xref: /external/slf4j/slf4j-ext/src/main/java/org/slf4j/agent/AgentPremain.java

package org.slf4j.agent;

import static org.slf4j.helpers.MessageFormatter.format;

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 {

  private static final String START_MSG = "Start at {}";
  private static final String STOP_MSG = "Stop at {}, execution time = {} ms";

  /**
   * 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) {

    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(format(START_MSG, new Date()));

    Thread hook = new Thread() {
      @Override
      public void run() {
        long timePassed = System.currentTimeMillis() - start;
        String message = format(STOP_MSG, new Date(), timePassed);
        System.err.println(message);
      }
    };
    Runtime.getRuntime().addShutdownHook(hook);
  }
}