1 /*
2 * Copyright (c) 1994, 2013, 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 be constructed. 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 * @jls 11.2 Compile-Time Checking of Exceptions
112 * @since 1.0
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 /**
134 * Holder class to defer initializing sentinel objects only used
135 * for serialization.
136 */
137 private static class SentinelHolder {
138 /**
139 * {@linkplain #setStackTrace(StackTraceElement[]) Setting the
140 * stack trace} to a one-element array containing this sentinel
141 * value indicates future attempts to set the stack trace will be
142 * ignored. The sentinel is equal to the result of calling:<br>
143 * {@code new StackTraceElement("", "", null, Integer.MIN_VALUE)}
144 */
145 public static final StackTraceElement STACK_TRACE_ELEMENT_SENTINEL =
146 new StackTraceElement("", "", null, Integer.MIN_VALUE);
147
148 /**
149 * Sentinel value used in the serial form to indicate an immutable
150 * stack trace.
151 */
152 public static final StackTraceElement[] STACK_TRACE_SENTINEL =
153 new StackTraceElement[] {STACK_TRACE_ELEMENT_SENTINEL};
154 }
155
156 /**
157 * A shared value for an empty stack.
158 */
159 private static final StackTraceElement[] UNASSIGNED_STACK = new StackTraceElement[0];
160
161 /*
162 * To allow Throwable objects to be made immutable and safely
163 * reused by the JVM, such as OutOfMemoryErrors, fields of
164 * Throwable that are writable in response to user actions, cause,
165 * stackTrace, and suppressedExceptions obey the following
166 * protocol:
167 *
168 * 1) The fields are initialized to a non-null sentinel value
169 * which indicates the value has logically not been set.
170 *
171 * 2) Writing a null to the field indicates further writes
172 * are forbidden
173 *
174 * 3) The sentinel value may be replaced with another non-null
175 * value.
176 *
177 * For example, implementations of the HotSpot JVM have
178 * preallocated OutOfMemoryError objects to provide for better
179 * diagnosability of that situation. These objects are created
180 * without calling the constructor for that class and the fields
181 * in question are initialized to null. To support this
182 * capability, any new fields added to Throwable that require
183 * being initialized to a non-null value require a coordinated JVM
184 * change.
185 */
186
187 /**
188 * The throwable that caused this throwable to get thrown, or null if this
189 * throwable was not caused by another throwable, or if the causative
190 * throwable is unknown. If this field is equal to this throwable itself,
191 * it indicates that the cause of this throwable has not yet been
192 * initialized.
193 *
194 * @serial
195 * @since 1.4
196 */
197 private Throwable cause = this;
198
199 /**
200 * The stack trace, as returned by {@link #getStackTrace()}.
201 *
202 * The field is initialized to a zero-length array. A {@code
203 * null} value of this field indicates subsequent calls to {@link
204 * #setStackTrace(StackTraceElement[])} and {@link
205 * #fillInStackTrace()} will be no-ops.
206 *
207 * @serial
208 * @since 1.4
209 */
210 private StackTraceElement[] stackTrace = UNASSIGNED_STACK;
211
212 // Setting this static field introduces an acceptable
213 // initialization dependency on a few java.util classes.
214 private static final List<Throwable> SUPPRESSED_SENTINEL = Collections.emptyList();
215
216 /**
217 * The list of suppressed exceptions, as returned by {@link
218 * #getSuppressed()}. The list is initialized to a zero-element
219 * unmodifiable sentinel list. When a serialized Throwable is
220 * read in, if the {@code suppressedExceptions} field points to a
221 * zero-element list, the field is reset to the sentinel value.
222 *
223 * @serial
224 * @since 1.7
225 */
226 private List<Throwable> suppressedExceptions = SUPPRESSED_SENTINEL;
227
228 /** Message for trying to suppress a null exception. */
229 private static final String NULL_CAUSE_MESSAGE = "Cannot suppress a null exception.";
230
231 /** Message for trying to suppress oneself. */
232 private static final String SELF_SUPPRESSION_MESSAGE = "Self-suppression not permitted";
233
234 /** Caption for labeling causative exception stack traces */
235 private static final String CAUSE_CAPTION = "Caused by: ";
236
237 /** Caption for labeling suppressed exception stack traces */
238 private static final String SUPPRESSED_CAPTION = "Suppressed: ";
239
240 /**
241 * Constructs a new throwable with {@code null} as its detail message.
242 * The cause is not initialized, and may subsequently be initialized by a
243 * call to {@link #initCause}.
244 *
245 * <p>The {@link #fillInStackTrace()} method is called to initialize
246 * the stack trace data in the newly created throwable.
247 */
248 public Throwable() {
249 fillInStackTrace();
250 }
251
252 /**
253 * Constructs a new throwable with the specified detail message. The
254 * cause is not initialized, and may subsequently be initialized by
255 * a call to {@link #initCause}.
256 *
257 * <p>The {@link #fillInStackTrace()} method is called to initialize
258 * the stack trace data in the newly created throwable.
259 *
260 * @param message the detail message. The detail message is saved for
261 * later retrieval by the {@link #getMessage()} method.
262 */
263 public Throwable(String message) {
264 fillInStackTrace();
265 detailMessage = message;
266 }
267
268 /**
269 * Constructs a new throwable with the specified detail message and
270 * cause. <p>Note that the detail message associated with
271 * {@code cause} is <i>not</i> automatically incorporated in
272 * this throwable's detail message.
273 *
274 * <p>The {@link #fillInStackTrace()} method is called to initialize
275 * the stack trace data in the newly created throwable.
276 *
277 * @param message the detail message (which is saved for later retrieval
278 * by the {@link #getMessage()} method).
279 * @param cause the cause (which is saved for later retrieval by the
280 * {@link #getCause()} method). (A {@code null} value is
281 * permitted, and indicates that the cause is nonexistent or
282 * unknown.)
283 * @since 1.4
284 */
285 public Throwable(String message, Throwable cause) {
286 fillInStackTrace();
287 detailMessage = message;
288 this.cause = cause;
289 }
290
291 /**
292 * Constructs a new throwable with the specified cause and a detail
293 * message of {@code (cause==null ? null : cause.toString())} (which
294 * typically contains the class and detail message of {@code cause}).
295 * This constructor is useful for throwables that are little more than
296 * wrappers for other throwables (for example, {@link
297 * java.security.PrivilegedActionException}).
298 *
299 * <p>The {@link #fillInStackTrace()} method is called to initialize
300 * the stack trace data in the newly created throwable.
301 *
302 * @param cause the cause (which is saved for later retrieval by the
303 * {@link #getCause()} method). (A {@code null} value is
304 * permitted, and indicates that the cause is nonexistent or
305 * unknown.)
306 * @since 1.4
307 */
308 public Throwable(Throwable cause) {
309 fillInStackTrace();
310 detailMessage = (cause==null ? null : cause.toString());
311 this.cause = cause;
312 }
313
314 /**
315 * Constructs a new throwable with the specified detail message,
316 * cause, {@linkplain #addSuppressed suppression} enabled or
317 * disabled, and writable stack trace enabled or disabled. If
318 * suppression is disabled, {@link #getSuppressed} for this object
319 * will return a zero-length array and calls to {@link
320 * #addSuppressed} that would otherwise append an exception to the
321 * suppressed list will have no effect. If the writable stack
322 * trace is false, this constructor will not call {@link
323 * #fillInStackTrace()}, a {@code null} will be written to the
324 * {@code stackTrace} field, and subsequent calls to {@code
325 * fillInStackTrace} and {@link
326 * #setStackTrace(StackTraceElement[])} will not set the stack
327 * trace. If the writable stack trace is false, {@link
328 * #getStackTrace} will return a zero length array.
329 *
330 * <p>Note that the other constructors of {@code Throwable} treat
331 * suppression as being enabled and the stack trace as being
332 * writable. Subclasses of {@code Throwable} should document any
333 * conditions under which suppression is disabled and document
334 * conditions under which the stack trace is not writable.
335 * Disabling of suppression should only occur in exceptional
336 * circumstances where special requirements exist, such as a
337 * virtual machine reusing exception objects under low-memory
338 * situations. Circumstances where a given exception object is
339 * repeatedly caught and rethrown, such as to implement control
340 * flow between two sub-systems, is another situation where
341 * immutable throwable objects would be appropriate.
342 *
343 * @param message the detail message.
344 * @param cause the cause. (A {@code null} value is permitted,
345 * and indicates that the cause is nonexistent or unknown.)
346 * @param enableSuppression whether or not suppression is enabled or disabled
347 * @param writableStackTrace whether or not the stack trace should be
348 * writable
349 *
350 * @see OutOfMemoryError
351 * @see NullPointerException
352 * @see ArithmeticException
353 * @since 1.7
354 */
355 protected Throwable(String message, Throwable cause,
356 boolean enableSuppression,
357 boolean writableStackTrace) {
358 if (writableStackTrace) {
359 fillInStackTrace();
360 } else {
361 stackTrace = null;
362 }
363 detailMessage = message;
364 this.cause = cause;
365 if (!enableSuppression)
366 suppressedExceptions = null;
367 }
368
369 /**
370 * Returns the detail message string of this throwable.
371 *
372 * @return the detail message string of this {@code Throwable} instance
373 * (which may be {@code null}).
374 */
375 public String getMessage() {
376 return detailMessage;
377 }
378
379 /**
380 * Creates a localized description of this throwable.
381 * Subclasses may override this method in order to produce a
382 * locale-specific message. For subclasses that do not override this
383 * method, the default implementation returns the same result as
384 * {@code getMessage()}.
385 *
386 * @return The localized description of this throwable.
387 * @since 1.1
388 */
389 public String getLocalizedMessage() {
390 return getMessage();
391 }
392
393 /**
394 * Returns the cause of this throwable or {@code null} if the
395 * cause is nonexistent or unknown. (The cause is the throwable that
396 * caused this throwable to get thrown.)
397 *
398 * <p>This implementation returns the cause that was supplied via one of
399 * the constructors requiring a {@code Throwable}, or that was set after
400 * creation with the {@link #initCause(Throwable)} method. While it is
401 * typically unnecessary to override this method, a subclass can override
402 * it to return a cause set by some other means. This is appropriate for
403 * a "legacy chained throwable" that predates the addition of chained
404 * exceptions to {@code Throwable}. Note that it is <i>not</i>
405 * necessary to override any of the {@code PrintStackTrace} methods,
406 * all of which invoke the {@code getCause} method to determine the
407 * cause of a throwable.
408 *
409 * @return the cause of this throwable or {@code null} if the
410 * cause is nonexistent or unknown.
411 * @since 1.4
412 */
413 public synchronized Throwable getCause() {
414 return (cause==this ? null : cause);
415 }
416
417 /**
418 * Initializes the <i>cause</i> of this throwable to the specified value.
419 * (The cause is the throwable that caused this throwable to get thrown.)
420 *
421 * <p>This method can be called at most once. It is generally called from
422 * within the constructor, or immediately after creating the
423 * throwable. If this throwable was created
424 * with {@link #Throwable(Throwable)} or
425 * {@link #Throwable(String,Throwable)}, this method cannot be called
426 * even once.
427 *
428 * <p>An example of using this method on a legacy throwable type
429 * without other support for setting the cause is:
430 *
431 * <pre>
432 * try {
433 * lowLevelOp();
434 * } catch (LowLevelException le) {
435 * throw (HighLevelException)
436 * new HighLevelException().initCause(le); // Legacy constructor
437 * }
438 * </pre>
439 *
440 * @param cause the cause (which is saved for later retrieval by the
441 * {@link #getCause()} method). (A {@code null} value is
442 * permitted, and indicates that the cause is nonexistent or
443 * unknown.)
444 * @return a reference to this {@code Throwable} instance.
445 * @throws IllegalArgumentException if {@code cause} is this
446 * throwable. (A throwable cannot be its own cause.)
447 * @throws IllegalStateException if this throwable was
448 * created with {@link #Throwable(Throwable)} or
449 * {@link #Throwable(String,Throwable)}, or this method has already
450 * been called on this throwable.
451 * @since 1.4
452 */
453 public synchronized Throwable initCause(Throwable cause) {
454 if (this.cause != this)
455 throw new IllegalStateException("Can't overwrite cause with " +
456 Objects.toString(cause, "a null"), this);
457 if (cause == this)
458 throw new IllegalArgumentException("Self-causation not permitted", this);
459 this.cause = cause;
460 return this;
461 }
462
463 /**
464 * Returns a short description of this throwable.
465 * The result is the concatenation of:
466 * <ul>
467 * <li> the {@linkplain Class#getName() name} of the class of this object
468 * <li> ": " (a colon and a space)
469 * <li> the result of invoking this object's {@link #getLocalizedMessage}
470 * method
471 * </ul>
472 * If {@code getLocalizedMessage} returns {@code null}, then just
473 * the class name is returned.
474 *
475 * @return a string representation of this throwable.
476 */
477 public String toString() {
478 String s = getClass().getName();
479 String message = getLocalizedMessage();
480 return (message != null) ? (s + ": " + message) : s;
481 }
482
483 /**
484 * Prints this throwable and its backtrace to the
485 * standard error stream. This method prints a stack trace for this
486 * {@code Throwable} object on the error output stream that is
487 * the value of the field {@code System.err}. The first line of
488 * output contains the result of the {@link #toString()} method for
489 * this object. Remaining lines represent data previously recorded by
490 * the method {@link #fillInStackTrace()}. The format of this
491 * information depends on the implementation, but the following
492 * example may be regarded as typical:
493 * <blockquote><pre>
494 * java.lang.NullPointerException
495 * at MyClass.mash(MyClass.java:9)
496 * at MyClass.crunch(MyClass.java:6)
497 * at MyClass.main(MyClass.java:3)
498 * </pre></blockquote>
499 * This example was produced by running the program:
500 * <pre>
501 * class MyClass {
502 * public static void main(String[] args) {
503 * crunch(null);
504 * }
505 * static void crunch(int[] a) {
506 * mash(a);
507 * }
508 * static void mash(int[] b) {
509 * System.out.println(b[0]);
510 * }
511 * }
512 * </pre>
513 * The backtrace for a throwable with an initialized, non-null cause
514 * should generally include the backtrace for the cause. The format
515 * of this information depends on the implementation, but the following
516 * example may be regarded as typical:
517 * <pre>
518 * HighLevelException: MidLevelException: LowLevelException
519 * at Junk.a(Junk.java:13)
520 * at Junk.main(Junk.java:4)
521 * Caused by: MidLevelException: LowLevelException
522 * at Junk.c(Junk.java:23)
523 * at Junk.b(Junk.java:17)
524 * at Junk.a(Junk.java:11)
525 * ... 1 more
526 * Caused by: LowLevelException
527 * at Junk.e(Junk.java:30)
528 * at Junk.d(Junk.java:27)
529 * at Junk.c(Junk.java:21)
530 * ... 3 more
531 * </pre>
532 * Note the presence of lines containing the characters {@code "..."}.
533 * These lines indicate that the remainder of the stack trace for this
534 * exception matches the indicated number of frames from the bottom of the
535 * stack trace of the exception that was caused by this exception (the
536 * "enclosing" exception). This shorthand can greatly reduce the length
537 * of the output in the common case where a wrapped exception is thrown
538 * from same method as the "causative exception" is caught. The above
539 * example was produced by running the program:
540 * <pre>
541 * public class Junk {
542 * public static void main(String args[]) {
543 * try {
544 * a();
545 * } catch(HighLevelException e) {
546 * e.printStackTrace();
547 * }
548 * }
549 * static void a() throws HighLevelException {
550 * try {
551 * b();
552 * } catch(MidLevelException e) {
553 * throw new HighLevelException(e);
554 * }
555 * }
556 * static void b() throws MidLevelException {
557 * c();
558 * }
559 * static void c() throws MidLevelException {
560 * try {
561 * d();
562 * } catch(LowLevelException e) {
563 * throw new MidLevelException(e);
564 * }
565 * }
566 * static void d() throws LowLevelException {
567 * e();
568 * }
569 * static void e() throws LowLevelException {
570 * throw new LowLevelException();
571 * }
572 * }
573 *
574 * class HighLevelException extends Exception {
575 * HighLevelException(Throwable cause) { super(cause); }
576 * }
577 *
578 * class MidLevelException extends Exception {
579 * MidLevelException(Throwable cause) { super(cause); }
580 * }
581 *
582 * class LowLevelException extends Exception {
583 * }
584 * </pre>
585 * As of release 7, the platform supports the notion of
586 * <i>suppressed exceptions</i> (in conjunction with the {@code
587 * try}-with-resources statement). Any exceptions that were
588 * suppressed in order to deliver an exception are printed out
589 * beneath the stack trace. The format of this information
590 * depends on the implementation, but the following example may be
591 * regarded as typical:
592 *
593 * <pre>
594 * Exception in thread "main" java.lang.Exception: Something happened
595 * at Foo.bar(Foo.java:10)
596 * at Foo.main(Foo.java:5)
597 * Suppressed: Resource$CloseFailException: Resource ID = 0
598 * at Resource.close(Resource.java:26)
599 * at Foo.bar(Foo.java:9)
600 * ... 1 more
601 * </pre>
602 * Note that the "... n more" notation is used on suppressed exceptions
603 * just at it is used on causes. Unlike causes, suppressed exceptions are
604 * indented beyond their "containing exceptions."
605 *
606 * <p>An exception can have both a cause and one or more suppressed
607 * exceptions:
608 * <pre>
609 * Exception in thread "main" java.lang.Exception: Main block
610 * at Foo3.main(Foo3.java:7)
611 * Suppressed: Resource$CloseFailException: Resource ID = 2
612 * at Resource.close(Resource.java:26)
613 * at Foo3.main(Foo3.java:5)
614 * Suppressed: Resource$CloseFailException: Resource ID = 1
615 * at Resource.close(Resource.java:26)
616 * at Foo3.main(Foo3.java:5)
617 * Caused by: java.lang.Exception: I did it
618 * at Foo3.main(Foo3.java:8)
619 * </pre>
620 * Likewise, a suppressed exception can have a cause:
621 * <pre>
622 * Exception in thread "main" java.lang.Exception: Main block
623 * at Foo4.main(Foo4.java:6)
624 * Suppressed: Resource2$CloseFailException: Resource ID = 1
625 * at Resource2.close(Resource2.java:20)
626 * at Foo4.main(Foo4.java:5)
627 * Caused by: java.lang.Exception: Rats, you caught me
628 * at Resource2$CloseFailException.<init>(Resource2.java:45)
629 * ... 2 more
630 * </pre>
631 */
632 public void printStackTrace() {
633 printStackTrace(System.err);
634 }
635
636 /**
637 * Prints this throwable and its backtrace to the specified print stream.
638 *
639 * @param s {@code PrintStream} to use for output
640 */
641 public void printStackTrace(PrintStream s) {
642 printStackTrace(new WrappedPrintStream(s));
643 }
644
645 private void printStackTrace(PrintStreamOrWriter s) {
646 // Guard against malicious overrides of Throwable.equals by
647 // using a Set with identity equality semantics.
648 Set<Throwable> dejaVu = Collections.newSetFromMap(new IdentityHashMap<>());
649 dejaVu.add(this);
650
651 synchronized (s.lock()) {
652 // Print our stack trace
653 s.println(this);
654 StackTraceElement[] trace = getOurStackTrace();
655 for (StackTraceElement traceElement : trace)
656 s.println("\tat " + traceElement);
657
658 // Print suppressed exceptions, if any
659 for (Throwable se : getSuppressed())
660 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, "\t", dejaVu);
661
662 // Print cause, if any
663 Throwable ourCause = getCause();
664 if (ourCause != null)
665 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, "", dejaVu);
666 }
667 }
668
669 /**
670 * Print our stack trace as an enclosed exception for the specified
671 * stack trace.
672 */
673 private void printEnclosedStackTrace(PrintStreamOrWriter s,
674 StackTraceElement[] enclosingTrace,
675 String caption,
676 String prefix,
677 Set<Throwable> dejaVu) {
678 assert Thread.holdsLock(s.lock());
679 if (dejaVu.contains(this)) {
680 s.println("\t[CIRCULAR REFERENCE:" + this + "]");
681 } else {
682 dejaVu.add(this);
683 // Compute number of frames in common between this and enclosing trace
684 StackTraceElement[] trace = getOurStackTrace();
685 int m = trace.length - 1;
686 int n = enclosingTrace.length - 1;
687 while (m >= 0 && n >=0 && trace[m].equals(enclosingTrace[n])) {
688 m--; n--;
689 }
690 int framesInCommon = trace.length - 1 - m;
691
692 // Print our stack trace
693 s.println(prefix + caption + this);
694 for (int i = 0; i <= m; i++)
695 s.println(prefix + "\tat " + trace[i]);
696 if (framesInCommon != 0)
697 s.println(prefix + "\t... " + framesInCommon + " more");
698
699 // Print suppressed exceptions, if any
700 for (Throwable se : getSuppressed())
701 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION,
702 prefix +"\t", dejaVu);
703
704 // Print cause, if any
705 Throwable ourCause = getCause();
706 if (ourCause != null)
707 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, prefix, dejaVu);
708 }
709 }
710
711 /**
712 * Prints this throwable and its backtrace to the specified
713 * print writer.
714 *
715 * @param s {@code PrintWriter} to use for output
716 * @since 1.1
717 */
718 public void printStackTrace(PrintWriter s) {
719 printStackTrace(new WrappedPrintWriter(s));
720 }
721
722 /**
723 * Wrapper class for PrintStream and PrintWriter to enable a single
724 * implementation of printStackTrace.
725 */
726 private abstract static class PrintStreamOrWriter {
727 /** Returns the object to be locked when using this StreamOrWriter */
728 abstract Object lock();
729
730 /** Prints the specified string as a line on this StreamOrWriter */
731 abstract void println(Object o);
732 }
733
734 private static class WrappedPrintStream extends PrintStreamOrWriter {
735 private final PrintStream printStream;
736
737 WrappedPrintStream(PrintStream printStream) {
738 this.printStream = printStream;
739 }
740
741 Object lock() {
742 return printStream;
743 }
744
745 void println(Object o) {
746 printStream.println(o);
747 }
748 }
749
750 private static class WrappedPrintWriter extends PrintStreamOrWriter {
751 private final PrintWriter printWriter;
752
753 WrappedPrintWriter(PrintWriter printWriter) {
754 this.printWriter = printWriter;
755 }
756
757 Object lock() {
758 return printWriter;
759 }
760
761 void println(Object o) {
762 printWriter.println(o);
763 }
764 }
765
766 /**
767 * Fills in the execution stack trace. This method records within this
768 * {@code Throwable} object information about the current state of
769 * the stack frames for the current thread.
770 *
771 * <p>If the stack trace of this {@code Throwable} {@linkplain
772 * Throwable#Throwable(String, Throwable, boolean, boolean) is not
773 * writable}, calling this method has no effect.
774 *
775 * @return a reference to this {@code Throwable} instance.
776 * @see java.lang.Throwable#printStackTrace()
777 */
778 public synchronized Throwable fillInStackTrace() {
779 if (stackTrace != null ||
780 backtrace != null /* Out of protocol state */ ) {
781 fillInStackTrace(0);
782 stackTrace = UNASSIGNED_STACK;
783 }
784 return this;
785 }
786
787 private native Throwable fillInStackTrace(int dummy);
788
789 /**
790 * Provides programmatic access to the stack trace information printed by
791 * {@link #printStackTrace()}. Returns an array of stack trace elements,
792 * each representing one stack frame. The zeroth element of the array
793 * (assuming the array's length is non-zero) represents the top of the
794 * stack, which is the last method invocation in the sequence. Typically,
795 * this is the point at which this throwable was created and thrown.
796 * The last element of the array (assuming the array's length is non-zero)
797 * represents the bottom of the stack, which is the first method invocation
798 * in the sequence.
799 *
800 * <p>Some virtual machines may, under some circumstances, omit one
801 * or more stack frames from the stack trace. In the extreme case,
802 * a virtual machine that has no stack trace information concerning
803 * this throwable is permitted to return a zero-length array from this
804 * method. Generally speaking, the array returned by this method will
805 * contain one element for every frame that would be printed by
806 * {@code printStackTrace}. Writes to the returned array do not
807 * affect future calls to this method.
808 *
809 * @return an array of stack trace elements representing the stack trace
810 * pertaining to this throwable.
811 * @since 1.4
812 */
813 public StackTraceElement[] getStackTrace() {
814 return getOurStackTrace().clone();
815 }
816
817 private synchronized StackTraceElement[] getOurStackTrace() {
818 // Initialize stack trace field with information from
819 // backtrace if this is the first call to this method
820 if (stackTrace == UNASSIGNED_STACK ||
821 (stackTrace == null && backtrace != null) /* Out of protocol state */) {
822 int depth = getStackTraceDepth();
823 stackTrace = new StackTraceElement[depth];
824 for (int i=0; i < depth; i++)
825 stackTrace[i] = getStackTraceElement(i);
826 } else if (stackTrace == null) {
827 return UNASSIGNED_STACK;
828 }
829 return stackTrace;
830 }
831
832 /**
833 * Sets the stack trace elements that will be returned by
834 * {@link #getStackTrace()} and printed by {@link #printStackTrace()}
835 * and related methods.
836 *
837 * This method, which is designed for use by RPC frameworks and other
838 * advanced systems, allows the client to override the default
839 * stack trace that is either generated by {@link #fillInStackTrace()}
840 * when a throwable is constructed or deserialized when a throwable is
841 * read from a serialization stream.
842 *
843 * <p>If the stack trace of this {@code Throwable} {@linkplain
844 * Throwable#Throwable(String, Throwable, boolean, boolean) is not
845 * writable}, calling this method has no effect other than
846 * validating its argument.
847 *
848 * @param stackTrace the stack trace elements to be associated with
849 * this {@code Throwable}. The specified array is copied by this
850 * call; changes in the specified array after the method invocation
851 * returns will have no affect on this {@code Throwable}'s stack
852 * trace.
853 *
854 * @throws NullPointerException if {@code stackTrace} is
855 * {@code null} or if any of the elements of
856 * {@code stackTrace} are {@code null}
857 *
858 * @since 1.4
859 */
860 public void setStackTrace(StackTraceElement[] stackTrace) {
861 // Validate argument
862 StackTraceElement[] defensiveCopy = stackTrace.clone();
863 for (int i = 0; i < defensiveCopy.length; i++) {
864 if (defensiveCopy[i] == null)
865 throw new NullPointerException("stackTrace[" + i + "]");
866 }
867
868 synchronized (this) {
869 if (this.stackTrace == null && // Immutable stack
870 backtrace == null) // Test for out of protocol state
871 return;
872 this.stackTrace = defensiveCopy;
873 }
874 }
875
876 /**
877 * Returns the number of elements in the stack trace (or 0 if the stack
878 * trace is unavailable).
879 *
880 * package-protection for use by SharedSecrets.
881 */
882 native int getStackTraceDepth();
883
884 /**
885 * Returns the specified element of the stack trace.
886 *
887 * package-protection for use by SharedSecrets.
888 *
889 * @param index index of the element to return.
890 * @throws IndexOutOfBoundsException if {@code index < 0 ||
891 * index >= getStackTraceDepth() }
892 */
893 native StackTraceElement getStackTraceElement(int index);
894
895 /**
896 * Reads a {@code Throwable} from a stream, enforcing
897 * well-formedness constraints on fields. Null entries and
898 * self-pointers are not allowed in the list of {@code
899 * suppressedExceptions}. Null entries are not allowed for stack
900 * trace elements. A null stack trace in the serial form results
901 * in a zero-length stack element array. A single-element stack
902 * trace whose entry is equal to {@code new StackTraceElement("",
903 * "", null, Integer.MIN_VALUE)} results in a {@code null} {@code
904 * stackTrace} field.
905 *
906 * Note that there are no constraints on the value the {@code
907 * cause} field can hold; both {@code null} and {@code this} are
908 * valid values for the field.
909 */
910 private void readObject(ObjectInputStream s)
911 throws IOException, ClassNotFoundException {
912 s.defaultReadObject(); // read in all fields
913 if (suppressedExceptions != null) {
914 List<Throwable> suppressed = null;
915 if (suppressedExceptions.isEmpty()) {
916 // Use the sentinel for a zero-length list
917 suppressed = SUPPRESSED_SENTINEL;
918 } else { // Copy Throwables to new list
919 suppressed = new ArrayList<>(1);
920 for (Throwable t : suppressedExceptions) {
921 // Enforce constraints on suppressed exceptions in
922 // case of corrupt or malicious stream.
923 if (t == null)
924 throw new NullPointerException(NULL_CAUSE_MESSAGE);
925 if (t == this)
926 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE);
927 suppressed.add(t);
928 }
929 }
930 suppressedExceptions = suppressed;
931 } // else a null suppressedExceptions field remains null
932
933 /*
934 * For zero-length stack traces, use a clone of
935 * UNASSIGNED_STACK rather than UNASSIGNED_STACK itself to
936 * allow identity comparison against UNASSIGNED_STACK in
937 * getOurStackTrace. The identity of UNASSIGNED_STACK in
938 * stackTrace indicates to the getOurStackTrace method that
939 * the stackTrace needs to be constructed from the information
940 * in backtrace.
941 */
942 if (stackTrace != null) {
943 if (stackTrace.length == 0) {
944 stackTrace = UNASSIGNED_STACK.clone();
945 } else if (stackTrace.length == 1 &&
946 // Check for the marker of an immutable stack trace
947 SentinelHolder.STACK_TRACE_ELEMENT_SENTINEL.equals(stackTrace[0])) {
948 stackTrace = null;
949 } else { // Verify stack trace elements are non-null.
950 for(StackTraceElement ste : stackTrace) {
951 if (ste == null)
952 throw new NullPointerException("null StackTraceElement in serial stream. ");
953 }
954 }
955 } else {
956 // A null stackTrace field in the serial form can result
957 // from an exception serialized without that field in
958 // older JDK releases; treat such exceptions as having
959 // empty stack traces.
960 stackTrace = UNASSIGNED_STACK.clone();
961 }
962 }
963
964 /**
965 * Write a {@code Throwable} object to a stream.
966 *
967 * A {@code null} stack trace field is represented in the serial
968 * form as a one-element array whose element is equal to {@code
969 * new StackTraceElement("", "", null, Integer.MIN_VALUE)}.
970 */
971 private synchronized void writeObject(ObjectOutputStream s)
972 throws IOException {
973 // Ensure that the stackTrace field is initialized to a
974 // non-null value, if appropriate. As of JDK 7, a null stack
975 // trace field is a valid value indicating the stack trace
976 // should not be set.
977 getOurStackTrace();
978
979 StackTraceElement[] oldStackTrace = stackTrace;
980 try {
981 if (stackTrace == null)
982 stackTrace = SentinelHolder.STACK_TRACE_SENTINEL;
983 s.defaultWriteObject();
984 } finally {
985 stackTrace = oldStackTrace;
986 }
987 }
988
989 /**
990 * Appends the specified exception to the exceptions that were
991 * suppressed in order to deliver this exception. This method is
992 * thread-safe and typically called (automatically and implicitly)
993 * by the {@code try}-with-resources statement.
994 *
995 * <p>The suppression behavior is enabled <em>unless</em> disabled
996 * {@linkplain #Throwable(String, Throwable, boolean, boolean) via
997 * a constructor}. When suppression is disabled, this method does
998 * nothing other than to validate its argument.
999 *
1000 * <p>Note that when one exception {@linkplain
1001 * #initCause(Throwable) causes} another exception, the first
1002 * exception is usually caught and then the second exception is
1003 * thrown in response. In other words, there is a causal
1004 * connection between the two exceptions.
1005 *
1006 * In contrast, there are situations where two independent
1007 * exceptions can be thrown in sibling code blocks, in particular
1008 * in the {@code try} block of a {@code try}-with-resources
1009 * statement and the compiler-generated {@code finally} block
1010 * which closes the resource.
1011 *
1012 * In these situations, only one of the thrown exceptions can be
1013 * propagated. In the {@code try}-with-resources statement, when
1014 * there are two such exceptions, the exception originating from
1015 * the {@code try} block is propagated and the exception from the
1016 * {@code finally} block is added to the list of exceptions
1017 * suppressed by the exception from the {@code try} block. As an
1018 * exception unwinds the stack, it can accumulate multiple
1019 * suppressed exceptions.
1020 *
1021 * <p>An exception may have suppressed exceptions while also being
1022 * caused by another exception. Whether or not an exception has a
1023 * cause is semantically known at the time of its creation, unlike
1024 * whether or not an exception will suppress other exceptions
1025 * which is typically only determined after an exception is
1026 * thrown.
1027 *
1028 * <p>Note that programmer written code is also able to take
1029 * advantage of calling this method in situations where there are
1030 * multiple sibling exceptions and only one can be propagated.
1031 *
1032 * @param exception the exception to be added to the list of
1033 * suppressed exceptions
1034 * @throws IllegalArgumentException if {@code exception} is this
1035 * throwable; a throwable cannot suppress itself.
1036 * @throws NullPointerException if {@code exception} is {@code null}
1037 * @since 1.7
1038 */
1039 public final synchronized void addSuppressed(Throwable exception) {
1040 if (exception == this)
1041 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE, exception);
1042
1043 if (exception == null)
1044 throw new NullPointerException(NULL_CAUSE_MESSAGE);
1045
1046 if (suppressedExceptions == null) // Suppressed exceptions not recorded
1047 return;
1048
1049 if (suppressedExceptions == SUPPRESSED_SENTINEL)
1050 suppressedExceptions = new ArrayList<>(1);
1051
1052 suppressedExceptions.add(exception);
1053 }
1054
1055 private static final Throwable[] EMPTY_THROWABLE_ARRAY = new Throwable[0];
1056
1057 /**
1058 * Returns an array containing all of the exceptions that were
1059 * suppressed, typically by the {@code try}-with-resources
1060 * statement, in order to deliver this exception.
1061 *
1062 * If no exceptions were suppressed or {@linkplain
1063 * #Throwable(String, Throwable, boolean, boolean) suppression is
1064 * disabled}, an empty array is returned. This method is
1065 * thread-safe. Writes to the returned array do not affect future
1066 * calls to this method.
1067 *
1068 * @return an array containing all of the exceptions that were
1069 * suppressed to deliver this exception.
1070 * @since 1.7
1071 */
1072 public final synchronized Throwable[] getSuppressed() {
1073 if (suppressedExceptions == SUPPRESSED_SENTINEL ||
1074 suppressedExceptions == null)
1075 return EMPTY_THROWABLE_ARRAY;
1076 else
1077 return suppressedExceptions.toArray(EMPTY_THROWABLE_ARRAY);
1078 }
1079 }