struts2迭代器的用法

Name

Required

Default

Evaluated

Type

Description

begin	false	0	false	Integer	if specified the iteration will start on that index
end	false	Size of the 'values' List or array, or 0 if 'step' is negative	false	Integer	if specified the iteration will end on that index(inclusive)
id	false		false	String	Deprecated. Use 'var' instead
status	false	false	false	Boolean	If specified, an instanceof IteratorStatus will be pushed into stack upon each iteration
step	false	1	false	Integer	if specified the iteration index will be increased by this value on each iteration. It can be a negative value, in which case 'begin' must be greater than 'end'
value	false		false	String	the iteratable source to iterate over, else an the object itself will be put into a newly created List
var	false		false	String	Name used to reference the value pushed into the Value Stack

Examples

The following example retrieves the value of the getDays() method of the current object on the value stack and uses it to iterate over. The <s:property/> tag prints out the current value of the iterator.

<s:iterator value="days">
  <p>day is: <s:property/></p>
</s:iterator>

The following example uses a Bean tag and places it into the ActionContext. The iterator tag will retrieve that object from the ActionContext and then calls its getDays() method as above. The status attribute is also used to create an IteratorStatus object, which in this example, its odd() method is used to alternate row colours:

<s:bean name="org.apache.struts2.example.IteratorExample" var="it">
  <s:param name="day" value="'foo'"/>
  <s:param name="day" value="'bar'"/>
</s:bean>
<p/>
<table border="0" cellspacing="0" cellpadding="1">
<tr>
  <th>Days of the week</th>
</tr>
<p/>
<s:iterator value="#it.days" status="rowstatus">
  <tr>
    <s:if test="#rowstatus.odd == true">
      <td style="background: grey"><s:property/></td>
    </s:if>
    <s:else>
      <td><s:property/></td>
    </s:else>
  </tr>
</s:iterator>
</table>

The next example will further demonstrate the use of the status attribute, using a DAO obtained from the action class through OGNL, iterating over groups and their users (in a security context). The last() method indicates if the current object is the last available in the iteration, and if not, we need to separate the users using a comma:

 <s:iterator value="groupDao.groups" status="groupStatus">
     <tr class="<s:if test="#groupStatus.odd == true ">odd</s:if><s:else>even</s:else>">
         <td><s:property value="name" /></td>
         <td><s:property value="description" /></td>
         <td>
             <s:iterator value="users" status="userStatus">
                 <s:property value="fullName" /><s:if test="!#userStatus.last">,</s:if>
             </s:iterator>
         </td>
     </tr>
 </s:iterator>

 

The next example iterates over a an action collection and passes every iterator value to another action. The trick here lies in the use of the '[0]' operator. It takes the current iterator value and passes it on to the edit action. Using the '[0]' operator has the same effect as using <s:property />. (The latter, however, does not work from inside the param tag).

     <s:action name="entries" var="entries"/>
     <s:iterator value="#entries.entries" >
         <s:property value="name" />
         <s:property />
         <s:push value="...">
             <s:action name="edit" var="edit" >
                 <s:param name="entry" value="[0]" />
             </s:action>
         </push>
     </s:iterator>

 

A loop that iterates 5 times

<s:iterator var="counter" begin="1" end="5" >
   <!-- current iteration value (1, ... 5) -->
   <s:property value="top" />
</s:iterator>

 

Another way to create a simple loop, similar to JSTL's <c:forEach begin="..." end="..." ...> is to use some OGNL magic, which provides some under-the-covers magic to make 0-n loops trivial. This example also loops five times.

<s:iterator status="stat" value="(5).{ #this }" >
   <s:property value="#stat.count" /> <!-- Note that "count" is 1-based, "index" is 0-based. -->
</s:iterator>

 

A loop that iterates over a partial list

<s:iterator value="{1,2,3,4,5}" begin="2" end="4" >
   <!-- current iteration value (2,3,4) -->
   <s:property value="top" />
</s:iterator>

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