For what tasks have you used agents according to your experience?

In my experience working with Java, I have used agents for various tasks, including:

• Java Agent for profiling and monitoring: for example, using ByteBuddy or the Java Instrumentation API to create agents that are embedded into the JVM and collect performance metrics, trace method calls, and help identify bottlenecks.

• Agents for dynamic bytecode modification: used for injecting logging, tracing, or fixing bugs without changing the source code, which is useful in large projects with limited access to the source.

• Agents for testing and debugging: for example, to inject mocks or simulate dependency behavior during integration tests.

An example of a simple Java agent that outputs a message when the JVM starts:

import java.lang.instrument.Instrumentation;

public class SimpleAgent {
    public static void premain(String agentArgs, Instrumentation inst) {
        System.out.println("Java Agent started with arguments: " + agentArgs);
    }
}

This agent is attached to the JVM via the parameter -javaagent:path/to/agent.jar.