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 /**
174 * Holder class to defer initializing sentinel objects only used
175 * for serialization.
176 */
177 private static class SentinelHolder {
178 /**
179 * {@linkplain #setStackTrace(StackTraceElement[]) Setting the
180 * stack trace} to a one-element array containing this sentinel
181 * value indicates future attempts to set the stack trace will be
182 * ignored. The sentinal is equal to the result of calling:<br>
183 * {@code new StackTraceElement("", "", null, Integer.MIN_VALUE)}
184 */
185 public static final StackTraceElement STACK_TRACE_ELEMENT_SENTINEL =
186 new StackTraceElement("", "", null, Integer.MIN_VALUE);
187
188 /**
189 * Sentinel value used in the serial form to indicate an immutable
190 * stack trace.
191 */
192 public static final StackTraceElement[] STACK_TRACE_SENTINEL =
193 new StackTraceElement[] {STACK_TRACE_ELEMENT_SENTINEL};
194 }
195
196 /**
197 * A value indicating the stack trace field has not yet been initialized.
198 */
199 private static final StackTraceElement[] EMPTY_STACK = new StackTraceElement[0];
200
201 /*
202 * To allow Throwable objects to be made immutable and safely
203 * reused by the JVM, such as OutOfMemoryErrors, the three fields
204 * of Throwable that are writable in response to user actions,
205 * cause, stackTrace, and suppressedExceptions obey the following
206 * protocol:
207 *
208 * 1) The fields are initialized to a non-null sentinel value
209 * which indicates the value has logically not been set.
210 *
211 * 2) Writing a null to the field indicates further writes
212 * are forbidden
213 *
214 * 3) The sentinel value may be replaced with another non-null
215 * value.
216 *
217 * For example, implementations of the HotSpot JVM have
218 * preallocated OutOfMemoryError objects to provide for better
219 * diagnosability of that situation. These objects are created
220 * without calling the constructor for that class and the fields
221 * in question are initialized to null. To support this
222 * capability, any new fields added to Throwable that require
223 * being initialized to a non-null value require a coordinated JVM
224 * change.
225 */
226
227 /**
228 * The throwable that caused this throwable to get thrown, or null if this
229 * throwable was not caused by another throwable, or if the causative
230 * throwable is unknown. If this field is equal to this throwable itself,
231 * it indicates that the cause of this throwable has not yet been
232 * initialized.
233 *
234 * @serial
235 * @since 1.4
236 */
237 private Throwable cause = this;
238
239 /**
240 * The stack trace, as returned by {@link #getStackTrace()}.
241 *
242 * The field is initialized to a zero-length array. A {@code
243 * null} value of this field indicates subsequent calls to {@link
244 * #setStackTrace()} will be be no-ops.
245 *
246 * @serial
247 * @since 1.4
248 */
249 private StackTraceElement[] stackTrace = EMPTY_STACK;
250
251 // Setting this static field introduces an acceptable
252 // initialization dependency on a few java.util classes.
253 private static final List<Throwable> suppressedSentinel =
254 Collections.unmodifiableList(new ArrayList<Throwable>(0));
255
256 /**
257 * The list of suppressed exceptions, as returned by {@link
258 * #getSuppressed()}. The list is initialized to a zero-element
259 * unmodifiable sentinel list. When a serialized Throwable is
260 * read in, if the {@code suppressedExceptions} field points to a
261 * zero-element list, the field is reset to the sentinel value.
262 *
263 * @serial
264 * @since 1.7
265 */
266 private List<Throwable> suppressedExceptions = suppressedSentinel;
267
268 /** Message for trying to suppress a null exception. */
269 private static final String NULL_CAUSE_MESSAGE = "Cannot suppress a null exception.";
270
271 /** Message for trying to suppress oneself. */
272 private static final String SELF_SUPPRESSION_MESSAGE = "Self-suppression not permitted";
273
274 /** Caption for labeling causative exception stack traces */
275 private static final String CAUSE_CAPTION = "Caused by: ";
276
277 /** Caption for labeling suppressed exception stack traces */
278 private static final String SUPPRESSED_CAPTION = "Suppressed: ";
279
280 /**
281 * Constructs a new throwable with {@code null} as its detail message.
282 * The cause is not initialized, and may subsequently be initialized by a
283 * call to {@link #initCause}.
284 *
285 * <p>The {@link #fillInStackTrace()} method is called to initialize
286 * the stack trace data in the newly created throwable.
287 */
288 public Throwable() {
289 fillInStackTrace();
290 }
291
292 /**
293 * Constructs a new throwable with the specified detail message. The
294 * cause is not initialized, and may subsequently be initialized by
295 * a call to {@link #initCause}.
296 *
297 * <p>The {@link #fillInStackTrace()} method is called to initialize
298 * the stack trace data in the newly created throwable.
299 *
300 * @param message the detail message. The detail message is saved for
301 * later retrieval by the {@link #getMessage()} method.
302 */
303 public Throwable(String message) {
304 fillInStackTrace();
305 detailMessage = message;
306 }
307
308 /**
309 * Constructs a new throwable with the specified detail message and
310 * cause. <p>Note that the detail message associated with
311 * {@code cause} is <i>not</i> automatically incorporated in
312 * this throwable's detail message.
313 *
314 * <p>The {@link #fillInStackTrace()} method is called to initialize
315 * the stack trace data in the newly created throwable.
316 *
317 * @param message the detail message (which is saved for later retrieval
318 * by the {@link #getMessage()} method).
319 * @param cause the cause (which is saved for later retrieval by the
320 * {@link #getCause()} method). (A {@code null} value is
321 * permitted, and indicates that the cause is nonexistent or
322 * unknown.)
323 * @since 1.4
324 */
325 public Throwable(String message, Throwable cause) {
326 fillInStackTrace();
327 detailMessage = message;
328 this.cause = cause;
329 }
330
331 /**
332 * Constructs a new throwable with the specified cause and a detail
333 * message of {@code (cause==null ? null : cause.toString())} (which
334 * typically contains the class and detail message of {@code cause}).
335 * This constructor is useful for throwables that are little more than
336 * wrappers for other throwables (for example, {@link
337 * java.security.PrivilegedActionException}).
338 *
339 * <p>The {@link #fillInStackTrace()} method is called to initialize
340 * the stack trace data in the newly created throwable.
341 *
342 * @param cause the cause (which is saved for later retrieval by the
343 * {@link #getCause()} method). (A {@code null} value is
344 * permitted, and indicates that the cause is nonexistent or
345 * unknown.)
346 * @since 1.4
347 */
348 public Throwable(Throwable cause) {
349 fillInStackTrace();
350 detailMessage = (cause==null ? null : cause.toString());
351 this.cause = cause;
352 }
353
354 /**
355 * Returns the detail message string of this throwable.
356 *
357 * @return the detail message string of this {@code Throwable} instance
358 * (which may be {@code null}).
359 */
360 public String getMessage() {
361 return detailMessage;
362 }
363
364 /**
365 * Creates a localized description of this throwable.
366 * Subclasses may override this method in order to produce a
367 * locale-specific message. For subclasses that do not override this
368 * method, the default implementation returns the same result as
369 * {@code getMessage()}.
370 *
371 * @return The localized description of this throwable.
372 * @since JDK1.1
373 */
374 public String getLocalizedMessage() {
375 return getMessage();
376 }
377
378 /**
379 * Returns the cause of this throwable or {@code null} if the
380 * cause is nonexistent or unknown. (The cause is the throwable that
381 * caused this throwable to get thrown.)
382 *
383 * <p>This implementation returns the cause that was supplied via one of
384 * the constructors requiring a {@code Throwable}, or that was set after
385 * creation with the {@link #initCause(Throwable)} method. While it is
386 * typically unnecessary to override this method, a subclass can override
387 * it to return a cause set by some other means. This is appropriate for
388 * a "legacy chained throwable" that predates the addition of chained
389 * exceptions to {@code Throwable}. Note that it is <i>not</i>
390 * necessary to override any of the {@code PrintStackTrace} methods,
391 * all of which invoke the {@code getCause} method to determine the
392 * cause of a throwable.
393 *
394 * @return the cause of this throwable or {@code null} if the
395 * cause is nonexistent or unknown.
396 * @since 1.4
397 */
398 public synchronized Throwable getCause() {
399 return (cause==this ? null : cause);
400 }
401
402 /**
403 * Initializes the <i>cause</i> of this throwable to the specified value.
404 * (The cause is the throwable that caused this throwable to get thrown.)
405 *
406 * <p>This method can be called at most once. It is generally called from
407 * within the constructor, or immediately after creating the
408 * throwable. If this throwable was created
409 * with {@link #Throwable(Throwable)} or
410 * {@link #Throwable(String,Throwable)}, this method cannot be called
411 * even once.
412 *
413 * @param cause the cause (which is saved for later retrieval by the
414 * {@link #getCause()} method). (A {@code null} value is
415 * permitted, and indicates that the cause is nonexistent or
416 * unknown.)
417 * @return a reference to this {@code Throwable} instance.
418 * @throws IllegalArgumentException if {@code cause} is this
419 * throwable. (A throwable cannot be its own cause.)
420 * @throws IllegalStateException if this throwable was
421 * created with {@link #Throwable(Throwable)} or
422 * {@link #Throwable(String,Throwable)}, or this method has already
423 * been called on this throwable.
424 * @since 1.4
425 */
426 public synchronized Throwable initCause(Throwable cause) {
427 if (this.cause != this)
428 throw new IllegalStateException("Can't overwrite cause");
429 if (cause == this)
430 throw new IllegalArgumentException("Self-causation not permitted");
431 this.cause = cause;
432 return this;
433 }
434
435 /**
436 * Returns a short description of this throwable.
437 * The result is the concatenation of:
438 * <ul>
439 * <li> the {@linkplain Class#getName() name} of the class of this object
440 * <li> ": " (a colon and a space)
441 * <li> the result of invoking this object's {@link #getLocalizedMessage}
442 * method
443 * </ul>
444 * If {@code getLocalizedMessage} returns {@code null}, then just
445 * the class name is returned.
446 *
447 * @return a string representation of this throwable.
448 */
449 public String toString() {
450 String s = getClass().getName();
451 String message = getLocalizedMessage();
452 return (message != null) ? (s + ": " + message) : s;
453 }
454
455 /**
456 * Prints this throwable and its backtrace to the
457 * standard error stream. This method prints a stack trace for this
458 * {@code Throwable} object on the error output stream that is
459 * the value of the field {@code System.err}. The first line of
460 * output contains the result of the {@link #toString()} method for
461 * this object. Remaining lines represent data previously recorded by
462 * the method {@link #fillInStackTrace()}. The format of this
463 * information depends on the implementation, but the following
464 * example may be regarded as typical:
465 * <blockquote><pre>
466 * java.lang.NullPointerException
467 * at MyClass.mash(MyClass.java:9)
468 * at MyClass.crunch(MyClass.java:6)
469 * at MyClass.main(MyClass.java:3)
470 * </pre></blockquote>
471 * This example was produced by running the program:
472 * <pre>
473 * class MyClass {
474 * public static void main(String[] args) {
475 * crunch(null);
476 * }
477 * static void crunch(int[] a) {
478 * mash(a);
479 * }
480 * static void mash(int[] b) {
481 * System.out.println(b[0]);
482 * }
483 * }
484 * </pre>
485 * The backtrace for a throwable with an initialized, non-null cause
486 * should generally include the backtrace for the cause. The format
487 * of this information depends on the implementation, but the following
488 * example may be regarded as typical:
489 * <pre>
490 * HighLevelException: MidLevelException: LowLevelException
491 * at Junk.a(Junk.java:13)
492 * at Junk.main(Junk.java:4)
493 * Caused by: MidLevelException: LowLevelException
494 * at Junk.c(Junk.java:23)
495 * at Junk.b(Junk.java:17)
496 * at Junk.a(Junk.java:11)
497 * ... 1 more
498 * Caused by: LowLevelException
499 * at Junk.e(Junk.java:30)
500 * at Junk.d(Junk.java:27)
501 * at Junk.c(Junk.java:21)
502 * ... 3 more
503 * </pre>
504 * Note the presence of lines containing the characters {@code "..."}.
505 * These lines indicate that the remainder of the stack trace for this
506 * exception matches the indicated number of frames from the bottom of the
507 * stack trace of the exception that was caused by this exception (the
508 * "enclosing" exception). This shorthand can greatly reduce the length
509 * of the output in the common case where a wrapped exception is thrown
510 * from same method as the "causative exception" is caught. The above
511 * example was produced by running the program:
512 * <pre>
513 * public class Junk {
514 * public static void main(String args[]) {
515 * try {
516 * a();
517 * } catch(HighLevelException e) {
518 * e.printStackTrace();
519 * }
520 * }
521 * static void a() throws HighLevelException {
522 * try {
523 * b();
524 * } catch(MidLevelException e) {
525 * throw new HighLevelException(e);
526 * }
527 * }
528 * static void b() throws MidLevelException {
529 * c();
530 * }
531 * static void c() throws MidLevelException {
532 * try {
533 * d();
534 * } catch(LowLevelException e) {
535 * throw new MidLevelException(e);
536 * }
537 * }
538 * static void d() throws LowLevelException {
539 * e();
540 * }
541 * static void e() throws LowLevelException {
542 * throw new LowLevelException();
543 * }
544 * }
545 *
546 * class HighLevelException extends Exception {
547 * HighLevelException(Throwable cause) { super(cause); }
548 * }
549 *
550 * class MidLevelException extends Exception {
551 * MidLevelException(Throwable cause) { super(cause); }
552 * }
553 *
554 * class LowLevelException extends Exception {
555 * }
556 * </pre>
557 * As of release 7, the platform supports the notion of
558 * <i>suppressed exceptions</i> (in conjunction with the {@code
559 * try}-with-resources statement). Any exceptions that were
560 * suppressed in order to deliver an exception are printed out
561 * beneath the stack trace. The format of this information
562 * depends on the implementation, but the following example may be
563 * regarded as typical:
564 *
565 * <pre>
566 * Exception in thread "main" java.lang.Exception: Something happened
567 * at Foo.bar(Foo.java:10)
568 * at Foo.main(Foo.java:5)
569 * Suppressed: Resource$CloseFailException: Resource ID = 0
570 * at Resource.close(Resource.java:26)
571 * at Foo.bar(Foo.java:9)
572 * ... 1 more
573 * </pre>
574 * Note that the "... n more" notation is used on suppressed exceptions
575 * just at it is used on causes. Unlike causes, suppressed exceptions are
576 * indented beyond their "containing exceptions."
577 *
578 * <p>An exception can have both a cause and one or more suppressed
579 * exceptions:
580 * <pre>
581 * Exception in thread "main" java.lang.Exception: Main block
582 * at Foo3.main(Foo3.java:7)
583 * Suppressed: Resource$CloseFailException: Resource ID = 2
584 * at Resource.close(Resource.java:26)
585 * at Foo3.main(Foo3.java:5)
586 * Suppressed: Resource$CloseFailException: Resource ID = 1
587 * at Resource.close(Resource.java:26)
588 * at Foo3.main(Foo3.java:5)
589 * Caused by: java.lang.Exception: I did it
590 * at Foo3.main(Foo3.java:8)
591 * </pre>
592 * Likewise, a suppressed exception can have a cause:
593 * <pre>
594 * Exception in thread "main" java.lang.Exception: Main block
595 * at Foo4.main(Foo4.java:6)
596 * Suppressed: Resource2$CloseFailException: Resource ID = 1
597 * at Resource2.close(Resource2.java:20)
598 * at Foo4.main(Foo4.java:5)
599 * Caused by: java.lang.Exception: Rats, you caught me
600 * at Resource2$CloseFailException.<init>(Resource2.java:45)
601 * ... 2 more
602 * </pre>
603 */
604 public void printStackTrace() {
605 printStackTrace(System.err);
606 }
607
608 /**
609 * Prints this throwable and its backtrace to the specified print stream.
610 *
611 * @param s {@code PrintStream} to use for output
612 */
613 public void printStackTrace(PrintStream s) {
614 printStackTrace(new WrappedPrintStream(s));
615 }
616
617 private void printStackTrace(PrintStreamOrWriter s) {
618 // Guard against malicious overrides of Throwable.equals by
619 // using a Set with identity equality semantics.
620 Set<Throwable> dejaVu =
621 Collections.newSetFromMap(new IdentityHashMap<Throwable, Boolean>());
622 dejaVu.add(this);
623
624 synchronized (s.lock()) {
625 // Print our stack trace
626 s.println(this);
627 StackTraceElement[] trace = getOurStackTrace();
628 for (StackTraceElement traceElement : trace)
629 s.println("\tat " + traceElement);
630
631 // Print suppressed exceptions, if any
632 for (Throwable se : getSuppressed())
633 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, "\t", dejaVu);
634
635 // Print cause, if any
636 Throwable ourCause = getCause();
637 if (ourCause != null)
638 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, "", dejaVu);
639 }
640 }
641
642 /**
643 * Print our stack trace as an enclosed exception for the specified
644 * stack trace.
645 */
646 private void printEnclosedStackTrace(PrintStreamOrWriter s,
647 StackTraceElement[] enclosingTrace,
648 String caption,
649 String prefix,
650 Set<Throwable> dejaVu) {
651 assert Thread.holdsLock(s.lock());
652 if (dejaVu.contains(this)) {
653 s.println("\t[CIRCULAR REFERENCE:" + this + "]");
654 } else {
655 dejaVu.add(this);
656 // Compute number of frames in common between this and enclosing trace
657 StackTraceElement[] trace = getOurStackTrace();
658 int m = trace.length - 1;
659 int n = enclosingTrace.length - 1;
660 while (m >= 0 && n >=0 && trace[m].equals(enclosingTrace[n])) {
661 m--; n--;
662 }
663 int framesInCommon = trace.length - 1 - m;
664
665 // Print our stack trace
666 s.println(prefix + caption + this);
667 for (int i = 0; i <= m; i++)
668 s.println(prefix + "\tat " + trace[i]);
669 if (framesInCommon != 0)
670 s.println(prefix + "\t... " + framesInCommon + " more");
671
672 // Print suppressed exceptions, if any
673 for (Throwable se : getSuppressed())
674 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION,
675 prefix +"\t", dejaVu);
676
677 // Print cause, if any
678 Throwable ourCause = getCause();
679 if (ourCause != null)
680 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, prefix, dejaVu);
681 }
682 }
683
684 /**
685 * Prints this throwable and its backtrace to the specified
686 * print writer.
687 *
688 * @param s {@code PrintWriter} to use for output
689 * @since JDK1.1
690 */
691 public void printStackTrace(PrintWriter s) {
692 printStackTrace(new WrappedPrintWriter(s));
693 }
694
695 /**
696 * Wrapper class for PrintStream and PrintWriter to enable a single
697 * implementation of printStackTrace.
698 */
699 private abstract static class PrintStreamOrWriter {
700 /** Returns the object to be locked when using this StreamOrWriter */
701 abstract Object lock();
702
703 /** Prints the specified string as a line on this StreamOrWriter */
704 abstract void println(Object o);
705 }
706
707 private static class WrappedPrintStream extends PrintStreamOrWriter {
708 private final PrintStream printStream;
709
710 WrappedPrintStream(PrintStream printStream) {
711 this.printStream = printStream;
712 }
713
714 Object lock() {
715 return printStream;
716 }
717
718 void println(Object o) {
719 printStream.println(o);
720 }
721 }
722
723 private static class WrappedPrintWriter extends PrintStreamOrWriter {
724 private final PrintWriter printWriter;
725
726 WrappedPrintWriter(PrintWriter printWriter) {
727 this.printWriter = printWriter;
728 }
729
730 Object lock() {
731 return printWriter;
732 }
733
734 void println(Object o) {
735 printWriter.println(o);
736 }
737 }
738
739 /**
740 * Fills in the execution stack trace. This method records within this
741 * {@code Throwable} object information about the current state of
742 * the stack frames for the current thread.
743 *
744 * <p>If the stack trace of this {@code Throwable} {@linkplain
745 * Throwable#setStackTrace(StackTraceElement[]) has been set} to
746 * {@code null}, calling this method has no effect.
747 *
748 * @return a reference to this {@code Throwable} instance.
749 * @see java.lang.Throwable#printStackTrace()
750 */
751 public synchronized Throwable fillInStackTrace() {
752 if (stackTrace != null)
753 return fillInStackTrace0();
754 else
755 return this;
756 }
757
758 private native Throwable fillInStackTrace0();
759
760 /**
761 * Provides programmatic access to the stack trace information printed by
762 * {@link #printStackTrace()}. Returns an array of stack trace elements,
763 * each representing one stack frame. The zeroth element of the array
764 * (assuming the array's length is non-zero) represents the top of the
765 * stack, which is the last method invocation in the sequence. Typically,
766 * this is the point at which this throwable was created and thrown.
767 * The last element of the array (assuming the array's length is non-zero)
768 * represents the bottom of the stack, which is the first method invocation
769 * in the sequence.
770 *
771 * <p>Some virtual machines may, under some circumstances, omit one
772 * or more stack frames from the stack trace. In the extreme case,
773 * a virtual machine that has no stack trace information concerning
774 * this throwable is permitted to return a zero-length array from this
775 * method. Generally speaking, the array returned by this method will
776 * contain one element for every frame that would be printed by
777 * {@code printStackTrace}.
778 *
779 * @return an array of stack trace elements representing the stack trace
780 * pertaining to this throwable.
781 * @since 1.4
782 */
783 public StackTraceElement[] getStackTrace() {
784 return getOurStackTrace().clone();
785 }
786
787 private synchronized StackTraceElement[] getOurStackTrace() {
788 // Initialize stack trace if this is the first call to this method
789 if (stackTrace == EMPTY_STACK) {
790 int depth = getStackTraceDepth();
791 stackTrace = new StackTraceElement[depth];
792 for (int i=0; i < depth; i++)
793 stackTrace[i] = getStackTraceElement(i);
794 } else if (stackTrace == null) {
795 return EMPTY_STACK;
796 }
797
798 return stackTrace;
799 }
800
801 /**
802 * Sets the stack trace elements that will be returned by
803 * {@link #getStackTrace()} and printed by {@link #printStackTrace()}
804 * and related methods.
805 *
806 * This method, which is designed for use by RPC frameworks and other
807 * advanced systems, allows the client to override the default
808 * stack trace that is either generated by {@link #fillInStackTrace()}
809 * when a throwable is constructed or deserialized when a throwable is
810 * read from a serialization stream.
811 *
812 * <p>If the stack trace is set to {@code null}, then future calls
813 * to this method have no effect on this {@code Throwable}.
814 *
815 * @param stackTrace the stack trace elements to be associated with
816 * this {@code Throwable}. The specified array is copied by this
817 * call; changes in the specified array after the method invocation
818 * returns will have no affect on this {@code Throwable}'s stack
819 * trace.
820 *
821 * @throws NullPointerException if any of the elements of
822 * {@code stackTrace} are {@code null}
823 *
824 * @since 1.4
825 */
826 public void setStackTrace(StackTraceElement[] stackTrace) {
827 if (this.stackTrace == null) // Immutable stack
828 return;
829
830 StackTraceElement[] defensiveCopy;
831
832 if (stackTrace == null) {
833 defensiveCopy = stackTrace;
834 } else {
835 defensiveCopy = stackTrace.clone();
836
837 for (int i = 0; i < defensiveCopy.length; i++) {
838 if (defensiveCopy[i] == null)
839 throw new NullPointerException("stackTrace[" + i + "]");
840 }
841 }
842
843 synchronized (this) {
844 this.stackTrace = defensiveCopy;
845 }
846 }
847
848 /**
849 * Returns the number of elements in the stack trace (or 0 if the stack
850 * trace is unavailable).
851 *
852 * package-protection for use by SharedSecrets.
853 */
854 native int getStackTraceDepth();
855
856 /**
857 * Returns the specified element of the stack trace.
858 *
859 * package-protection for use by SharedSecrets.
860 *
861 * @param index index of the element to return.
862 * @throws IndexOutOfBoundsException if {@code index < 0 ||
863 * index >= getStackTraceDepth() }
864 */
865 native StackTraceElement getStackTraceElement(int index);
866
867 /**
868 * Read a {@code Throwable} from a stream, enforcing
869 * well-formedness constraints on fields. Null entries and
870 * self-pointers are not allowed in the list of {@code
871 * suppressedExceptions}. Null entries are not allowed for stack
872 * trace elements. A single-element stack trace whose entry is
873 * equal to {@code new StackTraceElement("", "", null,
874 * Integer.MIN_VALUE)} results in a {@code null} {@code
875 * stackTrace} field.
876 *
877 * Note that there are no constraints on the value the {@code
878 * cause} field can hold; both {@code null} and this are valid
879 * values for the field.
880 */
881 private void readObject(ObjectInputStream s)
882 throws IOException, ClassNotFoundException {
883 s.defaultReadObject(); // read in all fields
884 List<Throwable> suppressed = null;
885 if (suppressedExceptions != null &&
886 !suppressedExceptions.isEmpty()) { // Copy Throwables to new list
887 suppressed = new ArrayList<Throwable>(1);
888 for (Throwable t : suppressedExceptions) {
889 // Enforce constraints on suppressed exceptions in
890 // case of corrupt or malicious stream.
891 if (t == null)
892 throw new NullPointerException(NULL_CAUSE_MESSAGE);
893 if (t == this)
894 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE);
895 suppressed.add(t);
896 }
897 }
898
899 // If suppressed is a zero-length list, use the sentinel
900 // value.
901 if (suppressed != null && suppressed.isEmpty())
902 suppressedExceptions = suppressedSentinel;
903 else
904 suppressedExceptions = suppressed;
905
906 // Check for the marker of an immutable stack trace
907 if (stackTrace != null) {
908 // Share zero-length stack traces
909 if (stackTrace.length == 0) {
910 stackTrace = EMPTY_STACK;
911 } else if (stackTrace.length == 1 &&
912 SentinelHolder.STACK_TRACE_ELEMENT_SENTINEL.equals(stackTrace[0])) {
913 stackTrace = null;
914 } else { // Verify stack trace elements are non-null.
915 for(StackTraceElement ste : stackTrace) {
916 if (ste == null)
917 throw new NullPointerException("null StackTraceElement in serial stream. ");
918 }
919 }
920 }
921
922 // A null stackTrace field in the serial form can result from
923 // an exception serialized without that field. Such exceptions
924 // are now treated as having immutable stack traces.
925 }
926
927 /**
928 * Write a {@code Throwable} object to a stream. A {@code null}
929 * stack trace field is represented in the serial form as a
930 * one-element array whose element is equal to {@code new
931 * StackTraceElement("", "", null, Integer.MIN_VALUE)}.
932 */
933 private synchronized void writeObject(ObjectOutputStream s)
934 throws IOException {
935 // Ensure that the stackTrace field is initialized to a
936 // non-null value, if appropriate. As of JDK 7, a null stack
937 // trace field is a valid value indicating the stack trace
938 // should not be set.
939 getOurStackTrace();
940 ObjectOutputStream.PutField fields = s.putFields();
941
942 fields.put("detailMessage", detailMessage);
943 fields.put("cause", cause);
944 // Serialize a null stacktrace using the stack trace sentinel.
945 if (stackTrace == null)
946 fields.put("stackTrace", SentinelHolder.STACK_TRACE_SENTINEL);
947 else
948 fields.put("stackTrace", stackTrace);
949 fields.put("suppressedExceptions", suppressedExceptions);
950
951 s.writeFields();
952 }
953
954 /**
955 * Adds the specified exception to the list of exceptions that
956 * were suppressed, typically by the {@code try}-with-resources
957 * statement, in order to deliver this exception.
958 *
959 * If the first exception to be suppressed is {@code null}, that
960 * indicates suppressed exception information will <em>not</em> be
961 * recorded for this exception. Subsequent calls to this method
962 * will not record any suppressed exceptions. Otherwise,
963 * attempting to suppress {@code null} after an exception has
964 * already been successfully suppressed results in a {@code
965 * NullPointerException}.
966 *
967 * <p>Note that when one exception {@linkplain
968 * #initCause(Throwable) causes} another exception, the first
969 * exception is usually caught and then the second exception is
970 * thrown in response. In contrast, when one exception suppresses
971 * another, two exceptions are thrown in sibling code blocks, such
972 * as in a {@code try} block and in its {@code finally} block, and
973 * control flow can only continue with one exception so the second
974 * is recorded as a suppressed exception of the first.
975 *
976 * @param exception the exception to be added to the list of
977 * suppressed exceptions
978 * @throws IllegalArgumentException if {@code exception} is this
979 * throwable; a throwable cannot suppress itself.
980 * @throws NullPointerException if {@code exception} is null and
981 * an exception has already been suppressed by this exception
982 * @since 1.7
983 */
984 public synchronized void addSuppressed(Throwable exception) {
985 if (exception == this)
986 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE);
987
988 if (exception == null) {
989 if (suppressedExceptions == suppressedSentinel) {
990 suppressedExceptions = null; // No suppression information recorded
991 return;
992 } else
993 throw new NullPointerException(NULL_CAUSE_MESSAGE);
994 } else {
995 assert exception != null && exception != this;
996
997 if (suppressedExceptions == null) // Suppressed exceptions not recorded
998 return;
999
1000 if (suppressedExceptions == suppressedSentinel)
1001 suppressedExceptions = new ArrayList<Throwable>(1);
1002
1003 assert suppressedExceptions != suppressedSentinel;
1004
1005 suppressedExceptions.add(exception);
1006 }
1007 }
1008
1009 private static final Throwable[] EMPTY_THROWABLE_ARRAY = new Throwable[0];
1010
1011 /**
1012 * Returns an array containing all of the exceptions that were
1013 * suppressed, typically by the {@code try}-with-resources
1014 * statement, in order to deliver this exception.
1015 *
1016 * If no exceptions were suppressed, an empty array is returned.
1017 *
1018 * @return an array containing all of the exceptions that were
1019 * suppressed to deliver this exception.
1020 * @since 1.7
1021 */
1022 public synchronized Throwable[] getSuppressed() {
1023 if (suppressedExceptions == suppressedSentinel ||
1024 suppressedExceptions == null)
1025 return EMPTY_THROWABLE_ARRAY;
1026 else
1027 return suppressedExceptions.toArray(EMPTY_THROWABLE_ARRAY);
1028 }
1029 }