1 /* 2 * Copyright (c) 1994, 2011, 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 50 * thread at the time it was created. It can also contain a message 51 * string that gives more information about the error. Over time, a 52 * throwable can {@linkplain Throwable#addSuppressed suppress} other 53 * throwables from being propagated. Finally, the throwable can also 54 * contain a <i>cause</i>: another throwable that caused this 55 * throwable to get thrown. The recording of this causal information 56 * is referred to as the <i>chained exception</i> facility, as the 57 * cause can, itself, have a cause, and so on, leading to a "chain" of 58 * exceptions, each caused by another. 59 * 60 * <p>One reason that a throwable may have a cause is that the class that 61 * throws it is built atop a lower layered abstraction, and an operation on 62 * the upper layer fails due to a failure in the lower layer. It would be bad 63 * design to let the throwable thrown by the lower layer propagate outward, as 64 * it is generally unrelated to the abstraction provided by the upper layer. 65 * Further, doing so would tie the API of the upper layer to the details of 66 * its implementation, assuming the lower layer's exception was a checked 67 * exception. Throwing a "wrapped exception" (i.e., an exception containing a 68 * cause) allows the upper layer to communicate the details of the failure to 69 * its caller without incurring either of these shortcomings. It preserves 70 * the flexibility to change the implementation of the upper layer without 71 * changing its API (in particular, the set of exceptions thrown by its 72 * methods). 73 * 74 * <p>A second reason that a throwable may have a cause is that the method 75 * that throws it must conform to a general-purpose interface that does not 76 * permit the method to throw the cause directly. For example, suppose 77 * a persistent collection conforms to the {@link java.util.Collection 78 * Collection} interface, and that its persistence is implemented atop 79 * {@code java.io}. Suppose the internals of the {@code add} method 80 * can throw an {@link java.io.IOException IOException}. The implementation 81 * can communicate the details of the {@code IOException} to its caller 82 * while conforming to the {@code Collection} interface by wrapping the 83 * {@code IOException} in an appropriate unchecked exception. (The 84 * specification for the persistent collection should indicate that it is 85 * capable of throwing such exceptions.) 86 * 87 * <p>A cause can be associated with a throwable in two ways: via a 88 * constructor that takes the cause as an argument, or via the 89 * {@link #initCause(Throwable)} method. New throwable classes that 90 * wish to allow causes to be associated with them should provide constructors 91 * that take a cause and delegate (perhaps indirectly) to one of the 92 * {@code Throwable} constructors that takes a cause. 93 * 94 * Because the {@code initCause} method is public, it allows a cause to be 95 * associated with any throwable, even a "legacy throwable" whose 96 * implementation predates the addition of the exception chaining mechanism to 97 * {@code Throwable}. 98 * 99 * <p>By convention, class {@code Throwable} and its subclasses have two 100 * constructors, one that takes no arguments and one that takes a 101 * {@code String} argument that can be used to produce a detail message. 102 * Further, those subclasses that might likely have a cause associated with 103 * them should have two more constructors, one that takes a 104 * {@code Throwable} (the cause), and one that takes a 105 * {@code String} (the detail message) and a {@code Throwable} (the 106 * cause). 107 * 108 * @author unascribed 109 * @author Josh Bloch (Added exception chaining and programmatic access to 110 * stack trace in 1.4.) 111 * @jls3 11.2 Compile-Time Checking of Exceptions 112 * @since JDK1.0 113 */ 114 public class Throwable implements Serializable { 115 /** use serialVersionUID from JDK 1.0.2 for interoperability */ 116 private static final long serialVersionUID = -3042686055658047285L; 117 118 /** 119 * Native code saves some indication of the stack backtrace in this slot. 120 */ 121 private transient Object backtrace; 122 123 /** 124 * Specific details about the Throwable. For example, for 125 * {@code FileNotFoundException}, this contains the name of 126 * the file that could not be found. 127 * 128 * @serial 129 */ 130 private String detailMessage; 131 132 /** 133 * A shared value for an empty stack. 134 */ 135 private static final StackTraceElement[] EMPTY_STACK = new StackTraceElement[0]; 136 137 /* 138 * To allow Throwable objects to be made immutable and safely 139 * reused by the JVM, such as OutOfMemoryErrors, fields of 140 * Throwable that are writable in response to user actions, cause 141 * and suppressedExceptions obey the following protocol: 142 * 143 * 1) The fields are initialized to a non-null sentinel value 144 * which indicates the value has logically not been set. 145 * 146 * 2) Writing a null to the field indicates further writes 147 * are forbidden 148 * 149 * 3) The sentinel value may be replaced with another non-null 150 * value. 151 * 152 * For example, implementations of the HotSpot JVM have 153 * preallocated OutOfMemoryError objects to provide for better 154 * diagnosability of that situation. These objects are created 155 * without calling the constructor for that class and the fields 156 * in question are initialized to null. To support this 157 * capability, any new fields added to Throwable that require 158 * being initialized to a non-null value require a coordinated JVM 159 * change. 160 */ 161 162 /** 163 * The throwable that caused this throwable to get thrown, or null if this 164 * throwable was not caused by another throwable, or if the causative 165 * throwable is unknown. If this field is equal to this throwable itself, 166 * it indicates that the cause of this throwable has not yet been 167 * initialized. 168 * 169 * @serial 170 * @since 1.4 171 */ 172 private Throwable cause = this; 173 174 /** 175 * The stack trace, as returned by {@link #getStackTrace()}. 176 * 177 * @serial 178 * @since 1.4 179 */ 180 private StackTraceElement[] stackTrace; 181 182 // Setting this static field introduces an acceptable 183 // initialization dependency on a few java.util classes. 184 private static final List<Throwable> SUPPRESSED_SENTINEL = 185 Collections.unmodifiableList(new ArrayList<Throwable>(0)); 186 187 /** 188 * The list of suppressed exceptions, as returned by {@link 189 * #getSuppressed()}. The list is initialized to a zero-element 190 * unmodifiable sentinel list. When a serialized Throwable is 191 * read in, if the {@code suppressedExceptions} field points to a 192 * zero-element list, the field is reset to the sentinel value. 193 * 194 * @serial 195 * @since 1.7 196 */ 197 private List<Throwable> suppressedExceptions = SUPPRESSED_SENTINEL; 198 199 /** Message for trying to suppress a null exception. */ 200 private static final String NULL_CAUSE_MESSAGE = "Cannot suppress a null exception."; 201 202 /** Message for trying to suppress oneself. */ 203 private static final String SELF_SUPPRESSION_MESSAGE = "Self-suppression not permitted"; 204 205 /** Caption for labeling causative exception stack traces */ 206 private static final String CAUSE_CAPTION = "Caused by: "; 207 208 /** Caption for labeling suppressed exception stack traces */ 209 private static final String SUPPRESSED_CAPTION = "Suppressed: "; 210 211 /** 212 * Constructs a new throwable with {@code null} as its detail message. 213 * The cause is not initialized, and may subsequently be initialized by a 214 * call to {@link #initCause}. 215 * 216 * <p>The {@link #fillInStackTrace()} method is called to initialize 217 * the stack trace data in the newly created throwable. 218 */ 219 public Throwable() { 220 fillInStackTrace(); 221 } 222 223 /** 224 * Constructs a new throwable with the specified detail message. The 225 * cause is not initialized, and may subsequently be initialized by 226 * a call to {@link #initCause}. 227 * 228 * <p>The {@link #fillInStackTrace()} method is called to initialize 229 * the stack trace data in the newly created throwable. 230 * 231 * @param message the detail message. The detail message is saved for 232 * later retrieval by the {@link #getMessage()} method. 233 */ 234 public Throwable(String message) { 235 fillInStackTrace(); 236 detailMessage = message; 237 } 238 239 /** 240 * Constructs a new throwable with the specified detail message and 241 * cause. <p>Note that the detail message associated with 242 * {@code cause} is <i>not</i> automatically incorporated in 243 * this throwable's detail message. 244 * 245 * <p>The {@link #fillInStackTrace()} method is called to initialize 246 * the stack trace data in the newly created throwable. 247 * 248 * @param message the detail message (which is saved for later retrieval 249 * by the {@link #getMessage()} method). 250 * @param cause the cause (which is saved for later retrieval by the 251 * {@link #getCause()} method). (A {@code null} value is 252 * permitted, and indicates that the cause is nonexistent or 253 * unknown.) 254 * @since 1.4 255 */ 256 public Throwable(String message, Throwable cause) { 257 fillInStackTrace(); 258 detailMessage = message; 259 this.cause = cause; 260 } 261 262 /** 263 * Constructs a new throwable with the specified cause and a detail 264 * message of {@code (cause==null ? null : cause.toString())} (which 265 * typically contains the class and detail message of {@code cause}). 266 * This constructor is useful for throwables that are little more than 267 * wrappers for other throwables (for example, {@link 268 * java.security.PrivilegedActionException}). 269 * 270 * <p>The {@link #fillInStackTrace()} method is called to initialize 271 * the stack trace data in the newly created throwable. 272 * 273 * @param cause the cause (which is saved for later retrieval by the 274 * {@link #getCause()} method). (A {@code null} value is 275 * permitted, and indicates that the cause is nonexistent or 276 * unknown.) 277 * @since 1.4 278 */ 279 public Throwable(Throwable cause) { 280 fillInStackTrace(); 281 detailMessage = (cause==null ? null : cause.toString()); 282 this.cause = cause; 283 } 284 285 /** 286 * Returns the detail message string of this throwable. 287 * 288 * @return the detail message string of this {@code Throwable} instance 289 * (which may be {@code null}). 290 */ 291 public String getMessage() { 292 return detailMessage; 293 } 294 295 /** 296 * Creates a localized description of this throwable. 297 * Subclasses may override this method in order to produce a 298 * locale-specific message. For subclasses that do not override this 299 * method, the default implementation returns the same result as 300 * {@code getMessage()}. 301 * 302 * @return The localized description of this throwable. 303 * @since JDK1.1 304 */ 305 public String getLocalizedMessage() { 306 return getMessage(); 307 } 308 309 /** 310 * Returns the cause of this throwable or {@code null} if the 311 * cause is nonexistent or unknown. (The cause is the throwable that 312 * caused this throwable to get thrown.) 313 * 314 * <p>This implementation returns the cause that was supplied via one of 315 * the constructors requiring a {@code Throwable}, or that was set after 316 * creation with the {@link #initCause(Throwable)} method. While it is 317 * typically unnecessary to override this method, a subclass can override 318 * it to return a cause set by some other means. This is appropriate for 319 * a "legacy chained throwable" that predates the addition of chained 320 * exceptions to {@code Throwable}. Note that it is <i>not</i> 321 * necessary to override any of the {@code PrintStackTrace} methods, 322 * all of which invoke the {@code getCause} method to determine the 323 * cause of a throwable. 324 * 325 * @return the cause of this throwable or {@code null} if the 326 * cause is nonexistent or unknown. 327 * @since 1.4 328 */ 329 public synchronized Throwable getCause() { 330 return (cause==this ? null : cause); 331 } 332 333 /** 334 * Initializes the <i>cause</i> of this throwable to the specified value. 335 * (The cause is the throwable that caused this throwable to get thrown.) 336 * 337 * <p>This method can be called at most once. It is generally called from 338 * within the constructor, or immediately after creating the 339 * throwable. If this throwable was created 340 * with {@link #Throwable(Throwable)} or 341 * {@link #Throwable(String,Throwable)}, this method cannot be called 342 * even once. 343 * 344 * @param cause the cause (which is saved for later retrieval by the 345 * {@link #getCause()} method). (A {@code null} value is 346 * permitted, and indicates that the cause is nonexistent or 347 * unknown.) 348 * @return a reference to this {@code Throwable} instance. 349 * @throws IllegalArgumentException if {@code cause} is this 350 * throwable. (A throwable cannot be its own cause.) 351 * @throws IllegalStateException if this throwable was 352 * created with {@link #Throwable(Throwable)} or 353 * {@link #Throwable(String,Throwable)}, or this method has already 354 * been called on this throwable. 355 * @since 1.4 356 */ 357 public synchronized Throwable initCause(Throwable cause) { 358 if (this.cause != this) 359 throw new IllegalStateException("Can't overwrite cause"); 360 if (cause == this) 361 throw new IllegalArgumentException("Self-causation not permitted"); 362 this.cause = cause; 363 return this; 364 } 365 366 /** 367 * Returns a short description of this throwable. 368 * The result is the concatenation of: 369 * <ul> 370 * <li> the {@linkplain Class#getName() name} of the class of this object 371 * <li> ": " (a colon and a space) 372 * <li> the result of invoking this object's {@link #getLocalizedMessage} 373 * method 374 * </ul> 375 * If {@code getLocalizedMessage} returns {@code null}, then just 376 * the class name is returned. 377 * 378 * @return a string representation of this throwable. 379 */ 380 public String toString() { 381 String s = getClass().getName(); 382 String message = getLocalizedMessage(); 383 return (message != null) ? (s + ": " + message) : s; 384 } 385 386 /** 387 * Prints this throwable and its backtrace to the 388 * standard error stream. This method prints a stack trace for this 389 * {@code Throwable} object on the error output stream that is 390 * the value of the field {@code System.err}. The first line of 391 * output contains the result of the {@link #toString()} method for 392 * this object. Remaining lines represent data previously recorded by 393 * the method {@link #fillInStackTrace()}. The format of this 394 * information depends on the implementation, but the following 395 * example may be regarded as typical: 396 * <blockquote><pre> 397 * java.lang.NullPointerException 398 * at MyClass.mash(MyClass.java:9) 399 * at MyClass.crunch(MyClass.java:6) 400 * at MyClass.main(MyClass.java:3) 401 * </pre></blockquote> 402 * This example was produced by running the program: 403 * <pre> 404 * class MyClass { 405 * public static void main(String[] args) { 406 * crunch(null); 407 * } 408 * static void crunch(int[] a) { 409 * mash(a); 410 * } 411 * static void mash(int[] b) { 412 * System.out.println(b[0]); 413 * } 414 * } 415 * </pre> 416 * The backtrace for a throwable with an initialized, non-null cause 417 * should generally include the backtrace for the cause. The format 418 * of this information depends on the implementation, but the following 419 * example may be regarded as typical: 420 * <pre> 421 * HighLevelException: MidLevelException: LowLevelException 422 * at Junk.a(Junk.java:13) 423 * at Junk.main(Junk.java:4) 424 * Caused by: MidLevelException: LowLevelException 425 * at Junk.c(Junk.java:23) 426 * at Junk.b(Junk.java:17) 427 * at Junk.a(Junk.java:11) 428 * ... 1 more 429 * Caused by: LowLevelException 430 * at Junk.e(Junk.java:30) 431 * at Junk.d(Junk.java:27) 432 * at Junk.c(Junk.java:21) 433 * ... 3 more 434 * </pre> 435 * Note the presence of lines containing the characters {@code "..."}. 436 * These lines indicate that the remainder of the stack trace for this 437 * exception matches the indicated number of frames from the bottom of the 438 * stack trace of the exception that was caused by this exception (the 439 * "enclosing" exception). This shorthand can greatly reduce the length 440 * of the output in the common case where a wrapped exception is thrown 441 * from same method as the "causative exception" is caught. The above 442 * example was produced by running the program: 443 * <pre> 444 * public class Junk { 445 * public static void main(String args[]) { 446 * try { 447 * a(); 448 * } catch(HighLevelException e) { 449 * e.printStackTrace(); 450 * } 451 * } 452 * static void a() throws HighLevelException { 453 * try { 454 * b(); 455 * } catch(MidLevelException e) { 456 * throw new HighLevelException(e); 457 * } 458 * } 459 * static void b() throws MidLevelException { 460 * c(); 461 * } 462 * static void c() throws MidLevelException { 463 * try { 464 * d(); 465 * } catch(LowLevelException e) { 466 * throw new MidLevelException(e); 467 * } 468 * } 469 * static void d() throws LowLevelException { 470 * e(); 471 * } 472 * static void e() throws LowLevelException { 473 * throw new LowLevelException(); 474 * } 475 * } 476 * 477 * class HighLevelException extends Exception { 478 * HighLevelException(Throwable cause) { super(cause); } 479 * } 480 * 481 * class MidLevelException extends Exception { 482 * MidLevelException(Throwable cause) { super(cause); } 483 * } 484 * 485 * class LowLevelException extends Exception { 486 * } 487 * </pre> 488 * As of release 7, the platform supports the notion of 489 * <i>suppressed exceptions</i> (in conjunction with the {@code 490 * try}-with-resources statement). Any exceptions that were 491 * suppressed in order to deliver an exception are printed out 492 * beneath the stack trace. The format of this information 493 * depends on the implementation, but the following example may be 494 * regarded as typical: 495 * 496 * <pre> 497 * Exception in thread "main" java.lang.Exception: Something happened 498 * at Foo.bar(Foo.java:10) 499 * at Foo.main(Foo.java:5) 500 * Suppressed: Resource$CloseFailException: Resource ID = 0 501 * at Resource.close(Resource.java:26) 502 * at Foo.bar(Foo.java:9) 503 * ... 1 more 504 * </pre> 505 * Note that the "... n more" notation is used on suppressed exceptions 506 * just at it is used on causes. Unlike causes, suppressed exceptions are 507 * indented beyond their "containing exceptions." 508 * 509 * <p>An exception can have both a cause and one or more suppressed 510 * exceptions: 511 * <pre> 512 * Exception in thread "main" java.lang.Exception: Main block 513 * at Foo3.main(Foo3.java:7) 514 * Suppressed: Resource$CloseFailException: Resource ID = 2 515 * at Resource.close(Resource.java:26) 516 * at Foo3.main(Foo3.java:5) 517 * Suppressed: Resource$CloseFailException: Resource ID = 1 518 * at Resource.close(Resource.java:26) 519 * at Foo3.main(Foo3.java:5) 520 * Caused by: java.lang.Exception: I did it 521 * at Foo3.main(Foo3.java:8) 522 * </pre> 523 * Likewise, a suppressed exception can have a cause: 524 * <pre> 525 * Exception in thread "main" java.lang.Exception: Main block 526 * at Foo4.main(Foo4.java:6) 527 * Suppressed: Resource2$CloseFailException: Resource ID = 1 528 * at Resource2.close(Resource2.java:20) 529 * at Foo4.main(Foo4.java:5) 530 * Caused by: java.lang.Exception: Rats, you caught me 531 * at Resource2$CloseFailException.<init>(Resource2.java:45) 532 * ... 2 more 533 * </pre> 534 */ 535 public void printStackTrace() { 536 printStackTrace(System.err); 537 } 538 539 /** 540 * Prints this throwable and its backtrace to the specified print stream. 541 * 542 * @param s {@code PrintStream} to use for output 543 */ 544 public void printStackTrace(PrintStream s) { 545 printStackTrace(new WrappedPrintStream(s)); 546 } 547 548 private void printStackTrace(PrintStreamOrWriter s) { 549 // Guard against malicious overrides of Throwable.equals by 550 // using a Set with identity equality semantics. 551 Set<Throwable> dejaVu = 552 Collections.newSetFromMap(new IdentityHashMap<Throwable, Boolean>()); 553 dejaVu.add(this); 554 555 synchronized (s.lock()) { 556 // Print our stack trace 557 s.println(this); 558 StackTraceElement[] trace = getOurStackTrace(); 559 for (StackTraceElement traceElement : trace) 560 s.println("\tat " + traceElement); 561 562 // Print suppressed exceptions, if any 563 for (Throwable se : getSuppressed()) 564 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, "\t", dejaVu); 565 566 // Print cause, if any 567 Throwable ourCause = getCause(); 568 if (ourCause != null) 569 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, "", dejaVu); 570 } 571 } 572 573 /** 574 * Print our stack trace as an enclosed exception for the specified 575 * stack trace. 576 */ 577 private void printEnclosedStackTrace(PrintStreamOrWriter s, 578 StackTraceElement[] enclosingTrace, 579 String caption, 580 String prefix, 581 Set<Throwable> dejaVu) { 582 assert Thread.holdsLock(s.lock()); 583 if (dejaVu.contains(this)) { 584 s.println("\t[CIRCULAR REFERENCE:" + this + "]"); 585 } else { 586 dejaVu.add(this); 587 // Compute number of frames in common between this and enclosing trace 588 StackTraceElement[] trace = getOurStackTrace(); 589 int m = trace.length - 1; 590 int n = enclosingTrace.length - 1; 591 while (m >= 0 && n >=0 && trace[m].equals(enclosingTrace[n])) { 592 m--; n--; 593 } 594 int framesInCommon = trace.length - 1 - m; 595 596 // Print our stack trace 597 s.println(prefix + caption + this); 598 for (int i = 0; i <= m; i++) 599 s.println(prefix + "\tat " + trace[i]); 600 if (framesInCommon != 0) 601 s.println(prefix + "\t... " + framesInCommon + " more"); 602 603 // Print suppressed exceptions, if any 604 for (Throwable se : getSuppressed()) 605 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, 606 prefix +"\t", dejaVu); 607 608 // Print cause, if any 609 Throwable ourCause = getCause(); 610 if (ourCause != null) 611 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, prefix, dejaVu); 612 } 613 } 614 615 /** 616 * Prints this throwable and its backtrace to the specified 617 * print writer. 618 * 619 * @param s {@code PrintWriter} to use for output 620 * @since JDK1.1 621 */ 622 public void printStackTrace(PrintWriter s) { 623 printStackTrace(new WrappedPrintWriter(s)); 624 } 625 626 /** 627 * Wrapper class for PrintStream and PrintWriter to enable a single 628 * implementation of printStackTrace. 629 */ 630 private abstract static class PrintStreamOrWriter { 631 /** Returns the object to be locked when using this StreamOrWriter */ 632 abstract Object lock(); 633 634 /** Prints the specified string as a line on this StreamOrWriter */ 635 abstract void println(Object o); 636 } 637 638 private static class WrappedPrintStream extends PrintStreamOrWriter { 639 private final PrintStream printStream; 640 641 WrappedPrintStream(PrintStream printStream) { 642 this.printStream = printStream; 643 } 644 645 Object lock() { 646 return printStream; 647 } 648 649 void println(Object o) { 650 printStream.println(o); 651 } 652 } 653 654 private static class WrappedPrintWriter extends PrintStreamOrWriter { 655 private final PrintWriter printWriter; 656 657 WrappedPrintWriter(PrintWriter printWriter) { 658 this.printWriter = printWriter; 659 } 660 661 Object lock() { 662 return printWriter; 663 } 664 665 void println(Object o) { 666 printWriter.println(o); 667 } 668 } 669 670 /** 671 * Fills in the execution stack trace. This method records within this 672 * {@code Throwable} object information about the current state of 673 * the stack frames for the current thread. 674 * 675 * @return a reference to this {@code Throwable} instance. 676 * @see java.lang.Throwable#printStackTrace() 677 */ 678 public synchronized native Throwable fillInStackTrace(); 679 680 /** 681 * Provides programmatic access to the stack trace information printed by 682 * {@link #printStackTrace()}. Returns an array of stack trace elements, 683 * each representing one stack frame. The zeroth element of the array 684 * (assuming the array's length is non-zero) represents the top of the 685 * stack, which is the last method invocation in the sequence. Typically, 686 * this is the point at which this throwable was created and thrown. 687 * The last element of the array (assuming the array's length is non-zero) 688 * represents the bottom of the stack, which is the first method invocation 689 * in the sequence. 690 * 691 * <p>Some virtual machines may, under some circumstances, omit one 692 * or more stack frames from the stack trace. In the extreme case, 693 * a virtual machine that has no stack trace information concerning 694 * this throwable is permitted to return a zero-length array from this 695 * method. Generally speaking, the array returned by this method will 696 * contain one element for every frame that would be printed by 697 * {@code printStackTrace}. 698 * 699 * @return an array of stack trace elements representing the stack trace 700 * pertaining to this throwable. 701 * @since 1.4 702 */ 703 public StackTraceElement[] getStackTrace() { 704 return getOurStackTrace().clone(); 705 } 706 707 private synchronized StackTraceElement[] getOurStackTrace() { 708 // Initialize stack trace if this is the first call to this method 709 if (stackTrace == null) { 710 int depth = getStackTraceDepth(); 711 stackTrace = new StackTraceElement[depth]; 712 for (int i=0; i < depth; i++) 713 stackTrace[i] = getStackTraceElement(i); 714 } 715 return stackTrace; 716 } 717 718 /** 719 * Sets the stack trace elements that will be returned by 720 * {@link #getStackTrace()} and printed by {@link #printStackTrace()} 721 * and related methods. 722 * 723 * This method, which is designed for use by RPC frameworks and other 724 * advanced systems, allows the client to override the default 725 * stack trace that is either generated by {@link #fillInStackTrace()} 726 * when a throwable is constructed or deserialized when a throwable is 727 * read from a serialization stream. 728 * 729 * @param stackTrace the stack trace elements to be associated with 730 * this {@code Throwable}. The specified array is copied by this 731 * call; changes in the specified array after the method invocation 732 * returns will have no affect on this {@code Throwable}'s stack 733 * trace. 734 * 735 * @throws NullPointerException if {@code stackTrace} is 736 * {@code null}, or if any of the elements of 737 * {@code stackTrace} are {@code null} 738 * 739 * @since 1.4 740 */ 741 public void setStackTrace(StackTraceElement[] stackTrace) { 742 StackTraceElement[] defensiveCopy = stackTrace.clone(); 743 for (int i = 0; i < defensiveCopy.length; i++) 744 if (defensiveCopy[i] == null) 745 throw new NullPointerException("stackTrace[" + i + "]"); 746 747 synchronized (this) { 748 this.stackTrace = defensiveCopy; 749 } 750 } 751 752 /** 753 * Returns the number of elements in the stack trace (or 0 if the stack 754 * trace is unavailable). 755 * 756 * package-protection for use by SharedSecrets. 757 */ 758 native int getStackTraceDepth(); 759 760 /** 761 * Returns the specified element of the stack trace. 762 * 763 * package-protection for use by SharedSecrets. 764 * 765 * @param index index of the element to return. 766 * @throws IndexOutOfBoundsException if {@code index < 0 || 767 * index >= getStackTraceDepth() } 768 */ 769 native StackTraceElement getStackTraceElement(int index); 770 771 /** 772 * Reads a {@code Throwable} from a stream, enforcing 773 * well-formedness constraints on fields. Null entries and 774 * self-pointers are not allowed in the list of {@code 775 * suppressedExceptions}. Null entries are not allowed for stack 776 * trace elements. 777 * 778 * Note that there are no constraints on the value the {@code 779 * cause} field can hold; both {@code null} and {@code this} are 780 * valid values for the field. 781 */ 782 private void readObject(ObjectInputStream s) 783 throws IOException, ClassNotFoundException { 784 s.defaultReadObject(); // read in all fields 785 if (suppressedExceptions != null) { 786 List<Throwable> suppressed = null; 787 if (suppressedExceptions.isEmpty()) { 788 // Use the sentinel for a zero-length list 789 suppressed = SUPPRESSED_SENTINEL; 790 } else { // Copy Throwables to new list 791 suppressed = new ArrayList<>(1); 792 for (Throwable t : suppressedExceptions) { 793 // Enforce constraints on suppressed exceptions in 794 // case of corrupt or malicious stream. 795 if (t == null) 796 throw new NullPointerException(NULL_CAUSE_MESSAGE); 797 if (t == this) 798 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE); 799 suppressed.add(t); 800 } 801 } 802 suppressedExceptions = suppressed; 803 } // else a null suppressedExceptions field remains null 804 805 if (stackTrace != null) { 806 for (StackTraceElement ste : stackTrace) { 807 if (ste == null) 808 throw new NullPointerException("null StackTraceElement in serial stream. "); 809 } 810 } else { 811 // A null stackTrace field in the serial form can result from 812 // an exception serialized without that field in older JDK releases. 813 stackTrace = EMPTY_STACK; 814 } 815 816 } 817 818 /** 819 * Write a {@code Throwable} object to a stream. 820 */ 821 private synchronized void writeObject(ObjectOutputStream s) 822 throws IOException { 823 getOurStackTrace(); // Ensure that stackTrace field is initialized. 824 s.defaultWriteObject(); 825 } 826 827 /** 828 * Appends the specified exception to the exceptions that were 829 * suppressed in order to deliver this exception. This method is 830 * typically called (automatically and implicitly) by the {@code 831 * try}-with-resources statement. 832 * 833 * If the first exception to be suppressed is {@code null}, that 834 * indicates suppressed exception information will <em>not</em> be 835 * recorded for this exception. Subsequent calls to this method 836 * will not record any suppressed exceptions. Otherwise, 837 * attempting to suppress {@code null} after an exception has 838 * already been successfully suppressed results in a {@code 839 * NullPointerException}. 840 * 841 * <p>Note that when one exception {@linkplain 842 * #initCause(Throwable) causes} another exception, the first 843 * exception is usually caught and then the second exception is 844 * thrown in response. In other words, there is a causal 845 * connection between the two exceptions. 846 * 847 * In contrast, there are situations where two independent 848 * exceptions can be thrown in sibling code blocks, in particular 849 * in the {@code try} block of a {@code try}-with-resources 850 * statement and the compiler-generated {@code finally} block 851 * which closes the resource. 852 * 853 * In these situations, only one of the thrown exceptions can be 854 * propagated. In the {@code try}-with-resources statement, when 855 * there are two such exceptions, the exception originating from 856 * the {@code try} block is propagated and the exception from the 857 * {@code finally} block is added to the list of exceptions 858 * suppressed by the exception from the {@code try} block. As an 859 * exception unwinds the stack, it can accumulate multiple 860 * suppressed exceptions. 861 * 862 * <p>An exception may have suppressed exceptions while also being 863 * caused by another exception. Whether or not an exception has a 864 * cause is semantically known at the time of its creation, unlike 865 * whether or not an exception will suppress other exceptions 866 * which is typically only determined after an exception is 867 * thrown. 868 * 869 * <p>Note that programmer written code is also able to take 870 * advantage of calling this method in situations where there are 871 * multiple sibling exceptions and only one can be propagated. 872 * 873 * @param exception the exception to be added to the list of 874 * suppressed exceptions 875 * @throws IllegalArgumentException if {@code exception} is this 876 * throwable; a throwable cannot suppress itself. 877 * @throws NullPointerException if {@code exception} is null and 878 * an exception has already been suppressed by this exception 879 * @since 1.7 880 */ 881 public final synchronized void addSuppressed(Throwable exception) { 882 if (exception == this) 883 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE); 884 885 if (exception == null) { 886 if (suppressedExceptions == SUPPRESSED_SENTINEL) { 887 suppressedExceptions = null; // No suppression information recorded 888 return; 889 } else 890 throw new NullPointerException(NULL_CAUSE_MESSAGE); 891 } else { 892 assert exception != null && exception != this; 893 894 if (suppressedExceptions == null) // Suppressed exceptions not recorded 895 return; 896 897 if (suppressedExceptions == SUPPRESSED_SENTINEL) 898 suppressedExceptions = new ArrayList<>(1); 899 900 assert suppressedExceptions != SUPPRESSED_SENTINEL; 901 902 suppressedExceptions.add(exception); 903 } 904 } 905 906 private static final Throwable[] EMPTY_THROWABLE_ARRAY = new Throwable[0]; 907 908 /** 909 * Returns an array containing all of the exceptions that were 910 * suppressed, typically by the {@code try}-with-resources 911 * statement, in order to deliver this exception. 912 * 913 * If no exceptions were suppressed, an empty array is returned. 914 * 915 * @return an array containing all of the exceptions that were 916 * suppressed to deliver this exception. 917 * @since 1.7 918 */ 919 public final synchronized Throwable[] getSuppressed() { 920 if (suppressedExceptions == SUPPRESSED_SENTINEL || 921 suppressedExceptions == null) 922 return EMPTY_THROWABLE_ARRAY; 923 else 924 return suppressedExceptions.toArray(EMPTY_THROWABLE_ARRAY); 925 } 926 }