Re: Preserving ordering in a Freemarker sequence when iterating over an OrderedBidiMap.

Stephen Smith wrote:
> Hi,
> 
> We're using an OrderedBidiMap from Commons Collections 3.x to store a mapping of
> keys<->values (the implementation we use is TreeBidiMap). Our Freemarker syntax
> is as follows:
> 
>     <#list subjectsMap?keys as subjectName>
>       ${subjectName}
>     </#if>
> 
> The problem is that the sequence is returning an unordered list of keys. The same
> Freemarker syntax seems to work with a LinkedHashMap, but I don't understand what
> Freemarker is doing under the hood when getting the map's keys. Surely it is just
> calling Map#keySet, in which case our ordering should be preserved?

I think the problem is that the DefaultObjectWrapper is copying the map, 
and by default, is using HashMap. The code in there is aware, for 
example, of things in java.util.* such as LinkedHashMap or TreeMap and 
will preserve order, but the default behavior with maps otherwise is to 
copy them into a HashMap.

Perhaps you need to explicitly use the BeansWrapper. Just use:

BeansWrapper bw = new BeansWrapper();
dataModel.put("subjectsMap", bw.wrap(subjectsMap));

Or, you could just set it as the default wrapper, and that would be 
something like:

freeMarkerConfig.setObjectWrapper(new BeansWrapper());


> 
> Is this a defect in Freemarker, 

Arguably, it is, though the whole issue is a bit complex...

> are we misusing the sequence syntax, or should we
> pass through the OrderedBidiMap's entry set and then call getKey and getValue on
> each bean?

For the moment, the solution would be to explicitly use 
freemarker.ext.beans.BeansWrapper.

JR

> 
> Thanks in advance
> 
> Stephen Smith
> 
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