Re: Apache Velocity : Verify if all substitutions are made

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Thanks for replying. It will work in my use case.

On Tue, Jun 13, 2023 at 7:14=E2=80=AFPM Christopher Schultz <
[email protected]> wrote:

> Debraj,
>
> On 6/13/23 05:38, Debraj Manna wrote:
> > Can someone let me know how I can verify a velocity context against a
> > template? Basically, I want to throw some error if all variables are no=
t
> > substituted in the velocity template.
> >
> > For example, let's say I have a velocity template, card.vm
> >
> >    card {
> >      type: CREDIT
> >      company: VISA
> >      name: "${firstName} ${lastName}"
> >    }
> >
> > The substitution is done like below
> >
> > VelocityEngine velocityEngine =3D new VelocityEngine();
> > velocityEngine.init();
> >
> > Template t =3D velocityEngine.getTemplate("card.vm");
> >
> > VelocityContext context =3D new VelocityContext();
> > context.put("firstName", "tuk");
> > StringWriter writer =3D new StringWriter();
> > t.merge( context, writer );
> >
> > In this case, I want to throw some error specifying that lastName is no=
t
> > replaced in template.
> >
> > Does velocity provide anything for this?
>
> No, but it would be easy to do. Instead of using the basic
> VelocityContext, wrap it in a custom one, something like this:
>
> public class WarningVelocityContext
>      extends VelocityContext
> {
>      public Object get(String key) {
>          Object o =3D super.get(key);
>
>          if(null =3D=3D o) {
>              throw new IllegalStateException("Key {" + key + "} has not
> been set");
>          }
>      }
> }
>
> Then in your code, wrap the context right before merging:
>
> t.merge(new WarningVelocityContext(context), writer);
>
> Note that this will throw exceptions for *anything* that's not found for
> any reason. If you try something like:
>
> $someObject.method()
>
> And "someObject" is null, then you'll get an error. It may be difficult
> to tell the difference between the things you "care about" and the
> things you do not. If you have a simple use-case, then probably this
> will work.
>
> -chris
>
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