Specifying a javaagent within the jar file to be run

Question

I'm developing an OpenJPA application (no webserver, regular java se app). In order to make OpenJPA work with my application, I need to set the openjpa-all-2.3.0.jar as a javaagent.

java -cp ... -javaagent:/full/path/to/openjpa-all-2.3.0.jar -jar app.jar

As I am packaging the openjpa.jar within the app.jar anyway, I am now wondering how it is possible to specify the javaagent, as a jar within my application jar file.

This didn't work

java -cp ".;.\app.jar" -javaagent:openjpa-all-2.3.0.jar pckg.Main

Answer 1

There's no way to do it. The JVM does not look at the classpath to find the specified agent; it is expecting a file path, and you also cannot specify file paths inside jar files.

JDK-4648386 is the related feature request, and was closed Won't Fix after 18 years.

However, what you can do is write code to copy the agent jar from a classpath resource to a temporary file, and then attach it to the current running JVM. The ByteBuddy Agent library provides tooling to do this.