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Dynamically load a Java Agent or acquire java.lang.instrument.Instrumentation via SPI

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/*-
 * #%L
 * io.earcam.instrumental.agent
 * %%
 * Copyright (C) 2018 earcam
 * %%
 * SPDX-License-Identifier: (BSD-3-Clause OR EPL-1.0 OR Apache-2.0 OR MIT)
 * 
 * You must choose to accept, in full - any individual or combination of 
 * the following licenses:
 * 
 * 	BSD-3-Clause
 * 	EPL-1.0
 * 	Apache-2.0
 * 	MIT
 * 
 * #L%
 */
package io.earcam.instrumental.agent;

import java.net.URI;
import java.nio.file.Path;

import io.earcam.unexceptional.Exceptional;

/**
 * Utility to load a java agent at runtime
 *
 * TODO could use a wrapper and allow load/unload, then have in junit teardown..
 *
 */
public final class DynamicAgent {

	private DynamicAgent()
	{}


	/**
	 * If the agentClass is located on the file system then a stub jar is created,
	 * otherwise the jar from which agentClass was loaded is used
	 *
	 * @param agentClass the agent class with agentmain, premain methods
	 * @param agentArguments the '-A' prefixed whole argument string
	 * @return The jar resource, which may have been created
	 */
	public static Path loadAgent(Class agentClass, String agentArguments)
	{
		Path sourceOfResource = StubAgentJar.jarForAgentClass(agentClass);
		loadAgent(sourceOfResource.toUri(), agentArguments);
		return sourceOfResource;
	}


	/**
	 * Load an existing agent jar file
	 *
	 * @param jar location of jar file containing agent
	 * @param agentArguments argument string to be supplied to agent
	 */
	public static void loadAgent(URI jar, String agentArguments)
	{
		Exceptional.accept(Attach::attach, jar, agentArguments);
	}
}