Velocity Engine Extension (Was: [Helma-dev] Template Engines)

[Juerg Lehni]

Thanks, Hannes.

I had to make the helma.framework.core.Prototype.getResources()  
function public.

My velocity extension is working quite well now.

It is caching templates and only parsing them when they changed, so  
performances should be high.

I created a HelmaExtension out of it, so if a app defines  
velocityEngine = true in app.properties, it will have a global  
variable called velocity, through which it can access the templates.

HopObjects then can define a render function like this:

function renderTemplate(name, param) {
	velocity.renderTemplate(this, name, param);
}

and from then on, the velocity extension can be used just like  
renderSkin.

I'd like to submit this for others ot use as well.

Would it make sense to create a CVS repository for it?

Jürg

Am 23.11.2005 um 15:43 schrieb Hannes Wallnoefer:

> I can't respond in length because I'm on the run, but the right place
> to implement a per-HopObject getResource would probably be
> helma.framework.core.Prototype. You have all your repositories and
> resources there. Then you'd need to implement a scripting stub in
> helma.scripting.rhino.HopObject, which shouldn't be too dificult.
>
> hope that helps, more later.
> hannes
>
> 2005/11/23, Juerg Lehni <juerg at scratchdisk.com>:
>> I started embeding Velocity in Helma now and roughly it's already
>> working.
>>
>> Accessing the request, response and session objects from velocity
>> templates is possible, and looping through passed arrays as well.
>>
>> But I'm struggling with how to nicely integrate it in Helma.
>>
>> My main problem is how to find the template resources in the
>> repositories in an easy way. The default files
>> (.skin, .js, .hac, .type) are cached in Prototype. For additional
>> file-types, I need to iterate through all the repositories and
>> subrepositories of the application.
>>
>> I wonder if there could be a function getResource() in HopObject that
>> would return the given resource in the prototype folder, regardless
>> of the extension. This would offer an easy hook for integrating the
>> template engine.
>>
>> Or maybe it should be a level higher, in the skin manager? Like this,
>> even external skin folders would be supported. But as Skins are
>> stored in parsed Skin objects, I would then need to access the skin's
>> getSource() property to get the raw source and create a tempalte from
>> that...
>>
>> Any pointers for this would be very appreciated, as I'm a bit blocked
>> right now.
>>
>> Jürg
>>
>> Am 23.11.2005 um 11:53 schrieb Juerg Lehni:
>>
>>>
>>> Am 23.11.2005 um 11:31 schrieb Hannes Wallnoefer:
>>>
>>>> 2005/11/23, Juerg Lehni <juerg at scratchdisk.com>:
>>>>> Another advantage of Rails seems to be the more flexible template
>>>>> engine that allows loops and if / else constructs in the templates
>>>>> (skins).
>>>>
>>>> Well, what Rails does is basically the same as Helma's old .hsp,  
>>>> i.e.
>>>> embedding Ruby code in templates. I really thought it was a good
>>>> thing
>>>> when we went over that. The critical question in this regard  
>>>> will be
>>>> how easy we can make it to implement macros in Helma 2.0.
>>>
>>> I agree that this is not a good idea. For Rails there's liquid now,
>>> which avoids this problem and offers programming constructs:
>>>
>>> http://home.leetsoft.com/liquid
>>>
>>>>
>>>>> I was wondering how this will be adressed in Helma 2.0? There are
>>>>> powerfull Java libraries around for this, e.g. Velocity ( http://
>>>>> jakarta.apache.org/velocity/ ) and FreeMaker ( http://
>>>>> freemarker.sourceforge.net/ ).
>>>>>
>>>>> Hannes, are you considering embeding one of those, or will Helma
>>>>> feature its own engine, that might implement the programming
>>>>> constructs in a way that is closer to the JavaScript syntax?
>>>>
>>>> I think it should be possible to use a third party templating  
>>>> engine
>>>> with Helma. There will be a proprietary implementation, though.
>>>>
>>>> One current idea, pretty offhand, is to use custom markup tags or
>>>> attributes:
>>>>
>>>> <div h:foreach="storylist">
>>>>   <h3 h:content="story.title">Title</h3>
>>>>   ...
>>>> </div>
>>>>
>>>> Explanation: If the h:foreach attribute evaluates to an array, the
>>>> inner skin is rendered on each array element. If statements  
>>>> could be
>>>> build in a similar fashion:
>>>>
>>>> <div h:if="story">
>>>>     <h3 h:content="story.title">Title</h3>
>>>>   ...
>>>> </div>
>>>>
>>>> As I said, I'm writing this offhand, we may already have done this
>>>> better somewhere on the mailing list.
>>>
>>> Interesting. But how would I add logic that is not bound to a html
>>> tag? I also wonder if it wouldn't become a bit hard to actually
>>> spot the logic parts in a skin if they're all nested inside tags
>>> (without using the editor's search function and searching for "h:").
>>>
>>> In Velocity, it looks like this:
>>>
>>> #foreach( $mud in $mudsOnSpecial )
>>>    #if ( $customer.hasPurchased($mud) )
>>>       <tr>
>>>         <td>
>>>           $flogger.getPromo( $mud )
>>>         </td>
>>>       </tr>
>>>    #end
>>> #end
>>>
>>> And this is a Liquid template:
>>>
>>> {% if user.age > 18 %}
>>>    <a href="...">pron here</a>
>>> {% else %}
>>>    <a href="http://www.disneyland.com/">disney</a>
>>> {% endif %}
>>>
>>> {% for item in array %}
>>>    {{ item }}
>>>  {% endfor %}
>>>
>>> This seems to be somehow easier to read.
>>>
>>>>> And is this something I could help with for 2.0?
>>>>
>>>> Yes, of course you can. Keep having good ideas, try out things,  
>>>> start
>>>> using dev.helma.org wiki :-)
>>>
>>> Ok! I'll play around a little and see what I come up with.
>>>
>>> Jürg
>>>
>>>>
>>>> hannes
>>>>
>>>>> Jürg_______________________________________________
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>>>>> Helma-dev at helma.org
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>>>>>
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