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: > <?xml version="1.0" encoding="UTF-8"?> > <project xmlns="http://maven.apache.org/POM/4.0.0"; > xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"; > xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 > http://maven.apache.org/xsd/maven-4.0.0.xsd";> > <modelVersion>4.0.0</modelVersion> > > <groupId>org.apache.guacamole.</groupId> > <artifactId>guac-listener</artifactId> > <packaging>jar</packaging> > <version>0.2</version> > > <name>guac-listener</name> > <!-- FIXME change it to the project's website --> > <!-- <url>http://www.example.com</url> --> > > <properties> > <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> > <maven.compiler.release>17</maven.compiler.release> > </properties> > > <dependencies> > <dependency> > <groupId>org.apache.guacamole</groupId> > <artifactId>guacamole-ext</artifactId> > <version>1.5.5</version> > </dependency> > </dependencies> > > <build> > <pluginManagement><!-- lock down plugins versions to avoid using Maven > defaults (may be moved to parent pom) --> > <plugins> > <!-- clean lifecycle, see > https://maven.apache.org/ref/current/maven-core/lifecycles.html#clean_Lifecycle > --> > <plugin> > <artifactId>maven-clean-plugin</artifactId> > <version>3.4.0</version> > </plugin> > <!-- default lifecycle, jar packaging: see > https://maven.apache.org/ref/current/maven-core/default-bindings.html#Plugin_bindings_for_jar_packaging > --> > <plugin> > <artifactId>maven-resources-plugin</artifactId> > <version>3.3.1</version> > </plugin> > <plugin> > <artifactId>maven-compiler-plugin</artifactId> > <version>3.13.0</version> > <configuration> > <source>1.8</source> > <target>1.8</target> > </configuration> > </plugin> > <plugin> > <artifactId>maven-surefire-plugin</artifactId> > <version>3.3.0</version> > </plugin> > <plugin> > <artifactId>maven-jar-plugin</artifactId> > <version>3.4.2</version> > </plugin> > <plugin> > <artifactId>maven-install-plugin</artifactId> > <version>3.1.2</version> > </plugin> > <plugin> > <artifactId>maven-deploy-plugin</artifactId> > <version>3.1.2</version> > </plugin> > <!-- site lifecycle, see > https://maven.apache.org/ref/current/maven-core/lifecycles.html#site_Lifecycle > --> > <plugin> > <artifactId>maven-site-plugin</artifactId> > <version>3.12.1</version> > </plugin> > <plugin> > <artifactId>maven-project-info-reports-plugin</artifactId> > <version>3.6.1</version> > </plugin> > </plugins> > </pluginManagement> > </build> > </project> Sent with [Proton Mail](https://proton.me/mail/home) secure email. On Wednesday, June 4th, 2025 at 4:07 AM, Michael Jumper <[email protected]> wrote: > On June 3, 2025 2:17:59 PM PDT, viktor_krumm <[email protected]> > wrote: > >> I am attempting to write an event listener using the documentation. I have >> successfully compiled a basic jar with Maven with no errors. When I load it >> into guacamole, I get "Extension guac-listener.jar could not be loaded: >> Listener class cannot be loaded (wrong version of API?)". >> >> My files are simple: >> >> guac-manifest.json: >> { >> >> "guacamoleVersion" : "1.5.5", >> >> "name" : "Guacamole Login Listener", >> "namespace" : "guac-listener", >> >> "listeners" : [ >> "org.apache.guacamole.event.LoginListener" >> ] >> } >> >> LoginListener.java: >> package org.apache.guacamole.event; >> >> import org.apache.guacamole.GuacamoleException; >> import org.apache.guacamole.net.event.listener.Listener; >> import java.io.FileWriter; >> import java.io.IOException; >> >> public class LoginListener implements Listener { >> >> @Override >> public void handleEvent(Object event) throws GuacamoleException { >> String path = "/tmp/dummy.txt"; >> String msg = "handler called!"; >> >> try (FileWriter writer = new FileWriter(path, true)) { >> writer.write(msg); >> } >> >> catch (IOException e) { >> System.out.println("Err"); >> } >> >> } >> >> } >> >> pom.xml dependencies: >> <dependencies> >> <dependency> >> <groupId>org.apache.guacamole</groupId> >> <artifactId>guacamole-ext</artifactId> >> <version>1.5.5</version> >> </dependency> >> </dependencies> >> My first guess is I am somehow linking the wrong library. The guacamole >> webserver is docker latest tag. >> >> Thanks >> >> Sent with [Proton Mail](https://proton.me/mail/home) secure email. > > If you extract the extension .jar as a zip file, do you see the expected > contents (guac-manifest.json at the root level plus your LoginListener class > nested beneath its package directories)? > > What do you see in the Guacamole logs with debug-level logging enabled? > > - Mike
