<body>
<h1>对map和set的迭代</h1> <% Map map = new HashMap(); map.put("1", "aa"); map.put("2", "bb"); //把map放入某个域对象 request.setAttribute("lstMap", map); //set Set set = new HashSet(); User user = new User(); user.setName("lihui"); user.setAge(20); set.add(user); user = new User(); user.setName("zhaoping"); user.setAge(30); set.add(user); user = new User(); user.setName("chengxiang"); user.setAge(10); set.add(user); request.setAttribute("sets", new HashSet()); request.setAttribute("lstSet", set); %> <h2>map</h2> <c:forEach items="${lstMap}" var="item"> Key=${item.key };Value=${item.value } <!-- Key=2;Value=bb Key=1;Value=aa --> </c:forEach> <br/> <h2>set</h2> <c:forEach items="${lstSet}" var="item"> ${item.name }:${item.age} </c:forEach> <br/> <h2>使用标签判断空</h2> <c:if test="${empty nihao}"> 没有该变量nihao </c:if> <br/> <c:if test="${empty sets}"> 没有元素sets </c:if> </body>输出：
对map和set的迭代
map
Key=2;Value=bb Key=1;Value=aa
set
chengxiang:10 lihui:20 zhaoping:30
使用标签判断空
没有该变量nihao
没有元素sets