适应jstl表达式中的  if     if-else  循环标签

<c:set var="age" value="2" scope="request"></c:set>

<c:if test="${age>18}">
<font color="green">你已经成年</font>
</c:if> 

if-else

<c:set var="age" value="2" scope="request"></c:set>

<c:choose>
<c:when test="${age>18}">
<font color="green">你已经成年</font>
</c:when>
<c:otherwise>
<font color="red">
你还未成年
</font>
</c:otherwise>
</c:choose>

普通的循环

 <c:forEach var="i" begin="1" end="10">
 中国${i}<br>
 </c:forEach>

遍历集合对象

<%
List<User> list=new ArrayList<>();
list.add(new User("中国1","123",70,"女",false));
list.add(new User("中国2","123",70,"女",false));
list.add(new User("中国3","123",70,"女",false));
list.add(new User("中国4","123",70,"女",false));
list.add(new User("中国5","123",70,"女",false));
request.setAttribute("list",list);
%>
<c:forEach items="${requestScope.list}" var="u">
${u.userName}<br>
</c:forEach>

我们先将list对象放进request 中

然后使用forEach遍历 

注意这里的items 必须是用el 表达式取到的

206-jstl中的条件标签和循环标签

<c: if   test=${age>=18}> <font color="green">你是成年人</font></c: if>

<c: choose>

<c:when  test=></c:when>

<c:  otherwise></c: otherwise>

</c:choose>

循环:

<c:forEach var="i"  begin="1"  end="10">

${i}<br/>

</c:forEach>

jstl表达式中if else 语句如下：

<c:set var="age" value="25" scope="request"></c:set>
<c:choose>
<c:when test="${age>=16 }">
<font color="green">你是成年人</font>
</c:when>
<c:otherwise>
<font color="rad">你未成年</font>
</c:otherwise>
</c:choose>

JSTL语句中的循环表达式：

取数据的时候都需要用到EL表达式${}来取值如：

例1

<c:forEach begin="1" end="15">
<%out.println("正在执行foreach语句"); %>
</c:forEach>

例2

<%
UserDao.addUser("A", new User("A", "男", 31, "shibin123", true));
UserDao.addUser("B", new User("B", "女", 32, "shibin123", true));
UserDao.addUser("C", new User("C", "女", 23, "shibin123", true));
UserDao.addUser("D", new User("D", "女", 34, "shibin123", true));
UserDao.addUser("E", new User("E", "女", 21, "shibin123", true));
UserDao.addUser("F", new User("F", "女", 23, "shibin123", true));
UserDao.addUser("G", new User("G", "男", 24, "shibin123", true));
Map ma=DBUtil.getUsers();
List list=new ArrayList();
list.addAll(ma.values());
request.setAttribute("list", list);
%>
<c:forEach items="${list }" var="us">
${us.name},${us.age},${us.sex},${us.password}<br>
</c:forEach>