slf4j-api/src/main/java/org/slf4j/LoggerFactory.java

/* 
 * Copyright (c) 2004-2007 QOS.ch
 * All rights reserved.
 * 
 * Permission is hereby granted, free  of charge, to any person obtaining
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 * distribute,  sublicense, and/or sell  copies of  the Software,  and to
 * permit persons to whom the Software  is furnished to do so, subject to
 * the following conditions:
 * 
 * The  above  copyright  notice  and  this permission  notice  shall  be
 * included in all copies or substantial portions of the Software.
 * 
 * THE  SOFTWARE IS  PROVIDED  "AS  IS", WITHOUT  WARRANTY  OF ANY  KIND,
 * EXPRESS OR  IMPLIED, INCLUDING  BUT NOT LIMITED  TO THE  WARRANTIES OF
 * MERCHANTABILITY,    FITNESS    FOR    A   PARTICULAR    PURPOSE    AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
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package org.slf4j;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

import org.slf4j.helpers.SubstituteLoggerFactory;
import org.slf4j.helpers.Util;
import org.slf4j.impl.StaticLoggerBinder;

/**
 * The <code>LoggerFactory</code> is a utility class producing Loggers for
 * various logging APIs, most notably for log4j, logback and JDK 1.4 logging.
 * Other implementations such as {@link org.slf4j.impl.NOPLogger NOPLogger} and
 * {@link org.slf4j.impl.SimpleLogger SimpleLogger} are also supported.
 * 
 * <p>
 * <code>LoggerFactory</code> is essentially a wrapper around an
 * {@link ILoggerFactory} instance bound with <code>LoggerFactory</code> at
 * compile time.
 * 
 * <p>
 * Please note that all methods in <code>LoggerFactory</code> are static.
 * 
 * @author Ceki G&uuml;lc&uuml;
 */
public final class LoggerFactory {

  static ILoggerFactory loggerFactory;

  static final String NO_STATICLOGGERBINDER_URL = "http://www.slf4j.org/codes.html#StaticLoggerBinder";
  static final String NULL_LF_URL = "http://www.slf4j.org/codes.html#null_LF";
  static final String VERSION_MISMATCH = "http://www.slf4j.org/codes.html#version_mismatch";
  static final String SUBSTITUTE_LOGGER_URL = "http://www.slf4j.org/codes.html#substituteLogger";

  /**
   * It is out responsibility to track version changes and manage the
   * compatibility list.
   * 
   * <p>
   */
  static private final String[] API_COMPATIBILITY_LIST = new String[] { "1.5.5" };

  // private constructor prevents instantiation
  private LoggerFactory() {
  }

  static {
    staticInitialize();
    versionSanityCheck();
  }

  private final static void staticInitialize() {
    try {
      // support re-entrant behavior.
      // See also http://bugzilla.slf4j.org/show_bug.cgi?id=106
      List loggerNameList = new ArrayList();
      loggerFactory = new SubstituteLoggerFactory(loggerNameList);
      loggerFactory = StaticLoggerBinder.SINGLETON.getLoggerFactory();
      emitSubstitureLoggerWarning(loggerNameList);
    } catch (NoClassDefFoundError ncde) {
      loggerFactory = null; // undo SubstituteLoggerFactory assignment
      String msg = ncde.getMessage();
      if (msg != null && msg.indexOf("org/slf4j/impl/StaticLoggerBinder") != -1) {
        Util
            .reportFailure("Failed to load class \"org.slf4j.impl.StaticLoggerBinder\".");
        Util.reportFailure("See " + NO_STATICLOGGERBINDER_URL
            + " for further details.");

      }
      throw ncde;
    } catch (Exception e) {
      loggerFactory = null; // undo SubstituteLoggerFactory assignment
      // we should never get here
      Util.reportFailure("Failed to instantiate logger ["
          + StaticLoggerBinder.SINGLETON.getLoggerFactoryClassStr() + "]", e);
    }
  }

  private final static void emitSubstitureLoggerWarning(List loggerNameList) {
    if (loggerNameList.size() == 0) {
      return;
    }
    Util
        .reportFailure("The following loggers will not work becasue they were created");
    Util
        .reportFailure("during the default configuration phase of the underlying logging system.");
    Util.reportFailure("See also " + SUBSTITUTE_LOGGER_URL);
    for (int i = 0; i < loggerNameList.size(); i++) {
      String loggerName = (String) loggerNameList.get(i);
      Util.reportFailure(loggerName);
    }
  }

  private final static void versionSanityCheck() {
    try {
      String requested = StaticLoggerBinder.REQUESTED_API_VERSION;

      boolean match = false;
      for (int i = 0; i < API_COMPATIBILITY_LIST.length; i++) {
        if (API_COMPATIBILITY_LIST[i].equals(requested)) {
          match = true;
        }
      }
      if (!match) {
        Util.reportFailure("The requested version " + requested
            + " of your slf4j-binding does not match any of "
            + Arrays.toString(API_COMPATIBILITY_LIST));
        Util.reportFailure("See " + VERSION_MISMATCH + " for further details.");
      }
    } catch (java.lang.NoSuchFieldError nsfe) {
      // given our large user base anbd SLF4J's commitment to backward
      // compatibility, we cannot cry
      // here. Only for implementations which willingly declare a
      // REQUESTED_API_VERSION field do we emit compatibility warnings.
    } catch (Throwable e) {
      // we should never reach here
      Util.reportFailure(
          "Unexpected problem occured during version sanity check", e);
    }
  }

  /**
   * Return a logger named according to the name parameter using the statically
   * bound {@link ILoggerFactory} instance.
   * 
   * @param name
   *                The name of the logger.
   * @return logger
   */
  public static Logger getLogger(String name) {
    if (loggerFactory == null) {
      throw new IllegalStateException(
          "Logging factory implementation cannot be null. See also "
              + NULL_LF_URL);
    }
    return loggerFactory.getLogger(name);
  }

  /**
   * Return a logger named corresponding to the class passed as parameter, using
   * the statically bound {@link ILoggerFactory} instance.
   * 
   * @param clazz
   *                the returned logger will be named after clazz
   * @return logger
   */
  public static Logger getLogger(Class clazz) {
    if (loggerFactory == null) {
      throw new IllegalStateException(
          "Logging factory implementation cannot be null. See also "
              + NULL_LF_URL);
    }
    return loggerFactory.getLogger(clazz.getName());
  }

  /**
   * Return the {@link ILoggerFactory} instance in use.
   * 
   * <p>
   * ILoggerFactory instance is bound with this class at compile time.
   * 
   * @return the ILoggerFactory instance in use
   */
  public static ILoggerFactory getILoggerFactory() {
    return loggerFactory;
  }
}