1 /* 2 * Copyright (c) 1994, 2011, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 26 package java.lang; 27 import java.io.*; 28 import java.util.*; 29 30 /** 31 * The {@code Throwable} class is the superclass of all errors and 32 * exceptions in the Java language. Only objects that are instances of this 33 * class (or one of its subclasses) are thrown by the Java Virtual Machine or 34 * can be thrown by the Java {@code throw} statement. Similarly, only 35 * this class or one of its subclasses can be the argument type in a 36 * {@code catch} clause. 37 * 38 * For the purposes of compile-time checking of exceptions, {@code 39 * Throwable} and any subclass of {@code Throwable} that is not also a 40 * subclass of either {@link RuntimeException} or {@link Error} are 41 * regarded as checked exceptions. 42 * 43 * <p>Instances of two subclasses, {@link java.lang.Error} and 44 * {@link java.lang.Exception}, are conventionally used to indicate 45 * that exceptional situations have occurred. Typically, these instances 46 * are freshly created in the context of the exceptional situation so 47 * as to include relevant information (such as stack trace data). 48 * 49 * <p>A throwable contains a snapshot of the execution stack of its 50 * thread at the time it was created. It can also contain a message 51 * string that gives more information about the error. Over time, a 52 * throwable can {@linkplain Throwable#addSuppressed suppress} other 53 * throwables from being propagated. Finally, the throwable can also 54 * contain a <i>cause</i>: another throwable that caused this 55 * throwable to be constructed. The recording of this causal information 56 * is referred to as the <i>chained exception</i> facility, as the 57 * cause can, itself, have a cause, and so on, leading to a "chain" of 58 * exceptions, each caused by another. 59 * 60 * <p>One reason that a throwable may have a cause is that the class that 61 * throws it is built atop a lower layered abstraction, and an operation on 62 * the upper layer fails due to a failure in the lower layer. It would be bad 63 * design to let the throwable thrown by the lower layer propagate outward, as 64 * it is generally unrelated to the abstraction provided by the upper layer. 65 * Further, doing so would tie the API of the upper layer to the details of 66 * its implementation, assuming the lower layer's exception was a checked 67 * exception. Throwing a "wrapped exception" (i.e., an exception containing a 68 * cause) allows the upper layer to communicate the details of the failure to 69 * its caller without incurring either of these shortcomings. It preserves 70 * the flexibility to change the implementation of the upper layer without 71 * changing its API (in particular, the set of exceptions thrown by its 72 * methods). 73 * 74 * <p>A second reason that a throwable may have a cause is that the method 75 * that throws it must conform to a general-purpose interface that does not 76 * permit the method to throw the cause directly. For example, suppose 77 * a persistent collection conforms to the {@link java.util.Collection 78 * Collection} interface, and that its persistence is implemented atop 79 * {@code java.io}. Suppose the internals of the {@code add} method 80 * can throw an {@link java.io.IOException IOException}. The implementation 81 * can communicate the details of the {@code IOException} to its caller 82 * while conforming to the {@code Collection} interface by wrapping the 83 * {@code IOException} in an appropriate unchecked exception. (The 84 * specification for the persistent collection should indicate that it is 85 * capable of throwing such exceptions.) 86 * 87 * <p>A cause can be associated with a throwable in two ways: via a 88 * constructor that takes the cause as an argument, or via the 89 * {@link #initCause(Throwable)} method. New throwable classes that 90 * wish to allow causes to be associated with them should provide constructors 91 * that take a cause and delegate (perhaps indirectly) to one of the 92 * {@code Throwable} constructors that takes a cause. 93 * 94 * Because the {@code initCause} method is public, it allows a cause to be 95 * associated with any throwable, even a "legacy throwable" whose 96 * implementation predates the addition of the exception chaining mechanism to 97 * {@code Throwable}. 98 * 99 * <p>By convention, class {@code Throwable} and its subclasses have two 100 * constructors, one that takes no arguments and one that takes a 101 * {@code String} argument that can be used to produce a detail message. 102 * Further, those subclasses that might likely have a cause associated with 103 * them should have two more constructors, one that takes a 104 * {@code Throwable} (the cause), and one that takes a 105 * {@code String} (the detail message) and a {@code Throwable} (the 106 * cause). 107 * 108 * @author unascribed 109 * @author Josh Bloch (Added exception chaining and programmatic access to 110 * stack trace in 1.4.) 111 * @jls3 11.2 Compile-Time Checking of Exceptions 112 * @since JDK1.0 113 */ 114 public class Throwable implements Serializable { 115 /** use serialVersionUID from JDK 1.0.2 for interoperability */ 116 private static final long serialVersionUID = -3042686055658047285L; 117 118 /** 119 * Native code saves some indication of the stack backtrace in this slot. 120 */ 121 private transient Object backtrace; 122 123 /** 124 * Specific details about the Throwable. For example, for 125 * {@code FileNotFoundException}, this contains the name of 126 * the file that could not be found. 127 * 128 * @serial 129 */ 130 private String detailMessage; 131 132 /** 133 * A shared value for an empty stack. 134 */ 135 private static final StackTraceElement[] EMPTY_STACK = new StackTraceElement[0]; 136 137 /* 138 * To allow Throwable objects to be made immutable and safely 139 * reused by the JVM, such as OutOfMemoryErrors, fields of 140 * Throwable that are writable in response to user actions, cause 141 * and suppressedExceptions obey the following protocol: 142 * 143 * 1) The fields are initialized to a non-null sentinel value 144 * which indicates the value has logically not been set. 145 * 146 * 2) Writing a null to the field indicates further writes 147 * are forbidden 148 * 149 * 3) The sentinel value may be replaced with another non-null 150 * value. 151 * 152 * For example, implementations of the HotSpot JVM have 153 * preallocated OutOfMemoryError objects to provide for better 154 * diagnosability of that situation. These objects are created 155 * without calling the constructor for that class and the fields 156 * in question are initialized to null. To support this 157 * capability, any new fields added to Throwable that require 158 * being initialized to a non-null value require a coordinated JVM 159 * change. 160 */ 161 162 /** 163 * The throwable that caused this throwable to get thrown, or null if this 164 * throwable was not caused by another throwable, or if the causative 165 * throwable is unknown. If this field is equal to this throwable itself, 166 * it indicates that the cause of this throwable has not yet been 167 * initialized. 168 * 169 * @serial 170 * @since 1.4 171 */ 172 private Throwable cause = this; 173 174 /** 175 * The stack trace, as returned by {@link #getStackTrace()}. 176 * 177 * @serial 178 * @since 1.4 179 */ 180 private StackTraceElement[] stackTrace; 181 182 // Setting this static field introduces an acceptable 183 // initialization dependency on a few java.util classes. 184 private static final List<Throwable> SUPPRESSED_SENTINEL = 185 Collections.unmodifiableList(new ArrayList<Throwable>(0)); 186 187 /** 188 * The list of suppressed exceptions, as returned by {@link 189 * #getSuppressed()}. The list is initialized to a zero-element 190 * unmodifiable sentinel list. When a serialized Throwable is 191 * read in, if the {@code suppressedExceptions} field points to a 192 * zero-element list, the field is reset to the sentinel value. 193 * 194 * @serial 195 * @since 1.7 196 */ 197 private List<Throwable> suppressedExceptions = SUPPRESSED_SENTINEL; 198 199 /** Message for trying to suppress a null exception. */ 200 private static final String NULL_CAUSE_MESSAGE = "Cannot suppress a null exception."; 201 202 /** Message for trying to suppress oneself. */ 203 private static final String SELF_SUPPRESSION_MESSAGE = "Self-suppression not permitted"; 204 205 /** Caption for labeling causative exception stack traces */ 206 private static final String CAUSE_CAPTION = "Caused by: "; 207 208 /** Caption for labeling suppressed exception stack traces */ 209 private static final String SUPPRESSED_CAPTION = "Suppressed: "; 210 211 /** 212 * Constructs a new throwable with {@code null} as its detail message. 213 * The cause is not initialized, and may subsequently be initialized by a 214 * call to {@link #initCause}. 215 * 216 * <p>The {@link #fillInStackTrace()} method is called to initialize 217 * the stack trace data in the newly created throwable. 218 */ 219 public Throwable() { 220 fillInStackTrace(); 221 } 222 223 /** 224 * Constructs a new throwable with the specified detail message. The 225 * cause is not initialized, and may subsequently be initialized by 226 * a call to {@link #initCause}. 227 * 228 * <p>The {@link #fillInStackTrace()} method is called to initialize 229 * the stack trace data in the newly created throwable. 230 * 231 * @param message the detail message. The detail message is saved for 232 * later retrieval by the {@link #getMessage()} method. 233 */ 234 public Throwable(String message) { 235 fillInStackTrace(); 236 detailMessage = message; 237 } 238 239 /** 240 * Constructs a new throwable with the specified detail message and 241 * cause. <p>Note that the detail message associated with 242 * {@code cause} is <i>not</i> automatically incorporated in 243 * this throwable's detail message. 244 * 245 * <p>The {@link #fillInStackTrace()} method is called to initialize 246 * the stack trace data in the newly created throwable. 247 * 248 * @param message the detail message (which is saved for later retrieval 249 * by the {@link #getMessage()} method). 250 * @param cause the cause (which is saved for later retrieval by the 251 * {@link #getCause()} method). (A {@code null} value is 252 * permitted, and indicates that the cause is nonexistent or 253 * unknown.) 254 * @since 1.4 255 */ 256 public Throwable(String message, Throwable cause) { 257 fillInStackTrace(); 258 detailMessage = message; 259 this.cause = cause; 260 } 261 262 /** 263 * Constructs a new throwable with the specified cause and a detail 264 * message of {@code (cause==null ? null : cause.toString())} (which 265 * typically contains the class and detail message of {@code cause}). 266 * This constructor is useful for throwables that are little more than 267 * wrappers for other throwables (for example, {@link 268 * java.security.PrivilegedActionException}). 269 * 270 * <p>The {@link #fillInStackTrace()} method is called to initialize 271 * the stack trace data in the newly created throwable. 272 * 273 * @param cause the cause (which is saved for later retrieval by the 274 * {@link #getCause()} method). (A {@code null} value is 275 * permitted, and indicates that the cause is nonexistent or 276 * unknown.) 277 * @since 1.4 278 */ 279 public Throwable(Throwable cause) { 280 fillInStackTrace(); 281 detailMessage = (cause==null ? null : cause.toString()); 282 this.cause = cause; 283 } 284 285 /** 286 * Constructs a new throwable with the specified detail message, 287 * cause, and {@linkplain #addSuppressed suppression} enabled or 288 * disabled. If suppression is disabled, {@link #getSuppressed} 289 * for this object will return a zero-length array and calls to 290 * {@link #addSuppressed} that would otherwise append an exception 291 * to the suppressed list will have no effect. 292 * 293 * <p>Note that the other constructors of {@code Throwable} treat 294 * suppression as being enabled. Subclasses of {@code Throwable} 295 * should document any conditions under which suppression is 296 * disabled. Disabling of suppression should only occur in 297 * exceptional circumstances where special requirements exist, 298 * such as a virtual machine reusing exception objects under 299 * low-memory situations. 300 * 301 * @param message the detail message. 302 * @param cause the cause. (A {@code null} value is permitted, 303 * and indicates that the cause is nonexistent or unknown.) 304 * @param enableSuppression whether or not suppression is enabled or disabled 305 * 306 * @see OutOfMemoryError 307 * @see NullPointerException 308 * @see ArithmeticException 309 * @since 1.7 310 */ 311 protected Throwable(String message, Throwable cause, 312 boolean enableSuppression) { 313 fillInStackTrace(); 314 detailMessage = message; 315 this.cause = cause; 316 if (!enableSuppression) 317 suppressedExceptions = null; 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 return stackTrace; 751 } 752 753 /** 754 * Sets the stack trace elements that will be returned by 755 * {@link #getStackTrace()} and printed by {@link #printStackTrace()} 756 * and related methods. 757 * 758 * This method, which is designed for use by RPC frameworks and other 759 * advanced systems, allows the client to override the default 760 * stack trace that is either generated by {@link #fillInStackTrace()} 761 * when a throwable is constructed or deserialized when a throwable is 762 * read from a serialization stream. 763 * 764 * @param stackTrace the stack trace elements to be associated with 765 * this {@code Throwable}. The specified array is copied by this 766 * call; changes in the specified array after the method invocation 767 * returns will have no affect on this {@code Throwable}'s stack 768 * trace. 769 * 770 * @throws NullPointerException if {@code stackTrace} is 771 * {@code null}, or if any of the elements of 772 * {@code stackTrace} are {@code null} 773 * 774 * @since 1.4 775 */ 776 public void setStackTrace(StackTraceElement[] stackTrace) { 777 StackTraceElement[] defensiveCopy = stackTrace.clone(); 778 for (int i = 0; i < defensiveCopy.length; i++) 779 if (defensiveCopy[i] == null) 780 throw new NullPointerException("stackTrace[" + i + "]"); 781 782 synchronized (this) { 783 this.stackTrace = defensiveCopy; 784 } 785 } 786 787 /** 788 * Returns the number of elements in the stack trace (or 0 if the stack 789 * trace is unavailable). 790 * 791 * package-protection for use by SharedSecrets. 792 */ 793 native int getStackTraceDepth(); 794 795 /** 796 * Returns the specified element of the stack trace. 797 * 798 * package-protection for use by SharedSecrets. 799 * 800 * @param index index of the element to return. 801 * @throws IndexOutOfBoundsException if {@code index < 0 || 802 * index >= getStackTraceDepth() } 803 */ 804 native StackTraceElement getStackTraceElement(int index); 805 806 /** 807 * Reads a {@code Throwable} from a stream, enforcing 808 * well-formedness constraints on fields. Null entries and 809 * self-pointers are not allowed in the list of {@code 810 * suppressedExceptions}. Null entries are not allowed for stack 811 * trace elements. 812 * 813 * Note that there are no constraints on the value the {@code 814 * cause} field can hold; both {@code null} and {@code this} are 815 * valid values for the field. 816 */ 817 private void readObject(ObjectInputStream s) 818 throws IOException, ClassNotFoundException { 819 s.defaultReadObject(); // read in all fields 820 if (suppressedExceptions != null) { 821 List<Throwable> suppressed = null; 822 if (suppressedExceptions.isEmpty()) { 823 // Use the sentinel for a zero-length list 824 suppressed = SUPPRESSED_SENTINEL; 825 } else { // Copy Throwables to new list 826 suppressed = new ArrayList<>(1); 827 for (Throwable t : suppressedExceptions) { 828 // Enforce constraints on suppressed exceptions in 829 // case of corrupt or malicious stream. 830 if (t == null) 831 throw new NullPointerException(NULL_CAUSE_MESSAGE); 832 if (t == this) 833 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE); 834 suppressed.add(t); 835 } 836 } 837 suppressedExceptions = suppressed; 838 } // else a null suppressedExceptions field remains null 839 840 if (stackTrace != null) { 841 for (StackTraceElement ste : stackTrace) { 842 if (ste == null) 843 throw new NullPointerException("null StackTraceElement in serial stream. "); 844 } 845 } else { 846 // A null stackTrace field in the serial form can result from 847 // an exception serialized without that field in older JDK releases. 848 stackTrace = EMPTY_STACK; 849 } 850 851 } 852 853 /** 854 * Write a {@code Throwable} object to a stream. 855 */ 856 private synchronized void writeObject(ObjectOutputStream s) 857 throws IOException { 858 getOurStackTrace(); // Ensure that stackTrace field is initialized. 859 s.defaultWriteObject(); 860 } 861 862 /** 863 * Appends the specified exception to the exceptions that were 864 * suppressed in order to deliver this exception. This method is 865 * typically called (automatically and implicitly) by the {@code 866 * try}-with-resources statement. 867 * 868 * <p>The suppression behavior is enabled <em>unless</em> disabled 869 * {@linkplain #Throwable(String, Throwable, boolean) via a 870 * constructor}. When suppression is disabled, this method does 871 * nothing other than to validate its argument. 872 * 873 * <p>Note that when one exception {@linkplain 874 * #initCause(Throwable) causes} another exception, the first 875 * exception is usually caught and then the second exception is 876 * thrown in response. In other words, there is a causal 877 * connection between the two exceptions. 878 * 879 * In contrast, there are situations where two independent 880 * exceptions can be thrown in sibling code blocks, in particular 881 * in the {@code try} block of a {@code try}-with-resources 882 * statement and the compiler-generated {@code finally} block 883 * which closes the resource. 884 * 885 * In these situations, only one of the thrown exceptions can be 886 * propagated. In the {@code try}-with-resources statement, when 887 * there are two such exceptions, the exception originating from 888 * the {@code try} block is propagated and the exception from the 889 * {@code finally} block is added to the list of exceptions 890 * suppressed by the exception from the {@code try} block. As an 891 * exception unwinds the stack, it can accumulate multiple 892 * suppressed exceptions. 893 * 894 * <p>An exception may have suppressed exceptions while also being 895 * caused by another exception. Whether or not an exception has a 896 * cause is semantically known at the time of its creation, unlike 897 * whether or not an exception will suppress other exceptions 898 * which is typically only determined after an exception is 899 * thrown. 900 * 901 * <p>Note that programmer written code is also able to take 902 * advantage of calling this method in situations where there are 903 * multiple sibling exceptions and only one can be propagated. 904 * 905 * @param exception the exception to be added to the list of 906 * suppressed exceptions 907 * @throws IllegalArgumentException if {@code exception} is this 908 * throwable; a throwable cannot suppress itself. 909 * @throws NullPointerException if {@code exception} is {@code null} 910 * @since 1.7 911 */ 912 public final synchronized void addSuppressed(Throwable exception) { 913 if (exception == this) 914 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE); 915 916 if (exception == null) 917 throw new NullPointerException(NULL_CAUSE_MESSAGE); 918 919 if (suppressedExceptions == null) // Suppressed exceptions not recorded 920 return; 921 922 if (suppressedExceptions == SUPPRESSED_SENTINEL) 923 suppressedExceptions = new ArrayList<>(1); 924 925 suppressedExceptions.add(exception); 926 } 927 928 private static final Throwable[] EMPTY_THROWABLE_ARRAY = new Throwable[0]; 929 930 /** 931 * Returns an array containing all of the exceptions that were 932 * suppressed, typically by the {@code try}-with-resources 933 * statement, in order to deliver this exception. 934 * 935 * If no exceptions were suppressed or {@linkplain 936 * Throwable(String, Throwable, boolean) suppression is disabled}, 937 * an empty array is returned. 938 * 939 * @return an array containing all of the exceptions that were 940 * suppressed to deliver this exception. 941 * @since 1.7 942 */ 943 public final synchronized Throwable[] getSuppressed() { 944 if (suppressedExceptions == SUPPRESSED_SENTINEL || 945 suppressedExceptions == null) 946 return EMPTY_THROWABLE_ARRAY; 947 else 948 return suppressedExceptions.toArray(EMPTY_THROWABLE_ARRAY); 949 } 950 }