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| <article class="container"> |
| <section class="col-md-12"> |
| <a class="edit-on-gh" href="https://github.com/apache/struts-site/edit/master/source/tag-developers/iterator-tag.md" title="Edit this page on GitHub">Edit on GitHub</a> |
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| <a href="tag-reference.html" title="back to Tag Reference"><< back to Tag Reference</a> |
| |
| <h1 id="iterator">iterator</h1> |
| |
| <p>Please make sure you have read the <a href="tag-syntax">Tag Syntax</a> document and understand how tag attribute syntax works.</p> |
| |
| <blockquote> |
| <p><strong>NOTE</strong>: The <code class="highlighter-rouge">id</code> attribute is deprecated in Struts 2.1.x, and has been replaced by the <code class="highlighter-rouge">var</code> attribute. |
| The <code class="highlighter-rouge">begin</code>, <code class="highlighter-rouge">end</code> and <code class="highlighter-rouge">step</code> attributes are only available from 2.1.7+</p> |
| </blockquote> |
| |
| <h2 id="description">Description</h2> |
| |
| <p>Iterator will iterate over a value. An iterable value can be any of: <code class="highlighter-rouge">java.util.Collection</code>, <code class="highlighter-rouge">java.util.Iterator</code>, |
| <code class="highlighter-rouge">java.util.Enumeration</code>, <code class="highlighter-rouge">java.util.Map</code>, or an array.</p> |
| |
| <p>Iterate over a iterable value</p> |
| |
| <h2 id="attributes">Attributes</h2> |
| |
| <table width="100%"> |
| <tr> |
| <td colspan="6"><h4>Dynamic Attributes Allowed:</h4> false</td> |
| </tr> |
| <tr> |
| <td colspan="6"> </td> |
| </tr> |
| <tr> |
| <th align="left" valign="top"><h4>Name</h4></th> |
| <th align="left" valign="top"><h4>Required</h4></th> |
| <th align="left" valign="top"><h4>Default</h4></th> |
| <th align="left" valign="top"><h4>Evaluated</h4></th> |
| <th align="left" valign="top"><h4>Type</h4></th> |
| <th align="left" valign="top"><h4>Description</h4></th> |
| </tr> |
| <tr> |
| <td align="left" valign="top">begin</td> |
| <td align="left" valign="top">false</td> |
| <td align="left" valign="top">0</td> |
| <td align="left" valign="top">false</td> |
| <td align="left" valign="top">Integer</td> |
| <td align="left" valign="top">if specified the iteration will start on that index</td> |
| </tr> |
| <tr> |
| <td align="left" valign="top">end</td> |
| <td align="left" valign="top">false</td> |
| <td align="left" valign="top">Size of the 'values' List or array, or 0 if 'step' is negative</td> |
| <td align="left" valign="top">false</td> |
| <td align="left" valign="top">Integer</td> |
| <td align="left" valign="top">if specified the iteration will end on that index(inclusive)</td> |
| </tr> |
| <tr> |
| <td align="left" valign="top">status</td> |
| <td align="left" valign="top">false</td> |
| <td align="left" valign="top">false</td> |
| <td align="left" valign="top">false</td> |
| <td align="left" valign="top">Boolean</td> |
| <td align="left" valign="top">If specified, an instanceof IteratorStatus will be pushed into stack upon each iteration</td> |
| </tr> |
| <tr> |
| <td align="left" valign="top">step</td> |
| <td align="left" valign="top">false</td> |
| <td align="left" valign="top">1</td> |
| <td align="left" valign="top">false</td> |
| <td align="left" valign="top">Integer</td> |
| <td align="left" valign="top">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'</td> |
| </tr> |
| <tr> |
| <td align="left" valign="top">value</td> |
| <td align="left" valign="top">false</td> |
| <td align="left" valign="top"></td> |
| <td align="left" valign="top">false</td> |
| <td align="left" valign="top">String</td> |
| <td align="left" valign="top">the iteratable source to iterate over, else an the object itself will be put into a newly created List</td> |
| </tr> |
| <tr> |
| <td align="left" valign="top">var</td> |
| <td align="left" valign="top">false</td> |
| <td align="left" valign="top"></td> |
| <td align="left" valign="top">false</td> |
| <td align="left" valign="top">String</td> |
| <td align="left" valign="top">Name used to reference the value pushed into the Value Stack (scope: action).</td> |
| </tr> |
| </table> |
| |
| <h2 id="examples">Examples</h2> |
| |
| <p>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 <code class="highlighter-rouge"><s:property/></code> tag prints out the current value of the iterator.</p> |
| |
| <pre><code class="language-jsp"><s:iterator value="days"> |
| <p>day is: <s:property/></p> |
| </s:iterator> |
| </code></pre> |
| |
| <p>The following example uses a {@link Bean} tag and places it into the ActionContext. The iterator tag will retrieve that |
| object from the <code class="highlighter-rouge">ActionContext</code> and then calls its <code class="highlighter-rouge">getDays()</code> method as above. The status attribute is also used |
| to create an <code class="highlighter-rouge">IteratorStatus</code> object, which in this example, its <code class="highlighter-rouge">odd()</code> method is used to alternate row colours:</p> |
| |
| <pre><code class="language-jsp"><s:bean name="org.apache.struts2.example.IteratorExample" var="it"> |
| <s:param name="day" value="'foo'"/> |
| <s:param name="day" value="'bar'"/> |
| </s:bean> |
| |
| <table border="0" cellspacing="0" cellpadding="1"> |
| <tr> |
| <th>Days of the week</th> |
| </tr> |
| |
| <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> |
| </code></pre> |
| |
| <p>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:</p> |
| |
| <pre><code class="language-jsp"><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> |
| </code></pre> |
| |
| <p>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 <code class="highlighter-rouge">[0]</code> operator. It takes the current iterator value and passes it on to the edit action. |
| Using the <code class="highlighter-rouge">[0]</code> operator has the same effect as using <code class="highlighter-rouge"><s:property /></code>. (The latter, however, does not work from inside |
| the <code class="highlighter-rouge">param</code> tag).</p> |
| |
| <pre><code class="language-jsp"><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> |
| </code></pre> |
| |
| <p>A loop that iterates 5 times</p> |
| |
| <pre><code class="language-jsp"><s:iterator var="counter" begin="1" end="5" > |
| <!-- current iteration value (1, ... 5) --> |
| <s:property value="top" /> |
| </s:iterator> |
| </code></pre> |
| |
| <p>Another way to create a simple loop, similar to JSTL’s <code class="highlighter-rouge"><c:forEach begin="..." end="..." ...></code> 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.</p> |
| |
| <pre><code class="language-jsp"><s:iterator status="stat" value="(5).{ #this }" > |
| <s:property value="#stat.count" /> <!-- Note that "count" is 1-based, "index" is 0-based. --> |
| </s:iterator> |
| </code></pre> |
| |
| <p>A loop that iterates over a partial list</p> |
| |
| <pre><code class="language-jsp"><s:iterator value="{1,2,3,4,5}" begin="2" end="4" > |
| <!-- current iteration value (2,3,4) --> |
| <s:property value="top" /> |
| </s:iterator> |
| </code></pre> |
| |
| <p>Another example when we can access a variable out of the current loop context and where name clashes with the current</p> |
| |
| <pre><code class="language-jsp"><s:select name="location" size="1" list="locations" listKey="key" |
| listValue="value" emptyOption="false" /> |
| |
| <s:iterator var="item" value="items" status="rowstatus"> |
| <s:url var="myUrl" action="itemDelete"> |
| <s:param name="id" value="#item.id" /> |
| <%-- Outer loop variable name [1]. as clash with item.location --%> |
| <s:param name="location" value="[1].location" /> |
| </s:url> |
| </s:iterator> |
| </code></pre> |
| |
| </section> |
| </article> |
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