1 /*
2 * Copyright (c) 1994, 2011, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.lang;
27 import java.io.*;
28 import java.util.*;
29
30 /**
31 * The {@code Throwable} class is the superclass of all errors and
32 * exceptions in the Java language. Only objects that are instances of this
33 * class (or one of its subclasses) are thrown by the Java Virtual Machine or
34 * can be thrown by the Java {@code throw} statement. Similarly, only
35 * this class or one of its subclasses can be the argument type in a
36 * {@code catch} clause.
37 *
38 * For the purposes of compile-time checking of exceptions, {@code
39 * Throwable} and any subclass of {@code Throwable} that is not also a
40 * subclass of either {@link RuntimeException} or {@link Error} are
41 * regarded as checked exceptions.
42 *
43 * <p>Instances of two subclasses, {@link java.lang.Error} and
44 * {@link java.lang.Exception}, are conventionally used to indicate
45 * that exceptional situations have occurred. Typically, these instances
46 * are freshly created in the context of the exceptional situation so
47 * as to include relevant information (such as stack trace data).
48 *
49 * <p>A throwable contains a snapshot of the execution stack of its
50 * thread at the time it was created. It can also contain a message
51 * string that gives more information about the error. Over time, a
52 * throwable can {@linkplain Throwable#addSuppressed suppress} other
53 * throwables from being propagated. Finally, the throwable can also
54 * contain a <i>cause</i>: another throwable that caused this
55 * throwable to be constructed. The recording of this causal information
56 * is referred to as the <i>chained exception</i> facility, as the
57 * cause can, itself, have a cause, and so on, leading to a "chain" of
58 * exceptions, each caused by another.
59 *
60 * <p>One reason that a throwable may have a cause is that the class that
61 * throws it is built atop a lower layered abstraction, and an operation on
62 * the upper layer fails due to a failure in the lower layer. It would be bad
63 * design to let the throwable thrown by the lower layer propagate outward, as
64 * it is generally unrelated to the abstraction provided by the upper layer.
65 * Further, doing so would tie the API of the upper layer to the details of
66 * its implementation, assuming the lower layer's exception was a checked
67 * exception. Throwing a "wrapped exception" (i.e., an exception containing a
68 * cause) allows the upper layer to communicate the details of the failure to
69 * its caller without incurring either of these shortcomings. It preserves
70 * the flexibility to change the implementation of the upper layer without
71 * changing its API (in particular, the set of exceptions thrown by its
72 * methods).
73 *
74 * <p>A second reason that a throwable may have a cause is that the method
75 * that throws it must conform to a general-purpose interface that does not
76 * permit the method to throw the cause directly. For example, suppose
77 * a persistent collection conforms to the {@link java.util.Collection
78 * Collection} interface, and that its persistence is implemented atop
79 * {@code java.io}. Suppose the internals of the {@code add} method
80 * can throw an {@link java.io.IOException IOException}. The implementation
81 * can communicate the details of the {@code IOException} to its caller
82 * while conforming to the {@code Collection} interface by wrapping the
83 * {@code IOException} in an appropriate unchecked exception. (The
84 * specification for the persistent collection should indicate that it is
85 * capable of throwing such exceptions.)
86 *
87 * <p>A cause can be associated with a throwable in two ways: via a
88 * constructor that takes the cause as an argument, or via the
89 * {@link #initCause(Throwable)} method. New throwable classes that
90 * wish to allow causes to be associated with them should provide constructors
91 * that take a cause and delegate (perhaps indirectly) to one of the
92 * {@code Throwable} constructors that takes a cause.
93 *
94 * Because the {@code initCause} method is public, it allows a cause to be
95 * associated with any throwable, even a "legacy throwable" whose
96 * implementation predates the addition of the exception chaining mechanism to
97 * {@code Throwable}.
98 *
99 * <p>By convention, class {@code Throwable} and its subclasses have two
100 * constructors, one that takes no arguments and one that takes a
101 * {@code String} argument that can be used to produce a detail message.
102 * Further, those subclasses that might likely have a cause associated with
103 * them should have two more constructors, one that takes a
104 * {@code Throwable} (the cause), and one that takes a
105 * {@code String} (the detail message) and a {@code Throwable} (the
106 * cause).
107 *
108 * @author unascribed
109 * @author Josh Bloch (Added exception chaining and programmatic access to
110 * stack trace in 1.4.)
111 * @jls3 11.2 Compile-Time Checking of Exceptions
112 * @since JDK1.0
113 */
114 public class Throwable implements Serializable {
115 /** use serialVersionUID from JDK 1.0.2 for interoperability */
116 private static final long serialVersionUID = -3042686055658047285L;
117
118 /**
119 * Native code saves some indication of the stack backtrace in this slot.
120 */
121 private transient Object backtrace;
122
123 /**
124 * Specific details about the Throwable. For example, for
125 * {@code FileNotFoundException}, this contains the name of
126 * the file that could not be found.
127 *
128 * @serial
129 */
130 private String detailMessage;
131
132
133 /**
134 * Holder class to defer initializing sentinel objects only used
135 * for serialization.
136 */
137 private static class SentinelHolder {
138 /**
139 * {@linkplain #setStackTrace(StackTraceElement[]) Setting the
140 * stack trace} to a one-element array containing this sentinel
141 * value indicates future attempts to set the stack trace will be
142 * ignored. The sentinal is equal to the result of calling:<br>
143 * {@code new StackTraceElement("", "", null, Integer.MIN_VALUE)}
144 */
145 public static final StackTraceElement STACK_TRACE_ELEMENT_SENTINEL =
146 new StackTraceElement("", "", null, Integer.MIN_VALUE);
147
148 /**
149 * Sentinel value used in the serial form to indicate an immutable
150 * stack trace.
151 */
152 public static final StackTraceElement[] STACK_TRACE_SENTINEL =
153 new StackTraceElement[] {STACK_TRACE_ELEMENT_SENTINEL};
154 }
155
156 /**
157 * A value indicating the stack trace field has not yet been initialized.
158 */
159 private static final StackTraceElement[] UNINITIALIZED_STACK =
160 new StackTraceElement[] {new StackTraceElement("UNINITIALIZED", "STACK", null, -1)};
161
162 /**
163 * A value indicating that the logical stack trace has been
164 * populated into the backtrace field.
165 */
166 private static final StackTraceElement[] FILLED_IN_STACK =
167 new StackTraceElement[] {new StackTraceElement("FILLED_IN", "STACK", null, -1)};
168
169 /**
170 * A shared value for an empty stack.
171 */
172 private static final StackTraceElement[] EMPTY_STACK = new StackTraceElement[0];
173
174 /*
175 * To allow Throwable objects to be made immutable and safely
176 * reused by the JVM, such as OutOfMemoryErrors, fields of
177 * Throwable that are writable in response to user actions, cause,
178 * stackTrace, and suppressedExceptions obey the following
179 * protocol:
180 *
181 * 1) The fields are initialized to a non-null sentinel value
182 * which indicates the value has logically not been set.
183 *
184 * 2) Writing a null to the field indicates further writes
185 * are forbidden
186 *
187 * 3) The sentinel value may be replaced with another non-null
188 * value.
189 *
190 * For example, implementations of the HotSpot JVM have
191 * preallocated OutOfMemoryError objects to provide for better
192 * diagnosability of that situation. These objects are created
193 * without calling the constructor for that class and the fields
194 * in question are initialized to null. To support this
195 * capability, any new fields added to Throwable that require
196 * being initialized to a non-null value require a coordinated JVM
197 * change.
198 */
199
200 /**
201 * The throwable that caused this throwable to get thrown, or null if this
202 * throwable was not caused by another throwable, or if the causative
203 * throwable is unknown. If this field is equal to this throwable itself,
204 * it indicates that the cause of this throwable has not yet been
205 * initialized.
206 *
207 * @serial
208 * @since 1.4
209 */
210 private Throwable cause = this;
211
212 /**
213 * The stack trace, as returned by {@link #getStackTrace()}.
214 *
215 * The field is initialized to a zero-length array. A {@code
216 * null} value of this field indicates subsequent calls to {@link
217 * #setStackTrace()} and {@link #fillInStackTrace} will be be no-ops.
218 *
219 * @serial
220 * @since 1.4
221 */
222 private StackTraceElement[] stackTrace = UNINITIALIZED_STACK;
223
224 // Setting this static field introduces an acceptable
225 // initialization dependency on a few java.util classes.
226 private static final List<Throwable> SUPPRESSED_SENTINEL =
227 Collections.unmodifiableList(new ArrayList<Throwable>(0));
228
229 /**
230 * The list of suppressed exceptions, as returned by {@link
231 * #getSuppressed()}. The list is initialized to a zero-element
232 * unmodifiable sentinel list. When a serialized Throwable is
233 * read in, if the {@code suppressedExceptions} field points to a
234 * zero-element list, the field is reset to the sentinel value.
235 *
236 * @serial
237 * @since 1.7
238 */
239 private List<Throwable> suppressedExceptions = SUPPRESSED_SENTINEL;
240
241 /** Message for trying to suppress a null exception. */
242 private static final String NULL_CAUSE_MESSAGE = "Cannot suppress a null exception.";
243
244 /** Message for trying to suppress oneself. */
245 private static final String SELF_SUPPRESSION_MESSAGE = "Self-suppression not permitted";
246
247 /** Caption for labeling causative exception stack traces */
248 private static final String CAUSE_CAPTION = "Caused by: ";
249
250 /** Caption for labeling suppressed exception stack traces */
251 private static final String SUPPRESSED_CAPTION = "Suppressed: ";
252
253 /**
254 * Constructs a new throwable with {@code null} as its detail message.
255 * The cause is not initialized, and may subsequently be initialized by a
256 * call to {@link #initCause}.
257 *
258 * <p>The {@link #fillInStackTrace()} method is called to initialize
259 * the stack trace data in the newly created throwable.
260 */
261 public Throwable() {
262 fillInStackTrace();
263 }
264
265 /**
266 * Constructs a new throwable with the specified detail message. The
267 * cause is not initialized, and may subsequently be initialized by
268 * a call to {@link #initCause}.
269 *
270 * <p>The {@link #fillInStackTrace()} method is called to initialize
271 * the stack trace data in the newly created throwable.
272 *
273 * @param message the detail message. The detail message is saved for
274 * later retrieval by the {@link #getMessage()} method.
275 */
276 public Throwable(String message) {
277 fillInStackTrace();
278 detailMessage = message;
279 }
280
281 /**
282 * Constructs a new throwable with the specified detail message and
283 * cause. <p>Note that the detail message associated with
284 * {@code cause} is <i>not</i> automatically incorporated in
285 * this throwable's detail message.
286 *
287 * <p>The {@link #fillInStackTrace()} method is called to initialize
288 * the stack trace data in the newly created throwable.
289 *
290 * @param message the detail message (which is saved for later retrieval
291 * by the {@link #getMessage()} method).
292 * @param cause the cause (which is saved for later retrieval by the
293 * {@link #getCause()} method). (A {@code null} value is
294 * permitted, and indicates that the cause is nonexistent or
295 * unknown.)
296 * @since 1.4
297 */
298 public Throwable(String message, Throwable cause) {
299 fillInStackTrace();
300 detailMessage = message;
301 this.cause = cause;
302 }
303
304 /**
305 * Constructs a new throwable with the specified cause and a detail
306 * message of {@code (cause==null ? null : cause.toString())} (which
307 * typically contains the class and detail message of {@code cause}).
308 * This constructor is useful for throwables that are little more than
309 * wrappers for other throwables (for example, {@link
310 * java.security.PrivilegedActionException}).
311 *
312 * <p>The {@link #fillInStackTrace()} method is called to initialize
313 * the stack trace data in the newly created throwable.
314 *
315 * @param cause the cause (which is saved for later retrieval by the
316 * {@link #getCause()} method). (A {@code null} value is
317 * permitted, and indicates that the cause is nonexistent or
318 * unknown.)
319 * @since 1.4
320 */
321 public Throwable(Throwable cause) {
322 fillInStackTrace();
323 detailMessage = (cause==null ? null : cause.toString());
324 this.cause = cause;
325 }
326
327 /**
328 * Constructs a new throwable with the specified detail message,
329 * cause, {@linkplain #addSuppressed suppression} enabled or
330 * disabled, and writable stack trace enabled or disabled. If
331 * suppression is disabled, {@link #getSuppressed} for this object
332 * will return a zero-length array and calls to {@link
333 * #addSuppressed} that would otherwise append an exception to the
334 * suppressed list will have no effect. If the writable stack
335 * trace is false, this constructor will not call {@link
336 * #fillInStackTrace()} and subsequent calls to {@code
337 * fillInStackTrace} and {@link
338 * #setStackTrace(StackTraceElement[])} will not set the stack
339 * trace. If the writable stack trace is false, {@link
340 * #getStackTrace} will return a zero length array.
341 *
342 * <p>Note that the other constructors of {@code Throwable} treat
343 * suppression as being enabled and the stack trace as being
344 * writable. Subclasses of {@code Throwable} should document any
345 * conditions under which suppression is disabled. Disabling of
346 * suppression should only occur in exceptional circumstances
347 * where special requirements exist, such as a virtual machine
348 * reusing exception objects under low-memory situations.
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 JDK1.1
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 * @param cause the cause (which is saved for later retrieval by the
436 * {@link #getCause()} method). (A {@code null} value is
437 * permitted, and indicates that the cause is nonexistent or
438 * unknown.)
439 * @return a reference to this {@code Throwable} instance.
440 * @throws IllegalArgumentException if {@code cause} is this
441 * throwable. (A throwable cannot be its own cause.)
442 * @throws IllegalStateException if this throwable was
443 * created with {@link #Throwable(Throwable)} or
444 * {@link #Throwable(String,Throwable)}, or this method has already
445 * been called on this throwable.
446 * @since 1.4
447 */
448 public synchronized Throwable initCause(Throwable cause) {
449 if (this.cause != this)
450 throw new IllegalStateException("Can't overwrite cause");
451 if (cause == this)
452 throw new IllegalArgumentException("Self-causation not permitted");
453 this.cause = cause;
454 return this;
455 }
456
457 /**
458 * Returns a short description of this throwable.
459 * The result is the concatenation of:
460 * <ul>
461 * <li> the {@linkplain Class#getName() name} of the class of this object
462 * <li> ": " (a colon and a space)
463 * <li> the result of invoking this object's {@link #getLocalizedMessage}
464 * method
465 * </ul>
466 * If {@code getLocalizedMessage} returns {@code null}, then just
467 * the class name is returned.
468 *
469 * @return a string representation of this throwable.
470 */
471 public String toString() {
472 String s = getClass().getName();
473 String message = getLocalizedMessage();
474 return (message != null) ? (s + ": " + message) : s;
475 }
476
477 /**
478 * Prints this throwable and its backtrace to the
479 * standard error stream. This method prints a stack trace for this
480 * {@code Throwable} object on the error output stream that is
481 * the value of the field {@code System.err}. The first line of
482 * output contains the result of the {@link #toString()} method for
483 * this object. Remaining lines represent data previously recorded by
484 * the method {@link #fillInStackTrace()}. The format of this
485 * information depends on the implementation, but the following
486 * example may be regarded as typical:
487 * <blockquote><pre>
488 * java.lang.NullPointerException
489 * at MyClass.mash(MyClass.java:9)
490 * at MyClass.crunch(MyClass.java:6)
491 * at MyClass.main(MyClass.java:3)
492 * </pre></blockquote>
493 * This example was produced by running the program:
494 * <pre>
495 * class MyClass {
496 * public static void main(String[] args) {
497 * crunch(null);
498 * }
499 * static void crunch(int[] a) {
500 * mash(a);
501 * }
502 * static void mash(int[] b) {
503 * System.out.println(b[0]);
504 * }
505 * }
506 * </pre>
507 * The backtrace for a throwable with an initialized, non-null cause
508 * should generally include the backtrace for the cause. The format
509 * of this information depends on the implementation, but the following
510 * example may be regarded as typical:
511 * <pre>
512 * HighLevelException: MidLevelException: LowLevelException
513 * at Junk.a(Junk.java:13)
514 * at Junk.main(Junk.java:4)
515 * Caused by: MidLevelException: LowLevelException
516 * at Junk.c(Junk.java:23)
517 * at Junk.b(Junk.java:17)
518 * at Junk.a(Junk.java:11)
519 * ... 1 more
520 * Caused by: LowLevelException
521 * at Junk.e(Junk.java:30)
522 * at Junk.d(Junk.java:27)
523 * at Junk.c(Junk.java:21)
524 * ... 3 more
525 * </pre>
526 * Note the presence of lines containing the characters {@code "..."}.
527 * These lines indicate that the remainder of the stack trace for this
528 * exception matches the indicated number of frames from the bottom of the
529 * stack trace of the exception that was caused by this exception (the
530 * "enclosing" exception). This shorthand can greatly reduce the length
531 * of the output in the common case where a wrapped exception is thrown
532 * from same method as the "causative exception" is caught. The above
533 * example was produced by running the program:
534 * <pre>
535 * public class Junk {
536 * public static void main(String args[]) {
537 * try {
538 * a();
539 * } catch(HighLevelException e) {
540 * e.printStackTrace();
541 * }
542 * }
543 * static void a() throws HighLevelException {
544 * try {
545 * b();
546 * } catch(MidLevelException e) {
547 * throw new HighLevelException(e);
548 * }
549 * }
550 * static void b() throws MidLevelException {
551 * c();
552 * }
553 * static void c() throws MidLevelException {
554 * try {
555 * d();
556 * } catch(LowLevelException e) {
557 * throw new MidLevelException(e);
558 * }
559 * }
560 * static void d() throws LowLevelException {
561 * e();
562 * }
563 * static void e() throws LowLevelException {
564 * throw new LowLevelException();
565 * }
566 * }
567 *
568 * class HighLevelException extends Exception {
569 * HighLevelException(Throwable cause) { super(cause); }
570 * }
571 *
572 * class MidLevelException extends Exception {
573 * MidLevelException(Throwable cause) { super(cause); }
574 * }
575 *
576 * class LowLevelException extends Exception {
577 * }
578 * </pre>
579 * As of release 7, the platform supports the notion of
580 * <i>suppressed exceptions</i> (in conjunction with the {@code
581 * try}-with-resources statement). Any exceptions that were
582 * suppressed in order to deliver an exception are printed out
583 * beneath the stack trace. The format of this information
584 * depends on the implementation, but the following example may be
585 * regarded as typical:
586 *
587 * <pre>
588 * Exception in thread "main" java.lang.Exception: Something happened
589 * at Foo.bar(Foo.java:10)
590 * at Foo.main(Foo.java:5)
591 * Suppressed: Resource$CloseFailException: Resource ID = 0
592 * at Resource.close(Resource.java:26)
593 * at Foo.bar(Foo.java:9)
594 * ... 1 more
595 * </pre>
596 * Note that the "... n more" notation is used on suppressed exceptions
597 * just at it is used on causes. Unlike causes, suppressed exceptions are
598 * indented beyond their "containing exceptions."
599 *
600 * <p>An exception can have both a cause and one or more suppressed
601 * exceptions:
602 * <pre>
603 * Exception in thread "main" java.lang.Exception: Main block
604 * at Foo3.main(Foo3.java:7)
605 * Suppressed: Resource$CloseFailException: Resource ID = 2
606 * at Resource.close(Resource.java:26)
607 * at Foo3.main(Foo3.java:5)
608 * Suppressed: Resource$CloseFailException: Resource ID = 1
609 * at Resource.close(Resource.java:26)
610 * at Foo3.main(Foo3.java:5)
611 * Caused by: java.lang.Exception: I did it
612 * at Foo3.main(Foo3.java:8)
613 * </pre>
614 * Likewise, a suppressed exception can have a cause:
615 * <pre>
616 * Exception in thread "main" java.lang.Exception: Main block
617 * at Foo4.main(Foo4.java:6)
618 * Suppressed: Resource2$CloseFailException: Resource ID = 1
619 * at Resource2.close(Resource2.java:20)
620 * at Foo4.main(Foo4.java:5)
621 * Caused by: java.lang.Exception: Rats, you caught me
622 * at Resource2$CloseFailException.<init>(Resource2.java:45)
623 * ... 2 more
624 * </pre>
625 */
626 public void printStackTrace() {
627 printStackTrace(System.err);
628 }
629
630 /**
631 * Prints this throwable and its backtrace to the specified print stream.
632 *
633 * @param s {@code PrintStream} to use for output
634 */
635 public void printStackTrace(PrintStream s) {
636 printStackTrace(new WrappedPrintStream(s));
637 }
638
639 private void printStackTrace(PrintStreamOrWriter s) {
640 // Guard against malicious overrides of Throwable.equals by
641 // using a Set with identity equality semantics.
642 Set<Throwable> dejaVu =
643 Collections.newSetFromMap(new IdentityHashMap<Throwable, Boolean>());
644 dejaVu.add(this);
645
646 synchronized (s.lock()) {
647 // Print our stack trace
648 s.println(this);
649 StackTraceElement[] trace = getOurStackTrace();
650 for (StackTraceElement traceElement : trace)
651 s.println("\tat " + traceElement);
652
653 // Print suppressed exceptions, if any
654 for (Throwable se : getSuppressed())
655 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, "\t", dejaVu);
656
657 // Print cause, if any
658 Throwable ourCause = getCause();
659 if (ourCause != null)
660 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, "", dejaVu);
661 }
662 }
663
664 /**
665 * Print our stack trace as an enclosed exception for the specified
666 * stack trace.
667 */
668 private void printEnclosedStackTrace(PrintStreamOrWriter s,
669 StackTraceElement[] enclosingTrace,
670 String caption,
671 String prefix,
672 Set<Throwable> dejaVu) {
673 assert Thread.holdsLock(s.lock());
674 if (dejaVu.contains(this)) {
675 s.println("\t[CIRCULAR REFERENCE:" + this + "]");
676 } else {
677 dejaVu.add(this);
678 // Compute number of frames in common between this and enclosing trace
679 StackTraceElement[] trace = getOurStackTrace();
680 int m = trace.length - 1;
681 int n = enclosingTrace.length - 1;
682 while (m >= 0 && n >=0 && trace[m].equals(enclosingTrace[n])) {
683 m--; n--;
684 }
685 int framesInCommon = trace.length - 1 - m;
686
687 // Print our stack trace
688 s.println(prefix + caption + this);
689 for (int i = 0; i <= m; i++)
690 s.println(prefix + "\tat " + trace[i]);
691 if (framesInCommon != 0)
692 s.println(prefix + "\t... " + framesInCommon + " more");
693
694 // Print suppressed exceptions, if any
695 for (Throwable se : getSuppressed())
696 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION,
697 prefix +"\t", dejaVu);
698
699 // Print cause, if any
700 Throwable ourCause = getCause();
701 if (ourCause != null)
702 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, prefix, dejaVu);
703 }
704 }
705
706 /**
707 * Prints this throwable and its backtrace to the specified
708 * print writer.
709 *
710 * @param s {@code PrintWriter} to use for output
711 * @since JDK1.1
712 */
713 public void printStackTrace(PrintWriter s) {
714 printStackTrace(new WrappedPrintWriter(s));
715 }
716
717 /**
718 * Wrapper class for PrintStream and PrintWriter to enable a single
719 * implementation of printStackTrace.
720 */
721 private abstract static class PrintStreamOrWriter {
722 /** Returns the object to be locked when using this StreamOrWriter */
723 abstract Object lock();
724
725 /** Prints the specified string as a line on this StreamOrWriter */
726 abstract void println(Object o);
727 }
728
729 private static class WrappedPrintStream extends PrintStreamOrWriter {
730 private final PrintStream printStream;
731
732 WrappedPrintStream(PrintStream printStream) {
733 this.printStream = printStream;
734 }
735
736 Object lock() {
737 return printStream;
738 }
739
740 void println(Object o) {
741 printStream.println(o);
742 }
743 }
744
745 private static class WrappedPrintWriter extends PrintStreamOrWriter {
746 private final PrintWriter printWriter;
747
748 WrappedPrintWriter(PrintWriter printWriter) {
749 this.printWriter = printWriter;
750 }
751
752 Object lock() {
753 return printWriter;
754 }
755
756 void println(Object o) {
757 printWriter.println(o);
758 }
759 }
760
761 /**
762 * Fills in the execution stack trace. This method records within this
763 * {@code Throwable} object information about the current state of
764 * the stack frames for the current thread.
765 *
766 * <p>If the stack trace of this {@code Throwable} {@linkplain
767 * Throwable#Throwable(String, Throwable, boolean, boolean) is not
768 * writable}, calling this method has no effect.
769 *
770 * @return a reference to this {@code Throwable} instance.
771 * @see java.lang.Throwable#printStackTrace()
772 */
773 public synchronized Throwable fillInStackTrace() {
774 if (stackTrace != null) {
775 fillInStackTrace(0);
776 stackTrace = FILLED_IN_STACK;
777 }
778 return this;
779 }
780
781 private native Throwable fillInStackTrace(int dummy);
782
783 /**
784 * Provides programmatic access to the stack trace information printed by
785 * {@link #printStackTrace()}. Returns an array of stack trace elements,
786 * each representing one stack frame. The zeroth element of the array
787 * (assuming the array's length is non-zero) represents the top of the
788 * stack, which is the last method invocation in the sequence. Typically,
789 * this is the point at which this throwable was created and thrown.
790 * The last element of the array (assuming the array's length is non-zero)
791 * represents the bottom of the stack, which is the first method invocation
792 * in the sequence.
793 *
794 * <p>Some virtual machines may, under some circumstances, omit one
795 * or more stack frames from the stack trace. In the extreme case,
796 * a virtual machine that has no stack trace information concerning
797 * this throwable is permitted to return a zero-length array from this
798 * method. Generally speaking, the array returned by this method will
799 * contain one element for every frame that would be printed by
800 * {@code printStackTrace}.
801 *
802 * @return an array of stack trace elements representing the stack trace
803 * pertaining to this throwable.
804 * @since 1.4
805 */
806 public StackTraceElement[] getStackTrace() {
807 return getOurStackTrace().clone();
808 }
809
810 private synchronized StackTraceElement[] getOurStackTrace() {
811 // Initialize stack trace field with information from
812 // backtrace if this is the first call to this method
813 if (stackTrace == FILLED_IN_STACK) {
814 int depth = getStackTraceDepth();
815 stackTrace = new StackTraceElement[depth];
816 for (int i=0; i < depth; i++)
817 stackTrace[i] = getStackTraceElement(i);
818 } else if (stackTrace == null) {
819 return EMPTY_STACK;
820 }
821 return stackTrace;
822 }
823
824 /**
825 * Sets the stack trace elements that will be returned by
826 * {@link #getStackTrace()} and printed by {@link #printStackTrace()}
827 * and related methods.
828 *
829 * This method, which is designed for use by RPC frameworks and other
830 * advanced systems, allows the client to override the default
831 * stack trace that is either generated by {@link #fillInStackTrace()}
832 * when a throwable is constructed or deserialized when a throwable is
833 * read from a serialization stream.
834 *
835 * <p>If the stack trace of this {@code Throwable} {@linkplain
836 * Throwable#Throwable(String, Throwable, boolean, boolean) is not
837 * writable}, calling this method has no effect other than
838 * validating its argument.
839 *
840 * @param stackTrace the stack trace elements to be associated with
841 * this {@code Throwable}. The specified array is copied by this
842 * call; changes in the specified array after the method invocation
843 * returns will have no affect on this {@code Throwable}'s stack
844 * trace.
845 *
846 * @throws NullPointerException if {@code stackTrace} is
847 * {@code null} or if any of the elements of
848 * {@code stackTrace} are {@code null}
849 *
850 * @since 1.4
851 */
852 public void setStackTrace(StackTraceElement[] stackTrace) {
853 Objects.requireNonNull(stackTrace);
854
855 if (this.stackTrace == null) // Immutable stack
856 return;
857
858 StackTraceElement[] defensiveCopy = stackTrace.clone();
859 for (int i = 0; i < defensiveCopy.length; i++) {
860 if (defensiveCopy[i] == null)
861 throw new NullPointerException("stackTrace[" + i + "]");
862 }
863
864 synchronized (this) {
865 this.stackTrace = defensiveCopy;
866 }
867 }
868
869 /**
870 * Returns the number of elements in the stack trace (or 0 if the stack
871 * trace is unavailable).
872 *
873 * package-protection for use by SharedSecrets.
874 */
875 native int getStackTraceDepth();
876
877 /**
878 * Returns the specified element of the stack trace.
879 *
880 * package-protection for use by SharedSecrets.
881 *
882 * @param index index of the element to return.
883 * @throws IndexOutOfBoundsException if {@code index < 0 ||
884 * index >= getStackTraceDepth() }
885 */
886 native StackTraceElement getStackTraceElement(int index);
887
888 /**
889 * Reads a {@code Throwable} from a stream, enforcing
890 * well-formedness constraints on fields. Null entries and
891 * self-pointers are not allowed in the list of {@code
892 * suppressedExceptions}. Null entries are not allowed for stack
893 * trace elements. A single-element stack trace whose entry is
894 * equal to {@code new StackTraceElement("", "", null,
895 * Integer.MIN_VALUE)} results in a {@code null} {@code
896 * stackTrace} field.
897 *
898 * Note that there are no constraints on the value the {@code
899 * cause} field can hold; both {@code null} and {@code this} are
900 * valid values for the field.
901 */
902 private void readObject(ObjectInputStream s)
903 throws IOException, ClassNotFoundException {
904 s.defaultReadObject(); // read in all fields
905 if (suppressedExceptions != null) {
906 List<Throwable> suppressed = null;
907 if (suppressedExceptions.isEmpty()) {
908 // Use the sentinel for a zero-length list
909 suppressed = SUPPRESSED_SENTINEL;
910 } else { // Copy Throwables to new list
911 suppressed = new ArrayList<>(1);
912 for (Throwable t : suppressedExceptions) {
913 // Enforce constraints on suppressed exceptions in
914 // case of corrupt or malicious stream.
915 if (t == null)
916 throw new NullPointerException(NULL_CAUSE_MESSAGE);
917 if (t == this)
918 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE);
919 suppressed.add(t);
920 }
921 }
922 suppressedExceptions = suppressed;
923 } // else a null suppressedExceptions field remains null
924
925 // Check for the marker of an immutable stack trace
926 if (stackTrace != null) {
927 // Share zero-length stack traces
928 if (stackTrace.length == 0) {
929 stackTrace = EMPTY_STACK;
930 } else if (stackTrace.length == 1 &&
931 SentinelHolder.STACK_TRACE_ELEMENT_SENTINEL.equals(stackTrace[0])) {
932 stackTrace = null;
933 } else { // Verify stack trace elements are non-null.
934 for(StackTraceElement ste : stackTrace) {
935 if (ste == null)
936 throw new NullPointerException("null StackTraceElement in serial stream. ");
937 }
938 }
939 }
940 // A null stackTrace field in the serial form can result from
941 // an exception serialized without that field. Such exceptions
942 // are now treated as having immutable stack traces.
943 }
944
945 /**
946 * Write a {@code Throwable} object to a stream.
947 *
948 * A {@code null} stack trace field is represented in the serial
949 * form as a one-element array whose element is equal to {@code
950 * new StackTraceElement("", "", null, Integer.MIN_VALUE)}.
951 */
952 private synchronized void writeObject(ObjectOutputStream s)
953 throws IOException {
954 // Ensure that the stackTrace field is initialized to a
955 // non-null value, if appropriate. As of JDK 7, a null stack
956 // trace field is a valid value indicating the stack trace
957 // should not be set.
958 getOurStackTrace();
959 ObjectOutputStream.PutField fields = s.putFields();
960
961 fields.put("detailMessage", detailMessage);
962 fields.put("cause", cause);
963 // Serialize a null stacktrace using the stack trace sentinel.
964 if (stackTrace == null)
965 fields.put("stackTrace", SentinelHolder.STACK_TRACE_SENTINEL);
966 else
967 fields.put("stackTrace", stackTrace);
968 fields.put("suppressedExceptions", suppressedExceptions);
969
970 s.writeFields();
971 }
972
973 /**
974 * Appends the specified exception to the exceptions that were
975 * suppressed in order to deliver this exception. This method is
976 * typically called (automatically and implicitly) by the {@code
977 * try}-with-resources statement.
978 *
979 * <p>The suppression behavior is enabled <em>unless</em> disabled
980 * {@linkplain #Throwable(String, Throwable, boolean) via a
981 * constructor}. When suppression is disabled, this method does
982 * nothing other than to validate its argument.
983 *
984 * <p>Note that when one exception {@linkplain
985 * #initCause(Throwable) causes} another exception, the first
986 * exception is usually caught and then the second exception is
987 * thrown in response. In other words, there is a causal
988 * connection between the two exceptions.
989 *
990 * In contrast, there are situations where two independent
991 * exceptions can be thrown in sibling code blocks, in particular
992 * in the {@code try} block of a {@code try}-with-resources
993 * statement and the compiler-generated {@code finally} block
994 * which closes the resource.
995 *
996 * In these situations, only one of the thrown exceptions can be
997 * propagated. In the {@code try}-with-resources statement, when
998 * there are two such exceptions, the exception originating from
999 * the {@code try} block is propagated and the exception from the
1000 * {@code finally} block is added to the list of exceptions
1001 * suppressed by the exception from the {@code try} block. As an
1002 * exception unwinds the stack, it can accumulate multiple
1003 * suppressed exceptions.
1004 *
1005 * <p>An exception may have suppressed exceptions while also being
1006 * caused by another exception. Whether or not an exception has a
1007 * cause is semantically known at the time of its creation, unlike
1008 * whether or not an exception will suppress other exceptions
1009 * which is typically only determined after an exception is
1010 * thrown.
1011 *
1012 * <p>Note that programmer written code is also able to take
1013 * advantage of calling this method in situations where there are
1014 * multiple sibling exceptions and only one can be propagated.
1015 *
1016 * @param exception the exception to be added to the list of
1017 * suppressed exceptions
1018 * @throws IllegalArgumentException if {@code exception} is this
1019 * throwable; a throwable cannot suppress itself.
1020 * @throws NullPointerException if {@code exception} is {@code null}
1021 * @since 1.7
1022 */
1023 public final synchronized void addSuppressed(Throwable exception) {
1024 if (exception == this)
1025 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE);
1026
1027 if (exception == null)
1028 throw new NullPointerException(NULL_CAUSE_MESSAGE);
1029
1030 if (suppressedExceptions == null) // Suppressed exceptions not recorded
1031 return;
1032
1033 if (suppressedExceptions == SUPPRESSED_SENTINEL)
1034 suppressedExceptions = new ArrayList<>(1);
1035
1036 suppressedExceptions.add(exception);
1037 }
1038
1039 private static final Throwable[] EMPTY_THROWABLE_ARRAY = new Throwable[0];
1040
1041 /**
1042 * Returns an array containing all of the exceptions that were
1043 * suppressed, typically by the {@code try}-with-resources
1044 * statement, in order to deliver this exception.
1045 *
1046 * If no exceptions were suppressed or {@linkplain
1047 * #Throwable(String, Throwable, boolean) suppression is disabled},
1048 * an empty array is returned.
1049 *
1050 * @return an array containing all of the exceptions that were
1051 * suppressed to deliver this exception.
1052 * @since 1.7
1053 */
1054 public final synchronized Throwable[] getSuppressed() {
1055 if (suppressedExceptions == SUPPRESSED_SENTINEL ||
1056 suppressedExceptions == null)
1057 return EMPTY_THROWABLE_ARRAY;
1058 else
1059 return suppressedExceptions.toArray(EMPTY_THROWABLE_ARRAY);
1060 }
1061 }