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POGet the class name of an array in JSTL
 

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    <p>I'm trying to build a url in a JSP from a <code>Map&lt;String, Object&gt;</code> of parameters. The existing code iterates through the map and adds c:params for the keys and values: </p> <pre><code>&lt;c:url value="/"&gt; &lt;c:forEach items="${myParamMap}" var="parameter"&gt; &lt;c:param name="${parameter.key}" value="${parameter.value}" /&gt; &lt;/c:forEach&gt; &lt;/c:url&gt; </code></pre> <p>I've run into the case where the value of an entry in the map is actually an array of Objects. My next attempt was to add a nested loop to iterate over the values as necessary:</p> <pre><code>&lt;c:url value="/"&gt; &lt;c:forEach items="${myParamMap}" var="parameter"&gt; &lt;c:forEach items="${parameter.value}" var="innerValue"&gt; &lt;c:param name="${parameter.key}" value="${innerValue}" /&gt; &lt;/c:forEach&gt; &lt;/c:forEach&gt; &lt;/c:url&gt; </code></pre> <p>But of course this breaks the normal situation where the value is not iterable. </p> <p>My next idea was to check whether the value is an array via some kind of "instanceof" check. The only way I could find on the internet to do this was: <code>${object.class.className == 'Whatever'}</code>. </p> <p>This does not work for arrays in JSTL because for the expression <code>${someArray.class}</code>, JSTL tries to convert the <code>.class</code> part into an integer in order to use it as an index (I can't believe someone thought this was a good idea).</p> <p>My next move is to use scriptlets but I'm still curious to see if there's a way to do this with pure JSTL.</p> <hr> <p>Using scriptlets is the way to go in this case. I ended up with something like:</p> <pre><code>&lt;c:set var="val" value="${parameter.value}"&gt; &lt;% boolean isArray = pageContext.getAttribute("val").getClass().isArray(); %&gt; &lt;c:choose&gt; &lt;c:when test="&lt;%= isArray &gt;"&gt; ... forEach loop to set all the params ... &lt;/c:when&gt; &lt;c:otherwise&gt; ... just set the param with key &amp; value ... &lt;/c:otherwise&gt; &lt;/c:choose&gt; </code></pre>
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    1. COThe `${paramValues}` is actually a `Map<String, String[]>`. Why not just treating it accordingly? As to your concrete problem, just use `object[0].class.name`, but you will always get `java.lang.String`.
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    2. COMy mistake, I'm not using paramValues. I'm using a Map<String, Object> from an in-house library. I'll edit my post to reflect this.
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