Freemarker - behavior of Built-ins with Iterables

I am observing strange behavior with Freemarker. I have an Iterable in reportModel.affectedJars. It is provided from a graph database - Tinkerpop/Titan.

${iterableHasContent(reportModel.affectedJars)?then("true", "false")}<br>
${reportModel.affectedJars?has_content?then("yes", "no")} has_content<br>
${reportModel.affectedJars?size}<br>
${reportModel.affectedJars}<br>
<#if reportModel.affectedJars?size == 0>
    <p>No archives containing CVE vulnerabilities were found.</p>
<#else>
    <#list reportModel.affectedJars.iterator() as file>
        Something...

iterableHasContent is an alternative of ?size. I would expect this to be quite consistent, in terms of:

false
no has_content
0
<p>No archives ...

But what is actually happening is:

false
yes has_content
6
--- and no iterations. ---

Which looks like there's some glitch that makes Freemarker think that the Iterable is not empty, but then when iterated, it gives no items. No exception is thrown.

I was trying to debug, but the debugger doesn't stop at the relevant code for some reason.

Is there something I am missing in ?size and ?has_content paradigms that allows this behavior?

Solution

Don't try do anything with that Iterable, except calling iterator() on it. The problem is that FreeMarker was created before Iterable was introduced, and it sees a pure Iterable (i.e., one which doesn't also implement Collection) as a generic object, rather than some listable thing. (Fixing this without breaking backward compatibility is not possible, though surely there should be a configuration option for it.) This is also where the size 6 comes from; it's the number of items in the hash, which contains its methods and JavaBean properties. Ugh...

So after you got the Itera*tor*, the next thing you will find that it doesn't support ?size. It supports ?has_content though. (This assumes that you are using the default object wrapper, not pure BeansWrapper, which is pure evil.) But if you can, use #list with a nested #else. Something like:

<#list reportModel.affectedJars.iterator() as file>
    Something...
<#else>
    <p>No archives containing CVE vulnerabilities were found.</p>
</#list>

or a more real life example:

<#list reportModel.affectedJars.iterator()>
    <p>Found some archives containing CVE vulnerabilities:</p>
    <#items as file>
       Something...
    </#items>
<#else>
    <p>No archives containing CVE vulnerabilities were found.</p>
</#list>