如何使用JSTL在HashMap中迭代ArrayList？

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>

Answer 3

you haven't closed c tag.try out this

 <c:forEach items="${logMap}" var="entry">
        Key = ${entry.key}, values = 
        <c:forEach items="${entry.value}" var="item" varStatus="loop">
            ${item} ${!loop.last ? ', ' : ''}
        </c:forEach><br>
    </c:forEach>

Answer 4

You can also loop round just the map.value its self if you know the key

<c:forEach var="value" items="${myMap[myObject.someInteger]}">
    ${value}
</c:forEach>