使用范围

下面有分页选项的时候 有一个PageBean就可以对该列表进行多种不同分页查询

PageBean对象的创建

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//分页Bean，它会在各层之间传递！
public class PageBean<T> {
	private int pageNow;//当前页码
	private int totalRecords;//总记录数
	private int pageSize;//每页记录数
	private String url;//请求路径和参数，例如：/BookServlet?method=findXXX&cid=1&bname=2
	private List<T> beanList;

	// 计算总页数
	public int getPageCount() {
		int pageCount = totalRecords / pageSize;
		return totalRecords % pageSize == 0 ? pageCount : pageCount + 1;
	}
	public int getPageNow() { return pageNow; }
	public void setPageNow(int pageNow) { this.pageNow = pageNow; }
	public int getTotalRecords() { return totalRecords; }
	public void setTotalRecords(int totalRecords) { this.totalRecords = totalRecords; }
	public int getPageSize() { return pageSize; }
	public void setPageSize(int pageSize) { this.pageSize = pageSize; }
	public String getUrl() { return url; }
	public void setUrl(String url) { this.url = url; }
	public List<T> getBeanList() { return beanList; }
	public void setBeanList(List<T> beanList) { this.beanList = beanList; }
}

封装每页记录数的类

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public class PageConstants {
   public static final int BOOK_PAGE_SIZE = 12;//图书每页记录数
   public static final int ORDER_PAGE_SIZE = 8;//订单每页记录数
}

Dao层

通用的查询方法

通用的查询方法只需要对应查询传过来sql语句与pageNow即可返回封装好的PagebBean对象与查询对象的List集合

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//写入sql 返回分页查询结果
public PageBean<Book> findByCriteria(String sql, int pageNow) {
    int pageSize = PageConstants.BOOK_PAGE_SIZE;//每页记录数
    int totalRecords = 0;
    //查询一共有多少条数据
    List<Book> list = template.query(sql,new BeanPropertyRowMapper<>(Book.class));
    //得到了总记录数
   for(Book book :list){
       totalRecords++;
   }
    //得到beanList，即当前页记录
    sql = sql+" order by orderBy limit ?,?";
    List<Book> beanList = template.query(sql,new BeanPropertyRowMapper<>(Book.class),
    (pageNow-1) * pageSize,pageSize);
    PageBean<Book> pb = new PageBean<>();
    //其中PageBean没有url，这个任务由Servlet完成
    pb.setBeanList(beanList);
    pb.setPageNow(pageNow);
    pb.setPageSize(pageSize);
    pb.setTotalRecords(totalRecords);
    return pb;
}

例如

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// 按书名模糊查询
public PageBean<Book> findByBname(String bname, int pageNow) {
        String sql="select * from t_book where bname like '%" + bname + "%'";
        return findByCriteria(sql,pageNow);
}

//多条件组合查询
public PageBean<Book> findByCombination(Book criteria, int pageNow) {
    String sql="select * from t_book where 1=1 ";
    if (!"".equals(criteria.getBname())){
        sql = sql+ "AND bname like '%" + criteria.getBname() +"%'";
    }
    if (!"".equals(criteria.getAuthor())){
        sql = sql+ "AND author like '%" + criteria.getAuthor() +"%'";
    }
    if (!"".equals(criteria.getPress())){
        sql = sql+ "AND press like '%" + criteria.getPress() +"%'";
    }
    //将sql传入findByCriteria方法即可
    return findByCriteria(sql, pageNow);
}

Service层

直接调用相应方法即可

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public PageBean<Book> findByBname(String bname, int pageNow)  {
    return bookDao.findByBname(bname,pageNow);
}

public PageBean<Book> findByCombination(Book book, int pageNow) {
    return bookDao.findByCombination(book,pageNow);
}

Servlet层

获取当前页码

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//获取当前页码
private int getPageNow(HttpServletRequest req) {
	//默认pageNow=1
    int pageNow = 1;
    String param = req.getParameter("pageNow");
    //用来确定传过来的pageNow是否为空 如果不为空就转成整形赋给pageNow
    //trim()方法用来返回字符串的副本，忽略前导空白和尾部空白
    if(param != null && !param.trim().isEmpty()) {
            pageNow = Integer.parseInt(param);
    }
    return pageNow;
}

获取需要分页的url

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/**
 * 截取url，页面中的分页导航中需要使用它做为超链接的目标！
 * http://localhost:8080/BookeWeb/user/bookServlet?methed=findByBname&bid=xxx&pageNow=3
 * /BookeWeb/user/bookServlet + methed=findByBname&bid=xxx&pageNow=3
 */
private String getUrl(HttpServletRequest req) {
    String url = req.getRequestURI() + "?" + req.getQueryString();
     //如果url中存在pageNow参数，截取掉，如果不存在那就不用截取。
    int index = url.lastIndexOf("&pageNow=");
    if(index != -1) {
        url = url.substring(0, index);
    }
    return url;
}

例如

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//按书名查
public String findByBname(HttpServletRequest req, HttpServletResponse resp)  {
    //1. 得到pageNow：如果页面传递，使用页面的，如果没传，pageNow=1
    int pageNow = getPageNow(req);
    //2. 得到url:
    String url = getUrl(req);
    String bname = req.getParameter("bname");
    PageBean<Book> pb = bookService.findByBname(bname, pageNow);
    //3. 给PageBean设置url，保存PageBean，转发到/jsps/book/list.jsp
    pb.setUrl(url);
    req.setAttribute("pb", pb);
    return "f:/jsps/book/list.jsp";
}

//组合查询
public String findByCombination(HttpServletRequest req, HttpServletResponse resp) {
    //1. 得到pageNow：如果页面传递，使用页面的，如果没传，pageNow=1
    int pageNow = getPageNow(req);
    //2. 得到url：...
    String url = getUrl(req);
    Book book = new Book();
    book.setBname(req.getParameter("bname"));
    book.setAuthor(req.getParameter("author"));
    book.setPress(req.getParameter("press"));
    PageBean<Book> pb = bookService.findByCombination(book, pageNow);
    //3. 给PageBean设置url，保存PageBean，转发到/jsps/book/list.jsp
    pb.setUrl(url);
    req.setAttribute("pb", pb);
    return "f:/jsps/book/list.jsp";
}

Jsp页面

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<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<script>
function _go() {
        var pageNow = $("#pageCode").val();//获取文本框中的当前页码
        if(!/^[1-9]\d*$/.test(pageNow)) {//对当前页码进行整数校验
            alert('请输入正确的页码！');
            return;
        }
        if(pageNow > ${pb.pageCount}) {//判断当前页码是否大于最大页
            alert('请输入正确的页码！');
            return;
        }
        location = "${pb.url}&pageNow=" + pageNow;
   }
</script>

<div class="divBody">
  <div class="divContent">

    <%--上一页 --%>
<c:choose>
    <c:when test="${pb.pageNow eq 1 }"><span class="spanBtnDisabled">上一页</span></c:when>
    <c:otherwise><a href="${pb.url}&pageNow=${pb.pageNow-1}" class="aBtn bold">上一页</a></c:otherwise>
</c:choose>
<%--
我们需要计算页码列表的开始和结束位置，即两个变量begin和end
计算它们需要通过当前页码！
1. 总页数不足6页--> begin=1, end=最大页
2. 通过公式设置begin和end，begin=当前页-1，end=当前页+3
3. 如果begin<1，那么让begin=1，end=6
4. 如果end>tp, 让begin=pageCount-5, end=pageCount
 --%>
        <c:choose>
            <%--1. 总页数不足6页--> begin=1, end=最大页--%>
            <c:when test="${pb.pageCount <= 6}">
                <c:set var="begin" value="1"></c:set>
                <c:set var="end" value="${pb.pageCount}"></c:set>
            </c:when>
            <c:otherwise>
                <%--2. 通过公式设置begin和end，begin=当前页-1，end=当前页+3--%>
                <c:set var="begin" value="${pb.pageNow-2}"></c:set>
                <c:set var="end" value="${pb.pageNow+3}"></c:set>
                <%--3. 如果begin<1，那么让begin=1，end=6--%>
                <c:if test="${begin <= 1}">
                    <c:set var="begin" value="1"></c:set>
                    <c:set var="end" value="6"></c:set>
                </c:if>
                <%--4. 如果end>tp, 让begin=pageCount-5, end=pageCount--%>
                <c:if test="${end >= pb.pageCount}">
                    <c:set var="begin" value="${pb.pageCount-5}"></c:set>
                    <c:set var="end" value="${pb.pageCount}"></c:set>
                </c:if>
            </c:otherwise>
        </c:choose>
           <%--开始根据获取到的begin和end来遍历生成页码--%>
        <c:forEach begin="${begin}" end="${end}" var="i">
            <c:choose>
                <%--如果是本页面就不生成链接--%>
                <c:when test="${pb.pageNow eq i}">
                    <span class="spanBtnSelect">${i}</span>
                </c:when>
                <c:otherwise>
                    <a href="${pb.url}&pageNow=${i}" class="aBtn">${i}</a>
                </c:otherwise>
            </c:choose>
        </c:forEach>
    <%-- 显示点点点 --%>
        <c:if test="${end < pb.pageCount}">
            <span class="spanApostrophe">...</span>
        </c:if>
     <%--下一页 --%>
        <c:choose>
            <c:when test="${pb.pageNow eq pb.pageCount }"><span class="spanBtnDisabled">下一页</span></c:when>
            <c:otherwise><a href="${pb.url}&pageNow=${pb.pageNow+1}" class="aBtn bold">下一页</a></c:otherwise>
        </c:choose>
    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
    <%-- 共N页 到M页 --%>
    <span>共${pb.pageCount}页</span>
    <span>到</span>
    <input type="text" class="inputPageCode" id="pageCode" value="${pb.pageNow}"/>
    <span>页</span>
    <a href="javascript:_go();" class="aSubmit">确定</a>
  </div>
</div>

使用时在jsp页面中导如即可

比如

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<%@include file="/jsps/pager/pager.jsp" %>