How to Iterate Through HashMaps in JSP Using JSTL and Avoid Scriptlets?-javaTutorial-php.cn

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How to Iterate Through HashMaps in JSP Using JSTL and Avoid Scriptlets?

Linda Hamilton

Dec 17, 2024 am 06:04 AM

How to Iterate Through HashMaps in JSP Using JSTL and Avoid Scriptlets?

Looping Through HashMaps in JSP

Traversing a HashMap in JSP is similar to doing so in plain Java code. Utilize the following loop structure:

<div class="code" style="position:relative; padding:0px; margin:0px;"><pre class="brush:php;toolbar:false">String key = entry.getKey();
String value = entry.getValue();
// ...

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}

Scriptlet Drawbacks

While scriptlets were previously common, they are now regarded as poor practice. Instead, we recommend using JSTL, which provides the tag for iterating over Maps, returning a Map.Entry object with getKey() and getValue() methods in each iteration.

<p><c:forEach items="${map}" var="entry"></p>
<div class="code" style="position:relative; padding:0px; margin:0px;"><pre class="brush:php;toolbar:false">Key = ${entry.key}, value = ${entry.value}<br>

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JSP Solution

To resolve your specific problem:

<p><select name="country"></p>
<div class="code" style="position:relative; padding:0px; margin:0px;"><pre class="brush:php;toolbar:false"><c:forEach items=&quot;${countries}&quot; var=&quot;country&quot;>
    <option value=&quot;${country.key}&quot;>${country.value}</option>
</c:forEach>

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To make ${countries} accessible in the requested scope, use a Servlet or ServletContextListener.

Example Use Cases

Here are examples of using Servlet or ServletContextListener:

<pre class="brush:php;toolbar:false">Map<String, String> countries = MainUtils.getCountries();
request.setAttribute(&quot;countries&quot;, countries);
request.getRequestDispatcher(&quot;/WEB-INF/page.jsp&quot;).forward(request, response);</p>
<p>}<br>

Or:

<pre class="brush:php;toolbar:false">Map<String, String> countries = MainUtils.getCountries();
event.getServletContext().setAttribute(&quot;countries&quot;, countries);</p>
<p>}<br>