1 /* 2 * Copyright (c) 1994, 2010, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 26 package java.lang; 27 import java.io.*; 28 import java.util.*; 29 30 /** 31 * The {@code Throwable} class is the superclass of all errors and 32 * exceptions in the Java language. Only objects that are instances of this 33 * class (or one of its subclasses) are thrown by the Java Virtual Machine or 34 * can be thrown by the Java {@code throw} statement. Similarly, only 35 * this class or one of its subclasses can be the argument type in a 36 * {@code catch} clause. 37 * 38 * For the purposes of compile-time checking of exceptions, {@code 39 * Throwable} and any subclass of {@code Throwable} that is not also a 40 * subclass of either {@link RuntimeException} or {@link Error} are 41 * regarded as checked exceptions. 42 * 43 * <p>Instances of two subclasses, {@link java.lang.Error} and 44 * {@link java.lang.Exception}, are conventionally used to indicate 45 * that exceptional situations have occurred. Typically, these instances 46 * are freshly created in the context of the exceptional situation so 47 * as to include relevant information (such as stack trace data). 48 * 49 * <p>A throwable contains a snapshot of the execution stack of its thread at 50 * the time it was created. It can also contain a message string that gives 51 * more information about the error. Finally, it can contain a <i>cause</i>: 52 * another throwable that caused this throwable to get thrown. The cause 53 * facility is new in release 1.4. It is also known as the <i>chained 54 * exception</i> facility, as the cause can, itself, have a cause, and so on, 55 * leading to a "chain" of exceptions, each caused by another. 56 * 57 * <p>One reason that a throwable may have a cause is that the class that 58 * throws it is built atop a lower layered abstraction, and an operation on 59 * the upper layer fails due to a failure in the lower layer. It would be bad 60 * design to let the throwable thrown by the lower layer propagate outward, as 61 * it is generally unrelated to the abstraction provided by the upper layer. 62 * Further, doing so would tie the API of the upper layer to the details of 63 * its implementation, assuming the lower layer's exception was a checked 64 * exception. Throwing a "wrapped exception" (i.e., an exception containing a 65 * cause) allows the upper layer to communicate the details of the failure to 66 * its caller without incurring either of these shortcomings. It preserves 67 * the flexibility to change the implementation of the upper layer without 68 * changing its API (in particular, the set of exceptions thrown by its 69 * methods). 70 * 71 * <p>A second reason that a throwable may have a cause is that the method 72 * that throws it must conform to a general-purpose interface that does not 73 * permit the method to throw the cause directly. For example, suppose 74 * a persistent collection conforms to the {@link java.util.Collection 75 * Collection} interface, and that its persistence is implemented atop 76 * {@code java.io}. Suppose the internals of the {@code add} method 77 * can throw an {@link java.io.IOException IOException}. The implementation 78 * can communicate the details of the {@code IOException} to its caller 79 * while conforming to the {@code Collection} interface by wrapping the 80 * {@code IOException} in an appropriate unchecked exception. (The 81 * specification for the persistent collection should indicate that it is 82 * capable of throwing such exceptions.) 83 * 84 * <p>A cause can be associated with a throwable in two ways: via a 85 * constructor that takes the cause as an argument, or via the 86 * {@link #initCause(Throwable)} method. New throwable classes that 87 * wish to allow causes to be associated with them should provide constructors 88 * that take a cause and delegate (perhaps indirectly) to one of the 89 * {@code Throwable} constructors that takes a cause. For example: 90 * <pre> 91 * try { 92 * lowLevelOp(); 93 * } catch (LowLevelException le) { 94 * throw new HighLevelException(le); // Chaining-aware constructor 95 * } 96 * </pre> 97 * Because the {@code initCause} method is public, it allows a cause to be 98 * associated with any throwable, even a "legacy throwable" whose 99 * implementation predates the addition of the exception chaining mechanism to 100 * {@code Throwable}. For example: 101 * <pre> 102 * try { 103 * lowLevelOp(); 104 * } catch (LowLevelException le) { 105 * throw (HighLevelException) 106 * new HighLevelException().initCause(le); // Legacy constructor 107 * } 108 * </pre> 109 * 110 * <p>Prior to release 1.4, there were many throwables that had their own 111 * non-standard exception chaining mechanisms ( 112 * {@link ExceptionInInitializerError}, {@link ClassNotFoundException}, 113 * {@link java.lang.reflect.UndeclaredThrowableException}, 114 * {@link java.lang.reflect.InvocationTargetException}, 115 * {@link java.io.WriteAbortedException}, 116 * {@link java.security.PrivilegedActionException}, 117 * {@link java.awt.print.PrinterIOException}, 118 * {@link java.rmi.RemoteException} and 119 * {@link javax.naming.NamingException}). 120 * All of these throwables have been retrofitted to 121 * use the standard exception chaining mechanism, while continuing to 122 * implement their "legacy" chaining mechanisms for compatibility. 123 * 124 * <p>Further, as of release 1.4, many general purpose {@code Throwable} 125 * classes (for example {@link Exception}, {@link RuntimeException}, 126 * {@link Error}) have been retrofitted with constructors that take 127 * a cause. This was not strictly necessary, due to the existence of the 128 * {@code initCause} method, but it is more convenient and expressive to 129 * delegate to a constructor that takes a cause. 130 * 131 * <p>By convention, class {@code Throwable} and its subclasses have two 132 * constructors, one that takes no arguments and one that takes a 133 * {@code String} argument that can be used to produce a detail message. 134 * Further, those subclasses that might likely have a cause associated with 135 * them should have two more constructors, one that takes a 136 * {@code Throwable} (the cause), and one that takes a 137 * {@code String} (the detail message) and a {@code Throwable} (the 138 * cause). 139 * 140 * <p>Also introduced in release 1.4 is the {@link #getStackTrace()} method, 141 * which allows programmatic access to the stack trace information that was 142 * previously available only in text form, via the various forms of the 143 * {@link #printStackTrace()} method. This information has been added to the 144 * <i>serialized representation</i> of this class so {@code getStackTrace} 145 * and {@code printStackTrace} will operate properly on a throwable that 146 * was obtained by deserialization. 147 * 148 * @author unascribed 149 * @author Josh Bloch (Added exception chaining and programmatic access to 150 * stack trace in 1.4.) 151 * @jls3 11.2 Compile-Time Checking of Exceptions 152 * @since JDK1.0 153 */ 154 public class Throwable implements Serializable { 155 /** use serialVersionUID from JDK 1.0.2 for interoperability */ 156 private static final long serialVersionUID = -3042686055658047285L; 157 158 /** 159 * Native code saves some indication of the stack backtrace in this slot. 160 */ 161 private transient Object backtrace; 162 163 /** 164 * Specific details about the Throwable. For example, for 165 * {@code FileNotFoundException}, this contains the name of 166 * the file that could not be found. 167 * 168 * @serial 169 */ 170 private String detailMessage; 171 172 /* 173 * To allow Throwable objects to be made immutable and safely 174 * reused by the JVM, such as pre-allocated OutOfMemoryErrors, the 175 * fields of Throwable that are writable in response to user 176 * actions, cause and suppressedExceptions, obey the following 177 * protocol: 178 * 179 * 1) The fields are initialized to a non-null sentinel value 180 * which indicates the value has logically not been set. 181 * 182 * 2) Writing a null to the field indicates further writes 183 * are forbidden 184 * 185 * 3) The sentinel value may be replaced with another non-null 186 * value. 187 * 188 * Implementations of the HotSpot JVM have preallocated 189 * OutOfMemoryError objects to provide for better diagnosability 190 * of that situation. These objects are created without calling 191 * the constructor for that class and the fields in question are 192 * initialized to null. To support this capability, any new 193 * fields added to Throwable that require being initialized to a 194 * non-null value require a coordinated JVM change. 195 */ 196 197 /** 198 * The throwable that caused this throwable to get thrown, or null if this 199 * throwable was not caused by another throwable, or if the causative 200 * throwable is unknown. If this field is equal to this throwable itself, 201 * it indicates that the cause of this throwable has not yet been 202 * initialized. 203 * 204 * @serial 205 * @since 1.4 206 */ 207 private Throwable cause = this; 208 209 /** 210 * The stack trace, as returned by {@link #getStackTrace()}. 211 * 212 * @serial 213 * @since 1.4 214 */ 215 private StackTraceElement[] stackTrace; 216 217 // Setting this static field introduces an acceptable 218 // initialization dependency on a few java.util classes. 219 private static final List<Throwable> suppressedSentinel = 220 Collections.unmodifiableList(new ArrayList<Throwable>(0)); 221 222 /** 223 * The list of suppressed exceptions, as returned by {@link 224 * #getSuppressed()}. The list is initialized to a zero-element 225 * unmodifiable sentinel list. When a serialized Throwable is 226 * read in, if the {@code suppressedExceptions} field points to a 227 * zero-element list, the field is reset to the sentinel value. 228 * 229 * @serial 230 * @since 1.7 231 */ 232 private List<Throwable> suppressedExceptions = suppressedSentinel; 233 234 /** Message for trying to suppress a null exception. */ 235 private static final String NULL_CAUSE_MESSAGE = "Cannot suppress a null exception."; 236 237 /** Message for trying to suppress oneself. */ 238 private static final String SELF_SUPPRESSION_MESSAGE = "Self-suppression not permitted"; 239 240 /** Caption for labeling causative exception stack traces */ 241 private static final String CAUSE_CAPTION = "Caused by: "; 242 243 /** Caption for labeling suppressed exception stack traces */ 244 private static final String SUPPRESSED_CAPTION = "Suppressed: "; 245 246 /** 247 * Constructs a new throwable with {@code null} as its detail message. 248 * The cause is not initialized, and may subsequently be initialized by a 249 * call to {@link #initCause}. 250 * 251 * <p>The {@link #fillInStackTrace()} method is called to initialize 252 * the stack trace data in the newly created throwable. 253 */ 254 public Throwable() { 255 fillInStackTrace(); 256 } 257 258 /** 259 * Constructs a new throwable with the specified detail message. The 260 * cause is not initialized, and may subsequently be initialized by 261 * a call to {@link #initCause}. 262 * 263 * <p>The {@link #fillInStackTrace()} method is called to initialize 264 * the stack trace data in the newly created throwable. 265 * 266 * @param message the detail message. The detail message is saved for 267 * later retrieval by the {@link #getMessage()} method. 268 */ 269 public Throwable(String message) { 270 fillInStackTrace(); 271 detailMessage = message; 272 } 273 274 /** 275 * Constructs a new throwable with the specified detail message and 276 * cause. <p>Note that the detail message associated with 277 * {@code cause} is <i>not</i> automatically incorporated in 278 * this throwable's detail message. 279 * 280 * <p>The {@link #fillInStackTrace()} method is called to initialize 281 * the stack trace data in the newly created throwable. 282 * 283 * @param message the detail message (which is saved for later retrieval 284 * by the {@link #getMessage()} method). 285 * @param cause the cause (which is saved for later retrieval by the 286 * {@link #getCause()} method). (A {@code null} value is 287 * permitted, and indicates that the cause is nonexistent or 288 * unknown.) 289 * @since 1.4 290 */ 291 public Throwable(String message, Throwable cause) { 292 fillInStackTrace(); 293 detailMessage = message; 294 this.cause = cause; 295 } 296 297 /** 298 * Constructs a new throwable with the specified cause and a detail 299 * message of {@code (cause==null ? null : cause.toString())} (which 300 * typically contains the class and detail message of {@code cause}). 301 * This constructor is useful for throwables that are little more than 302 * wrappers for other throwables (for example, {@link 303 * java.security.PrivilegedActionException}). 304 * 305 * <p>The {@link #fillInStackTrace()} method is called to initialize 306 * the stack trace data in the newly created throwable. 307 * 308 * @param cause the cause (which is saved for later retrieval by the 309 * {@link #getCause()} method). (A {@code null} value is 310 * permitted, and indicates that the cause is nonexistent or 311 * unknown.) 312 * @since 1.4 313 */ 314 public Throwable(Throwable cause) { 315 fillInStackTrace(); 316 detailMessage = (cause==null ? null : cause.toString()); 317 this.cause = cause; 318 } 319 320 /** 321 * Returns the detail message string of this throwable. 322 * 323 * @return the detail message string of this {@code Throwable} instance 324 * (which may be {@code null}). 325 */ 326 public String getMessage() { 327 return detailMessage; 328 } 329 330 /** 331 * Creates a localized description of this throwable. 332 * Subclasses may override this method in order to produce a 333 * locale-specific message. For subclasses that do not override this 334 * method, the default implementation returns the same result as 335 * {@code getMessage()}. 336 * 337 * @return The localized description of this throwable. 338 * @since JDK1.1 339 */ 340 public String getLocalizedMessage() { 341 return getMessage(); 342 } 343 344 /** 345 * Returns the cause of this throwable or {@code null} if the 346 * cause is nonexistent or unknown. (The cause is the throwable that 347 * caused this throwable to get thrown.) 348 * 349 * <p>This implementation returns the cause that was supplied via one of 350 * the constructors requiring a {@code Throwable}, or that was set after 351 * creation with the {@link #initCause(Throwable)} method. While it is 352 * typically unnecessary to override this method, a subclass can override 353 * it to return a cause set by some other means. This is appropriate for 354 * a "legacy chained throwable" that predates the addition of chained 355 * exceptions to {@code Throwable}. Note that it is <i>not</i> 356 * necessary to override any of the {@code PrintStackTrace} methods, 357 * all of which invoke the {@code getCause} method to determine the 358 * cause of a throwable. 359 * 360 * @return the cause of this throwable or {@code null} if the 361 * cause is nonexistent or unknown. 362 * @since 1.4 363 */ 364 public synchronized Throwable getCause() { 365 return (cause==this ? null : cause); 366 } 367 368 /** 369 * Initializes the <i>cause</i> of this throwable to the specified value. 370 * (The cause is the throwable that caused this throwable to get thrown.) 371 * 372 * <p>This method can be called at most once. It is generally called from 373 * within the constructor, or immediately after creating the 374 * throwable. If this throwable was created 375 * with {@link #Throwable(Throwable)} or 376 * {@link #Throwable(String,Throwable)}, this method cannot be called 377 * even once. 378 * 379 * @param cause the cause (which is saved for later retrieval by the 380 * {@link #getCause()} method). (A {@code null} value is 381 * permitted, and indicates that the cause is nonexistent or 382 * unknown.) 383 * @return a reference to this {@code Throwable} instance. 384 * @throws IllegalArgumentException if {@code cause} is this 385 * throwable. (A throwable cannot be its own cause.) 386 * @throws IllegalStateException if this throwable was 387 * created with {@link #Throwable(Throwable)} or 388 * {@link #Throwable(String,Throwable)}, or this method has already 389 * been called on this throwable. 390 * @since 1.4 391 */ 392 public synchronized Throwable initCause(Throwable cause) { 393 if (this.cause != this) 394 throw new IllegalStateException("Can't overwrite cause"); 395 if (cause == this) 396 throw new IllegalArgumentException("Self-causation not permitted"); 397 this.cause = cause; 398 return this; 399 } 400 401 /** 402 * Returns a short description of this throwable. 403 * The result is the concatenation of: 404 * <ul> 405 * <li> the {@linkplain Class#getName() name} of the class of this object 406 * <li> ": " (a colon and a space) 407 * <li> the result of invoking this object's {@link #getLocalizedMessage} 408 * method 409 * </ul> 410 * If {@code getLocalizedMessage} returns {@code null}, then just 411 * the class name is returned. 412 * 413 * @return a string representation of this throwable. 414 */ 415 public String toString() { 416 String s = getClass().getName(); 417 String message = getLocalizedMessage(); 418 return (message != null) ? (s + ": " + message) : s; 419 } 420 421 /** 422 * Prints this throwable and its backtrace to the 423 * standard error stream. This method prints a stack trace for this 424 * {@code Throwable} object on the error output stream that is 425 * the value of the field {@code System.err}. The first line of 426 * output contains the result of the {@link #toString()} method for 427 * this object. Remaining lines represent data previously recorded by 428 * the method {@link #fillInStackTrace()}. The format of this 429 * information depends on the implementation, but the following 430 * example may be regarded as typical: 431 * <blockquote><pre> 432 * java.lang.NullPointerException 433 * at MyClass.mash(MyClass.java:9) 434 * at MyClass.crunch(MyClass.java:6) 435 * at MyClass.main(MyClass.java:3) 436 * </pre></blockquote> 437 * This example was produced by running the program: 438 * <pre> 439 * class MyClass { 440 * public static void main(String[] args) { 441 * crunch(null); 442 * } 443 * static void crunch(int[] a) { 444 * mash(a); 445 * } 446 * static void mash(int[] b) { 447 * System.out.println(b[0]); 448 * } 449 * } 450 * </pre> 451 * The backtrace for a throwable with an initialized, non-null cause 452 * should generally include the backtrace for the cause. The format 453 * of this information depends on the implementation, but the following 454 * example may be regarded as typical: 455 * <pre> 456 * HighLevelException: MidLevelException: LowLevelException 457 * at Junk.a(Junk.java:13) 458 * at Junk.main(Junk.java:4) 459 * Caused by: MidLevelException: LowLevelException 460 * at Junk.c(Junk.java:23) 461 * at Junk.b(Junk.java:17) 462 * at Junk.a(Junk.java:11) 463 * ... 1 more 464 * Caused by: LowLevelException 465 * at Junk.e(Junk.java:30) 466 * at Junk.d(Junk.java:27) 467 * at Junk.c(Junk.java:21) 468 * ... 3 more 469 * </pre> 470 * Note the presence of lines containing the characters {@code "..."}. 471 * These lines indicate that the remainder of the stack trace for this 472 * exception matches the indicated number of frames from the bottom of the 473 * stack trace of the exception that was caused by this exception (the 474 * "enclosing" exception). This shorthand can greatly reduce the length 475 * of the output in the common case where a wrapped exception is thrown 476 * from same method as the "causative exception" is caught. The above 477 * example was produced by running the program: 478 * <pre> 479 * public class Junk { 480 * public static void main(String args[]) { 481 * try { 482 * a(); 483 * } catch(HighLevelException e) { 484 * e.printStackTrace(); 485 * } 486 * } 487 * static void a() throws HighLevelException { 488 * try { 489 * b(); 490 * } catch(MidLevelException e) { 491 * throw new HighLevelException(e); 492 * } 493 * } 494 * static void b() throws MidLevelException { 495 * c(); 496 * } 497 * static void c() throws MidLevelException { 498 * try { 499 * d(); 500 * } catch(LowLevelException e) { 501 * throw new MidLevelException(e); 502 * } 503 * } 504 * static void d() throws LowLevelException { 505 * e(); 506 * } 507 * static void e() throws LowLevelException { 508 * throw new LowLevelException(); 509 * } 510 * } 511 * 512 * class HighLevelException extends Exception { 513 * HighLevelException(Throwable cause) { super(cause); } 514 * } 515 * 516 * class MidLevelException extends Exception { 517 * MidLevelException(Throwable cause) { super(cause); } 518 * } 519 * 520 * class LowLevelException extends Exception { 521 * } 522 * </pre> 523 * As of release 7, the platform supports the notion of 524 * <i>suppressed exceptions</i> (in conjunction with the {@code 525 * try}-with-resources statement). Any exceptions that were 526 * suppressed in order to deliver an exception are printed out 527 * beneath the stack trace. The format of this information 528 * depends on the implementation, but the following example may be 529 * regarded as typical: 530 * 531 * <pre> 532 * Exception in thread "main" java.lang.Exception: Something happened 533 * at Foo.bar(Foo.java:10) 534 * at Foo.main(Foo.java:5) 535 * Suppressed: Resource$CloseFailException: Resource ID = 0 536 * at Resource.close(Resource.java:26) 537 * at Foo.bar(Foo.java:9) 538 * ... 1 more 539 * </pre> 540 * Note that the "... n more" notation is used on suppressed exceptions 541 * just at it is used on causes. Unlike causes, suppressed exceptions are 542 * indented beyond their "containing exceptions." 543 * 544 * <p>An exception can have both a cause and one or more suppressed 545 * exceptions: 546 * <pre> 547 * Exception in thread "main" java.lang.Exception: Main block 548 * at Foo3.main(Foo3.java:7) 549 * Suppressed: Resource$CloseFailException: Resource ID = 2 550 * at Resource.close(Resource.java:26) 551 * at Foo3.main(Foo3.java:5) 552 * Suppressed: Resource$CloseFailException: Resource ID = 1 553 * at Resource.close(Resource.java:26) 554 * at Foo3.main(Foo3.java:5) 555 * Caused by: java.lang.Exception: I did it 556 * at Foo3.main(Foo3.java:8) 557 * </pre> 558 * Likewise, a suppressed exception can have a cause: 559 * <pre> 560 * Exception in thread "main" java.lang.Exception: Main block 561 * at Foo4.main(Foo4.java:6) 562 * Suppressed: Resource2$CloseFailException: Resource ID = 1 563 * at Resource2.close(Resource2.java:20) 564 * at Foo4.main(Foo4.java:5) 565 * Caused by: java.lang.Exception: Rats, you caught me 566 * at Resource2$CloseFailException.<init>(Resource2.java:45) 567 * ... 2 more 568 * </pre> 569 */ 570 public void printStackTrace() { 571 printStackTrace(System.err); 572 } 573 574 /** 575 * Prints this throwable and its backtrace to the specified print stream. 576 * 577 * @param s {@code PrintStream} to use for output 578 */ 579 public void printStackTrace(PrintStream s) { 580 printStackTrace(new WrappedPrintStream(s)); 581 } 582 583 private void printStackTrace(PrintStreamOrWriter s) { 584 // Guard against malicious overrides of Throwable.equals by 585 // using a Set with identity equality semantics. 586 Set<Throwable> dejaVu = 587 Collections.newSetFromMap(new IdentityHashMap<Throwable, Boolean>()); 588 dejaVu.add(this); 589 590 synchronized (s.lock()) { 591 // Print our stack trace 592 s.println(this); 593 StackTraceElement[] trace = getOurStackTrace(); 594 for (StackTraceElement traceElement : trace) 595 s.println("\tat " + traceElement); 596 597 // Print suppressed exceptions, if any 598 for (Throwable se : getSuppressed()) 599 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, "\t", dejaVu); 600 601 // Print cause, if any 602 Throwable ourCause = getCause(); 603 if (ourCause != null) 604 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, "", dejaVu); 605 } 606 } 607 608 /** 609 * Print our stack trace as an enclosed exception for the specified 610 * stack trace. 611 */ 612 private void printEnclosedStackTrace(PrintStreamOrWriter s, 613 StackTraceElement[] enclosingTrace, 614 String caption, 615 String prefix, 616 Set<Throwable> dejaVu) { 617 assert Thread.holdsLock(s.lock()); 618 if (dejaVu.contains(this)) { 619 s.println("\t[CIRCULAR REFERENCE:" + this + "]"); 620 } else { 621 dejaVu.add(this); 622 // Compute number of frames in common between this and enclosing trace 623 StackTraceElement[] trace = getOurStackTrace(); 624 int m = trace.length - 1; 625 int n = enclosingTrace.length - 1; 626 while (m >= 0 && n >=0 && trace[m].equals(enclosingTrace[n])) { 627 m--; n--; 628 } 629 int framesInCommon = trace.length - 1 - m; 630 631 // Print our stack trace 632 s.println(prefix + caption + this); 633 for (int i = 0; i <= m; i++) 634 s.println(prefix + "\tat " + trace[i]); 635 if (framesInCommon != 0) 636 s.println(prefix + "\t... " + framesInCommon + " more"); 637 638 // Print suppressed exceptions, if any 639 for (Throwable se : getSuppressed()) 640 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, 641 prefix +"\t", dejaVu); 642 643 // Print cause, if any 644 Throwable ourCause = getCause(); 645 if (ourCause != null) 646 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, prefix, dejaVu); 647 } 648 } 649 650 /** 651 * Prints this throwable and its backtrace to the specified 652 * print writer. 653 * 654 * @param s {@code PrintWriter} to use for output 655 * @since JDK1.1 656 */ 657 public void printStackTrace(PrintWriter s) { 658 printStackTrace(new WrappedPrintWriter(s)); 659 } 660 661 /** 662 * Wrapper class for PrintStream and PrintWriter to enable a single 663 * implementation of printStackTrace. 664 */ 665 private abstract static class PrintStreamOrWriter { 666 /** Returns the object to be locked when using this StreamOrWriter */ 667 abstract Object lock(); 668 669 /** Prints the specified string as a line on this StreamOrWriter */ 670 abstract void println(Object o); 671 } 672 673 private static class WrappedPrintStream extends PrintStreamOrWriter { 674 private final PrintStream printStream; 675 676 WrappedPrintStream(PrintStream printStream) { 677 this.printStream = printStream; 678 } 679 680 Object lock() { 681 return printStream; 682 } 683 684 void println(Object o) { 685 printStream.println(o); 686 } 687 } 688 689 private static class WrappedPrintWriter extends PrintStreamOrWriter { 690 private final PrintWriter printWriter; 691 692 WrappedPrintWriter(PrintWriter printWriter) { 693 this.printWriter = printWriter; 694 } 695 696 Object lock() { 697 return printWriter; 698 } 699 700 void println(Object o) { 701 printWriter.println(o); 702 } 703 } 704 705 /** 706 * Fills in the execution stack trace. This method records within this 707 * {@code Throwable} object information about the current state of 708 * the stack frames for the current thread. 709 * 710 * @return a reference to this {@code Throwable} instance. 711 * @see java.lang.Throwable#printStackTrace() 712 */ 713 public synchronized native Throwable fillInStackTrace(); 714 715 /** 716 * Provides programmatic access to the stack trace information printed by 717 * {@link #printStackTrace()}. Returns an array of stack trace elements, 718 * each representing one stack frame. The zeroth element of the array 719 * (assuming the array's length is non-zero) represents the top of the 720 * stack, which is the last method invocation in the sequence. Typically, 721 * this is the point at which this throwable was created and thrown. 722 * The last element of the array (assuming the array's length is non-zero) 723 * represents the bottom of the stack, which is the first method invocation 724 * in the sequence. 725 * 726 * <p>Some virtual machines may, under some circumstances, omit one 727 * or more stack frames from the stack trace. In the extreme case, 728 * a virtual machine that has no stack trace information concerning 729 * this throwable is permitted to return a zero-length array from this 730 * method. Generally speaking, the array returned by this method will 731 * contain one element for every frame that would be printed by 732 * {@code printStackTrace}. 733 * 734 * @return an array of stack trace elements representing the stack trace 735 * pertaining to this throwable. 736 * @since 1.4 737 */ 738 public StackTraceElement[] getStackTrace() { 739 return getOurStackTrace().clone(); 740 } 741 742 private synchronized StackTraceElement[] getOurStackTrace() { 743 // Initialize stack trace if this is the first call to this method 744 if (stackTrace == null) { 745 int depth = getStackTraceDepth(); 746 stackTrace = new StackTraceElement[depth]; 747 for (int i=0; i < depth; i++) 748 stackTrace[i] = getStackTraceElement(i); 749 } 750 751 return stackTrace; 752 } 753 754 /** 755 * Sets the stack trace elements that will be returned by 756 * {@link #getStackTrace()} and printed by {@link #printStackTrace()} 757 * and related methods. 758 * 759 * This method, which is designed for use by RPC frameworks and other 760 * advanced systems, allows the client to override the default 761 * stack trace that is either generated by {@link #fillInStackTrace()} 762 * when a throwable is constructed or deserialized when a throwable is 763 * read from a serialization stream. 764 * 765 * @param stackTrace the stack trace elements to be associated with 766 * this {@code Throwable}. The specified array is copied by this 767 * call; changes in the specified array after the method invocation 768 * returns will have no affect on this {@code Throwable}'s stack 769 * trace. 770 * 771 * @throws NullPointerException if {@code stackTrace} is 772 * {@code null}, or if any of the elements of 773 * {@code stackTrace} are {@code null} 774 * 775 * @since 1.4 776 */ 777 public void setStackTrace(StackTraceElement[] stackTrace) { 778 StackTraceElement[] defensiveCopy = stackTrace.clone(); 779 for (int i = 0; i < defensiveCopy.length; i++) { 780 if (defensiveCopy[i] == null) 781 throw new NullPointerException("stackTrace[" + i + "]"); 782 } 783 784 synchronized (this) { 785 this.stackTrace = defensiveCopy; 786 } 787 } 788 789 /** 790 * Returns the number of elements in the stack trace (or 0 if the stack 791 * trace is unavailable). 792 * 793 * package-protection for use by SharedSecrets. 794 */ 795 native int getStackTraceDepth(); 796 797 /** 798 * Returns the specified element of the stack trace. 799 * 800 * package-protection for use by SharedSecrets. 801 * 802 * @param index index of the element to return. 803 * @throws IndexOutOfBoundsException if {@code index < 0 || 804 * index >= getStackTraceDepth() } 805 */ 806 native StackTraceElement getStackTraceElement(int index); 807 808 /** 809 * Read a {@code Throwable} from a stream, enforcing 810 * well-formedness constraints on fields. Null entries and 811 * self-pointers are not allowed in the list of {@code 812 * suppressedExceptions}. Null entries are not allowed for stack 813 * trace elements. 814 * 815 * Note that there are no constraints on the value the {@code 816 * cause} field can hold; both {@code null} and this are valid 817 * values for the field. 818 */ 819 private void readObject(ObjectInputStream s) 820 throws IOException, ClassNotFoundException { 821 s.defaultReadObject(); // read in all fields 822 List<Throwable> suppressed = null; 823 if (suppressedExceptions != null && 824 !suppressedExceptions.isEmpty()) { // Copy Throwables to new list 825 suppressed = new ArrayList<Throwable>(1); 826 for (Throwable t : suppressedExceptions) { 827 // Enforce constraints on suppressed exceptions in 828 // case of corrupt or malicious stream. 829 if (t == null) 830 throw new NullPointerException(NULL_CAUSE_MESSAGE); 831 if (t == this) 832 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE); 833 suppressed.add(t); 834 } 835 } 836 837 // If suppressed is a zero-length list, use the sentinel 838 // value. 839 if (suppressed != null && suppressed.isEmpty()) 840 suppressedExceptions = suppressedSentinel; 841 else 842 suppressedExceptions = suppressed; 843 844 if (stackTrace != null) { 845 for(StackTraceElement ste : stackTrace) { 846 if (ste == null) 847 throw new NullPointerException("null StackTraceElement in serial stream. "); 848 } 849 } else { // Treat a null stack trace as a missing stack trace 850 stackTrace = new StackTraceElement[0]; 851 } 852 } 853 854 /** 855 * Write a {@code Throwable} object to a stream. The stack trace 856 * will be non-{@code null}. 857 */ 858 private synchronized void writeObject(ObjectOutputStream s) 859 throws IOException { 860 getOurStackTrace(); // Ensure that stackTrace field is initialized. 861 s.defaultWriteObject(); 862 } 863 864 /** 865 * Adds the specified exception to the list of exceptions that 866 * were suppressed, typically by the {@code try}-with-resources 867 * statement, in order to deliver this exception. 868 * 869 * If the first exception to be suppressed is {@code null}, that 870 * indicates suppressed exception information will <em>not</em> be 871 * recorded for this exception. Subsequent calls to this method 872 * will not record any suppressed exceptions. Otherwise, 873 * attempting to suppress {@code null} after an exception has 874 * already been successfully suppressed results in a {@code 875 * NullPointerException}. 876 * 877 * <p>Note that when one exception {@linkplain 878 * #initCause(Throwable) causes} another exception, the first 879 * exception is usually caught and then the second exception is 880 * thrown in response. In contrast, when one exception suppresses 881 * another, two exceptions are thrown in sibling code blocks, such 882 * as in a {@code try} block and in its {@code finally} block, and 883 * control flow can only continue with one exception so the second 884 * is recorded as a suppressed exception of the first. 885 * 886 * @param exception the exception to be added to the list of 887 * suppressed exceptions 888 * @throws IllegalArgumentException if {@code exception} is this 889 * throwable; a throwable cannot suppress itself. 890 * @throws NullPointerException if {@code exception} is null and 891 * an exception has already been suppressed by this exception 892 * @since 1.7 893 */ 894 public synchronized void addSuppressed(Throwable exception) { 895 if (exception == this) 896 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE); 897 898 if (exception == null) { 899 if (suppressedExceptions == suppressedSentinel) { 900 suppressedExceptions = null; // No suppression information recorded 901 return; 902 } else 903 throw new NullPointerException(NULL_CAUSE_MESSAGE); 904 } else { 905 assert exception != null && exception != this; 906 907 if (suppressedExceptions == null) // Suppressed exceptions not recorded 908 return; 909 910 if (suppressedExceptions == suppressedSentinel) 911 suppressedExceptions = new ArrayList<Throwable>(1); 912 913 assert suppressedExceptions != suppressedSentinel; 914 915 suppressedExceptions.add(exception); 916 } 917 } 918 919 private static final Throwable[] EMPTY_THROWABLE_ARRAY = new Throwable[0]; 920 921 /** 922 * Returns an array containing all of the exceptions that were 923 * suppressed, typically by the {@code try}-with-resources 924 * statement, in order to deliver this exception. 925 * 926 * If no exceptions were suppressed, an empty array is returned. 927 * 928 * @return an array containing all of the exceptions that were 929 * suppressed to deliver this exception. 930 * @since 1.7 931 */ 932 public synchronized Throwable[] getSuppressed() { 933 if (suppressedExceptions == suppressedSentinel || 934 suppressedExceptions == null) 935 return EMPTY_THROWABLE_ARRAY; 936 else 937 return suppressedExceptions.toArray(EMPTY_THROWABLE_ARRAY); 938 } 939 }