Java标签实现分页

Java实现标签分页

      最近为了开发一个网站，里面要用分页功能，但是之前很少自己写分页标签，又不想用现成框架。所以自己参考了些资料，写了个分页例子测试了一下。

      代码主要分为三个类：

1. PageTag 分页标签类
2. Page 分页bean
3. Constant 设置常量

     Page代码：

/**
 *
 * @author byyang
 *
 */
public class Page
{
    private int current = 0;  //当前页，默认为第一页
    private int size;     //记录总数
    private int length;   //每页的长度
    private String url;   //访问路径

    public Page(int offset, int size, int length) {
        super();
        this.current = offset;
        this.size = size;
        this.length = length;
    }

    /**
     * 获取总页数
     * @return
     */
    public int pageCount(){
        int pagecount = 0;
        if(this.size % this.length == 0){
            pagecount = this.size / this.length;
        }else{
            pagecount = this.size / this.length + 1;
        }

        return pagecount;
    }

    //最后一页开始条数
    public int lastPageOffset(){
        return this.size - lastPageSize();
    }

    //最后一页页大小
    public int lastPageSize(){
        int lastpagesize = 0;
        if(this.size % this.length == 0){
            lastpagesize = this.length;
        }else{
            lastpagesize = this.size % this.length;
        }
        return lastpagesize;
    }

    //获取起始页
    public int getOffset() {
        return current;
    }
    //总记录数
    public int getSize() {
        return size;
    }
    //每页大小
    public int getLength() {
        return length;
    }
    //获取访问路径
    public String getUrl() {
        return url;
    }

    //上一页
    public int getLastOffset(){
        int offset = this.getOffset() - this.getLength();
        if(offset > 0){
            return offset;
        }else{
            return 0;
        }

    }
    //下一页
    public int getNextOffset(){
        int offset =  this.getOffset() + this.getLength();
        if(offset > this.getSize()){
            return getLastOffset();
        }else{
            return offset;
        }
    }

    public String getPageNavigation(){
        String pageNavigation = "";
        return pageNavigation;
    }

    public void setOffset(int offset) {
        this.current = offset;
    }

    public void setSize(int size) {
        this.size = size;
    }

    public void setLength(int length) {
        this.length = length;
    }

    public void setUrl(String url) {
        this.url = url;
    }
}

   现在我们要实现PageTag标签类，自定义标签有两种实现TagSupport和SimpleTagSupport，两个都能实现这个功能，这个看个人选择了。

import java.io.IOException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.tagext.TagSupport;

import com.byyang.util.Constants;
/**
 *  doStartTag()和doEndTag()返回值处理:
 * SKIP_BODY (0) ：跳过了开始和结束标签之间的代码。
 * EVAL_BODY_INCLUDE(1)：将body的内容输出到存在的输出流中
 * SKIP_PAGE(5)： 忽略剩下的页面。
 * EVAL_PAGE隐含(6)：继续执行下面的页
 * @author yangby
 *
 */
public class PageTag extends TagSupport{

   private String url;

   public String getUrl(){
     return this.url;
   }

   public void setUrl(String url) {
     this.url = url;
   }

   public int doEndTag()throws JspException{
     return EVAL_PAGE;
   }


 public int doStartTag() throws JspException{
     HttpServletRequest request = (HttpServletRequest)this.pageContext.getRequest();
     //获取分页bean
     Page page = (Page)request.getAttribute("pager");

     JspWriter out = this.pageContext.getOut();
     //拼接分页信息
     StringBuilder s = new StringBuilder();
     s.append("共 " + ((page.getSize() - 1) / page.getLength() + 1) + " 页   ");

     //设置当前页第一条记录索引
     String current = request.getParameter("current");
     if(current != null && !"".equals(current)){
      page.setOffset(Integer.parseInt(current));
     }
     if (page.getSize() > page.getLength()){
    //获取连接符pref
    String pref;
    if (this.url.indexOf("?") > -1){
    pref = "&";
    }else {
    pref = "?";
    }
    this.doStart(s, page, pref);
    this.doBody(s, page, pref);
    this.doEnd(s,page,pref);
     }else{
       s.append("    ");
     }
     s.append(" 共 " + page.getSize() + " 条记录");
     try{
       out.println(s.toString());
     }catch (IOException e){
       e.printStackTrace();
     }

     return SKIP_BODY;
   }

 /**
  * //拼接"首页"和"<"
  * @param s
  * @param page
  * @param pref
  */
 public void doStart(StringBuilder s,Page page,String pref){
       if (page.getOffset() > 0){
        s.append("<a href='" + this.url + pref +
           "current=0'>[首页]</a>
" + "<a href='" + this.url + pref +
           "current=" + page.getLastOffset() + "'>[<]</a>
");
       }else{
        s.append("<a href='" + this.url + pref + "current=0'>[首页]</a>
" );
       }
 }

 /**
  * 拼接"尾页"和">"
  * @param s
  * @param page
  * @param pref
  */
 public void doEnd(StringBuilder s,Page page,String pref){
       if (page.getOffset() < page.getSize() - page.getLength()) {
        s.append("<a href='" + this.url + pref + "current=" + page.getNextOffset() + "'>[>]</a>
" + "<a href='" +
           this.url + pref + "current=" + page.lastPageOffset() +
           "'>[尾页]</a>
");
       }else{
        s.append("
"+ "<a href='" +  this.url + pref + "current=" + page.lastPageOffset() + "'>[尾页]</a>
");
       }
 }

 /**
  * 数字连接
  * @param s
  * @param page
  * @param pref
  */
 public void doBody(StringBuilder s,Page page,String pref){
   //显示半径
       int radius = Constants.MAX_PAGE_INDEX / 2 * page.getLength();

       //显示数字的连接从第几条开始
       int startOffset;
       if ((page.getOffset() < radius) || (page.pageCount() <= Constants.MAX_PAGE_INDEX)){
        startOffset = 0;
       }else{
         if (page.getOffset() < page.getSize() - radius){
           startOffset = page.getOffset() - radius;
         }else{
           startOffset = (page.getSize() / page.getLength() - Constants.MAX_PAGE_INDEX) *
             page.getLength();
         }
       }
       for (int i = startOffset; (i < page.getSize()) && (i < startOffset + Constants.MAX_PAGE_INDEX * page.getLength()); ){
         if (i == page.getOffset()){
           s.append("<b>" + (i / page.getLength() + 1) + "</b>
");
         }else{
          s.append("<a href='" + this.url + pref + "current=" + i +
            "'>" + (i / page.getLength() + 1) + "</a>
");
         }
         i += page.getLength();
       }
 }
}

 静态参数类：

public class Constants {

    public static int PAGE_SIZE = 5; //每页大小
    public static int MAX_PAGE_INDEX = 5;//最多显示5个数字连接

}

编写tld文件mypage.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>2.5</tlib-version>
    <jsp-version>1.2</jsp-version>
    <short-name>mypage</short-name>
    <uri>	ag-page</uri>
    <tag>
        <name>page</name>
        <tag-class>com.byyang.tag.PageTag</tag-class>
        <body-content>pg</body-content>
        <attribute>
            <name>url</name>
            <required>true</required>
            <rtexprvalue>true</rtexprvalue>
        </attribute>
    </tag>
</taglib>

   配置web.xml

 <!-- 自定义标签 -->
 <jsp-config>
  <taglib>
    <taglib-uri>/tag-page</taglib-uri>
    <taglib-location>/WEB-INF/mypage.tld</taglib-location>
  </taglib>
</jsp-config>

在jsp页面中添加如下代码：

<%@ taglib uri="/tag-page" prefix="pg"%>

你可以放到一个公共jsp里面一块引。

现在咱们可以测试一下了：

在jsp页面代码：

<div align="center">
  <h2>图书列表</h2>
  <table border=1>
   <s:iterator var="book" status="index" value="books">
    <s:if test="#index.odd == true">
    <tr style="background-color: yellow">
    </s:if>
    <s:else>
    <tr>
    </s:else>
     <td align="right">图书名称：</td>
     <td align="left"><s:property value="book"/></td>
    </tr>
   </s:iterator>
  </table>
  <pg:page url="getBookList.action"></pg:page>
 </div>

Action中咱们设一个测试数据：

public class BookAction extends BaseAction {

 private String[] books;
 private BookService bookService = new BookService();

 public String execute() throws Exception {

  setBooks(bookService.getBookList());
  Page page = new Page(1,65,5);
  request.setAttribute("pager", page);

  return SUCCESS;

 }
 public String[] getBooks() {
  return books;
 }

 public void setBooks(String[] books) {
  this.books = books;
 }

}

 好的，接下来启动tomcat，查看页面效果：