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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      /**
89       * As of SLF4J version 1.7.14, StaticMDCBinder classes shipping in various bindings
90       * come with a getSingleton() method. Previously only a public field called SINGLETON 
91       * was available.
92       * 
93       * @return MDCAdapter
94       * @throws NoClassDefFoundError in case no binding is available
95       * @since 1.7.14
96       */
97      private static MDCAdapter bwCompatibleGetMDCAdapterFromBinder() throws NoClassDefFoundError {
98          try {
99              return StaticMDCBinder.getSingleton().getMDCA();
100         } catch (NoSuchMethodError nsme) {
101             // binding is probably a version of SLF4J older than 1.7.14
102             return StaticMDCBinder.SINGLETON.getMDCA();
103         }
104     }
105 
106     static {
107         try {
108             mdcAdapter = bwCompatibleGetMDCAdapterFromBinder();
109         } catch (NoClassDefFoundError ncde) {
110             mdcAdapter = new NOPMDCAdapter();
111             String msg = ncde.getMessage();
112             if (msg != null && msg.contains("StaticMDCBinder")) {
113                 Util.report("Failed to load class \"org.slf4j.impl.StaticMDCBinder\".");
114                 Util.report("Defaulting to no-operation MDCAdapter implementation.");
115                 Util.report("See " + NO_STATIC_MDC_BINDER_URL + " for further details.");
116             } else {
117                 throw ncde;
118             }
119         } catch (Exception e) {
120             // we should never get here
121             Util.report("MDC binding unsuccessful.", e);
122         }
123     }
124 
125     /**
126      * Put a diagnostic context value (the <code>val</code> parameter) as identified with the
127      * <code>key</code> parameter into the current thread's diagnostic context map. The
128      * <code>key</code> parameter cannot be null. The <code>val</code> parameter
129      * can be null only if the underlying implementation supports it.
130      * 
131      * <p>
132      * This method delegates all work to the MDC of the underlying logging system.
133      *
134      * @param key non-null key 
135      * @param val value to put in the map
136      * 
137      * @throws IllegalArgumentException
138      *           in case the "key" parameter is null
139      */
140     public static void put(String key, String val) throws IllegalArgumentException {
141         if (key == null) {
142             throw new IllegalArgumentException("key parameter cannot be null");
143         }
144         if (mdcAdapter == null) {
145             throw new IllegalStateException("MDCAdapter cannot be null. See also " + NULL_MDCA_URL);
146         }
147         mdcAdapter.put(key, val);
148     }
149 
150     /**
151      * Put a diagnostic context value (the <code>val</code> parameter) as identified with the
152      * <code>key</code> parameter into the current thread's diagnostic context map. The
153      * <code>key</code> parameter cannot be null. The <code>val</code> parameter
154      * can be null only if the underlying implementation supports it.
155      *
156      * <p>
157      * This method delegates all work to the MDC of the underlying logging system.
158      * <p>
159      * This method return a <code>Closeable</code> object who can remove <code>key</code> when
160      * <code>close</code> is called.
161      *
162      * <p>
163      * Useful with Java 7 for example :
164      * <code>
165      *   try(MDC.MDCCloseable closeable = MDC.putCloseable(key, value)) {
166      *     ....
167      *   }
168      * </code>
169      *
170      * @param key non-null key
171      * @param val value to put in the map
172      * @return a <code>Closeable</code> who can remove <code>key</code> when <code>close</code>
173      * is called.
174      *
175      * @throws IllegalArgumentException
176      *           in case the "key" parameter is null
177      */
178     public static MDCCloseable putCloseable(String key, String val) throws IllegalArgumentException {
179         put(key, val);
180         return new MDCCloseable(key);
181     }
182 
183     /**
184      * Get the diagnostic context identified by the <code>key</code> parameter. The
185      * <code>key</code> parameter cannot be null.
186      * 
187      * <p>
188      * This method delegates all work to the MDC of the underlying logging system.
189      *
190      * @param key  
191      * @return the string value identified by the <code>key</code> parameter.
192      * @throws IllegalArgumentException
193      *           in case the "key" parameter is null
194      */
195     public static String get(String key) throws IllegalArgumentException {
196         if (key == null) {
197             throw new IllegalArgumentException("key parameter cannot be null");
198         }
199 
200         if (mdcAdapter == null) {
201             throw new IllegalStateException("MDCAdapter cannot be null. See also " + NULL_MDCA_URL);
202         }
203         return mdcAdapter.get(key);
204     }
205 
206     /**
207      * Remove the diagnostic context identified by the <code>key</code> parameter using
208      * the underlying system's MDC implementation. The <code>key</code> parameter
209      * cannot be null. This method does nothing if there is no previous value
210      * associated with <code>key</code>.
211      *
212      * @param key  
213      * @throws IllegalArgumentException
214      *           in case the "key" parameter is null
215      */
216     public static void remove(String key) throws IllegalArgumentException {
217         if (key == null) {
218             throw new IllegalArgumentException("key parameter cannot be null");
219         }
220 
221         if (mdcAdapter == null) {
222             throw new IllegalStateException("MDCAdapter cannot be null. See also " + NULL_MDCA_URL);
223         }
224         mdcAdapter.remove(key);
225     }
226 
227     /**
228      * Clear all entries in the MDC of the underlying implementation.
229      */
230     public static void clear() {
231         if (mdcAdapter == null) {
232             throw new IllegalStateException("MDCAdapter cannot be null. See also " + NULL_MDCA_URL);
233         }
234         mdcAdapter.clear();
235     }
236 
237     /**
238      * Return a copy of the current thread's context map, with keys and values of
239      * type String. Returned value may be null.
240      * 
241      * @return A copy of the current thread's context map. May be null.
242      * @since 1.5.1
243      */
244     public static Map<String, String> getCopyOfContextMap() {
245         if (mdcAdapter == null) {
246             throw new IllegalStateException("MDCAdapter cannot be null. See also " + NULL_MDCA_URL);
247         }
248         return mdcAdapter.getCopyOfContextMap();
249     }
250 
251     /**
252      * Set the current thread's context map by first clearing any existing map and
253      * then copying the map passed as parameter. The context map passed as
254      * parameter must only contain keys and values of type String.
255      * 
256      * @param contextMap
257      *          must contain only keys and values of type String
258      * @since 1.5.1
259      */
260     public static void setContextMap(Map<String, String> contextMap) {
261         if (mdcAdapter == null) {
262             throw new IllegalStateException("MDCAdapter cannot be null. See also " + NULL_MDCA_URL);
263         }
264         mdcAdapter.setContextMap(contextMap);
265     }
266 
267     /**
268      * Returns the MDCAdapter instance currently in use.
269      * 
270      * @return the MDcAdapter instance currently in use.
271      * @since 1.4.2
272      */
273     public static MDCAdapter getMDCAdapter() {
274         return mdcAdapter;
275     }
276 
277 }