LogManager


1   package org.apache.velocity.runtime.log;
2   
3   /*
4    * Copyright 2001,2004 The Apache Software Foundation.
5    * 
6    * Licensed under the Apache License, Version 2.0 (the "License");
7    * you may not use this file except in compliance with the License.
8    * You may obtain a copy of the License at
9    * 
10   *      http://www.apache.org/licenses/LICENSE-2.0
11   * 
12   * Unless required by applicable law or agreed to in writing, software
13   * distributed under the License is distributed on an "AS IS" BASIS,
14   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15   * See the License for the specific language governing permissions and
16   * limitations under the License.
17   */
18  
19  import java.util.List  ;
20  import java.util.ArrayList  ;
21  import java.util.Iterator  ;
22  
23  import org.apache.velocity.runtime.RuntimeServices;
24  import org.apache.velocity.runtime.RuntimeConstants;
25  
26  /**
27   * <p>
28   * This class is responsible for instantiating the correct LoggingSystem
29   * </p>
30   *
31   * <p>
32   * The approach is :
33   * </p>
34   * <ul>
35   * <li> 
36   *      First try to see if the user is passing in a living object
37   *      that is a LogSystem, allowing the app to give is living
38   *      custom loggers.
39   *  </li>
40   *  <li> 
41   *       Next, run through the (possible) list of classes specified
42   *       specified as loggers, taking the first one that appears to 
43   *       work.  This is how we support finding either log4j or
44   *       logkit, whichever is in the classpath, as both are 
45   *       listed as defaults.
46   *  </li>
47   *  <li>
48   *      Finally, we turn to 'faith-based' logging, and hope that
49   *      logkit is in the classpath, and try for an AvalonLogSystem
50   *      as a final gasp.  After that, there is nothing we can do.
51   *  </li>
52   *
53   * @author <a HREF="mailto:jvanzyl@apache.org">Jason van Zyl</a>
54   * @author <a HREF="mailto:jon@latchkey.com">Jon S. Stevens</a>
55   * @author <a HREF="mailto:geirm@optonline.net">Geir Magnusson Jr.</a>
56   * @version $Id: LogManager.java,v 1.10.4.1 2004/03/03 23:22:56 geirm Exp $
57   */
58  public class LogManager
59  {
60      /**
61       *  Creates a new logging system or returns an existing one
62       *  specified by the application.
63       */
64      public static LogSystem createLogSystem( RuntimeServices rsvc )
65          throws Exception  
66      {
67          /*
68           *  if a logSystem was set as a configuation value, use that. 
69           *  This is any class the user specifies.
70           */
71  
72          Object   o = rsvc.getProperty( RuntimeConstants.RUNTIME_LOG_LOGSYSTEM );
73  
74          if (o != null && o instanceof LogSystem)
75          {
76              ((LogSystem) o).init( rsvc );
77  
78              return (LogSystem) o;
79          }
80    
81          /*
82           *  otherwise, see if a class was specified.  You
83           *  can put multiple classes, and we use the first one we find.
84           *
85           *  Note that the default value of this property contains both the
86           *  AvalonLogSystem and the SimpleLog4JLogSystem for convenience - 
87           *  so we use whichever we find.
88           */
89          
90          List   classes = null;
91          Object   obj = rsvc.getProperty( RuntimeConstants.RUNTIME_LOG_LOGSYSTEM_CLASS );
92  
93          /*
94           *  we might have a list, or not - so check
95           */
96  
97          if ( obj instanceof List  )
98          {
99              classes = (List  ) obj;
100         }
101         else if ( obj instanceof String  )
102         { 
103             classes = new ArrayList  ();
104             classes.add( obj );
105         }
106 
107         /*
108          *  now run through the list, trying each.  It's ok to 
109          *  fail with a class not found, as we do this to also
110          *  search out a default simple file logger
111          */
112 
113         for( Iterator   ii = classes.iterator(); ii.hasNext(); )
114         {
115             String   claz = (String  ) ii.next();
116 
117             if (claz != null && claz.length() > 0 )
118             {
119                 rsvc.info("Trying to use logger class " + claz );
120           
121                 try
122                 {
123                     o = Class.forName( claz ).newInstance();
124 
125                     if ( o instanceof LogSystem )
126                     {
127                         ((LogSystem) o).init( rsvc );
128 
129                         rsvc.info("Using logger class " + claz );
130 
131                         return (LogSystem) o;
132                     }
133                     else
134                     {
135                         rsvc.error("The specifid logger class " + claz + 
136                                    " isn't a valid LogSystem");
137                     }
138                 }
139                 catch( NoClassDefFoundError   ncdfe )
140                 {
141                     rsvc.debug("Couldn't find class " + claz 
142                                + " or necessary supporting classes in "
143                                + "classpath. Exception : " + ncdfe);
144                 }
145             }
146         }
147       
148         /*
149          *  if the above failed, then we are in deep doo-doo, as the 
150          *  above means that either the user specified a logging class
151          *  that we can't find, there weren't the necessary
152          *  dependencies in the classpath for it, or there were no
153          *  dependencies for the default loggers, log4j and logkit.
154          *  Since we really don't know, 
155          *  then take a wack at the AvalonLogSystem as a last resort.
156          */
157 
158         LogSystem als = null;
159 
160         try
161         {
162             als = new AvalonLogSystem();
163 
164             als.init( rsvc );
165         }
166         catch( NoClassDefFoundError   ncdfe )
167         {
168             String   errstr = "PANIC : Velocity cannot find any of the"
169                 + " specified or default logging systems in the classpath,"
170                 + " or the classpath doesn't contain the necessary classes"
171                 + " to support them."
172                 + " Please consult the documentation regarding logging."
173                 + " Exception : " + ncdfe;
174 
175             System.out.println( errstr );
176             System.err.println( errstr );
177 
178             throw ncdfe;
179         }
180 
181         rsvc.info("Using AvalonLogSystem as logger of final resort.");
182         
183         return als;
184     }
185 }
186 
187
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