It was not intuitive, but I was able to compile successfully. I did 3 things. I deleted my .m2 folder/cache. In <properties> I changed <maven.compiler.release>17</maven.compiler.release> to 8 instead of 17. In <plugin>/<artifactId>maven-compiler-plugin... I changed <source> and <target> to <release>8</release>.
This recompiled the jar correctly, and my dummy file was created. Sent with [Proton Mail](https://proton.me/mail/home) secure email. On Wednesday, June 4th, 2025 at 8:47 AM, Nick Couchman <vn...@apache.org> wrote: > On Wed, Jun 4, 2025 at 8:27 AM viktor_krumm <viktor_kr...@proton.me.invalid> > wrote: > >> Folder and file structure looks good. Debug log says: "Caused by: >> java.lang.UnsupportedClassVersionError: >> org/apache/guacamole/event/LoginListener has been compiled by a more recent >> version of the Java Runtime (class file version 61.0), this version of the >> Java Runtime only recognizes class file versions up to 52.0" >> >> This feels like a Maven issue. Full pom.xml: > > I don't think it's exactly a Maven issue - it sounds like the system or > environment you're using to compile your custom listener code is being > compiled with a Java version that is later than the one you're using to run > Tomcat and the Guacamole code. While compiled Java code generally works > across versions, if you compile with a later version of Java you can > sometimes run into issues, particularly if you're using features or options > in the code that aren't compatible with the version used to run the code. I > would suggest validation the versions of Java you're using, and make sure > that the one running your Tomcat and Guacamole Client environment is at least > as equivalent to the one you use to compile. > > -Nick
