前言

小编在前面的博客中已把通用分页细讲解了，今天我们来整理一下前两篇博客中的通用分页，可能很多细节方面在此不会重复啰嗦，所以需要的朋友欢迎去查阅
链接: 通用分页（一）.与通用分页（二）.
本章节重要的是梳理业务逻辑以及全部代码合在一起

通用分页的思路及步骤

准备工作的文字说明前面的通用分页中已说明，去查阅就好，本次直接从代码着手

最终实现的效果

所需要的所有类结构以及架包

代码实践

使用的数据库表

1.实体类Book.java

package com.xiaoqing.entity;public class Book {private int bid;private String bname;private float price;@Overridepublic String toString() {return "Book [bid=" + bid + ", bname=" + bname + ", price=" + price + "]";}public int getBid() {return bid;}public void setBid(int bid) {this.bid = bid;}public String getBname() {return bname;}public void setBname(String bname) {this.bname = bname;}public float getPrice() {return price;}public void setPrice(float price) {this.price = price;}public Book() {}public Book(int bid, String bname, float price) {this.bid = bid;this.bname = bname;this.price = price;}
}

2.共性部分BaseDao.java

package com.xiaoqing.dao;import java.lang.reflect.Field;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;import com.xiaoqing.util.DBAccess;
import com.xiaoqing.util.PageBean;public class BaseDao<T> {/*public List<T> executeQuery(String sql,Class clz,PageBean pageBean) throws SQLException, InstantiationException, IllegalAccessException{List<T> list=new ArrayList<T>();Connection con=DBAccess.getConnection();PreparedStatement ps = null;ResultSet rs = null;if(pageBean!=null&&!pageBean.isPagination()) {//想要分页---->列表需求//查询出符合条件的总记录数String countSql=getCountSql(sql);ps = con.prepareStatement(sql);rs = ps.executeQuery();if(rs.next()) {pageBean.setTotal(rs.getLong(1)+ "");}//查询出符合条件的结果集String pageSql=getPageSql(sql,pageBean);ps=con.prepareStatement(pageSql);rs=ps.executeQuery();System.out.println(ps);//展示想要看到的分页效果}else {//不想分页---->下拉框需求ps = con.prepareStatement(sql);rs = ps.executeQuery();System.out.println(ps);}T t;//为了节省内存，所以定义在while外面while(rs.next()) {//list.add(new k(rs.getInt("bid"), rs.getString("bname"), rs.getFloat("price")));*//*** Book b=new Book();* b.setBid(rs.getInt("bid"));* b.setBname(rs.getString("bname"));* b.setPrice(rs.getFloat("price"));* list.add(b);* * 实例化了一个对象* 给这一个空对象的每一个属性赋值* 将赋值完的对象添加到list集合中返回*//*t =(T)clz.newInstance();for (Field f : clz.getDeclaredFields()) {f.setAccessible(true);f.set(t, rs.getObject(f.getName()));}}DBAccess.close(con, ps, rs);return list;}*/
public List<T> executeQuery(String sql,Class clz,PageBean pageBean) throws SQLException, InstantiationException, IllegalAccessException{Connection con = DBAccess.getConnection();PreparedStatement pst = null;ResultSet rs = null;//判断是否分页if(pageBean!=null&&pageBean.isPagination()) {//想要分页的-----》列表需求//查询出符合条件的总记录数String countSql=getCountSql(sql);//重新执行countSqlpst=con.prepareStatement(countSql);rs=pst.executeQuery();if(rs.next()) {//设置总记录数pageBean.setTotal(rs.getLong(1)+ "");}//查询出符合条件的结果集String pageSql=getPageSql(sql,pageBean);pst=con.prepareStatement(pageSql);rs=pst.executeQuery();}else {//不想要分页的----》下拉框需求pst=con.prepareStatement(sql);rs=pst.executeQuery();}List<T> list=new ArrayList<T>();T t;//为了节省内存，所以定义在while外面while(rs.next()) {/*** 1.实例化一个book对象（该对象是空的，不是null）* 2.取book的所有属性，然后给其赋值* 	2.1 获取所有属性对象* 	2.2 给属性对象赋值* 3.赋完值的book对象装进list容器中*///反射实例化t =(T)clz.newInstance();//相当于Book b=new Book();//反射获取所以属性对象Field[] fields = clz.getDeclaredFields();//遍历for (Field field : fields) {//打开通道field.setAccessible(true);//给属性对象赋值field.set(t, rs.getObject(field.getName()));}//把对象增加到集合list.add(t);}DBAccess.close(con, pst, rs);return list;}public String getCountSql(String sql) {// TODO Auto-generated method stubreturn "select count(1) from ("+sql+") t";}/*** sql=select * from t_mvc_book where true and bname like '%圣墟%'；//原生sql* countSql=select count(1) from (select * from t_mvc_book where true and bname like '%圣墟%')* pageSql=select * from t_mvc_book where true and bname like '%圣墟%' limit 10,10;*/public String getPageSql(String sql,PageBean pageBean) {	return sql+" limit "+pageBean.getStartIndex()+","+pageBean.getRows();}	
}

3.写dao层（BookDao.java 继承BaseDao）

package com.xiaoqing.dao;import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;import com.xiaoqing.entity.Book;
import com.xiaoqing.util.DBAccess;
import com.xiaoqing.util.PageBean;
import com.xiaoqing.util.StringUtils;public class BookDao   extends  BaseDao<Book> {//通过反射改装后的通用查询方法public List<Book> list(Book book,PageBean pageBean) throws InstantiationException, IllegalAccessException, SQLException{String sql="select * from t_mvc_book where 1=1";String bname=book.getBname();if(StringUtils.isNotBlank(bname)) {sql+=" and bname like '%"+bname+"%'";}return super.executeQuery(sql, Book.class, pageBean);}
}

4.写分页工具类(pageBean.java)

package com.xiaoqing.util;import java.util.HashMap;
import java.util.Map;import javax.servlet.http.HttpServletRequest;/*** 分页工具类**/
public class PageBean {private int page = 1;// 当前页码private int rows = 10;// 页大小private int total = 0;//总记录数//上一次查询的urlprivate String url;//上一次查询所携带的查询条件private Map<String, String[]> parameterMap=new HashMap<String, String[]>();//对pagebean进行初始化public void setRequest(HttpServletRequest req) {//初始化jsp页面传递过来的当前页this.setPage(req.getParameter("page"));//初始化jsp页面传递过来的页大小this.setRows(req.getParameter("rows"));//初始化jsp页面 传递过来是否分页this.setPagination(req.getParameter("pagination"));//保留上一次的查询请求this.setUrl(req.getRequestURL().toString());//保留上一次的查询条件this.setParameterMap(req.getParameterMap());}public String getUrl() {return url;}public void setUrl(String url) {this.url = url;}public Map<String, String[]> getParameterMap() {return parameterMap;}public void setParameterMap(Map<String, String[]> parameterMap) {this.parameterMap = parameterMap;}private void setPage(String page) {if(StringUtils.isNotBlank(page)) {this.setPage(Integer.valueOf(page));}}private void setRows(String rows) {if(StringUtils.isNotBlank(rows)) {this.setRows(Integer.valueOf(rows));}}private void setPagination(String pagination) {//只有填了false字符串，才代表不分页this.setPagination(!"false".equals(pagination));;}private boolean pagination = true;// 是否分页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 + "]";}//上一页public int getPrevPage() {return this.page>1?this.page-1:this.page;}//下一页public int getNextPage() {return this.page<this.getMaxPage()?this.page+1:this.page;}//最大页public int getMaxPage() {return this.total%this.rows==0?this.total/this.rows:(this.total/this.rows)+1;}
}

5.封装分页标签类(PageTag.java)

package com.xiaoqing.tag;
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.xiaoqing.util.PageBean;public class PageTag extends BodyTagSupport{private static final long serialVersionUID = -258029245678348536L;private PageBean pageBean;public PageBean getPageBean() {return pageBean;}public void setPageBean(PageBean pageBean) {this.pageBean = pageBean;}@Overridepublic int doStartTag() throws JspException {// TODO Auto-generated method stubJspWriter out = pageContext.getOut();try {out.print(toHTML());} catch (Exception e) {// TODO: handle exceptione.printStackTrace();}return super.doStartTag();}private String toHTML() {// TODO Auto-generated method stubStringBuilder sb=new StringBuilder();//上一次查询的form表单的HTML拼接sb.append(" <form id='pageBeanForm' action='"+pageBean.getUrl()+"' method='post'>");//查第几页的数据sb.append(" <input type='hidden' name='page'>");Map<String, String[]> parameterMap = pageBean.getParameterMap();if(parameterMap.size()>0) {Set<Entry<String,String[]>> entrySet = parameterMap.entrySet();for (Entry<String, String[]> entry : entrySet) {if(!"page".equals(entry.getKey())) {for (String val : entry.getValue()) {sb.append("<input type='hidden' value='"+val+"' name='"+entry.getKey()+"'>");}}}}sb.append("</form> ");//默认展示前面4页，当前页 ，后面5也int page=pageBean.getPage();int max=pageBean.getMaxPage();int before=page>4?4:page-1;int after=10-1-before;//5after=max-page>after?after:max-page;//用来控制上一页的点击按钮特效的boolean startFlag=page>1;//用来控制下一页的点击按钮特效的boolean endFlag=page<max;//拼接分页条sb.append("<ul class='pagination'>");sb.append("<li class='page-item "+(startFlag ? "" : "")+"'><a class='page-link' href='javascript:gotoPage(1)'>首页</a></li>");sb.append("<li class='page-item "+(startFlag ? "" : "")+"'><a class='page-link' href='javascript:gotoPage("+pageBean.getPrevPage()+")'>&lt;</a></li>");//代表了当前页的前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>");//代表了当前页的后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 ? "" : "")+"'><a class='page-link' href='javascript:gotoPage("+pageBean.getNextPage()+")'>&gt;</a></li>");sb.append("<li class='page-item "+(endFlag ? "" : "")+"'><a class='page-link' href='javascript:gotoPage("+pageBean.getMaxPage()+")'>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();}
}

6.处理业务逻辑BookAction.java

package com.xiaoqing.web;import java.io.IOException;
import java.sql.SQLException;
import java.util.List;
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.xiaoqing.dao.BookDao;
import com.xiaoqing.entity.Book;
import com.xiaoqing.util.PageBean;
@WebServlet(name="book",urlPatterns="/book.action")
public class BookAction extends HttpServlet{private static final long serialVersionUID = 6817006004626927502L;private BookDao bookDao=new BookDao();@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// TODO Auto-generated method stubdoPost(req, resp);}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// TODO Auto-generated method stubBook book=new Book();book.setBname(req.getParameter("bname"));PageBean pageBean=new PageBean();pageBean.setRequest(req);try {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) {// TODO Auto-generated catch blocke.printStackTrace();}	}
}

7.配置字符编码过滤器(EncodingFiter.java)

package com.xiaoqing.util;import java.io.IOException;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.xml.ws.WebFault;/*** 中文乱码处理* */
@WebFilter(filterName="encodingFiter",urlPatterns="*.action")
public class EncodingFiter implements Filter {private String encoding = "UTF-8";// 默认字符集public EncodingFiter() {super();}public void destroy() {}public void doFilter(ServletRequest request, ServletResponse response,FilterChain chain) throws IOException, ServletException {HttpServletRequest req = (HttpServletRequest) request;HttpServletResponse res = (HttpServletResponse) response;// 中文处理必须放到 chain.doFilter(request, response)方法前面res.setContentType("text/html;charset=" + this.encoding);if (req.getMethod().equalsIgnoreCase("post")) {req.setCharacterEncoding(this.encoding);} else {Map map = req.getParameterMap();// 保存所有参数名=参数值(数组)的Map集合Set set = map.keySet();// 取出所有参数名Iterator it = set.iterator();while (it.hasNext()) {String name = (String) it.next();String[] values = (String[]) map.get(name);// 取出参数值[注：参数值为一个数组]for (int i = 0; i < values.length; i++) {values[i] = new String(values[i].getBytes("ISO-8859-1"),this.encoding);}}}chain.doFilter(request, response);}public void init(FilterConfig filterConfig) throws ServletException {String s = filterConfig.getInitParameter("encoding");// 璇诲彇web.xml鏂囦欢涓厤缃殑瀛楃闆�if (null != s && !s.trim().equals("")) {this.encoding = s.trim();}}}

8.展示页面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="/xiaoqing" prefix="z" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<link href="https://cdn.bootcdn.net/ajax/libs/twitter-bootstrap/4.5.0/css/bootstrap.css" rel="stylesheet">
<script src="https://cdn.bootcdn.net/ajax/libs/twitter-bootstrap/4.5.0/js/bootstrap.js"></script>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>书籍展示</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="${pageContext.request.contextPath }/book.action" method="post"><div class="form-group mb-2"><input type="text" name="bname" class="form-control-plaintext" id="staticEmail2"  placeholder="请输入书籍名称"></div><button type="submit" class="btn btn-primary mb-2">查询</button>
</form>
<table class="table table-striped"><thead><tr><th scope="col">书籍编号</th><th scope="col">书籍名字</th><th scope="col">书籍价格</th></tr></thead><tbody><c:forEach var="b" items="${bookList }"><tr><td>${b.bid }</td><td>${b.bname }</td><td>${b.price }</td></tr></c:forEach></tbody>
</table>
<z:page pageBean="${pageBean }"></z:page>
</body>
</html>

9.附加StringUtils类

package com.xiaoqing.util;public class StringUtils{// 私有的构造方法，保护此类不能在外部实例化private StringUtils() {}/*** 如果字符串等于null或去空格后等于""，则返回true，否则返回false* * @param s* @return*/public static boolean isBlank(String s) {boolean b = false;if (null == s || s.trim().equals("")) {b = true;}return b;}/*** 如果字符串不等于null或去空格后不等于""，则返回true，否则返回false* * @param s* @return*/public static boolean isNotBlank(String s) {return !isBlank(s);}
}

OK了，整个通用分页的流程就是这样，本篇博客讲的不是很详细，需要详细的通用分页讲解在小编前面的博客中有记录，不懂的欢迎大家评论！！！
谢谢！！