Unable to load instrumentation class in Spring Boot 3.x with Java 17

Answer

Based on current model knowledge, full Spring Boot 3.x auto-instrumentation is reported with New Relic Java agent 9.0.0 or newer on Java 17. The JVM flag -Dnewrelic.agent.disable_classloader_cache=true is commonly suggested to avoid class-loading conflicts during bootstrap. These points require current verification as agent support evolves.

Confirmed facts

• New Relic Java agent 8.x can run on Java 17 but does not include the Spring Boot 3.x instrumentation classes referenced in the research.
• The -javaagent option must precede the main application class or -jar argument on the command line.
• Agent debug logging can be enabled with -Dnewrelic.agent.log_level=debug to surface instrumentation load status.

Likely explanation

The "Unable to load instrumentation class" messages during bootstrap are consistent with an agent version older than the Spring Boot 3.x baseline, combined with Java 17 module system classloader behavior. Disabling the agent classloader cache forces instrumentation classes to be loaded via the application classloader, which can resolve the conflict.

Steps for this case

1. Verify the installed agent version from the jar META-INF/MANIFEST.MF or startup log. Plan to use 9.0.0 or newer for Spring Boot 3.x support.
2. Start the application with the agent and the classloader flag:

java -javaagent:/path/to/newrelic.jar \
     -Dnewrelic.agent.disable_classloader_cache=true \
     -jar your-app.jar

1. Restart and check agent logs for absence of "Unable to load instrumentation class" messages and for entries indicating successful instrumentation load.
2. Confirm Spring MVC and WebFlux transaction traces appear in the New Relic UI after a test request.

Note: Disabling the classloader cache can slightly increase startup time and memory usage. Monitor performance after applying the flag and ensure no other APM agents are present to avoid classpath conflicts.