AbstractOutputTarget


1   /* 
2    * Copyright 1999-2004 The Apache Software Foundation
3    * Licensed  under the  Apache License,  Version 2.0  (the "License");
4    * you may not use  this file  except in  compliance with the License.
5    * You may obtain a copy of the License at 
6    * 
7    *   http://www.apache.org/licenses/LICENSE-2.0
8    * 
9    * Unless required by applicable law or agreed to in writing, software
10   * distributed  under the  License is distributed on an "AS IS" BASIS,
11   * WITHOUT  WARRANTIES OR CONDITIONS  OF ANY KIND, either  express  or
12   * implied.
13   * 
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  package org.apache.log.output;
18  
19  import org.apache.log.LogEvent;
20  import org.apache.log.format.Formatter;
21  
22  /** Abstract output target.
23   *
24   * Any new output target that is writing to a single connected
25   * resource should extend this class directly or indirectly.
26   *
27   * @author <a HREF="mailto:dev@avalon.apache.org">Avalon Development Team</a>
28   * @author Peter Donald
29   */
30  public abstract class AbstractOutputTarget
31      extends AbstractTarget
32  {
33      /** Formatter for target. */
34      private Formatter m_formatter;
35  
36      /** Parameterless constructor.  */
37      public AbstractOutputTarget()
38      {
39      }
40  
41      /**
42       * Creation of a new abstract output target instance.
43       * @param formatter the formatter to apply
44       */
45      public AbstractOutputTarget( final Formatter formatter )
46      {
47          m_formatter = formatter;
48      }
49  
50      /** Returns the Formatter.
51       */
52      protected Formatter getFormatter()
53      {
54          return m_formatter;
55      }
56      
57      /**
58       * Abstract method to write data.
59       *
60       * @param data the data to be output
61       */
62      protected void write( final String   data )
63      {
64      }
65  
66      /**
67       * Process a log event.
68       * @param event the event to process
69       */
70      protected void doProcessEvent( LogEvent event )
71      {
72          final String   data = format( event );
73          write( data );
74      }
75  
76      /**
77       * Startup log session.
78       *
79       */
80      protected synchronized void open()
81      {
82          if( !isOpen() )
83          {
84              super.open();
85              writeHead();
86          }
87      }
88  
89      /**
90       * Shutdown target.
91       * Attempting to write to target after close() will cause errors to be logged.
92       *
93       */
94      public synchronized void close()
95      {
96          if( isOpen() )
97          {
98              writeTail();
99              super.close();
100         }
101     }
102 
103     /**
104      * Helper method to format an event into a string, using the formatter if available.
105      *
106      * @param event the LogEvent
107      * @return the formatted string
108      */
109     private String   format( final LogEvent event )
110     {
111         if( null != m_formatter )
112         {
113             return m_formatter.format( event );
114         }
115         else
116         {
117             return event.toString();
118         }
119     }
120 
121     /**
122      * Helper method to write out log head.
123      * The head initiates a session of logging.
124      */
125     private void writeHead()
126     {
127         if( !isOpen() )
128         {
129             return;
130         }
131 
132         final String   head = getHead();
133         if( null != head )
134         {
135             write( head );
136         }
137     }
138 
139     /**
140      * Helper method to write out log tail.
141      * The tail completes a session of logging.
142      */
143     private void writeTail()
144     {
145         if( !isOpen() )
146         {
147             return;
148         }
149 
150         final String   tail = getTail();
151         if( null != tail )
152         {
153             write( tail );
154         }
155     }
156 
157     /**
158      * Helper method to retrieve head for log session.
159      * TODO: Extract from formatter
160      *
161      * @return the head string
162      */
163     private String   getHead()
164     {
165         return null;
166     }
167 
168     /**
169      * Helper method to retrieve tail for log session.
170      * TODO: Extract from formatter
171      *
172      * @return the head string
173      */
174     private String   getTail()
175     {
176         return null;
177     }
178 }
179
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