4.5 应用EL

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4.5 应用EL的Demo

Demo1

示例app04a包含了一个JSP页面，该页面通过EL访问一个Address这个JavaBean并输出该bean的属性。该bean对象是另一个JavaBean(Employee)的一个属性，并用EL访问一个Map对象的内容，以及HTTP头部信息和会话标识。EmployeeServlet 类创建了所需的对象，并将这些对象放入到ServletRequest中，然后通过RequestDispatcher跳转到employee.jsp页面。

Employee类

这个类用来保存员工信息,员工有编号,姓名,地址等信息.其中地址信息用用单独的地址类来表示,如下所示:

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package app04a.model;
public class Employee
{
    // 员工编号
    private int id;
    // 员工姓名
    private String name;
    // 地址
    private Address address;
    public int getId()
    {
        return id;
    }
    public void setId(int id)
    {
        this.id = id;
    }
    public String getName()
    {
        return name;
    }
    public void setName(String name)
    {
        this.name = name;
    }
    public Address getAddress()
    {
        return address;
    }
    public void setAddress(Address address)
    {
        this.address = address;
    }
}

Address类

这个类用来保存地址信息,如下所示:

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package app04a.model;
public class Address
{
    // 国家
    private String country;
    // 省份
    private String province;
    // 城市
    private String city;
    // 地区
    private String district;
    // 街道名称
    private String streetName;
    // 街道编号
    private String streetNumber;
    // 邮政编码
    private String zipCode;
    /**
     * 获取国家.
     * 
     * @return
     */
    public String getCountry()
    {
        return country;
    }
    /**
     * 设置国家.
     * 
     * @param country
     */
    public void setCountry(String country)
    {
        this.country = country;
    }
    /**
     * 获取省份.
     * 
     * @return
     */
    public String getProvince()
    {
        return province;
    }
    /**
     * 设置省份.
     * 
     * @param province
     */
    public void setProvince(String province)
    {
        this.province = province;
    }
    /**
     * 获取城市.
     * 
     * @return
     */
    public String getCity()
    {
        return city;
    }
    /**
     * 设置城市.
     * 
     * @param city
     */
    public void setCity(String city)
    {
        this.city = city;
    }
    /**
     * 获取地区(县,等).
     * 
     * @return
     */
    public String getDistrict()
    {
        return district;
    }
    /**
     * 设置地区.
     * 
     * @param district
     */
    public void setDistrict(String district)
    {
        this.district = district;
    }
    /**
     * 获取街道名称.
     * 
     * @return
     */
    public String getStreetName()
    {
        return streetName;
    }
    /**
     * 设置街道名称.
     * 
     * @return
     */
    public void setStreetName(String streetName)
    {
        this.streetName = streetName;
    }
    /**
     * 获取街道编号.
     * 
     * @return
     */
    public String getStreetNumber()
    {
        return streetNumber;
    }
    /**
     * 设置街道编号
     * 
     * @param streetNumber
     */
    public void setStreetNumber(String streetNumber)
    {
        this.streetNumber = streetNumber;
    }
    /**
     * 获取邮政编码.
     * 
     * @return
     */
    public String getZipCode()
    {
        return zipCode;
    }
    /**
     * 设置邮政编码.
     * 
     * @param zipCode
     */
    public void setZipCode(String zipCode)
    {
        this.zipCode = zipCode;
    }
}

EmployeeServlet类

在这个类的doGet方法中,创建员工,创建员工的地址对象,然后把员工对象设为当前请求对象的属性。这样就完成了数据初始化话的操作,然后把请求转发到/employee.jsp这JSP页面，由该JSP页面进行显示.

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package app04a.servlet;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import app04a.model.Address;
import app04a.model.Employee;
@WebServlet(
    urlPatterns =
    {"/employee"}
)
public class EmployeeServlet extends HttpServlet
{
    private static final long serialVersionUID = 3398443364110578529L;
    @Override
    public void doGet(HttpServletRequest request,HttpServletResponse response)
        throws ServletException,IOException
    {
        // 创建地址对象
        Address address = new Address();
        address.setCountry("中国");
        address.setProvince("江苏");
        address.setCity("南京");
        address.setDistrict("玄武区");
        address.setStreetName("通往幸福的康庄大道");
        address.setStreetNumber("LoveYou233");
        address.setZipCode("16888");
        // 创建员工
        Employee employee = new Employee();
        employee.setId(1099);
        employee.setName("小明");
        employee.setAddress(address);
        // 把employee对象设置为请求对象的属性
        request.setAttribute("employee", employee);
        // 把请求转发给/employee.jsp,
        RequestDispatcher rd = request.getRequestDispatcher("/employee.jsp");
        rd.forward(request, response);
    }
}

employee.jsp页面

这个jsp页面通过EL表达式从请求对象中取出员工的信息,如下所示:

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<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<title>Employee</title>
<!-- 引入table CSS样式用到JS代码 -->
<script type="text/javascript" src="table.js"></script>
<!-- 引入table的css样式 -->
<link type="text/css" rel="styleSheet"  href="table.css" />
</head>
<body>
    <table class="altrowstable" id="alternatecolor">
        <tr>
            <td align='right'>姓名:</td>
            <td>${requestScope.employee.name}</td>
        </tr>
        <tr>
            <td align='right'>地址:</td>
            <td>${employee.address.country},${employee.address.province},${employee.address.city},${employee.address.district},${employee.address.streetName},${employee.address.streetNumber},${employee.address.zipCode}</td>
        </tr>
    </table>
</body>
</html>

在这个JSP页面中,通过表格来显示数据,为了美观这里加上了CSS和JS来实现明亮相间的表格效果,不过本篇的重点在于EL表达式,并不在JS,和CSS.

CSS文件

table.css:

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table.altrowstable {
    font-family: verdana, arial, sans-serif;
    font-size: 16px;
    color: #333333;
    border-width: 1px;
    border-color: #a9c6c9;
    border-collapse: collapse;
}
table.altrowstable th {
    border-width: 1px;
    padding: 8px;
    border-style: solid;
    border-color: #a9c6c9;
}
table.altrowstable td {
    border-width: 1px;
    padding: 8px;
    border-style: solid;
    border-color: #a9c6c9;
}
.oddrowcolor {
    background-color: #1f3de199;
}
.evenrowcolor {
    background-color: #2db6b6;
}

JS文件

table.js:这个JS代码回把表格设置成明暗相间的形式。

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function altRows(id) {
    if (document.getElementsByTagName) {
        var table = document.getElementById(id);
        var rows = table.getElementsByTagName("tr");
        for (i = 0; i < rows.length; i++) {
            if (i % 2 == 0) {
                rows[i].className = "evenrowcolor";
            } else {
                rows[i].className = "oddrowcolor";
            }
        }
    }
}
window.onload = function() {
    altRows('alternatecolor');
}

可以通过URL:http://localhost:8080/app04a/employee访问到EmployeeServlet这个Servlet,浏览器显示效果如下:
这里有一张图片

Demo2

在这个demo中,先是创建了一个Map,用来存放各个省份的省会。然后把这个Map设置为请求对象的属性,接着把请求转发到``这个JSP页面进行显示,如下所示。

ProvincialCapitalServlet

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package app04a.servlet;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
// 映射URL
@WebServlet(
    urlPatterns =
    {"/provincialcapital"}
)
public class ProvincialCapitalServlet extends HttpServlet
{
    private static final long serialVersionUID = -7130200218441279178L;
    @Override
    protected void doGet(HttpServletRequest request,
        HttpServletResponse response) throws ServletException,IOException
    {
        // 设置省会
        Map<String,String> provincialCapital = new HashMap<String,String>();
        provincialCapital.put("黑龙江", "哈尔滨");
        provincialCapital.put("吉林", "长春");
        provincialCapital.put("辽宁", "沈阳");
        provincialCapital.put("河北", "石家庄");
        provincialCapital.put("河南", "郑州");
        provincialCapital.put("山西", "太原");
        provincialCapital.put("山东", "济南");
        provincialCapital.put("江苏", "南京");
        provincialCapital.put("江西", "南昌");
        provincialCapital.put("湖南", "长沙");
        provincialCapital.put("湖北", "武汉");
        provincialCapital.put("云南", "昆明");
        provincialCapital.put("贵州", "贵阳");
        provincialCapital.put("四川", "成都");
        provincialCapital.put("福建", "福州");
        provincialCapital.put("广东", "广州");
        provincialCapital.put("陕西", "西安");
        provincialCapital.put("青海", "西宁");
        provincialCapital.put("浙江", "杭州");
        provincialCapital.put("甘肃", "兰州");
        provincialCapital.put("安徽", "合肥");
        provincialCapital.put("台湾", "台北");
        provincialCapital.put("海南", "海口");
        // 把省会信息设置为请求对象的属性.
        request.setAttribute("PC", provincialCapital);
        // 请求转发给jsp页面进行显示
        request.getRequestDispatcher("/ProvincialCapital.jsp").forward(request,
            response);
    }
}

ProvincialCapital.jsp

/app04a/WebContent/ProvincialCapital.jsp:

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<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>显示部分省会</title>
<script type="text/javascript" src="table.js"></script>
<!-- 引入table的css样式 -->
<link type="text/css" rel="styleSheet" href="table.css" />
</head>
<body>
    <table class="altrowstable" id="alternatecolor">
        <tr>
            <td align='right'>湖南的省会是:</td>
            <td>${requestScope.PC["湖南"]}</td>
        </tr>
        <tr>
            <td align='right'>江苏的省会是:</td>
            <td>${requestScope.PC["江苏"]}</td>
        </tr>
    </table>
</body>
</html>

EL表达式分析

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${requestScope.PC["江苏"]}

这个EL表达的意思是:从请求对象中的PC属性(Map)中取出key为江苏对应的值,
通过http://localhost:8080/app04a/provincialcapital这个URL就可访问这个Servlet,浏览器显示效果如下图所示:
这里有一张图片