Using the Liberty Maven Plugin, running in dev mode, I'm trying to start the Liberty server in suspended mode by setting the env var: WLP_DEBUG_SUSPEND=y. The server does launch listening on port 7777 for a debugger attachment but without waiting for the debugger, i.e. not in suspended mode.
My command is:
mvn liberty:dev -Dliberty.env.WLP_DEBUG_SUSPEND=y
The Liberty Maven Plugin purposely overrides the WLP_DEBUG_SUSPEND setting in "dev mode" in a way that prevents this type of usage.
As an alternative, you can launch Liberty via the "run" goal, and set the debugger JVM options including the suspend=y debugger config:
mvn liberty:run -Dliberty.jvm.debug='-agentlib:jdwp=transport=dt_socket,server=y,suspend=y,address=0.0.0.0:7777'
The run goal isn't the same as "dev mode" since it doesn't provide a "watcher" to update the server when pom.xml, application source, test, and config files are updated (like dev mode). But it does provide a quick way to launch Liberty with Maven with a single command so it can be a useful tool to be aware of.