通用分页02（前台分页）
- 分页的核心思想
- 优化pageBean
- 分页标签的制作过程
分页的核心思想
http://loccalhost:8080/mvc/book.action?bname=圣墟
1.第一次查询
为什么点击上面链接，显示的是第一页的数据，而不是第二页第三页的数据？
原因：pageBean默认 page=1，rows=10，pagination=true
2.第二次查询
pageBean page=2，rows=10，pagination=true
3.第三次查询
pageBean page=3，rows=10，pagination=true
4.结论优化pageBean：分页就是将上一次请求再发一次，只是页码变了，其他查询条件不变
优化pageBean
增加一个属性url，保留上一次发送的请求地址
增加一个属性paramMap，保留上一次发送的请求携带的参数,req.getParameterMap();
增加一个最大页的方法
增加一个下一页的方法
增加一个上一页的方法
初始化pageBean的方法
package com.zhulinjun.util;
import java.util.Map;
import javax.servlet.http.HttpServletRequest;
/**
* 分页工具类
*
*/
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
// 增加一个最大页的方法
public int maxPage() {
return this.total % this.rows ==0?
this.total / this.rows:
this.total / this.rows+1;
}
// 增加一个下一页的方法
public int nextPage() {
return this.page < this.maxPage() ?
this.page+1 : this.page;
}
// 增加一个上一页的方法
public int prevPage() {
return this.page > 1 ? this.page -1 : this.page;
}
public void setRequest(HttpServletRequest req) {
// 初始化默认查询第几页的数据(初始化pageBean的方法)
this.setPage(req.getParameter("page"));
this.setRows(req.getParameter("rows"));
this.setPagination(req.getParameter("pagination"));
// 保留上一次的url(增加一个属性url，保留上一次发送的请求地址)
this.setUrl(req.getRequestURL().toString());
// 保留携带的参数(增加一个属性paramMap，保留上一次发送的请求携带的参数)
this.setParamMap(req.getParameterMap());
}
public void setPage(String page) {
if(StringUtils.isNotBlank(page)) {
this.setPage(Integer.valueOf(page));
}
}
public void setRows(String rows) {
if(StringUtils.isNotBlank(rows))
this.setRows(Integer.valueOf(rows));
}
public void setPagination(String pagination) {
if(StringUtils.isBlank(pagination)) {
this.setPagination(!"false".equals(pagination));
}
}
private String url;
private Map paramMap;
public String getUrl() {
return url;
}
public void setUrl(String url) {
this.url = url;
}
public Map getParamMap() {
return paramMap;
}
public void setParamMap(Map paramMap) {
this.paramMap = paramMap;
}
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 + "]";
}
}
分页标签的制作过程
package com.zhulinjun.tag;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.tagext.BodyTagSupport;
import com.zhulinjun.util.PageBean;
import java.io.IOException;
import java.util.Map;
import java.util.Set;
/**
* @author 小李飞刀
* @site www.zking.com
*/
public class tag extends BodyTagSupport {
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 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("");
int page = pageBean.getPage();
int max = pageBean.maxPage();
int before = page > 4 ? 4 : page-1;
int after = 10 - 1 - before;
after = page+after > max ? max-page : after;
// disabled
boolean startFlag = page == 1;
boolean endFlag = max == page;
// 拼接分页条
sb.append("");
sb.append("- 首页
");
sb.append("- <
");
// 代表了当前页的前4页
for (int i = before; i > 0 ; i--) {
sb.append("- "+(page-i)+"
");
}
sb.append("- "+pageBean.getPage()+"
");
// 代表了当前页的后5页
for (int i = 1; i <= after; i++) {
sb.append("- "+(page+i)+"
");
}
sb.append("- >
");
sb.append("- 尾页
");
sb.append("- 到第页
");
sb.append("- 确定
");
sb.append("- 共"+pageBean.getTotal()+"条
");
sb.append("
");
// 拼接分页的js代码
sb.append("");
return sb.toString();
}
}
JSTL 1.1 core library
JSTL core
1.1
z
http://jsp.veryedu.cn
page
com.zhulinjun.tag.tag
JSP
pageBean
true
true
package com.zking.servlet;
import java.io.IOException;
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.zhulinjun.dao.BookDao;
import com.zhulinjun.entity.Book;
import com.zhulinjun.util.PageBean;
@WebServlet("/book.action")
public class BookServlet extends HttpServlet{
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doPost(req, resp);
}
@SuppressWarnings("unused")
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
// String bname = req.getParameter("bname");
map包含了浏览器传递到后台的所有参数键值对
// Map parameterMap = req.getParameterMap();
浏览器请求的地址
// String url = req.getRequestURI().toString();
PageBean pageBean=new PageBean();
pageBean.setRequest(req);
BookDao bookDao=new BookDao();
Book book = new Book();
book.setBname(req.getParameter("bname"));
try {
List books = bookDao.list(book, pageBean);
req.setAttribute("books", books);
// System.out.println(books);
} catch (Exception e) {
e.printStackTrace();
}
req.setAttribute("pageBean", pageBean);
System.out.println(pageBean);
req.getRequestDispatcher("bookList.jsp").forward(req, resp);
}
}
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<%@taglib prefix="z" uri="http://jsp.veryedu.cn"%>
书籍列表
书籍ID
书籍名
价格
${b.bid }
${b.bname }
${b.price }
package com.zhulinjun.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;
/**
* 中文乱码处理
*
*/
@WebFilter("*.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");// 读取web.xml文件中配置的字符集
if (null != s && !s.trim().equals("")) {
this.encoding = s.trim();
}
}
}