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 sun.misc.VM;
28
29 import java.io.*;
30 import java.util.*;
31
32 /**
33 * The {@code Throwable} class is the superclass of all errors and
34 * exceptions in the Java language. Only objects that are instances of this
35 * class (or one of its subclasses) are thrown by the Java Virtual Machine or
36 * can be thrown by the Java {@code throw} statement. Similarly, only
37 * this class or one of its subclasses can be the argument type in a
38 * {@code catch} clause.
39 *
40 * For the purposes of compile-time checking of exceptions, {@code
41 * Throwable} and any subclass of {@code Throwable} that is not also a
42 * subclass of either {@link RuntimeException} or {@link Error} are
43 * regarded as checked exceptions.
44 *
45 * <p>Instances of two subclasses, {@link java.lang.Error} and
46 * {@link java.lang.Exception}, are conventionally used to indicate
47 * that exceptional situations have occurred. Typically, these instances
48 * are freshly created in the context of the exceptional situation so
49 * as to include relevant information (such as stack trace data).
50 *
51 * <p>A throwable contains a snapshot of the execution stack of its
52 * thread at the time it was created. It can also contain a message
53 * string that gives more information about the error. Over time, a
54 * throwable can {@linkplain Throwable#addSuppressed suppress} other
55 * throwables from being propagated. Finally, the throwable can also
56 * contain a <i>cause</i>: another throwable that caused this
57 * throwable to be constructed. The recording of this causal information
58 * is referred to as the <i>chained exception</i> facility, as the
59 * cause can, itself, have a cause, and so on, leading to a "chain" of
60 * exceptions, each caused by another.
61 *
62 * <p>One reason that a throwable may have a cause is that the class that
63 * throws it is built atop a lower layered abstraction, and an operation on
64 * the upper layer fails due to a failure in the lower layer. It would be bad
65 * design to let the throwable thrown by the lower layer propagate outward, as
66 * it is generally unrelated to the abstraction provided by the upper layer.
67 * Further, doing so would tie the API of the upper layer to the details of
68 * its implementation, assuming the lower layer's exception was a checked
69 * exception. Throwing a "wrapped exception" (i.e., an exception containing a
70 * cause) allows the upper layer to communicate the details of the failure to
71 * its caller without incurring either of these shortcomings. It preserves
72 * the flexibility to change the implementation of the upper layer without
73 * changing its API (in particular, the set of exceptions thrown by its
74 * methods).
75 *
76 * <p>A second reason that a throwable may have a cause is that the method
77 * that throws it must conform to a general-purpose interface that does not
78 * permit the method to throw the cause directly. For example, suppose
79 * a persistent collection conforms to the {@link java.util.Collection
80 * Collection} interface, and that its persistence is implemented atop
81 * {@code java.io}. Suppose the internals of the {@code add} method
82 * can throw an {@link java.io.IOException IOException}. The implementation
83 * can communicate the details of the {@code IOException} to its caller
84 * while conforming to the {@code Collection} interface by wrapping the
85 * {@code IOException} in an appropriate unchecked exception. (The
86 * specification for the persistent collection should indicate that it is
87 * capable of throwing such exceptions.)
88 *
89 * <p>A cause can be associated with a throwable in two ways: via a
90 * constructor that takes the cause as an argument, or via the
91 * {@link #initCause(Throwable)} method. New throwable classes that
92 * wish to allow causes to be associated with them should provide constructors
93 * that take a cause and delegate (perhaps indirectly) to one of the
94 * {@code Throwable} constructors that takes a cause.
95 *
96 * Because the {@code initCause} method is public, it allows a cause to be
97 * associated with any throwable, even a "legacy throwable" whose
98 * implementation predates the addition of the exception chaining mechanism to
99 * {@code Throwable}.
100 *
101 * <p>By convention, class {@code Throwable} and its subclasses have two
102 * constructors, one that takes no arguments and one that takes a
103 * {@code String} argument that can be used to produce a detail message.
104 * Further, those subclasses that might likely have a cause associated with
105 * them should have two more constructors, one that takes a
106 * {@code Throwable} (the cause), and one that takes a
107 * {@code String} (the detail message) and a {@code Throwable} (the
108 * cause).
109 *
110 * @author unascribed
111 * @author Josh Bloch (Added exception chaining and programmatic access to
112 * stack trace in 1.4.)
113 * @jls 11.2 Compile-Time Checking of Exceptions
114 * @since 1.0
115 */
116 public class Throwable implements Serializable {
117 /** use serialVersionUID from JDK 1.0.2 for interoperability */
118 private static final long serialVersionUID = -3042686055658047285L;
119
120 /**
121 * Native code saves some indication of the stack backtrace in this slot.
122 */
123 private transient Object backtrace;
124
125 /**
126 * Specific details about the Throwable. For example, for
127 * {@code FileNotFoundException}, this contains the name of
128 * the file that could not be found.
129 *
130 * @serial
131 */
132 private String detailMessage;
133
134
135 /**
136 * Holder class to defer initializing sentinel objects only used
137 * for serialization.
138 */
139 private static class SentinelHolder {
140 /**
141 * {@linkplain #setStackTrace(StackTraceElement[]) Setting the
142 * stack trace} to a one-element array containing this sentinel
143 * value indicates future attempts to set the stack trace will be
144 * ignored. The sentinel is equal to the result of calling:<br>
145 * {@code new StackTraceElement("", "", null, Integer.MIN_VALUE)}
146 */
147 public static final StackTraceElement STACK_TRACE_ELEMENT_SENTINEL =
148 new StackTraceElement("", "", null, Integer.MIN_VALUE);
149
150 /**
151 * Sentinel value used in the serial form to indicate an immutable
152 * stack trace.
153 */
154 public static final StackTraceElement[] STACK_TRACE_SENTINEL =
155 new StackTraceElement[] {STACK_TRACE_ELEMENT_SENTINEL};
156 }
157
158 /**
159 * A shared value for an empty stack.
160 */
161 private static final StackTraceElement[] UNASSIGNED_STACK = new StackTraceElement[0];
162
163 /*
164 * To allow Throwable objects to be made immutable and safely
165 * reused by the JVM, such as OutOfMemoryErrors, fields of
166 * Throwable that are writable in response to user actions, cause,
167 * stackTrace, and suppressedExceptions obey the following
168 * protocol:
169 *
170 * 1) The fields are initialized to a non-null sentinel value
171 * which indicates the value has logically not been set.
172 *
173 * 2) Writing a null to the field indicates further writes
174 * are forbidden
175 *
176 * 3) The sentinel value may be replaced with another non-null
177 * value.
178 *
179 * For example, implementations of the HotSpot JVM have
180 * preallocated OutOfMemoryError objects to provide for better
181 * diagnosability of that situation. These objects are created
182 * without calling the constructor for that class and the fields
183 * in question are initialized to null. To support this
184 * capability, any new fields added to Throwable that require
185 * being initialized to a non-null value require a coordinated JVM
186 * change.
187 */
188
189 /**
190 * The throwable that caused this throwable to get thrown, or null if this
191 * throwable was not caused by another throwable, or if the causative
192 * throwable is unknown. If this field is equal to this throwable itself,
193 * it indicates that the cause of this throwable has not yet been
194 * initialized.
195 *
196 * @serial
197 * @since 1.4
198 */
199 private Throwable cause = this;
200
201 /**
202 * The stack trace, as returned by {@link #getStackTrace()}.
203 *
204 * The field is initialized to a zero-length array. A {@code
205 * null} value of this field indicates subsequent calls to {@link
206 * #setStackTrace(StackTraceElement[])} and {@link
207 * #fillInStackTrace()} will be no-ops.
208 *
209 * @serial
210 * @since 1.4
211 */
212 private StackTraceElement[] stackTrace = UNASSIGNED_STACK;
213
214 // Setting this static field introduces an acceptable
215 // initialization dependency on a few java.util classes.
216 private static final List<Throwable> SUPPRESSED_SENTINEL = Collections.emptyList();
217
218 /**
219 * The list of suppressed exceptions, as returned by {@link
220 * #getSuppressed()}. The list is initialized to a zero-element
221 * unmodifiable sentinel list. When a serialized Throwable is
222 * read in, if the {@code suppressedExceptions} field points to a
223 * zero-element list, the field is reset to the sentinel value.
224 *
225 * @serial
226 * @since 1.7
227 */
228 private List<Throwable> suppressedExceptions = SUPPRESSED_SENTINEL;
229
230 /** Message for trying to suppress a null exception. */
231 private static final String NULL_CAUSE_MESSAGE = "Cannot suppress a null exception.";
232
233 /** Message for trying to suppress oneself. */
234 private static final String SELF_SUPPRESSION_MESSAGE = "Self-suppression not permitted";
235
236 /** Caption for labeling causative exception stack traces */
237 private static final String CAUSE_CAPTION = "Caused by: ";
238
239 /** Caption for labeling suppressed exception stack traces */
240 private static final String SUPPRESSED_CAPTION = "Suppressed: ";
241
242 /**
243 * Constructs a new throwable with {@code null} as its detail message.
244 * The cause is not initialized, and may subsequently be initialized by a
245 * call to {@link #initCause}.
246 *
247 * <p>The {@link #fillInStackTrace()} method is called to initialize
248 * the stack trace data in the newly created throwable.
249 */
250 public Throwable() {
251 fillInStackTrace();
252 }
253
254 /**
255 * Constructs a new throwable with the specified detail message. The
256 * cause is not initialized, and may subsequently be initialized by
257 * a call to {@link #initCause}.
258 *
259 * <p>The {@link #fillInStackTrace()} method is called to initialize
260 * the stack trace data in the newly created throwable.
261 *
262 * @param message the detail message. The detail message is saved for
263 * later retrieval by the {@link #getMessage()} method.
264 */
265 public Throwable(String message) {
266 fillInStackTrace();
267 detailMessage = message;
268 }
269
270 /**
271 * Constructs a new throwable with the specified detail message and
272 * cause. <p>Note that the detail message associated with
273 * {@code cause} is <i>not</i> automatically incorporated in
274 * this throwable's detail message.
275 *
276 * <p>The {@link #fillInStackTrace()} method is called to initialize
277 * the stack trace data in the newly created throwable.
278 *
279 * @param message the detail message (which is saved for later retrieval
280 * by the {@link #getMessage()} method).
281 * @param cause the cause (which is saved for later retrieval by the
282 * {@link #getCause()} method). (A {@code null} value is
283 * permitted, and indicates that the cause is nonexistent or
284 * unknown.)
285 * @since 1.4
286 */
287 public Throwable(String message, Throwable cause) {
288 fillInStackTrace();
289 detailMessage = message;
290 this.cause = cause;
291 }
292
293 /**
294 * Constructs a new throwable with the specified cause and a detail
295 * message of {@code (cause==null ? null : cause.toString())} (which
296 * typically contains the class and detail message of {@code cause}).
297 * This constructor is useful for throwables that are little more than
298 * wrappers for other throwables (for example, {@link
299 * java.security.PrivilegedActionException}).
300 *
301 * <p>The {@link #fillInStackTrace()} method is called to initialize
302 * the stack trace data in the newly created throwable.
303 *
304 * @param cause the cause (which is saved for later retrieval by the
305 * {@link #getCause()} method). (A {@code null} value is
306 * permitted, and indicates that the cause is nonexistent or
307 * unknown.)
308 * @since 1.4
309 */
310 public Throwable(Throwable cause) {
311 fillInStackTrace();
312 detailMessage = (cause==null ? null : cause.toString());
313 this.cause = cause;
314 }
315
316 /**
317 * Constructs a new throwable with the specified detail message,
318 * cause, {@linkplain #addSuppressed suppression} enabled or
319 * disabled, and writable stack trace enabled or disabled. If
320 * suppression is disabled, {@link #getSuppressed} for this object
321 * will return a zero-length array and calls to {@link
322 * #addSuppressed} that would otherwise append an exception to the
323 * suppressed list will have no effect. If the writable stack
324 * trace is false, this constructor will not call {@link
325 * #fillInStackTrace()}, a {@code null} will be written to the
326 * {@code stackTrace} field, and subsequent calls to {@code
327 * fillInStackTrace} and {@link
328 * #setStackTrace(StackTraceElement[])} will not set the stack
329 * trace. If the writable stack trace is false, {@link
330 * #getStackTrace} will return a zero length array.
331 *
332 * <p>Note that the other constructors of {@code Throwable} treat
333 * suppression as being enabled and the stack trace as being
334 * writable. Subclasses of {@code Throwable} should document any
335 * conditions under which suppression is disabled and document
336 * conditions under which the stack trace is not writable.
337 * Disabling of suppression should only occur in exceptional
338 * circumstances where special requirements exist, such as a
339 * virtual machine reusing exception objects under low-memory
340 * situations. Circumstances where a given exception object is
341 * repeatedly caught and rethrown, such as to implement control
342 * flow between two sub-systems, is another situation where
343 * immutable throwable objects would be appropriate.
344 *
345 * @param message the detail message.
346 * @param cause the cause. (A {@code null} value is permitted,
347 * and indicates that the cause is nonexistent or unknown.)
348 * @param enableSuppression whether or not suppression is enabled or disabled
349 * @param writableStackTrace whether or not the stack trace should be
350 * writable
351 *
352 * @see OutOfMemoryError
353 * @see NullPointerException
354 * @see ArithmeticException
355 * @since 1.7
356 */
357 protected Throwable(String message, Throwable cause,
358 boolean enableSuppression,
359 boolean writableStackTrace) {
360 if (writableStackTrace) {
361 fillInStackTrace();
362 } else {
363 stackTrace = null;
364 }
365 detailMessage = message;
366 this.cause = cause;
367 if (!enableSuppression)
368 suppressedExceptions = null;
369 }
370
371 /**
372 * Returns the detail message string of this throwable.
373 *
374 * @return the detail message string of this {@code Throwable} instance
375 * (which may be {@code null}).
376 */
377 public String getMessage() {
378 return detailMessage;
379 }
380
381 /**
382 * Creates a localized description of this throwable.
383 * Subclasses may override this method in order to produce a
384 * locale-specific message. For subclasses that do not override this
385 * method, the default implementation returns the same result as
386 * {@code getMessage()}.
387 *
388 * @return The localized description of this throwable.
389 * @since 1.1
390 */
391 public String getLocalizedMessage() {
392 return getMessage();
393 }
394
395 /**
396 * Returns the cause of this throwable or {@code null} if the
397 * cause is nonexistent or unknown. (The cause is the throwable that
398 * caused this throwable to get thrown.)
399 *
400 * <p>This implementation returns the cause that was supplied via one of
401 * the constructors requiring a {@code Throwable}, or that was set after
402 * creation with the {@link #initCause(Throwable)} method. While it is
403 * typically unnecessary to override this method, a subclass can override
404 * it to return a cause set by some other means. This is appropriate for
405 * a "legacy chained throwable" that predates the addition of chained
406 * exceptions to {@code Throwable}. Note that it is <i>not</i>
407 * necessary to override any of the {@code PrintStackTrace} methods,
408 * all of which invoke the {@code getCause} method to determine the
409 * cause of a throwable.
410 *
411 * @return the cause of this throwable or {@code null} if the
412 * cause is nonexistent or unknown.
413 * @since 1.4
414 */
415 public synchronized Throwable getCause() {
416 return (cause==this ? null : cause);
417 }
418
419 /**
420 * Initializes the <i>cause</i> of this throwable to the specified value.
421 * (The cause is the throwable that caused this throwable to get thrown.)
422 *
423 * <p>This method can be called at most once. It is generally called from
424 * within the constructor, or immediately after creating the
425 * throwable. If this throwable was created
426 * with {@link #Throwable(Throwable)} or
427 * {@link #Throwable(String,Throwable)}, this method cannot be called
428 * even once.
429 *
430 * <p>An example of using this method on a legacy throwable type
431 * without other support for setting the cause is:
432 *
433 * <pre>
434 * try {
435 * lowLevelOp();
436 * } catch (LowLevelException le) {
437 * throw (HighLevelException)
438 * new HighLevelException().initCause(le); // Legacy constructor
439 * }
440 * </pre>
441 *
442 * @param cause the cause (which is saved for later retrieval by the
443 * {@link #getCause()} method). (A {@code null} value is
444 * permitted, and indicates that the cause is nonexistent or
445 * unknown.)
446 * @return a reference to this {@code Throwable} instance.
447 * @throws IllegalArgumentException if {@code cause} is this
448 * throwable. (A throwable cannot be its own cause.)
449 * @throws IllegalStateException if this throwable was
450 * created with {@link #Throwable(Throwable)} or
451 * {@link #Throwable(String,Throwable)}, or this method has already
452 * been called on this throwable.
453 * @since 1.4
454 */
455 public synchronized Throwable initCause(Throwable cause) {
456 if (this.cause != this)
457 throw new IllegalStateException("Can't overwrite cause with " +
458 Objects.toString(cause, "a null"), this);
459 if (cause == this)
460 throw new IllegalArgumentException("Self-causation not permitted", this);
461 this.cause = cause;
462 return this;
463 }
464
465 /**
466 * Returns a short description of this throwable.
467 * The result is the concatenation of:
468 * <ul>
469 * <li> the {@linkplain Class#getName() name} of the class of this object
470 * <li> ": " (a colon and a space)
471 * <li> the result of invoking this object's {@link #getLocalizedMessage}
472 * method
473 * </ul>
474 * If {@code getLocalizedMessage} returns {@code null}, then just
475 * the class name is returned.
476 *
477 * @return a string representation of this throwable.
478 */
479 public String toString() {
480 String s = getClass().getName();
481 String message = getLocalizedMessage();
482 return (message != null) ? (s + ": " + message) : s;
483 }
484
485 /**
486 * Prints this throwable and its backtrace to the
487 * standard error stream. This method prints a stack trace for this
488 * {@code Throwable} object on the error output stream that is
489 * the value of the field {@code System.err}. The first line of
490 * output contains the result of the {@link #toString()} method for
491 * this object. Remaining lines represent data previously recorded by
492 * the method {@link #fillInStackTrace()}. The format of this
493 * information depends on the implementation, but the following
494 * example may be regarded as typical:
495 * <blockquote><pre>
496 * java.lang.NullPointerException
497 * at MyClass.mash(MyClass.java:9)
498 * at MyClass.crunch(MyClass.java:6)
499 * at MyClass.main(MyClass.java:3)
500 * </pre></blockquote>
501 * This example was produced by running the program:
502 * <pre>
503 * class MyClass {
504 * public static void main(String[] args) {
505 * crunch(null);
506 * }
507 * static void crunch(int[] a) {
508 * mash(a);
509 * }
510 * static void mash(int[] b) {
511 * System.out.println(b[0]);
512 * }
513 * }
514 * </pre>
515 * The backtrace for a throwable with an initialized, non-null cause
516 * should generally include the backtrace for the cause. The format
517 * of this information depends on the implementation, but the following
518 * example may be regarded as typical:
519 * <pre>
520 * HighLevelException: MidLevelException: LowLevelException
521 * at Junk.a(Junk.java:13)
522 * at Junk.main(Junk.java:4)
523 * Caused by: MidLevelException: LowLevelException
524 * at Junk.c(Junk.java:23)
525 * at Junk.b(Junk.java:17)
526 * at Junk.a(Junk.java:11)
527 * ... 1 more
528 * Caused by: LowLevelException
529 * at Junk.e(Junk.java:30)
530 * at Junk.d(Junk.java:27)
531 * at Junk.c(Junk.java:21)
532 * ... 3 more
533 * </pre>
534 * Note the presence of lines containing the characters {@code "..."}.
535 * These lines indicate that the remainder of the stack trace for this
536 * exception matches the indicated number of frames from the bottom of the
537 * stack trace of the exception that was caused by this exception (the
538 * "enclosing" exception). This shorthand can greatly reduce the length
539 * of the output in the common case where a wrapped exception is thrown
540 * from same method as the "causative exception" is caught. The above
541 * example was produced by running the program:
542 * <pre>
543 * public class Junk {
544 * public static void main(String args[]) {
545 * try {
546 * a();
547 * } catch(HighLevelException e) {
548 * e.printStackTrace();
549 * }
550 * }
551 * static void a() throws HighLevelException {
552 * try {
553 * b();
554 * } catch(MidLevelException e) {
555 * throw new HighLevelException(e);
556 * }
557 * }
558 * static void b() throws MidLevelException {
559 * c();
560 * }
561 * static void c() throws MidLevelException {
562 * try {
563 * d();
564 * } catch(LowLevelException e) {
565 * throw new MidLevelException(e);
566 * }
567 * }
568 * static void d() throws LowLevelException {
569 * e();
570 * }
571 * static void e() throws LowLevelException {
572 * throw new LowLevelException();
573 * }
574 * }
575 *
576 * class HighLevelException extends Exception {
577 * HighLevelException(Throwable cause) { super(cause); }
578 * }
579 *
580 * class MidLevelException extends Exception {
581 * MidLevelException(Throwable cause) { super(cause); }
582 * }
583 *
584 * class LowLevelException extends Exception {
585 * }
586 * </pre>
587 * As of release 7, the platform supports the notion of
588 * <i>suppressed exceptions</i> (in conjunction with the {@code
589 * try}-with-resources statement). Any exceptions that were
590 * suppressed in order to deliver an exception are printed out
591 * beneath the stack trace. The format of this information
592 * depends on the implementation, but the following example may be
593 * regarded as typical:
594 *
595 * <pre>
596 * Exception in thread "main" java.lang.Exception: Something happened
597 * at Foo.bar(Foo.java:10)
598 * at Foo.main(Foo.java:5)
599 * Suppressed: Resource$CloseFailException: Resource ID = 0
600 * at Resource.close(Resource.java:26)
601 * at Foo.bar(Foo.java:9)
602 * ... 1 more
603 * </pre>
604 * Note that the "... n more" notation is used on suppressed exceptions
605 * just at it is used on causes. Unlike causes, suppressed exceptions are
606 * indented beyond their "containing exceptions."
607 *
608 * <p>An exception can have both a cause and one or more suppressed
609 * exceptions:
610 * <pre>
611 * Exception in thread "main" java.lang.Exception: Main block
612 * at Foo3.main(Foo3.java:7)
613 * Suppressed: Resource$CloseFailException: Resource ID = 2
614 * at Resource.close(Resource.java:26)
615 * at Foo3.main(Foo3.java:5)
616 * Suppressed: Resource$CloseFailException: Resource ID = 1
617 * at Resource.close(Resource.java:26)
618 * at Foo3.main(Foo3.java:5)
619 * Caused by: java.lang.Exception: I did it
620 * at Foo3.main(Foo3.java:8)
621 * </pre>
622 * Likewise, a suppressed exception can have a cause:
623 * <pre>
624 * Exception in thread "main" java.lang.Exception: Main block
625 * at Foo4.main(Foo4.java:6)
626 * Suppressed: Resource2$CloseFailException: Resource ID = 1
627 * at Resource2.close(Resource2.java:20)
628 * at Foo4.main(Foo4.java:5)
629 * Caused by: java.lang.Exception: Rats, you caught me
630 * at Resource2$CloseFailException.<init>(Resource2.java:45)
631 * ... 2 more
632 * </pre>
633 */
634 public void printStackTrace() {
635 printStackTrace(System.err);
636 }
637
638 /**
639 * Prints this throwable and its backtrace to the specified print stream.
640 *
641 * @param s {@code PrintStream} to use for output
642 */
643 public void printStackTrace(PrintStream s) {
644 printStackTrace(new WrappedPrintStream(s));
645 }
646
647 private void printStackTrace(PrintStreamOrWriter s) {
648 // Guard against malicious overrides of Throwable.equals by
649 // using a Set with identity equality semantics.
650 Set<Throwable> dejaVu = Collections.newSetFromMap(new IdentityHashMap<>());
651 dejaVu.add(this);
652
653 synchronized (s.lock()) {
654 // Print our stack trace
655 s.println(this);
656 StackTraceElement[] trace = getOurStackTrace();
657 for (StackTraceElement traceElement : trace)
658 s.println("\tat " + traceElement);
659
660 // Print suppressed exceptions, if any
661 for (Throwable se : getSuppressed())
662 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, "\t", dejaVu);
663
664 // Print cause, if any
665 Throwable ourCause = getCause();
666 if (ourCause != null)
667 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, "", dejaVu);
668 }
669 }
670
671 /**
672 * Print our stack trace as an enclosed exception for the specified
673 * stack trace.
674 */
675 private void printEnclosedStackTrace(PrintStreamOrWriter s,
676 StackTraceElement[] enclosingTrace,
677 String caption,
678 String prefix,
679 Set<Throwable> dejaVu) {
680 assert Thread.holdsLock(s.lock());
681 if (dejaVu.contains(this)) {
682 s.println("\t[CIRCULAR REFERENCE:" + this + "]");
683 } else {
684 dejaVu.add(this);
685 // Compute number of frames in common between this and enclosing trace
686 StackTraceElement[] trace = getOurStackTrace();
687 int m = trace.length - 1;
688 int n = enclosingTrace.length - 1;
689 while (m >= 0 && n >=0 && trace[m].equals(enclosingTrace[n])) {
690 m--; n--;
691 }
692 int framesInCommon = trace.length - 1 - m;
693
694 // Print our stack trace
695 s.println(prefix + caption + this);
696 for (int i = 0; i <= m; i++)
697 s.println(prefix + "\tat " + trace[i]);
698 if (framesInCommon != 0)
699 s.println(prefix + "\t... " + framesInCommon + " more");
700
701 // Print suppressed exceptions, if any
702 for (Throwable se : getSuppressed())
703 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION,
704 prefix +"\t", dejaVu);
705
706 // Print cause, if any
707 Throwable ourCause = getCause();
708 if (ourCause != null)
709 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, prefix, dejaVu);
710 }
711 }
712
713 /**
714 * Prints this throwable and its backtrace to the specified
715 * print writer.
716 *
717 * @param s {@code PrintWriter} to use for output
718 * @since 1.1
719 */
720 public void printStackTrace(PrintWriter s) {
721 printStackTrace(new WrappedPrintWriter(s));
722 }
723
724 /**
725 * Wrapper class for PrintStream and PrintWriter to enable a single
726 * implementation of printStackTrace.
727 */
728 private abstract static class PrintStreamOrWriter {
729 /** Returns the object to be locked when using this StreamOrWriter */
730 abstract Object lock();
731
732 /** Prints the specified string as a line on this StreamOrWriter */
733 abstract void println(Object o);
734 }
735
736 private static class WrappedPrintStream extends PrintStreamOrWriter {
737 private final PrintStream printStream;
738
739 WrappedPrintStream(PrintStream printStream) {
740 this.printStream = printStream;
741 }
742
743 Object lock() {
744 return printStream;
745 }
746
747 void println(Object o) {
748 printStream.println(o);
749 }
750 }
751
752 private static class WrappedPrintWriter extends PrintStreamOrWriter {
753 private final PrintWriter printWriter;
754
755 WrappedPrintWriter(PrintWriter printWriter) {
756 this.printWriter = printWriter;
757 }
758
759 Object lock() {
760 return printWriter;
761 }
762
763 void println(Object o) {
764 printWriter.println(o);
765 }
766 }
767
768 /**
769 * Fills in the execution stack trace. This method records within this
770 * {@code Throwable} object information about the current state of
771 * the stack frames for the current thread.
772 *
773 * <p>If the stack trace of this {@code Throwable} {@linkplain
774 * Throwable#Throwable(String, Throwable, boolean, boolean) is not
775 * writable}, calling this method has no effect.
776 *
777 * @return a reference to this {@code Throwable} instance.
778 * @see java.lang.Throwable#printStackTrace()
779 */
780 public synchronized Throwable fillInStackTrace() {
781 if (stackTrace != null ||
782 backtrace != null /* Out of protocol state */ ) {
783 if (backtrace == null && StackStreamFactory.useStackTrace(this)) {
784 backtrace = StackStreamFactory.makeStackTrace(this);
785 } else {
786 fillInStackTrace(0);
787 }
788 stackTrace = UNASSIGNED_STACK;
789 }
790 return this;
791 }
792
793 private native Throwable fillInStackTrace(int dummy);
794
795 /**
796 * Provides programmatic access to the stack trace information printed by
797 * {@link #printStackTrace()}. Returns an array of stack trace elements,
798 * each representing one stack frame. The zeroth element of the array
799 * (assuming the array's length is non-zero) represents the top of the
800 * stack, which is the last method invocation in the sequence. Typically,
801 * this is the point at which this throwable was created and thrown.
802 * The last element of the array (assuming the array's length is non-zero)
803 * represents the bottom of the stack, which is the first method invocation
804 * in the sequence.
805 *
806 * <p>Some virtual machines may, under some circumstances, omit one
807 * or more stack frames from the stack trace. In the extreme case,
808 * a virtual machine that has no stack trace information concerning
809 * this throwable is permitted to return a zero-length array from this
810 * method. Generally speaking, the array returned by this method will
811 * contain one element for every frame that would be printed by
812 * {@code printStackTrace}. Writes to the returned array do not
813 * affect future calls to this method.
814 *
815 * @return an array of stack trace elements representing the stack trace
816 * pertaining to this throwable.
817 * @since 1.4
818 */
819 public StackTraceElement[] getStackTrace() {
820 return getOurStackTrace().clone();
821 }
822
823 private synchronized StackTraceElement[] getOurStackTrace() {
824 // Initialize stack trace field with information from
825 // backtrace if this is the first call to this method
826 if (stackTrace == UNASSIGNED_STACK ||
827 (stackTrace == null && backtrace != null) /* Out of protocol state */) {
828 if (backtrace instanceof StackStreamFactory.StackTrace) {
829 stackTrace = ((StackStreamFactory.StackTrace)backtrace).getStackTraceElements();
830 } else {
831 int depth = getStackTraceDepth();
832 stackTrace = new StackTraceElement[depth];
833 for (int i = 0; i < depth; i++)
834 stackTrace[i] = getStackTraceElement(i);
835 }
836 } else if (stackTrace == null) {
837 return UNASSIGNED_STACK;
838 }
839 return stackTrace;
840 }
841
842 /**
843 * Sets the stack trace elements that will be returned by
844 * {@link #getStackTrace()} and printed by {@link #printStackTrace()}
845 * and related methods.
846 *
847 * This method, which is designed for use by RPC frameworks and other
848 * advanced systems, allows the client to override the default
849 * stack trace that is either generated by {@link #fillInStackTrace()}
850 * when a throwable is constructed or deserialized when a throwable is
851 * read from a serialization stream.
852 *
853 * <p>If the stack trace of this {@code Throwable} {@linkplain
854 * Throwable#Throwable(String, Throwable, boolean, boolean) is not
855 * writable}, calling this method has no effect other than
856 * validating its argument.
857 *
858 * @param stackTrace the stack trace elements to be associated with
859 * this {@code Throwable}. The specified array is copied by this
860 * call; changes in the specified array after the method invocation
861 * returns will have no affect on this {@code Throwable}'s stack
862 * trace.
863 *
864 * @throws NullPointerException if {@code stackTrace} is
865 * {@code null} or if any of the elements of
866 * {@code stackTrace} are {@code null}
867 *
868 * @since 1.4
869 */
870 public void setStackTrace(StackTraceElement[] stackTrace) {
871 // Validate argument
872 StackTraceElement[] defensiveCopy = stackTrace.clone();
873 for (int i = 0; i < defensiveCopy.length; i++) {
874 if (defensiveCopy[i] == null)
875 throw new NullPointerException("stackTrace[" + i + "]");
876 }
877
878 synchronized (this) {
879 if (this.stackTrace == null && // Immutable stack
880 backtrace == null) // Test for out of protocol state
881 return;
882 this.stackTrace = defensiveCopy;
883 }
884 }
885
886 /**
887 * Returns the number of elements in the stack trace (or 0 if the stack
888 * trace is unavailable).
889 *
890 * package-protection for use by SharedSecrets.
891 */
892 native int getStackTraceDepth();
893
894 /**
895 * Returns the specified element of the stack trace.
896 *
897 * package-protection for use by SharedSecrets.
898 *
899 * @param index index of the element to return.
900 * @throws IndexOutOfBoundsException if {@code index < 0 ||
901 * index >= getStackTraceDepth() }
902 */
903 native StackTraceElement getStackTraceElement(int index);
904
905 /**
906 * Reads a {@code Throwable} from a stream, enforcing
907 * well-formedness constraints on fields. Null entries and
908 * self-pointers are not allowed in the list of {@code
909 * suppressedExceptions}. Null entries are not allowed for stack
910 * trace elements. A null stack trace in the serial form results
911 * in a zero-length stack element array. A single-element stack
912 * trace whose entry is equal to {@code new StackTraceElement("",
913 * "", null, Integer.MIN_VALUE)} results in a {@code null} {@code
914 * stackTrace} field.
915 *
916 * Note that there are no constraints on the value the {@code
917 * cause} field can hold; both {@code null} and {@code this} are
918 * valid values for the field.
919 */
920 private void readObject(ObjectInputStream s)
921 throws IOException, ClassNotFoundException {
922 s.defaultReadObject(); // read in all fields
923 if (suppressedExceptions != null) {
924 List<Throwable> suppressed = null;
925 if (suppressedExceptions.isEmpty()) {
926 // Use the sentinel for a zero-length list
927 suppressed = SUPPRESSED_SENTINEL;
928 } else { // Copy Throwables to new list
929 suppressed = new ArrayList<>(1);
930 for (Throwable t : suppressedExceptions) {
931 // Enforce constraints on suppressed exceptions in
932 // case of corrupt or malicious stream.
933 if (t == null)
934 throw new NullPointerException(NULL_CAUSE_MESSAGE);
935 if (t == this)
936 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE);
937 suppressed.add(t);
938 }
939 }
940 suppressedExceptions = suppressed;
941 } // else a null suppressedExceptions field remains null
942
943 /*
944 * For zero-length stack traces, use a clone of
945 * UNASSIGNED_STACK rather than UNASSIGNED_STACK itself to
946 * allow identity comparison against UNASSIGNED_STACK in
947 * getOurStackTrace. The identity of UNASSIGNED_STACK in
948 * stackTrace indicates to the getOurStackTrace method that
949 * the stackTrace needs to be constructed from the information
950 * in backtrace.
951 */
952 if (stackTrace != null) {
953 if (stackTrace.length == 0) {
954 stackTrace = UNASSIGNED_STACK.clone();
955 } else if (stackTrace.length == 1 &&
956 // Check for the marker of an immutable stack trace
957 SentinelHolder.STACK_TRACE_ELEMENT_SENTINEL.equals(stackTrace[0])) {
958 stackTrace = null;
959 } else { // Verify stack trace elements are non-null.
960 for(StackTraceElement ste : stackTrace) {
961 if (ste == null)
962 throw new NullPointerException("null StackTraceElement in serial stream. ");
963 }
964 }
965 } else {
966 // A null stackTrace field in the serial form can result
967 // from an exception serialized without that field in
968 // older JDK releases; treat such exceptions as having
969 // empty stack traces.
970 stackTrace = UNASSIGNED_STACK.clone();
971 }
972 }
973
974 /**
975 * Write a {@code Throwable} object to a stream.
976 *
977 * A {@code null} stack trace field is represented in the serial
978 * form as a one-element array whose element is equal to {@code
979 * new StackTraceElement("", "", null, Integer.MIN_VALUE)}.
980 */
981 private synchronized void writeObject(ObjectOutputStream s)
982 throws IOException {
983 // Ensure that the stackTrace field is initialized to a
984 // non-null value, if appropriate. As of JDK 7, a null stack
985 // trace field is a valid value indicating the stack trace
986 // should not be set.
987 getOurStackTrace();
988
989 StackTraceElement[] oldStackTrace = stackTrace;
990 try {
991 if (stackTrace == null)
992 stackTrace = SentinelHolder.STACK_TRACE_SENTINEL;
993 s.defaultWriteObject();
994 } finally {
995 stackTrace = oldStackTrace;
996 }
997 }
998
999 /**
1000 * Appends the specified exception to the exceptions that were
1001 * suppressed in order to deliver this exception. This method is
1002 * thread-safe and typically called (automatically and implicitly)
1003 * by the {@code try}-with-resources statement.
1004 *
1005 * <p>The suppression behavior is enabled <em>unless</em> disabled
1006 * {@linkplain #Throwable(String, Throwable, boolean, boolean) via
1007 * a constructor}. When suppression is disabled, this method does
1008 * nothing other than to validate its argument.
1009 *
1010 * <p>Note that when one exception {@linkplain
1011 * #initCause(Throwable) causes} another exception, the first
1012 * exception is usually caught and then the second exception is
1013 * thrown in response. In other words, there is a causal
1014 * connection between the two exceptions.
1015 *
1016 * In contrast, there are situations where two independent
1017 * exceptions can be thrown in sibling code blocks, in particular
1018 * in the {@code try} block of a {@code try}-with-resources
1019 * statement and the compiler-generated {@code finally} block
1020 * which closes the resource.
1021 *
1022 * In these situations, only one of the thrown exceptions can be
1023 * propagated. In the {@code try}-with-resources statement, when
1024 * there are two such exceptions, the exception originating from
1025 * the {@code try} block is propagated and the exception from the
1026 * {@code finally} block is added to the list of exceptions
1027 * suppressed by the exception from the {@code try} block. As an
1028 * exception unwinds the stack, it can accumulate multiple
1029 * suppressed exceptions.
1030 *
1031 * <p>An exception may have suppressed exceptions while also being
1032 * caused by another exception. Whether or not an exception has a
1033 * cause is semantically known at the time of its creation, unlike
1034 * whether or not an exception will suppress other exceptions
1035 * which is typically only determined after an exception is
1036 * thrown.
1037 *
1038 * <p>Note that programmer written code is also able to take
1039 * advantage of calling this method in situations where there are
1040 * multiple sibling exceptions and only one can be propagated.
1041 *
1042 * @param exception the exception to be added to the list of
1043 * suppressed exceptions
1044 * @throws IllegalArgumentException if {@code exception} is this
1045 * throwable; a throwable cannot suppress itself.
1046 * @throws NullPointerException if {@code exception} is {@code null}
1047 * @since 1.7
1048 */
1049 public final synchronized void addSuppressed(Throwable exception) {
1050 if (exception == this)
1051 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE, exception);
1052
1053 if (exception == null)
1054 throw new NullPointerException(NULL_CAUSE_MESSAGE);
1055
1056 if (suppressedExceptions == null) // Suppressed exceptions not recorded
1057 return;
1058
1059 if (suppressedExceptions == SUPPRESSED_SENTINEL)
1060 suppressedExceptions = new ArrayList<>(1);
1061
1062 suppressedExceptions.add(exception);
1063 }
1064
1065 private static final Throwable[] EMPTY_THROWABLE_ARRAY = new Throwable[0];
1066
1067 /**
1068 * Returns an array containing all of the exceptions that were
1069 * suppressed, typically by the {@code try}-with-resources
1070 * statement, in order to deliver this exception.
1071 *
1072 * If no exceptions were suppressed or {@linkplain
1073 * #Throwable(String, Throwable, boolean, boolean) suppression is
1074 * disabled}, an empty array is returned. This method is
1075 * thread-safe. Writes to the returned array do not affect future
1076 * calls to this method.
1077 *
1078 * @return an array containing all of the exceptions that were
1079 * suppressed to deliver this exception.
1080 * @since 1.7
1081 */
1082 public final synchronized Throwable[] getSuppressed() {
1083 if (suppressedExceptions == SUPPRESSED_SENTINEL ||
1084 suppressedExceptions == null)
1085 return EMPTY_THROWABLE_ARRAY;
1086 else
1087 return suppressedExceptions.toArray(EMPTY_THROWABLE_ARRAY);
1088 }
1089 }