表达式语言(Expression Language,EL),EL表达式是用"${}"括起来的脚本,用来更方便的读取对象!
<%@ page language="java" contentType="text/html" pageEncoding="UTF-8"%>
<html>
<head>
<title>向session设置一个属性</title>
</head>
<body>
<%
//向session设置一个属性
session.setAttribute("name", "aaa");
System.out.println("向session设置了一个属性");
%>
</body>
</html>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title></title>
</head>
<body>
<%
String value = (String) session.getAttribute("name");
out.write(value);
%>
</body>
</html>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title></title>
</head>
<body>
${name}
</body>
</html>
${标识符}
<%
//向ServletContext设置一个属性
application.setAttribute("name", "aaa");
System.out.println("向application设置了一个属性");
%>
<%
${name}
%>
<jsp:useBean id="person" class="domain.Person" scope="session"/>
<jsp:setProperty name="person" property="age" value="22"/>
在2.jsp中取出Session的属性
<%
Person person = (Person) session.getAttribute("person");
System.out.println(person.getAge());
%>
//等同于person.getAge()
${person.age}
<%
List<Person> list = new ArrayList();
Person person1 = new Person();
person1.setUsername("zhongfucheng");
Person person2 = new Person();
person2.setUsername("ouzicheng");
list.add(person1);
list.add(person2);
session.setAttribute("list",list);
%>
<%
List<Person> list = (List) session.getAttribute("list");
out.write(list.get(0).getUsername()+"<br>");
out.write(list.get(1).getUsername());
%>
使用EL表达式又是怎么样的效果呢?我们来看看!
<%--取出list集合的第1个元素(下标从0开始),获取username属性--%>
${list[0].username}
<br>
<%--取出list集合的第2个元素,获取username属性--%>
${list[1].username}
<%
Map<String, Person> map = new HashMap<>();
Person person1 = new Person();
person1.setUsername("zhongfucheng1");
Person person2 = new Person();
person2.setUsername("ouzicheng1");
map.put("aa",person1);
map.put("bb",person2);
session.setAttribute("map",map);
%>
${map.aa.username}
<br>
${map.bb.username}
${map["1"].username}
<br>
${map["2"].username}
<%
List<Person> list = null;
%>
${list==null?"list集合为空":"list集合不为空"}
EL表达式主要是来对内容的显示,为了显示的方便,EL表达式提供了11个内置对象。
<%--pageContext内置对象--%>
<%
pageContext.setAttribute("pageContext1", "pageContext");
%>
pageContext内置对象:${pageContext.getAttribute("pageContext1")}
<br>
<%--pageScope内置对象--%>
<%
pageContext.setAttribute("pageScope1","pageScope");
%>
pageScope内置对象:${pageScope.pageScope1}
<br>
<%--requestScope内置对象--%>
<%
request.setAttribute("request1","reqeust");
%>
requestScope内置对象:${requestScope.request1}
<br>
<%--sessionScope内置对象--%>
<%
session.setAttribute("session1", "session");
%>
sessionScope内置对象:${sessionScope.session1}
<br>
<%--applicationScope内置对象--%>
<%
application.setAttribute("application1","application");
%>
applicationScopt内置对象:${applicationScope.application1}
<br>
<%--header内置对象--%>
header内置对象:${header.Host}
<br>
<%--headerValues内置对象,取出第一个Cookie--%>
headerValues内置对象:${headerValues.Cookie[0]}
<br>
<%--Cookie内置对象--%>
<%
Cookie cookie = new Cookie("Cookie1", "cookie");
%>
Cookie内置对象:${cookie.JSESSIONID.value}
<br>
<%--initParam内置对象,需要为该Context配置参数才能看出效果【jsp配置的无效!亲测】--%>
initParam内置对象:${initParam.name}
<br>
注意事项:
${cookie.key}
取的是cookie对象,如访问cookie的名称和值,须${cookie.key.name}
或${cookie.key.value}
<form action="/zhongfucheng/1.jsp" method="post">
用户名:<input type="text" name="username"><br>
年龄:<input type="text " name="age"><br>
爱好:
<input type="checkbox" name="hobbies" value="football">足球
<input type="checkbox" name="hobbies" value="basketball">篮球
<input type="checkbox" name="hobbies" value="table tennis">兵乓球<br>
<input type="submit" value="提交"><br>
</form>
${param.username}
<br>
${param.age}
<br>
//没有学习jstl之前就一个一个写吧。
${paramValues.hobbies[0]}
<br>
${paramValues.hobbies[1]}
<br>
${paramValues.hobbies[2]}
<br>
EL表达式最大的特点就是:如果获取到的数据为null,输出空白字符串""!这个特点可以让我们数据回显
<%--模拟数据回显场景--%>
<%
User user = new User();
user.setGender("male");
//数据回显
request.setAttribute("user",user);
%>
<input type="radio" name="gender" value="male" ${user.gender=='male'?'checked':'' }>男
<input type="radio" name="gender" value="female" ${user.gender=='female'?'checked':'' }>女
EL自定义函数用于扩展EL表达式的功能,可以让EL表达式完成普通Java程序代码所能完成的功能
步骤:
public static String filter(String message) {
if (message == null)
return (null);
char content[] = new char[message.length()];
message.getChars(0, message.length(), content, 0);
StringBuilder result = new StringBuilder(content.length + 50);
for (int i = 0; i < content.length; i++) {
switch (content[i]) {
case '<':
result.append("<");
break;
case '>':
result.append(">");
break;
case '&':
result.append("&");
break;
case '"':
result.append(""");
break;
default:
result.append(content[i]);
}
}
return (result.toString());
}
<?xml version="1.0" encoding="ISO-8859-1"?>
<taglib xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-jsptaglibrary_2_1.xsd"
version="2.1">
<tlib-version>1.0</tlib-version>
<short-name>myshortname</short-name>
<uri>/zhongfucheng</uri>
<!--函数的描述-->
<function>
<!--函数的名字-->
<name>filter</name>
<!--函数位置-->
<function-class>utils.HTMLFilter</function-class>
<!--函数的方法声明-->
<function-signature>java.lang.String filter(java.lang.String)</function-signature>
</function>
</taglib>
<%@ page language="java" contentType="text/html" pageEncoding="UTF-8" %>
<%@taglib prefix="fn" uri="/WEB-INF/zhongfucheng.tld" %>
<html>
<head>
<title></title>
</head>
<body>
//完成了HTML转义的功能
${fn:filter("<a href='#'>点我</a>")}
</body>
</html>
<%@taglib prefix="fn" uri="http://java.sun.com/jsp/jstl/functions" %>
contains:${fn:contains("zhongfucheng",zhong )}<br>
containsIgnoreCase:${fn:containsIgnoreCase("zhongfucheng",ZHONG )}<br>
endsWith:${fn:endsWith("zhongfucheng","eng" )}<br>
escapeXml:${fn:escapeXml("<zhongfucheng>你是谁呀</zhongfucheng>")}<br>
indexOf:${fn:indexOf("zhongfucheng","g" )}<br>
length:${fn:length("zhongfucheng")}<br>
replace:${fn:replace("zhongfucheng","zhong" ,"ou" )}<br>
split:${fn:split("zhong,fu,cheng","," )}<br>
startsWith:${fn:startsWith("zhongfucheng","zho" )}<br>
substring:${fn:substring("zhongfucheng","2" , fn:length("zhongfucheng"))}<br>
substringAfter:${fn:substringAfter("zhongfucheng","zhong" )}<br>
substringBefore:${fn:substringBefore("zhongfucheng","fu" )}<br>
toLowerCase:${fn:toLowerCase("zhonGFUcheng")}<br>
toUpperCase:${fn:toUpperCase("zhongFUcheng")}<br>
trim:${fn:trim(" zhong fucheng ")}<br>
<%--将分割成的字符数组用"."拼接成一个字符串--%>
join:${fn:join(fn:split("zhong,fu,cheng","," ),"." )}<br>
<%
User user = new User();
String likes[] = {"sing"};
user.setLikes(likes);
//数据回显
request.setAttribute("user",user);
%>
<%--java的字符数组以","号分割开,首先拼接成一个字符串,再判读该字符串有没有包含关键字,如果有就checked--%>
<input type="checkbox"${ fn:contains(fn:join(user.likes,","),"sing")?'checked':'' }>唱歌
<input type="checkbox"${ fn:contains(fn:join(user.likes,","),"dance")?'checked':'' }>跳舞
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