前言

今天博主所讲解一个网站或者app常见的分页功能，看完这篇会有想象不到的收获。试想一下我每一个类别都需要写一套分页或者修改吗？这样会造成不必要的麻烦和代码的冗余。

博主也是对分页进行了一个封装，避免了代码的冗余，在通用分页详解【上】也进行了详细介绍，本篇会对其进行优化讲解。接下来将让博主带你们去如何运用在网页中😊

一、通用分页的核心思想

将上一次查询请求再发一次，只不过页码变了。

二、PageBean的分页要素及优化

page—当前页
rows—条目数
url—处理查询的url
Map<String, String[]> parameterMap----上一次查询的条件
pagination—是否分页—视图层传递过来
total—总记录数—后台查出来

也新增了获取最大页码、上一页、下一页和初始化数据的方法

三、SQL的通用

在通用分页详解【上】中没有提到，这里也说明一下

1.获取总记录数

// 获取总共行数private String getCountSql(String sql) {return "select count(1) from (" + sql + ") t";}

2.获取分页语句

// 获取分页语句private String getPageSql(String sql, PageBean pageBean) {return sql += " limit  " + pageBean.getStartIndex() + "," + pageBean.getRows();}

四、PageTag的核心逻辑见解

五、运行流程

案例运用

注意：

博主是利用bootstrap官网中的组件写的jsp

贴上地址：警告框（Alert） · Bootstrap v4 中文文档 v4.6 | Bootstrap 中文网

注意博主的jsp界面运行的时候要联网的哦！不然样式显示不出来

1.pageBean优化

package com.ctb.utils;import java.util.Map;import javax.servlet.http.HttpServletRequest;/*** 分页工具类* * @author biao**/
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 String url;// 保留上一次发送的请求地址private Map<String, String[]> maps;// 保留上一次发送的请求携带的参数// 最大页public int maxPage() {return this.total % this.rows == 0 ? this.total / this.rows : this.total / this.rows + 1;}// 下一页public int nextPage() {return this.page < this.maxPage() ? this.page + 1 : this.page;}// 上一页public int prevPage() {return this.page > 1 ? this.page - 1 : this.page;}//初始化数据public void setRequest(HttpServletRequest req) {//初始化默认查询第几页的数据this.setPage(req.getParameter("page"));this.setRows(req.getParameter("rows"));this.setPagination(req.getParameter("pagination"));//保留上一次的URLthis.setUrl(req.getRequestURL().toString());//保留携带的参数this.setmaps(req.getParameterMap());}//初始化默认是否分页public void setPagination(String pagination) {if (StringUtils.isNotBlank(pagination))this.setPagination(!"false".equals(pagination));}//初始化默认查询的条数public void setRows(String rows) {if (StringUtils.isNotBlank(rows))this.setRows(Integer.valueOf(rows));}//初始化默认查询第几页的数据public void setPage(String page) {if (StringUtils.isNotBlank(page))this.setPage(Integer.valueOf(page));}public String getUrl() {return url;}public void setUrl(String url) {this.url = url;}public Map<String, String[]> getmaps() {return maps;}public void setmaps(Map<String, String[]> maps) {this.maps = maps;}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;}@Overridepublic String toString() {return "PageBean [page=" + page + ", rows=" + rows + ", total=" + total + ", pagination=" + pagination + "]";}}

2.tld文件

<!DOCTYPE taglibPUBLIC "-//Sun Microsystems, Inc.//DTD JSP Tag Library 1.2//EN""http://java.sun.com/dtd/web-jsptaglibrary_1_2.dtd">
<!-- 标签库描述符 -->
<taglib xmlns="http://java.sun.com/JSP/TagLibraryDescriptor"><tlib-version>1.0</tlib-version><jsp-version>1.2</jsp-version><short-name>Simple Tags</short-name><uri>/com.ctb</uri><tag><name>page</name><tag-class>com.ctb.tag.PageTag</tag-class><body-content>JSP</body-content><attribute><name>pageBean</name><required>true</required><rtexprvalue>true</rtexprvalue></attribute></tag></taglib>

3.分页标签助手类

package com.ctb.tag;import java.io.IOException;
import java.util.Map;
import java.util.Set;import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.tagext.BodyTagSupport;import com.ctb.utils.PageBean;/*** page助手类* @author biao* */
public class PageTag extends BodyTagSupport {private PageBean pageBean;public PageBean getPageBean() {return pageBean;}public void setPageBean(PageBean pageBean) {this.pageBean = pageBean;}@Overridepublic int doStartTag() throws JspException {JspWriter out = pageContext.getOut();try {out.print(toHTML());} catch (IOException e) {e.printStackTrace();}return SKIP_BODY;}private String toHTML() {StringBuilder sb = new StringBuilder();//        这里拼接的是一个上一次发送的请求以及携带的参数，唯一改变的就是页码sb.append("<form id='pageBeanForm' action='"+pageBean.getUrl()+"' method='post'>");
//        sb.append("<input type='hidden' name='methodName' value='list'>");sb.append("<input type='hidden' name='page'>");
//        重要设置拼接操作，将上一次请求参数携带到下一次Map<String, String[]> paMap = pageBean.getmaps();if(paMap !=null && paMap.size()>0){Set<Map.Entry<String, String[]>> entrySet = paMap.entrySet();for (Map.Entry<String, String[]> entry : entrySet) {for (String val : entry.getValue()) {if(!"page".equals(entry.getKey())){sb.append("<input type='hidden' name='"+entry.getKey()+"' value='"+val+"'>");}}}}sb.append("</form>");//获取当前页int page = pageBean.getPage();//获取最大页int max = pageBean.maxPage();//获取前面展示页数，如果当前页数大于4的话那么前面就显示4页，否则就当前页数-1int before = page > 4 ? 4 : page-1;//获取后面部分展示页，默认的10-当前占用的自身-前面显示数int after = 10 - 1 - before;//判断当前页码和后面的页码是否大于最大页数after = page+after > max ? max-page : after;//用来控制上一页的点击按钮特效的：如果是第一页就禁用首页和上一页--disabledboolean startFlag = page == 1;//同上--如果是最后一页就禁用尾页和下一页boolean endFlag = max == page;// 拼接分页条sb.append("<ul class='pagination'>");sb.append("<li class='page-item "+(startFlag ? "disabled" : "")+"'><a class='page-link' href='javascript:gotoPage(1)'>首页</a></li>");sb.append("<li class='page-item "+(startFlag ? "disabled" : "")+"'><a class='page-link' href='javascript:gotoPage("+pageBean.prevPage()+")'>&lt;</a></li>");//当前页的前4页for (int i = before; i > 0 ; i--) {sb.append("<li class='page-item'><a class='page-link' href='javascript:gotoPage("+(page-i)+")'>"+(page-i)+"</a></li>");}sb.append("<li class='page-item active'><a class='page-link' href='javascript:gotoPage("+pageBean.getPage()+")'>"+pageBean.getPage()+"</a></li>");//当前页的后5页for (int i = 1; i <= after; i++) {sb.append("<li class='page-item'><a class='page-link' href='javascript:gotoPage("+(page+i)+")'>"+(page+i)+"</a></li>");}sb.append("<li class='page-item "+(endFlag ? "disabled" : "")+"'><a class='page-link' href='javascript:gotoPage("+pageBean.nextPage()+")'>&gt;</a></li>");sb.append("<li class='page-item "+(endFlag ? "disabled" : "")+"'><a class='page-link' href='javascript:gotoPage("+pageBean.maxPage()+")'>尾页</a></li>");sb.append("<li class='page-item go-input'><b>到第</b><input class='page-link' type='text' id='skipPage' name='' /><b>页</b></li>");sb.append("<li class='page-item go'><a class='page-link' href='javascript:skipPage()'>确定</a></li>");sb.append("<li class='page-item'><b>共"+pageBean.getTotal()+"条</b></li>");sb.append("</ul>");//        拼接分页的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) > "+max+") {");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();}
}

4.Servlet层

package com.ctb.servlet;import java.io.IOException;
import java.util.List;
import java.util.Map;import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;import com.ctb.dao.BookDao;
import com.ctb.entity.Book;
import com.ctb.utils.PageBean;/*** 数据显示以及分页模糊查询* @author biao**/
@WebServlet("/book.action")
public class BookServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {this.doPost(req, resp);}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {PageBean pageBean = new PageBean();//初始化pageBean.setRequest(req);//实例化bookdao类BookDao bookDao = new BookDao();//实例化实体--书Book book = new Book();//获取模糊查询内容中的关键字book.setBname(req.getParameter("bname"));try {//调用分页模糊查询的方法List<Book> books = bookDao.list2(book, pageBean);//将数据保存到request作用域中req.setAttribute("books", books);} catch (Exception e) {e.printStackTrace();}//将数据保存在request作用域中req.setAttribute("pageBean", pageBean);//跳转req.getRequestDispatcher("booklist.jsp").forward(req, resp);}
}

5.jsp页面

<%@ 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="/com.ctb" prefix="t" %>
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<linkhref="https://cdn.bootcdn.net/ajax/libs/twitter-bootstrap/4.5.0/css/bootstrap.css"rel="stylesheet">
<scriptsrc="https://cdn.bootcdn.net/ajax/libs/twitter-bootstrap/4.5.0/js/bootstrap.js"></script>
<title>书籍列表</title>
<style type="text/css">
.page-item input {padding: 0;width: 40px;height: 100%;text-align: center;margin: 0 6px;
}.page-item input, .page-item b {line-height: 38px;float: left;font-weight: 400;
}.page-item.go-input {margin: 0 10px;
}
</style>
</head>
<body><form class="form-inline"action="${pageContext.request.contextPath }/book.action" method="post"><div class="form-group mb-2"><input type="text" class="form-control-plaintext" name="bname"placeholder="请输入书籍名称"></div><button type="submit" class="btn btn-primary mb-2">查询</button></form><table class="table table-striped"><thead><tr><th scope="col">书籍ID</th><th scope="col">书籍名</th><th scope="col">价格</th></tr></thead><tbody><c:forEach items="${books }" var="b"><tr><td>${b.bid }</td><td>${b.bname }</td><td>${b.price }</td></tr></c:forEach>	</tbody></table><t:page pageBean="${pageBean }"></t:page></body>
</html>