This repo demonstrates how to build a native image of a java application that uses ClassGraph with GraalVM.

Install GraalVM

$ mvn clean package

Execute the java image

$ java -jar target/classgraph-on-graalvm-1.0-SNAPSHOT.jar
Initializing class com.softinstigate.App
annotated classes [com.softinstigate.FindMe]
	annotated method executeMe
Executing targets [{ com.softinstigate.FindMe, executeMe }]
	class annotation name: findMe
	class annotation priority: 10
	method annotation name: executeMe
	method annotation priority: 10
Hello World!!

Execute the native image

$ ./target/cog
Executing targets [{ com.softinstigate.FindMe, executeMe }]
	class annotation name: findMe
	class annotation priority: 10
	method annotation name: executeMe
	method annotation priority: 10
Hello World!!

ClassGraph.scan() simply doesn't work at runtime on a native image. However it does work at build time (see Build-Time-Scanning on ClassGraph wiki).

The native-image.properties includes the following option:

--initialize-at-build-time=com.softinstigate.App,io.github.classgraph.,nonapi.io.github.classgraph.

com.softinstigate.App performs the class scanning at class initialization time defining:

public class App {
    static {
        // here executes ClassGraph.scan()
    }
}

Since the class com.softinstigate.App is initialized at build time by native-image, the scanning occurs.

The found classes are saved to a static field and used in the class. The example code looks for classes and methods with given annotations and them invoke the methods using reflection.

Since reflection is used, native-image must run properly configured. The following section provides instructions on how to automatically generate the configuration.

See Reflection Use in Native Images from GraalVM documentation.

Run the app with the native-image-agent

$ mvn clean package
$ java -agentlib:native-image-agent=config-merge-dir=src/main/resources/META-INF/native-image/com.softinstigate/classgraph-on-graalvm/ -jar target/classgraph-on-graalvm-1.0-SNAPSHOT.jar