# A few question about jvm target (again)

**URL:** https://community.haxe.org/t/a-few-question-about-jvm-target-again/2905
**Category:** Haxe
**Tags:** haxe-jvm
**Created:** [February 16, 2021, 1:26pm UTC](https://community.haxe.org/t/a-few-question-about-jvm-target-again/2905 "2021-02-16T13:26:08Z")
**Posts on this page:** 1
**Page:** 1

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### Author: ![AlexKotik](https://avatars.discourse-cdn.com/v2/letter/a/2bfe46/32.png) [@AlexKotik](https://community.haxe.org/u/AlexKotik)
#### Post date: [February 16, 2021, 1:26pm UTC](https://community.haxe.org/t/a-few-question-about-jvm-target-again/2905/1 "2021-02-16T13:26:08Z")

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So I tested the 4.2.0 feature of adding a folder full of jars with ‘–java-lib’ argument, and it didn’t work. Java failed with “An unexpected error occurred while trying to open file”. It seems I’m stuck with this issue: [[jvm] An unexpected error occurred while trying to open file Main.jar · Issue #9775 · HaxeFoundation/haxe · GitHub](https://github.com/HaxeFoundation/haxe/issues/9775) but I’m not sure. Using the “–java-lib-extern” and adding the jar folder to the class path manually works, so it seems that the issue is all about a lot of jars beeing added to MANIFEST.MF in the jar. But anyway using “–java-lib-extern” is not convinient, so is there I way I can fix that in my project?

Is it possible to build a so called “fat jar” with Haxe? Fat jars are jar files that contains all it’s dependencies in itself. Jar files are zip-files by nature, so it shouldn’t be that hard, right? Maybe there might be some troubles that different jar files have different manifests, I don’t know.

How do I convert Java types to Haxe types in general? For example the libraries that I use return java.util.Date object, what is a proper way to convert it to haxe.Date? Google doesn’t help me with this one. What about other types?