1 /* 2 * Copyright (c) 1994, 2006, 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 * The throwable that caused this throwable to get thrown, or null if this 174 * throwable was not caused by another throwable, or if the causative 175 * throwable is unknown. If this field is equal to this throwable itself, 176 * it indicates that the cause of this throwable has not yet been 177 * initialized. 178 * 179 * @serial 180 * @since 1.4 181 */ 182 private Throwable cause = this; 183 184 /** 185 * The stack trace, as returned by {@link #getStackTrace()}. 186 * 187 * @serial 188 * @since 1.4 189 */ 190 private StackTraceElement[] stackTrace; 191 /* 192 * This field is lazily initialized on first use or serialization and 193 * nulled out when fillInStackTrace is called. 194 */ 195 196 /** 197 * The list of suppressed exceptions, as returned by 198 * {@link #getSuppressedExceptions()}. 199 * 200 * @serial 201 * @since 1.7 202 */ 203 private List<Throwable> suppressedExceptions = Collections.emptyList(); 204 205 /** Message for trying to suppress a null exception. */ 206 private static final String NULL_CAUSE_MESSAGE = "Cannot suppress a null exception."; 207 208 /** Caption for labeling causative exception stack traces */ 209 private static final String CAUSE_CAPTION = "Caused by: "; 210 211 /** Caption for labeling suppressed exception stack traces */ 212 private static final String SUPPRESSED_CAPTION = "Suppressed: "; 213 214 /** 215 * Constructs a new throwable with {@code null} as its detail message. 216 * The cause is not initialized, and may subsequently be initialized by a 217 * call to {@link #initCause}. 218 * 219 * <p>The {@link #fillInStackTrace()} method is called to initialize 220 * the stack trace data in the newly created throwable. 221 */ 222 public Throwable() { 223 fillInStackTrace(); 224 } 225 226 /** 227 * Constructs a new throwable with the specified detail message. The 228 * cause is not initialized, and may subsequently be initialized by 229 * a call to {@link #initCause}. 230 * 231 * <p>The {@link #fillInStackTrace()} method is called to initialize 232 * the stack trace data in the newly created throwable. 233 * 234 * @param message the detail message. The detail message is saved for 235 * later retrieval by the {@link #getMessage()} method. 236 */ 237 public Throwable(String message) { 238 fillInStackTrace(); 239 detailMessage = message; 240 } 241 242 /** 243 * Constructs a new throwable with the specified detail message and 244 * cause. <p>Note that the detail message associated with 245 * {@code cause} is <i>not</i> automatically incorporated in 246 * this throwable's detail message. 247 * 248 * <p>The {@link #fillInStackTrace()} method is called to initialize 249 * the stack trace data in the newly created throwable. 250 * 251 * @param message the detail message (which is saved for later retrieval 252 * by the {@link #getMessage()} method). 253 * @param cause the cause (which is saved for later retrieval by the 254 * {@link #getCause()} method). (A {@code null} value is 255 * permitted, and indicates that the cause is nonexistent or 256 * unknown.) 257 * @since 1.4 258 */ 259 public Throwable(String message, Throwable cause) { 260 fillInStackTrace(); 261 detailMessage = message; 262 this.cause = cause; 263 } 264 265 /** 266 * Constructs a new throwable with the specified cause and a detail 267 * message of {@code (cause==null ? null : cause.toString())} (which 268 * typically contains the class and detail message of {@code cause}). 269 * This constructor is useful for throwables that are little more than 270 * wrappers for other throwables (for example, {@link 271 * java.security.PrivilegedActionException}). 272 * 273 * <p>The {@link #fillInStackTrace()} method is called to initialize 274 * the stack trace data in the newly created throwable. 275 * 276 * @param cause the cause (which is saved for later retrieval by the 277 * {@link #getCause()} method). (A {@code null} value is 278 * permitted, and indicates that the cause is nonexistent or 279 * unknown.) 280 * @since 1.4 281 */ 282 public Throwable(Throwable cause) { 283 fillInStackTrace(); 284 detailMessage = (cause==null ? null : cause.toString()); 285 this.cause = cause; 286 } 287 288 /** 289 * Returns the detail message string of this throwable. 290 * 291 * @return the detail message string of this {@code Throwable} instance 292 * (which may be {@code null}). 293 */ 294 public String getMessage() { 295 return detailMessage; 296 } 297 298 /** 299 * Creates a localized description of this throwable. 300 * Subclasses may override this method in order to produce a 301 * locale-specific message. For subclasses that do not override this 302 * method, the default implementation returns the same result as 303 * {@code getMessage()}. 304 * 305 * @return The localized description of this throwable. 306 * @since JDK1.1 307 */ 308 public String getLocalizedMessage() { 309 return getMessage(); 310 } 311 312 /** 313 * Returns the cause of this throwable or {@code null} if the 314 * cause is nonexistent or unknown. (The cause is the throwable that 315 * caused this throwable to get thrown.) 316 * 317 * <p>This implementation returns the cause that was supplied via one of 318 * the constructors requiring a {@code Throwable}, or that was set after 319 * creation with the {@link #initCause(Throwable)} method. While it is 320 * typically unnecessary to override this method, a subclass can override 321 * it to return a cause set by some other means. This is appropriate for 322 * a "legacy chained throwable" that predates the addition of chained 323 * exceptions to {@code Throwable}. Note that it is <i>not</i> 324 * necessary to override any of the {@code PrintStackTrace} methods, 325 * all of which invoke the {@code getCause} method to determine the 326 * cause of a throwable. 327 * 328 * @return the cause of this throwable or {@code null} if the 329 * cause is nonexistent or unknown. 330 * @since 1.4 331 */ 332 public Throwable getCause() { 333 return (cause==this ? null : cause); 334 } 335 336 /** 337 * Initializes the <i>cause</i> of this throwable to the specified value. 338 * (The cause is the throwable that caused this throwable to get thrown.) 339 * 340 * <p>This method can be called at most once. It is generally called from 341 * within the constructor, or immediately after creating the 342 * throwable. If this throwable was created 343 * with {@link #Throwable(Throwable)} or 344 * {@link #Throwable(String,Throwable)}, this method cannot be called 345 * even once. 346 * 347 * @param cause the cause (which is saved for later retrieval by the 348 * {@link #getCause()} method). (A {@code null} value is 349 * permitted, and indicates that the cause is nonexistent or 350 * unknown.) 351 * @return a reference to this {@code Throwable} instance. 352 * @throws IllegalArgumentException if {@code cause} is this 353 * throwable. (A throwable cannot be its own cause.) 354 * @throws IllegalStateException if this throwable was 355 * created with {@link #Throwable(Throwable)} or 356 * {@link #Throwable(String,Throwable)}, or this method has already 357 * been called on this throwable. 358 * @since 1.4 359 */ 360 public synchronized Throwable initCause(Throwable cause) { 361 if (this.cause != this) 362 throw new IllegalStateException("Can't overwrite cause"); 363 if (cause == this) 364 throw new IllegalArgumentException("Self-causation not permitted"); 365 this.cause = cause; 366 return this; 367 } 368 369 /** 370 * Returns a short description of this throwable. 371 * The result is the concatenation of: 372 * <ul> 373 * <li> the {@linkplain Class#getName() name} of the class of this object 374 * <li> ": " (a colon and a space) 375 * <li> the result of invoking this object's {@link #getLocalizedMessage} 376 * method 377 * </ul> 378 * If {@code getLocalizedMessage} returns {@code null}, then just 379 * the class name is returned. 380 * 381 * @return a string representation of this throwable. 382 */ 383 public String toString() { 384 String s = getClass().getName(); 385 String message = getLocalizedMessage(); 386 return (message != null) ? (s + ": " + message) : s; 387 } 388 389 /** 390 * Prints this throwable and its backtrace to the 391 * standard error stream. This method prints a stack trace for this 392 * {@code Throwable} object on the error output stream that is 393 * the value of the field {@code System.err}. The first line of 394 * output contains the result of the {@link #toString()} method for 395 * this object. Remaining lines represent data previously recorded by 396 * the method {@link #fillInStackTrace()}. The format of this 397 * information depends on the implementation, but the following 398 * example may be regarded as typical: 399 * <blockquote><pre> 400 * java.lang.NullPointerException 401 * at MyClass.mash(MyClass.java:9) 402 * at MyClass.crunch(MyClass.java:6) 403 * at MyClass.main(MyClass.java:3) 404 * </pre></blockquote> 405 * This example was produced by running the program: 406 * <pre> 407 * class MyClass { 408 * public static void main(String[] args) { 409 * crunch(null); 410 * } 411 * static void crunch(int[] a) { 412 * mash(a); 413 * } 414 * static void mash(int[] b) { 415 * System.out.println(b[0]); 416 * } 417 * } 418 * </pre> 419 * The backtrace for a throwable with an initialized, non-null cause 420 * should generally include the backtrace for the cause. The format 421 * of this information depends on the implementation, but the following 422 * example may be regarded as typical: 423 * <pre> 424 * HighLevelException: MidLevelException: LowLevelException 425 * at Junk.a(Junk.java:13) 426 * at Junk.main(Junk.java:4) 427 * Caused by: MidLevelException: LowLevelException 428 * at Junk.c(Junk.java:23) 429 * at Junk.b(Junk.java:17) 430 * at Junk.a(Junk.java:11) 431 * ... 1 more 432 * Caused by: LowLevelException 433 * at Junk.e(Junk.java:30) 434 * at Junk.d(Junk.java:27) 435 * at Junk.c(Junk.java:21) 436 * ... 3 more 437 * </pre> 438 * Note the presence of lines containing the characters {@code "..."}. 439 * These lines indicate that the remainder of the stack trace for this 440 * exception matches the indicated number of frames from the bottom of the 441 * stack trace of the exception that was caused by this exception (the 442 * "enclosing" exception). This shorthand can greatly reduce the length 443 * of the output in the common case where a wrapped exception is thrown 444 * from same method as the "causative exception" is caught. The above 445 * example was produced by running the program: 446 * <pre> 447 * public class Junk { 448 * public static void main(String args[]) { 449 * try { 450 * a(); 451 * } catch(HighLevelException e) { 452 * e.printStackTrace(); 453 * } 454 * } 455 * static void a() throws HighLevelException { 456 * try { 457 * b(); 458 * } catch(MidLevelException e) { 459 * throw new HighLevelException(e); 460 * } 461 * } 462 * static void b() throws MidLevelException { 463 * c(); 464 * } 465 * static void c() throws MidLevelException { 466 * try { 467 * d(); 468 * } catch(LowLevelException e) { 469 * throw new MidLevelException(e); 470 * } 471 * } 472 * static void d() throws LowLevelException { 473 * e(); 474 * } 475 * static void e() throws LowLevelException { 476 * throw new LowLevelException(); 477 * } 478 * } 479 * 480 * class HighLevelException extends Exception { 481 * HighLevelException(Throwable cause) { super(cause); } 482 * } 483 * 484 * class MidLevelException extends Exception { 485 * MidLevelException(Throwable cause) { super(cause); } 486 * } 487 * 488 * class LowLevelException extends Exception { 489 * } 490 * </pre> 491 * As of release 7, the platform supports the notion of 492 * <i>suppressed exceptions</i> (in conjunction with automatic 493 * resource management blocks). Any exceptions that were 494 * suppressed in order to deliver an exception are printed out 495 * beneath the stack trace. The format of this information 496 * depends on the implementation, but the following example may be 497 * regarded as typical: 498 * 499 * <pre> 500 * Exception in thread "main" java.lang.Exception: Something happened 501 * at Foo.bar(Foo.java:10) 502 * at Foo.main(Foo.java:5) 503 * Suppressed: Resource$CloseFailException: Resource ID = 0 504 * at Resource.close(Resource.java:26) 505 * at Foo.bar(Foo.java:9) 506 * ... 1 more 507 * </pre> 508 * Note that the "... n more" notation is used on suppressed exceptions 509 * just at it is used on causes. Unlike causes, suppressed exceptions are 510 * indented beyond their "containing exceptions." 511 * 512 * <p>An exception can have both a cause and one or more suppressed 513 * exceptions: 514 * <pre> 515 * Exception in thread "main" java.lang.Exception: Main block 516 * at Foo3.main(Foo3.java:7) 517 * Suppressed: Resource$CloseFailException: Resource ID = 2 518 * at Resource.close(Resource.java:26) 519 * at Foo3.main(Foo3.java:5) 520 * Suppressed: Resource$CloseFailException: Resource ID = 1 521 * at Resource.close(Resource.java:26) 522 * at Foo3.main(Foo3.java:5) 523 * Caused by: java.lang.Exception: I did it 524 * at Foo3.main(Foo3.java:8) 525 * </pre> 526 * Likewise, a suppressed exception can have a cause: 527 * <pre> 528 * Exception in thread "main" java.lang.Exception: Main block 529 * at Foo4.main(Foo4.java:6) 530 * Suppressed: Resource2$CloseFailException: Resource ID = 1 531 * at Resource2.close(Resource2.java:20) 532 * at Foo4.main(Foo4.java:5) 533 * Caused by: java.lang.Exception: Rats, you caught me 534 * at Resource2$CloseFailException.<init>(Resource2.java:45) 535 * ... 2 more 536 * </pre> 537 */ 538 public void printStackTrace() { 539 printStackTrace(System.err); 540 } 541 542 /** 543 * Prints this throwable and its backtrace to the specified print stream. 544 * 545 * @param s {@code PrintStream} to use for output 546 */ 547 public void printStackTrace(PrintStream s) { 548 printStackTrace(new WrappedPrintStream(s)); 549 } 550 551 private void printStackTrace(PrintStreamOrWriter s) { 552 // Guard against malicious overrides of Throwable.equals by 553 // using a Set with identity equality semantics. 554 Set<Throwable> dejaVu = 555 Collections.newSetFromMap(new IdentityHashMap<Throwable, Boolean>()); 556 dejaVu.add(this); 557 558 synchronized (s.lock()) { 559 // Print our stack trace 560 s.println(this); 561 StackTraceElement[] trace = getOurStackTrace(); 562 for (StackTraceElement traceElement : trace) 563 s.println("\tat " + traceElement); 564 565 // Print suppressed exceptions, if any 566 for (Throwable se : suppressedExceptions) 567 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, "\t", dejaVu); 568 569 // Print cause, if any 570 Throwable ourCause = getCause(); 571 if (ourCause != null) 572 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, "", dejaVu); 573 } 574 } 575 576 /** 577 * Print our stack trace as an enclosed exception for the specified 578 * stack trace. 579 */ 580 private void printEnclosedStackTrace(PrintStreamOrWriter s, 581 StackTraceElement[] enclosingTrace, 582 String caption, 583 String prefix, 584 Set<Throwable> dejaVu) { 585 assert Thread.holdsLock(s.lock()); 586 if (dejaVu.contains(this)) { 587 s.println("\t[CIRCULAR REFERENCE:" + this + "]"); 588 } else { 589 dejaVu.add(this); 590 // Compute number of frames in common between this and enclosing trace 591 StackTraceElement[] trace = getOurStackTrace(); 592 int m = trace.length - 1; 593 int n = enclosingTrace.length - 1; 594 while (m >= 0 && n >=0 && trace[m].equals(enclosingTrace[n])) { 595 m--; n--; 596 } 597 int framesInCommon = trace.length - 1 - m; 598 599 // Print our stack trace 600 s.println(prefix + caption + this); 601 for (int i = 0; i <= m; i++) 602 s.println(prefix + "\tat " + trace[i]); 603 if (framesInCommon != 0) 604 s.println(prefix + "\t... " + framesInCommon + " more"); 605 606 // Print suppressed exceptions, if any 607 for (Throwable se : suppressedExceptions) 608 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, 609 prefix +"\t", dejaVu); 610 611 // Print cause, if any 612 Throwable ourCause = getCause(); 613 if (ourCause != null) 614 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, prefix, dejaVu); 615 } 616 } 617 618 /** 619 * Prints this throwable and its backtrace to the specified 620 * print writer. 621 * 622 * @param s {@code PrintWriter} to use for output 623 * @since JDK1.1 624 */ 625 public void printStackTrace(PrintWriter s) { 626 printStackTrace(new WrappedPrintWriter(s)); 627 } 628 629 /** 630 * Wrapper class for PrintStream and PrintWriter to enable a single 631 * implementation of printStackTrace. 632 */ 633 private abstract static class PrintStreamOrWriter { 634 /** Returns the object to be locked when using this StreamOrWriter */ 635 abstract Object lock(); 636 637 /** Prints the specified string as a line on this StreamOrWriter */ 638 abstract void println(Object o); 639 } 640 641 private static class WrappedPrintStream extends PrintStreamOrWriter { 642 private final PrintStream printStream; 643 644 WrappedPrintStream(PrintStream printStream) { 645 this.printStream = printStream; 646 } 647 648 Object lock() { 649 return printStream; 650 } 651 652 void println(Object o) { 653 printStream.println(o); 654 } 655 } 656 657 private static class WrappedPrintWriter extends PrintStreamOrWriter { 658 private final PrintWriter printWriter; 659 660 WrappedPrintWriter(PrintWriter printWriter) { 661 this.printWriter = printWriter; 662 } 663 664 Object lock() { 665 return printWriter; 666 } 667 668 void println(Object o) { 669 printWriter.println(o); 670 } 671 } 672 673 /** 674 * Fills in the execution stack trace. This method records within this 675 * {@code Throwable} object information about the current state of 676 * the stack frames for the current thread. 677 * 678 * @return a reference to this {@code Throwable} instance. 679 * @see java.lang.Throwable#printStackTrace() 680 */ 681 public synchronized native Throwable fillInStackTrace(); 682 683 /** 684 * Provides programmatic access to the stack trace information printed by 685 * {@link #printStackTrace()}. Returns an array of stack trace elements, 686 * each representing one stack frame. The zeroth element of the array 687 * (assuming the array's length is non-zero) represents the top of the 688 * stack, which is the last method invocation in the sequence. Typically, 689 * this is the point at which this throwable was created and thrown. 690 * The last element of the array (assuming the array's length is non-zero) 691 * represents the bottom of the stack, which is the first method invocation 692 * in the sequence. 693 * 694 * <p>Some virtual machines may, under some circumstances, omit one 695 * or more stack frames from the stack trace. In the extreme case, 696 * a virtual machine that has no stack trace information concerning 697 * this throwable is permitted to return a zero-length array from this 698 * method. Generally speaking, the array returned by this method will 699 * contain one element for every frame that would be printed by 700 * {@code printStackTrace}. 701 * 702 * @return an array of stack trace elements representing the stack trace 703 * pertaining to this throwable. 704 * @since 1.4 705 */ 706 public StackTraceElement[] getStackTrace() { 707 return getOurStackTrace().clone(); 708 } 709 710 private synchronized StackTraceElement[] getOurStackTrace() { 711 // Initialize stack trace if this is the first call to this method 712 if (stackTrace == null) { 713 int depth = getStackTraceDepth(); 714 stackTrace = new StackTraceElement[depth]; 715 for (int i=0; i < depth; i++) 716 stackTrace[i] = getStackTraceElement(i); 717 } 718 return stackTrace; 719 } 720 721 /** 722 * Sets the stack trace elements that will be returned by 723 * {@link #getStackTrace()} and printed by {@link #printStackTrace()} 724 * and related methods. 725 * 726 * This method, which is designed for use by RPC frameworks and other 727 * advanced systems, allows the client to override the default 728 * stack trace that is either generated by {@link #fillInStackTrace()} 729 * when a throwable is constructed or deserialized when a throwable is 730 * read from a serialization stream. 731 * 732 * @param stackTrace the stack trace elements to be associated with 733 * this {@code Throwable}. The specified array is copied by this 734 * call; changes in the specified array after the method invocation 735 * returns will have no affect on this {@code Throwable}'s stack 736 * trace. 737 * 738 * @throws NullPointerException if {@code stackTrace} is 739 * {@code null}, or if any of the elements of 740 * {@code stackTrace} are {@code null} 741 * 742 * @since 1.4 743 */ 744 public void setStackTrace(StackTraceElement[] stackTrace) { 745 StackTraceElement[] defensiveCopy = stackTrace.clone(); 746 for (int i = 0; i < defensiveCopy.length; i++) 747 if (defensiveCopy[i] == null) 748 throw new NullPointerException("stackTrace[" + i + "]"); 749 750 this.stackTrace = defensiveCopy; 751 } 752 753 /** 754 * Returns the number of elements in the stack trace (or 0 if the stack 755 * trace is unavailable). 756 * 757 * package-protection for use by SharedSecrets. 758 */ 759 native int getStackTraceDepth(); 760 761 /** 762 * Returns the specified element of the stack trace. 763 * 764 * package-protection for use by SharedSecrets. 765 * 766 * @param index index of the element to return. 767 * @throws IndexOutOfBoundsException if {@code index < 0 || 768 * index >= getStackTraceDepth() } 769 */ 770 native StackTraceElement getStackTraceElement(int index); 771 772 private void readObject(ObjectInputStream s) 773 throws IOException, ClassNotFoundException { 774 s.defaultReadObject(); // read in all fields 775 List<Throwable> suppressed = Collections.emptyList(); 776 if (suppressedExceptions != null && 777 !suppressedExceptions.isEmpty()) { // Copy Throwables to new list 778 suppressed = new ArrayList<Throwable>(); 779 for(Throwable t : suppressedExceptions) { 780 if (t == null) 781 throw new NullPointerException(NULL_CAUSE_MESSAGE); 782 suppressed.add(t); 783 } 784 } 785 suppressedExceptions = suppressed; 786 } 787 788 private synchronized void writeObject(ObjectOutputStream s) 789 throws IOException 790 { 791 getOurStackTrace(); // Ensure that stackTrace field is initialized. 792 s.defaultWriteObject(); 793 } 794 795 /** 796 * Adds the specified exception to the list of exceptions that 797 * were suppressed, typically by the automatic resource management 798 * statement, in order to deliver this exception. 799 * 800 * <p>Note that when one exception {@linkplain 801 * #initCause(Throwable) causes} another exception, the first 802 * exception is usually caught and then the second exception is 803 * thrown in response. In contrast, when when one exception 804 * suppresses another, two exceptions are thrown in sibling code 805 * blocks, such as in a {@code try} block and in its {@code 806 * finally} block, and control flow can only continue with one 807 * exception so the second is recorded as a suppressed exception 808 * of the first. 809 * 810 * @param exception the exception to be added to the list of 811 * suppressed exceptions 812 * @throws NullPointerException if {@code exception} is null 813 * @throws IllegalArgumentException if {@code exception} is this 814 * throwable; a throwable cannot suppress itself. 815 * @since 1.7 816 */ 817 public synchronized void addSuppressedException(Throwable exception) { 818 if (exception == null) 819 throw new NullPointerException(NULL_CAUSE_MESSAGE); 820 if (exception == this) 821 throw new IllegalArgumentException("Self-suppression not permitted"); 822 823 if (suppressedExceptions.size() == 0) 824 suppressedExceptions = new ArrayList<Throwable>(); 825 suppressedExceptions.add(exception); 826 } 827 828 private static final Throwable[] EMPTY_THROWABLE_ARRAY = new Throwable[0]; 829 830 /** 831 * Returns an array containing all of the exceptions that were 832 * suppressed, typically by the automatic resource management 833 * statement, in order to deliver this exception. 834 * 835 * @return an array containing all of the exceptions that were 836 * suppressed to deliver this exception. 837 * @since 1.7 838 */ 839 public Throwable[] getSuppressedExceptions() { 840 return suppressedExceptions.toArray(EMPTY_THROWABLE_ARRAY); 841 } 842 }