Re: Documentation regarding Custom Utility Class for Velocity

It depends on what you mean by velocity tools.

As the description on http://velocity.apache.org/tools/releases/2.0/
says, a tool is just a Plain Old Java Object, so any Java object can act
as a tool.

Officially, a "tool" is something that can be automatically placed in
the context when you have a more complex/automatic Velocity Engine
setup, like VelocityViewServlet or VelocityStruts, or using one of the
configuration mechanisms listed on
http://velocity.apache.org/tools/devel/config.html

Unofficially, if you're working directly with the engine, you can place
any object in the VelocityContext when rendering a parsed template.

So, there's no restriction on the class that you're using as a tool,
other than:

- only public methods can be invoked from Velocity, but there can be
helper private methods if they help you organize the code
- if the tool is automatically instantiated, it must have a public
constructor with no parameters; if you instantiate it manually, you can
pass as many arguments as you want in the constructor

On 08/08/2013 12:06 PM, O. Olson wrote:
> Hi,
> 
>     I am wondering if there is any documentation on writing your own Utility Class or Custom Tool to add to Velocity. The only place I found some help is http://www.sergiy.ca/how-to-create-custom-tools-for-apache-velocity/  (There is something regarding Custom Tools at http://velocity.apache.org/tools/releases/2.0/creatingtools.html   - but I could not find anything regarding  Utility Classes that we can push into the Velocity Context.)
> 
>     Originally, I was thinking of doing my processing/customization in Velocimacros, but that is turning out to be a bit more complex/cumbersome than I expected. I am thinking of doing this in Java, and pushing the results to the Velocity Context as a single object/utility class instance. For purposes of discussion let us assume, I do something like the following in Java:
>     VelocityContext context;
>     context.put("myUtil", new MyUtil());
>     
>     I'd appreciate if I could get answers/ideas on:
> 
> 1.    I am wondering if MyUtil() needs to be static across requests.  I intend MyUtil() to provide easy access and manipulation of the current request. Hence, I would probably do something like the following in Java:
> 
> context.put("myUtil", new MyUtil(currentWebRequest));
> 
>     i.e. I would instantiate MyUtil with the current Web Request. MyUtil could then provide easy access to say the Number of Rows in the Request. So in the Template I could do:
> 
>     $myUtil.NumRows
> 
> If MyUtil() is static, this would not work, because different requests would have different number of Rows. Should the Utility Class/Object be static? The example mentioned above shows only static methods, hence my question.
> 
> 2.    Should my Utility class follow the bean syntax i.e. for the above example of  $myUtil.NumRows in the template, would I need to declare something like the following in the MyUtil Java class:
> 
> public int getNumRows() { }
> 
> 3.    What would be a good way to pass a Constant from Java to the Template? Should I use the bean syntax again? E.g. in the template
> $myUtil.JAVA_CONSTANT
> 
>     Would I need to have something like:
> public int getJAVA_CONSTANT () { }
> 
> Thank you in advance for your help,
> O. O.
> 
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-- 
Sergiu Dumitriu
http://purl.org/net/sergiu