分页中的一种方法

首先此技术是自定义jsp标签。
commons.tld中内容如下

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE taglib
  PUBLIC "-//Sun Microsystems, Inc.//DTD JSP Tag Library 1.2//EN"
  "http://java.sun.com/dtd/web-jsptaglibrary_1_2.dtd">
<taglib>
    <tlib-version>2.0</tlib-version>
    <jsp-version>1.2</jsp-version>
    <short-name>arley</short-name>
    <uri>http://arley.cn/common/</uri>
    <display-name>Common Tag</display-name>
    <description>Common Tag library</description>
 
    <tag>
        <name>page</name>
        <tag-class>com.itheima.crm.common.NavigationTag</tag-class>
        <body-content>JSP</body-content>
        <description>create navigation for paging</description>
        <attribute>
            <name>bean</name>
            <rtexprvalue>true</rtexprvalue>
        </attribute>
        <attribute>
            <name>number</name>
            <rtexprvalue>true</rtexprvalue>
        </attribute>
        <attribute>
            <name>url</name>
            <required>true</required>
            <rtexprvalue>true</rtexprvalue>
        </attribute>
    </tag>
</taglib>

定义类为，commons.tld中引用此类

import java.io.IOException;
import java.util.Map;
 
 
import javax.servlet.http.HttpServletRequest;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.tagext.TagSupport;
 
 
import org.apache.taglibs.standard.tag.common.core.UrlSupport;
 
 
/**
 * 显示格式 上一页 1 2 3 4 5 6 7 8 9 10下一页
 */
public class NavigationTag extends TagSupport {
    static final long serialVersionUID = 2372405317744358833L;
    
    /**
     * request 中用于保存Page<E> 对象的变量名,默认为“page”
     */
    private String bean = "page";
    
    /**
     * 分页跳转的url地址,此属性必须
     */
    private String url = null;
    
    /**
     * 显示页码数量
     */
    private int number = 10;
    
    @Override
    public int doStartTag() throws JspException {
        JspWriter writer = pageContext.getOut();
        HttpServletRequest request = (HttpServletRequest) pageContext.getRequest();
        Page page = (Page)request.getAttribute(bean); 
        if (page == null) 
            return SKIP_BODY;
        url = resolveUrl(url, pageContext);
        try {
            //计算总页数
            int pageCount = page.getTotal() / page.getSize();
            if (page.getTotal() % page.getSize() > 0) {
                pageCount++;
            }
            writer.print("<nav><ul class=\"pagination\">");
            //显示“上一页”按钮
            if (page.getPage() > 1) {
                String preUrl = append(url, "page", page.getPage() - 1);
                preUrl = append(preUrl, "rows", page.getSize());
                writer.print("<li><a href=\"" + preUrl + "\">上一页</a></li>");
            } else {
                writer.print("<li class=\"disabled\"><a href=\"#\">上一页</a></li>");
            }
            //显示当前页码的前5页码和后4页码 1 2 3 4 5 6 7 8 9 10
            //若1 则 1 2 3 4 5 6 7 8 9 10, 
            //若5 则 1 2 3 4 5 6 7 8 9 10,若10  则 5 6 7 8 9 10 11 12 13 14
            int indexPage = (page.getPage() - 5 > 0)? page.getPage() - 5 : 1;  
            for(int i=1; i <= number && indexPage <= pageCount; indexPage++, i++) {
                if(indexPage == page.getPage()) {
                    writer.print( "<li class=\"active\"><a href=\"#\">"+indexPage+"<span class=\"sr-only\">(current)</span></a></li>");
                    continue;
                }
                String pageUrl  = append(url, "page", indexPage);
                pageUrl = append(pageUrl, "rows", page.getSize());
                writer.print("<li><a href=\"" + pageUrl + "\">"+ indexPage +"</a></li>");
            }
            //显示“下一页”按钮
            if (page.getPage() < pageCount) {
                String nextUrl  = append(url, "page", page.getPage() + 1);
                nextUrl = append(nextUrl, "rows", page.getSize());
                writer.print("<li><a href=\"" + nextUrl + "\">下一页</a></li>");
            } else {
                writer.print("<li class=\"disabled\"><a href=\"#\">下一页</a></li>");
            }
            writer.print("</nav>");
        } catch (IOException e) {
            e.printStackTrace();
        }
        return SKIP_BODY;
    }
    
    private String append(String url, String key, int value) {
 
 
        return append(url, key, String.valueOf(value));
    }
    
    /**
     * 为url 参加参数对儿
     * 
     * @param url
     * @param key
     * @param value
     * @return
     */
    private String append(String url, String key, String value) {
        if (url == null || url.trim().length() == 0) {
            return "";
        }
 
 
        if (url.indexOf("?") == -1) {
            url = url + "?" + key + "=" + value;
        } else {
            if(url.endsWith("?")) {
                url = url + key + "=" + value;
            } else {
                url = url + "&amp;" + key + "=" + value;
            }
        }
        
        return url;
    }
    
    /**
     * 为url 添加翻页请求参数
     * 
     * @param url
     * @param pageContext
     * @return
     * @throws javax.servlet.jsp.JspException
     */
    private String resolveUrl(String url, javax.servlet.jsp.PageContext pageContext) throws JspException{
        //UrlSupport.resolveUrl(url, context, pageContext)
        Map params = pageContext.getRequest().getParameterMap();
        for (Object key:params.keySet()) {
            if ("page".equals(key) || "rows".equals(key)) continue;
            Object value = params.get(key);
            if (value == null) continue;
            if (value.getClass().isArray()) {
                url = append(url, key.toString(), ((String[])value)[0]);
            } else if (value instanceof String) {
                url = append(url, key.toString(), value.toString());
            }
        }
        return url;
    }
    
    
 
 
    /**
     * @return the bean
     */
    public String getBean() {
        return bean;
    }
 
 
    /**
     * @param bean the bean to set
     */
    public void setBean(String bean) {
        this.bean = bean;
    }
 
 
    /**
     * @return the url
     */
    public String getUrl() {
        return url;
    }
 
 
    /**
     * @param url the url to set
     */
    public void setUrl(String url) {
        this.url = url;
    }
 
 
    public void setNumber(int number) {
        this.number = number;
    }
    
}

page类必不可少，4属性，当前页，每页显示条数，总记录数，查询数据

import java.util.List;
 
public class Page<T> {
    
    private int total;
    private int page;
    private int size;
    private List<T> rows;
    public int getTotal() {
        return total;
    }
    public void setTotal(int total) {
        this.total = total;
    }
    public int getPage() {
        return page;
    }
    public void setPage(int page) {
        this.page = page;
    }
    public int getSize() {
        return size;
    }
    public void setSize(int size) {
        this.size = size;
    }
    public List<T> getRows() {
        return rows;
    }
    public void setRows(List<T> rows) {
        this.rows = rows;
    }
}

在web.xml写入

<jsp-config>
        <taglib>
            <taglib-uri>http://itcast.cn/common/</taglib-uri>
            <taglib-location>/common/commons.tld</taglib-location>
        </taglib>
 </jsp-config>

在页面中引用

<%@ taglib prefix="itheima" uri="http://itcast.cn/common/"%>

在需要显示分页按钮的地方写入标签、

<div class="col-md-12 text-right">
    <itheima:page url="${pageContext.request.contextPath }/customer/list.action" />
</div>

url为必填属性,请求路径,

bean="" 在request中取出的key 默认为page

number="" 每页显示数据条数 默认10条

点击页码会传给后台当前页数,参数name为page,所以要使用page属性接收.