How to iterate an ArrayList inside a HashMap using JSTL?

Question

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 1

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(); } 

See also:

• How to loop through a HashMap in JSP?
• Show JDBC ResultSet in HTML in JSP page using MVC and DAO pattern
• How to loop over something a specified number of times in JSTL?

Answer 2

Did you try something like this?

<c:forEach var='item' items='${map}'>     <c:forEach var='arrayItem' items='${item.value}' />       ...     </c:forEach> </c:forEach>