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https://issues.apache.org/jira/browse/VELOCITY-911?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16810905#comment-16810905
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Claude Brisson commented on VELOCITY-911:
-----------------------------------------
Docs updated with your suggestions. The user guide now states:
{code}
...
- $foo is an object (other than a string, a number or a collection) which is
not null (and for which the standard public methods for querying the object
size, length or boolean/string representations, if they exist, indicate a
non-empty, non-zero, non-false object).
...
{code}
and the #if directive configuration reference has been reworded as suggested.
> Incorrect evaluation of IF-Directive for objects with isEmpty-method
> --------------------------------------------------------------------
>
> Key: VELOCITY-911
> URL: https://issues.apache.org/jira/browse/VELOCITY-911
> Project: Velocity
> Issue Type: Bug
> Affects Versions: 2.0, 2.1
> Reporter: M. Luppi
> Assignee: Claude Brisson
> Priority: Major
> Attachments: VelocityIsEmptyBugMCVE.java, mcve-project.zip,
> template.vm
>
>
> With Velocity 2.0 the logic of evaluation for IF-Directives changed and now
> uses an extended approach to determine whether it is true. This bug report
> only refers to the case where $foo is an +object+. The documentation for 2.0
> and 2.1 state as follows:
> {quote}The variable $foo is evaluated to determine whether it is true, which
> will happen under one of those circumstances: [...]
> $foo is an object (other than a string, a number or a collection) which is
> not null
> _Source:
> [http://velocity.apache.org/engine/2.0/user-guide.html#if-elseif-else|http://velocity.apache.org/engine/2.0/user-guide.html#if-elseif-else]_
> {quote}
> After a long debugging session I have found that objects with a public
> isEmpty-method are not being handled according to the documentation cited
> above. Thereby, such objects are evaluated as false if there is an
> isEmpty-method that returns false. The correct evaluation result according to
> the documentation should be true since the object is not null and not a
> string, a number or a collection.
> It gets even more confusing when we take access modifiers into account. If
> the access of the isEmpty-method is not public, the behaviour is as it should
> be. When we make it public, however, the above explained bug occurs in
> version 2.0 as well as 2.1.
> See the attached classes and the template or the whole project of the MCVE
> (minimal, complete, and verifiable example) as ZIP.
> _The output of the test is as follows:_
> {code:java}
> null object
> -----------
> [ OK ] Expected.
> non-null object with isEmpty-method (public)
> --------------------------------------------
> isEmpty evaluates to true
> [FAIL] Not expected since object is not null.
> isEmpty evaluates to false
> [ OK ] Expected.
> non-null object with isEmpty-method (package-private)
> -----------------------------------------------------
> isEmpty evaluates to true
> [ OK ] Expected.
> isEmpty evaluates to false
> [ OK ] Expected.
> {code}
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