JSP_EL&JSTL常用操作，家中必备！

╰半橙微兮° 2023-06-17 11:55 2阅读 0赞

**JSTL（JavaServer Pages Standard Tag Library，JSP）标准标记库**  
**JSTL引入了expression language（EL表达式）**

使用JSTL需要标签导入

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
    
    <%@ taglib prefix="fn" uri="http://java.sun.com/jsp/jstl/functions" %>

**<c:if>**

<c:if test="${... }">
    	add some html
    </c:if>
    //没有else结构，所以只能一个if一个if的写。

**<c:choose>**

<c:choose>
    	<c:when test="${...}">
    		do some html
    	</c:when>
    	<c:when test="${... }">
    		do some html
    	</c:when>
    	<c:otherwise>
    		do some html
    	</c:otherwise>
    </c:choose>
    //和java中switch语句类似

**<c:set>**

<c:set var="name"  value="value"></c:set>
    //设置或修改变量

**<c:foreach>**

//for循环
    <c:forEach items="${...List }" var="v" varStatus="vs"> 
    	//v就是对象
    	//vs.count,vs.index...
    	do some html...
    </c:forEach>

## EL表达式 ##

${
        error}
    	
    	${
        requestScope.error }
    	${
        sessionScope.error }
    	
    	
    	${
        sessionScope.user.account }
    	${
        sessionScope.user.password }
    	${
        user.name }
    	
    	
    	${
        map.key }
    	${
        map.keyObj.attr }
    	//用<c:foreach>遍历Map
    	<c:foreach items="${...Map}" var="obj">
    		${
        obj.key }
    		${
        obj.value}
    	</c:foreach>
    	
    	
    	${
        number+1}
    	${
        number%2==0 }
    	${
        number%2==0?'偶数':'奇数' }
    	
    	
    	${
        empty ... }
    	${
        not empty ... }
    	
    	
    	${
        array[0] }