1 /*
2 * Copyright (c) 1994, 2019, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.lang;
27
28 import java.io.*;
29 import java.util.*;
30
31 /**
32 * The {@code Throwable} class is the superclass of all errors and
33 * exceptions in the Java language. Only objects that are instances of this
34 * class (or one of its subclasses) are thrown by the Java Virtual Machine or
35 * can be thrown by the Java {@code throw} statement. Similarly, only
36 * this class or one of its subclasses can be the argument type in a
37 * {@code catch} clause.
38 *
39 * For the purposes of compile-time checking of exceptions, {@code
40 * Throwable} and any subclass of {@code Throwable} that is not also a
41 * subclass of either {@link RuntimeException} or {@link Error} are
42 * regarded as checked exceptions.
43 *
44 * <p>Instances of two subclasses, {@link java.lang.Error} and
45 * {@link java.lang.Exception}, are conventionally used to indicate
46 * that exceptional situations have occurred. Typically, these instances
47 * are freshly created in the context of the exceptional situation so
48 * as to include relevant information (such as stack trace data).
49 *
50 * <p>A throwable contains a snapshot of the execution stack of its
51 * thread at the time it was created. It can also contain a message
52 * string that gives more information about the error. Over time, a
53 * throwable can {@linkplain Throwable#addSuppressed suppress} other
54 * throwables from being propagated. Finally, the throwable can also
55 * contain a <i>cause</i>: another throwable that caused this
56 * throwable to be constructed. The recording of this causal information
57 * is referred to as the <i>chained exception</i> facility, as the
58 * cause can, itself, have a cause, and so on, leading to a "chain" of
59 * exceptions, each caused by another.
60 *
61 * <p>One reason that a throwable may have a cause is that the class that
62 * throws it is built atop a lower layered abstraction, and an operation on
63 * the upper layer fails due to a failure in the lower layer. It would be bad
64 * design to let the throwable thrown by the lower layer propagate outward, as
65 * it is generally unrelated to the abstraction provided by the upper layer.
66 * Further, doing so would tie the API of the upper layer to the details of
67 * its implementation, assuming the lower layer's exception was a checked
68 * exception. Throwing a "wrapped exception" (i.e., an exception containing a
69 * cause) allows the upper layer to communicate the details of the failure to
70 * its caller without incurring either of these shortcomings. It preserves
71 * the flexibility to change the implementation of the upper layer without
72 * changing its API (in particular, the set of exceptions thrown by its
73 * methods).
74 *
75 * <p>A second reason that a throwable may have a cause is that the method
76 * that throws it must conform to a general-purpose interface that does not
77 * permit the method to throw the cause directly. For example, suppose
78 * a persistent collection conforms to the {@link java.util.Collection
79 * Collection} interface, and that its persistence is implemented atop
80 * {@code java.io}. Suppose the internals of the {@code add} method
81 * can throw an {@link java.io.IOException IOException}. The implementation
82 * can communicate the details of the {@code IOException} to its caller
83 * while conforming to the {@code Collection} interface by wrapping the
84 * {@code IOException} in an appropriate unchecked exception. (The
85 * specification for the persistent collection should indicate that it is
86 * capable of throwing such exceptions.)
87 *
88 * <p>A cause can be associated with a throwable in two ways: via a
89 * constructor that takes the cause as an argument, or via the
90 * {@link #initCause(Throwable)} method. New throwable classes that
91 * wish to allow causes to be associated with them should provide constructors
92 * that take a cause and delegate (perhaps indirectly) to one of the
93 * {@code Throwable} constructors that takes a cause.
94 *
95 * Because the {@code initCause} method is public, it allows a cause to be
96 * associated with any throwable, even a "legacy throwable" whose
97 * implementation predates the addition of the exception chaining mechanism to
98 * {@code Throwable}.
99 *
100 * <p>By convention, class {@code Throwable} and its subclasses have two
101 * constructors, one that takes no arguments and one that takes a
102 * {@code String} argument that can be used to produce a detail message.
103 * Further, those subclasses that might likely have a cause associated with
104 * them should have two more constructors, one that takes a
105 * {@code Throwable} (the cause), and one that takes a
106 * {@code String} (the detail message) and a {@code Throwable} (the
107 * cause).
108 *
109 * @author unascribed
110 * @author Josh Bloch (Added exception chaining and programmatic access to
111 * stack trace in 1.4.)
112 * @jls 11.2 Compile-Time Checking of Exceptions
113 * @since 1.0
114 */
115 public class Throwable implements Serializable {
116 /** use serialVersionUID from JDK 1.0.2 for interoperability */
117 @java.io.Serial
118 private static final long serialVersionUID = -3042686055658047285L;
119
120 /**
121 * The JVM saves some indication of the stack backtrace in this slot.
122 */
123 private transient Object backtrace;
124
125 /**
126 * Specific details about the Throwable. For example, for
127 * {@code FileNotFoundException}, this contains the name of
128 * the file that could not be found.
129 *
130 * @serial
131 */
132 private String detailMessage;
133
134
135 /**
136 * Holder class to defer initializing sentinel objects only used
137 * for serialization.
138 */
139 private static class SentinelHolder {
140 /**
141 * {@linkplain #setStackTrace(StackTraceElement[]) Setting the
142 * stack trace} to a one-element array containing this sentinel
143 * value indicates future attempts to set the stack trace will be
144 * ignored. The sentinel is equal to the result of calling:<br>
145 * {@code new StackTraceElement("", "", null, Integer.MIN_VALUE)}
146 */
147 public static final StackTraceElement STACK_TRACE_ELEMENT_SENTINEL =
148 new StackTraceElement("", "", null, Integer.MIN_VALUE);
149
150 /**
151 * Sentinel value used in the serial form to indicate an immutable
152 * stack trace.
153 */
154 public static final StackTraceElement[] STACK_TRACE_SENTINEL =
155 new StackTraceElement[] {STACK_TRACE_ELEMENT_SENTINEL};
156 }
157
158 /**
159 * A shared value for an empty stack.
160 */
161 private static final StackTraceElement[] UNASSIGNED_STACK = new StackTraceElement[0];
162
163 /*
164 * To allow Throwable objects to be made immutable and safely
165 * reused by the JVM, such as OutOfMemoryErrors, fields of
166 * Throwable that are writable in response to user actions, cause,
167 * stackTrace, and suppressedExceptions obey the following
168 * protocol:
169 *
170 * 1) The fields are initialized to a non-null sentinel value
171 * which indicates the value has logically not been set.
172 *
173 * 2) Writing a null to the field indicates further writes
174 * are forbidden
175 *
176 * 3) The sentinel value may be replaced with another non-null
177 * value.
178 *
179 * For example, implementations of the HotSpot JVM have
180 * preallocated OutOfMemoryError objects to provide for better
181 * diagnosability of that situation. These objects are created
182 * without calling the constructor for that class and the fields
183 * in question are initialized to null. To support this
184 * capability, any new fields added to Throwable that require
185 * being initialized to a non-null value require a coordinated JVM
186 * change.
187 */
188
189 /**
190 * The throwable that caused this throwable to get thrown, or null if this
191 * throwable was not caused by another throwable, or if the causative
192 * throwable is unknown. If this field is equal to this throwable itself,
193 * it indicates that the cause of this throwable has not yet been
194 * initialized.
195 *
196 * @serial
197 * @since 1.4
198 */
199 private Throwable cause = this;
200
201 /**
202 * The stack trace, as returned by {@link #getStackTrace()}.
203 *
204 * The field is initialized to a zero-length array. A {@code
205 * null} value of this field indicates subsequent calls to {@link
206 * #setStackTrace(StackTraceElement[])} and {@link
207 * #fillInStackTrace()} will be no-ops.
208 *
209 * @serial
210 * @since 1.4
211 */
212 private StackTraceElement[] stackTrace = UNASSIGNED_STACK;
213
214 /**
215 * The JVM code sets the depth of the backtrace for later retrieval
216 */
217 private transient int depth;
218
219 // Setting this static field introduces an acceptable
220 // initialization dependency on a few java.util classes.
221 private static final List<Throwable> SUPPRESSED_SENTINEL = Collections.emptyList();
222
223 /**
224 * The list of suppressed exceptions, as returned by {@link
225 * #getSuppressed()}. The list is initialized to a zero-element
226 * unmodifiable sentinel list. When a serialized Throwable is
227 * read in, if the {@code suppressedExceptions} field points to a
228 * zero-element list, the field is reset to the sentinel value.
229 *
230 * @serial
231 * @since 1.7
232 */
233 private List<Throwable> suppressedExceptions = SUPPRESSED_SENTINEL;
234
235 /** Message for trying to suppress a null exception. */
236 private static final String NULL_CAUSE_MESSAGE = "Cannot suppress a null exception.";
237
238 /** Message for trying to suppress oneself. */
239 private static final String SELF_SUPPRESSION_MESSAGE = "Self-suppression not permitted";
240
241 /** Caption for labeling causative exception stack traces */
242 private static final String CAUSE_CAPTION = "Caused by: ";
243
244 /** Caption for labeling suppressed exception stack traces */
245 private static final String SUPPRESSED_CAPTION = "Suppressed: ";
246
247 /**
248 * Constructs a new throwable with {@code null} as its detail message.
249 * The cause is not initialized, and may subsequently be initialized by a
250 * call to {@link #initCause}.
251 *
252 * <p>The {@link #fillInStackTrace()} method is called to initialize
253 * the stack trace data in the newly created throwable.
254 */
255 public Throwable() {
256 fillInStackTrace();
257 }
258
259 /**
260 * Constructs a new throwable with the specified detail message. The
261 * cause is not initialized, and may subsequently be initialized by
262 * a call to {@link #initCause}.
263 *
264 * <p>The {@link #fillInStackTrace()} method is called to initialize
265 * the stack trace data in the newly created throwable.
266 *
267 * @param message the detail message. The detail message is saved for
268 * later retrieval by the {@link #getMessage()} method.
269 */
270 public Throwable(String message) {
271 fillInStackTrace();
272 detailMessage = message;
273 }
274
275 /**
276 * Constructs a new throwable with the specified detail message and
277 * cause. <p>Note that the detail message associated with
278 * {@code cause} is <i>not</i> automatically incorporated in
279 * this throwable's detail message.
280 *
281 * <p>The {@link #fillInStackTrace()} method is called to initialize
282 * the stack trace data in the newly created throwable.
283 *
284 * @param message the detail message (which is saved for later retrieval
285 * by the {@link #getMessage()} method).
286 * @param cause the cause (which is saved for later retrieval by the
287 * {@link #getCause()} method). (A {@code null} value is
288 * permitted, and indicates that the cause is nonexistent or
289 * unknown.)
290 * @since 1.4
291 */
292 public Throwable(String message, Throwable cause) {
293 fillInStackTrace();
294 detailMessage = message;
295 this.cause = cause;
296 }
297
298 /**
299 * Constructs a new throwable with the specified cause and a detail
300 * message of {@code (cause==null ? null : cause.toString())} (which
301 * typically contains the class and detail message of {@code cause}).
302 * This constructor is useful for throwables that are little more than
303 * wrappers for other throwables (for example, {@link
304 * java.security.PrivilegedActionException}).
305 *
306 * <p>The {@link #fillInStackTrace()} method is called to initialize
307 * the stack trace data in the newly created throwable.
308 *
309 * @param cause the cause (which is saved for later retrieval by the
310 * {@link #getCause()} method). (A {@code null} value is
311 * permitted, and indicates that the cause is nonexistent or
312 * unknown.)
313 * @since 1.4
314 */
315 public Throwable(Throwable cause) {
316 fillInStackTrace();
317 detailMessage = (cause==null ? null : cause.toString());
318 this.cause = cause;
319 }
320
321 /**
322 * Constructs a new throwable with the specified detail message,
323 * cause, {@linkplain #addSuppressed suppression} enabled or
324 * disabled, and writable stack trace enabled or disabled. If
325 * suppression is disabled, {@link #getSuppressed} for this object
326 * will return a zero-length array and calls to {@link
327 * #addSuppressed} that would otherwise append an exception to the
328 * suppressed list will have no effect. If the writable stack
329 * trace is false, this constructor will not call {@link
330 * #fillInStackTrace()}, a {@code null} will be written to the
331 * {@code stackTrace} field, and subsequent calls to {@code
332 * fillInStackTrace} and {@link
333 * #setStackTrace(StackTraceElement[])} will not set the stack
334 * trace. If the writable stack trace is false, {@link
335 * #getStackTrace} will return a zero length array.
336 *
337 * <p>Note that the other constructors of {@code Throwable} treat
338 * suppression as being enabled and the stack trace as being
339 * writable. Subclasses of {@code Throwable} should document any
340 * conditions under which suppression is disabled and document
341 * conditions under which the stack trace is not writable.
342 * Disabling of suppression should only occur in exceptional
343 * circumstances where special requirements exist, such as a
344 * virtual machine reusing exception objects under low-memory
345 * situations. Circumstances where a given exception object is
346 * repeatedly caught and rethrown, such as to implement control
347 * flow between two sub-systems, is another situation where
348 * immutable throwable objects would be appropriate.
349 *
350 * @param message the detail message.
351 * @param cause the cause. (A {@code null} value is permitted,
352 * and indicates that the cause is nonexistent or unknown.)
353 * @param enableSuppression whether or not suppression is enabled or disabled
354 * @param writableStackTrace whether or not the stack trace should be
355 * writable
356 *
357 * @see OutOfMemoryError
358 * @see NullPointerException
359 * @see ArithmeticException
360 * @since 1.7
361 */
362 protected Throwable(String message, Throwable cause,
363 boolean enableSuppression,
364 boolean writableStackTrace) {
365 if (writableStackTrace) {
366 fillInStackTrace();
367 } else {
368 stackTrace = null;
369 }
370 detailMessage = message;
371 this.cause = cause;
372 if (!enableSuppression)
373 suppressedExceptions = null;
374 }
375
376 /**
377 * Returns the detail message string of this throwable.
378 *
379 * @return the detail message string of this {@code Throwable} instance
380 * (which may be {@code null}).
381 */
382 public String getMessage() {
383 return detailMessage;
384 }
385
386 /**
387 * Creates a localized description of this throwable.
388 * Subclasses may override this method in order to produce a
389 * locale-specific message. For subclasses that do not override this
390 * method, the default implementation returns the same result as
391 * {@code getMessage()}.
392 *
393 * @return The localized description of this throwable.
394 * @since 1.1
395 */
396 public String getLocalizedMessage() {
397 return getMessage();
398 }
399
400 /**
401 * Returns the cause of this throwable or {@code null} if the
402 * cause is nonexistent or unknown. (The cause is the throwable that
403 * caused this throwable to get thrown.)
404 *
405 * <p>This implementation returns the cause that was supplied via one of
406 * the constructors requiring a {@code Throwable}, or that was set after
407 * creation with the {@link #initCause(Throwable)} method. While it is
408 * typically unnecessary to override this method, a subclass can override
409 * it to return a cause set by some other means. This is appropriate for
410 * a "legacy chained throwable" that predates the addition of chained
411 * exceptions to {@code Throwable}. Note that it is <i>not</i>
412 * necessary to override any of the {@code PrintStackTrace} methods,
413 * all of which invoke the {@code getCause} method to determine the
414 * cause of a throwable.
415 *
416 * @return the cause of this throwable or {@code null} if the
417 * cause is nonexistent or unknown.
418 * @since 1.4
419 */
420 public synchronized Throwable getCause() {
421 return (cause==this ? null : cause);
422 }
423
424 /**
425 * Initializes the <i>cause</i> of this throwable to the specified value.
426 * (The cause is the throwable that caused this throwable to get thrown.)
427 *
428 * <p>This method can be called at most once. It is generally called from
429 * within the constructor, or immediately after creating the
430 * throwable. If this throwable was created
431 * with {@link #Throwable(Throwable)} or
432 * {@link #Throwable(String,Throwable)}, this method cannot be called
433 * even once.
434 *
435 * <p>An example of using this method on a legacy throwable type
436 * without other support for setting the cause is:
437 *
438 * <pre>
439 * try {
440 * lowLevelOp();
441 * } catch (LowLevelException le) {
442 * throw (HighLevelException)
443 * new HighLevelException().initCause(le); // Legacy constructor
444 * }
445 * </pre>
446 *
447 * @param cause the cause (which is saved for later retrieval by the
448 * {@link #getCause()} method). (A {@code null} value is
449 * permitted, and indicates that the cause is nonexistent or
450 * unknown.)
451 * @return a reference to this {@code Throwable} instance.
452 * @throws IllegalArgumentException if {@code cause} is this
453 * throwable. (A throwable cannot be its own cause.)
454 * @throws IllegalStateException if this throwable was
455 * created with {@link #Throwable(Throwable)} or
456 * {@link #Throwable(String,Throwable)}, or this method has already
457 * been called on this throwable.
458 * @since 1.4
459 */
460 public synchronized Throwable initCause(Throwable cause) {
461 if (this.cause != this)
462 throw new IllegalStateException("Can't overwrite cause with " +
463 Objects.toString(cause, "a null"), this);
464 if (cause == this)
465 throw new IllegalArgumentException("Self-causation not permitted", this);
466 this.cause = cause;
467 return this;
468 }
469
470 /*
471 * This is called by readObject of a few exceptions such as
472 * ClassNotFoundException and ExceptionInInitializerError to deserialize
473 * a stream output from an older runtime version where the cause may
474 * have set to null.
475 */
476 final void setCause(Throwable t) {
477 this.cause = t;
478 }
479
480 /**
481 * Returns a short description of this throwable.
482 * The result is the concatenation of:
483 * <ul>
484 * <li> the {@linkplain Class#getName() name} of the class of this object
485 * <li> ": " (a colon and a space)
486 * <li> the result of invoking this object's {@link #getLocalizedMessage}
487 * method
488 * </ul>
489 * If {@code getLocalizedMessage} returns {@code null}, then just
490 * the class name is returned.
491 *
492 * @return a string representation of this throwable.
493 */
494 public String toString() {
495 String s = getClass().getName();
496 String message = getLocalizedMessage();
497 return (message != null) ? (s + ": " + message) : s;
498 }
499
500 /**
501 * Prints this throwable and its backtrace to the
502 * standard error stream. This method prints a stack trace for this
503 * {@code Throwable} object on the error output stream that is
504 * the value of the field {@code System.err}. The first line of
505 * output contains the result of the {@link #toString()} method for
506 * this object. Remaining lines represent data previously recorded by
507 * the method {@link #fillInStackTrace()}. The format of this
508 * information depends on the implementation, but the following
509 * example may be regarded as typical:
510 * <blockquote><pre>
511 * java.lang.NullPointerException
512 * at MyClass.mash(MyClass.java:9)
513 * at MyClass.crunch(MyClass.java:6)
514 * at MyClass.main(MyClass.java:3)
515 * </pre></blockquote>
516 * This example was produced by running the program:
517 * <pre>
518 * class MyClass {
519 * public static void main(String[] args) {
520 * crunch(null);
521 * }
522 * static void crunch(int[] a) {
523 * mash(a);
524 * }
525 * static void mash(int[] b) {
526 * System.out.println(b[0]);
527 * }
528 * }
529 * </pre>
530 * The backtrace for a throwable with an initialized, non-null cause
531 * should generally include the backtrace for the cause. The format
532 * of this information depends on the implementation, but the following
533 * example may be regarded as typical:
534 * <pre>
535 * HighLevelException: MidLevelException: LowLevelException
536 * at Junk.a(Junk.java:13)
537 * at Junk.main(Junk.java:4)
538 * Caused by: MidLevelException: LowLevelException
539 * at Junk.c(Junk.java:23)
540 * at Junk.b(Junk.java:17)
541 * at Junk.a(Junk.java:11)
542 * ... 1 more
543 * Caused by: LowLevelException
544 * at Junk.e(Junk.java:30)
545 * at Junk.d(Junk.java:27)
546 * at Junk.c(Junk.java:21)
547 * ... 3 more
548 * </pre>
549 * Note the presence of lines containing the characters {@code "..."}.
550 * These lines indicate that the remainder of the stack trace for this
551 * exception matches the indicated number of frames from the bottom of the
552 * stack trace of the exception that was caused by this exception (the
553 * "enclosing" exception). This shorthand can greatly reduce the length
554 * of the output in the common case where a wrapped exception is thrown
555 * from same method as the "causative exception" is caught. The above
556 * example was produced by running the program:
557 * <pre>
558 * public class Junk {
559 * public static void main(String args[]) {
560 * try {
561 * a();
562 * } catch(HighLevelException e) {
563 * e.printStackTrace();
564 * }
565 * }
566 * static void a() throws HighLevelException {
567 * try {
568 * b();
569 * } catch(MidLevelException e) {
570 * throw new HighLevelException(e);
571 * }
572 * }
573 * static void b() throws MidLevelException {
574 * c();
575 * }
576 * static void c() throws MidLevelException {
577 * try {
578 * d();
579 * } catch(LowLevelException e) {
580 * throw new MidLevelException(e);
581 * }
582 * }
583 * static void d() throws LowLevelException {
584 * e();
585 * }
586 * static void e() throws LowLevelException {
587 * throw new LowLevelException();
588 * }
589 * }
590 *
591 * class HighLevelException extends Exception {
592 * HighLevelException(Throwable cause) { super(cause); }
593 * }
594 *
595 * class MidLevelException extends Exception {
596 * MidLevelException(Throwable cause) { super(cause); }
597 * }
598 *
599 * class LowLevelException extends Exception {
600 * }
601 * </pre>
602 * As of release 7, the platform supports the notion of
603 * <i>suppressed exceptions</i> (in conjunction with the {@code
604 * try}-with-resources statement). Any exceptions that were
605 * suppressed in order to deliver an exception are printed out
606 * beneath the stack trace. The format of this information
607 * depends on the implementation, but the following example may be
608 * regarded as typical:
609 *
610 * <pre>
611 * Exception in thread "main" java.lang.Exception: Something happened
612 * at Foo.bar(Foo.java:10)
613 * at Foo.main(Foo.java:5)
614 * Suppressed: Resource$CloseFailException: Resource ID = 0
615 * at Resource.close(Resource.java:26)
616 * at Foo.bar(Foo.java:9)
617 * ... 1 more
618 * </pre>
619 * Note that the "... n more" notation is used on suppressed exceptions
620 * just as it is used on causes. Unlike causes, suppressed exceptions are
621 * indented beyond their "containing exceptions."
622 *
623 * <p>An exception can have both a cause and one or more suppressed
624 * exceptions:
625 * <pre>
626 * Exception in thread "main" java.lang.Exception: Main block
627 * at Foo3.main(Foo3.java:7)
628 * Suppressed: Resource$CloseFailException: Resource ID = 2
629 * at Resource.close(Resource.java:26)
630 * at Foo3.main(Foo3.java:5)
631 * Suppressed: Resource$CloseFailException: Resource ID = 1
632 * at Resource.close(Resource.java:26)
633 * at Foo3.main(Foo3.java:5)
634 * Caused by: java.lang.Exception: I did it
635 * at Foo3.main(Foo3.java:8)
636 * </pre>
637 * Likewise, a suppressed exception can have a cause:
638 * <pre>
639 * Exception in thread "main" java.lang.Exception: Main block
640 * at Foo4.main(Foo4.java:6)
641 * Suppressed: Resource2$CloseFailException: Resource ID = 1
642 * at Resource2.close(Resource2.java:20)
643 * at Foo4.main(Foo4.java:5)
644 * Caused by: java.lang.Exception: Rats, you caught me
645 * at Resource2$CloseFailException.<init>(Resource2.java:45)
646 * ... 2 more
647 * </pre>
648 */
649 public void printStackTrace() {
650 printStackTrace(System.err);
651 }
652
653 /**
654 * Prints this throwable and its backtrace to the specified print stream.
655 *
656 * @param s {@code PrintStream} to use for output
657 */
658 public void printStackTrace(PrintStream s) {
659 printStackTrace(new WrappedPrintStream(s));
660 }
661
662 private void printStackTrace(PrintStreamOrWriter s) {
663 // Guard against malicious overrides of Throwable.equals by
664 // using a Set with identity equality semantics.
665 Set<Throwable> dejaVu = Collections.newSetFromMap(new IdentityHashMap<>());
666 dejaVu.add(this);
667
668 synchronized (s.lock()) {
669 // Print our stack trace
670 s.println(this);
671 StackTraceElement[] trace = getOurStackTrace();
672 for (StackTraceElement traceElement : trace)
673 s.println("\tat " + traceElement);
674
675 // Print suppressed exceptions, if any
676 for (Throwable se : getSuppressed())
677 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, "\t", dejaVu);
678
679 // Print cause, if any
680 Throwable ourCause = getCause();
681 if (ourCause != null)
682 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, "", dejaVu);
683 }
684 }
685
686 /**
687 * Print our stack trace as an enclosed exception for the specified
688 * stack trace.
689 */
690 private void printEnclosedStackTrace(PrintStreamOrWriter s,
691 StackTraceElement[] enclosingTrace,
692 String caption,
693 String prefix,
694 Set<Throwable> dejaVu) {
695 assert Thread.holdsLock(s.lock());
696 if (dejaVu.contains(this)) {
697 s.println(prefix + caption + "[CIRCULAR REFERENCE: " + this + "]");
698 } else {
699 dejaVu.add(this);
700 // Compute number of frames in common between this and enclosing trace
701 StackTraceElement[] trace = getOurStackTrace();
702 int m = trace.length - 1;
703 int n = enclosingTrace.length - 1;
704 while (m >= 0 && n >=0 && trace[m].equals(enclosingTrace[n])) {
705 m--; n--;
706 }
707 int framesInCommon = trace.length - 1 - m;
708
709 // Print our stack trace
710 s.println(prefix + caption + this);
711 for (int i = 0; i <= m; i++)
712 s.println(prefix + "\tat " + trace[i]);
713 if (framesInCommon != 0)
714 s.println(prefix + "\t... " + framesInCommon + " more");
715
716 // Print suppressed exceptions, if any
717 for (Throwable se : getSuppressed())
718 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION,
719 prefix +"\t", dejaVu);
720
721 // Print cause, if any
722 Throwable ourCause = getCause();
723 if (ourCause != null)
724 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, prefix, dejaVu);
725 }
726 }
727
728 /**
729 * Prints this throwable and its backtrace to the specified
730 * print writer.
731 *
732 * @param s {@code PrintWriter} to use for output
733 * @since 1.1
734 */
735 public void printStackTrace(PrintWriter s) {
736 printStackTrace(new WrappedPrintWriter(s));
737 }
738
739 /**
740 * Wrapper class for PrintStream and PrintWriter to enable a single
741 * implementation of printStackTrace.
742 */
743 private abstract static class PrintStreamOrWriter {
744 /** Returns the object to be locked when using this StreamOrWriter */
745 abstract Object lock();
746
747 /** Prints the specified string as a line on this StreamOrWriter */
748 abstract void println(Object o);
749 }
750
751 private static class WrappedPrintStream extends PrintStreamOrWriter {
752 private final PrintStream printStream;
753
754 WrappedPrintStream(PrintStream printStream) {
755 this.printStream = printStream;
756 }
757
758 Object lock() {
759 return printStream;
760 }
761
762 void println(Object o) {
763 printStream.println(o);
764 }
765 }
766
767 private static class WrappedPrintWriter extends PrintStreamOrWriter {
768 private final PrintWriter printWriter;
769
770 WrappedPrintWriter(PrintWriter printWriter) {
771 this.printWriter = printWriter;
772 }
773
774 Object lock() {
775 return printWriter;
776 }
777
778 void println(Object o) {
779 printWriter.println(o);
780 }
781 }
782
783 /**
784 * Fills in the execution stack trace. This method records within this
785 * {@code Throwable} object information about the current state of
786 * the stack frames for the current thread.
787 *
788 * <p>If the stack trace of this {@code Throwable} {@linkplain
789 * Throwable#Throwable(String, Throwable, boolean, boolean) is not
790 * writable}, calling this method has no effect.
791 *
792 * @return a reference to this {@code Throwable} instance.
793 * @see java.lang.Throwable#printStackTrace()
794 */
795 public synchronized Throwable fillInStackTrace() {
796 if (stackTrace != null ||
797 backtrace != null /* Out of protocol state */ ) {
798 fillInStackTrace(0);
799 stackTrace = UNASSIGNED_STACK;
800 }
801 return this;
802 }
803
804 private native Throwable fillInStackTrace(int dummy);
805
806 /**
807 * Provides programmatic access to the stack trace information printed by
808 * {@link #printStackTrace()}. Returns an array of stack trace elements,
809 * each representing one stack frame. The zeroth element of the array
810 * (assuming the array's length is non-zero) represents the top of the
811 * stack, which is the last method invocation in the sequence. Typically,
812 * this is the point at which this throwable was created and thrown.
813 * The last element of the array (assuming the array's length is non-zero)
814 * represents the bottom of the stack, which is the first method invocation
815 * in the sequence.
816 *
817 * <p>Some virtual machines may, under some circumstances, omit one
818 * or more stack frames from the stack trace. In the extreme case,
819 * a virtual machine that has no stack trace information concerning
820 * this throwable is permitted to return a zero-length array from this
821 * method. Generally speaking, the array returned by this method will
822 * contain one element for every frame that would be printed by
823 * {@code printStackTrace}. Writes to the returned array do not
824 * affect future calls to this method.
825 *
826 * @return an array of stack trace elements representing the stack trace
827 * pertaining to this throwable.
828 * @since 1.4
829 */
830 public StackTraceElement[] getStackTrace() {
831 return getOurStackTrace().clone();
832 }
833
834 private synchronized StackTraceElement[] getOurStackTrace() {
835 // Initialize stack trace field with information from
836 // backtrace if this is the first call to this method
837 if (stackTrace == UNASSIGNED_STACK ||
838 (stackTrace == null && backtrace != null) /* Out of protocol state */) {
839 stackTrace = StackTraceElement.of(this, depth);
840 } else if (stackTrace == null) {
841 return UNASSIGNED_STACK;
842 }
843 return stackTrace;
844 }
845
846 /**
847 * Sets the stack trace elements that will be returned by
848 * {@link #getStackTrace()} and printed by {@link #printStackTrace()}
849 * and related methods.
850 *
851 * This method, which is designed for use by RPC frameworks and other
852 * advanced systems, allows the client to override the default
853 * stack trace that is either generated by {@link #fillInStackTrace()}
854 * when a throwable is constructed or deserialized when a throwable is
855 * read from a serialization stream.
856 *
857 * <p>If the stack trace of this {@code Throwable} {@linkplain
858 * Throwable#Throwable(String, Throwable, boolean, boolean) is not
859 * writable}, calling this method has no effect other than
860 * validating its argument.
861 *
862 * @param stackTrace the stack trace elements to be associated with
863 * this {@code Throwable}. The specified array is copied by this
864 * call; changes in the specified array after the method invocation
865 * returns will have no affect on this {@code Throwable}'s stack
866 * trace.
867 *
868 * @throws NullPointerException if {@code stackTrace} is
869 * {@code null} or if any of the elements of
870 * {@code stackTrace} are {@code null}
871 *
872 * @since 1.4
873 */
874 public void setStackTrace(StackTraceElement[] stackTrace) {
875 // Validate argument
876 StackTraceElement[] defensiveCopy = stackTrace.clone();
877 for (int i = 0; i < defensiveCopy.length; i++) {
878 if (defensiveCopy[i] == null)
879 throw new NullPointerException("stackTrace[" + i + "]");
880 }
881
882 synchronized (this) {
883 if (this.stackTrace == null && // Immutable stack
884 backtrace == null) // Test for out of protocol state
885 return;
886 this.stackTrace = defensiveCopy;
887 }
888 }
889
890 /**
891 * Reads a {@code Throwable} from a stream, enforcing
892 * well-formedness constraints on fields. Null entries and
893 * self-pointers are not allowed in the list of {@code
894 * suppressedExceptions}. Null entries are not allowed for stack
895 * trace elements. A null stack trace in the serial form results
896 * in a zero-length stack element array. A single-element stack
897 * trace whose entry is equal to {@code new StackTraceElement("",
898 * "", null, Integer.MIN_VALUE)} results in a {@code null} {@code
899 * stackTrace} field.
900 *
901 * Note that there are no constraints on the value the {@code
902 * cause} field can hold; both {@code null} and {@code this} are
903 * valid values for the field.
904 */
905 @java.io.Serial
906 private void readObject(ObjectInputStream s)
907 throws IOException, ClassNotFoundException {
908 s.defaultReadObject(); // read in all fields
909
910 // Set suppressed exceptions and stack trace elements fields
911 // to marker values until the contents from the serial stream
912 // are validated.
913 List<Throwable> candidateSuppressedExceptions = suppressedExceptions;
914 suppressedExceptions = SUPPRESSED_SENTINEL;
915
916 StackTraceElement[] candidateStackTrace = stackTrace;
917 stackTrace = UNASSIGNED_STACK.clone();
918
919 if (candidateSuppressedExceptions != null) {
920 int suppressedSize = validateSuppressedExceptionsList(candidateSuppressedExceptions);
921 if (suppressedSize > 0) { // Copy valid Throwables to new list
922 var suppList = new ArrayList<Throwable>(Math.min(100, suppressedSize));
923
924 for (Throwable t : candidateSuppressedExceptions) {
925 // Enforce constraints on suppressed exceptions in
926 // case of corrupt or malicious stream.
927 Objects.requireNonNull(t, NULL_CAUSE_MESSAGE);
928 if (t == this)
929 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE);
930 suppList.add(t);
931 }
932 // If there are any invalid suppressed exceptions,
933 // implicitly use the sentinel value assigned earlier.
934 suppressedExceptions = suppList;
935 }
936 } else {
937 suppressedExceptions = null;
938 }
939
940 /*
941 * For zero-length stack traces, use a clone of
942 * UNASSIGNED_STACK rather than UNASSIGNED_STACK itself to
943 * allow identity comparison against UNASSIGNED_STACK in
944 * getOurStackTrace. The identity of UNASSIGNED_STACK in
945 * stackTrace indicates to the getOurStackTrace method that
946 * the stackTrace needs to be constructed from the information
947 * in backtrace.
948 */
949 if (candidateStackTrace != null) {
950 // Work from a clone of the candidateStackTrace to ensure
951 // consistency of checks.
952 candidateStackTrace = candidateStackTrace.clone();
953 if (candidateStackTrace.length >= 1) {
954 if (candidateStackTrace.length == 1 &&
955 // Check for the marker of an immutable stack trace
956 SentinelHolder.STACK_TRACE_ELEMENT_SENTINEL.equals(candidateStackTrace[0])) {
957 stackTrace = null;
958 } else { // Verify stack trace elements are non-null.
959 for (StackTraceElement ste : candidateStackTrace) {
960 Objects.requireNonNull(ste, "null StackTraceElement in serial stream.");
961 }
962 stackTrace = candidateStackTrace;
963 }
964 }
965 }
966 // A null stackTrace field in the serial form can result from
967 // an exception serialized without that field in older JDK
968 // releases; treat such exceptions as having empty stack
969 // traces by leaving stackTrace assigned to a clone of
970 // UNASSIGNED_STACK.
971 }
972
973 private int validateSuppressedExceptionsList(List<Throwable> deserSuppressedExceptions)
974 throws IOException {
975 if (!Object.class.getModule().
976 equals(deserSuppressedExceptions.getClass().getModule())) {
977 throw new StreamCorruptedException("List implementation not in base module.");
978 } else {
979 int size = deserSuppressedExceptions.size();
980 if (size < 0) {
981 throw new StreamCorruptedException("Negative list size reported.");
982 }
983 return size;
984 }
985 }
986
987 /**
988 * Write a {@code Throwable} object to a stream.
989 *
990 * A {@code null} stack trace field is represented in the serial
991 * form as a one-element array whose element is equal to {@code
992 * new StackTraceElement("", "", null, Integer.MIN_VALUE)}.
993 */
994 @java.io.Serial
995 private synchronized void writeObject(ObjectOutputStream s)
996 throws IOException {
997 // Ensure that the stackTrace field is initialized to a
998 // non-null value, if appropriate. As of JDK 7, a null stack
999 // trace field is a valid value indicating the stack trace
1000 // should not be set.
1001 getOurStackTrace();
1002
1003 StackTraceElement[] oldStackTrace = stackTrace;
1004 try {
1005 if (stackTrace == null)
1006 stackTrace = SentinelHolder.STACK_TRACE_SENTINEL;
1007 s.defaultWriteObject();
1008 } finally {
1009 stackTrace = oldStackTrace;
1010 }
1011 }
1012
1013 /**
1014 * Appends the specified exception to the exceptions that were
1015 * suppressed in order to deliver this exception. This method is
1016 * thread-safe and typically called (automatically and implicitly)
1017 * by the {@code try}-with-resources statement.
1018 *
1019 * <p>The suppression behavior is enabled <em>unless</em> disabled
1020 * {@linkplain #Throwable(String, Throwable, boolean, boolean) via
1021 * a constructor}. When suppression is disabled, this method does
1022 * nothing other than to validate its argument.
1023 *
1024 * <p>Note that when one exception {@linkplain
1025 * #initCause(Throwable) causes} another exception, the first
1026 * exception is usually caught and then the second exception is
1027 * thrown in response. In other words, there is a causal
1028 * connection between the two exceptions.
1029 *
1030 * In contrast, there are situations where two independent
1031 * exceptions can be thrown in sibling code blocks, in particular
1032 * in the {@code try} block of a {@code try}-with-resources
1033 * statement and the compiler-generated {@code finally} block
1034 * which closes the resource.
1035 *
1036 * In these situations, only one of the thrown exceptions can be
1037 * propagated. In the {@code try}-with-resources statement, when
1038 * there are two such exceptions, the exception originating from
1039 * the {@code try} block is propagated and the exception from the
1040 * {@code finally} block is added to the list of exceptions
1041 * suppressed by the exception from the {@code try} block. As an
1042 * exception unwinds the stack, it can accumulate multiple
1043 * suppressed exceptions.
1044 *
1045 * <p>An exception may have suppressed exceptions while also being
1046 * caused by another exception. Whether or not an exception has a
1047 * cause is semantically known at the time of its creation, unlike
1048 * whether or not an exception will suppress other exceptions
1049 * which is typically only determined after an exception is
1050 * thrown.
1051 *
1052 * <p>Note that programmer written code is also able to take
1053 * advantage of calling this method in situations where there are
1054 * multiple sibling exceptions and only one can be propagated.
1055 *
1056 * @param exception the exception to be added to the list of
1057 * suppressed exceptions
1058 * @throws IllegalArgumentException if {@code exception} is this
1059 * throwable; a throwable cannot suppress itself.
1060 * @throws NullPointerException if {@code exception} is {@code null}
1061 * @since 1.7
1062 */
1063 public final synchronized void addSuppressed(Throwable exception) {
1064 if (exception == this)
1065 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE, exception);
1066
1067 Objects.requireNonNull(exception, NULL_CAUSE_MESSAGE);
1068
1069 if (suppressedExceptions == null) // Suppressed exceptions not recorded
1070 return;
1071
1072 if (suppressedExceptions == SUPPRESSED_SENTINEL)
1073 suppressedExceptions = new ArrayList<>(1);
1074
1075 suppressedExceptions.add(exception);
1076 }
1077
1078 private static final Throwable[] EMPTY_THROWABLE_ARRAY = new Throwable[0];
1079
1080 /**
1081 * Returns an array containing all of the exceptions that were
1082 * suppressed, typically by the {@code try}-with-resources
1083 * statement, in order to deliver this exception.
1084 *
1085 * If no exceptions were suppressed or {@linkplain
1086 * #Throwable(String, Throwable, boolean, boolean) suppression is
1087 * disabled}, an empty array is returned. This method is
1088 * thread-safe. Writes to the returned array do not affect future
1089 * calls to this method.
1090 *
1091 * @return an array containing all of the exceptions that were
1092 * suppressed to deliver this exception.
1093 * @since 1.7
1094 */
1095 public final synchronized Throwable[] getSuppressed() {
1096 if (suppressedExceptions == SUPPRESSED_SENTINEL ||
1097 suppressedExceptions == null)
1098 return EMPTY_THROWABLE_ARRAY;
1099 else
1100 return suppressedExceptions.toArray(EMPTY_THROWABLE_ARRAY);
1101 }
1102 }