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, and {@linkplain #addSuppressed suppression} enabled or
330 * disabled. If suppression is disabled, {@link #getSuppressed}
331 * for this object will return a zero-length array and calls to
332 * {@link #addSuppressed} that would otherwise append an exception
333 * to the suppressed list will have no effect.
334 *
335 * <p>Note that the other constructors of {@code Throwable} treat
336 * suppression as being enabled. Subclasses of {@code Throwable}
337 * should document any conditions under which suppression is
338 * disabled. Disabling of suppression should only occur in
339 * exceptional circumstances where special requirements exist,
340 * such as a virtual machine reusing exception objects under
341 * low-memory situations.
342 *
343 * @param message the detail message.
344 * @param cause the cause. (A {@code null} value is permitted,
345 * and indicates that the cause is nonexistent or unknown.)
346 * @param enableSuppression whether or not suppression is enabled or disabled
347 *
348 * @see OutOfMemoryError
349 * @see NullPointerException
350 * @see ArithmeticException
351 * @since 1.7
352 */
353 protected Throwable(String message, Throwable cause,
354 boolean enableSuppression) {
355 fillInStackTrace();
356 detailMessage = message;
357 this.cause = cause;
358 if (!enableSuppression)
359 suppressedExceptions = null;
360 }
361
362 /**
363 * Returns the detail message string of this throwable.
364 *
365 * @return the detail message string of this {@code Throwable} instance
366 * (which may be {@code null}).
367 */
368 public String getMessage() {
369 return detailMessage;
370 }
371
372 /**
373 * Creates a localized description of this throwable.
374 * Subclasses may override this method in order to produce a
375 * locale-specific message. For subclasses that do not override this
376 * method, the default implementation returns the same result as
377 * {@code getMessage()}.
378 *
379 * @return The localized description of this throwable.
380 * @since JDK1.1
381 */
382 public String getLocalizedMessage() {
383 return getMessage();
384 }
385
386 /**
387 * Returns the cause of this throwable or {@code null} if the
388 * cause is nonexistent or unknown. (The cause is the throwable that
389 * caused this throwable to get thrown.)
390 *
391 * <p>This implementation returns the cause that was supplied via one of
392 * the constructors requiring a {@code Throwable}, or that was set after
393 * creation with the {@link #initCause(Throwable)} method. While it is
394 * typically unnecessary to override this method, a subclass can override
395 * it to return a cause set by some other means. This is appropriate for
396 * a "legacy chained throwable" that predates the addition of chained
397 * exceptions to {@code Throwable}. Note that it is <i>not</i>
398 * necessary to override any of the {@code PrintStackTrace} methods,
399 * all of which invoke the {@code getCause} method to determine the
400 * cause of a throwable.
401 *
402 * @return the cause of this throwable or {@code null} if the
403 * cause is nonexistent or unknown.
404 * @since 1.4
405 */
406 public synchronized Throwable getCause() {
407 return (cause==this ? null : cause);
408 }
409
410 /**
411 * Initializes the <i>cause</i> of this throwable to the specified value.
412 * (The cause is the throwable that caused this throwable to get thrown.)
413 *
414 * <p>This method can be called at most once. It is generally called from
415 * within the constructor, or immediately after creating the
416 * throwable. If this throwable was created
417 * with {@link #Throwable(Throwable)} or
418 * {@link #Throwable(String,Throwable)}, this method cannot be called
419 * even once.
420 *
421 * @param cause the cause (which is saved for later retrieval by the
422 * {@link #getCause()} method). (A {@code null} value is
423 * permitted, and indicates that the cause is nonexistent or
424 * unknown.)
425 * @return a reference to this {@code Throwable} instance.
426 * @throws IllegalArgumentException if {@code cause} is this
427 * throwable. (A throwable cannot be its own cause.)
428 * @throws IllegalStateException if this throwable was
429 * created with {@link #Throwable(Throwable)} or
430 * {@link #Throwable(String,Throwable)}, or this method has already
431 * been called on this throwable.
432 * @since 1.4
433 */
434 public synchronized Throwable initCause(Throwable cause) {
435 if (this.cause != this)
436 throw new IllegalStateException("Can't overwrite cause");
437 if (cause == this)
438 throw new IllegalArgumentException("Self-causation not permitted");
439 this.cause = cause;
440 return this;
441 }
442
443 /**
444 * Returns a short description of this throwable.
445 * The result is the concatenation of:
446 * <ul>
447 * <li> the {@linkplain Class#getName() name} of the class of this object
448 * <li> ": " (a colon and a space)
449 * <li> the result of invoking this object's {@link #getLocalizedMessage}
450 * method
451 * </ul>
452 * If {@code getLocalizedMessage} returns {@code null}, then just
453 * the class name is returned.
454 *
455 * @return a string representation of this throwable.
456 */
457 public String toString() {
458 String s = getClass().getName();
459 String message = getLocalizedMessage();
460 return (message != null) ? (s + ": " + message) : s;
461 }
462
463 /**
464 * Prints this throwable and its backtrace to the
465 * standard error stream. This method prints a stack trace for this
466 * {@code Throwable} object on the error output stream that is
467 * the value of the field {@code System.err}. The first line of
468 * output contains the result of the {@link #toString()} method for
469 * this object. Remaining lines represent data previously recorded by
470 * the method {@link #fillInStackTrace()}. The format of this
471 * information depends on the implementation, but the following
472 * example may be regarded as typical:
473 * <blockquote><pre>
474 * java.lang.NullPointerException
475 * at MyClass.mash(MyClass.java:9)
476 * at MyClass.crunch(MyClass.java:6)
477 * at MyClass.main(MyClass.java:3)
478 * </pre></blockquote>
479 * This example was produced by running the program:
480 * <pre>
481 * class MyClass {
482 * public static void main(String[] args) {
483 * crunch(null);
484 * }
485 * static void crunch(int[] a) {
486 * mash(a);
487 * }
488 * static void mash(int[] b) {
489 * System.out.println(b[0]);
490 * }
491 * }
492 * </pre>
493 * The backtrace for a throwable with an initialized, non-null cause
494 * should generally include the backtrace for the cause. The format
495 * of this information depends on the implementation, but the following
496 * example may be regarded as typical:
497 * <pre>
498 * HighLevelException: MidLevelException: LowLevelException
499 * at Junk.a(Junk.java:13)
500 * at Junk.main(Junk.java:4)
501 * Caused by: MidLevelException: LowLevelException
502 * at Junk.c(Junk.java:23)
503 * at Junk.b(Junk.java:17)
504 * at Junk.a(Junk.java:11)
505 * ... 1 more
506 * Caused by: LowLevelException
507 * at Junk.e(Junk.java:30)
508 * at Junk.d(Junk.java:27)
509 * at Junk.c(Junk.java:21)
510 * ... 3 more
511 * </pre>
512 * Note the presence of lines containing the characters {@code "..."}.
513 * These lines indicate that the remainder of the stack trace for this
514 * exception matches the indicated number of frames from the bottom of the
515 * stack trace of the exception that was caused by this exception (the
516 * "enclosing" exception). This shorthand can greatly reduce the length
517 * of the output in the common case where a wrapped exception is thrown
518 * from same method as the "causative exception" is caught. The above
519 * example was produced by running the program:
520 * <pre>
521 * public class Junk {
522 * public static void main(String args[]) {
523 * try {
524 * a();
525 * } catch(HighLevelException e) {
526 * e.printStackTrace();
527 * }
528 * }
529 * static void a() throws HighLevelException {
530 * try {
531 * b();
532 * } catch(MidLevelException e) {
533 * throw new HighLevelException(e);
534 * }
535 * }
536 * static void b() throws MidLevelException {
537 * c();
538 * }
539 * static void c() throws MidLevelException {
540 * try {
541 * d();
542 * } catch(LowLevelException e) {
543 * throw new MidLevelException(e);
544 * }
545 * }
546 * static void d() throws LowLevelException {
547 * e();
548 * }
549 * static void e() throws LowLevelException {
550 * throw new LowLevelException();
551 * }
552 * }
553 *
554 * class HighLevelException extends Exception {
555 * HighLevelException(Throwable cause) { super(cause); }
556 * }
557 *
558 * class MidLevelException extends Exception {
559 * MidLevelException(Throwable cause) { super(cause); }
560 * }
561 *
562 * class LowLevelException extends Exception {
563 * }
564 * </pre>
565 * As of release 7, the platform supports the notion of
566 * <i>suppressed exceptions</i> (in conjunction with the {@code
567 * try}-with-resources statement). Any exceptions that were
568 * suppressed in order to deliver an exception are printed out
569 * beneath the stack trace. The format of this information
570 * depends on the implementation, but the following example may be
571 * regarded as typical:
572 *
573 * <pre>
574 * Exception in thread "main" java.lang.Exception: Something happened
575 * at Foo.bar(Foo.java:10)
576 * at Foo.main(Foo.java:5)
577 * Suppressed: Resource$CloseFailException: Resource ID = 0
578 * at Resource.close(Resource.java:26)
579 * at Foo.bar(Foo.java:9)
580 * ... 1 more
581 * </pre>
582 * Note that the "... n more" notation is used on suppressed exceptions
583 * just at it is used on causes. Unlike causes, suppressed exceptions are
584 * indented beyond their "containing exceptions."
585 *
586 * <p>An exception can have both a cause and one or more suppressed
587 * exceptions:
588 * <pre>
589 * Exception in thread "main" java.lang.Exception: Main block
590 * at Foo3.main(Foo3.java:7)
591 * Suppressed: Resource$CloseFailException: Resource ID = 2
592 * at Resource.close(Resource.java:26)
593 * at Foo3.main(Foo3.java:5)
594 * Suppressed: Resource$CloseFailException: Resource ID = 1
595 * at Resource.close(Resource.java:26)
596 * at Foo3.main(Foo3.java:5)
597 * Caused by: java.lang.Exception: I did it
598 * at Foo3.main(Foo3.java:8)
599 * </pre>
600 * Likewise, a suppressed exception can have a cause:
601 * <pre>
602 * Exception in thread "main" java.lang.Exception: Main block
603 * at Foo4.main(Foo4.java:6)
604 * Suppressed: Resource2$CloseFailException: Resource ID = 1
605 * at Resource2.close(Resource2.java:20)
606 * at Foo4.main(Foo4.java:5)
607 * Caused by: java.lang.Exception: Rats, you caught me
608 * at Resource2$CloseFailException.<init>(Resource2.java:45)
609 * ... 2 more
610 * </pre>
611 */
612 public void printStackTrace() {
613 printStackTrace(System.err);
614 }
615
616 /**
617 * Prints this throwable and its backtrace to the specified print stream.
618 *
619 * @param s {@code PrintStream} to use for output
620 */
621 public void printStackTrace(PrintStream s) {
622 printStackTrace(new WrappedPrintStream(s));
623 }
624
625 private void printStackTrace(PrintStreamOrWriter s) {
626 // Guard against malicious overrides of Throwable.equals by
627 // using a Set with identity equality semantics.
628 Set<Throwable> dejaVu =
629 Collections.newSetFromMap(new IdentityHashMap<Throwable, Boolean>());
630 dejaVu.add(this);
631
632 synchronized (s.lock()) {
633 // Print our stack trace
634 s.println(this);
635 StackTraceElement[] trace = getOurStackTrace();
636 for (StackTraceElement traceElement : trace)
637 s.println("\tat " + traceElement);
638
639 // Print suppressed exceptions, if any
640 for (Throwable se : getSuppressed())
641 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, "\t", dejaVu);
642
643 // Print cause, if any
644 Throwable ourCause = getCause();
645 if (ourCause != null)
646 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, "", dejaVu);
647 }
648 }
649
650 /**
651 * Print our stack trace as an enclosed exception for the specified
652 * stack trace.
653 */
654 private void printEnclosedStackTrace(PrintStreamOrWriter s,
655 StackTraceElement[] enclosingTrace,
656 String caption,
657 String prefix,
658 Set<Throwable> dejaVu) {
659 assert Thread.holdsLock(s.lock());
660 if (dejaVu.contains(this)) {
661 s.println("\t[CIRCULAR REFERENCE:" + this + "]");
662 } else {
663 dejaVu.add(this);
664 // Compute number of frames in common between this and enclosing trace
665 StackTraceElement[] trace = getOurStackTrace();
666 int m = trace.length - 1;
667 int n = enclosingTrace.length - 1;
668 while (m >= 0 && n >=0 && trace[m].equals(enclosingTrace[n])) {
669 m--; n--;
670 }
671 int framesInCommon = trace.length - 1 - m;
672
673 // Print our stack trace
674 s.println(prefix + caption + this);
675 for (int i = 0; i <= m; i++)
676 s.println(prefix + "\tat " + trace[i]);
677 if (framesInCommon != 0)
678 s.println(prefix + "\t... " + framesInCommon + " more");
679
680 // Print suppressed exceptions, if any
681 for (Throwable se : getSuppressed())
682 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION,
683 prefix +"\t", dejaVu);
684
685 // Print cause, if any
686 Throwable ourCause = getCause();
687 if (ourCause != null)
688 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, prefix, dejaVu);
689 }
690 }
691
692 /**
693 * Prints this throwable and its backtrace to the specified
694 * print writer.
695 *
696 * @param s {@code PrintWriter} to use for output
697 * @since JDK1.1
698 */
699 public void printStackTrace(PrintWriter s) {
700 printStackTrace(new WrappedPrintWriter(s));
701 }
702
703 /**
704 * Wrapper class for PrintStream and PrintWriter to enable a single
705 * implementation of printStackTrace.
706 */
707 private abstract static class PrintStreamOrWriter {
708 /** Returns the object to be locked when using this StreamOrWriter */
709 abstract Object lock();
710
711 /** Prints the specified string as a line on this StreamOrWriter */
712 abstract void println(Object o);
713 }
714
715 private static class WrappedPrintStream extends PrintStreamOrWriter {
716 private final PrintStream printStream;
717
718 WrappedPrintStream(PrintStream printStream) {
719 this.printStream = printStream;
720 }
721
722 Object lock() {
723 return printStream;
724 }
725
726 void println(Object o) {
727 printStream.println(o);
728 }
729 }
730
731 private static class WrappedPrintWriter extends PrintStreamOrWriter {
732 private final PrintWriter printWriter;
733
734 WrappedPrintWriter(PrintWriter printWriter) {
735 this.printWriter = printWriter;
736 }
737
738 Object lock() {
739 return printWriter;
740 }
741
742 void println(Object o) {
743 printWriter.println(o);
744 }
745 }
746
747 /**
748 * Fills in the execution stack trace. This method records within this
749 * {@code Throwable} object information about the current state of
750 * the stack frames for the current thread.
751 *
752 * <p>If the stack trace of this {@code Throwable} {@linkplain
753 * Throwable#setStackTrace(StackTraceElement[]) has been set} to
754 * {@code null}, calling this method has no effect.
755 *
756 * @return a reference to this {@code Throwable} instance.
757 * @see java.lang.Throwable#printStackTrace()
758 */
759 public synchronized Throwable fillInStackTrace() {
760 if (stackTrace != null) {
761 fillInStackTrace(0);
762 stackTrace = FILLED_IN_STACK;
763 }
764 return this;
765 }
766
767 private native Throwable fillInStackTrace(int dummy);
768
769 /**
770 * Provides programmatic access to the stack trace information printed by
771 * {@link #printStackTrace()}. Returns an array of stack trace elements,
772 * each representing one stack frame. The zeroth element of the array
773 * (assuming the array's length is non-zero) represents the top of the
774 * stack, which is the last method invocation in the sequence. Typically,
775 * this is the point at which this throwable was created and thrown.
776 * The last element of the array (assuming the array's length is non-zero)
777 * represents the bottom of the stack, which is the first method invocation
778 * in the sequence.
779 *
780 * <p>Some virtual machines may, under some circumstances, omit one
781 * or more stack frames from the stack trace. In the extreme case,
782 * a virtual machine that has no stack trace information concerning
783 * this throwable is permitted to return a zero-length array from this
784 * method. Generally speaking, the array returned by this method will
785 * contain one element for every frame that would be printed by
786 * {@code printStackTrace}.
787 *
788 * @return an array of stack trace elements representing the stack trace
789 * pertaining to this throwable.
790 * @since 1.4
791 */
792 public StackTraceElement[] getStackTrace() {
793 return getOurStackTrace().clone();
794 }
795
796 private synchronized StackTraceElement[] getOurStackTrace() {
797 // Initialize stack trace field with information from
798 // backtrace if this is the first call to this method
799 if (stackTrace == FILLED_IN_STACK) {
800 int depth = getStackTraceDepth();
801 stackTrace = new StackTraceElement[depth];
802 for (int i=0; i < depth; i++)
803 stackTrace[i] = getStackTraceElement(i);
804 } else if (stackTrace == null) {
805 return EMPTY_STACK;
806 }
807 return stackTrace;
808 }
809
810 /**
811 * Sets the stack trace elements that will be returned by
812 * {@link #getStackTrace()} and printed by {@link #printStackTrace()}
813 * and related methods.
814 *
815 * This method, which is designed for use by RPC frameworks and other
816 * advanced systems, allows the client to override the default
817 * stack trace that is either generated by {@link #fillInStackTrace()}
818 * when a throwable is constructed or deserialized when a throwable is
819 * read from a serialization stream.
820 *
821 * <p>If the stack trace is set to {@code null}, then future calls
822 * to this method have no effect on this {@code Throwable}.
823 *
824 * @param stackTrace the stack trace elements to be associated with
825 * this {@code Throwable}. The specified array is copied by this
826 * call; changes in the specified array after the method invocation
827 * returns will have no affect on this {@code Throwable}'s stack
828 * trace.
829 *
830 * @throws NullPointerException if any of the elements of
831 * {@code stackTrace} are {@code null}
832 *
833 * @since 1.4
834 */
835 public void setStackTrace(StackTraceElement[] stackTrace) {
836 if (this.stackTrace == null) // Immutable stack
837 return;
838
839 StackTraceElement[] defensiveCopy;
840
841 if (stackTrace == null) {
842 defensiveCopy = stackTrace;
843 } else {
844 defensiveCopy = stackTrace.clone();
845
846 for (int i = 0; i < defensiveCopy.length; i++) {
847 if (defensiveCopy[i] == null)
848 throw new NullPointerException("stackTrace[" + i + "]");
849 }
850 }
851
852 synchronized (this) {
853 this.stackTrace = defensiveCopy;
854 }
855 }
856
857 /**
858 * Returns the number of elements in the stack trace (or 0 if the stack
859 * trace is unavailable).
860 *
861 * package-protection for use by SharedSecrets.
862 */
863 native int getStackTraceDepth();
864
865 /**
866 * Returns the specified element of the stack trace.
867 *
868 * package-protection for use by SharedSecrets.
869 *
870 * @param index index of the element to return.
871 * @throws IndexOutOfBoundsException if {@code index < 0 ||
872 * index >= getStackTraceDepth() }
873 */
874 native StackTraceElement getStackTraceElement(int index);
875
876 /**
877 * Reads a {@code Throwable} from a stream, enforcing
878 * well-formedness constraints on fields. Null entries and
879 * self-pointers are not allowed in the list of {@code
880 * suppressedExceptions}. Null entries are not allowed for stack
881 * trace elements. A single-element stack trace whose entry is
882 * equal to {@code new StackTraceElement("", "", null,
883 * Integer.MIN_VALUE)} results in a {@code null} {@code
884 * stackTrace} field.
885 *
886 * Note that there are no constraints on the value the {@code
887 * cause} field can hold; both {@code null} and {@code this} are
888 * valid values for the field.
889 */
890 private void readObject(ObjectInputStream s)
891 throws IOException, ClassNotFoundException {
892 s.defaultReadObject(); // read in all fields
893 if (suppressedExceptions != null) {
894 List<Throwable> suppressed = null;
895 if (suppressedExceptions.isEmpty()) {
896 // Use the sentinel for a zero-length list
897 suppressed = SUPPRESSED_SENTINEL;
898 } else { // Copy Throwables to new list
899 suppressed = new ArrayList<>(1);
900 for (Throwable t : suppressedExceptions) {
901 // Enforce constraints on suppressed exceptions in
902 // case of corrupt or malicious stream.
903 if (t == null)
904 throw new NullPointerException(NULL_CAUSE_MESSAGE);
905 if (t == this)
906 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE);
907 suppressed.add(t);
908 }
909 }
910 suppressedExceptions = suppressed;
911 } // else a null suppressedExceptions field remains null
912
913 // Check for the marker of an immutable stack trace
914 if (stackTrace != null) {
915 // Share zero-length stack traces
916 if (stackTrace.length == 0) {
917 stackTrace = EMPTY_STACK;
918 } else if (stackTrace.length == 1 &&
919 SentinelHolder.STACK_TRACE_ELEMENT_SENTINEL.equals(stackTrace[0])) {
920 stackTrace = null;
921 } else { // Verify stack trace elements are non-null.
922 for(StackTraceElement ste : stackTrace) {
923 if (ste == null)
924 throw new NullPointerException("null StackTraceElement in serial stream. ");
925 }
926 }
927 }
928 // A null stackTrace field in the serial form can result from
929 // an exception serialized without that field. Such exceptions
930 // are now treated as having immutable stack traces.
931 }
932
933 /**
934 * Write a {@code Throwable} object to a stream.
935 *
936 * A {@code null} stack trace field is represented in the serial
937 * form as a one-element array whose element is equal to {@code
938 * new StackTraceElement("", "", null, Integer.MIN_VALUE)}.
939 */
940 private synchronized void writeObject(ObjectOutputStream s)
941 throws IOException {
942 // Ensure that the stackTrace field is initialized to a
943 // non-null value, if appropriate. As of JDK 7, a null stack
944 // trace field is a valid value indicating the stack trace
945 // should not be set.
946 getOurStackTrace();
947 ObjectOutputStream.PutField fields = s.putFields();
948
949 fields.put("detailMessage", detailMessage);
950 fields.put("cause", cause);
951 // Serialize a null stacktrace using the stack trace sentinel.
952 if (stackTrace == null)
953 fields.put("stackTrace", SentinelHolder.STACK_TRACE_SENTINEL);
954 else
955 fields.put("stackTrace", stackTrace);
956 fields.put("suppressedExceptions", suppressedExceptions);
957
958 s.writeFields();
959 }
960
961 /**
962 * Appends the specified exception to the exceptions that were
963 * suppressed in order to deliver this exception. This method is
964 * typically called (automatically and implicitly) by the {@code
965 * try}-with-resources statement.
966 *
967 * <p>The suppression behavior is enabled <em>unless</em> disabled
968 * {@linkplain #Throwable(String, Throwable, boolean) via a
969 * constructor}. When suppression is disabled, this method does
970 * nothing other than to validate its argument.
971 *
972 * <p>Note that when one exception {@linkplain
973 * #initCause(Throwable) causes} another exception, the first
974 * exception is usually caught and then the second exception is
975 * thrown in response. In other words, there is a causal
976 * connection between the two exceptions.
977 *
978 * In contrast, there are situations where two independent
979 * exceptions can be thrown in sibling code blocks, in particular
980 * in the {@code try} block of a {@code try}-with-resources
981 * statement and the compiler-generated {@code finally} block
982 * which closes the resource.
983 *
984 * In these situations, only one of the thrown exceptions can be
985 * propagated. In the {@code try}-with-resources statement, when
986 * there are two such exceptions, the exception originating from
987 * the {@code try} block is propagated and the exception from the
988 * {@code finally} block is added to the list of exceptions
989 * suppressed by the exception from the {@code try} block. As an
990 * exception unwinds the stack, it can accumulate multiple
991 * suppressed exceptions.
992 *
993 * <p>An exception may have suppressed exceptions while also being
994 * caused by another exception. Whether or not an exception has a
995 * cause is semantically known at the time of its creation, unlike
996 * whether or not an exception will suppress other exceptions
997 * which is typically only determined after an exception is
998 * thrown.
999 *
1000 * <p>Note that programmer written code is also able to take
1001 * advantage of calling this method in situations where there are
1002 * multiple sibling exceptions and only one can be propagated.
1003 *
1004 * @param exception the exception to be added to the list of
1005 * suppressed exceptions
1006 * @throws IllegalArgumentException if {@code exception} is this
1007 * throwable; a throwable cannot suppress itself.
1008 * @throws NullPointerException if {@code exception} is {@code null}
1009 * @since 1.7
1010 */
1011 public final synchronized void addSuppressed(Throwable exception) {
1012 if (exception == this)
1013 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE);
1014
1015 if (exception == null)
1016 throw new NullPointerException(NULL_CAUSE_MESSAGE);
1017
1018 if (suppressedExceptions == null) // Suppressed exceptions not recorded
1019 return;
1020
1021 if (suppressedExceptions == SUPPRESSED_SENTINEL)
1022 suppressedExceptions = new ArrayList<>(1);
1023
1024 suppressedExceptions.add(exception);
1025 }
1026
1027 private static final Throwable[] EMPTY_THROWABLE_ARRAY = new Throwable[0];
1028
1029 /**
1030 * Returns an array containing all of the exceptions that were
1031 * suppressed, typically by the {@code try}-with-resources
1032 * statement, in order to deliver this exception.
1033 *
1034 * If no exceptions were suppressed or {@linkplain
1035 * #Throwable(String, Throwable, boolean) suppression is disabled},
1036 * an empty array is returned.
1037 *
1038 * @return an array containing all of the exceptions that were
1039 * suppressed to deliver this exception.
1040 * @since 1.7
1041 */
1042 public final synchronized Throwable[] getSuppressed() {
1043 if (suppressedExceptions == SUPPRESSED_SENTINEL ||
1044 suppressedExceptions == null)
1045 return EMPTY_THROWABLE_ARRAY;
1046 else
1047 return suppressedExceptions.toArray(EMPTY_THROWABLE_ARRAY);
1048 }
1049 }