How to loop through a HashMap in JSP?
How can I loop through a HashMap in JSP?
<%
HashMap<String, String> countries = MainUtils.getCountries(l);
%>
<select name="country">
<%
// Here I need to loop through countries.
%>
</select>
Answer
Just the same way as you would do in normal Java code.
for (Map.Entry<String, String> entry : countries.entrySet()) {
String key = entry.getKey();
String value = entry.getValue();
// ...
}
However, scriptlets (raw Java code in JSP files, those <% %> things) are considered a poor practice. I recommend to install JSTL (just drop the JAR file in /WEB-INF/lib and declare the needed taglibs in top of JSP). It has a <c:forEach> tag which can iterate over among others Maps. Every iteration will give you a Map.Entry back which in turn has getKey() and getValue() methods.
Here's a basic example:
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<c:forEach items="${map}" var="entry">
Key = ${entry.key}, value = ${entry.value}<br>
</c:forEach>
Thus your particular issue can be solved as follows:
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<select name="country">
<c:forEach items="${countries}" var="country">
<option value="${country.key}">${country.value}</option>
</c:forEach>
</select>
You need a Servlet or a ServletContextListener to place the ${countries} in the desired scope. If this list is supposed to be request-based, then use the Servlet's doGet():
protected void doGet(HttpServletRequest request, HttpServletResponse response) {
Map<String, String> countries = MainUtils.getCountries();
request.setAttribute("countries", countries);
request.getRequestDispatcher("/WEB-INF/page.jsp").forward(request, response);
}
Or if this list is supposed to be an application-wide constant, then use ServletContextListener's contextInitialized() so that it will be loaded only once and kept in memory:
public void contextInitialized(ServletContextEvent event) {
Map<String, String> countries = MainUtils.getCountries();
event.getServletContext().setAttribute("countries", countries);
}
In both cases the countries will be available in EL by ${countries}.
Hope this helps.