Log.java

/**
 * Licensed to The Apereo Foundation under one or more contributor license
 * agreements. See the NOTICE file distributed with this work for additional
 * information regarding copyright ownership.
 *
 *
 * The Apereo Foundation licenses this file to you under the Educational
 * Community License, Version 2.0 (the "License"); you may not use this file
 * except in compliance with the License. You may obtain a copy of the License
 * at:
 *
 *   http://opensource.org/licenses/ecl2.txt
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
 * License for the specific language governing permissions and limitations under
 * the License.
 *
 */

package org.opencastproject.util;

import static java.lang.String.format;

import org.opencastproject.fun.juc.Immutables;
import org.opencastproject.fun.juc.Iterables;
import org.opencastproject.fun.juc.Mutables;
import org.opencastproject.util.data.Prelude;

import org.apache.commons.lang3.StringUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.slf4j.spi.LocationAwareLogger;

import java.util.Collection;
import java.util.List;
import java.util.Stack;
import java.util.UUID;

/**
 * A logger that maintains a "unit of work" context to facilitate the grouping of log statements.
 * <p>
 * Log methods that take message formats and arguments use the
 * {@link String#format(java.util.Locale, String, Object...)} string format syntax.
 */
public final class Log {
  /** The number of seconds in a minute. */
  private static final int SECONDS_IN_MINUTES = 60;

  /** The number of seconds in an hour. */
  private static final int SECONDS_IN_HOURS = 3600;

  private static final String FQCN = Log.class.getName();

  private static final String JVM_SESSION = randomString();

  /** Hold the context stack. */
  private static final ThreadLocal<Stack<String>> ctx = new ThreadLocal<Stack<String>>() {
    @Override protected Stack<String> initialValue() {
      return Mutables.stack(JVM_SESSION);
    }
  };

  /** Hold the current unit of work hierarchy as a string ready to use for the log methods. */
  private static final ThreadLocal<String> current = new ThreadLocal<String>() {
    @Override protected String initialValue() {
      return ctxAsString();
    }
  };

  private final Logger logger;
  private final boolean isLocationAware;

  /** Create a new logger from an slf4j logger. */
  public Log(Logger logger) {
    this.logger = logger;
    this.isLocationAware = logger instanceof LocationAwareLogger;
  }

  /**
   * Create a new log instance based on an slf4j logger for class <code>clazz</code>.
   *
   * @see org.slf4j.LoggerFactory#getLogger(Class)
   */
  public static Log mk(Class<?> clazz) {
    return new Log(LoggerFactory.getLogger(clazz));
  }

  private static void updateCurrent() {
    current.set(ctxAsString());
  }

  private static String ctxAsString() {
    return Iterables.mkString(ctx.get(), "_", "[>", "] ");
  }

  private static String randomString() {
    return UUID.randomUUID().toString().split("-")[0];
  }

  /** Start a new unit of work. */
  public void startUnitOfWork() {
    ctx.get().push(randomString());
    updateCurrent();
  }

  /** End a unit of work. */
  public void endUnitOfWork() {
    if (ctx.get().size() > 1) {
      ctx.get().pop();
      updateCurrent();
    }
  }

  /** Continue a log context. */
  public void continueContext(Collection<String> init) {
    ctx.set(Mutables.stack(init));
    updateCurrent();
  }

  /**
   * Renders a string representation of seconds that is easier to read by showing hours, minutes and seconds.
   *
   * @param seconds
   *          The number of seconds that you want to represent in hours, minutes and remainder seconds.
   * @return A human readable string representation of seconds into hours, minutes and seconds.
   */
  public static String getHumanReadableTimeString(long seconds) {
    String result = "";
    long hours = seconds / SECONDS_IN_HOURS;
    if (hours == 1) {
      result += hours + " hour ";
    } else if (hours > 1) {
      result += hours + " hours ";
    }
    long minutes = (seconds % SECONDS_IN_HOURS) / SECONDS_IN_MINUTES;
    if (minutes == 1) {
      result += minutes + " minute ";
    } else if (minutes > 1) {
      result += minutes + " minutes ";
    }
    long remainderSeconds = (seconds % SECONDS_IN_HOURS) % SECONDS_IN_MINUTES;
    if (remainderSeconds == 1) {
      result += remainderSeconds + " second";
    } else if (remainderSeconds > 1) {
      result += remainderSeconds + " seconds";
    }
    result = StringUtils.trim(result);
    return result;
  }

  /** Return the current log context. */
  public List<String> getContext() {
    return Immutables.mk(ctx.get());
  }

  public void debug(String msg) {
    log(LocationAwareLogger.DEBUG_INT, null, msg);
  }

  public void debug(String msg, Object... args) {
    log(LocationAwareLogger.DEBUG_INT, null, msg, args);
  }

  public void info(String msg) {
    log(LocationAwareLogger.INFO_INT, null, msg);
  }

  public void info(String msg, Object... args) {
    log(LocationAwareLogger.INFO_INT, null, msg, args);
  }

  public void warn(String msg) {
    log(LocationAwareLogger.WARN_INT, null, msg);
  }

  public void warn(String msg, Object... args) {
    log(LocationAwareLogger.WARN_INT, null, msg, args);
  }

  public void warn(Throwable t, String msg) {
    log(LocationAwareLogger.WARN_INT, t, msg);
  }

  public void error(String msg) {
    log(LocationAwareLogger.ERROR_INT, null, msg);
  }

  public void error(String msg, Object... args) {
    log(LocationAwareLogger.ERROR_INT, null, msg, args);
  }

  public void error(Throwable t, String msg, Object... args) {
    log(LocationAwareLogger.ERROR_INT, t, msg, args);
  }

  /** <code>t</code> maybe null */
  private void log(int level, Throwable t, String format, Object... args) {
    final String msg = current.get() + format(convertCurlyBraces(format), args);
    if (isLocationAware) {
      ((LocationAwareLogger) logger).log(null, FQCN, level, msg, null, t);
    } else {
      switch (level) {
        case LocationAwareLogger.INFO_INT:
          logger.info(msg);
          break;
        case LocationAwareLogger.WARN_INT:
          logger.warn(msg);
          break;
        case LocationAwareLogger.ERROR_INT:
          logger.error(msg);
          break;
        default:
          Prelude.unexhaustiveMatch();
      }
    }
  }

  private static String convertCurlyBraces(String format) {
    if (format == null)
      return "(null message)";

    return format.replaceAll("\\{\\}", "%s");
  }
}