1 /*
2 * Copyright (c) 1994, 2013, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.lang;
27 import java.io.*;
28 import java.util.*;
29 import java.util.function.Consumer;
30 import java.util.function.Function;
31 import java.util.function.Predicate;
32 import java.util.stream.Collector;
33
34 /**
35 * The {@code Throwable} class is the superclass of all errors and
36 * exceptions in the Java language. Only objects that are instances of this
37 * class (or one of its subclasses) are thrown by the Java Virtual Machine or
38 * can be thrown by the Java {@code throw} statement. Similarly, only
39 * this class or one of its subclasses can be the argument type in a
40 * {@code catch} clause.
41 *
42 * For the purposes of compile-time checking of exceptions, {@code
43 * Throwable} and any subclass of {@code Throwable} that is not also a
44 * subclass of either {@link RuntimeException} or {@link Error} are
45 * regarded as checked exceptions.
46 *
47 * <p>Instances of two subclasses, {@link java.lang.Error} and
48 * {@link java.lang.Exception}, are conventionally used to indicate
49 * that exceptional situations have occurred. Typically, these instances
50 * are freshly created in the context of the exceptional situation so
51 * as to include relevant information (such as stack trace data).
52 *
53 * <p>A throwable contains a snapshot of the execution stack of its
54 * thread at the time it was created. It can also contain a message
55 * string that gives more information about the error. Over time, a
56 * throwable can {@linkplain Throwable#addSuppressed suppress} other
57 * throwables from being propagated. Finally, the throwable can also
58 * contain a <i>cause</i>: another throwable that caused this
59 * throwable to be constructed. The recording of this causal information
60 * is referred to as the <i>chained exception</i> facility, as the
61 * cause can, itself, have a cause, and so on, leading to a "chain" of
62 * exceptions, each caused by another.
63 *
64 * <p>One reason that a throwable may have a cause is that the class that
65 * throws it is built atop a lower layered abstraction, and an operation on
66 * the upper layer fails due to a failure in the lower layer. It would be bad
67 * design to let the throwable thrown by the lower layer propagate outward, as
68 * it is generally unrelated to the abstraction provided by the upper layer.
69 * Further, doing so would tie the API of the upper layer to the details of
70 * its implementation, assuming the lower layer's exception was a checked
71 * exception. Throwing a "wrapped exception" (i.e., an exception containing a
72 * cause) allows the upper layer to communicate the details of the failure to
73 * its caller without incurring either of these shortcomings. It preserves
74 * the flexibility to change the implementation of the upper layer without
75 * changing its API (in particular, the set of exceptions thrown by its
76 * methods).
77 *
78 * <p>A second reason that a throwable may have a cause is that the method
79 * that throws it must conform to a general-purpose interface that does not
80 * permit the method to throw the cause directly. For example, suppose
81 * a persistent collection conforms to the {@link java.util.Collection
82 * Collection} interface, and that its persistence is implemented atop
83 * {@code java.io}. Suppose the internals of the {@code add} method
84 * can throw an {@link java.io.IOException IOException}. The implementation
85 * can communicate the details of the {@code IOException} to its caller
86 * while conforming to the {@code Collection} interface by wrapping the
87 * {@code IOException} in an appropriate unchecked exception. (The
88 * specification for the persistent collection should indicate that it is
89 * capable of throwing such exceptions.)
90 *
91 * <p>A cause can be associated with a throwable in two ways: via a
92 * constructor that takes the cause as an argument, or via the
93 * {@link #initCause(Throwable)} method. New throwable classes that
94 * wish to allow causes to be associated with them should provide constructors
95 * that take a cause and delegate (perhaps indirectly) to one of the
96 * {@code Throwable} constructors that takes a cause.
97 *
98 * Because the {@code initCause} method is public, it allows a cause to be
99 * associated with any throwable, even a "legacy throwable" whose
100 * implementation predates the addition of the exception chaining mechanism to
101 * {@code Throwable}.
102 *
103 * <p>By convention, class {@code Throwable} and its subclasses have two
104 * constructors, one that takes no arguments and one that takes a
105 * {@code String} argument that can be used to produce a detail message.
106 * Further, those subclasses that might likely have a cause associated with
107 * them should have two more constructors, one that takes a
108 * {@code Throwable} (the cause), and one that takes a
109 * {@code String} (the detail message) and a {@code Throwable} (the
110 * cause).
111 *
112 * @author unascribed
113 * @author Josh Bloch (Added exception chaining and programmatic access to
114 * stack trace in 1.4.)
115 * @jls 11.2 Compile-Time Checking of Exceptions
116 * @since JDK1.0
117 */
118 public class Throwable implements Serializable {
119 /** use serialVersionUID from JDK 1.0.2 for interoperability */
120 private static final long serialVersionUID = -3042686055658047285L;
121
122 /**
123 * Native code saves some indication of the stack backtrace in this slot.
124 */
125 private transient Object backtrace;
126
127 /**
128 * Specific details about the Throwable. For example, for
129 * {@code FileNotFoundException}, this contains the name of
130 * the file that could not be found.
131 *
132 * @serial
133 */
134 private String detailMessage;
135
136
137 /**
138 * Holder class to defer initializing sentinel objects only used
139 * for serialization.
140 */
141 private static class SentinelHolder {
142 /**
143 * {@linkplain #setStackTrace(StackTraceElement[]) Setting the
144 * stack trace} to a one-element array containing this sentinel
145 * value indicates future attempts to set the stack trace will be
146 * ignored. The sentinal is equal to the result of calling:<br>
147 * {@code new StackTraceElement("", "", null, Integer.MIN_VALUE)}
148 */
149 public static final StackTraceElement STACK_TRACE_ELEMENT_SENTINEL =
150 new StackTraceElement("", "", null, Integer.MIN_VALUE);
151
152 /**
153 * Sentinel value used in the serial form to indicate an immutable
154 * stack trace.
155 */
156 public static final StackTraceElement[] STACK_TRACE_SENTINEL =
157 new StackTraceElement[] {STACK_TRACE_ELEMENT_SENTINEL};
158 }
159
160 /**
161 * A shared value for an empty stack.
162 */
163 private static final StackTraceElement[] UNASSIGNED_STACK = new StackTraceElement[0];
164
165 /*
166 * To allow Throwable objects to be made immutable and safely
167 * reused by the JVM, such as OutOfMemoryErrors, fields of
168 * Throwable that are writable in response to user actions, cause,
169 * stackTrace, and suppressedExceptions obey the following
170 * protocol:
171 *
172 * 1) The fields are initialized to a non-null sentinel value
173 * which indicates the value has logically not been set.
174 *
175 * 2) Writing a null to the field indicates further writes
176 * are forbidden
177 *
178 * 3) The sentinel value may be replaced with another non-null
179 * value.
180 *
181 * For example, implementations of the HotSpot JVM have
182 * preallocated OutOfMemoryError objects to provide for better
183 * diagnosability of that situation. These objects are created
184 * without calling the constructor for that class and the fields
185 * in question are initialized to null. To support this
186 * capability, any new fields added to Throwable that require
187 * being initialized to a non-null value require a coordinated JVM
188 * change.
189 */
190
191 /**
192 * The throwable that caused this throwable to get thrown, or null if this
193 * throwable was not caused by another throwable, or if the causative
194 * throwable is unknown. If this field is equal to this throwable itself,
195 * it indicates that the cause of this throwable has not yet been
196 * initialized.
197 *
198 * @serial
199 * @since 1.4
200 */
201 private Throwable cause = this;
202
203 /**
204 * The stack trace, as returned by {@link #getStackTrace()}.
205 *
206 * The field is initialized to a zero-length array. A {@code
207 * null} value of this field indicates subsequent calls to {@link
208 * #setStackTrace(StackTraceElement[])} and {@link
209 * #fillInStackTrace()} will be be no-ops.
210 *
211 * @serial
212 * @since 1.4
213 */
214 private StackTraceElement[] stackTrace = UNASSIGNED_STACK;
215
216 // Setting this static field introduces an acceptable
217 // initialization dependency on a few java.util classes.
218 private static final List<Throwable> SUPPRESSED_SENTINEL =
219 Collections.unmodifiableList(new ArrayList<Throwable>(0));
220
221 /**
222 * The list of suppressed exceptions, as returned by {@link
223 * #getSuppressed()}. The list is initialized to a zero-element
224 * unmodifiable sentinel list. When a serialized Throwable is
225 * read in, if the {@code suppressedExceptions} field points to a
226 * zero-element list, the field is reset to the sentinel value.
227 *
228 * @serial
229 * @since 1.7
230 */
231 private List<Throwable> suppressedExceptions = SUPPRESSED_SENTINEL;
232
233 /** Message for trying to suppress a null exception. */
234 private static final String NULL_CAUSE_MESSAGE = "Cannot suppress a null exception.";
235
236 /** Message for trying to suppress oneself. */
237 private static final String SELF_SUPPRESSION_MESSAGE = "Self-suppression not permitted";
238
239 /** Caption for labeling causative exception stack traces */
240 private static final String CAUSE_CAPTION = "Caused by: ";
241
242 /** Caption for labeling suppressed exception stack traces */
243 private static final String SUPPRESSED_CAPTION = "Suppressed: ";
244
245 /**
246 * Constructs a new throwable with {@code null} as its detail message.
247 * The cause is not initialized, and may subsequently be initialized by a
248 * call to {@link #initCause}.
249 *
250 * <p>The {@link #fillInStackTrace()} method is called to initialize
251 * the stack trace data in the newly created throwable.
252 */
253 public Throwable() {
254 fillInStackTrace();
255 }
256
257 /**
258 * Constructs a new throwable with the specified detail message. The
259 * cause is not initialized, and may subsequently be initialized by
260 * a call to {@link #initCause}.
261 *
262 * <p>The {@link #fillInStackTrace()} method is called to initialize
263 * the stack trace data in the newly created throwable.
264 *
265 * @param message the detail message. The detail message is saved for
266 * later retrieval by the {@link #getMessage()} method.
267 */
268 public Throwable(String message) {
269 fillInStackTrace();
270 detailMessage = message;
271 }
272
273 /**
274 * Constructs a new throwable with the specified detail message and
275 * cause. <p>Note that the detail message associated with
276 * {@code cause} is <i>not</i> automatically incorporated in
277 * this throwable's detail message.
278 *
279 * <p>The {@link #fillInStackTrace()} method is called to initialize
280 * the stack trace data in the newly created throwable.
281 *
282 * @param message the detail message (which is saved for later retrieval
283 * by the {@link #getMessage()} method).
284 * @param cause the cause (which is saved for later retrieval by the
285 * {@link #getCause()} method). (A {@code null} value is
286 * permitted, and indicates that the cause is nonexistent or
287 * unknown.)
288 * @since 1.4
289 */
290 public Throwable(String message, Throwable cause) {
291 fillInStackTrace();
292 detailMessage = message;
293 this.cause = cause;
294 }
295
296 /**
297 * Constructs a new throwable with the specified cause and a detail
298 * message of {@code (cause==null ? null : cause.toString())} (which
299 * typically contains the class and detail message of {@code cause}).
300 * This constructor is useful for throwables that are little more than
301 * wrappers for other throwables (for example, {@link
302 * java.security.PrivilegedActionException}).
303 *
304 * <p>The {@link #fillInStackTrace()} method is called to initialize
305 * the stack trace data in the newly created throwable.
306 *
307 * @param cause the cause (which is saved for later retrieval by the
308 * {@link #getCause()} method). (A {@code null} value is
309 * permitted, and indicates that the cause is nonexistent or
310 * unknown.)
311 * @since 1.4
312 */
313 public Throwable(Throwable cause) {
314 fillInStackTrace();
315 detailMessage = (cause==null ? null : cause.toString());
316 this.cause = cause;
317 }
318
319 /**
320 * Constructs a new throwable with the specified detail message,
321 * cause, {@linkplain #addSuppressed suppression} enabled or
322 * disabled, and writable stack trace enabled or disabled. If
323 * suppression is disabled, {@link #getSuppressed} for this object
324 * will return a zero-length array and calls to {@link
325 * #addSuppressed} that would otherwise append an exception to the
326 * suppressed list will have no effect. If the writable stack
327 * trace is false, this constructor will not call {@link
328 * #fillInStackTrace()}, a {@code null} will be written to the
329 * {@code stackTrace} field, and subsequent calls to {@code
330 * fillInStackTrace} and {@link
331 * #setStackTrace(StackTraceElement[])} will not set the stack
332 * trace. If the writable stack trace is false, {@link
333 * #getStackTrace} will return a zero length array.
334 *
335 * <p>Note that the other constructors of {@code Throwable} treat
336 * suppression as being enabled and the stack trace as being
337 * writable. Subclasses of {@code Throwable} should document any
338 * conditions under which suppression is disabled and document
339 * conditions under which the stack trace is not writable.
340 * Disabling of suppression should only occur in exceptional
341 * circumstances where special requirements exist, such as a
342 * virtual machine reusing exception objects under low-memory
343 * situations. Circumstances where a given exception object is
344 * repeatedly caught and rethrown, such as to implement control
345 * flow between two sub-systems, is another situation where
346 * immutable throwable objects would be appropriate.
347 *
348 * @param message the detail message.
349 * @param cause the cause. (A {@code null} value is permitted,
350 * and indicates that the cause is nonexistent or unknown.)
351 * @param enableSuppression whether or not suppression is enabled or disabled
352 * @param writableStackTrace whether or not the stack trace should be
353 * writable
354 *
355 * @see OutOfMemoryError
356 * @see NullPointerException
357 * @see ArithmeticException
358 * @since 1.7
359 */
360 protected Throwable(String message, Throwable cause,
361 boolean enableSuppression,
362 boolean writableStackTrace) {
363 if (writableStackTrace) {
364 fillInStackTrace();
365 } else {
366 stackTrace = null;
367 }
368 detailMessage = message;
369 this.cause = cause;
370 if (!enableSuppression)
371 suppressedExceptions = null;
372 }
373
374 /**
375 * Returns the detail message string of this throwable.
376 *
377 * @return the detail message string of this {@code Throwable} instance
378 * (which may be {@code null}).
379 */
380 public String getMessage() {
381 return detailMessage;
382 }
383
384 /**
385 * Creates a localized description of this throwable.
386 * Subclasses may override this method in order to produce a
387 * locale-specific message. For subclasses that do not override this
388 * method, the default implementation returns the same result as
389 * {@code getMessage()}.
390 *
391 * @return The localized description of this throwable.
392 * @since JDK1.1
393 */
394 public String getLocalizedMessage() {
395 return getMessage();
396 }
397
398 /**
399 * Returns the cause of this throwable or {@code null} if the
400 * cause is nonexistent or unknown. (The cause is the throwable that
401 * caused this throwable to get thrown.)
402 *
403 * <p>This implementation returns the cause that was supplied via one of
404 * the constructors requiring a {@code Throwable}, or that was set after
405 * creation with the {@link #initCause(Throwable)} method. While it is
406 * typically unnecessary to override this method, a subclass can override
407 * it to return a cause set by some other means. This is appropriate for
408 * a "legacy chained throwable" that predates the addition of chained
409 * exceptions to {@code Throwable}. Note that it is <i>not</i>
410 * necessary to override any of the {@code PrintStackTrace} methods,
411 * all of which invoke the {@code getCause} method to determine the
412 * cause of a throwable.
413 *
414 * @return the cause of this throwable or {@code null} if the
415 * cause is nonexistent or unknown.
416 * @since 1.4
417 */
418 public synchronized Throwable getCause() {
419 return (cause==this ? null : cause);
420 }
421
422 /**
423 * Initializes the <i>cause</i> of this throwable to the specified value.
424 * (The cause is the throwable that caused this throwable to get thrown.)
425 *
426 * <p>This method can be called at most once. It is generally called from
427 * within the constructor, or immediately after creating the
428 * throwable. If this throwable was created
429 * with {@link #Throwable(Throwable)} or
430 * {@link #Throwable(String,Throwable)}, this method cannot be called
431 * even once.
432 *
433 * <p>An example of using this method on a legacy throwable type
434 * without other support for setting the cause is:
435 *
436 * <pre>
437 * try {
438 * lowLevelOp();
439 * } catch (LowLevelException le) {
440 * throw (HighLevelException)
441 * new HighLevelException().initCause(le); // Legacy constructor
442 * }
443 * </pre>
444 *
445 * @param cause the cause (which is saved for later retrieval by the
446 * {@link #getCause()} method). (A {@code null} value is
447 * permitted, and indicates that the cause is nonexistent or
448 * unknown.)
449 * @return a reference to this {@code Throwable} instance.
450 * @throws IllegalArgumentException if {@code cause} is this
451 * throwable. (A throwable cannot be its own cause.)
452 * @throws IllegalStateException if this throwable was
453 * created with {@link #Throwable(Throwable)} or
454 * {@link #Throwable(String,Throwable)}, or this method has already
455 * been called on this throwable.
456 * @since 1.4
457 */
458 public synchronized Throwable initCause(Throwable cause) {
459 if (this.cause != this)
460 throw new IllegalStateException("Can't overwrite cause with " +
461 Objects.toString(cause, "a null"), this);
462 if (cause == this)
463 throw new IllegalArgumentException("Self-causation not permitted", this);
464 this.cause = cause;
465 return this;
466 }
467
468 /**
469 * Returns a short description of this throwable.
470 * The result is the concatenation of:
471 * <ul>
472 * <li> the {@linkplain Class#getName() name} of the class of this object
473 * <li> ": " (a colon and a space)
474 * <li> the result of invoking this object's {@link #getLocalizedMessage}
475 * method
476 * </ul>
477 * If {@code getLocalizedMessage} returns {@code null}, then just
478 * the class name is returned.
479 *
480 * @return a string representation of this throwable.
481 */
482 public String toString() {
483 String s = getClass().getName();
484 String message = getLocalizedMessage();
485 return (message != null) ? (s + ": " + message) : s;
486 }
487
488 /**
489 * Prints this throwable and its backtrace to the
490 * standard error stream. This method prints a stack trace for this
491 * {@code Throwable} object on the error output stream that is
492 * the value of the field {@code System.err}. The first line of
493 * output contains the result of the {@link #toString()} method for
494 * this object. Remaining lines represent data previously recorded by
495 * the method {@link #fillInStackTrace()}. The format of this
496 * information depends on the implementation, but the following
497 * example may be regarded as typical:
498 * <blockquote><pre>
499 * java.lang.NullPointerException
500 * at MyClass.mash(MyClass.java:9)
501 * at MyClass.crunch(MyClass.java:6)
502 * at MyClass.main(MyClass.java:3)
503 * </pre></blockquote>
504 * This example was produced by running the program:
505 * <pre>
506 * class MyClass {
507 * public static void main(String[] args) {
508 * crunch(null);
509 * }
510 * static void crunch(int[] a) {
511 * mash(a);
512 * }
513 * static void mash(int[] b) {
514 * System.out.println(b[0]);
515 * }
516 * }
517 * </pre>
518 * The backtrace for a throwable with an initialized, non-null cause
519 * should generally include the backtrace for the cause. The format
520 * of this information depends on the implementation, but the following
521 * example may be regarded as typical:
522 * <pre>
523 * HighLevelException: MidLevelException: LowLevelException
524 * at Junk.a(Junk.java:13)
525 * at Junk.main(Junk.java:4)
526 * Caused by: MidLevelException: LowLevelException
527 * at Junk.c(Junk.java:23)
528 * at Junk.b(Junk.java:17)
529 * at Junk.a(Junk.java:11)
530 * ... 1 more
531 * Caused by: LowLevelException
532 * at Junk.e(Junk.java:30)
533 * at Junk.d(Junk.java:27)
534 * at Junk.c(Junk.java:21)
535 * ... 3 more
536 * </pre>
537 * Note the presence of lines containing the characters {@code "..."}.
538 * These lines indicate that the remainder of the stack trace for this
539 * exception matches the indicated number of frames from the bottom of the
540 * stack trace of the exception that was caused by this exception (the
541 * "enclosing" exception). This shorthand can greatly reduce the length
542 * of the output in the common case where a wrapped exception is thrown
543 * from same method as the "causative exception" is caught. The above
544 * example was produced by running the program:
545 * <pre>
546 * public class Junk {
547 * public static void main(String args[]) {
548 * try {
549 * a();
550 * } catch(HighLevelException e) {
551 * e.printStackTrace();
552 * }
553 * }
554 * static void a() throws HighLevelException {
555 * try {
556 * b();
557 * } catch(MidLevelException e) {
558 * throw new HighLevelException(e);
559 * }
560 * }
561 * static void b() throws MidLevelException {
562 * c();
563 * }
564 * static void c() throws MidLevelException {
565 * try {
566 * d();
567 * } catch(LowLevelException e) {
568 * throw new MidLevelException(e);
569 * }
570 * }
571 * static void d() throws LowLevelException {
572 * e();
573 * }
574 * static void e() throws LowLevelException {
575 * throw new LowLevelException();
576 * }
577 * }
578 *
579 * class HighLevelException extends Exception {
580 * HighLevelException(Throwable cause) { super(cause); }
581 * }
582 *
583 * class MidLevelException extends Exception {
584 * MidLevelException(Throwable cause) { super(cause); }
585 * }
586 *
587 * class LowLevelException extends Exception {
588 * }
589 * </pre>
590 * As of release 7, the platform supports the notion of
591 * <i>suppressed exceptions</i> (in conjunction with the {@code
592 * try}-with-resources statement). Any exceptions that were
593 * suppressed in order to deliver an exception are printed out
594 * beneath the stack trace. The format of this information
595 * depends on the implementation, but the following example may be
596 * regarded as typical:
597 *
598 * <pre>
599 * Exception in thread "main" java.lang.Exception: Something happened
600 * at Foo.bar(Foo.java:10)
601 * at Foo.main(Foo.java:5)
602 * Suppressed: Resource$CloseFailException: Resource ID = 0
603 * at Resource.close(Resource.java:26)
604 * at Foo.bar(Foo.java:9)
605 * ... 1 more
606 * </pre>
607 * Note that the "... n more" notation is used on suppressed exceptions
608 * just at it is used on causes. Unlike causes, suppressed exceptions are
609 * indented beyond their "containing exceptions."
610 *
611 * <p>An exception can have both a cause and one or more suppressed
612 * exceptions:
613 * <pre>
614 * Exception in thread "main" java.lang.Exception: Main block
615 * at Foo3.main(Foo3.java:7)
616 * Suppressed: Resource$CloseFailException: Resource ID = 2
617 * at Resource.close(Resource.java:26)
618 * at Foo3.main(Foo3.java:5)
619 * Suppressed: Resource$CloseFailException: Resource ID = 1
620 * at Resource.close(Resource.java:26)
621 * at Foo3.main(Foo3.java:5)
622 * Caused by: java.lang.Exception: I did it
623 * at Foo3.main(Foo3.java:8)
624 * </pre>
625 * Likewise, a suppressed exception can have a cause:
626 * <pre>
627 * Exception in thread "main" java.lang.Exception: Main block
628 * at Foo4.main(Foo4.java:6)
629 * Suppressed: Resource2$CloseFailException: Resource ID = 1
630 * at Resource2.close(Resource2.java:20)
631 * at Foo4.main(Foo4.java:5)
632 * Caused by: java.lang.Exception: Rats, you caught me
633 * at Resource2$CloseFailException.<init>(Resource2.java:45)
634 * ... 2 more
635 * </pre>
636 */
637 public void printStackTrace() {
638 printStackTrace(System.err);
639 }
640
641 /**
642 * Prints this throwable and its backtrace to the specified print stream.
643 *
644 * @param s {@code PrintStream} to use for output
645 */
646 public void printStackTrace(PrintStream s) {
647 printStackTrace(new WrappedPrintStream(s));
648 }
649
650 private void printStackTrace(PrintStreamOrWriter s) {
651 // Guard against malicious overrides of Throwable.equals by
652 // using a Set with identity equality semantics.
653 Set<Throwable> dejaVu =
654 Collections.newSetFromMap(new IdentityHashMap<Throwable, Boolean>());
655 dejaVu.add(this);
656
657 synchronized (s.lock()) {
658 // Print our stack trace
659 s.println(this);
660 StackTraceElement[] trace = getOurStackTrace();
661 for (StackTraceElement traceElement : trace)
662 s.println("\tat " + traceElement);
663
664 // Print suppressed exceptions, if any
665 for (Throwable se : getSuppressed())
666 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, "\t", dejaVu);
667
668 // Print cause, if any
669 Throwable ourCause = getCause();
670 if (ourCause != null)
671 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, "", dejaVu);
672 }
673 }
674
675 /**
676 * Print our stack trace as an enclosed exception for the specified
677 * stack trace.
678 */
679 private void printEnclosedStackTrace(PrintStreamOrWriter s,
680 StackTraceElement[] enclosingTrace,
681 String caption,
682 String prefix,
683 Set<Throwable> dejaVu) {
684 assert Thread.holdsLock(s.lock());
685 if (dejaVu.contains(this)) {
686 s.println("\t[CIRCULAR REFERENCE:" + this + "]");
687 } else {
688 dejaVu.add(this);
689 // Compute number of frames in common between this and enclosing trace
690 StackTraceElement[] trace = getOurStackTrace();
691 int m = trace.length - 1;
692 int n = enclosingTrace.length - 1;
693 while (m >= 0 && n >=0 && trace[m].equals(enclosingTrace[n])) {
694 m--; n--;
695 }
696 int framesInCommon = trace.length - 1 - m;
697
698 // Print our stack trace
699 s.println(prefix + caption + this);
700 for (int i = 0; i <= m; i++)
701 s.println(prefix + "\tat " + trace[i]);
702 if (framesInCommon != 0)
703 s.println(prefix + "\t... " + framesInCommon + " more");
704
705 // Print suppressed exceptions, if any
706 for (Throwable se : getSuppressed())
707 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION,
708 prefix +"\t", dejaVu);
709
710 // Print cause, if any
711 Throwable ourCause = getCause();
712 if (ourCause != null)
713 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, prefix, dejaVu);
714 }
715 }
716
717 /**
718 * Prints this throwable and its backtrace to the specified
719 * print writer.
720 *
721 * @param s {@code PrintWriter} to use for output
722 * @since JDK1.1
723 */
724 public void printStackTrace(PrintWriter s) {
725 printStackTrace(new WrappedPrintWriter(s));
726 }
727
728 /**
729 * Wrapper class for PrintStream and PrintWriter to enable a single
730 * implementation of printStackTrace.
731 */
732 private abstract static class PrintStreamOrWriter {
733 /** Returns the object to be locked when using this StreamOrWriter */
734 abstract Object lock();
735
736 /** Prints the specified string as a line on this StreamOrWriter */
737 abstract void println(Object o);
738 }
739
740 private static class WrappedPrintStream extends PrintStreamOrWriter {
741 private final PrintStream printStream;
742
743 WrappedPrintStream(PrintStream printStream) {
744 this.printStream = printStream;
745 }
746
747 Object lock() {
748 return printStream;
749 }
750
751 void println(Object o) {
752 printStream.println(o);
753 }
754 }
755
756 private static class WrappedPrintWriter extends PrintStreamOrWriter {
757 private final PrintWriter printWriter;
758
759 WrappedPrintWriter(PrintWriter printWriter) {
760 this.printWriter = printWriter;
761 }
762
763 Object lock() {
764 return printWriter;
765 }
766
767 void println(Object o) {
768 printWriter.println(o);
769 }
770 }
771
772 /**
773 * Fills in the execution stack trace. This method records within this
774 * {@code Throwable} object information about the current state of
775 * the stack frames for the current thread.
776 *
777 * <p>If the stack trace of this {@code Throwable} {@linkplain
778 * Throwable#Throwable(String, Throwable, boolean, boolean) is not
779 * writable}, calling this method has no effect.
780 *
781 * @return a reference to this {@code Throwable} instance.
782 * @see java.lang.Throwable#printStackTrace()
783 */
784 public synchronized Throwable fillInStackTrace() {
785 if (stackTrace != null ||
786 backtrace != null /* Out of protocol state */ ) {
787 fillInStackTrace(0);
788 stackTrace = UNASSIGNED_STACK;
789 }
790 return this;
791 }
792
793 private native Throwable fillInStackTrace(int dummy);
794
795 /**
796 * Provides programmatic access to the stack trace information printed by
797 * {@link #printStackTrace()}. Returns an array of stack trace elements,
798 * each representing one stack frame. The zeroth element of the array
799 * (assuming the array's length is non-zero) represents the top of the
800 * stack, which is the last method invocation in the sequence. Typically,
801 * this is the point at which this throwable was created and thrown.
802 * The last element of the array (assuming the array's length is non-zero)
803 * represents the bottom of the stack, which is the first method invocation
804 * in the sequence.
805 *
806 * <p>Some virtual machines may, under some circumstances, omit one
807 * or more stack frames from the stack trace. In the extreme case,
808 * a virtual machine that has no stack trace information concerning
809 * this throwable is permitted to return a zero-length array from this
810 * method. Generally speaking, the array returned by this method will
811 * contain one element for every frame that would be printed by
812 * {@code printStackTrace}. Writes to the returned array do not
813 * affect future calls to this method.
814 *
815 * @return an array of stack trace elements representing the stack trace
816 * pertaining to this throwable.
817 * @since 1.4
818 */
819 public StackTraceElement[] getStackTrace() {
820 return getOurStackTrace().clone();
821 }
822
823 /**
824 * Performs the given action for each {@code StackFrameInfo} representing
825 * a stack trace element of this stack trace.
826 *
827 * @param action a consumer traversing a stream of StackFrameInfo
828 *
829 * @throws SecurityException if a security manager exists and its
830 * {@code checkPermission} method denies access to traverse stack.
831 * @throws UnsupportedOperationException if this object is not thrown by
832 * the running Java virtual machine.
833 *
834 * @since 1.8
835 */
836 public <T> void walkStackTrace(Consumer<StackFrameInfo> action) {
837 if (backtrace == null)
838 throw new UnsupportedOperationException();
839
840 Thread.checkStackWalkPermission();
841 StackStream.build(getStackTrace()).walk(action);
842 }
843
844 /**
845 * Performs the given action for each {@linkplain StackFrameInfo stack frames}
846 * representing a stack trace element of this stack trace
847 * that match the given predicate.
848 *
849 * @param predicate a predicate to apply to the stack walk
850 * @param action a consumer traversing a stream of StackFrameInfo
851 *
852 * @throws SecurityException if a security manager exists and its
853 * {@code checkPermission} method denies access to traverse stack.
854 * @throws UnsupportedOperationException if this object is not thrown by
855 * the running Java virtual machine.
856 * @since 1.8
857 */
858 public void walkStackTrace(Predicate<StackFrameInfo> predicate,
859 Consumer<StackFrameInfo> action) {
860 if (backtrace == null)
861 throw new UnsupportedOperationException();
862 Thread.checkStackWalkPermission();
863 StackStream.build(getStackTrace()).walk(predicate, action);
864 }
865
866 private synchronized StackTraceElement[] getOurStackTrace() {
867 // Initialize stack trace field with information from
868 // backtrace if this is the first call to this method
869 if (stackTrace == UNASSIGNED_STACK ||
870 (stackTrace == null && backtrace != null) /* Out of protocol state */) {
871 int depth = getStackTraceDepth();
872 stackTrace = new StackTraceElement[depth];
873 for (int i=0; i < depth; i++)
874 stackTrace[i] = getStackTraceElement(i);
875 } else if (stackTrace == null) {
876 return UNASSIGNED_STACK;
877 }
878 return stackTrace;
879 }
880
881 /**
882 * Sets the stack trace elements that will be returned by
883 * {@link #getStackTrace()} and printed by {@link #printStackTrace()}
884 * and related methods.
885 *
886 * This method, which is designed for use by RPC frameworks and other
887 * advanced systems, allows the client to override the default
888 * stack trace that is either generated by {@link #fillInStackTrace()}
889 * when a throwable is constructed or deserialized when a throwable is
890 * read from a serialization stream.
891 *
892 * <p>If the stack trace of this {@code Throwable} {@linkplain
893 * Throwable#Throwable(String, Throwable, boolean, boolean) is not
894 * writable}, calling this method has no effect other than
895 * validating its argument.
896 *
897 * @param stackTrace the stack trace elements to be associated with
898 * this {@code Throwable}. The specified array is copied by this
899 * call; changes in the specified array after the method invocation
900 * returns will have no affect on this {@code Throwable}'s stack
901 * trace.
902 *
903 * @throws NullPointerException if {@code stackTrace} is
904 * {@code null} or if any of the elements of
905 * {@code stackTrace} are {@code null}
906 *
907 * @since 1.4
908 */
909 public void setStackTrace(StackTraceElement[] stackTrace) {
910 // Validate argument
911 StackTraceElement[] defensiveCopy = stackTrace.clone();
912 for (int i = 0; i < defensiveCopy.length; i++) {
913 if (defensiveCopy[i] == null)
914 throw new NullPointerException("stackTrace[" + i + "]");
915 }
916
917 synchronized (this) {
918 if (this.stackTrace == null && // Immutable stack
919 backtrace == null) // Test for out of protocol state
920 return;
921 this.stackTrace = defensiveCopy;
922 }
923 }
924
925 /**
926 * Returns the number of elements in the stack trace (or 0 if the stack
927 * trace is unavailable).
928 *
929 * package-protection for use by SharedSecrets.
930 */
931 native int getStackTraceDepth();
932
933 /**
934 * Returns the specified element of the stack trace.
935 *
936 * package-protection for use by SharedSecrets.
937 *
938 * @param index index of the element to return.
939 * @throws IndexOutOfBoundsException if {@code index < 0 ||
940 * index >= getStackTraceDepth() }
941 */
942 native StackTraceElement getStackTraceElement(int index);
943
944 /**
945 * Reads a {@code Throwable} from a stream, enforcing
946 * well-formedness constraints on fields. Null entries and
947 * self-pointers are not allowed in the list of {@code
948 * suppressedExceptions}. Null entries are not allowed for stack
949 * trace elements. A null stack trace in the serial form results
950 * in a zero-length stack element array. A single-element stack
951 * trace whose entry is equal to {@code new StackTraceElement("",
952 * "", null, Integer.MIN_VALUE)} results in a {@code null} {@code
953 * stackTrace} field.
954 *
955 * Note that there are no constraints on the value the {@code
956 * cause} field can hold; both {@code null} and {@code this} are
957 * valid values for the field.
958 */
959 private void readObject(ObjectInputStream s)
960 throws IOException, ClassNotFoundException {
961 s.defaultReadObject(); // read in all fields
962 if (suppressedExceptions != null) {
963 List<Throwable> suppressed = null;
964 if (suppressedExceptions.isEmpty()) {
965 // Use the sentinel for a zero-length list
966 suppressed = SUPPRESSED_SENTINEL;
967 } else { // Copy Throwables to new list
968 suppressed = new ArrayList<>(1);
969 for (Throwable t : suppressedExceptions) {
970 // Enforce constraints on suppressed exceptions in
971 // case of corrupt or malicious stream.
972 if (t == null)
973 throw new NullPointerException(NULL_CAUSE_MESSAGE);
974 if (t == this)
975 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE);
976 suppressed.add(t);
977 }
978 }
979 suppressedExceptions = suppressed;
980 } // else a null suppressedExceptions field remains null
981
982 /*
983 * For zero-length stack traces, use a clone of
984 * UNASSIGNED_STACK rather than UNASSIGNED_STACK itself to
985 * allow identity comparison against UNASSIGNED_STACK in
986 * getOurStackTrace. The identity of UNASSIGNED_STACK in
987 * stackTrace indicates to the getOurStackTrace method that
988 * the stackTrace needs to be constructed from the information
989 * in backtrace.
990 */
991 if (stackTrace != null) {
992 if (stackTrace.length == 0) {
993 stackTrace = UNASSIGNED_STACK.clone();
994 } else if (stackTrace.length == 1 &&
995 // Check for the marker of an immutable stack trace
996 SentinelHolder.STACK_TRACE_ELEMENT_SENTINEL.equals(stackTrace[0])) {
997 stackTrace = null;
998 } else { // Verify stack trace elements are non-null.
999 for(StackTraceElement ste : stackTrace) {
1000 if (ste == null)
1001 throw new NullPointerException("null StackTraceElement in serial stream. ");
1002 }
1003 }
1004 } else {
1005 // A null stackTrace field in the serial form can result
1006 // from an exception serialized without that field in
1007 // older JDK releases; treat such exceptions as having
1008 // empty stack traces.
1009 stackTrace = UNASSIGNED_STACK.clone();
1010 }
1011 }
1012
1013 /**
1014 * Write a {@code Throwable} object to a stream.
1015 *
1016 * A {@code null} stack trace field is represented in the serial
1017 * form as a one-element array whose element is equal to {@code
1018 * new StackTraceElement("", "", null, Integer.MIN_VALUE)}.
1019 */
1020 private synchronized void writeObject(ObjectOutputStream s)
1021 throws IOException {
1022 // Ensure that the stackTrace field is initialized to a
1023 // non-null value, if appropriate. As of JDK 7, a null stack
1024 // trace field is a valid value indicating the stack trace
1025 // should not be set.
1026 getOurStackTrace();
1027
1028 StackTraceElement[] oldStackTrace = stackTrace;
1029 try {
1030 if (stackTrace == null)
1031 stackTrace = SentinelHolder.STACK_TRACE_SENTINEL;
1032 s.defaultWriteObject();
1033 } finally {
1034 stackTrace = oldStackTrace;
1035 }
1036 }
1037
1038 /**
1039 * Appends the specified exception to the exceptions that were
1040 * suppressed in order to deliver this exception. This method is
1041 * thread-safe and typically called (automatically and implicitly)
1042 * by the {@code try}-with-resources statement.
1043 *
1044 * <p>The suppression behavior is enabled <em>unless</em> disabled
1045 * {@linkplain #Throwable(String, Throwable, boolean, boolean) via
1046 * a constructor}. When suppression is disabled, this method does
1047 * nothing other than to validate its argument.
1048 *
1049 * <p>Note that when one exception {@linkplain
1050 * #initCause(Throwable) causes} another exception, the first
1051 * exception is usually caught and then the second exception is
1052 * thrown in response. In other words, there is a causal
1053 * connection between the two exceptions.
1054 *
1055 * In contrast, there are situations where two independent
1056 * exceptions can be thrown in sibling code blocks, in particular
1057 * in the {@code try} block of a {@code try}-with-resources
1058 * statement and the compiler-generated {@code finally} block
1059 * which closes the resource.
1060 *
1061 * In these situations, only one of the thrown exceptions can be
1062 * propagated. In the {@code try}-with-resources statement, when
1063 * there are two such exceptions, the exception originating from
1064 * the {@code try} block is propagated and the exception from the
1065 * {@code finally} block is added to the list of exceptions
1066 * suppressed by the exception from the {@code try} block. As an
1067 * exception unwinds the stack, it can accumulate multiple
1068 * suppressed exceptions.
1069 *
1070 * <p>An exception may have suppressed exceptions while also being
1071 * caused by another exception. Whether or not an exception has a
1072 * cause is semantically known at the time of its creation, unlike
1073 * whether or not an exception will suppress other exceptions
1074 * which is typically only determined after an exception is
1075 * thrown.
1076 *
1077 * <p>Note that programmer written code is also able to take
1078 * advantage of calling this method in situations where there are
1079 * multiple sibling exceptions and only one can be propagated.
1080 *
1081 * @param exception the exception to be added to the list of
1082 * suppressed exceptions
1083 * @throws IllegalArgumentException if {@code exception} is this
1084 * throwable; a throwable cannot suppress itself.
1085 * @throws NullPointerException if {@code exception} is {@code null}
1086 * @since 1.7
1087 */
1088 public final synchronized void addSuppressed(Throwable exception) {
1089 if (exception == this)
1090 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE, exception);
1091
1092 if (exception == null)
1093 throw new NullPointerException(NULL_CAUSE_MESSAGE);
1094
1095 if (suppressedExceptions == null) // Suppressed exceptions not recorded
1096 return;
1097
1098 if (suppressedExceptions == SUPPRESSED_SENTINEL)
1099 suppressedExceptions = new ArrayList<>(1);
1100
1101 suppressedExceptions.add(exception);
1102 }
1103
1104 private static final Throwable[] EMPTY_THROWABLE_ARRAY = new Throwable[0];
1105
1106 /**
1107 * Returns an array containing all of the exceptions that were
1108 * suppressed, typically by the {@code try}-with-resources
1109 * statement, in order to deliver this exception.
1110 *
1111 * If no exceptions were suppressed or {@linkplain
1112 * #Throwable(String, Throwable, boolean, boolean) suppression is
1113 * disabled}, an empty array is returned. This method is
1114 * thread-safe. Writes to the returned array do not affect future
1115 * calls to this method.
1116 *
1117 * @return an array containing all of the exceptions that were
1118 * suppressed to deliver this exception.
1119 * @since 1.7
1120 */
1121 public final synchronized Throwable[] getSuppressed() {
1122 if (suppressedExceptions == SUPPRESSED_SENTINEL ||
1123 suppressedExceptions == null)
1124 return EMPTY_THROWABLE_ARRAY;
1125 else
1126 return suppressedExceptions.toArray(EMPTY_THROWABLE_ARRAY);
1127 }
1128 }