JSP 标准标签库（JSTL）

不念不忘少年蓝@ 2022-01-22 03:13 355阅读 0赞

# 产生原因 #

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3NjUxMjY3_size_16_color_FFFFFF_t_70]![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3NjUxMjY3_size_16_color_FFFFFF_t_70 1]

# JSTL操作符 #

*  el表达式的取值默认顺序: pageScope requestScope sessionScope applicationScope
 *  结构：采用.导航，也称为存取器 $\{ [user.name][]\} $\{ [user.class.name][]\} 、输出map $\{mapValue.key1\} 、输出数组 $\{strArray\[1\]\} 、输出list $\{list\[1\].name\}
 *  el表达式的运算  
    $\{1+2\}= 3  
    $\{10/5\}= 2.0  
    $\{10%3\}= 1  
    $\{10 div 2\}= 5.0  
    $\{10 mod 4\}= 2
 *  el表达式对应的运算符  
    ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3NjUxMjY3_size_16_color_FFFFFF_t_70 2]

*  el表达式判断是否为空

<table> 
 <thead> 
  <tr> 
   <th>jsp</th> 
   <th>JSTL</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>request.setAttribute(“value1”,null)</td> 
   <td>${empty requestScope.value1} = true</td> 
  </tr> 
  <tr> 
   <td>request.setAttribute(“value2”,"")</td> 
   <td>${empty requestScope.value1} = true</td> 
  </tr> 
  <tr> 
   <td>request.setAttribute(“value3”,new ArrayList())</td> 
   <td>${empty requestScope.value1} = true</td> 
  </tr> 
  <tr> 
   <td>request.setAttribute(“value4”,“i love you”)</td> 
   <td>${empty requestScope.value1} = false</td> 
  </tr> 
  <tr> 
   <td>request.setAttribute(“value4”,“i love you”)</td> 
   <td>${!empty requestScope.value1} = true</td> 
  </tr> 
 </tbody> 
</table>

*  jar及配置

web.xml

<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
    xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" 
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" 
    id="WebApp_ID" version="2.4">

大于等于2.4 方可支持jstl ，先引入 standard.jar 和 jstl.jar  
jstl标签的用法 在页面引入 `<%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>`  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3NjUxMjY3_size_16_color_FFFFFF_t_70 3]  
输出标签 -----------

<c:out value="ppp" />                                              输出   ppp 
     <c:out value="null" default="ddd"/>                                输出   ddd   可以设置默认值 
     <c:out value="<font color="red">kkk</font>" escapeXml="false"/>    输出 红色的kkk    默认的escapeXml为true

赋值标签 -----------

<c:set value="123" var="jj" scope="session" />       此时有个名为jj，值为123的session ，默认的scope为page 
                       ${jj}                                             在页面打印出123 
                    <c:remove var="jj" />                                将其删除,可以指定scope，默认为page

逻辑标签 -----------

<c:if test="?" />                                   ?：代表条件 可以用el表达式      
                     
                     <c:choose> 
                         <c:when test="?"> 
                            ......                                         相当于 if...else...   c:when 可以有多个,相当于else if 
                         </c:when> 
                         <otherwise> 
                           ...... 
                         </otherwise> 
                     </choose>

循环控制标签 -----------

<c:forEach items="${list}" var="u" >                   ${list}是一个集合 
                         ${u.name} 
                     </c:forEach> 
                     
                     
                     <c:forEach items="${list}" var="u" varStatu="ss">                  
                         <c:choose> 
                         <c:when test="u.age % 2 == 0"> 
                            <tr bgColor="red">                                  如果集合中的数字是偶数，则当行为红色 
                         </c:when> 
                         <otherwise> 
                            <tr>    
                         </otherwise> 
                         </choose> 
                     </c:forEach> 
                     
                     
                     <c:forEach items="${list}" var="u" begin="2" end="8" step="2">                 输出下表(从0开始)为2到8的元素，每次递增2 
                         ${u.name}                                                                  将输出u[2].name  u[4].name  u[6].name  u[8].name 
                     </c:forEach> 
                                       
                     Map m = new Map(); 
                     m.put("k1","v1");         
                     m.put("k2","v2");         
                     request.setAttribute("mapValue",m); 
                     
                     <c:forEach items="mapValue" var="ma"> 
                         ${ma.key} = ${ma.value}                                 输出：  k1=v1  k2=v2   
                     </c:forEach>

间隔符控制标签-------------

request.setAttribute("str","1,2,3,4,5");      
                    
                    <c:forTokens items="str" delims="," var="de">             
                        ${de}                                                  输出 12345 
                    </c:forTokens>

捕获异常标签 ----------

<c:catch var="info"> 
                       <% 
                         Integer.parseInt("sdfsdf");                 
                       %>        
                   </c:catch> 
                   
                   ${info}                                             输出：异常信息

导入页面标签 -----------

<c:import url="http://www.baidu.com" />            相当于include

链接标签 ------------

<c:url value="http://www.baidu.com" var="v"/> 
                       <c:param name="name" value="jack" /> 
                       <c:param name="age" value="20" /> 
                   </url>     
                   
                   ${v}              输出        http://www.baidu.com?name=jack&age=20

重定向标签 ------------

<c:redirect context="/company" url="/index.jsp">   定位到名叫company的项目下的index.jsp页面

# 使用JSTL： #

引入JSTL的相关的jar包.
    在页面中引入标签库.<%@ taglib uri=”” prefix=””%>

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## jstl标签 ##

<body>
          <h1>jstl标签</h1>
          <c:set var="name" value="张三" scope="page"></c:set>
          ${name }
    
          
          <c:set var="city" value="上海" scope="page"></c:set>
          <c:out value="${city }" default="北京"></c:out>
          <c:out value="<h1>标题一</h1>" escapeXml="false"></c:out>
    
          <c:set var="n1" value="10" scope="page"></c:set>
          <c:set var="n2" value="20" scope="page"></c:set>
          <c:if test="${n1<n2 }" var="flag" scope="page">
            n1小于n2!
          </c:if>
           <c:if test="${flag }">
            n1小于n2!
          </c:if>
          <br/>
           <c:set var="n1" value="30" scope="page"></c:set>
          <c:set var="n2" value="20" scope="page"></c:set>
          <c:if test="${n1>=n2 }" var="flag" scope="page">
            n1大于等于n2!
          </c:if>
          <c:if test="${flag }">
            n1大于等于n2!
          </c:if>
      </body>

## JSTL常用标签:forEach ##

<body>
            <h1>JSTL常用标签:forEach</h1>
            <h3>遍历数组</h3>
            <%
                String[] arr = {"张三","李四","王五"};
                pageContext.setAttribute("Arr", arr);
             %>
             <c:forEach var="i" items="${Arr }">
                ${i } 
             </c:forEach>
    
             <h3>遍历List集合</h3>
             <%
                List<String> list = new ArrayList<String>();
                list.add("孙六");
                list.add("钱六");
                list.add("赵七");
                pageContext.setAttribute("List", list);
              %>
              <c:forEach var="i" items="${List }">
                ${i }
              </c:forEach>
    
              <h3>遍历Map集合</h3>
              <%
                    Map<String,String> map = new HashMap<String,String>();
                    map.put("a", "钱一");
                    map.put("b", "刘二");
                    map.put("c", "朱三");
                    pageContext.setAttribute("Map", map);
               %>
               <c:forEach var="entry" items="${Map }">
                ${entry.key }-${entry.value }
               </c:forEach>
    
               <h3>遍历从1到10</h3>
               <c:forEach var="i" begin="1" end="10">
                ${ i }
               </c:forEach>
    
               <h3>遍历从100到300,step=5</h3>
               
               <c:forEach var="i" begin="100" end="300" step="5" varStatus="status">
                    <c:if test="${status.count % 3 == 0 }">
                        <font color="red">${i }</font>
                    </c:if>
                    <c:if test="${status.count % 3 != 0 }">
                        ${i }
                    </c:if>
               </c:forEach>
      </body>

## JSTL提供的EL的函数库 ##

(<%@ taglib uri=”http://java.sun.com/jsp/jstl/functions” prefix=”fn” %>)

<body>
     <h1>JSTL提供的EL的函数库</h1>
     
     ${ fn:contains("Hello World","Hello") }
     ${ fn:length("Hello") }
     ${ fn:toLowerCase("ASDFG") }
    
     
     
     <c:forEach var="i" items="${ fn:split('a-c-b-d-r','-') }">
       ${i }
     </c:forEach>
    </body>

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[user.name]: http://user.name
[user.class.name]: http://user.class.name
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