1 /*
2 * Copyright (c) 1994, 2011, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.lang;
27 import java.io.*;
28 import java.util.*;
29
30 /**
31 * The {@code Throwable} class is the superclass of all errors and
32 * exceptions in the Java language. Only objects that are instances of this
33 * class (or one of its subclasses) are thrown by the Java Virtual Machine or
34 * can be thrown by the Java {@code throw} statement. Similarly, only
35 * this class or one of its subclasses can be the argument type in a
36 * {@code catch} clause.
37 *
38 * For the purposes of compile-time checking of exceptions, {@code
39 * Throwable} and any subclass of {@code Throwable} that is not also a
40 * subclass of either {@link RuntimeException} or {@link Error} are
41 * regarded as checked exceptions.
42 *
43 * <p>Instances of two subclasses, {@link java.lang.Error} and
44 * {@link java.lang.Exception}, are conventionally used to indicate
45 * that exceptional situations have occurred. Typically, these instances
46 * are freshly created in the context of the exceptional situation so
47 * as to include relevant information (such as stack trace data).
48 *
49 * <p>A throwable contains a snapshot of the execution stack of its
50 * thread at the time it was created. It can also contain a message
51 * string that gives more information about the error. Over time, a
52 * throwable can {@linkplain Throwable#addSuppressed suppress} other
53 * throwables from being propagated. Finally, the throwable can also
54 * contain a <i>cause</i>: another throwable that caused this
55 * throwable to get thrown. The recording of this causal information
56 * is referred to as the <i>chained exception</i> facility, as the
57 * cause can, itself, have a cause, and so on, leading to a "chain" of
58 * exceptions, each caused by another.
59 *
60 * <p>One reason that a throwable may have a cause is that the class that
61 * throws it is built atop a lower layered abstraction, and an operation on
62 * the upper layer fails due to a failure in the lower layer. It would be bad
63 * design to let the throwable thrown by the lower layer propagate outward, as
64 * it is generally unrelated to the abstraction provided by the upper layer.
65 * Further, doing so would tie the API of the upper layer to the details of
66 * its implementation, assuming the lower layer's exception was a checked
67 * exception. Throwing a "wrapped exception" (i.e., an exception containing a
68 * cause) allows the upper layer to communicate the details of the failure to
69 * its caller without incurring either of these shortcomings. It preserves
70 * the flexibility to change the implementation of the upper layer without
71 * changing its API (in particular, the set of exceptions thrown by its
72 * methods).
73 *
74 * <p>A second reason that a throwable may have a cause is that the method
75 * that throws it must conform to a general-purpose interface that does not
76 * permit the method to throw the cause directly. For example, suppose
77 * a persistent collection conforms to the {@link java.util.Collection
78 * Collection} interface, and that its persistence is implemented atop
79 * {@code java.io}. Suppose the internals of the {@code add} method
80 * can throw an {@link java.io.IOException IOException}. The implementation
81 * can communicate the details of the {@code IOException} to its caller
82 * while conforming to the {@code Collection} interface by wrapping the
83 * {@code IOException} in an appropriate unchecked exception. (The
84 * specification for the persistent collection should indicate that it is
85 * capable of throwing such exceptions.)
86 *
87 * <p>A cause can be associated with a throwable in two ways: via a
88 * constructor that takes the cause as an argument, or via the
89 * {@link #initCause(Throwable)} method. New throwable classes that
90 * wish to allow causes to be associated with them should provide constructors
91 * that take a cause and delegate (perhaps indirectly) to one of the
92 * {@code Throwable} constructors that takes a cause.
93 *
94 * Because the {@code initCause} method is public, it allows a cause to be
95 * associated with any throwable, even a "legacy throwable" whose
96 * implementation predates the addition of the exception chaining mechanism to
97 * {@code Throwable}.
98 *
99 * <p>By convention, class {@code Throwable} and its subclasses have two
100 * constructors, one that takes no arguments and one that takes a
101 * {@code String} argument that can be used to produce a detail message.
102 * Further, those subclasses that might likely have a cause associated with
103 * them should have two more constructors, one that takes a
104 * {@code Throwable} (the cause), and one that takes a
105 * {@code String} (the detail message) and a {@code Throwable} (the
106 * cause).
107 *
108 * @author unascribed
109 * @author Josh Bloch (Added exception chaining and programmatic access to
110 * stack trace in 1.4.)
111 * @jls3 11.2 Compile-Time Checking of Exceptions
112 * @since JDK1.0
113 */
114 public class Throwable implements Serializable {
115 /** use serialVersionUID from JDK 1.0.2 for interoperability */
116 private static final long serialVersionUID = -3042686055658047285L;
117
118 /**
119 * Native code saves some indication of the stack backtrace in this slot.
120 */
121 private transient Object backtrace;
122
123 /**
124 * Specific details about the Throwable. For example, for
125 * {@code FileNotFoundException}, this contains the name of
126 * the file that could not be found.
127 *
128 * @serial
129 */
130 private String detailMessage;
131
132 /**
133 * A shared value for an empty stack.
134 */
135 private static final StackTraceElement[] EMPTY_STACK = new StackTraceElement[0];
136
137 /*
138 * To allow Throwable objects to be made immutable and safely
139 * reused by the JVM, such as OutOfMemoryErrors, fields of
140 * Throwable that are writable in response to user actions, cause
141 * and suppressedExceptions obey the following protocol:
142 *
143 * 1) The fields are initialized to a non-null sentinel value
144 * which indicates the value has logically not been set.
145 *
146 * 2) Writing a null to the field indicates further writes
147 * are forbidden
148 *
149 * 3) The sentinel value may be replaced with another non-null
150 * value.
151 *
152 * For example, implementations of the HotSpot JVM have
153 * preallocated OutOfMemoryError objects to provide for better
154 * diagnosability of that situation. These objects are created
155 * without calling the constructor for that class and the fields
156 * in question are initialized to null. To support this
157 * capability, any new fields added to Throwable that require
158 * being initialized to a non-null value require a coordinated JVM
159 * change.
160 */
161
162 /**
163 * The throwable that caused this throwable to get thrown, or null if this
164 * throwable was not caused by another throwable, or if the causative
165 * throwable is unknown. If this field is equal to this throwable itself,
166 * it indicates that the cause of this throwable has not yet been
167 * initialized.
168 *
169 * @serial
170 * @since 1.4
171 */
172 private Throwable cause = this;
173
174 /**
175 * The stack trace, as returned by {@link #getStackTrace()}.
176 *
177 * @serial
178 * @since 1.4
179 */
180 private StackTraceElement[] stackTrace;
181
182 // Setting this static field introduces an acceptable
183 // initialization dependency on a few java.util classes.
184 private static final List<Throwable> SUPPRESSED_SENTINEL =
185 Collections.unmodifiableList(new ArrayList<Throwable>(0));
186
187 /**
188 * The list of suppressed exceptions, as returned by {@link
189 * #getSuppressed()}. The list is initialized to a zero-element
190 * unmodifiable sentinel list. When a serialized Throwable is
191 * read in, if the {@code suppressedExceptions} field points to a
192 * zero-element list, the field is reset to the sentinel value.
193 *
194 * @serial
195 * @since 1.7
196 */
197 private List<Throwable> suppressedExceptions = SUPPRESSED_SENTINEL;
198
199 /** Message for trying to suppress a null exception. */
200 private static final String NULL_CAUSE_MESSAGE = "Cannot suppress a null exception.";
201
202 /** Message for trying to suppress oneself. */
203 private static final String SELF_SUPPRESSION_MESSAGE = "Self-suppression not permitted";
204
205 /** Caption for labeling causative exception stack traces */
206 private static final String CAUSE_CAPTION = "Caused by: ";
207
208 /** Caption for labeling suppressed exception stack traces */
209 private static final String SUPPRESSED_CAPTION = "Suppressed: ";
210
211 /**
212 * Constructs a new throwable with {@code null} as its detail message.
213 * The cause is not initialized, and may subsequently be initialized by a
214 * call to {@link #initCause}.
215 *
216 * <p>The {@link #fillInStackTrace()} method is called to initialize
217 * the stack trace data in the newly created throwable.
218 */
219 public Throwable() {
220 fillInStackTrace();
221 }
222
223 /**
224 * Constructs a new throwable with the specified detail message. The
225 * cause is not initialized, and may subsequently be initialized by
226 * a call to {@link #initCause}.
227 *
228 * <p>The {@link #fillInStackTrace()} method is called to initialize
229 * the stack trace data in the newly created throwable.
230 *
231 * @param message the detail message. The detail message is saved for
232 * later retrieval by the {@link #getMessage()} method.
233 */
234 public Throwable(String message) {
235 fillInStackTrace();
236 detailMessage = message;
237 }
238
239 /**
240 * Constructs a new throwable with the specified detail message and
241 * cause. <p>Note that the detail message associated with
242 * {@code cause} is <i>not</i> automatically incorporated in
243 * this throwable's detail message.
244 *
245 * <p>The {@link #fillInStackTrace()} method is called to initialize
246 * the stack trace data in the newly created throwable.
247 *
248 * @param message the detail message (which is saved for later retrieval
249 * by the {@link #getMessage()} method).
250 * @param cause the cause (which is saved for later retrieval by the
251 * {@link #getCause()} method). (A {@code null} value is
252 * permitted, and indicates that the cause is nonexistent or
253 * unknown.)
254 * @since 1.4
255 */
256 public Throwable(String message, Throwable cause) {
257 fillInStackTrace();
258 detailMessage = message;
259 this.cause = cause;
260 }
261
262 /**
263 * Constructs a new throwable with the specified cause and a detail
264 * message of {@code (cause==null ? null : cause.toString())} (which
265 * typically contains the class and detail message of {@code cause}).
266 * This constructor is useful for throwables that are little more than
267 * wrappers for other throwables (for example, {@link
268 * java.security.PrivilegedActionException}).
269 *
270 * <p>The {@link #fillInStackTrace()} method is called to initialize
271 * the stack trace data in the newly created throwable.
272 *
273 * @param cause the cause (which is saved for later retrieval by the
274 * {@link #getCause()} method). (A {@code null} value is
275 * permitted, and indicates that the cause is nonexistent or
276 * unknown.)
277 * @since 1.4
278 */
279 public Throwable(Throwable cause) {
280 fillInStackTrace();
281 detailMessage = (cause==null ? null : cause.toString());
282 this.cause = cause;
283 }
284
285 /**
286 * Returns the detail message string of this throwable.
287 *
288 * @return the detail message string of this {@code Throwable} instance
289 * (which may be {@code null}).
290 */
291 public String getMessage() {
292 return detailMessage;
293 }
294
295 /**
296 * Creates a localized description of this throwable.
297 * Subclasses may override this method in order to produce a
298 * locale-specific message. For subclasses that do not override this
299 * method, the default implementation returns the same result as
300 * {@code getMessage()}.
301 *
302 * @return The localized description of this throwable.
303 * @since JDK1.1
304 */
305 public String getLocalizedMessage() {
306 return getMessage();
307 }
308
309 /**
310 * Returns the cause of this throwable or {@code null} if the
311 * cause is nonexistent or unknown. (The cause is the throwable that
312 * caused this throwable to get thrown.)
313 *
314 * <p>This implementation returns the cause that was supplied via one of
315 * the constructors requiring a {@code Throwable}, or that was set after
316 * creation with the {@link #initCause(Throwable)} method. While it is
317 * typically unnecessary to override this method, a subclass can override
318 * it to return a cause set by some other means. This is appropriate for
319 * a "legacy chained throwable" that predates the addition of chained
320 * exceptions to {@code Throwable}. Note that it is <i>not</i>
321 * necessary to override any of the {@code PrintStackTrace} methods,
322 * all of which invoke the {@code getCause} method to determine the
323 * cause of a throwable.
324 *
325 * @return the cause of this throwable or {@code null} if the
326 * cause is nonexistent or unknown.
327 * @since 1.4
328 */
329 public synchronized Throwable getCause() {
330 return (cause==this ? null : cause);
331 }
332
333 /**
334 * Initializes the <i>cause</i> of this throwable to the specified value.
335 * (The cause is the throwable that caused this throwable to get thrown.)
336 *
337 * <p>This method can be called at most once. It is generally called from
338 * within the constructor, or immediately after creating the
339 * throwable. If this throwable was created
340 * with {@link #Throwable(Throwable)} or
341 * {@link #Throwable(String,Throwable)}, this method cannot be called
342 * even once.
343 *
344 * @param cause the cause (which is saved for later retrieval by the
345 * {@link #getCause()} method). (A {@code null} value is
346 * permitted, and indicates that the cause is nonexistent or
347 * unknown.)
348 * @return a reference to this {@code Throwable} instance.
349 * @throws IllegalArgumentException if {@code cause} is this
350 * throwable. (A throwable cannot be its own cause.)
351 * @throws IllegalStateException if this throwable was
352 * created with {@link #Throwable(Throwable)} or
353 * {@link #Throwable(String,Throwable)}, or this method has already
354 * been called on this throwable.
355 * @since 1.4
356 */
357 public synchronized Throwable initCause(Throwable cause) {
358 if (this.cause != this)
359 throw new IllegalStateException("Can't overwrite cause");
360 if (cause == this)
361 throw new IllegalArgumentException("Self-causation not permitted");
362 this.cause = cause;
363 return this;
364 }
365
366 /**
367 * Returns a short description of this throwable.
368 * The result is the concatenation of:
369 * <ul>
370 * <li> the {@linkplain Class#getName() name} of the class of this object
371 * <li> ": " (a colon and a space)
372 * <li> the result of invoking this object's {@link #getLocalizedMessage}
373 * method
374 * </ul>
375 * If {@code getLocalizedMessage} returns {@code null}, then just
376 * the class name is returned.
377 *
378 * @return a string representation of this throwable.
379 */
380 public String toString() {
381 String s = getClass().getName();
382 String message = getLocalizedMessage();
383 return (message != null) ? (s + ": " + message) : s;
384 }
385
386 /**
387 * Prints this throwable and its backtrace to the
388 * standard error stream. This method prints a stack trace for this
389 * {@code Throwable} object on the error output stream that is
390 * the value of the field {@code System.err}. The first line of
391 * output contains the result of the {@link #toString()} method for
392 * this object. Remaining lines represent data previously recorded by
393 * the method {@link #fillInStackTrace()}. The format of this
394 * information depends on the implementation, but the following
395 * example may be regarded as typical:
396 * <blockquote><pre>
397 * java.lang.NullPointerException
398 * at MyClass.mash(MyClass.java:9)
399 * at MyClass.crunch(MyClass.java:6)
400 * at MyClass.main(MyClass.java:3)
401 * </pre></blockquote>
402 * This example was produced by running the program:
403 * <pre>
404 * class MyClass {
405 * public static void main(String[] args) {
406 * crunch(null);
407 * }
408 * static void crunch(int[] a) {
409 * mash(a);
410 * }
411 * static void mash(int[] b) {
412 * System.out.println(b[0]);
413 * }
414 * }
415 * </pre>
416 * The backtrace for a throwable with an initialized, non-null cause
417 * should generally include the backtrace for the cause. The format
418 * of this information depends on the implementation, but the following
419 * example may be regarded as typical:
420 * <pre>
421 * HighLevelException: MidLevelException: LowLevelException
422 * at Junk.a(Junk.java:13)
423 * at Junk.main(Junk.java:4)
424 * Caused by: MidLevelException: LowLevelException
425 * at Junk.c(Junk.java:23)
426 * at Junk.b(Junk.java:17)
427 * at Junk.a(Junk.java:11)
428 * ... 1 more
429 * Caused by: LowLevelException
430 * at Junk.e(Junk.java:30)
431 * at Junk.d(Junk.java:27)
432 * at Junk.c(Junk.java:21)
433 * ... 3 more
434 * </pre>
435 * Note the presence of lines containing the characters {@code "..."}.
436 * These lines indicate that the remainder of the stack trace for this
437 * exception matches the indicated number of frames from the bottom of the
438 * stack trace of the exception that was caused by this exception (the
439 * "enclosing" exception). This shorthand can greatly reduce the length
440 * of the output in the common case where a wrapped exception is thrown
441 * from same method as the "causative exception" is caught. The above
442 * example was produced by running the program:
443 * <pre>
444 * public class Junk {
445 * public static void main(String args[]) {
446 * try {
447 * a();
448 * } catch(HighLevelException e) {
449 * e.printStackTrace();
450 * }
451 * }
452 * static void a() throws HighLevelException {
453 * try {
454 * b();
455 * } catch(MidLevelException e) {
456 * throw new HighLevelException(e);
457 * }
458 * }
459 * static void b() throws MidLevelException {
460 * c();
461 * }
462 * static void c() throws MidLevelException {
463 * try {
464 * d();
465 * } catch(LowLevelException e) {
466 * throw new MidLevelException(e);
467 * }
468 * }
469 * static void d() throws LowLevelException {
470 * e();
471 * }
472 * static void e() throws LowLevelException {
473 * throw new LowLevelException();
474 * }
475 * }
476 *
477 * class HighLevelException extends Exception {
478 * HighLevelException(Throwable cause) { super(cause); }
479 * }
480 *
481 * class MidLevelException extends Exception {
482 * MidLevelException(Throwable cause) { super(cause); }
483 * }
484 *
485 * class LowLevelException extends Exception {
486 * }
487 * </pre>
488 * As of release 7, the platform supports the notion of
489 * <i>suppressed exceptions</i> (in conjunction with the {@code
490 * try}-with-resources statement). Any exceptions that were
491 * suppressed in order to deliver an exception are printed out
492 * beneath the stack trace. The format of this information
493 * depends on the implementation, but the following example may be
494 * regarded as typical:
495 *
496 * <pre>
497 * Exception in thread "main" java.lang.Exception: Something happened
498 * at Foo.bar(Foo.java:10)
499 * at Foo.main(Foo.java:5)
500 * Suppressed: Resource$CloseFailException: Resource ID = 0
501 * at Resource.close(Resource.java:26)
502 * at Foo.bar(Foo.java:9)
503 * ... 1 more
504 * </pre>
505 * Note that the "... n more" notation is used on suppressed exceptions
506 * just at it is used on causes. Unlike causes, suppressed exceptions are
507 * indented beyond their "containing exceptions."
508 *
509 * <p>An exception can have both a cause and one or more suppressed
510 * exceptions:
511 * <pre>
512 * Exception in thread "main" java.lang.Exception: Main block
513 * at Foo3.main(Foo3.java:7)
514 * Suppressed: Resource$CloseFailException: Resource ID = 2
515 * at Resource.close(Resource.java:26)
516 * at Foo3.main(Foo3.java:5)
517 * Suppressed: Resource$CloseFailException: Resource ID = 1
518 * at Resource.close(Resource.java:26)
519 * at Foo3.main(Foo3.java:5)
520 * Caused by: java.lang.Exception: I did it
521 * at Foo3.main(Foo3.java:8)
522 * </pre>
523 * Likewise, a suppressed exception can have a cause:
524 * <pre>
525 * Exception in thread "main" java.lang.Exception: Main block
526 * at Foo4.main(Foo4.java:6)
527 * Suppressed: Resource2$CloseFailException: Resource ID = 1
528 * at Resource2.close(Resource2.java:20)
529 * at Foo4.main(Foo4.java:5)
530 * Caused by: java.lang.Exception: Rats, you caught me
531 * at Resource2$CloseFailException.<init>(Resource2.java:45)
532 * ... 2 more
533 * </pre>
534 */
535 public void printStackTrace() {
536 printStackTrace(System.err);
537 }
538
539 /**
540 * Prints this throwable and its backtrace to the specified print stream.
541 *
542 * @param s {@code PrintStream} to use for output
543 */
544 public void printStackTrace(PrintStream s) {
545 printStackTrace(new WrappedPrintStream(s));
546 }
547
548 private void printStackTrace(PrintStreamOrWriter s) {
549 // Guard against malicious overrides of Throwable.equals by
550 // using a Set with identity equality semantics.
551 Set<Throwable> dejaVu =
552 Collections.newSetFromMap(new IdentityHashMap<Throwable, Boolean>());
553 dejaVu.add(this);
554
555 synchronized (s.lock()) {
556 // Print our stack trace
557 s.println(this);
558 StackTraceElement[] trace = getOurStackTrace();
559 for (StackTraceElement traceElement : trace)
560 s.println("\tat " + traceElement);
561
562 // Print suppressed exceptions, if any
563 for (Throwable se : getSuppressed())
564 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, "\t", dejaVu);
565
566 // Print cause, if any
567 Throwable ourCause = getCause();
568 if (ourCause != null)
569 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, "", dejaVu);
570 }
571 }
572
573 /**
574 * Print our stack trace as an enclosed exception for the specified
575 * stack trace.
576 */
577 private void printEnclosedStackTrace(PrintStreamOrWriter s,
578 StackTraceElement[] enclosingTrace,
579 String caption,
580 String prefix,
581 Set<Throwable> dejaVu) {
582 assert Thread.holdsLock(s.lock());
583 if (dejaVu.contains(this)) {
584 s.println("\t[CIRCULAR REFERENCE:" + this + "]");
585 } else {
586 dejaVu.add(this);
587 // Compute number of frames in common between this and enclosing trace
588 StackTraceElement[] trace = getOurStackTrace();
589 int m = trace.length - 1;
590 int n = enclosingTrace.length - 1;
591 while (m >= 0 && n >=0 && trace[m].equals(enclosingTrace[n])) {
592 m--; n--;
593 }
594 int framesInCommon = trace.length - 1 - m;
595
596 // Print our stack trace
597 s.println(prefix + caption + this);
598 for (int i = 0; i <= m; i++)
599 s.println(prefix + "\tat " + trace[i]);
600 if (framesInCommon != 0)
601 s.println(prefix + "\t... " + framesInCommon + " more");
602
603 // Print suppressed exceptions, if any
604 for (Throwable se : getSuppressed())
605 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION,
606 prefix +"\t", dejaVu);
607
608 // Print cause, if any
609 Throwable ourCause = getCause();
610 if (ourCause != null)
611 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, prefix, dejaVu);
612 }
613 }
614
615 /**
616 * Prints this throwable and its backtrace to the specified
617 * print writer.
618 *
619 * @param s {@code PrintWriter} to use for output
620 * @since JDK1.1
621 */
622 public void printStackTrace(PrintWriter s) {
623 printStackTrace(new WrappedPrintWriter(s));
624 }
625
626 /**
627 * Wrapper class for PrintStream and PrintWriter to enable a single
628 * implementation of printStackTrace.
629 */
630 private abstract static class PrintStreamOrWriter {
631 /** Returns the object to be locked when using this StreamOrWriter */
632 abstract Object lock();
633
634 /** Prints the specified string as a line on this StreamOrWriter */
635 abstract void println(Object o);
636 }
637
638 private static class WrappedPrintStream extends PrintStreamOrWriter {
639 private final PrintStream printStream;
640
641 WrappedPrintStream(PrintStream printStream) {
642 this.printStream = printStream;
643 }
644
645 Object lock() {
646 return printStream;
647 }
648
649 void println(Object o) {
650 printStream.println(o);
651 }
652 }
653
654 private static class WrappedPrintWriter extends PrintStreamOrWriter {
655 private final PrintWriter printWriter;
656
657 WrappedPrintWriter(PrintWriter printWriter) {
658 this.printWriter = printWriter;
659 }
660
661 Object lock() {
662 return printWriter;
663 }
664
665 void println(Object o) {
666 printWriter.println(o);
667 }
668 }
669
670 /**
671 * Fills in the execution stack trace. This method records within this
672 * {@code Throwable} object information about the current state of
673 * the stack frames for the current thread.
674 *
675 * @return a reference to this {@code Throwable} instance.
676 * @see java.lang.Throwable#printStackTrace()
677 */
678 public synchronized native Throwable fillInStackTrace();
679
680 /**
681 * Provides programmatic access to the stack trace information printed by
682 * {@link #printStackTrace()}. Returns an array of stack trace elements,
683 * each representing one stack frame. The zeroth element of the array
684 * (assuming the array's length is non-zero) represents the top of the
685 * stack, which is the last method invocation in the sequence. Typically,
686 * this is the point at which this throwable was created and thrown.
687 * The last element of the array (assuming the array's length is non-zero)
688 * represents the bottom of the stack, which is the first method invocation
689 * in the sequence.
690 *
691 * <p>Some virtual machines may, under some circumstances, omit one
692 * or more stack frames from the stack trace. In the extreme case,
693 * a virtual machine that has no stack trace information concerning
694 * this throwable is permitted to return a zero-length array from this
695 * method. Generally speaking, the array returned by this method will
696 * contain one element for every frame that would be printed by
697 * {@code printStackTrace}.
698 *
699 * @return an array of stack trace elements representing the stack trace
700 * pertaining to this throwable.
701 * @since 1.4
702 */
703 public StackTraceElement[] getStackTrace() {
704 return getOurStackTrace().clone();
705 }
706
707 private synchronized StackTraceElement[] getOurStackTrace() {
708 // Initialize stack trace if this is the first call to this method
709 if (stackTrace == null) {
710 int depth = getStackTraceDepth();
711 stackTrace = new StackTraceElement[depth];
712 for (int i=0; i < depth; i++)
713 stackTrace[i] = getStackTraceElement(i);
714 }
715 return stackTrace;
716 }
717
718 /**
719 * Sets the stack trace elements that will be returned by
720 * {@link #getStackTrace()} and printed by {@link #printStackTrace()}
721 * and related methods.
722 *
723 * This method, which is designed for use by RPC frameworks and other
724 * advanced systems, allows the client to override the default
725 * stack trace that is either generated by {@link #fillInStackTrace()}
726 * when a throwable is constructed or deserialized when a throwable is
727 * read from a serialization stream.
728 *
729 * @param stackTrace the stack trace elements to be associated with
730 * this {@code Throwable}. The specified array is copied by this
731 * call; changes in the specified array after the method invocation
732 * returns will have no affect on this {@code Throwable}'s stack
733 * trace.
734 *
735 * @throws NullPointerException if {@code stackTrace} is
736 * {@code null}, or if any of the elements of
737 * {@code stackTrace} are {@code null}
738 *
739 * @since 1.4
740 */
741 public void setStackTrace(StackTraceElement[] stackTrace) {
742 StackTraceElement[] defensiveCopy = stackTrace.clone();
743 for (int i = 0; i < defensiveCopy.length; i++)
744 if (defensiveCopy[i] == null)
745 throw new NullPointerException("stackTrace[" + i + "]");
746
747 synchronized (this) {
748 this.stackTrace = defensiveCopy;
749 }
750 }
751
752 /**
753 * Returns the number of elements in the stack trace (or 0 if the stack
754 * trace is unavailable).
755 *
756 * package-protection for use by SharedSecrets.
757 */
758 native int getStackTraceDepth();
759
760 /**
761 * Returns the specified element of the stack trace.
762 *
763 * package-protection for use by SharedSecrets.
764 *
765 * @param index index of the element to return.
766 * @throws IndexOutOfBoundsException if {@code index < 0 ||
767 * index >= getStackTraceDepth() }
768 */
769 native StackTraceElement getStackTraceElement(int index);
770
771 /**
772 * Reads a {@code Throwable} from a stream, enforcing
773 * well-formedness constraints on fields. Null entries and
774 * self-pointers are not allowed in the list of {@code
775 * suppressedExceptions}. Null entries are not allowed for stack
776 * trace elements.
777 *
778 * Note that there are no constraints on the value the {@code
779 * cause} field can hold; both {@code null} and {@code this} are
780 * valid values for the field.
781 */
782 private void readObject(ObjectInputStream s)
783 throws IOException, ClassNotFoundException {
784 s.defaultReadObject(); // read in all fields
785 if (suppressedExceptions != null) {
786 List<Throwable> suppressed = null;
787 if (suppressedExceptions.isEmpty()) {
788 // Use the sentinel for a zero-length list
789 suppressed = SUPPRESSED_SENTINEL;
790 } else { // Copy Throwables to new list
791 suppressed = new ArrayList<>(1);
792 for (Throwable t : suppressedExceptions) {
793 // Enforce constraints on suppressed exceptions in
794 // case of corrupt or malicious stream.
795 if (t == null)
796 throw new NullPointerException(NULL_CAUSE_MESSAGE);
797 if (t == this)
798 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE);
799 suppressed.add(t);
800 }
801 }
802 suppressedExceptions = suppressed;
803 } // else a null suppressedExceptions field remains null
804
805 if (stackTrace != null) {
806 for (StackTraceElement ste : stackTrace) {
807 if (ste == null)
808 throw new NullPointerException("null StackTraceElement in serial stream. ");
809 }
810 } else {
811 // A null stackTrace field in the serial form can result from
812 // an exception serialized without that field in older JDK releases.
813 stackTrace = EMPTY_STACK;
814 }
815
816 }
817
818 /**
819 * Write a {@code Throwable} object to a stream.
820 */
821 private synchronized void writeObject(ObjectOutputStream s)
822 throws IOException {
823 getOurStackTrace(); // Ensure that stackTrace field is initialized.
824 s.defaultWriteObject();
825 }
826
827 /**
828 * Appends the specified exception to the exceptions that were
829 * suppressed in order to deliver this exception. This method is
830 * typically called (automatically and implicitly) by the {@code
831 * try}-with-resources statement.
832 *
833 * If the first exception to be suppressed is {@code null}, that
834 * indicates suppressed exception information will <em>not</em> be
835 * recorded for this exception. Subsequent calls to this method
836 * will not record any suppressed exceptions. Otherwise,
837 * attempting to suppress {@code null} after an exception has
838 * already been successfully suppressed results in a {@code
839 * NullPointerException}.
840 *
841 * <p>Note that when one exception {@linkplain
842 * #initCause(Throwable) causes} another exception, the first
843 * exception is usually caught and then the second exception is
844 * thrown in response. In other words, there is a causal
845 * connection between the two exceptions.
846 *
847 * In contrast, there are situations where two independent
848 * exceptions can be thrown in sibling code blocks, in particular
849 * in the {@code try} block of a {@code try}-with-resources
850 * statement and the compiler-generated {@code finally} block
851 * which closes the resource.
852 *
853 * In these situations, only one of the thrown exceptions can be
854 * propagated. In the {@code try}-with-resources statement, when
855 * there are two such exceptions, the exception originating from
856 * the {@code try} block is propagated and the exception from the
857 * {@code finally} block is added to the list of exceptions
858 * suppressed by the exception from the {@code try} block. As an
859 * exception unwinds the stack, it can accumulate multiple
860 * suppressed exceptions.
861 *
862 * <p>An exception may have suppressed exceptions while also being
863 * caused by another exception. Whether or not an exception has a
864 * cause is semantically known at the time of its creation, unlike
865 * whether or not an exception will suppress other exceptions
866 * which is typically only determined after an exception is
867 * thrown.
868 *
869 * <p>Note that programmer written code is also able to take
870 * advantage of calling this method in situations where there are
871 * multiple sibling exceptions and only one can be propagated.
872 *
873 * @param exception the exception to be added to the list of
874 * suppressed exceptions
875 * @throws IllegalArgumentException if {@code exception} is this
876 * throwable; a throwable cannot suppress itself.
877 * @throws NullPointerException if {@code exception} is null and
878 * an exception has already been suppressed by this exception
879 * @since 1.7
880 */
881 public final synchronized void addSuppressed(Throwable exception) {
882 if (exception == this)
883 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE);
884
885 if (exception == null) {
886 if (suppressedExceptions == SUPPRESSED_SENTINEL) {
887 suppressedExceptions = null; // No suppression information recorded
888 return;
889 } else
890 throw new NullPointerException(NULL_CAUSE_MESSAGE);
891 } else {
892 assert exception != null && exception != this;
893
894 if (suppressedExceptions == null) // Suppressed exceptions not recorded
895 return;
896
897 if (suppressedExceptions == SUPPRESSED_SENTINEL)
898 suppressedExceptions = new ArrayList<>(1);
899
900 assert suppressedExceptions != SUPPRESSED_SENTINEL;
901
902 suppressedExceptions.add(exception);
903 }
904 }
905
906 private static final Throwable[] EMPTY_THROWABLE_ARRAY = new Throwable[0];
907
908 /**
909 * Returns an array containing all of the exceptions that were
910 * suppressed, typically by the {@code try}-with-resources
911 * statement, in order to deliver this exception.
912 *
913 * If no exceptions were suppressed, an empty array is returned.
914 *
915 * @return an array containing all of the exceptions that were
916 * suppressed to deliver this exception.
917 * @since 1.7
918 */
919 public final synchronized Throwable[] getSuppressed() {
920 if (suppressedExceptions == SUPPRESSED_SENTINEL ||
921 suppressedExceptions == null)
922 return EMPTY_THROWABLE_ARRAY;
923 else
924 return suppressedExceptions.toArray(EMPTY_THROWABLE_ARRAY);
925 }
926 }