1 package org.apache.commons.digester3.plugins;
2
3 /*
4 * Licensed to the Apache Software Foundation (ASF) under one
5 * or more contributor license agreements. See the NOTICE file
6 * distributed with this work for additional information
7 * regarding copyright ownership. The ASF licenses this file
8 * to you under the Apache License, Version 2.0 (the
9 * "License"); you may not use this file except in compliance
10 * with the License. You may obtain a copy of the License at
11 *
12 * http://www.apache.org/licenses/LICENSE-2.0
13 *
14 * Unless required by applicable law or agreed to in writing,
15 * software distributed under the License is distributed on an
16 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
17 * KIND, either express or implied. See the License for the
18 * specific language governing permissions and limitations
19 * under the License.
20 */
21
22 import org.apache.commons.digester3.Digester;
23 import org.apache.commons.logging.Log;
24
25 /**
26 * Simple utility class to assist in logging.
27 * <p>
28 * This class is intended only for the use of the code in the plugins packages. No "user" code should use this package.
29 * <p>
30 * The Digester module has an interesting approach to logging: all logging should be done via the Log object stored on
31 * the digester instance that the object *doing* the logging is associated with.
32 * <p>
33 * This is done because apparently some "container"-type applications such as Avalon and Tomcat need to be able to
34 * configure different logging for different <i>instances</i> of the Digester class which have been loaded from the same
35 * ClassLoader [info from Craig McClanahan]. Not only the logging of the Digester instance should be affected; all
36 * objects associated with that Digester instance should obey the reconfiguration of their owning Digester instance's
37 * logging. The current solution is to force all objects to output logging info via a single Log object stored on the
38 * Digester instance they are associated with.
39 * <p>
40 * Of course this causes problems if logging is attempted before an object <i>has</i> a valid reference to its owning
41 * Digester. The getLogging method provided here resolves this issue by returning a Log object which silently discards
42 * all logging output in this situation.
43 * <p>
44 * And it also implies that logging filtering can no longer be applied to subcomponents of the Digester, because all
45 * logging is done via a single Log object (a single Category). C'est la vie...
46 *
47 * @since 1.6
48 */
49 class LogUtils
50 {
51
52 /**
53 * Get the Log object associated with the specified Digester instance, or a "no-op" logging object if the digester
54 * reference is null.
55 * <p>
56 * You should use this method instead of digester.getLogger() in any situation where the digester might be null.
57 */
58 static Log getLogger( Digester digester )
59 {
60 if ( digester == null )
61 {
62 return new org.apache.commons.logging.impl.NoOpLog();
63 }
64
65 return digester.getLogger();
66 }
67
68 }