ChainableIOException


1   /*
2    * ChainableIOException.java
3    *
4    * Created on 30. Oktober 2004, 03:08
5    */
6   /*
7    * Copyright 2005 Schlichtherle IT Services
8    *
9    * Licensed under the Apache License, Version 2.0 (the "License");
10   * you may not use this file except in compliance with the License.
11   * You may obtain a copy of the License at
12   *
13   *     http://www.apache.org/licenses/LICENSE-2.0
14   *
15   * Unless required by applicable law or agreed to in writing, software
16   * distributed under the License is distributed on an "AS IS" BASIS,
17   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
18   * See the License for the specific language governing permissions and
19   * limitations under the License.
20   */
21  
22  package de.schlichtherle.io;
23  
24  import java.io.IOException  ;
25  import java.io.OutputStreamWriter  ;
26  import java.io.PrintStream  ;
27  import java.io.PrintWriter  ;
28  import java.util.Comparator  ;
29  
30  /**
31   * Represents a chain of {@link IOException}s.
32   * This class supports chaining exceptions for reasons other than causes
33   * (which is a functionality already provided by J2SE 1.4 and later).
34   * A <code>ChainableIOException</code> can be used to implement an algorithm
35   * which must be able to continue with some work although one or more
36   * <code>IOException</code>s have occured.
37   * <p>
38   * For example, when looping through a list of files, an algorithm might
39   * encounter an <code>IOException</code> when processing a file element in the list.
40   * However, it may still be required to process the remaining files in the list
41   * before actually throwing the corresponding <code>IOException</code>.
42   * Hence, whenever this algorithm encounters an <code>IOException</code>,
43   * it would catch the <code>IOException</code>, create a
44   * <code>ChainableIOException</code> for it and continue processing the
45   * remainder of the list.
46   * Finally, at the end of the algorithm, if any <code>IOException</code>s
47   * have occured, the <code>ChainableIOException</code> chain would get sorted
48   * according to priority (see {@link #getPriority()} and
49   * {@link #sortPriority()}) and finally thrown.
50   * This would allow a client application to filter the exceptions by priority
51   * with a simple try-catch statement, ensuring that no other exception of
52   * higher priority is in the catched exception chain.
53   * <p>
54   * <b>Note:</b> This is not related to the cause concept of exceptions in
55   * J2SE 1.4 and higher. Exceptions chained by this class are <b>not</b>
56   * causes of each other, but have just been merely collected over time
57   * and then thrown as one exception (list).
58   * 
59   * @see File#update()
60   * @see File#umount()
61   *
62   * @author Christian Schlichtherle
63   * @version @version@
64   * @since TrueZIP 6.0 (generalized from the former
65   *        <code>ArchiveControllerException</code>).
66   */
67  public class ChainableIOException extends IOException   implements Cloneable   {
68  
69      /**
70       * Compares two ZIP controller exceptions in descending order of their
71       * priority.
72       * If the priority is equal, the elements are compared in descending
73       * order of their appearance.
74       */
75      // Note: Not private for unit testing purposes only!
76      static final Comparator   PRIORITY_COMP = new Comparator  () {
77          public int compare(Object   o1, Object   o2) {
78              final int cmp = ((ChainableIOException) o1).getPriority()
79                            - ((ChainableIOException) o2).getPriority();
80              return cmp != 0 ? cmp : APPEARANCE_COMP.compare(o1, o2);
81          }
82      };
83      
84      /**
85       * Compares two ZIP controller exceptions in descending order of their
86       * appearance.
87       */
88      // Note: Not private for unit testing purposes only!
89      static final Comparator   APPEARANCE_COMP = new Comparator  () {
90          public int compare(Object   o1, Object   o2) {
91              return ((ChainableIOException) o1).getAppearance()
92                   - ((ChainableIOException) o2).getAppearance();
93          }
94      };
95  
96      private static int maxPrintExceptions = 5;
97  
98      /**
99       * @see #printStackTrace(PrintStream)
100      * @see #printStackTrace(PrintWriter)
101      */
102     public static int getMaxPrintExceptions() {
103         return maxPrintExceptions;
104     }
105     
106     /**
107      * @see #printStackTrace(PrintStream)
108      * @see #printStackTrace(PrintWriter)
109      */
110     public static void setMaxPrintExceptions(int maxPrintExcepions) {
111         ChainableIOException.maxPrintExceptions = maxPrintExcepions;
112     }
113     
114     /**
115      * The tail chain of this exception chain.
116      * Maybe <tt>null</tt> if there are no more exceptions.
117      * If this exception chain has not been reordered,
118      * the head of the tail is either <tt>null</tt> or an exception which
119      * occured before this exception was created.
120      * <p>
121      * Please note that this is totally unrelated to a possible cause for
122      * this exception!
123      */
124     private ChainableIOException prior;
125 
126     private final int appearance;
127 
128     int maxAppearance;
129 
130     /**
131      * Constructs a new exception with the specified prior exception.
132      *
133      * @param  priorException An exception that happened before and that was
134      *         caught - may be <tt>null</tt>.
135      * 
136      * @see ChainableIOException
137      */
138     public ChainableIOException(ChainableIOException priorException) {
139         this(priorException, null, null);
140     }
141 
142     /**
143      * Constructs a new exception with the specified prior exception
144      * and a message.
145      *
146      * @param  priorException An exception that happened before and that was
147      *         caught - may be <tt>null</tt>.
148      * @param  message The message for this exception.
149      * 
150      * @see ChainableIOException
151      */
152     public ChainableIOException(
153             ChainableIOException priorException,
154             String   message) {
155         this(priorException, message, null);
156     }
157     
158     /**
159      * Constructs a new exception with the specified prior exception and the
160      * cause.
161      *
162      * @param  priorException An exception that happened before and that was
163      *         caught - may be <tt>null</tt>.
164      * @param  cause The cause (which is saved for later retrieval by the
165      *         {@link #getCause()} method).  (A <tt>null</tt> value is
166      *         permitted, and indicates that the cause is nonexistent or
167      *         unknown.).
168      * 
169      * @see ChainableIOException
170      */
171     public ChainableIOException(
172             ChainableIOException priorException,
173             IOException   cause) {
174         this(priorException, null, cause);
175     }
176 
177     /**
178      * Constructs a new exception with the specified prior exception,
179      * a message and a cause.
180      *
181      * @param  priorException An exception that happened before and that was
182      *         caught - may be <tt>null</tt>.
183      * @param  message The message for this exception.
184      * @param  cause The cause (which is saved for later retrieval by the
185      *         {@link #getCause()} method).  (A <tt>null</tt> value is
186      *         permitted, and indicates that the cause is nonexistent or
187      *         unknown.).
188      * 
189      * @see ChainableIOException
190      */
191     public ChainableIOException(
192             ChainableIOException priorException,
193             String   message,
194             IOException   cause) {
195         super(message);
196         this.prior = priorException;
197         if (cause != null)
198             initCause(cause);
199         if (priorException != null)
200             maxAppearance = priorException.maxAppearance + 1;
201         else
202             maxAppearance = 0;
203         appearance = maxAppearance;
204     }
205 
206     /**
207      * Returns a <em>shallow</em> clone of this exception.
208      */
209     public Object   clone() {
210         try {
211             return super.clone();
212         } catch (CloneNotSupportedException   cannotHappen) {
213             throw new AssertionError  (cannotHappen);
214         }
215     }
216 
217     /**
218      * Returns the priority for this class of exception.
219      * This should always return the same value for all instances of a
220      * particular class.
221      *
222      * @return 0 for all instances of this class.
223      */
224     public int getPriority() {
225         return 0;
226     }
227 
228     /**
229      * @return The order of appearance for this ZIP exception.
230      */
231     public final int getAppearance() {
232         return appearance;
233     }
234 
235     /**
236      * @return The exception chain represented by the prior exception,
237      *         or <code>null</code> if no prior exception exists.
238      */
239     public ChainableIOException getPrior() {
240         return prior;
241     }
242 
243     /**
244      * Sorts the elements of this exception chain in descending order
245      * of their priority.
246      * If the priority of two elements is equal, they are sorted in descending
247      * order of their appearance.
248      *
249      * @return The sorted exception chain, consisting of cloned elements where
250      *         required to enforce the immutability of this class.
251      *         This is a non-destructive sort, i.e. elements already in order
252      *         are guaranteed not to get rearranged.
253      *         If and only if all elements are in order, this exception chain
254      *         is returned and no elements are cloned.
255      */
256     public ChainableIOException sortPriority() {
257         return sort(PRIORITY_COMP);
258     }
259     
260     /**
261      * Sorts the elements of this exception chain in descending order
262      * of their appearance.
263      *
264      * @return The sorted exception chain, consisting of cloned elements where
265      *         required to enforce the immutability of this class.
266      *         This is a non-destructive sort, i.e. elements already in order
267      *         are guaranteed not to get rearranged.
268      *         If and only if all elements are in order, this exception chain
269      *         is returned and no elements are cloned.
270      */
271     public ChainableIOException sortAppearance() {
272         return sort(APPEARANCE_COMP);
273     }
274     
275     private ChainableIOException sort(final Comparator   comp) {
276         if (prior != null) {
277             final ChainableIOException sortedPrior = prior.sort(comp);
278             if (sortedPrior == prior && comp.compare(this, prior) >= 0)
279                 return this;
280             else
281                 return sortedPrior.insert((ChainableIOException) clone(), comp);
282         } else {
283             return this;
284         }
285     }
286 
287     private ChainableIOException insert(
288             final ChainableIOException element,
289             final Comparator   comp) {
290         if (comp.compare(element, this) >= 0) {
291             // Prepend to chain.
292             element.prior = this;
293             element.maxAppearance = Math.max(element.appearance, maxAppearance);
294             return element;
295         } else {
296             // Insert element in the prior exception chain.
297             final ChainableIOException clone
298                     = (ChainableIOException) clone();
299             if (prior != null) {
300                 clone.prior = prior.insert(element, comp);
301                 clone.maxAppearance = Math.max(clone.appearance, clone.prior.maxAppearance);
302             } else {
303                 element.prior = null;
304                 clone.prior = element;
305                 clone.maxAppearance = element.maxAppearance;
306             }
307             return clone;
308         }
309     }
310     
311     /**
312      * Prints up to {@link #getMaxPrintExceptions()} exceptions in this
313      * chain to the provided {@link PrintStream}.
314      * <p>
315      * Exceptions are printed in ascending order of this chain.
316      * If this chain has not been sorted, this results in the exceptions being
317      * printed in order of their appearance.
318      * <p>
319      * If more exceptions are in this chain than are allowed to be printed,
320      * then the printed message starts with a line indicating the number of
321      * exceptions which have been omitted from the beginning of this chain.
322      * Thus, this exception is always printed as the last exception in the
323      * list.
324      */
325     public void printStackTrace(PrintStream   s) {
326         printStackTrace(s, getMaxPrintExceptions());
327     }
328 
329     /**
330      * Prints up to <code>maxExceptions()</code> exceptions in this
331      * chain to the provided {@link PrintStream}.
332      * <p>
333      * Exceptions are printed in ascending order of this chain.
334      * If this chain has not been sorted, this results in the exceptions being
335      * printed in order of their appearance.
336      * <p>
337      * If more exceptions are in this chain than are allowed to be printed,
338      * then the printed message starts with a line indicating the number of
339      * exceptions which have been omitted from the beginning of this chain.
340      * Thus, this exception is always printed as the last exception in the
341      * list.
342      */
343     public void printStackTrace(PrintStream   s, int maxExceptions) {
344         maxExceptions--;
345 
346         if (prior != null) {
347             if (maxExceptions > 0) {
348                 prior.printStackTrace(s, maxExceptions);
349                 s.println("Followed, but not caused by:");
350             } else {
351                 s.println("(Omitting " + prior.getNumExceptions() + " exception(s) at the start of this list)");
352             }
353         }
354 
355         super.printStackTrace(s);
356     }
357 
358     private int getNumExceptions() {
359         return prior != null ? prior.getNumExceptions() + 1 : 1;
360     }
361 
362     /**
363      * Prints up to {@link #getMaxPrintExceptions()} exceptions in this
364      * chain to the provided {@link PrintStream}.
365      * <p>
366      * Exceptions are printed in ascending order of this chain.
367      * If this chain has not been sorted, this results in the exceptions being
368      * printed in order of their appearance.
369      * <p>
370      * If more exceptions are in this chain than are allowed to be printed,
371      * then the printed message starts with a line indicating the number of
372      * exceptions which have been omitted from the beginning of this chain.
373      * Thus, this exception is always printed as the last exception in the
374      * list.
375      */
376     public void printStackTrace(PrintWriter   s) {
377         printStackTrace(s, getMaxPrintExceptions());
378     }
379 
380     /**
381      * Prints up to <code>maxExceptions()</code> exceptions in this
382      * chain to the provided {@link PrintStream}.
383      * <p>
384      * Exceptions are printed in ascending order of this chain.
385      * If this chain has not been sorted, this results in the exceptions being
386      * printed in order of their appearance.
387      * <p>
388      * If more exceptions are in this chain than are allowed to be printed,
389      * then the printed message starts with a line indicating the number of
390      * exceptions which have been omitted from the beginning of this chain.
391      * Thus, this exception is always printed as the last exception in the
392      * list.
393      */
394     public void printStackTrace(PrintWriter   s, int maxExceptions) {
395         maxExceptions--;
396 
397         if (prior != null) {
398             if (maxExceptions > 0) {
399                 prior.printStackTrace(s, maxExceptions);
400                 s.println("Followed, but not caused by:");
401             } else {
402                 s.println("(Omitting " + prior.getNumExceptions() + " exception(s) at the start of this list)");
403             }
404         }
405 
406         super.printStackTrace(s);
407     }
408 }
409
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