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