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 * A shared value for an empty stack. 174 */ 175 private static final StackTraceElement[] EMPTY_STACK = new StackTraceElement[0]; 176 177 /* 178 * To allow Throwable objects to be made immutable and safely 179 * reused by the JVM, such as OutOfMemoryErrors, fields of 180 * Throwable that are writable in response to user actions, cause 181 * and suppressedExceptions obey the following protocol: 182 * 183 * 1) The fields are initialized to a non-null sentinel value 184 * which indicates the value has logically not been set. 185 * 186 * 2) Writing a null to the field indicates further writes 187 * are forbidden 188 * 189 * 3) The sentinel value may be replaced with another non-null 190 * value. 191 * 192 * For example, implementations of the HotSpot JVM have 193 * preallocated OutOfMemoryError objects to provide for better 194 * diagnosability of that situation. These objects are created 195 * without calling the constructor for that class and the fields 196 * in question are initialized to null. To support this 197 * capability, any new fields added to Throwable that require 198 * being initialized to a non-null value require a coordinated JVM 199 * change. 200 */ 201 202 /** 203 * The throwable that caused this throwable to get thrown, or null if this 204 * throwable was not caused by another throwable, or if the causative 205 * throwable is unknown. If this field is equal to this throwable itself, 206 * it indicates that the cause of this throwable has not yet been 207 * initialized. 208 * 209 * @serial 210 * @since 1.4 211 */ 212 private Throwable cause = this; 213 214 /** 215 * The stack trace, as returned by {@link #getStackTrace()}. 216 * 217 * @serial 218 * @since 1.4 219 */ 220 private StackTraceElement[] stackTrace; 221 222 // Setting this static field introduces an acceptable 223 // initialization dependency on a few java.util classes. 224 private static final List<Throwable> SUPPRESSED_SENTINEL = 225 Collections.unmodifiableList(new ArrayList<Throwable>(0)); 226 227 /** 228 * The list of suppressed exceptions, as returned by {@link 229 * #getSuppressed()}. The list is initialized to a zero-element 230 * unmodifiable sentinel list. When a serialized Throwable is 231 * read in, if the {@code suppressedExceptions} field points to a 232 * zero-element list, the field is reset to the sentinel value. 233 * 234 * @serial 235 * @since 1.7 236 */ 237 private List<Throwable> suppressedExceptions = SUPPRESSED_SENTINEL; 238 239 /** Message for trying to suppress a null exception. */ 240 private static final String NULL_CAUSE_MESSAGE = "Cannot suppress a null exception."; 241 242 /** Message for trying to suppress oneself. */ 243 private static final String SELF_SUPPRESSION_MESSAGE = "Self-suppression not permitted"; 244 245 /** Caption for labeling causative exception stack traces */ 246 private static final String CAUSE_CAPTION = "Caused by: "; 247 248 /** Caption for labeling suppressed exception stack traces */ 249 private static final String SUPPRESSED_CAPTION = "Suppressed: "; 250 251 /** 252 * Constructs a new throwable with {@code null} as its detail message. 253 * The cause is not initialized, and may subsequently be initialized by a 254 * call to {@link #initCause}. 255 * 256 * <p>The {@link #fillInStackTrace()} method is called to initialize 257 * the stack trace data in the newly created throwable. 258 */ 259 public Throwable() { 260 fillInStackTrace(); 261 } 262 263 /** 264 * Constructs a new throwable with the specified detail message. The 265 * cause is not initialized, and may subsequently be initialized by 266 * a call to {@link #initCause}. 267 * 268 * <p>The {@link #fillInStackTrace()} method is called to initialize 269 * the stack trace data in the newly created throwable. 270 * 271 * @param message the detail message. The detail message is saved for 272 * later retrieval by the {@link #getMessage()} method. 273 */ 274 public Throwable(String message) { 275 fillInStackTrace(); 276 detailMessage = message; 277 } 278 279 /** 280 * Constructs a new throwable with the specified detail message and 281 * cause. <p>Note that the detail message associated with 282 * {@code cause} is <i>not</i> automatically incorporated in 283 * this throwable's detail message. 284 * 285 * <p>The {@link #fillInStackTrace()} method is called to initialize 286 * the stack trace data in the newly created throwable. 287 * 288 * @param message the detail message (which is saved for later retrieval 289 * by the {@link #getMessage()} method). 290 * @param cause the cause (which is saved for later retrieval by the 291 * {@link #getCause()} method). (A {@code null} value is 292 * permitted, and indicates that the cause is nonexistent or 293 * unknown.) 294 * @since 1.4 295 */ 296 public Throwable(String message, Throwable cause) { 297 fillInStackTrace(); 298 detailMessage = message; 299 this.cause = cause; 300 } 301 302 /** 303 * Constructs a new throwable with the specified cause and a detail 304 * message of {@code (cause==null ? null : cause.toString())} (which 305 * typically contains the class and detail message of {@code cause}). 306 * This constructor is useful for throwables that are little more than 307 * wrappers for other throwables (for example, {@link 308 * java.security.PrivilegedActionException}). 309 * 310 * <p>The {@link #fillInStackTrace()} method is called to initialize 311 * the stack trace data in the newly created throwable. 312 * 313 * @param cause the cause (which is saved for later retrieval by the 314 * {@link #getCause()} method). (A {@code null} value is 315 * permitted, and indicates that the cause is nonexistent or 316 * unknown.) 317 * @since 1.4 318 */ 319 public Throwable(Throwable cause) { 320 fillInStackTrace(); 321 detailMessage = (cause==null ? null : cause.toString()); 322 this.cause = cause; 323 } 324 325 /** 326 * Returns the detail message string of this throwable. 327 * 328 * @return the detail message string of this {@code Throwable} instance 329 * (which may be {@code null}). 330 */ 331 public String getMessage() { 332 return detailMessage; 333 } 334 335 /** 336 * Creates a localized description of this throwable. 337 * Subclasses may override this method in order to produce a 338 * locale-specific message. For subclasses that do not override this 339 * method, the default implementation returns the same result as 340 * {@code getMessage()}. 341 * 342 * @return The localized description of this throwable. 343 * @since JDK1.1 344 */ 345 public String getLocalizedMessage() { 346 return getMessage(); 347 } 348 349 /** 350 * Returns the cause of this throwable or {@code null} if the 351 * cause is nonexistent or unknown. (The cause is the throwable that 352 * caused this throwable to get thrown.) 353 * 354 * <p>This implementation returns the cause that was supplied via one of 355 * the constructors requiring a {@code Throwable}, or that was set after 356 * creation with the {@link #initCause(Throwable)} method. While it is 357 * typically unnecessary to override this method, a subclass can override 358 * it to return a cause set by some other means. This is appropriate for 359 * a "legacy chained throwable" that predates the addition of chained 360 * exceptions to {@code Throwable}. Note that it is <i>not</i> 361 * necessary to override any of the {@code PrintStackTrace} methods, 362 * all of which invoke the {@code getCause} method to determine the 363 * cause of a throwable. 364 * 365 * @return the cause of this throwable or {@code null} if the 366 * cause is nonexistent or unknown. 367 * @since 1.4 368 */ 369 public synchronized Throwable getCause() { 370 return (cause==this ? null : cause); 371 } 372 373 /** 374 * Initializes the <i>cause</i> of this throwable to the specified value. 375 * (The cause is the throwable that caused this throwable to get thrown.) 376 * 377 * <p>This method can be called at most once. It is generally called from 378 * within the constructor, or immediately after creating the 379 * throwable. If this throwable was created 380 * with {@link #Throwable(Throwable)} or 381 * {@link #Throwable(String,Throwable)}, this method cannot be called 382 * even once. 383 * 384 * @param cause the cause (which is saved for later retrieval by the 385 * {@link #getCause()} method). (A {@code null} value is 386 * permitted, and indicates that the cause is nonexistent or 387 * unknown.) 388 * @return a reference to this {@code Throwable} instance. 389 * @throws IllegalArgumentException if {@code cause} is this 390 * throwable. (A throwable cannot be its own cause.) 391 * @throws IllegalStateException if this throwable was 392 * created with {@link #Throwable(Throwable)} or 393 * {@link #Throwable(String,Throwable)}, or this method has already 394 * been called on this throwable. 395 * @since 1.4 396 */ 397 public synchronized Throwable initCause(Throwable cause) { 398 if (this.cause != this) 399 throw new IllegalStateException("Can't overwrite cause"); 400 if (cause == this) 401 throw new IllegalArgumentException("Self-causation not permitted"); 402 this.cause = cause; 403 return this; 404 } 405 406 /** 407 * Returns a short description of this throwable. 408 * The result is the concatenation of: 409 * <ul> 410 * <li> the {@linkplain Class#getName() name} of the class of this object 411 * <li> ": " (a colon and a space) 412 * <li> the result of invoking this object's {@link #getLocalizedMessage} 413 * method 414 * </ul> 415 * If {@code getLocalizedMessage} returns {@code null}, then just 416 * the class name is returned. 417 * 418 * @return a string representation of this throwable. 419 */ 420 public String toString() { 421 String s = getClass().getName(); 422 String message = getLocalizedMessage(); 423 return (message != null) ? (s + ": " + message) : s; 424 } 425 426 /** 427 * Prints this throwable and its backtrace to the 428 * standard error stream. This method prints a stack trace for this 429 * {@code Throwable} object on the error output stream that is 430 * the value of the field {@code System.err}. The first line of 431 * output contains the result of the {@link #toString()} method for 432 * this object. Remaining lines represent data previously recorded by 433 * the method {@link #fillInStackTrace()}. The format of this 434 * information depends on the implementation, but the following 435 * example may be regarded as typical: 436 * <blockquote><pre> 437 * java.lang.NullPointerException 438 * at MyClass.mash(MyClass.java:9) 439 * at MyClass.crunch(MyClass.java:6) 440 * at MyClass.main(MyClass.java:3) 441 * </pre></blockquote> 442 * This example was produced by running the program: 443 * <pre> 444 * class MyClass { 445 * public static void main(String[] args) { 446 * crunch(null); 447 * } 448 * static void crunch(int[] a) { 449 * mash(a); 450 * } 451 * static void mash(int[] b) { 452 * System.out.println(b[0]); 453 * } 454 * } 455 * </pre> 456 * The backtrace for a throwable with an initialized, non-null cause 457 * should generally include the backtrace for the cause. The format 458 * of this information depends on the implementation, but the following 459 * example may be regarded as typical: 460 * <pre> 461 * HighLevelException: MidLevelException: LowLevelException 462 * at Junk.a(Junk.java:13) 463 * at Junk.main(Junk.java:4) 464 * Caused by: MidLevelException: LowLevelException 465 * at Junk.c(Junk.java:23) 466 * at Junk.b(Junk.java:17) 467 * at Junk.a(Junk.java:11) 468 * ... 1 more 469 * Caused by: LowLevelException 470 * at Junk.e(Junk.java:30) 471 * at Junk.d(Junk.java:27) 472 * at Junk.c(Junk.java:21) 473 * ... 3 more 474 * </pre> 475 * Note the presence of lines containing the characters {@code "..."}. 476 * These lines indicate that the remainder of the stack trace for this 477 * exception matches the indicated number of frames from the bottom of the 478 * stack trace of the exception that was caused by this exception (the 479 * "enclosing" exception). This shorthand can greatly reduce the length 480 * of the output in the common case where a wrapped exception is thrown 481 * from same method as the "causative exception" is caught. The above 482 * example was produced by running the program: 483 * <pre> 484 * public class Junk { 485 * public static void main(String args[]) { 486 * try { 487 * a(); 488 * } catch(HighLevelException e) { 489 * e.printStackTrace(); 490 * } 491 * } 492 * static void a() throws HighLevelException { 493 * try { 494 * b(); 495 * } catch(MidLevelException e) { 496 * throw new HighLevelException(e); 497 * } 498 * } 499 * static void b() throws MidLevelException { 500 * c(); 501 * } 502 * static void c() throws MidLevelException { 503 * try { 504 * d(); 505 * } catch(LowLevelException e) { 506 * throw new MidLevelException(e); 507 * } 508 * } 509 * static void d() throws LowLevelException { 510 * e(); 511 * } 512 * static void e() throws LowLevelException { 513 * throw new LowLevelException(); 514 * } 515 * } 516 * 517 * class HighLevelException extends Exception { 518 * HighLevelException(Throwable cause) { super(cause); } 519 * } 520 * 521 * class MidLevelException extends Exception { 522 * MidLevelException(Throwable cause) { super(cause); } 523 * } 524 * 525 * class LowLevelException extends Exception { 526 * } 527 * </pre> 528 * As of release 7, the platform supports the notion of 529 * <i>suppressed exceptions</i> (in conjunction with the {@code 530 * try}-with-resources statement). Any exceptions that were 531 * suppressed in order to deliver an exception are printed out 532 * beneath the stack trace. The format of this information 533 * depends on the implementation, but the following example may be 534 * regarded as typical: 535 * 536 * <pre> 537 * Exception in thread "main" java.lang.Exception: Something happened 538 * at Foo.bar(Foo.java:10) 539 * at Foo.main(Foo.java:5) 540 * Suppressed: Resource$CloseFailException: Resource ID = 0 541 * at Resource.close(Resource.java:26) 542 * at Foo.bar(Foo.java:9) 543 * ... 1 more 544 * </pre> 545 * Note that the "... n more" notation is used on suppressed exceptions 546 * just at it is used on causes. Unlike causes, suppressed exceptions are 547 * indented beyond their "containing exceptions." 548 * 549 * <p>An exception can have both a cause and one or more suppressed 550 * exceptions: 551 * <pre> 552 * Exception in thread "main" java.lang.Exception: Main block 553 * at Foo3.main(Foo3.java:7) 554 * Suppressed: Resource$CloseFailException: Resource ID = 2 555 * at Resource.close(Resource.java:26) 556 * at Foo3.main(Foo3.java:5) 557 * Suppressed: Resource$CloseFailException: Resource ID = 1 558 * at Resource.close(Resource.java:26) 559 * at Foo3.main(Foo3.java:5) 560 * Caused by: java.lang.Exception: I did it 561 * at Foo3.main(Foo3.java:8) 562 * </pre> 563 * Likewise, a suppressed exception can have a cause: 564 * <pre> 565 * Exception in thread "main" java.lang.Exception: Main block 566 * at Foo4.main(Foo4.java:6) 567 * Suppressed: Resource2$CloseFailException: Resource ID = 1 568 * at Resource2.close(Resource2.java:20) 569 * at Foo4.main(Foo4.java:5) 570 * Caused by: java.lang.Exception: Rats, you caught me 571 * at Resource2$CloseFailException.<init>(Resource2.java:45) 572 * ... 2 more 573 * </pre> 574 */ 575 public void printStackTrace() { 576 printStackTrace(System.err); 577 } 578 579 /** 580 * Prints this throwable and its backtrace to the specified print stream. 581 * 582 * @param s {@code PrintStream} to use for output 583 */ 584 public void printStackTrace(PrintStream s) { 585 printStackTrace(new WrappedPrintStream(s)); 586 } 587 588 private void printStackTrace(PrintStreamOrWriter s) { 589 // Guard against malicious overrides of Throwable.equals by 590 // using a Set with identity equality semantics. 591 Set<Throwable> dejaVu = 592 Collections.newSetFromMap(new IdentityHashMap<Throwable, Boolean>()); 593 dejaVu.add(this); 594 595 synchronized (s.lock()) { 596 // Print our stack trace 597 s.println(this); 598 StackTraceElement[] trace = getOurStackTrace(); 599 for (StackTraceElement traceElement : trace) 600 s.println("\tat " + traceElement); 601 602 // Print suppressed exceptions, if any 603 for (Throwable se : getSuppressed()) 604 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, "\t", dejaVu); 605 606 // Print cause, if any 607 Throwable ourCause = getCause(); 608 if (ourCause != null) 609 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, "", dejaVu); 610 } 611 } 612 613 /** 614 * Print our stack trace as an enclosed exception for the specified 615 * stack trace. 616 */ 617 private void printEnclosedStackTrace(PrintStreamOrWriter s, 618 StackTraceElement[] enclosingTrace, 619 String caption, 620 String prefix, 621 Set<Throwable> dejaVu) { 622 assert Thread.holdsLock(s.lock()); 623 if (dejaVu.contains(this)) { 624 s.println("\t[CIRCULAR REFERENCE:" + this + "]"); 625 } else { 626 dejaVu.add(this); 627 // Compute number of frames in common between this and enclosing trace 628 StackTraceElement[] trace = getOurStackTrace(); 629 int m = trace.length - 1; 630 int n = enclosingTrace.length - 1; 631 while (m >= 0 && n >=0 && trace[m].equals(enclosingTrace[n])) { 632 m--; n--; 633 } 634 int framesInCommon = trace.length - 1 - m; 635 636 // Print our stack trace 637 s.println(prefix + caption + this); 638 for (int i = 0; i <= m; i++) 639 s.println(prefix + "\tat " + trace[i]); 640 if (framesInCommon != 0) 641 s.println(prefix + "\t... " + framesInCommon + " more"); 642 643 // Print suppressed exceptions, if any 644 for (Throwable se : getSuppressed()) 645 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, 646 prefix +"\t", dejaVu); 647 648 // Print cause, if any 649 Throwable ourCause = getCause(); 650 if (ourCause != null) 651 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, prefix, dejaVu); 652 } 653 } 654 655 /** 656 * Prints this throwable and its backtrace to the specified 657 * print writer. 658 * 659 * @param s {@code PrintWriter} to use for output 660 * @since JDK1.1 661 */ 662 public void printStackTrace(PrintWriter s) { 663 printStackTrace(new WrappedPrintWriter(s)); 664 } 665 666 /** 667 * Wrapper class for PrintStream and PrintWriter to enable a single 668 * implementation of printStackTrace. 669 */ 670 private abstract static class PrintStreamOrWriter { 671 /** Returns the object to be locked when using this StreamOrWriter */ 672 abstract Object lock(); 673 674 /** Prints the specified string as a line on this StreamOrWriter */ 675 abstract void println(Object o); 676 } 677 678 private static class WrappedPrintStream extends PrintStreamOrWriter { 679 private final PrintStream printStream; 680 681 WrappedPrintStream(PrintStream printStream) { 682 this.printStream = printStream; 683 } 684 685 Object lock() { 686 return printStream; 687 } 688 689 void println(Object o) { 690 printStream.println(o); 691 } 692 } 693 694 private static class WrappedPrintWriter extends PrintStreamOrWriter { 695 private final PrintWriter printWriter; 696 697 WrappedPrintWriter(PrintWriter printWriter) { 698 this.printWriter = printWriter; 699 } 700 701 Object lock() { 702 return printWriter; 703 } 704 705 void println(Object o) { 706 printWriter.println(o); 707 } 708 } 709 710 /** 711 * Fills in the execution stack trace. This method records within this 712 * {@code Throwable} object information about the current state of 713 * the stack frames for the current thread. 714 * 715 * @return a reference to this {@code Throwable} instance. 716 * @see java.lang.Throwable#printStackTrace() 717 */ 718 public synchronized native Throwable fillInStackTrace(); 719 720 /** 721 * Provides programmatic access to the stack trace information printed by 722 * {@link #printStackTrace()}. Returns an array of stack trace elements, 723 * each representing one stack frame. The zeroth element of the array 724 * (assuming the array's length is non-zero) represents the top of the 725 * stack, which is the last method invocation in the sequence. Typically, 726 * this is the point at which this throwable was created and thrown. 727 * The last element of the array (assuming the array's length is non-zero) 728 * represents the bottom of the stack, which is the first method invocation 729 * in the sequence. 730 * 731 * <p>Some virtual machines may, under some circumstances, omit one 732 * or more stack frames from the stack trace. In the extreme case, 733 * a virtual machine that has no stack trace information concerning 734 * this throwable is permitted to return a zero-length array from this 735 * method. Generally speaking, the array returned by this method will 736 * contain one element for every frame that would be printed by 737 * {@code printStackTrace}. 738 * 739 * @return an array of stack trace elements representing the stack trace 740 * pertaining to this throwable. 741 * @since 1.4 742 */ 743 public StackTraceElement[] getStackTrace() { 744 return getOurStackTrace().clone(); 745 } 746 747 private synchronized StackTraceElement[] getOurStackTrace() { 748 // Initialize stack trace if this is the first call to this method 749 if (stackTrace == null) { 750 int depth = getStackTraceDepth(); 751 stackTrace = new StackTraceElement[depth]; 752 for (int i=0; i < depth; i++) 753 stackTrace[i] = getStackTraceElement(i); 754 } 755 return stackTrace; 756 } 757 758 /** 759 * Sets the stack trace elements that will be returned by 760 * {@link #getStackTrace()} and printed by {@link #printStackTrace()} 761 * and related methods. 762 * 763 * This method, which is designed for use by RPC frameworks and other 764 * advanced systems, allows the client to override the default 765 * stack trace that is either generated by {@link #fillInStackTrace()} 766 * when a throwable is constructed or deserialized when a throwable is 767 * read from a serialization stream. 768 * 769 * @param stackTrace the stack trace elements to be associated with 770 * this {@code Throwable}. The specified array is copied by this 771 * call; changes in the specified array after the method invocation 772 * returns will have no affect on this {@code Throwable}'s stack 773 * trace. 774 * 775 * @throws NullPointerException if {@code stackTrace} is 776 * {@code null}, or if any of the elements of 777 * {@code stackTrace} are {@code null} 778 * 779 * @since 1.4 780 */ 781 public void setStackTrace(StackTraceElement[] stackTrace) { 782 StackTraceElement[] defensiveCopy = stackTrace.clone(); 783 for (int i = 0; i < defensiveCopy.length; i++) 784 if (defensiveCopy[i] == null) 785 throw new NullPointerException("stackTrace[" + i + "]"); 786 787 synchronized (this) { 788 this.stackTrace = defensiveCopy; 789 } 790 } 791 792 /** 793 * Returns the number of elements in the stack trace (or 0 if the stack 794 * trace is unavailable). 795 * 796 * package-protection for use by SharedSecrets. 797 */ 798 native int getStackTraceDepth(); 799 800 /** 801 * Returns the specified element of the stack trace. 802 * 803 * package-protection for use by SharedSecrets. 804 * 805 * @param index index of the element to return. 806 * @throws IndexOutOfBoundsException if {@code index < 0 || 807 * index >= getStackTraceDepth() } 808 */ 809 native StackTraceElement getStackTraceElement(int index); 810 811 /** 812 * Read a {@code Throwable} from a stream, enforcing 813 * well-formedness constraints on fields. Null entries and 814 * self-pointers are not allowed in the list of {@code 815 * suppressedExceptions}. Null entries are not allowed for stack 816 * trace elements. 817 * 818 * Note that there are no constraints on the value the {@code 819 * cause} field can hold; both {@code null} and {@code this} are 820 * valid values for the field. 821 */ 822 private void readObject(ObjectInputStream s) 823 throws IOException, ClassNotFoundException { 824 s.defaultReadObject(); // read in all fields 825 if (suppressedExceptions != null) { 826 List<Throwable> suppressed = null; 827 if (suppressedExceptions.isEmpty()) { 828 // Use the sentinel for a zero-length list 829 suppressed = SUPPRESSED_SENTINEL; 830 } else { // Copy Throwables to new list 831 suppressed = new ArrayList<>(1); 832 for (Throwable t : suppressedExceptions) { 833 // Enforce constraints on suppressed exceptions in 834 // case of corrupt or malicious stream. 835 if (t == null) 836 throw new NullPointerException(NULL_CAUSE_MESSAGE); 837 if (t == this) 838 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE); 839 suppressed.add(t); 840 } 841 } 842 suppressedExceptions = suppressed; 843 } // else a null suppressedExceptions field remains null 844 845 if (stackTrace != null) { 846 for (StackTraceElement ste : stackTrace) { 847 if (ste == null) 848 throw new NullPointerException("null StackTraceElement in serial stream. "); 849 } 850 } else { 851 // A null stackTrace field in the serial form can result from 852 // an exception serialized without that field in older JDK releases. 853 stackTrace = EMPTY_STACK; 854 } 855 856 } 857 858 /** 859 * Write a {@code Throwable} object to a stream. 860 */ 861 private synchronized void writeObject(ObjectOutputStream s) 862 throws IOException { 863 getOurStackTrace(); // Ensure that stackTrace field is initialized. 864 s.defaultWriteObject(); 865 } 866 867 /** 868 * Adds the specified exception to the list of exceptions that 869 * were suppressed, typically by the {@code try}-with-resources 870 * statement, in order to deliver this exception. 871 * 872 * If the first exception to be suppressed is {@code null}, that 873 * indicates suppressed exception information will <em>not</em> be 874 * recorded for this exception. Subsequent calls to this method 875 * will not record any suppressed exceptions. Otherwise, 876 * attempting to suppress {@code null} after an exception has 877 * already been successfully suppressed results in a {@code 878 * NullPointerException}. 879 * 880 * <p>Note that when one exception {@linkplain 881 * #initCause(Throwable) causes} another exception, the first 882 * exception is usually caught and then the second exception is 883 * thrown in response. In contrast, when one exception suppresses 884 * another, two exceptions are thrown in sibling code blocks, such 885 * as in a {@code try} block and in its {@code finally} block, and 886 * control flow can only continue with one exception so the second 887 * is recorded as a suppressed exception of the first. 888 * 889 * @param exception the exception to be added to the list of 890 * suppressed exceptions 891 * @throws IllegalArgumentException if {@code exception} is this 892 * throwable; a throwable cannot suppress itself. 893 * @throws NullPointerException if {@code exception} is null and 894 * an exception has already been suppressed by this exception 895 * @since 1.7 896 */ 897 public final synchronized void addSuppressed(Throwable exception) { 898 if (exception == this) 899 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE); 900 901 if (exception == null) { 902 if (suppressedExceptions == SUPPRESSED_SENTINEL) { 903 suppressedExceptions = null; // No suppression information recorded 904 return; 905 } else 906 throw new NullPointerException(NULL_CAUSE_MESSAGE); 907 } else { 908 assert exception != null && exception != this; 909 910 if (suppressedExceptions == null) // Suppressed exceptions not recorded 911 return; 912 913 if (suppressedExceptions == SUPPRESSED_SENTINEL) 914 suppressedExceptions = new ArrayList<>(1); 915 916 assert suppressedExceptions != SUPPRESSED_SENTINEL; 917 918 suppressedExceptions.add(exception); 919 } 920 } 921 922 private static final Throwable[] EMPTY_THROWABLE_ARRAY = new Throwable[0]; 923 924 /** 925 * Returns an array containing all of the exceptions that were 926 * suppressed, typically by the {@code try}-with-resources 927 * statement, in order to deliver this exception. 928 * 929 * If no exceptions were suppressed, an empty array is returned. 930 * 931 * @return an array containing all of the exceptions that were 932 * suppressed to deliver this exception. 933 * @since 1.7 934 */ 935 public final synchronized Throwable[] getSuppressed() { 936 if (suppressedExceptions == SUPPRESSED_SENTINEL || 937 suppressedExceptions == null) 938 return EMPTY_THROWABLE_ARRAY; 939 else 940 return suppressedExceptions.toArray(EMPTY_THROWABLE_ARRAY); 941 } 942 }