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