java-例子：MVC模式，用jstl和el输出数据到jsp页面.

例子：利用session完成购物车.

domain：

package cn.itcast.cd.jsp.domain;

public class User {
	private String name;
	private String password;
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public String getPassword() {
		return password;
	}
	public void setPassword(String password) {
		this.password = password;
	}
	@Override
	public String toString() {
		return "User [name=" + name + ", password=" + password + "]";
	}
}

package cn.itcast.cd.jsp.domain;

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

public class ShoppingCar {
	private List<ShoppingCarItem> list = new ArrayList<ShoppingCarItem>();

	public List<ShoppingCarItem> getList() {
		return list;
	}
	
	public void add(ShoppingCarItem item){
		list.add(item);
	}
	
	public void remove(String id){
		for (ShoppingCarItem item : list) {
			if (id.equals(item.getId())){
				list.remove(item);
				break;
			}
		} 
	}
}

package cn.itcast.cd.jsp.domain;

public class ShoppingCarItem {
	private String id;
	private String name;
	private double price;
	private Integer number;
	public String getId() {
		return id;
	}
	public void setId(String id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public double getPrice() {
		return price;
	}
	public void setPrice(double price) {
		this.price = price;
	}
	public Integer getNumber() {
		return number;
	}
	public void setNumber(Integer number) {
		this.number = number;
	}
}

package cn.itcast.cd.utils;

public class Utils {
	public static boolean hasLength(String str) {
		return str != null && !"".equals(str);
	}
}

servlet：

package cn.itcast.cd.servlet;

import java.io.IOException;
import java.io.PrintWriter;

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

import cn.itcast.cd.jsp.domain.User;

/**
 * Servlet implementation class LoginServlet
 */
public class LoginServlet extends HttpServlet {
	protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		request.setCharacterEncoding("UTF-8");
		
		//获取参数
		String name = request.getParameter("name");
		String password = request.getParameter("password");
		
		//封装对象
		User user = new User();
		user.setPassword(password);
		user.setName(name);		
		
		HttpSession session = request.getSession();
		session.setAttribute("user", user);
		
		//显示到页面
		RequestDispatcher dispatcher = request.getRequestDispatcher("/welcome.jsp");
		dispatcher.forward(request, response);
		
	}

}

package cn.itcast.cd.servlet;

import java.io.IOException;

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

import cn.itcast.cd.jsp.domain.ShoppingCar;
import cn.itcast.cd.jsp.domain.ShoppingCarItem;

/**
 * Servlet implementation class BuyServlet
 */
public class BuyServlet extends HttpServlet {

	@Override
	protected void service(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		request.setCharacterEncoding("UTF-8");
		String name = request.getParameter("name");
		String number = request.getParameter("number");
		
		ShoppingCarItem item = new ShoppingCarItem();
		item.setName(name);
		item.setNumber(Integer.parseInt(number));
		
		HttpSession session = request.getSession();
		ShoppingCar car = (ShoppingCar)session.getAttribute("car");
		if (car == null) {
			//car为空，则创建一个购物车，并放到session中，否则，session中有购物车，不需要再添加到session中.
			car = new ShoppingCar();
			session.setAttribute("car", car);
		}
		car.add(item);
		
		RequestDispatcher dispatcher = request.getRequestDispatcher("/car.jsp");
		dispatcher.forward(request, response);
		
	}

}

package cn.itcast.cd.servlet;

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

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

import cn.itcast.cd.jsp.domain.ShoppingCar;
import cn.itcast.cd.jsp.domain.ShoppingCarItem;

/**
 * Servlet implementation class ShowServlet
 */
public class ShowServlet extends HttpServlet {
	protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		request.setCharacterEncoding("UTF-8");
		
		HttpSession session = request.getSession();
		ShoppingCar car = (ShoppingCar)session.getAttribute("car");
		
		RequestDispatcher dispatcher = request.getRequestDispatcher("/car.jsp");
		dispatcher.forward(request, response);
	}

}

登陆页面：

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
	<form action="/login" method="post">	
		<table border="0" cellpadding="3" cellspacing="0">
			<tr>
				<td>用户名：</td>
				<td><input type="text" name="name"/></td>
			</tr>
			<tr>
				<td>密&emsp;码：</td>
				<td><input type="password" name="password"/></td>
			</tr>
			<tr>
				<td colspan="2" align="center">
					<input type="submit" value="登 陆"/>
				</td>
			</tr>
		</table>
	</form>
</body>
</html>

欢迎页面：

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
	欢迎回来！<font color="blue"><b><i>${sessionScope.user.name}</i></bi></font><br/>
	<a href="/buy.jsp">开始购物</a>
	<a href="/show">管理购物车</a>
</body>
</html>

购买页面：

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
	<form action="/buy" method="post">	
		<table border="0" cellpadding="3" cellspacing="0">
			<tr>
				<td>商品名称：</td>
				<td>
					<select name="name">
						<option>鼠标</option>
						<option>键盘</option>
						<option>显示器</option>						
					</select>
				</td>
			</tr>
			<tr>
				<td>数&emsp;&emsp;量：</td>
				<td><input type="text" name="number"/></td>
			</tr>
			<tr>
				<td colspan="2" align="center">
					<input type="submit" value="购买"/>
				</td>
			</tr>
		</table>
	</form>
</body>
</html>

<%@ page language="java" contentType="text/html; charset=UTF-8"
	pageEncoding="UTF-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
 	<c:choose>
 		<c:when test="${empty sessionScope.car}">
 			购物车没有任何商品......
 		</c:when>
 		<c:otherwise>
 			
		<table>
			<tr>
				<th>商品名称</th>
				<th>商品数量</th>
			</tr>
			<c:forEach items="${sessionScope.car.list}" var="item">
				<tr>
					<td>${item.name }</td>
					<td>${item.number }</td>
				</tr>
			</c:forEach>
		</table>
		</c:otherwise>
	</c:choose>
	<form action="/buy.jsp" method="post">
		<input type
		="submit" value="继续购物"/>
	</form>
</body>
</html>