001 /* java.lang.Throwable -- Root class for all Exceptions and Errors
002 Copyright (C) 1998, 1999, 2002, 2004, 2005 Free Software Foundation, Inc.
003
004 This file is part of GNU Classpath.
005
006 GNU Classpath is free software; you can redistribute it and/or modify
007 it under the terms of the GNU General Public License as published by
008 the Free Software Foundation; either version 2, or (at your option)
009 any later version.
010
011 GNU Classpath is distributed in the hope that it will be useful, but
012 WITHOUT ANY WARRANTY; without even the implied warranty of
013 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
014 General Public License for more details.
015
016 You should have received a copy of the GNU General Public License
017 along with GNU Classpath; see the file COPYING. If not, write to the
018 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
019 02110-1301 USA.
020
021 Linking this library statically or dynamically with other modules is
022 making a combined work based on this library. Thus, the terms and
023 conditions of the GNU General Public License cover the whole
024 combination.
025
026 As a special exception, the copyright holders of this library give you
027 permission to link this library with independent modules to produce an
028 executable, regardless of the license terms of these independent
029 modules, and to copy and distribute the resulting executable under
030 terms of your choice, provided that you also meet, for each linked
031 independent module, the terms and conditions of the license of that
032 module. An independent module is a module which is not derived from
033 or based on this library. If you modify this library, you may extend
034 this exception to your version of the library, but you are not
035 obligated to do so. If you do not wish to do so, delete this
036 exception statement from your version. */
037
038 package java.lang;
039
040 import gnu.classpath.SystemProperties;
041
042 import gnu.java.lang.CPStringBuilder;
043
044 import java.io.PrintStream;
045 import java.io.PrintWriter;
046 import java.io.Serializable;
047
048 /**
049 * Throwable is the superclass of all exceptions that can be raised.
050 *
051 * <p>There are two special cases: {@link Error} and {@link RuntimeException}:
052 * these two classes (and their subclasses) are considered unchecked
053 * exceptions, and are either frequent enough or catastrophic enough that you
054 * do not need to declare them in <code>throws</code> clauses. Everything
055 * else is a checked exception, and is ususally a subclass of
056 * {@link Exception}; these exceptions have to be handled or declared.
057 *
058 * <p>Instances of this class are usually created with knowledge of the
059 * execution context, so that you can get a stack trace of the problem spot
060 * in the code. Also, since JDK 1.4, Throwables participate in "exception
061 * chaining." This means that one exception can be caused by another, and
062 * preserve the information of the original.
063 *
064 * <p>One reason this is useful is to wrap exceptions to conform to an
065 * interface. For example, it would be bad design to require all levels
066 * of a program interface to be aware of the low-level exceptions thrown
067 * at one level of abstraction. Another example is wrapping a checked
068 * exception in an unchecked one, to communicate that failure occured
069 * while still obeying the method throws clause of a superclass.
070 *
071 * <p>A cause is assigned in one of two ways; but can only be assigned once
072 * in the lifetime of the Throwable. There are new constructors added to
073 * several classes in the exception hierarchy that directly initialize the
074 * cause, or you can use the <code>initCause</code> method. This second
075 * method is especially useful if the superclass has not been retrofitted
076 * with new constructors:<br>
077 * <pre>
078 * try
079 * {
080 * lowLevelOp();
081 * }
082 * catch (LowLevelException lle)
083 * {
084 * throw (HighLevelException) new HighLevelException().initCause(lle);
085 * }
086 * </pre>
087 * Notice the cast in the above example; without it, your method would need
088 * a throws clase that declared Throwable, defeating the purpose of chainig
089 * your exceptions.
090 *
091 * <p>By convention, exception classes have two constructors: one with no
092 * arguments, and one that takes a String for a detail message. Further,
093 * classes which are likely to be used in an exception chain also provide
094 * a constructor that takes a Throwable, with or without a detail message
095 * string.
096 *
097 * <p>Another 1.4 feature is the StackTrace, a means of reflection that
098 * allows the program to inspect the context of the exception, and which is
099 * serialized, so that remote procedure calls can correctly pass exceptions.
100 *
101 * @author Brian Jones
102 * @author John Keiser
103 * @author Mark Wielaard
104 * @author Tom Tromey
105 * @author Eric Blake (ebb9@email.byu.edu)
106 * @since 1.0
107 * @status updated to 1.4
108 */
109 public class Throwable implements Serializable
110 {
111 /**
112 * Compatible with JDK 1.0+.
113 */
114 private static final long serialVersionUID = -3042686055658047285L;
115
116 /**
117 * The detail message.
118 *
119 * @serial specific details about the exception, may be null
120 */
121 private final String detailMessage;
122
123 /**
124 * The cause of the throwable, including null for an unknown or non-chained
125 * cause. This may only be set once; so the field is set to
126 * <code>this</code> until initialized.
127 *
128 * @serial the cause, or null if unknown, or this if not yet set
129 * @since 1.4
130 */
131 private Throwable cause = this;
132
133 /**
134 * The stack trace, in a serialized form.
135 *
136 * @serial the elements of the stack trace; this is non-null, and has
137 * no null entries
138 * @since 1.4
139 */
140 private StackTraceElement[] stackTrace;
141
142 /**
143 * Instantiate this Throwable with an empty message. The cause remains
144 * uninitialized. {@link #fillInStackTrace()} will be called to set
145 * up the stack trace.
146 */
147 public Throwable()
148 {
149 this((String) null);
150 }
151
152 /**
153 * Instantiate this Throwable with the given message. The cause remains
154 * uninitialized. {@link #fillInStackTrace()} will be called to set
155 * up the stack trace.
156 *
157 * @param message the message to associate with the Throwable
158 */
159 public Throwable(String message)
160 {
161 fillInStackTrace();
162 detailMessage = message;
163 }
164
165 /**
166 * Instantiate this Throwable with the given message and cause. Note that
167 * the message is unrelated to the message of the cause.
168 * {@link #fillInStackTrace()} will be called to set up the stack trace.
169 *
170 * @param message the message to associate with the Throwable
171 * @param cause the cause, may be null
172 * @since 1.4
173 */
174 public Throwable(String message, Throwable cause)
175 {
176 this(message);
177 this.cause = cause;
178 }
179
180 /**
181 * Instantiate this Throwable with the given cause. The message is then
182 * built as <code>cause == null ? null : cause.toString()</code>.
183 * {@link #fillInStackTrace()} will be called to set up the stack trace.
184 *
185 * @param cause the cause, may be null
186 * @since 1.4
187 */
188 public Throwable(Throwable cause)
189 {
190 this(cause == null ? null : cause.toString(), cause);
191 }
192
193 /**
194 * Get the message associated with this Throwable.
195 *
196 * @return the error message associated with this Throwable, may be null
197 */
198 public String getMessage()
199 {
200 return detailMessage;
201 }
202
203 /**
204 * Get a localized version of this Throwable's error message.
205 * This method must be overridden in a subclass of Throwable
206 * to actually produce locale-specific methods. The Throwable
207 * implementation just returns getMessage().
208 *
209 * @return a localized version of this error message
210 * @see #getMessage()
211 * @since 1.1
212 */
213 public String getLocalizedMessage()
214 {
215 return getMessage();
216 }
217
218 /**
219 * Returns the cause of this exception, or null if the cause is not known
220 * or non-existant. This cause is initialized by the new constructors,
221 * or by calling initCause.
222 *
223 * @return the cause of this Throwable
224 * @since 1.4
225 */
226 public Throwable getCause()
227 {
228 return cause == this ? null : cause;
229 }
230
231 /**
232 * Initialize the cause of this Throwable. This may only be called once
233 * during the object lifetime, including implicitly by chaining
234 * constructors.
235 *
236 * @param cause the cause of this Throwable, may be null
237 * @return this
238 * @throws IllegalArgumentException if cause is this (a Throwable can't be
239 * its own cause!)
240 * @throws IllegalStateException if the cause has already been set
241 * @since 1.4
242 */
243 public Throwable initCause(Throwable cause)
244 {
245 if (cause == this)
246 throw new IllegalArgumentException();
247 if (this.cause != this)
248 throw new IllegalStateException();
249 this.cause = cause;
250 return this;
251 }
252
253 /**
254 * Get a human-readable representation of this Throwable. The detail message
255 * is retrieved by getLocalizedMessage(). Then, with a null detail
256 * message, this string is simply the object's class name; otherwise
257 * the string is <code>getClass().getName() + ": " + message</code>.
258 *
259 * @return a human-readable String represting this Throwable
260 */
261 public String toString()
262 {
263 String msg = getLocalizedMessage();
264 return getClass().getName() + (msg == null ? "" : ": " + msg);
265 }
266
267 /**
268 * Print a stack trace to the standard error stream. This stream is the
269 * current contents of <code>System.err</code>. The first line of output
270 * is the result of {@link #toString()}, and the remaining lines represent
271 * the data created by {@link #fillInStackTrace()}. While the format is
272 * unspecified, this implementation uses the suggested format, demonstrated
273 * by this example:<br>
274 * <pre>
275 * public class Junk
276 * {
277 * public static void main(String args[])
278 * {
279 * try
280 * {
281 * a();
282 * }
283 * catch(HighLevelException e)
284 * {
285 * e.printStackTrace();
286 * }
287 * }
288 * static void a() throws HighLevelException
289 * {
290 * try
291 * {
292 * b();
293 * }
294 * catch(MidLevelException e)
295 * {
296 * throw new HighLevelException(e);
297 * }
298 * }
299 * static void b() throws MidLevelException
300 * {
301 * c();
302 * }
303 * static void c() throws MidLevelException
304 * {
305 * try
306 * {
307 * d();
308 * }
309 * catch(LowLevelException e)
310 * {
311 * throw new MidLevelException(e);
312 * }
313 * }
314 * static void d() throws LowLevelException
315 * {
316 * e();
317 * }
318 * static void e() throws LowLevelException
319 * {
320 * throw new LowLevelException();
321 * }
322 * }
323 * class HighLevelException extends Exception
324 * {
325 * HighLevelException(Throwable cause) { super(cause); }
326 * }
327 * class MidLevelException extends Exception
328 * {
329 * MidLevelException(Throwable cause) { super(cause); }
330 * }
331 * class LowLevelException extends Exception
332 * {
333 * }
334 * </pre>
335 * <p>
336 * <pre>
337 * HighLevelException: MidLevelException: LowLevelException
338 * at Junk.a(Junk.java:13)
339 * at Junk.main(Junk.java:4)
340 * Caused by: MidLevelException: LowLevelException
341 * at Junk.c(Junk.java:23)
342 * at Junk.b(Junk.java:17)
343 * at Junk.a(Junk.java:11)
344 * ... 1 more
345 * Caused by: LowLevelException
346 * at Junk.e(Junk.java:30)
347 * at Junk.d(Junk.java:27)
348 * at Junk.c(Junk.java:21)
349 * ... 3 more
350 * </pre>
351 */
352 public void printStackTrace()
353 {
354 printStackTrace(System.err);
355 }
356
357 /**
358 * Print a stack trace to the specified PrintStream. See
359 * {@link #printStackTrace()} for the sample format.
360 *
361 * @param s the PrintStream to write the trace to
362 */
363 public void printStackTrace(PrintStream s)
364 {
365 s.print(stackTraceString());
366 }
367
368 /**
369 * Prints the exception, the detailed message and the stack trace
370 * associated with this Throwable to the given <code>PrintWriter</code>.
371 * The actual output written is implemention specific. Use the result of
372 * <code>getStackTrace()</code> when more precise information is needed.
373 *
374 * <p>This implementation first prints a line with the result of this
375 * object's <code>toString()</code> method.
376 * <br>
377 * Then for all elements given by <code>getStackTrace</code> it prints
378 * a line containing three spaces, the string "at " and the result of calling
379 * the <code>toString()</code> method on the <code>StackTraceElement</code>
380 * object. If <code>getStackTrace()</code> returns an empty array it prints
381 * a line containing three spaces and the string
382 * "<<No stacktrace available>>".
383 * <br>
384 * Then if <code>getCause()</code> doesn't return null it adds a line
385 * starting with "Caused by: " and the result of calling
386 * <code>toString()</code> on the cause.
387 * <br>
388 * Then for every cause (of a cause, etc) the stacktrace is printed the
389 * same as for the top level <code>Throwable</code> except that as soon
390 * as all the remaining stack frames of the cause are the same as the
391 * the last stack frames of the throwable that the cause is wrapped in
392 * then a line starting with three spaces and the string "... X more" is
393 * printed, where X is the number of remaining stackframes.
394 *
395 * @param pw the PrintWriter to write the trace to
396 * @since 1.1
397 */
398 public void printStackTrace (PrintWriter pw)
399 {
400 pw.print(stackTraceString());
401 }
402
403 /*
404 * We use inner class to avoid a static initializer in this basic class.
405 */
406 private static class StaticData
407 {
408 static final String nl = SystemProperties.getProperty("line.separator");
409 }
410
411 // Create whole stack trace in a stringbuffer so we don't have to print
412 // it line by line. This prevents printing multiple stack traces from
413 // different threads to get mixed up when written to the same PrintWriter.
414 private String stackTraceString()
415 {
416 CPStringBuilder sb = new CPStringBuilder();
417
418 // Main stacktrace
419 StackTraceElement[] stack = getStackTrace();
420 stackTraceStringBuffer(sb, this.toString(), stack, 0);
421
422 // The cause(s)
423 Throwable cause = getCause();
424 while (cause != null)
425 {
426 // Cause start first line
427 sb.append("Caused by: ");
428
429 // Cause stacktrace
430 StackTraceElement[] parentStack = stack;
431 stack = cause.getStackTrace();
432 if (parentStack == null || parentStack.length == 0)
433 stackTraceStringBuffer(sb, cause.toString(), stack, 0);
434 else
435 {
436 int equal = 0; // Count how many of the last stack frames are equal
437 int frame = stack.length-1;
438 int parentFrame = parentStack.length-1;
439 while (frame > 0 && parentFrame > 0)
440 {
441 if (stack[frame].equals(parentStack[parentFrame]))
442 {
443 equal++;
444 frame--;
445 parentFrame--;
446 }
447 else
448 break;
449 }
450 stackTraceStringBuffer(sb, cause.toString(), stack, equal);
451 }
452 cause = cause.getCause();
453 }
454
455 return sb.toString();
456 }
457
458 // Adds to the given StringBuffer a line containing the name and
459 // all stacktrace elements minus the last equal ones.
460 private static void stackTraceStringBuffer(CPStringBuilder sb, String name,
461 StackTraceElement[] stack, int equal)
462 {
463 String nl = StaticData.nl;
464 // (finish) first line
465 sb.append(name);
466 sb.append(nl);
467
468 // The stacktrace
469 if (stack == null || stack.length == 0)
470 {
471 sb.append(" <<No stacktrace available>>");
472 sb.append(nl);
473 }
474 else
475 {
476 for (int i = 0; i < stack.length-equal; i++)
477 {
478 sb.append(" at ");
479 sb.append(stack[i] == null ? "<<Unknown>>" : stack[i].toString());
480 sb.append(nl);
481 }
482 if (equal > 0)
483 {
484 sb.append(" ...");
485 sb.append(equal);
486 sb.append(" more");
487 sb.append(nl);
488 }
489 }
490 }
491
492 /**
493 * Fill in the stack trace with the current execution stack.
494 *
495 * @return this same throwable
496 * @see #printStackTrace()
497 */
498 public Throwable fillInStackTrace()
499 {
500 vmState = VMThrowable.fillInStackTrace(this);
501 stackTrace = null; // Should be regenerated when used.
502
503 return this;
504 }
505
506 /**
507 * Provides access to the information printed in {@link #printStackTrace()}.
508 * The array is non-null, with no null entries, although the virtual
509 * machine is allowed to skip stack frames. If the array is not 0-length,
510 * then slot 0 holds the information on the stack frame where the Throwable
511 * was created (or at least where <code>fillInStackTrace()</code> was
512 * called).
513 *
514 * @return an array of stack trace information, as available from the VM
515 * @since 1.4
516 */
517 public StackTraceElement[] getStackTrace()
518 {
519 if (stackTrace == null)
520 if (vmState == null)
521 stackTrace = new StackTraceElement[0];
522 else
523 {
524 stackTrace = vmState.getStackTrace(this);
525 vmState = null; // No longer needed
526 }
527
528 return stackTrace;
529 }
530
531 /**
532 * Change the stack trace manually. This method is designed for remote
533 * procedure calls, which intend to alter the stack trace before or after
534 * serialization according to the context of the remote call.
535 * <p>
536 * The contents of the given stacktrace is copied so changes to the
537 * original array do not change the stack trace elements of this
538 * throwable.
539 *
540 * @param stackTrace the new trace to use
541 * @throws NullPointerException if stackTrace is null or has null elements
542 * @since 1.4
543 */
544 public void setStackTrace(StackTraceElement[] stackTrace)
545 {
546 int i = stackTrace.length;
547 StackTraceElement[] st = new StackTraceElement[i];
548
549 while (--i >= 0)
550 {
551 st[i] = stackTrace[i];
552 if (st[i] == null)
553 throw new NullPointerException("Element " + i + " null");
554 }
555
556 this.stackTrace = st;
557 }
558
559 /**
560 * VM state when fillInStackTrace was called.
561 * Used by getStackTrace() to get an array of StackTraceElements.
562 * Cleared when no longer needed.
563 */
564 private transient VMThrowable vmState;
565 }