1 /*
2 * Copyright (c) 1994, 2016, 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 jdk.internal.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 * The JVM 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 /**
215 * The JVM code sets the depth of the backtrace for later retrieval
216 */
217 private transient int depth;
218
219 // Setting this static field introduces an acceptable
220 // initialization dependency on a few java.util classes.
221 private static final List<Throwable> SUPPRESSED_SENTINEL = Collections.emptyList();
222
223 /**
224 * The list of suppressed exceptions, as returned by {@link
225 * #getSuppressed()}. The list is initialized to a zero-element
226 * unmodifiable sentinel list. When a serialized Throwable is
227 * read in, if the {@code suppressedExceptions} field points to a
228 * zero-element list, the field is reset to the sentinel value.
229 *
230 * @serial
231 * @since 1.7
232 */
233 private List<Throwable> suppressedExceptions = SUPPRESSED_SENTINEL;
234
235 /** Message for trying to suppress a null exception. */
236 private static final String NULL_CAUSE_MESSAGE = "Cannot suppress a null exception.";
237
238 /** Message for trying to suppress oneself. */
239 private static final String SELF_SUPPRESSION_MESSAGE = "Self-suppression not permitted";
240
241 /** Caption for labeling causative exception stack traces */
242 private static final String CAUSE_CAPTION = "Caused by: ";
243
244 /** Caption for labeling suppressed exception stack traces */
245 private static final String SUPPRESSED_CAPTION = "Suppressed: ";
246
247 /**
248 * Constructs a new throwable with {@code null} as its detail message.
249 * The cause is not initialized, and may subsequently be initialized by a
250 * call to {@link #initCause}.
251 *
252 * <p>The {@link #fillInStackTrace()} method is called to initialize
253 * the stack trace data in the newly created throwable.
254 */
255 public Throwable() {
256 fillInStackTrace();
257 }
258
259 /**
260 * Constructs a new throwable with the specified detail message. The
261 * cause is not initialized, and may subsequently be initialized by
262 * a call to {@link #initCause}.
263 *
264 * <p>The {@link #fillInStackTrace()} method is called to initialize
265 * the stack trace data in the newly created throwable.
266 *
267 * @param message the detail message. The detail message is saved for
268 * later retrieval by the {@link #getMessage()} method.
269 */
270 public Throwable(String message) {
271 fillInStackTrace();
272 detailMessage = message;
273 }
274
275 /**
276 * Constructs a new throwable with the specified detail message and
277 * cause. <p>Note that the detail message associated with
278 * {@code cause} is <i>not</i> automatically incorporated in
279 * this throwable's detail message.
280 *
281 * <p>The {@link #fillInStackTrace()} method is called to initialize
282 * the stack trace data in the newly created throwable.
283 *
284 * @param message the detail message (which is saved for later retrieval
285 * by the {@link #getMessage()} method).
286 * @param cause the cause (which is saved for later retrieval by the
287 * {@link #getCause()} method). (A {@code null} value is
288 * permitted, and indicates that the cause is nonexistent or
289 * unknown.)
290 * @since 1.4
291 */
292 public Throwable(String message, Throwable cause) {
293 fillInStackTrace();
294 detailMessage = message;
295 this.cause = cause;
296 }
297
298 /**
299 * Constructs a new throwable with the specified cause and a detail
300 * message of {@code (cause==null ? null : cause.toString())} (which
301 * typically contains the class and detail message of {@code cause}).
302 * This constructor is useful for throwables that are little more than
303 * wrappers for other throwables (for example, {@link
304 * java.security.PrivilegedActionException}).
305 *
306 * <p>The {@link #fillInStackTrace()} method is called to initialize
307 * the stack trace data in the newly created throwable.
308 *
309 * @param cause the cause (which is saved for later retrieval by the
310 * {@link #getCause()} method). (A {@code null} value is
311 * permitted, and indicates that the cause is nonexistent or
312 * unknown.)
313 * @since 1.4
314 */
315 public Throwable(Throwable cause) {
316 fillInStackTrace();
317 detailMessage = (cause==null ? null : cause.toString());
318 this.cause = cause;
319 }
320
321 /**
322 * Constructs a new throwable with the specified detail message,
323 * cause, {@linkplain #addSuppressed suppression} enabled or
324 * disabled, and writable stack trace enabled or disabled. If
325 * suppression is disabled, {@link #getSuppressed} for this object
326 * will return a zero-length array and calls to {@link
327 * #addSuppressed} that would otherwise append an exception to the
328 * suppressed list will have no effect. If the writable stack
329 * trace is false, this constructor will not call {@link
330 * #fillInStackTrace()}, a {@code null} will be written to the
331 * {@code stackTrace} field, and subsequent calls to {@code
332 * fillInStackTrace} and {@link
333 * #setStackTrace(StackTraceElement[])} will not set the stack
334 * trace. If the writable stack trace is false, {@link
335 * #getStackTrace} will return a zero length array.
336 *
337 * <p>Note that the other constructors of {@code Throwable} treat
338 * suppression as being enabled and the stack trace as being
339 * writable. Subclasses of {@code Throwable} should document any
340 * conditions under which suppression is disabled and document
341 * conditions under which the stack trace is not writable.
342 * Disabling of suppression should only occur in exceptional
343 * circumstances where special requirements exist, such as a
344 * virtual machine reusing exception objects under low-memory
345 * situations. Circumstances where a given exception object is
346 * repeatedly caught and rethrown, such as to implement control
347 * flow between two sub-systems, is another situation where
348 * immutable throwable objects would be appropriate.
349 *
350 * @param message the detail message.
351 * @param cause the cause. (A {@code null} value is permitted,
352 * and indicates that the cause is nonexistent or unknown.)
353 * @param enableSuppression whether or not suppression is enabled or disabled
354 * @param writableStackTrace whether or not the stack trace should be
355 * writable
356 *
357 * @see OutOfMemoryError
358 * @see NullPointerException
359 * @see ArithmeticException
360 * @since 1.7
361 */
362 protected Throwable(String message, Throwable cause,
363 boolean enableSuppression,
364 boolean writableStackTrace) {
365 if (writableStackTrace) {
366 fillInStackTrace();
367 } else {
368 stackTrace = null;
369 }
370 detailMessage = message;
371 this.cause = cause;
372 if (!enableSuppression)
373 suppressedExceptions = null;
374 }
375
376 /**
377 * Returns the detail message string of this throwable.
378 *
379 * @return the detail message string of this {@code Throwable} instance
380 * (which may be {@code null}).
381 */
382 public String getMessage() {
383 return detailMessage;
384 }
385
386 /**
387 * Creates a localized description of this throwable.
388 * Subclasses may override this method in order to produce a
389 * locale-specific message. For subclasses that do not override this
390 * method, the default implementation returns the same result as
391 * {@code getMessage()}.
392 *
393 * @return The localized description of this throwable.
394 * @since 1.1
395 */
396 public String getLocalizedMessage() {
397 return getMessage();
398 }
399
400 /**
401 * Returns the cause of this throwable or {@code null} if the
402 * cause is nonexistent or unknown. (The cause is the throwable that
403 * caused this throwable to get thrown.)
404 *
405 * <p>This implementation returns the cause that was supplied via one of
406 * the constructors requiring a {@code Throwable}, or that was set after
407 * creation with the {@link #initCause(Throwable)} method. While it is
408 * typically unnecessary to override this method, a subclass can override
409 * it to return a cause set by some other means. This is appropriate for
410 * a "legacy chained throwable" that predates the addition of chained
411 * exceptions to {@code Throwable}. Note that it is <i>not</i>
412 * necessary to override any of the {@code PrintStackTrace} methods,
413 * all of which invoke the {@code getCause} method to determine the
414 * cause of a throwable.
415 *
416 * @return the cause of this throwable or {@code null} if the
417 * cause is nonexistent or unknown.
418 * @since 1.4
419 */
420 public synchronized Throwable getCause() {
421 return (cause==this ? null : cause);
422 }
423
424 /**
425 * Initializes the <i>cause</i> of this throwable to the specified value.
426 * (The cause is the throwable that caused this throwable to get thrown.)
427 *
428 * <p>This method can be called at most once. It is generally called from
429 * within the constructor, or immediately after creating the
430 * throwable. If this throwable was created
431 * with {@link #Throwable(Throwable)} or
432 * {@link #Throwable(String,Throwable)}, this method cannot be called
433 * even once.
434 *
435 * <p>An example of using this method on a legacy throwable type
436 * without other support for setting the cause is:
437 *
438 * <pre>
439 * try {
440 * lowLevelOp();
441 * } catch (LowLevelException le) {
442 * throw (HighLevelException)
443 * new HighLevelException().initCause(le); // Legacy constructor
444 * }
445 * </pre>
446 *
447 * @param cause the cause (which is saved for later retrieval by the
448 * {@link #getCause()} method). (A {@code null} value is
449 * permitted, and indicates that the cause is nonexistent or
450 * unknown.)
451 * @return a reference to this {@code Throwable} instance.
452 * @throws IllegalArgumentException if {@code cause} is this
453 * throwable. (A throwable cannot be its own cause.)
454 * @throws IllegalStateException if this throwable was
455 * created with {@link #Throwable(Throwable)} or
456 * {@link #Throwable(String,Throwable)}, or this method has already
457 * been called on this throwable.
458 * @since 1.4
459 */
460 public synchronized Throwable initCause(Throwable cause) {
461 if (this.cause != this)
462 throw new IllegalStateException("Can't overwrite cause with " +
463 Objects.toString(cause, "a null"), this);
464 if (cause == this)
465 throw new IllegalArgumentException("Self-causation not permitted", this);
466 this.cause = cause;
467 return this;
468 }
469
470 /**
471 * Returns a short description of this throwable.
472 * The result is the concatenation of:
473 * <ul>
474 * <li> the {@linkplain Class#getName() name} of the class of this object
475 * <li> ": " (a colon and a space)
476 * <li> the result of invoking this object's {@link #getLocalizedMessage}
477 * method
478 * </ul>
479 * If {@code getLocalizedMessage} returns {@code null}, then just
480 * the class name is returned.
481 *
482 * @return a string representation of this throwable.
483 */
484 public String toString() {
485 String s = getClass().getName();
486 String message = getLocalizedMessage();
487 return (message != null) ? (s + ": " + message) : s;
488 }
489
490 /**
491 * Prints this throwable and its backtrace to the
492 * standard error stream. This method prints a stack trace for this
493 * {@code Throwable} object on the error output stream that is
494 * the value of the field {@code System.err}. The first line of
495 * output contains the result of the {@link #toString()} method for
496 * this object. Remaining lines represent data previously recorded by
497 * the method {@link #fillInStackTrace()}. The format of this
498 * information depends on the implementation, but the following
499 * example may be regarded as typical:
500 * <blockquote><pre>
501 * java.lang.NullPointerException
502 * at MyClass.mash(MyClass.java:9)
503 * at MyClass.crunch(MyClass.java:6)
504 * at MyClass.main(MyClass.java:3)
505 * </pre></blockquote>
506 * This example was produced by running the program:
507 * <pre>
508 * class MyClass {
509 * public static void main(String[] args) {
510 * crunch(null);
511 * }
512 * static void crunch(int[] a) {
513 * mash(a);
514 * }
515 * static void mash(int[] b) {
516 * System.out.println(b[0]);
517 * }
518 * }
519 * </pre>
520 * The backtrace for a throwable with an initialized, non-null cause
521 * should generally include the backtrace for the cause. The format
522 * of this information depends on the implementation, but the following
523 * example may be regarded as typical:
524 * <pre>
525 * HighLevelException: MidLevelException: LowLevelException
526 * at Junk.a(Junk.java:13)
527 * at Junk.main(Junk.java:4)
528 * Caused by: MidLevelException: LowLevelException
529 * at Junk.c(Junk.java:23)
530 * at Junk.b(Junk.java:17)
531 * at Junk.a(Junk.java:11)
532 * ... 1 more
533 * Caused by: LowLevelException
534 * at Junk.e(Junk.java:30)
535 * at Junk.d(Junk.java:27)
536 * at Junk.c(Junk.java:21)
537 * ... 3 more
538 * </pre>
539 * Note the presence of lines containing the characters {@code "..."}.
540 * These lines indicate that the remainder of the stack trace for this
541 * exception matches the indicated number of frames from the bottom of the
542 * stack trace of the exception that was caused by this exception (the
543 * "enclosing" exception). This shorthand can greatly reduce the length
544 * of the output in the common case where a wrapped exception is thrown
545 * from same method as the "causative exception" is caught. The above
546 * example was produced by running the program:
547 * <pre>
548 * public class Junk {
549 * public static void main(String args[]) {
550 * try {
551 * a();
552 * } catch(HighLevelException e) {
553 * e.printStackTrace();
554 * }
555 * }
556 * static void a() throws HighLevelException {
557 * try {
558 * b();
559 * } catch(MidLevelException e) {
560 * throw new HighLevelException(e);
561 * }
562 * }
563 * static void b() throws MidLevelException {
564 * c();
565 * }
566 * static void c() throws MidLevelException {
567 * try {
568 * d();
569 * } catch(LowLevelException e) {
570 * throw new MidLevelException(e);
571 * }
572 * }
573 * static void d() throws LowLevelException {
574 * e();
575 * }
576 * static void e() throws LowLevelException {
577 * throw new LowLevelException();
578 * }
579 * }
580 *
581 * class HighLevelException extends Exception {
582 * HighLevelException(Throwable cause) { super(cause); }
583 * }
584 *
585 * class MidLevelException extends Exception {
586 * MidLevelException(Throwable cause) { super(cause); }
587 * }
588 *
589 * class LowLevelException extends Exception {
590 * }
591 * </pre>
592 * As of release 7, the platform supports the notion of
593 * <i>suppressed exceptions</i> (in conjunction with the {@code
594 * try}-with-resources statement). Any exceptions that were
595 * suppressed in order to deliver an exception are printed out
596 * beneath the stack trace. The format of this information
597 * depends on the implementation, but the following example may be
598 * regarded as typical:
599 *
600 * <pre>
601 * Exception in thread "main" java.lang.Exception: Something happened
602 * at Foo.bar(Foo.java:10)
603 * at Foo.main(Foo.java:5)
604 * Suppressed: Resource$CloseFailException: Resource ID = 0
605 * at Resource.close(Resource.java:26)
606 * at Foo.bar(Foo.java:9)
607 * ... 1 more
608 * </pre>
609 * Note that the "... n more" notation is used on suppressed exceptions
610 * just at it is used on causes. Unlike causes, suppressed exceptions are
611 * indented beyond their "containing exceptions."
612 *
613 * <p>An exception can have both a cause and one or more suppressed
614 * exceptions:
615 * <pre>
616 * Exception in thread "main" java.lang.Exception: Main block
617 * at Foo3.main(Foo3.java:7)
618 * Suppressed: Resource$CloseFailException: Resource ID = 2
619 * at Resource.close(Resource.java:26)
620 * at Foo3.main(Foo3.java:5)
621 * Suppressed: Resource$CloseFailException: Resource ID = 1
622 * at Resource.close(Resource.java:26)
623 * at Foo3.main(Foo3.java:5)
624 * Caused by: java.lang.Exception: I did it
625 * at Foo3.main(Foo3.java:8)
626 * </pre>
627 * Likewise, a suppressed exception can have a cause:
628 * <pre>
629 * Exception in thread "main" java.lang.Exception: Main block
630 * at Foo4.main(Foo4.java:6)
631 * Suppressed: Resource2$CloseFailException: Resource ID = 1
632 * at Resource2.close(Resource2.java:20)
633 * at Foo4.main(Foo4.java:5)
634 * Caused by: java.lang.Exception: Rats, you caught me
635 * at Resource2$CloseFailException.<init>(Resource2.java:45)
636 * ... 2 more
637 * </pre>
638 */
639 public void printStackTrace() {
640 printStackTrace(System.err);
641 }
642
643 /**
644 * Prints this throwable and its backtrace to the specified print stream.
645 *
646 * @param s {@code PrintStream} to use for output
647 */
648 public void printStackTrace(PrintStream s) {
649 printStackTrace(new WrappedPrintStream(s));
650 }
651
652 private void printStackTrace(PrintStreamOrWriter s) {
653 // Guard against malicious overrides of Throwable.equals by
654 // using a Set with identity equality semantics.
655 Set<Throwable> dejaVu = Collections.newSetFromMap(new IdentityHashMap<>());
656 dejaVu.add(this);
657
658 synchronized (s.lock()) {
659 // Print our stack trace
660 s.println(this);
661 StackTraceElement[] trace = getOurStackTrace();
662 for (StackTraceElement traceElement : trace)
663 s.println("\tat " + traceElement);
664
665 // Print suppressed exceptions, if any
666 for (Throwable se : getSuppressed())
667 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, "\t", dejaVu);
668
669 // Print cause, if any
670 Throwable ourCause = getCause();
671 if (ourCause != null)
672 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, "", dejaVu);
673 }
674 }
675
676 /**
677 * Print our stack trace as an enclosed exception for the specified
678 * stack trace.
679 */
680 private void printEnclosedStackTrace(PrintStreamOrWriter s,
681 StackTraceElement[] enclosingTrace,
682 String caption,
683 String prefix,
684 Set<Throwable> dejaVu) {
685 assert Thread.holdsLock(s.lock());
686 if (dejaVu.contains(this)) {
687 s.println("\t[CIRCULAR REFERENCE:" + this + "]");
688 } else {
689 dejaVu.add(this);
690 // Compute number of frames in common between this and enclosing trace
691 StackTraceElement[] trace = getOurStackTrace();
692 int m = trace.length - 1;
693 int n = enclosingTrace.length - 1;
694 while (m >= 0 && n >=0 && trace[m].equals(enclosingTrace[n])) {
695 m--; n--;
696 }
697 int framesInCommon = trace.length - 1 - m;
698
699 // Print our stack trace
700 s.println(prefix + caption + this);
701 for (int i = 0; i <= m; i++)
702 s.println(prefix + "\tat " + trace[i]);
703 if (framesInCommon != 0)
704 s.println(prefix + "\t... " + framesInCommon + " more");
705
706 // Print suppressed exceptions, if any
707 for (Throwable se : getSuppressed())
708 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION,
709 prefix +"\t", dejaVu);
710
711 // Print cause, if any
712 Throwable ourCause = getCause();
713 if (ourCause != null)
714 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, prefix, dejaVu);
715 }
716 }
717
718 /**
719 * Prints this throwable and its backtrace to the specified
720 * print writer.
721 *
722 * @param s {@code PrintWriter} to use for output
723 * @since 1.1
724 */
725 public void printStackTrace(PrintWriter s) {
726 printStackTrace(new WrappedPrintWriter(s));
727 }
728
729 /**
730 * Wrapper class for PrintStream and PrintWriter to enable a single
731 * implementation of printStackTrace.
732 */
733 private abstract static class PrintStreamOrWriter {
734 /** Returns the object to be locked when using this StreamOrWriter */
735 abstract Object lock();
736
737 /** Prints the specified string as a line on this StreamOrWriter */
738 abstract void println(Object o);
739 }
740
741 private static class WrappedPrintStream extends PrintStreamOrWriter {
742 private final PrintStream printStream;
743
744 WrappedPrintStream(PrintStream printStream) {
745 this.printStream = printStream;
746 }
747
748 Object lock() {
749 return printStream;
750 }
751
752 void println(Object o) {
753 printStream.println(o);
754 }
755 }
756
757 private static class WrappedPrintWriter extends PrintStreamOrWriter {
758 private final PrintWriter printWriter;
759
760 WrappedPrintWriter(PrintWriter printWriter) {
761 this.printWriter = printWriter;
762 }
763
764 Object lock() {
765 return printWriter;
766 }
767
768 void println(Object o) {
769 printWriter.println(o);
770 }
771 }
772
773 /**
774 * Fills in the execution stack trace. This method records within this
775 * {@code Throwable} object information about the current state of
776 * the stack frames for the current thread.
777 *
778 * <p>If the stack trace of this {@code Throwable} {@linkplain
779 * Throwable#Throwable(String, Throwable, boolean, boolean) is not
780 * writable}, calling this method has no effect.
781 *
782 * @return a reference to this {@code Throwable} instance.
783 * @see java.lang.Throwable#printStackTrace()
784 */
785 public synchronized Throwable fillInStackTrace() {
786 if (stackTrace != null ||
787 backtrace != null /* Out of protocol state */ ) {
788 if (backtrace == null && StackStreamFactory.useStackTrace(this)) {
789 backtrace = StackStreamFactory.makeStackTrace(this);
790 } else {
791 fillInStackTrace(0);
792 }
793 stackTrace = UNASSIGNED_STACK;
794 }
795 return this;
796 }
797
798 private native Throwable fillInStackTrace(int dummy);
799
800 /**
801 * Provides programmatic access to the stack trace information printed by
802 * {@link #printStackTrace()}. Returns an array of stack trace elements,
803 * each representing one stack frame. The zeroth element of the array
804 * (assuming the array's length is non-zero) represents the top of the
805 * stack, which is the last method invocation in the sequence. Typically,
806 * this is the point at which this throwable was created and thrown.
807 * The last element of the array (assuming the array's length is non-zero)
808 * represents the bottom of the stack, which is the first method invocation
809 * in the sequence.
810 *
811 * <p>Some virtual machines may, under some circumstances, omit one
812 * or more stack frames from the stack trace. In the extreme case,
813 * a virtual machine that has no stack trace information concerning
814 * this throwable is permitted to return a zero-length array from this
815 * method. Generally speaking, the array returned by this method will
816 * contain one element for every frame that would be printed by
817 * {@code printStackTrace}. Writes to the returned array do not
818 * affect future calls to this method.
819 *
820 * @return an array of stack trace elements representing the stack trace
821 * pertaining to this throwable.
822 * @since 1.4
823 */
824 public StackTraceElement[] getStackTrace() {
825 return getOurStackTrace().clone();
826 }
827
828 private synchronized StackTraceElement[] getOurStackTrace() {
829 // Initialize stack trace field with information from
830 // backtrace if this is the first call to this method
831 if (stackTrace == UNASSIGNED_STACK ||
832 (stackTrace == null && backtrace != null) /* Out of protocol state */) {
833 if (backtrace instanceof StackStreamFactory.StackTrace) {
834 stackTrace = ((StackStreamFactory.StackTrace)backtrace).getStackTraceElements();
835 } else {
836 stackTrace = new StackTraceElement[depth];
837 for (int i = 0; i < depth; i++) {
838 stackTrace[i] = new StackTraceElement();
839 }
840 getStackTraceElements(stackTrace);
841 }
842 } else if (stackTrace == null) {
843 return UNASSIGNED_STACK;
844 }
845 return stackTrace;
846 }
847
848 /**
849 * Sets the stack trace elements that will be returned by
850 * {@link #getStackTrace()} and printed by {@link #printStackTrace()}
851 * and related methods.
852 *
853 * This method, which is designed for use by RPC frameworks and other
854 * advanced systems, allows the client to override the default
855 * stack trace that is either generated by {@link #fillInStackTrace()}
856 * when a throwable is constructed or deserialized when a throwable is
857 * read from a serialization stream.
858 *
859 * <p>If the stack trace of this {@code Throwable} {@linkplain
860 * Throwable#Throwable(String, Throwable, boolean, boolean) is not
861 * writable}, calling this method has no effect other than
862 * validating its argument.
863 *
864 * @param stackTrace the stack trace elements to be associated with
865 * this {@code Throwable}. The specified array is copied by this
866 * call; changes in the specified array after the method invocation
867 * returns will have no affect on this {@code Throwable}'s stack
868 * trace.
869 *
870 * @throws NullPointerException if {@code stackTrace} is
871 * {@code null} or if any of the elements of
872 * {@code stackTrace} are {@code null}
873 *
874 * @since 1.4
875 */
876 public void setStackTrace(StackTraceElement[] stackTrace) {
877 // Validate argument
878 StackTraceElement[] defensiveCopy = stackTrace.clone();
879 for (int i = 0; i < defensiveCopy.length; i++) {
880 if (defensiveCopy[i] == null)
881 throw new NullPointerException("stackTrace[" + i + "]");
882 }
883
884 synchronized (this) {
885 if (this.stackTrace == null && // Immutable stack
886 backtrace == null) // Test for out of protocol state
887 return;
888 this.stackTrace = defensiveCopy;
889 }
890 }
891
892 /**
893 * Gets the stack trace elements.
894 * @param elements
895 * @throws IndexOutOfBoundsException if {@code elements.length != depth }
896 */
897 private native void getStackTraceElements(StackTraceElement[] elements);
898
899 /**
900 * Reads a {@code Throwable} from a stream, enforcing
901 * well-formedness constraints on fields. Null entries and
902 * self-pointers are not allowed in the list of {@code
903 * suppressedExceptions}. Null entries are not allowed for stack
904 * trace elements. A null stack trace in the serial form results
905 * in a zero-length stack element array. A single-element stack
906 * trace whose entry is equal to {@code new StackTraceElement("",
907 * "", null, Integer.MIN_VALUE)} results in a {@code null} {@code
908 * stackTrace} field.
909 *
910 * Note that there are no constraints on the value the {@code
911 * cause} field can hold; both {@code null} and {@code this} are
912 * valid values for the field.
913 */
914 private void readObject(ObjectInputStream s)
915 throws IOException, ClassNotFoundException {
916 s.defaultReadObject(); // read in all fields
917 if (suppressedExceptions != null) {
918 List<Throwable> suppressed = null;
919 if (suppressedExceptions.isEmpty()) {
920 // Use the sentinel for a zero-length list
921 suppressed = SUPPRESSED_SENTINEL;
922 } else { // Copy Throwables to new list
923 suppressed = new ArrayList<>(1);
924 for (Throwable t : suppressedExceptions) {
925 // Enforce constraints on suppressed exceptions in
926 // case of corrupt or malicious stream.
927 if (t == null)
928 throw new NullPointerException(NULL_CAUSE_MESSAGE);
929 if (t == this)
930 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE);
931 suppressed.add(t);
932 }
933 }
934 suppressedExceptions = suppressed;
935 } // else a null suppressedExceptions field remains null
936
937 /*
938 * For zero-length stack traces, use a clone of
939 * UNASSIGNED_STACK rather than UNASSIGNED_STACK itself to
940 * allow identity comparison against UNASSIGNED_STACK in
941 * getOurStackTrace. The identity of UNASSIGNED_STACK in
942 * stackTrace indicates to the getOurStackTrace method that
943 * the stackTrace needs to be constructed from the information
944 * in backtrace.
945 */
946 if (stackTrace != null) {
947 if (stackTrace.length == 0) {
948 stackTrace = UNASSIGNED_STACK.clone();
949 } else if (stackTrace.length == 1 &&
950 // Check for the marker of an immutable stack trace
951 SentinelHolder.STACK_TRACE_ELEMENT_SENTINEL.equals(stackTrace[0])) {
952 stackTrace = null;
953 } else { // Verify stack trace elements are non-null.
954 for(StackTraceElement ste : stackTrace) {
955 if (ste == null)
956 throw new NullPointerException("null StackTraceElement in serial stream. ");
957 }
958 }
959 } else {
960 // A null stackTrace field in the serial form can result
961 // from an exception serialized without that field in
962 // older JDK releases; treat such exceptions as having
963 // empty stack traces.
964 stackTrace = UNASSIGNED_STACK.clone();
965 }
966 }
967
968 /**
969 * Write a {@code Throwable} object to a stream.
970 *
971 * A {@code null} stack trace field is represented in the serial
972 * form as a one-element array whose element is equal to {@code
973 * new StackTraceElement("", "", null, Integer.MIN_VALUE)}.
974 */
975 private synchronized void writeObject(ObjectOutputStream s)
976 throws IOException {
977 // Ensure that the stackTrace field is initialized to a
978 // non-null value, if appropriate. As of JDK 7, a null stack
979 // trace field is a valid value indicating the stack trace
980 // should not be set.
981 getOurStackTrace();
982
983 StackTraceElement[] oldStackTrace = stackTrace;
984 try {
985 if (stackTrace == null)
986 stackTrace = SentinelHolder.STACK_TRACE_SENTINEL;
987 s.defaultWriteObject();
988 } finally {
989 stackTrace = oldStackTrace;
990 }
991 }
992
993 /**
994 * Appends the specified exception to the exceptions that were
995 * suppressed in order to deliver this exception. This method is
996 * thread-safe and typically called (automatically and implicitly)
997 * by the {@code try}-with-resources statement.
998 *
999 * <p>The suppression behavior is enabled <em>unless</em> disabled
1000 * {@linkplain #Throwable(String, Throwable, boolean, boolean) via
1001 * a constructor}. When suppression is disabled, this method does
1002 * nothing other than to validate its argument.
1003 *
1004 * <p>Note that when one exception {@linkplain
1005 * #initCause(Throwable) causes} another exception, the first
1006 * exception is usually caught and then the second exception is
1007 * thrown in response. In other words, there is a causal
1008 * connection between the two exceptions.
1009 *
1010 * In contrast, there are situations where two independent
1011 * exceptions can be thrown in sibling code blocks, in particular
1012 * in the {@code try} block of a {@code try}-with-resources
1013 * statement and the compiler-generated {@code finally} block
1014 * which closes the resource.
1015 *
1016 * In these situations, only one of the thrown exceptions can be
1017 * propagated. In the {@code try}-with-resources statement, when
1018 * there are two such exceptions, the exception originating from
1019 * the {@code try} block is propagated and the exception from the
1020 * {@code finally} block is added to the list of exceptions
1021 * suppressed by the exception from the {@code try} block. As an
1022 * exception unwinds the stack, it can accumulate multiple
1023 * suppressed exceptions.
1024 *
1025 * <p>An exception may have suppressed exceptions while also being
1026 * caused by another exception. Whether or not an exception has a
1027 * cause is semantically known at the time of its creation, unlike
1028 * whether or not an exception will suppress other exceptions
1029 * which is typically only determined after an exception is
1030 * thrown.
1031 *
1032 * <p>Note that programmer written code is also able to take
1033 * advantage of calling this method in situations where there are
1034 * multiple sibling exceptions and only one can be propagated.
1035 *
1036 * @param exception the exception to be added to the list of
1037 * suppressed exceptions
1038 * @throws IllegalArgumentException if {@code exception} is this
1039 * throwable; a throwable cannot suppress itself.
1040 * @throws NullPointerException if {@code exception} is {@code null}
1041 * @since 1.7
1042 */
1043 public final synchronized void addSuppressed(Throwable exception) {
1044 if (exception == this)
1045 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE, exception);
1046
1047 if (exception == null)
1048 throw new NullPointerException(NULL_CAUSE_MESSAGE);
1049
1050 if (suppressedExceptions == null) // Suppressed exceptions not recorded
1051 return;
1052
1053 if (suppressedExceptions == SUPPRESSED_SENTINEL)
1054 suppressedExceptions = new ArrayList<>(1);
1055
1056 suppressedExceptions.add(exception);
1057 }
1058
1059 private static final Throwable[] EMPTY_THROWABLE_ARRAY = new Throwable[0];
1060
1061 /**
1062 * Returns an array containing all of the exceptions that were
1063 * suppressed, typically by the {@code try}-with-resources
1064 * statement, in order to deliver this exception.
1065 *
1066 * If no exceptions were suppressed or {@linkplain
1067 * #Throwable(String, Throwable, boolean, boolean) suppression is
1068 * disabled}, an empty array is returned. This method is
1069 * thread-safe. Writes to the returned array do not affect future
1070 * calls to this method.
1071 *
1072 * @return an array containing all of the exceptions that were
1073 * suppressed to deliver this exception.
1074 * @since 1.7
1075 */
1076 public final synchronized Throwable[] getSuppressed() {
1077 if (suppressedExceptions == SUPPRESSED_SENTINEL ||
1078 suppressedExceptions == null)
1079 return EMPTY_THROWABLE_ARRAY;
1080 else
1081 return suppressedExceptions.toArray(EMPTY_THROWABLE_ARRAY);
1082 }
1083 }