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1   /**
2    * Copyright (c) 2004-2011 QOS.ch
3    * All rights reserved.
4    *
5    * Permission is hereby granted, free  of charge, to any person obtaining
6    * a  copy  of this  software  and  associated  documentation files  (the
7    * "Software"), to  deal in  the Software without  restriction, including
8    * without limitation  the rights to  use, copy, modify,  merge, publish,
9    * distribute,  sublicense, and/or sell  copies of  the Software,  and to
10   * permit persons to whom the Software  is furnished to do so, subject to
11   * the following conditions:
12   *
13   * The  above  copyright  notice  and  this permission  notice  shall  be
14   * included in all copies or substantial portions of the Software.
15   *
16   * THE  SOFTWARE IS  PROVIDED  "AS  IS", WITHOUT  WARRANTY  OF ANY  KIND,
17   * EXPRESS OR  IMPLIED, INCLUDING  BUT NOT LIMITED  TO THE  WARRANTIES OF
18   * MERCHANTABILITY,    FITNESS    FOR    A   PARTICULAR    PURPOSE    AND
19   * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
20   * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
21   * OF CONTRACT, TORT OR OTHERWISE,  ARISING FROM, OUT OF OR IN CONNECTION
22   * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
23   *
24   */
25  package org.slf4j;
26  
27  import java.io.Closeable;
28  import java.util.Map;
29  
30  import org.slf4j.helpers.NOPMDCAdapter;
31  import org.slf4j.helpers.BasicMDCAdapter;
32  import org.slf4j.helpers.Util;
33  import org.slf4j.impl.StaticMDCBinder;
34  import org.slf4j.spi.MDCAdapter;
35  
36  /**
37   * This class hides and serves as a substitute for the underlying logging
38   * system's MDC implementation.
39   * 
40   * <p>
41   * If the underlying logging system offers MDC functionality, then SLF4J's MDC,
42   * i.e. this class, will delegate to the underlying system's MDC. Note that at
43   * this time, only two logging systems, namely log4j and logback, offer MDC
44   * functionality. For java.util.logging which does not support MDC,
45   * {@link BasicMDCAdapter} will be used. For other systems, i.e slf4j-simple
46   * and slf4j-nop, {@link NOPMDCAdapter} will be used.
47   *
48   * <p>
49   * Thus, as a SLF4J user, you can take advantage of MDC in the presence of log4j,
50   * logback, or java.util.logging, but without forcing these systems as
51   * dependencies upon your users.
52   * 
53   * <p>
54   * For more information on MDC please see the <a
55   * href="http://logback.qos.ch/manual/mdc.html">chapter on MDC</a> in the
56   * logback manual.
57   * 
58   * <p>
59   * Please note that all methods in this class are static.
60   * 
61   * @author Ceki G&uuml;lc&uuml;
62   * @since 1.4.1
63   */
64  public class MDC {
65  
66      static final String NULL_MDCA_URL = "http://www.slf4j.org/codes.html#null_MDCA";
67      static final String NO_STATIC_MDC_BINDER_URL = "http://www.slf4j.org/codes.html#no_static_mdc_binder";
68      static MDCAdapter mdcAdapter;
69  
70      /**
71       * An adapter to remove the key when done.
72       */
73      public static class MDCCloseable implements Closeable {
74          private final String key;
75  
76          private MDCCloseable(String key) {
77              this.key = key;
78          }
79  
80          public void close() {
81              MDC.remove(this.key);
82          }
83      }
84  
85      private MDC() {
86      }
87  
88      static {
89          try {
90              mdcAdapter = StaticMDCBinder.SINGLETON.getMDCA();
91          } catch (NoClassDefFoundError ncde) {
92              mdcAdapter = new NOPMDCAdapter();
93              String msg = ncde.getMessage();
94              if (msg != null && msg.indexOf("StaticMDCBinder") != -1) {
95                  Util.report("Failed to load class \"org.slf4j.impl.StaticMDCBinder\".");
96                  Util.report("Defaulting to no-operation MDCAdapter implementation.");
97                  Util.report("See " + NO_STATIC_MDC_BINDER_URL + " for further details.");
98              } else {
99                  throw ncde;
100             }
101         } catch (Exception e) {
102             // we should never get here
103             Util.report("MDC binding unsuccessful.", e);
104         }
105     }
106 
107     /**
108      * Put a diagnostic context value (the <code>val</code> parameter) as identified with the
109      * <code>key</code> parameter into the current thread's diagnostic context map. The
110      * <code>key</code> parameter cannot be null. The <code>val</code> parameter
111      * can be null only if the underlying implementation supports it.
112      * 
113      * <p>
114      * This method delegates all work to the MDC of the underlying logging system.
115      *
116      * @param key non-null key 
117      * @param val value to put in the map
118      * 
119      * @throws IllegalArgumentException
120      *           in case the "key" parameter is null
121      */
122     public static void put(String key, String val) throws IllegalArgumentException {
123         if (key == null) {
124             throw new IllegalArgumentException("key parameter cannot be null");
125         }
126         if (mdcAdapter == null) {
127             throw new IllegalStateException("MDCAdapter cannot be null. See also " + NULL_MDCA_URL);
128         }
129         mdcAdapter.put(key, val);
130     }
131 
132     /**
133      * Put a diagnostic context value (the <code>val</code> parameter) as identified with the
134      * <code>key</code> parameter into the current thread's diagnostic context map. The
135      * <code>key</code> parameter cannot be null. The <code>val</code> parameter
136      * can be null only if the underlying implementation supports it.
137      *
138      * <p>
139      * This method delegates all work to the MDC of the underlying logging system.
140      * <p>
141      * This method return a <code>Closeable</code> object who can remove <code>key</code> when
142      * <code>close</code> is called.
143      *
144      * <p>
145      * Useful with Java 7 for example :
146      * <code>
147      *   try(MDC.MDCCloseable closeable = MDC.putCloseable(key, value)) {
148      *     ....
149      *   }
150      * </code>
151      *
152      * @param key non-null key
153      * @param val value to put in the map
154      * @return a <code>Closeable</code> who can remove <code>key</code> when <code>close</code>
155      * is called.
156      *
157      * @throws IllegalArgumentException
158      *           in case the "key" parameter is null
159      */
160     public static MDCCloseable putCloseable(String key, String val) throws IllegalArgumentException {
161         put(key, val);
162         return new MDCCloseable(key);
163     }
164 
165     /**
166      * Get the diagnostic context identified by the <code>key</code> parameter. The
167      * <code>key</code> parameter cannot be null.
168      * 
169      * <p>
170      * This method delegates all work to the MDC of the underlying logging system.
171      *
172      * @param key  
173      * @return the string value identified by the <code>key</code> parameter.
174      * @throws IllegalArgumentException
175      *           in case the "key" parameter is null
176      */
177     public static String get(String key) throws IllegalArgumentException {
178         if (key == null) {
179             throw new IllegalArgumentException("key parameter cannot be null");
180         }
181 
182         if (mdcAdapter == null) {
183             throw new IllegalStateException("MDCAdapter cannot be null. See also " + NULL_MDCA_URL);
184         }
185         return mdcAdapter.get(key);
186     }
187 
188     /**
189      * Remove the diagnostic context identified by the <code>key</code> parameter using
190      * the underlying system's MDC implementation. The <code>key</code> parameter
191      * cannot be null. This method does nothing if there is no previous value
192      * associated with <code>key</code>.
193      *
194      * @param key  
195      * @throws IllegalArgumentException
196      *           in case the "key" parameter is null
197      */
198     public static void remove(String key) throws IllegalArgumentException {
199         if (key == null) {
200             throw new IllegalArgumentException("key parameter cannot be null");
201         }
202 
203         if (mdcAdapter == null) {
204             throw new IllegalStateException("MDCAdapter cannot be null. See also " + NULL_MDCA_URL);
205         }
206         mdcAdapter.remove(key);
207     }
208 
209     /**
210      * Clear all entries in the MDC of the underlying implementation.
211      */
212     public static void clear() {
213         if (mdcAdapter == null) {
214             throw new IllegalStateException("MDCAdapter cannot be null. See also " + NULL_MDCA_URL);
215         }
216         mdcAdapter.clear();
217     }
218 
219     /**
220      * Return a copy of the current thread's context map, with keys and values of
221      * type String. Returned value may be null.
222      * 
223      * @return A copy of the current thread's context map. May be null.
224      * @since 1.5.1
225      */
226     public static Map<String, String> getCopyOfContextMap() {
227         if (mdcAdapter == null) {
228             throw new IllegalStateException("MDCAdapter cannot be null. See also " + NULL_MDCA_URL);
229         }
230         return mdcAdapter.getCopyOfContextMap();
231     }
232 
233     /**
234      * Set the current thread's context map by first clearing any existing map and
235      * then copying the map passed as parameter. The context map passed as
236      * parameter must only contain keys and values of type String.
237      * 
238      * @param contextMap
239      *          must contain only keys and values of type String
240      * @since 1.5.1
241      */
242     public static void setContextMap(Map<String, String> contextMap) {
243         if (mdcAdapter == null) {
244             throw new IllegalStateException("MDCAdapter cannot be null. See also " + NULL_MDCA_URL);
245         }
246         mdcAdapter.setContextMap(contextMap);
247     }
248 
249     /**
250      * Returns the MDCAdapter instance currently in use.
251      * 
252      * @return the MDcAdapter instance currently in use.
253      * @since 1.4.2
254      */
255     public static MDCAdapter getMDCAdapter() {
256         return mdcAdapter;
257     }
258 
259 }