EL&&JSTL
EL表达式概念Expression Language 表达式语言。 作用替换和简化jsp页面中java代码的编写 语法${表达式} 注意jsp默认支持el表达式的。 EL表达式的使用运算运算符:
示例: <%@ page import="java.util.List" %> <%@ page import="java.util.ArrayList" %> <%@ page contentType="text/html;charset=UTF-8" language="java" %> <html> <head> <title>EL表达式</title> </head> <body> <%-- 1. 算数运算符: + - * /(div) %(mod) 2. 比较运算符: > < >= <= == != 3. 逻辑运算符: &&(and) ||(or) !(not) 4. 空运算符: empty 功能:用于判断字符串、集合、数组对象是否为null或者长度是否为0 ${empty list}:判断字符串、集合、数组对象是否为null或者长度为0 ${not empty str}:表示判断字符串、集合、数组对象是否不为null 并且长度 > 0 --%> <h3>算数运算符</h3> ${ 1 + 6}<br> ${ 9 - 6}<br> ${ 2 * 3}<br> ${ 2 div 3}<br> <%--div 表示乘法运算,mod表示除法运算 --%> ${ 9 / 3}<br> ${ 9 % 3}<br> ${ 9 mod 3}<br> <h3>比较运算符</h3> ${ 1 == 6}<br> <h3>逻辑运算符</h3> ${ 3 > 4 && 3 < 4}<br> ${ 3 > 4 and 3 < 4}<br> <h3>empty运算符</h3> <% String str = "asd"; String str1 = ""; request.setAttribute("str",str); request.setAttribute("str1",str1); List list = new ArrayList(); request.setAttribute("list",list); %> ${str}<br> ${empty str1}<br> ${empty str}<br> ${not empty str}<br> ${empty list}<br> ${not empty list}<br> </body> </html> 示例运行结果: 获取值el表达式只能从域对象中获取值
示例: <%@ page import="domain.User" %> <%@ page import="java.util.*" %> <%@ page contentType="text/html;charset=UTF-8" language="java" %> <html> <head> <title>el获取数据</title> </head> <body> <% User user = new User(); user.setName("哈哈哈"); user.setAge(22); user.setBirthday(new Date()); request.setAttribute("u",user); List list = new ArrayList(); list.add("aaa"); list.add("bbb"); list.add(user); request.setAttribute("list",list); Map map = new HashMap(); map.put("sname","嘿嘿嘿"); map.put("sage",25); map.put("sgender","女"); map.put("user",user); request.setAttribute("map",map); %> <h3>el获取域中存储的对象值</h3> ${requestScope.u}<br> ${requestScope.u.name}<br> ${u.name}<br> ${u.birStr}<br> <h3>获取list的值</h3> ${list}<br> ${list[0]}<br> ${list[1]}<br> ${list[2].name}<br> ${list[2].age}<br> ${list[10]}<br> <%-- 注意,在User.java中如果没有重写tostring方法后,出现数组越界时会显示空字符串,即无任何显示,不会报错,如果重写tostring方法,则会报错 --%> <h3>获取Map的值</h3> ${map}<br> ${map.sname}<br> ${map.sage}<br> ${map.sgender}<br> ${map["sgender"]}<br> ${map.user.name}<br> ${map.user.age}<br> <%--注意,此处的user是键,是""里的user,不是逗号后面的引用,两者只是名称相同--%> </body> </html> 示例运行效果: 隐式对象
示例: <%@ page contentType="text/html;charset=UTF-8" language="java" %> <html> <head> <title>el隐式对象</title> </head> <body> <%-- ${pageContext.request.contextPath}:动态获取虚拟目录 --%> ${pageContext.request}<br> <h3>在JSP页面中动态获取虚拟目录</h3> ${pageContext.request.contextPath}<br> </body> </html> JSTL概念JavaServer Pages Tag Library JSP标准标签库
作用用于简化和替换jsp页面上的java代码 使用步骤
常用的JSTL标签
示例: <%@ page import="java.util.ArrayList" %> <%@ page import="java.util.List" %> <%@ page contentType="text/html;charset=UTF-8" language="java" %> <%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %> <html> <head> <title>if标签</title> </head> <body> <% //判断request域中的一个list集合是否为空,如果不为null,则遍历集合中的元素 List list = new ArrayList(); list.add("aaaa"); request.setAttribute("list",list); request.setAttribute("number",3); %> <c:if test="${not empty list}"> 遍历集合中的元素 </c:if> <br> <br> <c:if test="${number % 2 != 0}"> ${number}为奇数 </c:if> </body> </html>
示例: <%@ page contentType="text/html;charset=UTF-8" language="java" %> <%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %> <html> <head> <title>choose标签</title> </head> <body> <%-- 数字编号对应星期几实现 1.域中存储一数字 2.使用choose标签取出数字 相当于switch声明 3.使用when标签做数字判断 相当于case 4.otherwise标签做其他情况的声明 相当于default --%> <% request.setAttribute("number",3); %> <c:choose> <c:when test="${number == 1}">周一</c:when> <c:when test="${number == 2}">周二</c:when> <c:when test="${number == 3}">周三</c:when> <c:when test="${number == 4}">周四</c:when> <c:when test="${number == 5}">周五</c:when> <c:when test="${number == 6}">周六</c:when> <c:when test="${number == 7}">周日</c:when> <c:otherwise>输入形式不正确</c:otherwise> </c:choose> </body> </html>
示例: <%@ page import="java.util.List" %> <%@ page import="java.util.ArrayList" %> <%@ page contentType="text/html;charset=UTF-8" language="java" %> <%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %> <html> <head> <title>foreach标签</title> </head> <body> <c:forEach begin="1" end="10" var="i" step="1"> ${i}<br> </c:forEach> <% List list = new ArrayList(); list.add("aaaa"); list.add("ssss"); list.add("dddd"); request.setAttribute("list",list); %> <c:forEach items="${list}" var="str" varStatus="s"> ${s.index} ${s.count} ${str}<br> </c:forEach> </body> </html> 练习
实现: <%@ page import="java.util.ArrayList" %> <%@ page import="java.util.List" %> <%@ page import="domain.User" %> <%@ page import="java.util.Date" %> <%@ page contentType="text/html;charset=UTF-8" language="java" %> <%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %> <html> <head> <title>test</title> </head> <body> <% List list = new ArrayList(); list.add(new User("哈哈",22,new Date())); list.add(new User("嘿嘿",23,new Date())); list.add(new User("哈喽",25,new Date())); request.setAttribute("list",list); %> <table border="1" width="500" align="center"> <tr> <th>编号</th> <th>姓名</th> <th>年龄</th> <th>生日</th> </tr> <%--数据行--%> <c:forEach items="${list}" var="user" varStatus="s"> <c:if test="${s.count % 2 != 0}"> <tr bgcolor="#ffc0cb"> <td>${s.count}</td> <td>${user.name}</td> <td>${user.age}</td> <td>${user.birStr}</td> </tr> </c:if> <c:if test="${s.count % 2 == 0}"> <tr bgcolor="#ff00ff"> <td>${s.count}</td> <td>${user.name}</td> <td>${user.age}</td> <td>${user.birStr}</td> </tr> </c:if> </c:forEach> </table> </body> </html> 运行效果: (编辑:李大同) 【声明】本站内容均来自网络,其相关言论仅代表作者个人观点,不代表本站立场。若无意侵犯到您的权利,请及时与联系站长删除相关内容! |