How to iterate an ArrayList inside a HashMap using JSTL?
I have a map like this,
Map<Integer,ArrayList<Object>> myMap = new LinkedHashMap<Integer,ArrayList<Object>>();
Now I have to iterate this Map and then the ArrayList inside the map. How can I do this using JSTL?
Answer
You can use JSTL <c:forEach> tag to iterate over arrays, collections and maps.
In case of arrays and collections, every iteration the var will give you just the currently iterated item right away.
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<c:forEach items="${collectionOrArray}" var="item">
Item = ${item}<br>
</c:forEach>
In case of maps, every iteration the var will give you a Map.Entry object which in turn has getKey() and getValue() methods.
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<c:forEach items="${map}" var="entry">
Key = ${entry.key}, value = ${entry.value}<br>
</c:forEach>
In your particular case, the ${entry.value} is actually a List, thus you need to iterate over it as well:
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<c:forEach items="${map}" var="entry">
Key = ${entry.key}, values =
<c:forEach items="${entry.value}" var="item" varStatus="loop">
${item} ${!loop.last ? ', ' : ''}
</c:forEach><br>
</c:forEach>
The varStatus is there just for convenience ;)
To understand better what's all going on here, here's a plain Java translation:
for (Entry<String, List<Object>> entry : map.entrySet()) {
out.print("Key = " + entry.getKey() + ", values = ");
for (Iterator<Object> iter = entry.getValue().iterator(); iter.hasNext();) {
Object item = iter.next();
out.print(item + (iter.hasNext() ? ", " : ""));
}
out.println();
}