BasicMDCAdapter.java

/**
 * Copyright (c) 2004-2011 QOS.ch
 * All rights reserved.
 *
 * Permission is hereby granted, free  of charge, to any person obtaining
 * a  copy  of this  software  and  associated  documentation files  (the
 * "Software"), to  deal in  the Software without  restriction, including
 * without limitation  the rights to  use, copy, modify,  merge, publish,
 * 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
 * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
 * OF CONTRACT, TORT OR OTHERWISE,  ARISING FROM, OUT OF OR IN CONNECTION
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package org.slf4j.helpers;

import org.slf4j.spi.MDCAdapter;

import java.util.*;
import java.util.Map;

/**
 * Basic MDC implementation, which can be used with logging systems that lack
 * out-of-the-box MDC support.
 * 
 * This code was initially inspired by  logback's LogbackMDCAdapter. However,
 * LogbackMDCAdapter has evolved and is now considerably more sophisticated.
 *
 * @author Ceki Gulcu
 * @author Maarten Bosteels
 * 
 * @since 1.5.0
 */
public class BasicMDCAdapter implements MDCAdapter {

  private InheritableThreadLocal<Map<String, String>> inheritableThreadLocal 
    = new InheritableThreadLocal<Map<String, String>>();

  static boolean isJDK14() {
    try {
      String javaVersion = System.getProperty("java.version");
      return javaVersion.startsWith("1.4");
    } catch(SecurityException se) {
      // punt and assume JDK 1.5 or later
      return false;
    }
  }

  static boolean IS_JDK14 = isJDK14();


  /**
   * Put a context value (the <code>val</code> parameter) as identified with
   * the <code>key</code> parameter into the current thread's context map.
   * Note that contrary to log4j, the <code>val</code> parameter can be null.
   * 
   * <p>
   * If the current thread does not have a context map it is created as a side
   * effect of this call.
   * 
   * @throws IllegalArgumentException
   *                 in case the "key" parameter is null
   */
  public void put(String key, String val) {
    if (key == null) {
      throw new IllegalArgumentException("key cannot be null");
    }
    Map<String, String> map = (Map<String, String>) inheritableThreadLocal.get();
    if (map == null) {
      map = Collections.<String, String>synchronizedMap(new HashMap<String, String>());
      inheritableThreadLocal.set(map);
    }
    map.put(key, val);
  }

  /**
   * Get the context identified by the <code>key</code> parameter.
   */
  public String get(String key) {
    Map<String, String> Map = (Map<String, String>) inheritableThreadLocal.get();
    if ((Map != null) && (key != null)) {
      return (String) Map.get(key);
    } else {
      return null;
    }
  }

  /**
   * Remove the the context identified by the <code>key</code> parameter.
   */
  public void remove(String key) {
    Map<String, String> map = (Map<String, String>) inheritableThreadLocal.get();
    if (map != null) {
      map.remove(key);
    }
  }

  /**
   * Clear all entries in the MDC.
   */
  public void clear() {
    Map<String, String> map = (Map<String, String>) inheritableThreadLocal.get();
    if (map != null) {
      map.clear();
      // the InheritableThreadLocal.remove method was introduced in JDK 1.5
      // Thus, invoking clear() on previous JDK 1.4 will fail
      if(isJDK14()) {
        inheritableThreadLocal.set(null);
      }  else {
        inheritableThreadLocal.remove();
      }
    }
  }

  /**
   * Returns the keys in the MDC as a {@link Set} of {@link String}s The
   * returned value can be null.
   * 
   * @return the keys in the MDC
   */
  public Set<String> getKeys() {
    Map<String, String> map = (Map<String, String>) inheritableThreadLocal.get();
    if (map != null) {
      return map.keySet();
    } else {
      return null;
    }
  }
  /**
   * Return a copy of the current thread's context map. 
   * Returned value may be null.
   * 
   */
  public Map<String, String> getCopyOfContextMap() {
    Map<String, String> oldMap = (Map<String, String>) inheritableThreadLocal.get();
    if (oldMap != null) {
       Map<String, String> newMap = Collections.<String, String>synchronizedMap(new HashMap<String, String>());
       synchronized (oldMap) {
         newMap.putAll(oldMap);
       }
       return  newMap;
    } else {
      return null;
    }
  }

  public void setContextMap(Map<String, String> contextMap) {
    Map<String, String> map = Collections.<String, String>synchronizedMap(new HashMap<String, String>(contextMap));
    inheritableThreadLocal.set(map);
  }

}