JavaWeb.EL与JSTL的使用_gjstl-优快云博客

本文链接：https://blog.youkuaiyun.com/weixin_64938628/article/details/124280710

本文档展示了如何使用EL表达式和JSTL标签替换JSP中的原生Java代码，以实现购物车功能的分页。通过在IGoodsDao接口和其实现类GoodsDaoImpl中增加分页方法，以及在GoodsBizImpl中调用这些方法，实现了数据查询和分页显示。在index.jsp和doIndex.jsp中应用JSTL标签进行数据遍历和分页导航，使得代码更加简洁。

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前言：在上一篇我们讲了EL表达式和JSTL标签，在这一篇中我们用EL和JSTL将之前的购物车代码中的<%=xx.xx%>代码替代。

首先需要导包，这个就不用我多讲了，然后需要在页面上引用<%@ taglib prefix="c" uri="http://java.sun.com/jsp/gjstl/core"%>。同时我们再增加一个分页功能。

增加分页功能需要在IGoodsDao等包传入参数，然后重新调用方法。还需要新建一个doIndex.jsp处理index.jsp(我的主页面)。

IGoodsDao.java代码

package com.zking.dao;

import java.util.List;

import com.zking.pojo.Goods;

public interface IGoodsDao {

	//查询所有
	List<Goods> getAll(int page);
	//查询单个
	Goods getOne(Integer id);
	//查询所有页数
	int getRowCount(); 

}

GoodsDaoImpl.java代码

package com.zking.dao.impl;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.List;

import com.zking.dao.IGoodsDao;
import com.zking.pojo.Goods;
import com.zking.pojo.User;
import com.zking.util.DBHelper;

public class GoodsDaolmpl implements IGoodsDao{

	
	private Connection con;
	private PreparedStatement ps;
	private ResultSet rs;
	
	@Override
	public List<Goods> getAll(int page) {
		int size=5;//页面数据条数
		int begin=(page-1)*size+1;
		int end=page*size;
		List<Goods> list = new ArrayList<Goods>();
		try {
			con=DBHelper.getCon();
			String sql="select * from (select a.*,rownum myr from shop_goods a) b where myr between ? and ?";
			ps=con.prepareStatement(sql);
			ps.setInt(1,begin);
			ps.setInt(2,end);
			rs=ps.executeQuery();
			while(rs.next()) {
				Goods goods=new Goods();
				goods.setId(rs.getInt(1));
				goods.setName(rs.getString(2));
				goods.setPrice(rs.getInt(3));
				goods.setInfo(rs.getString(4));
				list.add(goods);
			}
			return list;
		} catch (Exception e) {
			e.printStackTrace();
		}finally {
			DBHelper.close(con, ps, rs);
		}
		return list;
  }
	 
	@Override
    public Goods getOne(Integer id) {
        try {
            con = DBHelper.getCon();
            ps = con.prepareStatement("select * from shop_goods where id=?");
            ps.setInt(1, id);
            rs = ps.executeQuery();
            if (rs.next()) {
                Goods goods = new Goods();
                goods.setId(rs.getInt(1));
                goods.setName(rs.getString(2));
                goods.setPrice(rs.getInt(3));
                goods.setInfo(rs.getString(4));
                return goods;
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            DBHelper.close(con, ps, rs);
        }
        return null;
    }

	@Override
	public int getRowCount() {
		   try {
	            con = DBHelper.getCon();
	            ps = con.prepareStatement("select count(1) from shop_goods");
	            rs = ps.executeQuery();
	            if(rs.next()) {
	            	return rs.getInt(1);
	            }
	        } catch (Exception e) {
	            e.printStackTrace();
	        } finally {
	            DBHelper.close(con, ps, rs);
	        }
		return 0;
	}
}

IGoodsBiz.java代码

package com.zking.biz;

import java.util.List;

import com.zking.pojo.Goods;

public interface IGoodsBiz {

	List<Goods> getAll(int page);
	//查询单个
	Goods getOne(Integer id);
	//查询所有页数
	int getRowCount(); 
}

GoodsBizImpl.java代码

package com.zking.biz.impl;

import java.util.List;

import com.zking.biz.IGoodsBiz;
import com.zking.dao.IGoodsDao;
import com.zking.dao.impl.GoodsDaolmpl;
import com.zking.pojo.Goods;

public class GoodsBizlmpl implements IGoodsBiz{
	
	  private IGoodsDao goodsDao=new GoodsDaolmpl();

	  @Override
	    public List<Goods> getAll(int page) {
	        return goodsDao.getAll(page);
	    }

	    @Override
	    public Goods getOne(Integer id) {
	        return goodsDao.getOne(id);
	    }

		@Override
		public int getRowCount() {
			// TODO Auto-generated method stub
			return goodsDao.getRowCount();
		}

}

index.jsp代码

<%@page import="org.apache.jasper.tagplugins.jstl.core.ForEach"%>
<%@page import="com.zking.pojo.Goods"%>
<%@page import="com.zking.biz.impl.GoodsBizlmpl"%>
<%@page import="com.zking.biz.IGoodsBiz"%>
<%@page import="com.zking.pojo.User"%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
<!DOCTYPE html>
<html lang="zh">
<head>
    <meta charset="UTF-8">
    <title>Document</title>
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <link rel="stylesheet" href="${pageContext.request.contextPath}/bootstrap-3.3.7-dist/css/bootstrap.css">
    <script src="${pageContext.request.contextPath}/bootstrap-3.3.7-dist/js/jquery-3.5.1.js"></script>
    <script src="${pageContext.request.contextPath}/bootstrap-3.3.7-dist/js/bootstrap.js"></script>
    <style>

        td:nth-child(3)::before{
            content: "$";
        }

    </style>
</head>

<body>
<c:if test="${sessionScope.user == null }">
<c:redirect url="login.jsp"/>
</c:if>
<c:if test="${goods == null}">
<c:redirect url="doIndex.jsp"/>
</c:if>
    <div class="jumbotron">
        <div class="container">
            <h1>欢迎光临嘿嘿嘿SuperMarket</h1>
            <p>尊贵的${sessionScope.user.account }</p>
            <p><a href="car.jsp" class="btn btn-primary">🛒</a></p>
        </div>
    </div>
<div class="container">
    <table class="table">
        <tr>
            <th>商品序号</th>
            <th>商品名称</th>
            <th>商品单价</th>
            <th>商品描述</th>
            <th>操作</th>
        </tr>
       <c:forEach items="${goods }"  var="g">
        <tr>
            <td>${g.id}</td>
            <td>${g.name}</td>
            <td>${g.price}</td>
            <td>${g.info }</td>
            <td>
                <div class="btn-group btn-group-xs">
                    <a href="doAddCar.jsp?id=${g.id}" class="btn btn-primary">添加购物车</a>
                </div>
            </td>
        </tr>
      </c:forEach>
    </table>
 <!-- style="text-align:center;" 居中 -->
 <!-- 分页 -->
<div style="text-align:center;">
  <ul class="pagination">
  <li>
       <a href="doIndex.jsp?ipage=${Math.max(ipage-1,1)}">
       <span >&laquo;</span>
       </a>
  </li>
  <c:forEach begin="1" end="${maxPage}" var="i">
    <li class="${ipage==i?"active":" "}">
    <a href="doIndex.jsp?ipage=${i}">${i}</a>
    </li>
  </c:forEach>
  <li>
       <a href="doIndex.jsp?ipage=${ipage+1}" >
       <span >&raquo;</span>
  </a>
  </li>																														
  </ul>
</div>
 </div>
</body>
</html>

doIndex.jsp代码

<%@page import="com.zking.biz.impl.GoodsBizlmpl"%>
<%@page import="com.zking.biz.IGoodsBiz"%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
     <%
       String parameter = request.getParameter("ipage");
       int ipage=1;//默认第一页
       if(parameter!=null){
    	   ipage=Integer.parseInt(parameter);
       }
       
       //得到商品的Biz
       IGoodsBiz goodsBiz=new GoodsBizlmpl();
       //将商品查询出来 并且放到请求域当中
       request.setAttribute("goods", goodsBiz.getAll(ipage));
       //算出也数，带导index.jsp
       int row = goodsBiz.getRowCount();

       request.setAttribute("maxPage", (int)Math.ceil(row*1.0/4)) ;
       
       request.setAttribute("ipage", ipage);
       //把数据携带导index.jsp
       request.getRequestDispatcher("index.jsp").forward(request,response);
       %>

car.jsp代码

<%@page import="com.zking.vo.CarItem"%>
<%@page import="java.util.List"%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
<!DOCTYPE html>
<html lang="zh">

<head>
    <meta charset="UTF-8">
    <title>Document</title>
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <link rel="stylesheet" href="${pageContext.request.contextPath}/bootstrap-3.3.7-dist/css/bootstrap.css">
    <script src="${pageContext.request.contextPath}/bootstrap-3.3.7-dist/js/jquery-3.5.1.js"></script>
    <script src="${pageContext.request.contextPath}/bootstrap-3.3.7-dist/js/bootstrap.js"></script>
    <style>
        td:nth-child(4)::before,
        small {
            content: "$";
        }

        * {
            outline: none !important;
        }

        td,
        th {
            text-align: center;
        }

        input {
            text-align: center;
        }
    </style>
</head>

<body>
    <div class="jumbotron">
        <div class="container">
            <h1>欢迎光临嘿嘿嘿购物车🛒</h1>
            <p>尊贵的${user.account}</p>
            <p>
              <a href="doExit.jsp" class="btn btn-warning">退出登陆</a>
            </p>
        </div>
    </div>
    <table class="table">
        <tr>
            <th>商品序号</th>
            <th>商品名称</th>
            <th>商品个数</th>
            <th>商品总价</th>
            <th>操作</th>
        </tr>
       <c:forEach items="${car }"  var="c">
        <tr>
            <td style="line-height: 30.5px;">${c.goods.id }</td>
            <td style="line-height: 30.5px;">${c.goods.name }</td>
            <td>
                <div class="input-group" style="width: 120px;margin: auto;">
                    <span class="input-group-btn">
                        <a href="doUpdCar.jsp?id=${c.goods.id }&type=0"  class="btn btn-default" type="button">-</a>
                    </span>
                    <input type="number" onblur="location.href='doUpdCar.jsp?id=${c.goods.id}&count='+this.value"  
                    value="${c.count}" type="text" class="form-control">
                    <span class="input-group-btn">
                        <a href="doUpdCar.jsp?id=${c.goods.id}&type=1" class="btn btn-default" type="button">+</a>
                    </span>
                </div>
            </td>
            <td style="line-height: 30.5px;">${c.sum}</td>
            <td style="line-height: 30.5px;">
                <a href="doDelCar.jsp?id=${c.goods.id}" class="btn btn-primary">删除</a>
            </td>
        </tr>
    </c:forEach>
  </table>
    <h1 class="alert alert-info">
        当前购物车总价
        <small>xx</small>
        <a href="doClear.jsp" class="btn btn-danger">点我结算</a>
    </h1>
</body></html>

把商品添加进购物车的代码（doAddCar.jsp）最后的页面跳转改为跳转到doIndex.jsp.