Jsp自定義標(biāo)簽實(shí)現(xiàn)分頁

首先引入自定義標(biāo)簽知識(shí)點(diǎn)：
自定義標(biāo)簽
1、封裝邏輯的java
邏輯代碼
輸入頁面的內(nèi)容
2、用描述文件描述標(biāo)簽
注冊有個(gè)標(biāo)簽
3、使用
引用標(biāo)簽庫（taglib uri）
運(yùn)用標(biāo)簽

接下來是自定義標(biāo)簽的一個(gè)小demo：
首先寫好邏輯代碼MyTag

package cn.com.demo.tags;

import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Date;

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

public class MyTag extends BodyTagSupport {

    @Override
    public int doEndTag() throws JspException {
        //處理數(shù)據(jù)
        Date date = new Date();
        SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");
        String dateString = format.format(date);
        JspWriter out = this.pageContext.getOut();
        try {
            out.println(dateString);
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return super.doEndTag();
    }
    
}

接下來考慮到安全性，就在WEB-INF文件中創(chuàng)建tld子文件，再在其中創(chuàng)建XXX.tld，對寫好的java代碼綁定到一個(gè)標(biāo)簽中(例子中將寫好的MyTag綁定到time：

<?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>1.0</tlib-version>
 <jsp-version>1.2</jsp-version>
 <short-name>mytags</short-name>
 
 <tag>
    <name>time</name>
    <tag-class>cn.com.demo.tags.MyTag</tag-class>
    <body-content>empty</body-content>
 </tag>
</taglib>

最后就可以在jsp中使用了，不過首先還是得先引入：

<%@taglib uri="/WEB-INF/tld/mytags.tld" prefix="m"%>

然后在代碼中就可以直接像jsp標(biāo)簽?zāi)菢邮褂昧耍?/p> 

<body>
    <m:time/>
  </body>

現(xiàn)在開始實(shí)現(xiàn)分頁的邏輯：
首先創(chuàng)建一個(gè)javaBean

package cn.com.demo.entity;

public class User {
private String username;
private int age;
public String getUsername() {
    return username;
}
public void setUsername(String username) {
    this.username = username;
}
public int getAge() {
    return age;
}
public void setAge(int age) {
    this.age = age;
}

}

然后模擬已經(jīng)連接數(shù)據(jù)庫的邏輯：

package cn.com.demo.service;

import java.util.ArrayList;
import java.util.List;

import cn.com.demo.entity.User;

public class UserService {
    public List<User> findByPage(int pageNo)
    {
        List<User> list = null;
        int sumCount = this.findUserCount();
        int first = (pageNo-1)*5;
        int last = pageNo*5;
        if(last>=sumCount)
        {
            last = sumCount;
        }
        
        list = new ArrayList<User>();
        User user = null;
        for(int i=first;i<=last;i++)
        {
            user = new User();
            user.setAge(i);
            user.setUsername("user"+i);
            list.add(user);
        }
        return list;
    }
    
    public int findUserCount()
    {
        return 18;
    }
    
    public int findTotalPageNo()
    {
        int sumNo = 0;
        int count = this.findUserCount();
        sumNo = count/5;
        if(sumNo%5!=0)
        {
            sumNo = sumNo+1;
        }
        return sumNo;
    }
}

然后實(shí)現(xiàn)Servlet，其中需要向頁面?zhèn)?個(gè)值（總頁數(shù)、當(dāng)前頁、當(dāng)前查找的數(shù)據(jù)）

package cn.com.demo.servlet;


import java.io.IOException;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import cn.com.demo.entity.User;
import cn.com.demo.service.UserService;

public class SearchUserServlet extends HttpServlet {

    @Override
    protected void service(HttpServletRequest req, HttpServletResponse res)
            throws ServletException, IOException {
        String pageNoStr = req.getParameter("pageNo");
        int pageNo = 1;
        try{
        pageNo = Integer.parseInt(pageNoStr);
        }catch (Exception e) {
            // TODO: handle exception
        }
        UserService userService = new UserService();
        
        //獲取總頁數(shù)
        int sumPageNo = userService.findTotalPageNo();
        if(pageNo>=sumPageNo)
        {
            pageNo = sumPageNo;
        }
        if(pageNo<=1)
        {
            pageNo = 1;
        }
        List<User> list = userService.findByPage(pageNo);
        req.setAttribute("pageNo",pageNo);
        req.setAttribute("sumPageNo", sumPageNo);
        req.setAttribute("list",list);
        req.getRequestDispatcher("index.jsp").forward(req, res);
    }

}

最后是前端代碼，使用Js來控制頁碼的變換：

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <base href="<%=basePath%>">
    
    <title>My JSP 'index.jsp' starting page</title>
    <meta http-equiv="pragma" content="no-cache">
    <meta http-equiv="cache-control" content="no-cache">
    <meta http-equiv="expires" content="0">    
    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
    <meta http-equiv="description" content="This is my page">
    <!--
    <link rel="stylesheet" type="text/css" href="styles.css">
    -->
  </head>
  
  <body>
  <table>
  <tr>
  <td>用戶名</td>
  <td>年齡</td>
  </tr>
  
  <c:forEach items="${list}" var="user">
  <tr>
  <td>${user.username }</td>
  <td>${user.age }</td>
  </tr>
  </c:forEach>
  <tr align="center">
  <td>
  <a href="javascript:void" onclick="toFirst()">首頁</a>
  <a href="javascript:void" onclick="toPrev()">上一頁</a>
  <a href="javascript:void" onclick="toNext()">下一頁</a>
  <a href="javascript:void" onclick="toLast()">末頁</a>
  </td>
  </tr>
  </table>
  </body>
  
  <script type="text/javascript">
    var pageNo = ${pageNo};
    var sumPageNo = ${sumPageNo};
    function toFirst(){
        pageNo = 1;
        toViewPage();
    }
    function toLast(){
        pageNo = sumPageNo;
        toViewPage();
    }
    function toNext(){
        pageNo = pageNo+1;
        if(pageNo>sumPageNo)
        {
            pageNo = sumPageNo;
        }
        toViewPage();
    }
    function toPrev(){
        pageNo = pageNo-1;
        if(pageNo<1)
        {
            pageNo =1 ;
        }
        toViewPage();
    }
    function toViewPage(){
        location.href="searchUserServlet?pageNo="+pageNo+"&"+Math.random();
    }
  </script>
  
</html>

當(dāng)解決上述兩個(gè)問題時(shí)，就可以開始研究分頁自定義標(biāo)簽的思路了，能夠復(fù)用的部分就是“首頁、上一頁、下一頁、末頁”這控制分頁的超鏈接，因?yàn)轱@示數(shù)據(jù)會(huì)因?yàn)閿?shù)據(jù)庫字段的不同而不同，所以不能夠復(fù)用。所以創(chuàng)建一個(gè)自定義tag:

package cn.com.demo.tag;

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

public class PageTag extends BodyTagSupport {
    private String pageNoName;
    private String sumPageName;
    private String url;
    public String getPageNoName() {
        return pageNoName;
    }
    public void setPageNoName(String pageNoName) {
        this.pageNoName = pageNoName;
    }
    public String getSumPageName() {
        return sumPageName;
    }
    public void setSumPageName(String sumPageName) {
        this.sumPageName = sumPageName;
    }
    public String getUrl() {
        return url;
    }
    public void setUrl(String url) {
        this.url = url;
    }
    @Override
    public int doEndTag() throws JspException {
        JspWriter out = this.pageContext.getOut();
        try{
            out.println("<a href='javascript:void' onclick='toFirst()'>首頁</a>");
            out.println(" <a href='javascript:void' onclick='toPrev()'>上一頁</a>");
            out.println(" <a href='javascript:void' onclick='toNext()'>下一頁</a>");
            out.println(" <a href='javascript:void' onclick='toLast()'>末頁</a>");
            out.println("  <script type='text/javascript'>");
            Object value = pageContext.getRequest().getAttribute(this.pageNoName);
            out.println("   var pageNo = "+value+";");
            value = pageContext.getRequest().getAttribute(this.sumPageName);
            out.println("   var sumPageNo = "+value+";");
            out.println("   function toFirst(){");
            out.println("   pageNo = 1;");
            out.println("       toViewPage();");
            out.println("   }");
            out.println("       function toLast(){");
            out.println("       pageNo = sumPageNo;");
            out.println("               toViewPage();");
            out.println("   }");
            out.println("function toNext(){");
            out.println("pageNo = pageNo+1;");
            out.println("if(pageNo>sumPageNo)");
            out.println("{");
            out.println("pageNo = sumPageNo;");
            out.println("}");
            out.println("toViewPage();");
            out.println("}");
            out.println("function toPrev(){");
            out.println("pageNo = pageNo-1;");
            out.println("if(pageNo<1)");
            out.println("{");
            out.println("   pageNo =1 ;");
            out.println("}");
            out.println("toViewPage();");
            out.println("}");
            out.println("function toViewPage(){");
            value = pageContext.getRequest().getAttribute(this.pageNoName);
            out.println("location.href='"+url+"?"+this.pageNoName+"='+pageNo+'&'+Math.random();");
            out.println("}");
            out.println("  </script>");
        }catch (Exception e) {
            // TODO: handle exception
        }
        return super.doEndTag();
    }
    
}

對其進(jìn)行配置：

<?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>1.0</tlib-version>
 <jsp-version>1.2</jsp-version>
 <short-name>matags</short-name>
 <uri>http://mytags</uri>
 
 <tag>
    <name>page</name>
    <tag-class>cn.com.demo.tag.PageTag</tag-class>
    <body-content>empty</body-content>
    
    <attribute>
        <name>pageNoName</name>
        <required>true</required>
        <rtexprvalue>true</rtexprvalue>
        <type>java.lang.String</type>
    </attribute>
    <attribute>
        <name>sumPageName</name>
        <required>true</required>
        <rtexprvalue>true</rtexprvalue>
        <type>java.lang.String</type>
    </attribute>
    <attribute>
        <name>url</name>
        <required>true</required>
        <type>java.lang.String</type>
    </attribute>
 </tag>
</taglib>

最后頁面就可以改為：

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<%@taglib uri="http://mytags" prefix="t"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <base href="<%=basePath%>">
    
    <title>My JSP 'tttttt.jsp' starting page</title>
    <meta http-equiv="pragma" content="no-cache">
    <meta http-equiv="cache-control" content="no-cache">
    <meta http-equiv="expires" content="0">    
    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
    <meta http-equiv="description" content="This is my page">
    <!--
    <link rel="stylesheet" type="text/css" href="styles.css">
    -->
  </head>
  
  <body>
  <table>
  <tr>
  <td>用戶名</td>
  <td>年齡</td>
  </tr>
  
  <c:forEach items="${list}" var="user">
  <tr>
  <td>${user.username }</td>
  <td>${user.age }</td>
  </tr>
  </c:forEach>
  <tr align="center">
  <td>
  <t:page url="searchUserServlet" pageNoName="pageNo" sumPageName="sumPageNo"/>
  </td>
  </tr>
  </table>
  </body>
  

  
</html>
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