1 /*
2 * Copyright (c) 1994, 2010, 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 thread at
50 * the time it was created. It can also contain a message string that gives
51 * more information about the error. Finally, it can contain a <i>cause</i>:
52 * another throwable that caused this throwable to get thrown. The cause
53 * facility is new in release 1.4. It is also known as the <i>chained
54 * exception</i> facility, as the cause can, itself, have a cause, and so on,
55 * leading to a "chain" of exceptions, each caused by another.
56 *
57 * <p>One reason that a throwable may have a cause is that the class that
58 * throws it is built atop a lower layered abstraction, and an operation on
59 * the upper layer fails due to a failure in the lower layer. It would be bad
60 * design to let the throwable thrown by the lower layer propagate outward, as
61 * it is generally unrelated to the abstraction provided by the upper layer.
62 * Further, doing so would tie the API of the upper layer to the details of
63 * its implementation, assuming the lower layer's exception was a checked
64 * exception. Throwing a "wrapped exception" (i.e., an exception containing a
65 * cause) allows the upper layer to communicate the details of the failure to
66 * its caller without incurring either of these shortcomings. It preserves
67 * the flexibility to change the implementation of the upper layer without
68 * changing its API (in particular, the set of exceptions thrown by its
69 * methods).
70 *
71 * <p>A second reason that a throwable may have a cause is that the method
72 * that throws it must conform to a general-purpose interface that does not
73 * permit the method to throw the cause directly. For example, suppose
74 * a persistent collection conforms to the {@link java.util.Collection
75 * Collection} interface, and that its persistence is implemented atop
76 * {@code java.io}. Suppose the internals of the {@code add} method
77 * can throw an {@link java.io.IOException IOException}. The implementation
78 * can communicate the details of the {@code IOException} to its caller
79 * while conforming to the {@code Collection} interface by wrapping the
80 * {@code IOException} in an appropriate unchecked exception. (The
81 * specification for the persistent collection should indicate that it is
82 * capable of throwing such exceptions.)
83 *
84 * <p>A cause can be associated with a throwable in two ways: via a
85 * constructor that takes the cause as an argument, or via the
86 * {@link #initCause(Throwable)} method. New throwable classes that
87 * wish to allow causes to be associated with them should provide constructors
88 * that take a cause and delegate (perhaps indirectly) to one of the
89 * {@code Throwable} constructors that takes a cause. For example:
90 * <pre>
91 * try {
92 * lowLevelOp();
93 * } catch (LowLevelException le) {
94 * throw new HighLevelException(le); // Chaining-aware constructor
95 * }
96 * </pre>
97 * Because the {@code initCause} method is public, it allows a cause to be
98 * associated with any throwable, even a "legacy throwable" whose
99 * implementation predates the addition of the exception chaining mechanism to
100 * {@code Throwable}. For example:
101 * <pre>
102 * try {
103 * lowLevelOp();
104 * } catch (LowLevelException le) {
105 * throw (HighLevelException)
106 * new HighLevelException().initCause(le); // Legacy constructor
107 * }
108 * </pre>
109 *
110 * <p>Prior to release 1.4, there were many throwables that had their own
111 * non-standard exception chaining mechanisms (
112 * {@link ExceptionInInitializerError}, {@link ClassNotFoundException},
113 * {@link java.lang.reflect.UndeclaredThrowableException},
114 * {@link java.lang.reflect.InvocationTargetException},
115 * {@link java.io.WriteAbortedException},
116 * {@link java.security.PrivilegedActionException},
117 * {@link java.awt.print.PrinterIOException},
118 * {@link java.rmi.RemoteException} and
119 * {@link javax.naming.NamingException}).
120 * All of these throwables have been retrofitted to
121 * use the standard exception chaining mechanism, while continuing to
122 * implement their "legacy" chaining mechanisms for compatibility.
123 *
124 * <p>Further, as of release 1.4, many general purpose {@code Throwable}
125 * classes (for example {@link Exception}, {@link RuntimeException},
126 * {@link Error}) have been retrofitted with constructors that take
127 * a cause. This was not strictly necessary, due to the existence of the
128 * {@code initCause} method, but it is more convenient and expressive to
129 * delegate to a constructor that takes a cause.
130 *
131 * <p>By convention, class {@code Throwable} and its subclasses have two
132 * constructors, one that takes no arguments and one that takes a
133 * {@code String} argument that can be used to produce a detail message.
134 * Further, those subclasses that might likely have a cause associated with
135 * them should have two more constructors, one that takes a
136 * {@code Throwable} (the cause), and one that takes a
137 * {@code String} (the detail message) and a {@code Throwable} (the
138 * cause).
139 *
140 * <p>Also introduced in release 1.4 is the {@link #getStackTrace()} method,
141 * which allows programmatic access to the stack trace information that was
142 * previously available only in text form, via the various forms of the
143 * {@link #printStackTrace()} method. This information has been added to the
144 * <i>serialized representation</i> of this class so {@code getStackTrace}
145 * and {@code printStackTrace} will operate properly on a throwable that
146 * was obtained by deserialization.
147 *
148 * @author unascribed
149 * @author Josh Bloch (Added exception chaining and programmatic access to
150 * stack trace in 1.4.)
151 * @jls3 11.2 Compile-Time Checking of Exceptions
152 * @since JDK1.0
153 */
154 public class Throwable implements Serializable {
155 /** use serialVersionUID from JDK 1.0.2 for interoperability */
156 private static final long serialVersionUID = -3042686055658047285L;
157
158 /**
159 * Native code saves some indication of the stack backtrace in this slot.
160 */
161 private transient Object backtrace;
162
163 /**
164 * Specific details about the Throwable. For example, for
165 * {@code FileNotFoundException}, this contains the name of
166 * the file that could not be found.
167 *
168 * @serial
169 */
170 private String detailMessage;
171
172 /*
173 * To allow Throwable objects to be made immutable and safely
174 * reused by the JVM, such as OutOfMemoryErrors, the three fields
175 * of Throwable that are writable in response to user actions,
176 * cause, stackTrace, and suppressedExceptions obey the following
177 * protocol:
178 *
179 * 1) The fields and initialized to a non-null sentinel value
180 *
181 * 2) Writing a null to the field indicates further writes
182 * are forbidden
183 *
184 * 3) The sentinel value may be replaced with another non-null
185 * value.
186 *
187 * For example, implementations of the HotSpot JVM have
188 * preallocated OutOfMemoryError objects to provide for better
189 * diagnosability of that situation. These objects are created
190 * without calling the constructor for that class and the fields
191 * in question are initialized to null. To support this
192 * capability, any new fields added to Throwable that require
193 * being initialized to a non-null value require a coordinated JVM
194 * change.
195 */
196
197 /**
198 * The throwable that caused this throwable to get thrown, or null if this
199 * throwable was not caused by another throwable, or if the causative
200 * throwable is unknown. If this field is equal to this throwable itself,
201 * it indicates that the cause of this throwable has not yet been
202 * initialized.
203 *
204 * @serial
205 * @since 1.4
206 */
207 private Throwable cause = this;
208
209 /**
210 * The stack trace, as returned by {@link #getStackTrace()}.
211 *
212 * @serial
213 * @since 1.4
214 */
215 private StackTraceElement[] stackTrace;
216 /*
217 * This field above is lazily initialized on first use or
218 * serialization and nulled out when fillInStackTrace is called.
219 */
220
221 // Setting this static field introduces an acceptable
222 // initialization dependency on a few java.util classes.
223 private static final List<Throwable> suppressedSentinel =
224 Collections.unmodifiableList(new ArrayList<Throwable>(0));
225
226 /**
227 * The list of suppressed exceptions, as returned by
228 * {@link #getSuppressed()}.
229 *
230 * @serial
231 * @since 1.7
232 */
233 private List<Throwable> suppressedExceptions = suppressedSentinel;
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 * Returns the detail message string of this throwable.
323 *
324 * @return the detail message string of this {@code Throwable} instance
325 * (which may be {@code null}).
326 */
327 public String getMessage() {
328 return detailMessage;
329 }
330
331 /**
332 * Creates a localized description of this throwable.
333 * Subclasses may override this method in order to produce a
334 * locale-specific message. For subclasses that do not override this
335 * method, the default implementation returns the same result as
336 * {@code getMessage()}.
337 *
338 * @return The localized description of this throwable.
339 * @since JDK1.1
340 */
341 public String getLocalizedMessage() {
342 return getMessage();
343 }
344
345 /**
346 * Returns the cause of this throwable or {@code null} if the
347 * cause is nonexistent or unknown. (The cause is the throwable that
348 * caused this throwable to get thrown.)
349 *
350 * <p>This implementation returns the cause that was supplied via one of
351 * the constructors requiring a {@code Throwable}, or that was set after
352 * creation with the {@link #initCause(Throwable)} method. While it is
353 * typically unnecessary to override this method, a subclass can override
354 * it to return a cause set by some other means. This is appropriate for
355 * a "legacy chained throwable" that predates the addition of chained
356 * exceptions to {@code Throwable}. Note that it is <i>not</i>
357 * necessary to override any of the {@code PrintStackTrace} methods,
358 * all of which invoke the {@code getCause} method to determine the
359 * cause of a throwable.
360 *
361 * @return the cause of this throwable or {@code null} if the
362 * cause is nonexistent or unknown.
363 * @since 1.4
364 */
365 public synchronized Throwable getCause() {
366 return (cause==this ? null : cause);
367 }
368
369 /**
370 * Initializes the <i>cause</i> of this throwable to the specified value.
371 * (The cause is the throwable that caused this throwable to get thrown.)
372 *
373 * <p>This method can be called at most once. It is generally called from
374 * within the constructor, or immediately after creating the
375 * throwable. If this throwable was created
376 * with {@link #Throwable(Throwable)} or
377 * {@link #Throwable(String,Throwable)}, this method cannot be called
378 * even once.
379 *
380 * @param cause the cause (which is saved for later retrieval by the
381 * {@link #getCause()} method). (A {@code null} value is
382 * permitted, and indicates that the cause is nonexistent or
383 * unknown.)
384 * @return a reference to this {@code Throwable} instance.
385 * @throws IllegalArgumentException if {@code cause} is this
386 * throwable. (A throwable cannot be its own cause.)
387 * @throws IllegalStateException if this throwable was
388 * created with {@link #Throwable(Throwable)} or
389 * {@link #Throwable(String,Throwable)}, or this method has already
390 * been called on this throwable.
391 * @since 1.4
392 */
393 public synchronized Throwable initCause(Throwable cause) {
394 if (this.cause != this)
395 throw new IllegalStateException("Can't overwrite cause");
396 if (cause == this)
397 throw new IllegalArgumentException("Self-causation not permitted");
398 this.cause = cause;
399 return this;
400 }
401
402 /**
403 * Returns a short description of this throwable.
404 * The result is the concatenation of:
405 * <ul>
406 * <li> the {@linkplain Class#getName() name} of the class of this object
407 * <li> ": " (a colon and a space)
408 * <li> the result of invoking this object's {@link #getLocalizedMessage}
409 * method
410 * </ul>
411 * If {@code getLocalizedMessage} returns {@code null}, then just
412 * the class name is returned.
413 *
414 * @return a string representation of this throwable.
415 */
416 public String toString() {
417 String s = getClass().getName();
418 String message = getLocalizedMessage();
419 return (message != null) ? (s + ": " + message) : s;
420 }
421
422 /**
423 * Prints this throwable and its backtrace to the
424 * standard error stream. This method prints a stack trace for this
425 * {@code Throwable} object on the error output stream that is
426 * the value of the field {@code System.err}. The first line of
427 * output contains the result of the {@link #toString()} method for
428 * this object. Remaining lines represent data previously recorded by
429 * the method {@link #fillInStackTrace()}. The format of this
430 * information depends on the implementation, but the following
431 * example may be regarded as typical:
432 * <blockquote><pre>
433 * java.lang.NullPointerException
434 * at MyClass.mash(MyClass.java:9)
435 * at MyClass.crunch(MyClass.java:6)
436 * at MyClass.main(MyClass.java:3)
437 * </pre></blockquote>
438 * This example was produced by running the program:
439 * <pre>
440 * class MyClass {
441 * public static void main(String[] args) {
442 * crunch(null);
443 * }
444 * static void crunch(int[] a) {
445 * mash(a);
446 * }
447 * static void mash(int[] b) {
448 * System.out.println(b[0]);
449 * }
450 * }
451 * </pre>
452 * The backtrace for a throwable with an initialized, non-null cause
453 * should generally include the backtrace for the cause. The format
454 * of this information depends on the implementation, but the following
455 * example may be regarded as typical:
456 * <pre>
457 * HighLevelException: MidLevelException: LowLevelException
458 * at Junk.a(Junk.java:13)
459 * at Junk.main(Junk.java:4)
460 * Caused by: MidLevelException: LowLevelException
461 * at Junk.c(Junk.java:23)
462 * at Junk.b(Junk.java:17)
463 * at Junk.a(Junk.java:11)
464 * ... 1 more
465 * Caused by: LowLevelException
466 * at Junk.e(Junk.java:30)
467 * at Junk.d(Junk.java:27)
468 * at Junk.c(Junk.java:21)
469 * ... 3 more
470 * </pre>
471 * Note the presence of lines containing the characters {@code "..."}.
472 * These lines indicate that the remainder of the stack trace for this
473 * exception matches the indicated number of frames from the bottom of the
474 * stack trace of the exception that was caused by this exception (the
475 * "enclosing" exception). This shorthand can greatly reduce the length
476 * of the output in the common case where a wrapped exception is thrown
477 * from same method as the "causative exception" is caught. The above
478 * example was produced by running the program:
479 * <pre>
480 * public class Junk {
481 * public static void main(String args[]) {
482 * try {
483 * a();
484 * } catch(HighLevelException e) {
485 * e.printStackTrace();
486 * }
487 * }
488 * static void a() throws HighLevelException {
489 * try {
490 * b();
491 * } catch(MidLevelException e) {
492 * throw new HighLevelException(e);
493 * }
494 * }
495 * static void b() throws MidLevelException {
496 * c();
497 * }
498 * static void c() throws MidLevelException {
499 * try {
500 * d();
501 * } catch(LowLevelException e) {
502 * throw new MidLevelException(e);
503 * }
504 * }
505 * static void d() throws LowLevelException {
506 * e();
507 * }
508 * static void e() throws LowLevelException {
509 * throw new LowLevelException();
510 * }
511 * }
512 *
513 * class HighLevelException extends Exception {
514 * HighLevelException(Throwable cause) { super(cause); }
515 * }
516 *
517 * class MidLevelException extends Exception {
518 * MidLevelException(Throwable cause) { super(cause); }
519 * }
520 *
521 * class LowLevelException extends Exception {
522 * }
523 * </pre>
524 * As of release 7, the platform supports the notion of
525 * <i>suppressed exceptions</i> (in conjunction with the {@code
526 * try}-with-resources statement). Any exceptions that were
527 * suppressed in order to deliver an exception are printed out
528 * beneath the stack trace. The format of this information
529 * depends on the implementation, but the following example may be
530 * regarded as typical:
531 *
532 * <pre>
533 * Exception in thread "main" java.lang.Exception: Something happened
534 * at Foo.bar(Foo.java:10)
535 * at Foo.main(Foo.java:5)
536 * Suppressed: Resource$CloseFailException: Resource ID = 0
537 * at Resource.close(Resource.java:26)
538 * at Foo.bar(Foo.java:9)
539 * ... 1 more
540 * </pre>
541 * Note that the "... n more" notation is used on suppressed exceptions
542 * just at it is used on causes. Unlike causes, suppressed exceptions are
543 * indented beyond their "containing exceptions."
544 *
545 * <p>An exception can have both a cause and one or more suppressed
546 * exceptions:
547 * <pre>
548 * Exception in thread "main" java.lang.Exception: Main block
549 * at Foo3.main(Foo3.java:7)
550 * Suppressed: Resource$CloseFailException: Resource ID = 2
551 * at Resource.close(Resource.java:26)
552 * at Foo3.main(Foo3.java:5)
553 * Suppressed: Resource$CloseFailException: Resource ID = 1
554 * at Resource.close(Resource.java:26)
555 * at Foo3.main(Foo3.java:5)
556 * Caused by: java.lang.Exception: I did it
557 * at Foo3.main(Foo3.java:8)
558 * </pre>
559 * Likewise, a suppressed exception can have a cause:
560 * <pre>
561 * Exception in thread "main" java.lang.Exception: Main block
562 * at Foo4.main(Foo4.java:6)
563 * Suppressed: Resource2$CloseFailException: Resource ID = 1
564 * at Resource2.close(Resource2.java:20)
565 * at Foo4.main(Foo4.java:5)
566 * Caused by: java.lang.Exception: Rats, you caught me
567 * at Resource2$CloseFailException.<init>(Resource2.java:45)
568 * ... 2 more
569 * </pre>
570 */
571 public void printStackTrace() {
572 printStackTrace(System.err);
573 }
574
575 /**
576 * Prints this throwable and its backtrace to the specified print stream.
577 *
578 * @param s {@code PrintStream} to use for output
579 */
580 public void printStackTrace(PrintStream s) {
581 printStackTrace(new WrappedPrintStream(s));
582 }
583
584 private void printStackTrace(PrintStreamOrWriter s) {
585 // Guard against malicious overrides of Throwable.equals by
586 // using a Set with identity equality semantics.
587 Set<Throwable> dejaVu =
588 Collections.newSetFromMap(new IdentityHashMap<Throwable, Boolean>());
589 dejaVu.add(this);
590
591 synchronized (s.lock()) {
592 // Print our stack trace
593 s.println(this);
594 StackTraceElement[] trace = getOurStackTrace();
595 for (StackTraceElement traceElement : trace)
596 s.println("\tat " + traceElement);
597
598 // Print suppressed exceptions, if any
599 for (Throwable se : getSuppressed())
600 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, "\t", dejaVu);
601
602 // Print cause, if any
603 Throwable ourCause = getCause();
604 if (ourCause != null)
605 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, "", dejaVu);
606 }
607 }
608
609 /**
610 * Print our stack trace as an enclosed exception for the specified
611 * stack trace.
612 */
613 private void printEnclosedStackTrace(PrintStreamOrWriter s,
614 StackTraceElement[] enclosingTrace,
615 String caption,
616 String prefix,
617 Set<Throwable> dejaVu) {
618 assert Thread.holdsLock(s.lock());
619 if (dejaVu.contains(this)) {
620 s.println("\t[CIRCULAR REFERENCE:" + this + "]");
621 } else {
622 dejaVu.add(this);
623 // Compute number of frames in common between this and enclosing trace
624 StackTraceElement[] trace = getOurStackTrace();
625 int m = trace.length - 1;
626 int n = enclosingTrace.length - 1;
627 while (m >= 0 && n >=0 && trace[m].equals(enclosingTrace[n])) {
628 m--; n--;
629 }
630 int framesInCommon = trace.length - 1 - m;
631
632 // Print our stack trace
633 s.println(prefix + caption + this);
634 for (int i = 0; i <= m; i++)
635 s.println(prefix + "\tat " + trace[i]);
636 if (framesInCommon != 0)
637 s.println(prefix + "\t... " + framesInCommon + " more");
638
639 // Print suppressed exceptions, if any
640 for (Throwable se : getSuppressed())
641 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION,
642 prefix +"\t", dejaVu);
643
644 // Print cause, if any
645 Throwable ourCause = getCause();
646 if (ourCause != null)
647 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, prefix, dejaVu);
648 }
649 }
650
651 /**
652 * Prints this throwable and its backtrace to the specified
653 * print writer.
654 *
655 * @param s {@code PrintWriter} to use for output
656 * @since JDK1.1
657 */
658 public void printStackTrace(PrintWriter s) {
659 printStackTrace(new WrappedPrintWriter(s));
660 }
661
662 /**
663 * Wrapper class for PrintStream and PrintWriter to enable a single
664 * implementation of printStackTrace.
665 */
666 private abstract static class PrintStreamOrWriter {
667 /** Returns the object to be locked when using this StreamOrWriter */
668 abstract Object lock();
669
670 /** Prints the specified string as a line on this StreamOrWriter */
671 abstract void println(Object o);
672 }
673
674 private static class WrappedPrintStream extends PrintStreamOrWriter {
675 private final PrintStream printStream;
676
677 WrappedPrintStream(PrintStream printStream) {
678 this.printStream = printStream;
679 }
680
681 Object lock() {
682 return printStream;
683 }
684
685 void println(Object o) {
686 printStream.println(o);
687 }
688 }
689
690 private static class WrappedPrintWriter extends PrintStreamOrWriter {
691 private final PrintWriter printWriter;
692
693 WrappedPrintWriter(PrintWriter printWriter) {
694 this.printWriter = printWriter;
695 }
696
697 Object lock() {
698 return printWriter;
699 }
700
701 void println(Object o) {
702 printWriter.println(o);
703 }
704 }
705
706 /**
707 * Fills in the execution stack trace. This method records within this
708 * {@code Throwable} object information about the current state of
709 * the stack frames for the current thread.
710 *
711 * @return a reference to this {@code Throwable} instance.
712 * @see java.lang.Throwable#printStackTrace()
713 */
714 public synchronized native Throwable fillInStackTrace();
715
716 /**
717 * Provides programmatic access to the stack trace information printed by
718 * {@link #printStackTrace()}. Returns an array of stack trace elements,
719 * each representing one stack frame. The zeroth element of the array
720 * (assuming the array's length is non-zero) represents the top of the
721 * stack, which is the last method invocation in the sequence. Typically,
722 * this is the point at which this throwable was created and thrown.
723 * The last element of the array (assuming the array's length is non-zero)
724 * represents the bottom of the stack, which is the first method invocation
725 * in the sequence.
726 *
727 * <p>Some virtual machines may, under some circumstances, omit one
728 * or more stack frames from the stack trace. In the extreme case,
729 * a virtual machine that has no stack trace information concerning
730 * this throwable is permitted to return a zero-length array from this
731 * method. Generally speaking, the array returned by this method will
732 * contain one element for every frame that would be printed by
733 * {@code printStackTrace}.
734 *
735 * @return an array of stack trace elements representing the stack trace
736 * pertaining to this throwable.
737 * @since 1.4
738 */
739 public StackTraceElement[] getStackTrace() {
740 return getOurStackTrace().clone();
741 }
742
743 private synchronized StackTraceElement[] getOurStackTrace() {
744 // Initialize stack trace if this is the first call to this method
745 if (stackTrace == null) {
746 int depth = getStackTraceDepth();
747 stackTrace = new StackTraceElement[depth];
748 for (int i=0; i < depth; i++)
749 stackTrace[i] = getStackTraceElement(i);
750 }
751 return stackTrace;
752 }
753
754 /**
755 * Sets the stack trace elements that will be returned by
756 * {@link #getStackTrace()} and printed by {@link #printStackTrace()}
757 * and related methods.
758 *
759 * This method, which is designed for use by RPC frameworks and other
760 * advanced systems, allows the client to override the default
761 * stack trace that is either generated by {@link #fillInStackTrace()}
762 * when a throwable is constructed or deserialized when a throwable is
763 * read from a serialization stream.
764 *
765 * @param stackTrace the stack trace elements to be associated with
766 * this {@code Throwable}. The specified array is copied by this
767 * call; changes in the specified array after the method invocation
768 * returns will have no affect on this {@code Throwable}'s stack
769 * trace.
770 *
771 * @throws NullPointerException if {@code stackTrace} is
772 * {@code null}, or if any of the elements of
773 * {@code stackTrace} are {@code null}
774 *
775 * @since 1.4
776 */
777 public void setStackTrace(StackTraceElement[] stackTrace) {
778 StackTraceElement[] defensiveCopy = stackTrace.clone();
779 for (int i = 0; i < defensiveCopy.length; i++)
780 if (defensiveCopy[i] == null)
781 throw new NullPointerException("stackTrace[" + i + "]");
782
783 synchronized (this) {
784 this.stackTrace = defensiveCopy;
785 }
786 }
787
788 /**
789 * Returns the number of elements in the stack trace (or 0 if the stack
790 * trace is unavailable).
791 *
792 * package-protection for use by SharedSecrets.
793 */
794 native int getStackTraceDepth();
795
796 /**
797 * Returns the specified element of the stack trace.
798 *
799 * package-protection for use by SharedSecrets.
800 *
801 * @param index index of the element to return.
802 * @throws IndexOutOfBoundsException if {@code index < 0 ||
803 * index >= getStackTraceDepth() }
804 */
805 native StackTraceElement getStackTraceElement(int index);
806
807 private void readObject(ObjectInputStream s)
808 throws IOException, ClassNotFoundException {
809 s.defaultReadObject(); // read in all fields
810 List<Throwable> suppressed = null;
811 if (suppressedExceptions != null &&
812 !suppressedExceptions.isEmpty()) { // Copy Throwables to new list
813 suppressed = new ArrayList<Throwable>(1);
814 for (Throwable t : suppressedExceptions) {
815 // Enforce constraints on suppressed exceptions in
816 // case of corrupt or malicious stream.
817 if (t == null)
818 throw new NullPointerException(NULL_CAUSE_MESSAGE);
819 if (t == this)
820 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE);
821 suppressed.add(t);
822 }
823 }
824
825 // If suppressed is a zero-length list, use the sentinel
826 // value.
827 if (suppressed != null && suppressed.isEmpty())
828 suppressedExceptions = suppressedSentinel;
829 else
830 suppressedExceptions = suppressed;
831
832 // Note that there are no constraints on the value the cause
833 // field can hold; both null and this are valid values for the
834 // field.
835 }
836
837 private synchronized void writeObject(ObjectOutputStream s)
838 throws IOException
839 {
840 getOurStackTrace(); // Ensure that stackTrace field is initialized.
841 s.defaultWriteObject();
842 }
843
844 /**
845 * Adds the specified exception to the list of exceptions that
846 * were suppressed, typically by the {@code try}-with-resources
847 * statement, in order to deliver this exception.
848 *
849 * If the first exception to be suppressed is {@code null}, that
850 * indicates suppressed exception information will <em>not</em> be
851 * recorded for this exception. Subsequent calls to this method
852 * will not record any suppressed exceptions. Otherwise,
853 * attempting to suppress {@code null} after an exception has
854 * already been successfully suppressed results in a {@code
855 * NullPointerException}.
856 *
857 * <p>Note that when one exception {@linkplain
858 * #initCause(Throwable) causes} another exception, the first
859 * exception is usually caught and then the second exception is
860 * thrown in response. In contrast, when one exception suppresses
861 * another, two exceptions are thrown in sibling code blocks, such
862 * as in a {@code try} block and in its {@code finally} block, and
863 * control flow can only continue with one exception so the second
864 * is recorded as a suppressed exception of the first.
865 *
866 * @param exception the exception to be added to the list of
867 * suppressed exceptions
868 * @throws IllegalArgumentException if {@code exception} is this
869 * throwable; a throwable cannot suppress itself.
870 * @throws NullPointerException if {@code exception} is null and
871 * an exception has already been suppressed by this exception
872 * @since 1.7
873 */
874 public synchronized void addSuppressed(Throwable exception) {
875 if (exception == this)
876 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE);
877
878 if (exception == null) {
879 if (suppressedExceptions == suppressedSentinel) {
880 suppressedExceptions = null; // No suppression information recorded
881 return;
882 } else
883 throw new NullPointerException(NULL_CAUSE_MESSAGE);
884 } else {
885 assert exception != null && exception != this;
886
887 if (suppressedExceptions == null) // Suppressed exceptions not recorded
888 return;
889
890 if (suppressedExceptions == suppressedSentinel)
891 suppressedExceptions = new ArrayList<Throwable>(1);
892
893 assert suppressedExceptions != suppressedSentinel;
894
895 suppressedExceptions.add(exception);
896 }
897 }
898
899 private static final Throwable[] EMPTY_THROWABLE_ARRAY = new Throwable[0];
900
901 /**
902 * Returns an array containing all of the exceptions that were
903 * suppressed, typically by the {@code try}-with-resources
904 * statement, in order to deliver this exception.
905 *
906 * If no exceptions were suppressed, an empty array is returned.
907 *
908 * @return an array containing all of the exceptions that were
909 * suppressed to deliver this exception.
910 * @since 1.7
911 */
912 public synchronized Throwable[] getSuppressed() {
913 if (suppressedExceptions == suppressedSentinel ||
914 suppressedExceptions == null)
915 return EMPTY_THROWABLE_ARRAY;
916 else
917 return suppressedExceptions.toArray(EMPTY_THROWABLE_ARRAY);
918 }
919 }