java分页--标签版

自定义标签的方法实现分页

首先需要一个分页对象，在某个pojo里面加上这三条属性并生成get set方法

//当前页
  	private Integer page;
  	//每页数
  	private Integer size = 10; 
  	//开始行
  	private Integer startRow = 0;

再加入自定义标签的两个类

package cn.wave.commons.util;

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;

/**
 * 显示格式 上一页 1 2 3 4 5 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 = 5;
    
    @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2页码和后两页码 
            //若1 则 1 2 3 4 5, 若2 则 1 2 3 4 5, 若3 则1 2 3 4 5,
            //若4 则 2 3 4 5 6 ,若10  则 8 9 10 11 12
            int indexPage = (page.getPage() - 2 > 0)? page.getPage() - 2 : 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

package cn.wave.commons.util;

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;
	}
    
	
    
}

标签模板文件，在WEB-INF下建一个tld文件夹，在把这个文件放进去，命名commons.tld

<?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>common</short-name>
	<uri>http://itcast.cn/common/</uri>
	<display-name>Common Tag</display-name>
	<description>Common Tag library</description>

	<tag>
		<name>page</name>
		<tag-class>cn.wave.commons.util.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>

然后再jsp页面导入标签库

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

jsp里面的for循环后加入标签

<div id="dataDiv">
        <img src="images/result.gif" />
        <table class="dt" border="1px">
            <tr id="firstTr">
                <th>部门ID</th>
                <th>部门名称</th>
                <th>编辑</th>
            </tr>
            
            <c:forEach items="${page.rows}" var="item">

                <tr class="tdbg1">

                    <td>${item.id}</td>
                    <td>${item.depName}</td>
                    <td>
                        <a href="updateDepartment.jsp?id=${item.id}&depName=${item.depName}">
                            <img src="img/modify.gif" />
                        </a>
                        <a href="<c:url value='/DepartmentServlet?method=delete&id=${item.id}'/> ">
                            <img src="img/delete.gif" />
                        </a>
                    </td>
                </tr>
            </c:forEach>
        </table>
    </div>
    <!-- 把这个插入就行，这里面的样式是bootstrap里面的-->
    <div class="col-md-12 text-right">
		<itheima:page url="${pageContext.request.contextPath }/DepartmentServlet?method=selectAll" />
	</div> 

servlet方法，就是一直获取最开始定义的分页对象，然后把这个对象放进page里面

Map<String, String[]> map = request.getParameterMap();
       Department department = CommonUtils.toBean(map, Department.class);
    	cn.wave.commons.util.Page<Department> page = departmentService.selectAll(department);
		request.setAttribute("page", page);

service

public Page<Department> selectAll(Department department){
        Page<Department> page = new Page<Department>();
        page.setSize(5);
        department.setSize(5);
        if (null !=department.getPage()) {
			page.setPage(department.getPage());
			department.setStartRow((department.getPage() -1)*department.getSize());
		}
        page.setTotal(departmentDao.count());
		page.setRows(departmentDao.selectAll(department));
        return  page;
    }

dao里面查询的时候加上limit，再加一个count方法

public List<Department> selectAll(Department department){
        Connection con = DBUtil.getConnection();
        PreparedStatement ptmt = null;
        ResultSet res = null;
        String sql = "select * from crm_department limit ?,?";
        List<Department> list = new ArrayList<>();

        try {
            ptmt = con.prepareStatement(sql);
            ptmt.setInt(1, department.getStartRow());
            ptmt.setInt(2, department.getSize());
            res = ptmt.executeQuery();
            while(res.next()){
                Department department1 = new Department();
                department1.setId(res.getInt("id"));
                department1.setDepName(res.getString("depName"));
                department1.setIsCancel(res.getInt("isCancel"));
                list.add(department1);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return  list;
    }
public int count(){
        Connection con = DBUtil.getConnection();
        PreparedStatement ptmt = null;
        ResultSet res = null;
        String sql = "select count(*) from crm_department ";
        int total = 0;

        try {
            ptmt = con.prepareStatement(sql);
            res = ptmt.executeQuery();
            if(res.next()){
            	total = res.getInt(1);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return  total;
    }

分页完成