AgentPremain.java

package org.slf4j.agent;

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.lang.instrument.Instrumentation;
import java.util.Date;
import java.util.Properties;

import org.slf4j.instrumentation.LogTransformer;

/**
 * Entry point for slf4j-ext when used as a Java agent.
 * 
 */
public class AgentPremain {

	/**
	 * JavaAgent premain entry point as specified in the MANIFEST.MF file. See
	 * {@link http
	 * ://java.sun.com/javase/6/docs/api/java/lang/instrument/package-
	 * summary.html} for details.
	 * 
	 * @param agentArgument
	 *            string provided after "=" up to first space
	 * @param instrumentation
	 *            instrumentation environment provided by the JVM
	 */
	public static void premain(String agentArgument,
			Instrumentation instrumentation) {

		// We cannot do sanity checks for slf4j here as the jars loaded
		// by the application are not visible here.

		LogTransformer.Builder builder = new LogTransformer.Builder();
		builder = builder.addEntryExit(true);

		if (agentArgument != null) {
			Properties args = parseArguments(agentArgument, ",");

			if (args.containsKey(AgentOptions.VERBOSE)) {
				builder = builder.verbose(true);
			}

			if (args.containsKey(AgentOptions.TIME)) {
				printStartStopTimes();
			}

			if (args.containsKey(AgentOptions.IGNORE)) {
				String ignore = args.getProperty(AgentOptions.IGNORE);
				builder = builder.ignore(ignore.split(":"));
			}

			if (args.containsKey(AgentOptions.LEVEL)) {
				builder = builder.level(args.getProperty(AgentOptions.LEVEL));
			}
		}

		instrumentation.addTransformer(builder.build());
	}

	/**
	 * Consider the argument string to be a property file (by converting the
	 * splitter character to line feeds), and then reading it like any other
	 * property file.
	 * 
	 * 
	 * @param agentArgument
	 *            string given by instrumentation framework
	 * @param separator
	 *            String to convert to line feeds
	 * @return argument converted to properties
	 */
	private static Properties parseArguments(String agentArgument,
			String separator) {
		Properties p = new Properties();
		try {
			String argumentAsLines = agentArgument.replaceAll(separator, "\n");
			p.load(new ByteArrayInputStream(argumentAsLines.getBytes()));
		} catch (IOException e) {
			String s = "Could not load arguments as properties";
			throw new RuntimeException(s, e);
		}
		return p;
	}

	/**
	 * Print the start message to System.err with the time NOW, and register a
	 * shutdown hook which will print the stop message to System.err with the
	 * time then and the number of milliseconds passed since.
	 * 
	 */
	private static void printStartStopTimes() {
		final long start = System.currentTimeMillis();

		System.err.println("Start at " + new Date());

		Thread hook = new Thread() {
			@Override
			public void run() {
				long timePassed = System.currentTimeMillis() - start;
				System.err.println("Stop at " + new Date()
						+ ", execution time = " + timePassed + " ms");
			}
		};
		Runtime.getRuntime().addShutdownHook(hook);
	}
}