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</code> 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</code> statement. Similarly, only 35 * this class or one of its subclasses can be the argument type in a 36 * <code>catch</code> 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 * <tt>java.io</tt>. Suppose the internals of the <tt>add</tt> method 77 * can throw an {@link java.io.IOException IOException}. The implementation 78 * can communicate the details of the <tt>IOException</tt> to its caller 79 * while conforming to the <tt>Collection</tt> interface by wrapping the 80 * <tt>IOException</tt> 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 * <tt>Throwable</tt> 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 <tt>initCause</tt> 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 * <tt>Throwable</tt>. 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 <tt>Throwable</tt> 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 * <tt>initCause</tt> 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</code> and its subclasses have two 132 * constructors, one that takes no arguments and one that takes a 133 * <code>String</code> 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</code> (the cause), and one that takes a 137 * <code>String</code> (the detail message) and a <code>Throwable</code> (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 <tt>getStackTrace</tt> 145 * and <tt>printStackTrace</tt> 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 * <tt>FileNotFoundException</tt>, 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 /** 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</code> 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</code> 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 <tt>null</tt> 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 <tt>(cause==null ? null : cause.toString())</tt> (which 265 * typically contains the class and detail message of <tt>cause</tt>). 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 <tt>null</tt> 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 <tt>Throwable</tt> instance 289 * (which may be <tt>null</tt>). 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()</code>. 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</code> 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 <tt>Throwable</tt>, 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 <tt>Throwable</tt>. Note that it is <i>not</i> 321 * necessary to override any of the <tt>PrintStackTrace</tt> methods, 322 * all of which invoke the <tt>getCause</tt> method to determine the 323 * cause of a throwable. 324 * 325 * @return the cause of this throwable or <code>null</code> if the 326 * cause is nonexistent or unknown. 327 * @since 1.4 328 */ 329 public 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 <tt>null</tt> value is 346 * permitted, and indicates that the cause is nonexistent or 347 * unknown.) 348 * @return a reference to this <code>Throwable</code> instance. 349 * @throws IllegalArgumentException if <code>cause</code> 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 <tt>getLocalizedMessage</tt> returns <tt>null</tt>, 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</code> object on the error output stream that is 390 * the value of the field <code>System.err</code>. 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 <tt>"..."</tt>. 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 automatic 490 * resource management blocks). 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</code> 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 synchronized (s.lock()) { 550 // Print our stack trace 551 s.println(this); 552 StackTraceElement[] trace = getOurStackTrace(); 553 for (StackTraceElement traceElement : trace) 554 s.println("\tat " + traceElement); 555 556 // Print suppressed exceptions, if any 557 for (Throwable se : suppressedExceptions) 558 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, "\t"); 559 560 // Print cause, if any 561 Throwable ourCause = getCause(); 562 if (ourCause != null) 563 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, ""); 564 } 565 } 566 567 /** 568 * Print our stack trace as an enclosed exception for the specified 569 * stack trace. 570 */ 571 private void printEnclosedStackTrace(PrintStreamOrWriter s, 572 StackTraceElement[] enclosingTrace, String caption, String prefix) { 573 assert Thread.holdsLock(s.lock()); 574 575 // Compute number of frames in common between this and enclosing trace 576 StackTraceElement[] trace = getOurStackTrace(); 577 int m = trace.length-1, n = enclosingTrace.length-1; 578 while (m >= 0 && n >=0 && trace[m].equals(enclosingTrace[n])) { 579 m--; n--; 580 } 581 int framesInCommon = trace.length - 1 - m; 582 583 // Print our stack trace 584 s.println(prefix + caption + this); 585 for (int i = 0; i <= m; i++) 586 s.println(prefix + "\tat " + trace[i]); 587 if (framesInCommon != 0) 588 s.println(prefix + "\t... " + framesInCommon + " more"); 589 590 // Print suppressed exceptions, if any 591 for (Throwable se : suppressedExceptions) 592 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, 593 prefix +"\t"); 594 595 // Print cause, if any 596 Throwable ourCause = getCause(); 597 if (ourCause != null) 598 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, prefix); 599 } 600 601 /** 602 * Prints this throwable and its backtrace to the specified 603 * print writer. 604 * 605 * @param s <code>PrintWriter</code> to use for output 606 * @since JDK1.1 607 */ 608 public void printStackTrace(PrintWriter s) { 609 printStackTrace(new WrappedPrintWriter(s)); 610 } 611 612 /** 613 * Wrapper class for PrintStream and PrintWirter to enable a single 614 * implementation of printStackTrace. 615 */ 616 private abstract static class PrintStreamOrWriter { 617 /** Returns the object to be locked when using this StreamOrWriter */ 618 abstract Object lock(); 619 620 /** Prints the specified string as a line on this StreamOrWriter */ 621 abstract void println(Object o); 622 } 623 624 private static class WrappedPrintStream extends PrintStreamOrWriter { 625 private final PrintStream printStream; 626 627 WrappedPrintStream(PrintStream printStream) { 628 this.printStream = printStream; 629 } 630 631 Object lock() { 632 return printStream; 633 } 634 635 void println(Object o) { 636 printStream.println(o); 637 } 638 } 639 640 private static class WrappedPrintWriter extends PrintStreamOrWriter { 641 private final PrintWriter printWriter; 642 643 WrappedPrintWriter(PrintWriter printWriter) { 644 this.printWriter = printWriter; 645 } 646 647 Object lock() { 648 return printWriter; 649 } 650 651 void println(Object o) { 652 printWriter.println(o); 653 } 654 } 655 656 /** 657 * Fills in the execution stack trace. This method records within this 658 * <code>Throwable</code> object information about the current state of 659 * the stack frames for the current thread. 660 * 661 * @return a reference to this <code>Throwable</code> instance. 662 * @see java.lang.Throwable#printStackTrace() 663 */ 664 public synchronized native Throwable fillInStackTrace(); 665 666 /** 667 * Provides programmatic access to the stack trace information printed by 668 * {@link #printStackTrace()}. Returns an array of stack trace elements, 669 * each representing one stack frame. The zeroth element of the array 670 * (assuming the array's length is non-zero) represents the top of the 671 * stack, which is the last method invocation in the sequence. Typically, 672 * this is the point at which this throwable was created and thrown. 673 * The last element of the array (assuming the array's length is non-zero) 674 * represents the bottom of the stack, which is the first method invocation 675 * in the sequence. 676 * 677 * <p>Some virtual machines may, under some circumstances, omit one 678 * or more stack frames from the stack trace. In the extreme case, 679 * a virtual machine that has no stack trace information concerning 680 * this throwable is permitted to return a zero-length array from this 681 * method. Generally speaking, the array returned by this method will 682 * contain one element for every frame that would be printed by 683 * <tt>printStackTrace</tt>. 684 * 685 * @return an array of stack trace elements representing the stack trace 686 * pertaining to this throwable. 687 * @since 1.4 688 */ 689 public StackTraceElement[] getStackTrace() { 690 return getOurStackTrace().clone(); 691 } 692 693 private synchronized StackTraceElement[] getOurStackTrace() { 694 // Initialize stack trace if this is the first call to this method 695 if (stackTrace == null) { 696 int depth = getStackTraceDepth(); 697 stackTrace = new StackTraceElement[depth]; 698 for (int i=0; i < depth; i++) 699 stackTrace[i] = getStackTraceElement(i); 700 } 701 return stackTrace; 702 } 703 704 /** 705 * Sets the stack trace elements that will be returned by 706 * {@link #getStackTrace()} and printed by {@link #printStackTrace()} 707 * and related methods. 708 * 709 * This method, which is designed for use by RPC frameworks and other 710 * advanced systems, allows the client to override the default 711 * stack trace that is either generated by {@link #fillInStackTrace()} 712 * when a throwable is constructed or deserialized when a throwable is 713 * read from a serialization stream. 714 * 715 * @param stackTrace the stack trace elements to be associated with 716 * this <code>Throwable</code>. The specified array is copied by this 717 * call; changes in the specified array after the method invocation 718 * returns will have no affect on this <code>Throwable</code>'s stack 719 * trace. 720 * 721 * @throws NullPointerException if <code>stackTrace</code> is 722 * <code>null</code>, or if any of the elements of 723 * <code>stackTrace</code> are <code>null</code> 724 * 725 * @since 1.4 726 */ 727 public void setStackTrace(StackTraceElement[] stackTrace) { 728 StackTraceElement[] defensiveCopy = stackTrace.clone(); 729 for (int i = 0; i < defensiveCopy.length; i++) 730 if (defensiveCopy[i] == null) 731 throw new NullPointerException("stackTrace[" + i + "]"); 732 733 this.stackTrace = defensiveCopy; 734 } 735 736 /** 737 * Returns the number of elements in the stack trace (or 0 if the stack 738 * trace is unavailable). 739 * 740 * package-protection for use by SharedSecrets. 741 */ 742 native int getStackTraceDepth(); 743 744 /** 745 * Returns the specified element of the stack trace. 746 * 747 * package-protection for use by SharedSecrets. 748 * 749 * @param index index of the element to return. 750 * @throws IndexOutOfBoundsException if <tt>index < 0 || 751 * index >= getStackTraceDepth() </tt> 752 */ 753 native StackTraceElement getStackTraceElement(int index); 754 755 private synchronized void writeObject(java.io.ObjectOutputStream s) 756 throws IOException 757 { 758 getOurStackTrace(); // Ensure that stackTrace field is initialized. 759 s.defaultWriteObject(); 760 } 761 762 /** 763 * Adds the specified exception to the list of exceptions that 764 * were suppressed, typically by the automatic resource management 765 * statement, in order to deliver this exception. 766 * 767 * @param exception the exception to be added to the list of 768 * suppressed exceptions 769 * @throws NullPointerException if {@code exception} is null 770 * @since 1.7 771 */ 772 public synchronized void addSuppressedException(Throwable exception) { 773 if (exception == null) 774 throw new NullPointerException(); 775 776 if (suppressedExceptions.size() == 0) 777 suppressedExceptions = new ArrayList<Throwable>(); 778 suppressedExceptions.add(exception); 779 } 780 781 private static final Throwable[] EMPTY_THROWABLE_ARRAY = new Throwable[0]; 782 783 /** 784 * Returns an array containing all of the exceptions that were 785 * suppressed, typically by the automatic resource management 786 * statement, in order to deliver this exception. 787 * 788 * @return an array containing all of the exceptions that were 789 * suppressed to deliver this exception. 790 * @since 1.7 791 */ 792 public Throwable[] getSuppressedExceptions() { 793 return suppressedExceptions.toArray(EMPTY_THROWABLE_ARRAY); 794 } 795 }