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

Hi Jonathan,

Thanks for your explanation. Your answer makes a lot of sense, but as we using Freemarker in conjunction with Spring we 
can't access a Freemarker ObjectWrapper directly without exposing it in the Spring application context, which seems like 
a bit of a smell. So, our current workaround is to put our OrderedBidiMap inside a LinkedHashMap before sending it to 
the Freemarker ViewResolver.

I haven't had a chance yet to poke around inside the Freemarker codebase, but I'm a little hazy on why Freemarker knows 
about java.util.Map implementations specifically within java.util.*, but not other packages. Is Freemarker explicitly 
checking map implementation type for performance reasons?

Thanks

Steve.

---
Stephen Smith, MEng (Wales).
http://www.stephen-smith.co.uk/

Jonathan Revusky wrote:
> 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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> 
> 
> 

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