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