第8章 JSP和EL----补充

浏览数：18 / 时间：2015年06月09日

8.1 El及其在JSP中的重要地位

引入EL（Expresin Language）主要原因之一是，希望不依赖脚本元素就能创建表示层Jsp页面。脚本元素一般是用Java编写的代码，可以嵌入到一个

Jsp页面中。之所以想在Jsp中嵌入脚本元素，主要是受应用需求的驱使。要求使用脚本元素的主要应用需求如下：

为Jsp提供流程控制

设置Jsp页面局部变量，并在以后访问

要提供复杂表达式（涉及Java对象）的值

访问一个任意Java对象的属性

调用JavaBean或其它Java对象的方法

经验告诉我们，在Jsp中使用脚本元素，会使大型项目从长远来看很难维护。理想情况下，应尽一切可能创建没有脚本元素的Jsp

为了创建完全没有脚本元素也能正常工作的Jsp，它应满足上述5个应用需求，而且无需使用嵌入的Java代码。前两项由JSTL处理，后三项由EL解决

8.2 EL语法

${expression}

由${ 开头，接着expression是EL的表达式，最后以 }结尾。在这里${ 符号被视为EL的起始点，所以如果在Jsp网页中要显示${ 字符串，必须在前面加

上反斜杠符号\，亦即写成\${ 的格式，或者写成${ ‘ ${ ’ }，也就是用EL来输出${ 符号。在EL中要输出一个字符串，可将此字符串放在一对单引

号或双引号内。

8.3 EL运算符

1.算术运算符

2.关系运算符

3.逻辑运算符

4.条件运算符

5.验证运算符

6. 运算符的优先级

补充:EL内置对象:

1..与[]运算符:

2.与存储有关的内置对象

applicationScope

sessionScope

requetScope

pageScope

但是4个隐含对象只能有业取得某个范围的属性值即jsp中的getAttribute(String name),不能取得其他信息.

3.与输入有关的内置对象

param

paramValues

4.其它内置对象

cookis

header内置对象

initParam内置对象

pageContext内置对象

例8-3 访问javaBean属性

eighth_example2.jsp

<%@ page contentType="text/html; charset=gb2312" language="java" %>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<link href="css/style.css" type="text/css" rel="stylesheet">
<title>用户注册</title>
</head>

<body>
<table width="659" height="425" border="0" align="center" cellpadding="0" cellspacing="0"background="image/backgrounb.jpg">
<tr>
    <td height="71" align="center">用户注册</td>
</tr>
<tr>
    <td valign="top">
    <form name="form" method="post" action="getInfo.jsp">

    <table width="346" border="1" align="center" cellpadding="0" cellspacing="0">
      <tr align="center">
        <td width="113" height="30">用 户 名：</td>
        <td width="227"><input type="text" name="account"></td>
      </tr>
      <tr align="center">
        <td height="30">密    码：</td>
        <td><input type="password" name="password"></td>
      </tr>
      <tr align="center">
        <td height="30">姓    名：</td>
        <td><input type="text" name="username"></td>
      </tr>
      <tr align="center">
        <td height="30">年    龄：</td>
        <td><input type="text" name="age"></td>
      </tr>
      <tr align="center">
        <td height="30">性    别：</td>
        <td><input type="text" name="sex"></td>
      </tr>
      </table>
        <table width="346" border="0" align="center">
          <tr align="center">
            <td>
              <input type="submit" name="Submit" value="提交">   
              <input type="reset" name="Submit2" value="清除">
            </td>
          </tr>
        </table>
    </form>

    </td>
</tr>
</table>
</body>
</html>

getInfo.jsp

<%@ page contentType="text/html; charset=gb2312" %>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<link href="css/style.css" type="text/css" rel="stylesheet">
<jsp:useBean id="userBean" scope="request" class="pfc.UserBean"/>
<%
request.setCharacterEncoding("gb2312");
userBean.setAccount(request.getParameter("account"));
userBean.setPassword(request.getParameter("password"));
userBean.setAge(request.getParameter("age"));
userBean.setSex(request.getParameter("sex"));
userBean.setUsername(request.getParameter("username"));
%>

</head>
<body>
<table width="659" height="425" border="0" align="center" cellpadding="0" cellspacing="0"background="image/backgrounb.jpg">
<tr>
    <td height="71" align="center">用户注册信息是</td>
</tr>
<tr>
    <td valign="top">
    <table width="346" border="1" align="center" cellpadding="0" cellspacing="0">
      <tr align="center">
        <td width="113" height="30">用 户 名：</td>
        <td width="227">${userBean.account}</td>
      </tr>
      <tr align="center">
        <td height="30">密    码：</td>
        <td>${userBean.password}</td>
      </tr>
      <tr align="center">
        <td height="30">姓    名：</td>
        <td>${userBean.username}</td>
      </tr>
      <tr align="center">
        <td height="30">年    龄：</td>
        <td>${userBean.age}</td>
      </tr>
      <tr align="center">
        <td height="30">性    别：</td>
        <td>${userBean.sex}</td>
      </tr>
         </table>
        </td>
</tr>
</table>
</body>
</html>

UserBean.java

package pfc;

public class UserBean {
    public String account = "";
    public String password = "";
    public String username= "";
    public String age= "";
    public String sex= "";
    public String getAccount() {
        return account;
    }
    public void setAccount(String account) {
        this.account = account;
    }
    public String getAge() {
        return age;
    }
    public void setAge(String age) {
        this.age = age;
    }
    public String getSex() {
        return sex;
    }
    public void setSex(String sex) {
        this.sex = sex;
    }
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }


}

运行结果一

例4：pageContext隐含对象的应用，eighth_example3.jsp

<%@ page pageEncoding="gb2312"%>
<html>
    <head>
        <title>pageContext隐含对象的调用</title>
        <link href="css/style.css" type="text/css" rel="stylesheet">
<body>
<p align="center">pageContext隐含对象的调用</p>
<table width="737" border="1" align="center">
<tr align="center">
    <td>pageContext隐含对象的调用</td>
    <td >说明</td>
    <td >调用结果</td>
</tr>
<tr>
    <td>\${pageContext.request.queryString}</td>
    <td>获取参数</td>
    <td>${pageContext.request.queryString}</td>
</tr>
<tr>
    <td>\${pageContext.request.requestURL}</td>
    <td>获取当前网页的地址，但是包含请求的参数</td>
    <td>${pageContext.request.requestURL}</td>
</tr>
<tr>
    <td>\${pageContext.request.contextPath}</td>
    <td>web应用的名称</td>
    <td>${pageContext.request.contextPath}</td>
</tr>
<tr>
    <td>\${pageContext.request.method}</td>
    <td>获取HTTP的方法（GET或POST）</td>
    <td>${pageContext.request.method}</td>
</tr>
<tr>
    <td>\${pageContext.request.remoteAddr}</td>
    <td>获取用户的IP地址</td>
    <td>${pageContext.request.remoteAddr}</td>
</tr>
</table>
</body>
</html>

例5：获取参数隐含对象的应用，eighth_example4.jsp

eighth_example4.jsp

<%@ page pageEncoding="gb2312"%>
<html>
<link href="css/style.css" type="text/css" rel="stylesheet">
<body>
<p align="center">param和paramValues隐含对象的应用</p>

<form name="form" method="post" action="getPara.jsp">
<table width="426" border="0" align="center" cellpadding="0" cellspacing="0">
<tr>
    <td width="108" height="30">姓名</td>
    <td width="298" height="30"><input type="text" name="name"></td>
</tr>
<tr>
    <td height="30">性别</td>
    <td height="30">
      <input type="radio" name="sex" value="男">
    男    
    <input type="radio" name="sex" value="女">
    女</td>
</tr>
<tr>
    <td height="30">年龄</td>
    <td height="30"><input type="text" name="age"></td>
</tr>
<tr>
    <td height="30">职业</td>
    <td height="30"><input type="text" name="profession"></td>
</tr>
<tr>
    <td height="30">您喜欢的高校</td>
    <td height="30">
      <input type="checkbox" name="school" value="清华">
    清华
    <input type="checkbox" name="school" value="北大">
    北大
    <input type="checkbox" name="school" value="北大方正软件学院">
    北大方正软件学院
    <input type="checkbox" name="school" value="其他">
    其他</td>
</tr>
<tr align="center">
    <td height="30" colspan="2">

        <input type="submit" name="Submit" value="提交">
     

      <input type="reset" name="Submit2" value="清除">


    </td>
</tr>
</table></form>
</body>
</html>

getPara.jsp:

<%@ page pageEncoding="gb2312"%>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
        <link href="css/style.css" type="text/css" rel="stylesheet">
<%request.setCharacterEncoding("gb2312");%>

</head>

<body>
<p align="center">param和paramValues隐含对象的参数</p>
<table width="416" border="0" align="center" cellpadding="0" cellspacing="0">
<tr>
    <td width="108" height="30">姓名</td>
    <td width="298" height="30">${param.name}</td>
</tr>
<tr>
    <td height="30">性别</td>
    <td height="30">${param.sex}</td>
</tr>
<tr>
    <td height="30">年龄</td>
    <td height="30">${param.age}</td>
</tr>
<tr>
    <td height="30">职业</td>
    <td height="30">${param.profession}</td>
</tr>
<tr>
    <td height="30">您喜欢的高校</td>
    <td height="30">${paramValues.school[0]} ${paramValues.school[1]} ${paramValues.school[2]} ${paramValues.school[3]}</td>
</tr>
</table>
</body>
</html>

例8-6 访问作用域范围隐含对象的应用

<%@ page contentType="text/html; charset=gb2312" language="java" %>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<title>EL中pageScope、requestScope、sessionScope、applicationScope隐含对象</title>
</head>
<%
pageContext.setAttribute("name","作用域为page",PageContext.PAGE_SCOPE);
pageContext.setAttribute("name","作用域为request",PageContext.REQUEST_SCOPE);
pageContext.setAttribute("name","作用域为session",PageContext.SESSION_SCOPE);
pageContext.setAttribute("name","作用域为application",PageContext.APPLICATION_SCOPE);
%>
<body>
\${name}:${name}<br>
\${pageScope}:${pageScope.name}<br>
\${requestScope}:${requestScope.name}<br>
\${sessionScope}:${sessionScope.name}<br>
\${applicationScope}:${applicationScope.name}
</body>
</html>

例7 访问Servlet中的作用域，eighth_example6.jsp

eighth_example6.jsp

<%@ page contentType="text/html; charset=gb2312" %>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />

<link href="css/style.css" rel="stylesheet" type="text/css">
<title>访问Servlet</title>
<style type="text/css">

</style></head>
<body>
<p align="center">访问Servlet</p>
<table width="402" height="100" border="0" align="center">
<tr>
    <td width="143">作用域为request：</td>
    <td width="306">${university1}</td>
</tr>

<tr>
    <td>作用域为session：</td>
    <td>${university2}、${university3}</td>
</tr>

<tr>
    <td>作用域为application：</td>
    <td>${university4}</td>
</tr>

<tr>
    <td>访问数组：</td>
    <td>${city[0]}、${city[1]}、${city[2]}</td>
</tr>

    <tr>
    <td>访问List集合：</td>
    <td>${majorList[0]}、${majorList[1]}、${majorList[2]}</td>
</tr>

</table>
</body>
</html>

UserInfoServlet.java

package pfc;
import java.io.IOException;
import javax.servlet.*;
import javax.servlet.http.*;
public class UserInfoServlet extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // 作用域为request
        request.setAttribute("university1", "清华");
        // 作用域为session
        HttpSession session = request.getSession();
        session.setAttribute("university2", "北大");
        session.setAttribute("university3", "南大");
        // 作用域为application
        ServletContext application = getServletContext();
        application.setAttribute("university4", "天大");
        // 作用域为session,访问数组
        String city[] = { "北京", "天津", "南京" };
        session.setAttribute("city", city);
        // 作用域为session，访问List容器
        java.util.List<String> majorList = new java.util.ArrayList<String>();
        majorList.add("软件技术");
        majorList.add("软件测试");
        majorList.add("游戏软件");
        session.setAttribute("majorList", majorList);
        RequestDispatcher dispatcher = request
                .getRequestDispatcher("eighth_example6.jsp");
        dispatcher.forward(request, response);
    }
}

8.5 函数

由于在Jsp 2.0中，程序代码是独立放在Java class里， EL必须要有一个机制可以调用Java class 的方法，而这个机制即是函数。一个函数可以对应到一个Java class的public static method，这个对应是通过中介的文件，即标签库描述文件（Tag Library Descriptor,TLD）来完成。类必须声明为public 的，而类内被调用的方法必须声明为public static的

例 8-8 eighth_example7.jsp

<%@ page contentType="text/html; charset=gb2312" %>
<%@ taglib prefix="fun" uri ="/WEB-INF/function.tld"%>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312"/>
<link href="css/style.css" type="text/css" rel="stylesheet" />
<title>自定义函数的应用</title>
</head>
<style type="text/css">

</style>
<body>
<p align="center">自定义函数的应用</p>
<form name="form1" method="post" action="eighth_example7.jsp">

<table width="300" border="0" align="center" cellpadding="0" cellspacing="0">
<tr>
    <td width="272" align="center">
    第一个字符串<input type="text" name="first" value="${param.first}">  
    </td>
</tr>
   <tr>
    <td width="272" align="center">
    第二个字符串<input type="text" name="second" value="${param.second}">  
    </td>
</tr>
<tr>
    <td width="272" align="center">
    <input type="submit" name="Submit" value="提交">
</td>
</tr>
</table>
</form>
<table width="300" border="0" align="center" cellpadding="0" cellspacing="0">
<tr align="center">
    <td width="189" height="25">说明</td>
    <td width="111">输出结果</td>
</tr>
<tr align="center">
    <td height="25">将第一个字符串内容反向输出</td>
    <td>${fun:reverse(param.first)}</td>
</tr>
   <tr align="center">
    <td height="25">将第一个字符串内容转换为大写字母</td>
    <td>${fun:cape(param.first)}</td>
</tr>
<tr align="center">
    <td height="25">将两个字符串内容连接</td>
       <td>${fun:connect(param.first,param.second)}</td>
</tr>

</table>
</body>
</html>

KindMethod.java

package pfc;
public class KindMethod {
    // 反向输出
    public static String reverse(String text) {
        return new StringBuffer(text).reverse().toString();
    }
    // 转换成大写字母
    public static String cape(String text) {
        return text.toUpperCase();
    }
    public static String connect(String x, String y) {
        return x+y;
    }
}

function.tld

<?xml version="1.0" encoding="UTF-8" ?>
<taglib xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-jsptaglibrary_2_0.xsd"
version="2.0">
<description>library</description>
<display-name>functions</display-name>
<tlib-version>1.1</tlib-version>
<short-name>fun</short-name>
<function>
    <description>reverse</description>
    <name>reverse</name>
    <function-class>pfc.KindMethod</function-class>
    <function-signature>java.lang.String reverse( java.lang.String )</function-signature>
</function>
   <function>
    <description>cape</description>
    <name>cape</name>
    <function-class>pfc.KindMethod</function-class>
    <function-signature>java.lang.String cape( java.lang.String )</function-signature>
</function>
<function>
    <description>connect</description>
    <name>connect</name>
    <function-class>pfc.KindMethod</function-class>
    <function-signature>java.lang.String connect( java.lang.String, java.lang.String)</function-signature>
</function>
</taglib>

表8.5 function.tld的说明

description 函数说明

name 函数名称

function-class 实现此函数java类名称

function-signature 用来实现此函数的java mthod声明