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