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1   /*
2    * $Header: /home/cvs/jakarta-commons/httpclient/src/java/org/apache/commons/httpclient/util/ExceptionUtil.java,v 1.4 2004/05/13 04:01:22 mbecke Exp $
3    * $Revision: 1.4 $
4    * $Date: 2004/05/13 04:01:22 $
5    *
6    * ====================================================================
7    *
8    *  Copyright 1999-2004 The Apache Software Foundation
9    *
10   *  Licensed under the Apache License, Version 2.0 (the "License");
11   *  you may not use this file except in compliance with the License.
12   *  You may obtain a copy of the License at
13   *
14   *      http://www.apache.org/licenses/LICENSE-2.0
15   *
16   *  Unless required by applicable law or agreed to in writing, software
17   *  distributed under the License is distributed on an "AS IS" BASIS,
18   *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
19   *  See the License for the specific language governing permissions and
20   *  limitations under the License.
21   * ====================================================================
22   *
23   * This software consists of voluntary contributions made by many
24   * individuals on behalf of the Apache Software Foundation.  For more
25   * information on the Apache Software Foundation, please see
26   * <http://www.apache.org/>.
27   *
28   */
29  package org.apache.commons.httpclient.util;
30  
31  import java.lang.reflect.Method;
32  
33  import org.apache.commons.logging.Log;
34  import org.apache.commons.logging.LogFactory;
35  
36  /***
37   * The home for utility methods that handle various exception-related tasks.
38   * 
39   * @author <a href="mailto:oleg@ural.ru">Oleg Kalnichevski</a>
40   * @author <a href="mailto:laura@lwerner.org">Laura Werner</a>
41   * 
42   * @since 3.0
43   */
44  public class ExceptionUtil {
45  
46      /*** Log object for this class. */
47      private static final Log LOG = LogFactory.getLog(ExceptionUtil.class);
48  
49      /*** A reference to Throwable's initCause method, or null if it's not there in this JVM */
50      static private final Method initCause = getInitCauseMethod();
51  
52      /***
53       * Returns a <code>Method<code> allowing access to
54       * {@link Throwable.initCause(Throwable) initCause} method of {@link Throwable},
55       * or <code>null</code> if the method
56       * does not exist.
57       * 
58       * @return A <code>Method<code> for <code>Throwable.initCause</code>, or
59       * <code>null</code> if unavailable.
60       */ 
61      static private Method getInitCauseMethod() {
62          try {
63              Class[] paramsClasses = new Class[] { Throwable.class };
64              return Throwable.class.getMethod("initCause", paramsClasses);
65          } catch (NoSuchMethodException e) {
66              return null;
67          }
68      }
69      
70      /*** 
71       * If we're running on JDK 1.4 or later, initialize the cause for the given throwable.
72       * 
73       * @param  throwable The throwable.
74       * @param  cause     The cause of the throwable.
75       */
76      public static void initCause(Throwable throwable, Throwable cause) {
77          if (initCause != null) {
78              try {
79                  initCause.invoke(throwable, new Object[] { cause });
80              } catch (Exception e) {
81                  LOG.warn("Exception invoking Throwable.initCause", e);
82              }
83          }
84      }
85  }