库统计count()
每页起始记录数　　　　 =（当前页-1）*每页显示记录数+1

总共101条记录，每页显示10条
第一页： 1-10
第二页： 11-20
第三页： 21-30

每页结尾记录数　　　　 =当前页*每页显示记录数

1、通用的查询方法代码实现

导入jar包

commons-beanutils-1.8.0.jar
commons-logging.jar
jstl-1.2.jar
mysql-connector-java-5.1.44-bin.jar
standard-1.1.2.jar

连接数据库之前查看自己的用户名、密码、数据库名是否正确

isOracle：false
isSQLServer：false
isMysql：true
数据库连接(关闭)成功

#mysql
driver=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/db_book?useUnicode=true&characterEncoding=UTF-8
user=root
pwd=root

BookServlet.java

package com.huang.web;

import java.io.IOException;
import java.sql.SQLException;
import java.util.List;
import java.util.Map;

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

import com.huang.dao.BookDao;
import com.huang.entity.Book;
import com.huang.util.PageBean;

public class BookServlet extends HttpServlet {

    private static final long serialVersionUID = 2331970325281408992L;

    private BookDao bookDao=new BookDao();
    
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req, resp);
    }
    
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String bname=req.getParameter("bname");
//        bname=new String(bname.getBytes("ISO-8859-1"),"UTF-8");
        Book book=new Book();  
        book.setBname(bname);
        
//        Map<String, String[]> parameterMap=req.getParameterMap();
//        StringBuffer url=req.getRequestURL();  
        
        
        PageBean pagebean=new PageBean();
         try {
             pagebean.setRequest(req);
            List<Book> list=this.bookDao.list(book, pagebean);
            req.setAttribute("bookList", list);
            req.setAttribute("pageBean", pagebean);
            req.getRequestDispatcher("/bookList.jsp").forward(req, resp);
        } catch (InstantiationException | IllegalAccessException | SQLException e) {
            e.printStackTrace();
        }
    }
    
}

bookList.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
    <%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
     <%@taglib uri="/huang" prefix="z"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
<h2>小说目录</h2>
    <br>
    <form action="${pageContext.request.contextPath}/bookServlet.action"
        method="post">
        书名：<input type="text" name="bname"> <input type="submit"
            value="确定">
            <!-- <input type="hidden" name="pagination" value="false">
            <input type="hidden" name="rows" value="20"> -->
    </form>
    <table border="1" width="100%">
        <tr>
            <td>编号</td>
            <td>名称</td>
            <td>价格</td>
        </tr>
        <c:forEach items="${bookList }" var="b">
            <tr>
                <td>${b.bid }</td>
                <td>${b.bname }</td>
                <td>${b.price }</td>
            </tr>
        </c:forEach>
    </table>

    <z:page pageBean="${pageBean }"></z:page>
    
</body>
</html>

PageBean.java

package com.huang.util;

import java.util.HashMap;
import java.util.Map;

import javax.servlet.http.HttpServletRequest;

public class PageBean {

    private int page = 1;// 页码

    private int rows = 10;// 页大小

    private int total = 0;// 总记录数

    private boolean pagination = true;// 是否分页
    
    private Map<String, String[]> paMap=new HashMap<>();
    private String url;
    
    public void setRequest(HttpServletRequest req) {
        
        //保存上一次请求所携带的参数
        this.setPaMap(req.getParameterMap());
        this.setUrl(req.getRequestURI().toString());
//        在jsp页面来控制是否分页
        this.setPagination(req.getParameter("pagination"));
//        在jsp页面 控制一页展示多少条
        this.setRows(req.getParameter("rows"));
        this.setPage(req.getParameter("page"));
    }
    
    
    public void setPage(String page) {
        this.page=StringUtils.isNotBlank(page) ? Integer.valueOf(page) : this.page;
        
    }


    public void setPagination(String pagination) {
        this.pagination=StringUtils.isNotBlank(pagination) ? !"false".equals(pagination) : this.pagination;
    }

    public void setRows(String rows) {
        this.rows=StringUtils.isNotBlank(rows) ? Integer.valueOf(rows) : this.rows;
    }

    public Map<String, String[]> getPaMap() {
        return paMap;
    }

    public void setPaMap(Map<String, String[]> paMap) {
        this.paMap = paMap;
    }

    public String getUrl() {
        return url;
    }

    public void setUrl(String url) {
        this.url = url;
    }

    public PageBean() {
        super();
    }

    public int getPage() {
        return page;
    }

    public void setPage(int page) {
        this.page = page;
    }

    public int getRows() {
        return rows;
    }

    public void setRows(int rows) {
        this.rows = rows;
    }

    public int getTotal() {
        return total;
    }

    public void setTotal(int total) {
        this.total = total;
    }

    public void setTotal(String total) {
        this.total = Integer.parseInt(total);
    }

    public boolean isPagination() {
        return pagination;
    }

    public void setPagination(boolean pagination) {
        this.pagination = pagination;
    }

    /**
     * 获得起始记录的下标
     * 
     * @return
     */
    public int getStartIndex() {
        return (this.page - 1) * this.rows;
    }

    @Override
    public String toString() {
        return "PageBean [page=" + page + ", rows=" + rows + ", total=" + total + ", pagination=" + pagination + "]";
    }

    /**
     * 获取最大的页码数
     * @return
     */
    public int getMaxpage() {
        return this.total % this.rows==0 ?  this.total/this.rows :  this.total/this.rows+1;
    }
    
    /**
     * 获取下一页
     * @return
     */
    public int getNextpage() {
        return this.page< this.getMaxpage() ? this.page+1 : this.page;
    }
    
    /**
     * 获取上一页
     */
    public int getPreviousPage() {
        return this.page > 1 ? this.page-1 : this.page;
    }
    
}

Web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1">
  <display-name>T226_pagebean</display-name>
  <filter>
          <filter-name>encodingFiter</filter-name>
          <filter-class>com.huang.util.EncodingFiter</filter-class>
  </filter>
  
  <filter-mapping>
      <filter-name>encodingFiter</filter-name>
      <servlet-name> *.action</servlet-name>
  </filter-mapping>
  
  
  <servlet>
          <servlet-name>bookServlet</servlet-name>
          <servlet-class>com.huang.web.BookServlet</servlet-class>
  </servlet>
  <servlet-mapping>
      <servlet-name>bookServlet</servlet-name>
      <url-pattern>/bookServlet.action</url-pattern>
  </servlet-mapping>
</web-app>

z.tld

<?xml version="1.0" encoding="UTF-8" ?>

<taglib xmlns="http://java.sun.com/xml/ns/j2ee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-jsptaglibrary_2_0.xsd"
    version="2.0">
    
  <description>huang 1.1 core library</description>
  <display-name>huang core</display-name>
  <tlib-version>1.1</tlib-version>
  <short-name>c</short-name>
 <uri>/huang</uri>
    
    <tag>
         <!--库中的标签（类似c:set c:out的定义）-->
        <name>page</name>
        <!-- 是标签运行具体代码，也就是助手类，下面填写的是助手类的全路径名 -->
        <tag-class>com.huang.tag.PageTag</tag-class>
        <body-content>JSP</body-content>
        <attribute>
        <!-- 该标签的属性 -->
        <name>pageBean</name>
        <!-- 该属性是否必填 -->
        <required>true</required>
        <!-- 是否支持表达式 -->
        <rtexprvalue>true</rtexprvalue>
        </attribute>
    </tag> 
      
      
      
</taglib>

PageTag.java

package com.huang.tag;

import java.io.IOException;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.tagext.BodyTagSupport;

import com.huang.util.PageBean;

public class PageTag extends BodyTagSupport {

    private static final long serialVersionUID = -7819663757698266331L;

    private PageBean pageBean;

    public PageBean getPageBean() {
        return pageBean;
    }

    public void setPageBean(PageBean pageBean) {
        this.pageBean = pageBean;
    }
    
    @Override
    public int doStartTag() throws JspException {
        JspWriter out=pageContext.getOut();
        try {
            out.print(toHTML());
        } catch (IOException e) {
            e.printStackTrace();
        }
        return super.doStartTag();
    }

    private String toHTML() {
        StringBuilder sb=new StringBuilder();
//        拼接下一次发送请求所要提交的隐藏的form表单
        sb.append("<form id='pageBeanForm' action='"+pageBean.getUrl()+"' method='post'>");
        sb.append("<input type='hidden' name='page'>");
        
        Map<String, String[]> paMap=pageBean.getPaMap();
        if(paMap!=null&&paMap.size()>0) {
            Set<Entry<String, String[]>> entrySet=paMap.entrySet();
            for (Entry<String, String[]> entry : entrySet) {
//                上一次请求可能携带页码name=page的参数，但是该参数在前面已经单独赋值
//                为什么要单独赋值呢？因为上一次请求是第一页的数据，下一次可能是第二页，
//                因为这前后请求page对应的值是不一样的，需要单独赋值
                if("page".equals(entry.getKey())) {
                    for (String val : entry.getValue()) {
                        sb.append("<input type='hidden' name='"+entry.getKey()+"' value='"+val+"'>");
                    }
                }
            }
        }
        sb.append("</form>");
        
//        拼接分页条
        sb.append("<div style='text-align: right; font-size: 12px;'>");
        sb.append("每页"+pageBean.getRows()+"条，共"+pageBean.getTotal()+"条，第"+pageBean.getPage()+"页，共"+pageBean.getMaxpage()+"页&nbsp;&nbsp;<a");
        sb.append(" href='javascript:gotoPage(1)'>首页</a>&nbsp;&nbsp;<a");
        sb.append(" href='javascript:gotoPage("+pageBean.getPreviousPage()+")'>上一页</a>&nbsp;&nbsp;<a");
        sb.append("href='javascript:gotoPage("+pageBean.getNextpage()+")'>下一页</a>&nbsp;&nbsp;<a");
        sb.append("href='javascript:gotoPage("+pageBean.getMaxpage()+")'>尾页</a>&nbsp;&nbsp;<input type='text'");
        sb.append("id='skipPage'");
        sb.append("style='text-align: center; font-size: 12px; width: 50px;'>&nbsp;&nbsp;<a");
        sb.append("href='javascript:skipPage()'>Go</a>");
        sb.append("</div>");
        
//         拼接分页所需要的js代码
        sb.append("<script type='text/javascript'>");
        sb.append(" function gotoPage(page) {");
        sb.append("        document.getElementById('pageBeanForm').page.value = page;");
        sb.append("        document.getElementById('pageBeanForm').submit();");
        sb.append(" }");
        sb.append(" function skipPage() {");
        sb.append("            var page = document.getElementById('skipPage').value;");
        sb.append("            if(!page || isNaN(page) || parseInt(page)<1 || parseInt(page)>maxPage){");
        sb.append("                alert('请输入1~N的数字');");
        sb.append("             return;");
        sb.append("             }");
        sb.append("            gotoPage(page);");
        sb.append("     }");
        sb.append("</script>");
        
        
        return sb.toString();
    }
    
}

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