Intellij and Project Reactor
Hi all,
Am wondering if anyone has encountered this issue.
I can no longer update my Intellij, since it seems any version with ‘2025’ in its name has lost support for Project Reactor (Mono/Flux) debugging. What I mean by this is that in the ‘evaluate expression’ window, in versions from 2024 and below, you can evaluate a Mono/Flux and see their contents (presumably the debugger is calling ‘block’ on them). However, in the newer versions, the debugger just hangs forever, writing “collecting data…”.
I work a lot with Project Reactor, which means I cannot afford to not be able to debug Mono/Flux. So for now I am forced to never upgrade Intellij to the newer versions.
I've tried upgrading several times in 2025, checking if this was fixed, but it never was, and I am always forced to downgrade again.
Would appreciate any insights.
Thanks!
Adam
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Hi Adam,
The issue could be related to this one: https://youtrack.jetbrains.com/issue/IDEA-309087
Does it help if you disable the “Threads” view and/or use the option to “Restore Default Layout” in the Debugger view settings?
If it doesn't help, would it be possible for you to provide:
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Hi Arina,
Apparently the only solution currently is to disable the feature as per
https://youtrack.jetbrains.com/issue/IDEA-373676/Reactive-Flow-Evaluation-results-in-Collecting-data...
@run 3 We ran into something similar a while back. One thing worth checking is whether the issue only happens in the "Evaluate Expression" window or also when inspecting variables directly in the Variables pane. If it's limited to evaluation, it could be a regression in the debugger rather than Reactor support itself. If you haven't already, it might be worth creating a minimal reproducible project and filing a YouTrack issue so JetBrains can investigate.