一.理解分页思想

1.分页的实质

1.1（自我概述）

1.2（专业术语）

二.优化pageBean

1.添加一部分分页需要类

	public String getUrl() {
		return url;
	}

	/**
	 * @param url the url to set
	 */
	public void setUrl(String url) {
		this.url = url;
	}

	/**
	 * @return the paramMap
	 */
	public Map<String, String[]> getParamMap() {
		return paramMap;
	}

	/**
	 * @param paramMap the paramMap to set
	 */
	public void setParamMap(Map<String, String[]> paramMap) {
		this.paramMap = paramMap;
	}


	// 对pagebean进行初始化
	public void setRequest(HttpServletRequest req) {
		// 初始化默认查询第几页数据
		this.setPage(req.getParameter("page")); 
		// 初始化的页大小
		this.setRows(req.getParameter("rows"));
		// 初始化是否分页
		this.setPagination(req.getParameter("pagination"));
		// 保留上一次url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 void setParameterMap(Map<String, String[]>paramMap) {
		this.paramMap = paramMap;
	}

	private void setPagination(String pagination) {
		// 只有填写了false字符串，才代表不分页
		if (StringUtils.isNotBlank(pagination))
		this.setPagination(!"false".equals(pagination));
	}

	private void setRows(String rows) {
		if (StringUtils.isNotBlank(rows))
			this.setRows(Integer.valueOf(rows));
	}
	private void setPage(String page) {
		if (StringUtils.isNotBlank(page))
			this.setPage(Integer.valueOf(page));
	}

	// 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;
		}


	
    private       String   url;
    private    Map<String, String[]>paramMap;

三.分页自定义jsp标签

1为什么要使用自定义分页jsp标签？

1.1自我理解

1.2专业术语

2.实现自定义分页标签

1.首先建立连接类

package com.lz.tag;

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

import com.lz.utils.PageBean;

import java.io.IOException;
import java.util.Map;
import java.util.Set;
/**
 * 
 * @author lzzxq
 *
 */
public class PageTag 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("<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.getParamMap();
		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>");

		int page = pageBean.getPage();
		int max = pageBean.getMaxPage();
		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("<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.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 ? "disabled" : "")
				+ "'><a class='page-link' href='javascript:gotoPage(" + pageBean.getNextPage() + ")'>&gt;</a></li>");
		sb.append("<li class='page-item " + (endFlag ? "disabled" : "")
				+ "'><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();
	}
}

2.建立tid

<!DOCTYPE taglib
  PUBLIC "-//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>/lz</uri>
	
	<tag>
		<name>page</name>
		<tag-class>com.lz.tag.PageTag</tag-class>
		<!--该标签有标签体-->
		<body-content>jsp</body-content>
		<attribute>
			<name>pageBean</name>
			<required>true</required>
			<rtexprvalue>true</rtexprvalue>
		</attribute>
		
	
	</tag>
	
	

</taglib>

3.导入jsp即可

<%@taglib  prefix="z"   uri="/lz"%>

3.servelt编写，过滤器

1.servelt代码实现

package com.lz.servelt;

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.lz.dao.BookDao;
import com.lz.entity.Book;
import com.lz.utils.PageBean;

@WebServlet("/book.action")
public class BookServelt extends HttpServlet {
	
	private static final String UNUSED = "unused";
	/**
	 *  
	 */ 
	private static final long serialVersionUID = 1L;

	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
	
	doPost(request, response);
	} 
	
	@SuppressWarnings(UNUSED)
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

		PageBean  pageBean=new PageBean();
		pageBean.setRequest(request);
		BookDao  bd=new  BookDao();
		Book  bk=new Book();
		bk.setBname(request.getParameter("bname"));
		try {
		List<Book>book=	bd.list(bk, pageBean);
//		System.out.println(book);
		request.setAttribute("book",book);
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		
		request.setAttribute("pageBean",pageBean);

	request.getRequestDispatcher("bookList.jsp").forward(request, response);
	}

}

2.处理乱码

package com.lz.utils;
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;

@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();
		}
	}

}