JavaWeb-JSTL迭代操作

冷不防 2023-08-17 17:41 131阅读 0赞

## 迭代操作 ##

**<c:forEach>：可以对数组，collection，map进行遍历，begin(对于集合begin从0开始算)，end,step**

**<c:forEach>为循环控制，它可以将集合(collection)中的成员循序浏览一遍。运作方式为当条件符合时，就会持续重复执行<c: forEach>的本体内容**

**属性：**

<table> 
 <tbody> 
 <tr> 
 <td>名称</td> 
 <td>说明</td> 
 <td>EL</td> 
 <td>类型</td> 
 <td>必须</td> 
 <td>默认值</td> 
 </tr> 
 <tr> 
 <td>var</td> 
 <td>用来存放现在指到的成员</td> 
 <td>N</td> 
 <td>String</td> 
 <td>否</td> 
 <td>无</td> 
 </tr> 
 <tr> 
 <td>items</td> 
 <td>被迭代的集合对象</td> 
 <td>Y</td> 
 <td> Arrays Collection Iterator Map Enumeration String </td> 
 <td>否</td> 
 <td>无</td> 
 </tr> 
 <tr> 
 <td>varStatus</td> 
 <td>用来存放现在指到的相关成员信息</td> 
 <td>N</td> 
 <td>String</td> 
 <td>否</td> 
 <td>无</td> 
 </tr> 
 <tr> 
 <td>begin</td> 
 <td>开始的位置</td> 
 <td>Y</td> 
 <td>int</td> 
 <td>否</td> 
 <td>0</td> 
 </tr> 
 <tr> 
 <td>end</td> 
 <td>结束的位置</td> 
 <td>Y</td> 
 <td>int</td> 
 <td>否</td> 
 <td>最后一个成员</td> 
 </tr> 
 <tr> 
 <td>step</td> 
 <td>每次迭代的间隔数</td> 
 <td>Y</td> 
 <td>int</td> 
 <td>否</td> 
 <td>1</td> 
 </tr> 
 </tbody> 
</table>

**varStatus的属性：**

<table> 
 <tbody> 
 <tr> 
 <td>属性</td> 
 <td>类型</td> 
 <td>意义</td> 
 </tr> 
 <tr> 
 <td>index</td> 
 <td>number</td> 
 <td>现在指到成员的索引</td> 
 </tr> 
 <tr> 
 <td>count</td> 
 <td>number</td> 
 <td>总共指到成员的总数</td> 
 </tr> 
 <tr> 
 <td>first</td> 
 <td>boolean</td> 
 <td>现在指到的成员是否为第一个成员</td> 
 </tr> 
 <tr> 
 <td>last</td> 
 <td>boolean</td> 
 <td>现在指到的成员是否为最后一个成员</td> 
 </tr> 
 </tbody> 
</table>

**<!---collection 跟数组遍历相同->**

<%
 List<Customer> custs = new ArrayList<Customer>();
 custs.add(new Customer("1","AAA"));
 custs.add(new Customer("2","BBB"));
 custs.add(new Customer("3","CCC"));
 custs.add(new Customer("4","DDD"));
 custs.add(new Customer("5","EEE"));
 custs.add(new Customer("6","FFF"));
 
 request.setAttribute("custs",custs);
 %>
 
 <c:forEach items="${requestScope.custs}" begin="1" step="2" end="5" var="cust">
 ${cust.id} -- ${cust.name} 
 </c:forEach>

**![1642540-20190715150456305-238634291.png][]**

<%
 List<Customer> custs = new ArrayList<Customer>();
 custs.add(new Customer("1","AAA"));
 custs.add(new Customer("2","BBB"));
 custs.add(new Customer("3","CCC"));
 custs.add(new Customer("4","DDD"));
 custs.add(new Customer("5","EEE"));
 custs.add(new Customer("6","FFF"));
 
 request.setAttribute("custs",custs);
 %>
 
 <c:forEach items="${requestScope.custs}" varStatus="status" var="cust">
 ${status.index} : ${status.count} : ${status.first} : ${status.last} : ${cust.id} : ${cust.name} 
 </c:forEach>

![1642540-20190715150248757-841898054.png][]

****

<%
 Map<String,Customer> map = new HashMap<String, Customer>();
 map.put("a",new Customer("1","AAA"));
 map.put("b",new Customer("2","BBB"));
 map.put("c",new Customer("3","CCC"));
 map.put("e",new Customer("4","DDD"));
 map.put("f",new Customer("5","EEE"));
 map.put("g",new Customer("6","FFF"));
 
 request.setAttribute("map",map);
 %>
 
 <c:forEach items="${requestScope.custs}" varStatus="status" var="cust">
 ${cust.key} - ${cust.value.id} - ${cust.value.name} 
 </c:forEach>

****

<%
 String [] names = new String[]{"A","B","C"};
 request.setAttribute("names",names);
 %>
 
 <c:forEach var="name" items="${names}">${name}--</c:forEach>

## <c: forTokens>：处理字符串，类似于String的split()方法 ##

**<c:forTokens>用来浏览一字符串中所有的成员，其成员是由定义符号(delimiters)所分隔的。**

去掉，号

<c:set value="a,b,c,d,e;f:g" var="test" scope="request"></c:set>
 
 <c:forTokens items="${requestScope.test}" delims="," var="s">
 ${s} 
 </c:forTokens>

![1642540-20190715152250068-931703377.png][]

转载于:https://www.cnblogs.com/yangHS/p/11187973.html

[1642540-20190715150456305-238634291.png]: /images/20230808/910c153e598746d6b004a648ac7b3c6c.png
[1642540-20190715150248757-841898054.png]: /images/20230808/0f8a37de3f10422b9cab428648387eda.png
[1642540-20190715152250068-931703377.png]: /images/20230808/c38189368637477b89b29b666f3f13cc.png