Lists created from Stream.toList() cannot be rendered correctly

[grzegorzbor]

Thymeleaf 3.0.15, no Spring

Create a list from Stream, using the new Stream.toList() method (new method added in java 17 i think), and add this list to the Thymeleaf model.

Then in Thymeleaf template, call size() or isEmpty() on this list , e.g. th:if="${list.isEmpty}"
and thymeleaf throws the exception:
Unable to make public boolean java.util.ImmutableCollections$ListN.isEmpty() accessible: module java.base does not "opens java.util" to unnamed module

The workaround is to use the "old style" Stream.collect(Collectors.toList()) - this works fine.

[danielfernandez]

I have not been able to reproduce this, your scenario works for me in 3.0.15. Please provide a sample project (ideally Spring Boot -based) demonstrating the issue.

[grzegorzbor]

Hi Daniel

The whole point is not to use Spring. Spring injects the custom dialect, and with that custom dialect, i think it works fine. The problem is when you use the standard Thymleaf dialect. I'm attaching the simple test app. There 4 lines marked with "works" or "does not work", just uncomment each of them to compare results.
thymeal_collection_problem.zip

[jmiguelsamper]

Hi @grzegorzbor

I checked your sample project and I think this is just a typo, instead of

th:if="${list.isEmpty}"

it should be

th:if="${list.isEmpty()}"

Otherwise, you are not calling the isEmpty() method but asking Thymeleaf to print the value of the property "isEmpty".

The same happened to me this morning and I arrived to your issue report :-)

[grzegorzbor]

Hmm i doubt it is the case.

Firstly, the error reported by thymeleaf was
Unable to make public boolean java.util.ImmutableCollections$ListN.isEmpty() accessible: module java.base does not "opens java.util" to unnamed module

so it quite clearly tries to call the isEmpty() method.

Secondly, it doesn't explain why it fails on the Stream.toList(), but works fine with Stream.collect(Collectors.toList())