java-例子：MVC模式，用jstl和el输出数据到jsp页面.

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);
}
}

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);
}

}

<%@ 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 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>

<%@ 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>

<%@ 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  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>