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 * @jls 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 /** 134 * Holder class to defer initializing sentinel objects only used 135 * for serialization. 136 */ 137 private static class SentinelHolder { 138 /** 139 * {@linkplain #setStackTrace(StackTraceElement[]) Setting the 140 * stack trace} to a one-element array containing this sentinel 141 * value indicates future attempts to set the stack trace will be 142 * ignored. The sentinal is equal to the result of calling:<br> 143 * {@code new StackTraceElement("", "", null, Integer.MIN_VALUE)} 144 */ 145 public static final StackTraceElement STACK_TRACE_ELEMENT_SENTINEL = 146 new StackTraceElement("", "", null, Integer.MIN_VALUE); 147 148 /** 149 * Sentinel value used in the serial form to indicate an immutable 150 * stack trace. 151 */ 152 public static final StackTraceElement[] STACK_TRACE_SENTINEL = 153 new StackTraceElement[] {STACK_TRACE_ELEMENT_SENTINEL}; 154 } 155 156 /** 157 * A shared value for an empty stack. 158 */ 159 private static final StackTraceElement[] UNASSIGNED_STACK = new StackTraceElement[0]; 160 161 /* 162 * To allow Throwable objects to be made immutable and safely 163 * reused by the JVM, such as OutOfMemoryErrors, fields of 164 * Throwable that are writable in response to user actions, cause, 165 * stackTrace, and suppressedExceptions obey the following 166 * protocol: 167 * 168 * 1) The fields are initialized to a non-null sentinel value 169 * which indicates the value has logically not been set. 170 * 171 * 2) Writing a null to the field indicates further writes 172 * are forbidden 173 * 174 * 3) The sentinel value may be replaced with another non-null 175 * value. 176 * 177 * For example, implementations of the HotSpot JVM have 178 * preallocated OutOfMemoryError objects to provide for better 179 * diagnosability of that situation. These objects are created 180 * without calling the constructor for that class and the fields 181 * in question are initialized to null. To support this 182 * capability, any new fields added to Throwable that require 183 * being initialized to a non-null value require a coordinated JVM 184 * change. 185 */ 186 187 /** 188 * The throwable that caused this throwable to get thrown, or null if this 189 * throwable was not caused by another throwable, or if the causative 190 * throwable is unknown. If this field is equal to this throwable itself, 191 * it indicates that the cause of this throwable has not yet been 192 * initialized. 193 * 194 * @serial 195 * @since 1.4 196 */ 197 private Throwable cause = this; 198 199 /** 200 * The stack trace, as returned by {@link #getStackTrace()}. 201 * 202 * The field is initialized to a zero-length array. A {@code 203 * null} value of this field indicates subsequent calls to {@link 204 * #setStackTrace(StackTraceElement[])} and {@link 205 * #fillInStackTrace()} will be be no-ops. 206 * 207 * @serial 208 * @since 1.4 209 */ 210 private StackTraceElement[] stackTrace = UNASSIGNED_STACK; 211 212 // Setting this static field introduces an acceptable 213 // initialization dependency on a few java.util classes. 214 private static final List<Throwable> SUPPRESSED_SENTINEL = 215 Collections.unmodifiableList(new ArrayList<Throwable>(0)); 216 217 /** 218 * The list of suppressed exceptions, as returned by {@link 219 * #getSuppressed()}. The list is initialized to a zero-element 220 * unmodifiable sentinel list. When a serialized Throwable is 221 * read in, if the {@code suppressedExceptions} field points to a 222 * zero-element list, the field is reset to the sentinel value. 223 * 224 * @serial 225 * @since 1.7 226 */ 227 private List<Throwable> suppressedExceptions = SUPPRESSED_SENTINEL; 228 229 /** Message for trying to suppress a null exception. */ 230 private static final String NULL_CAUSE_MESSAGE = "Cannot suppress a null exception."; 231 232 /** Message for trying to suppress oneself. */ 233 private static final String SELF_SUPPRESSION_MESSAGE = "Self-suppression not permitted"; 234 235 /** Caption for labeling causative exception stack traces */ 236 private static final String CAUSE_CAPTION = "Caused by: "; 237 238 /** Caption for labeling suppressed exception stack traces */ 239 private static final String SUPPRESSED_CAPTION = "Suppressed: "; 240 241 /** 242 * Constructs a new throwable with {@code null} as its detail message. 243 * The cause is not initialized, and may subsequently be initialized by a 244 * call to {@link #initCause}. 245 * 246 * <p>The {@link #fillInStackTrace()} method is called to initialize 247 * the stack trace data in the newly created throwable. 248 */ 249 public Throwable() { 250 fillInStackTrace(); 251 } 252 253 /** 254 * Constructs a new throwable with the specified detail message. The 255 * cause is not initialized, and may subsequently be initialized by 256 * a call to {@link #initCause}. 257 * 258 * <p>The {@link #fillInStackTrace()} method is called to initialize 259 * the stack trace data in the newly created throwable. 260 * 261 * @param message the detail message. The detail message is saved for 262 * later retrieval by the {@link #getMessage()} method. 263 */ 264 public Throwable(String message) { 265 fillInStackTrace(); 266 detailMessage = message; 267 } 268 269 /** 270 * Constructs a new throwable with the specified detail message and 271 * cause. <p>Note that the detail message associated with 272 * {@code cause} is <i>not</i> automatically incorporated in 273 * this throwable's detail message. 274 * 275 * <p>The {@link #fillInStackTrace()} method is called to initialize 276 * the stack trace data in the newly created throwable. 277 * 278 * @param message the detail message (which is saved for later retrieval 279 * by the {@link #getMessage()} method). 280 * @param cause the cause (which is saved for later retrieval by the 281 * {@link #getCause()} method). (A {@code null} value is 282 * permitted, and indicates that the cause is nonexistent or 283 * unknown.) 284 * @since 1.4 285 */ 286 public Throwable(String message, Throwable cause) { 287 fillInStackTrace(); 288 detailMessage = message; 289 this.cause = cause; 290 } 291 292 /** 293 * Constructs a new throwable with the specified cause and a detail 294 * message of {@code (cause==null ? null : cause.toString())} (which 295 * typically contains the class and detail message of {@code cause}). 296 * This constructor is useful for throwables that are little more than 297 * wrappers for other throwables (for example, {@link 298 * java.security.PrivilegedActionException}). 299 * 300 * <p>The {@link #fillInStackTrace()} method is called to initialize 301 * the stack trace data in the newly created throwable. 302 * 303 * @param cause the cause (which is saved for later retrieval by the 304 * {@link #getCause()} method). (A {@code null} value is 305 * permitted, and indicates that the cause is nonexistent or 306 * unknown.) 307 * @since 1.4 308 */ 309 public Throwable(Throwable cause) { 310 fillInStackTrace(); 311 detailMessage = (cause==null ? null : cause.toString()); 312 this.cause = cause; 313 } 314 315 /** 316 * Constructs a new throwable with the specified detail message, 317 * cause, {@linkplain #addSuppressed suppression} enabled or 318 * disabled, and writable stack trace enabled or disabled. If 319 * suppression is disabled, {@link #getSuppressed} for this object 320 * will return a zero-length array and calls to {@link 321 * #addSuppressed} that would otherwise append an exception to the 322 * suppressed list will have no effect. If the writable stack 323 * trace is false, this constructor will not call {@link 324 * #fillInStackTrace()}, a {@code null} will be written to the 325 * {@code stackTrace} field, and subsequent calls to {@code 326 * fillInStackTrace} and {@link 327 * #setStackTrace(StackTraceElement[])} will not set the stack 328 * trace. If the writable stack trace is false, {@link 329 * #getStackTrace} will return a zero length array. 330 * 331 * <p>Note that the other constructors of {@code Throwable} treat 332 * suppression as being enabled and the stack trace as being 333 * writable. Subclasses of {@code Throwable} should document any 334 * conditions under which suppression is disabled and document 335 * conditions under which the stack trace is not writable. 336 * Disabling of suppression should only occur in exceptional 337 * circumstances where special requirements exist, such as a 338 * virtual machine reusing exception objects under low-memory 339 * situations. 340 * 341 * @param message the detail message. 342 * @param cause the cause. (A {@code null} value is permitted, 343 * and indicates that the cause is nonexistent or unknown.) 344 * @param enableSuppression whether or not suppression is enabled or disabled 345 * @param writableStackTrace whether or not the stack trace should be 346 * writable 347 * 348 * @see OutOfMemoryError 349 * @see NullPointerException 350 * @see ArithmeticException 351 * @since 1.7 352 */ 353 protected Throwable(String message, Throwable cause, 354 boolean enableSuppression, 355 boolean writableStackTrace) { 356 if (writableStackTrace) { 357 fillInStackTrace(); 358 } else { 359 stackTrace = null; 360 } 361 detailMessage = message; 362 this.cause = cause; 363 if (!enableSuppression) 364 suppressedExceptions = null; 365 } 366 367 /** 368 * Returns the detail message string of this throwable. 369 * 370 * @return the detail message string of this {@code Throwable} instance 371 * (which may be {@code null}). 372 */ 373 public String getMessage() { 374 return detailMessage; 375 } 376 377 /** 378 * Creates a localized description of this throwable. 379 * Subclasses may override this method in order to produce a 380 * locale-specific message. For subclasses that do not override this 381 * method, the default implementation returns the same result as 382 * {@code getMessage()}. 383 * 384 * @return The localized description of this throwable. 385 * @since JDK1.1 386 */ 387 public String getLocalizedMessage() { 388 return getMessage(); 389 } 390 391 /** 392 * Returns the cause of this throwable or {@code null} if the 393 * cause is nonexistent or unknown. (The cause is the throwable that 394 * caused this throwable to get thrown.) 395 * 396 * <p>This implementation returns the cause that was supplied via one of 397 * the constructors requiring a {@code Throwable}, or that was set after 398 * creation with the {@link #initCause(Throwable)} method. While it is 399 * typically unnecessary to override this method, a subclass can override 400 * it to return a cause set by some other means. This is appropriate for 401 * a "legacy chained throwable" that predates the addition of chained 402 * exceptions to {@code Throwable}. Note that it is <i>not</i> 403 * necessary to override any of the {@code PrintStackTrace} methods, 404 * all of which invoke the {@code getCause} method to determine the 405 * cause of a throwable. 406 * 407 * @return the cause of this throwable or {@code null} if the 408 * cause is nonexistent or unknown. 409 * @since 1.4 410 */ 411 public synchronized Throwable getCause() { 412 return (cause==this ? null : cause); 413 } 414 415 /** 416 * Initializes the <i>cause</i> of this throwable to the specified value. 417 * (The cause is the throwable that caused this throwable to get thrown.) 418 * 419 * <p>This method can be called at most once. It is generally called from 420 * within the constructor, or immediately after creating the 421 * throwable. If this throwable was created 422 * with {@link #Throwable(Throwable)} or 423 * {@link #Throwable(String,Throwable)}, this method cannot be called 424 * even once. 425 * 426 * @param cause the cause (which is saved for later retrieval by the 427 * {@link #getCause()} method). (A {@code null} value is 428 * permitted, and indicates that the cause is nonexistent or 429 * unknown.) 430 * @return a reference to this {@code Throwable} instance. 431 * @throws IllegalArgumentException if {@code cause} is this 432 * throwable. (A throwable cannot be its own cause.) 433 * @throws IllegalStateException if this throwable was 434 * created with {@link #Throwable(Throwable)} or 435 * {@link #Throwable(String,Throwable)}, or this method has already 436 * been called on this throwable. 437 * @since 1.4 438 */ 439 public synchronized Throwable initCause(Throwable cause) { 440 if (this.cause != this) 441 throw new IllegalStateException("Can't overwrite cause"); 442 if (cause == this) 443 throw new IllegalArgumentException("Self-causation not permitted"); 444 this.cause = cause; 445 return this; 446 } 447 448 /** 449 * Returns a short description of this throwable. 450 * The result is the concatenation of: 451 * <ul> 452 * <li> the {@linkplain Class#getName() name} of the class of this object 453 * <li> ": " (a colon and a space) 454 * <li> the result of invoking this object's {@link #getLocalizedMessage} 455 * method 456 * </ul> 457 * If {@code getLocalizedMessage} returns {@code null}, then just 458 * the class name is returned. 459 * 460 * @return a string representation of this throwable. 461 */ 462 public String toString() { 463 String s = getClass().getName(); 464 String message = getLocalizedMessage(); 465 return (message != null) ? (s + ": " + message) : s; 466 } 467 468 /** 469 * Prints this throwable and its backtrace to the 470 * standard error stream. This method prints a stack trace for this 471 * {@code Throwable} object on the error output stream that is 472 * the value of the field {@code System.err}. The first line of 473 * output contains the result of the {@link #toString()} method for 474 * this object. Remaining lines represent data previously recorded by 475 * the method {@link #fillInStackTrace()}. The format of this 476 * information depends on the implementation, but the following 477 * example may be regarded as typical: 478 * <blockquote><pre> 479 * java.lang.NullPointerException 480 * at MyClass.mash(MyClass.java:9) 481 * at MyClass.crunch(MyClass.java:6) 482 * at MyClass.main(MyClass.java:3) 483 * </pre></blockquote> 484 * This example was produced by running the program: 485 * <pre> 486 * class MyClass { 487 * public static void main(String[] args) { 488 * crunch(null); 489 * } 490 * static void crunch(int[] a) { 491 * mash(a); 492 * } 493 * static void mash(int[] b) { 494 * System.out.println(b[0]); 495 * } 496 * } 497 * </pre> 498 * The backtrace for a throwable with an initialized, non-null cause 499 * should generally include the backtrace for the cause. The format 500 * of this information depends on the implementation, but the following 501 * example may be regarded as typical: 502 * <pre> 503 * HighLevelException: MidLevelException: LowLevelException 504 * at Junk.a(Junk.java:13) 505 * at Junk.main(Junk.java:4) 506 * Caused by: MidLevelException: LowLevelException 507 * at Junk.c(Junk.java:23) 508 * at Junk.b(Junk.java:17) 509 * at Junk.a(Junk.java:11) 510 * ... 1 more 511 * Caused by: LowLevelException 512 * at Junk.e(Junk.java:30) 513 * at Junk.d(Junk.java:27) 514 * at Junk.c(Junk.java:21) 515 * ... 3 more 516 * </pre> 517 * Note the presence of lines containing the characters {@code "..."}. 518 * These lines indicate that the remainder of the stack trace for this 519 * exception matches the indicated number of frames from the bottom of the 520 * stack trace of the exception that was caused by this exception (the 521 * "enclosing" exception). This shorthand can greatly reduce the length 522 * of the output in the common case where a wrapped exception is thrown 523 * from same method as the "causative exception" is caught. The above 524 * example was produced by running the program: 525 * <pre> 526 * public class Junk { 527 * public static void main(String args[]) { 528 * try { 529 * a(); 530 * } catch(HighLevelException e) { 531 * e.printStackTrace(); 532 * } 533 * } 534 * static void a() throws HighLevelException { 535 * try { 536 * b(); 537 * } catch(MidLevelException e) { 538 * throw new HighLevelException(e); 539 * } 540 * } 541 * static void b() throws MidLevelException { 542 * c(); 543 * } 544 * static void c() throws MidLevelException { 545 * try { 546 * d(); 547 * } catch(LowLevelException e) { 548 * throw new MidLevelException(e); 549 * } 550 * } 551 * static void d() throws LowLevelException { 552 * e(); 553 * } 554 * static void e() throws LowLevelException { 555 * throw new LowLevelException(); 556 * } 557 * } 558 * 559 * class HighLevelException extends Exception { 560 * HighLevelException(Throwable cause) { super(cause); } 561 * } 562 * 563 * class MidLevelException extends Exception { 564 * MidLevelException(Throwable cause) { super(cause); } 565 * } 566 * 567 * class LowLevelException extends Exception { 568 * } 569 * </pre> 570 * As of release 7, the platform supports the notion of 571 * <i>suppressed exceptions</i> (in conjunction with the {@code 572 * try}-with-resources statement). Any exceptions that were 573 * suppressed in order to deliver an exception are printed out 574 * beneath the stack trace. The format of this information 575 * depends on the implementation, but the following example may be 576 * regarded as typical: 577 * 578 * <pre> 579 * Exception in thread "main" java.lang.Exception: Something happened 580 * at Foo.bar(Foo.java:10) 581 * at Foo.main(Foo.java:5) 582 * Suppressed: Resource$CloseFailException: Resource ID = 0 583 * at Resource.close(Resource.java:26) 584 * at Foo.bar(Foo.java:9) 585 * ... 1 more 586 * </pre> 587 * Note that the "... n more" notation is used on suppressed exceptions 588 * just at it is used on causes. Unlike causes, suppressed exceptions are 589 * indented beyond their "containing exceptions." 590 * 591 * <p>An exception can have both a cause and one or more suppressed 592 * exceptions: 593 * <pre> 594 * Exception in thread "main" java.lang.Exception: Main block 595 * at Foo3.main(Foo3.java:7) 596 * Suppressed: Resource$CloseFailException: Resource ID = 2 597 * at Resource.close(Resource.java:26) 598 * at Foo3.main(Foo3.java:5) 599 * Suppressed: Resource$CloseFailException: Resource ID = 1 600 * at Resource.close(Resource.java:26) 601 * at Foo3.main(Foo3.java:5) 602 * Caused by: java.lang.Exception: I did it 603 * at Foo3.main(Foo3.java:8) 604 * </pre> 605 * Likewise, a suppressed exception can have a cause: 606 * <pre> 607 * Exception in thread "main" java.lang.Exception: Main block 608 * at Foo4.main(Foo4.java:6) 609 * Suppressed: Resource2$CloseFailException: Resource ID = 1 610 * at Resource2.close(Resource2.java:20) 611 * at Foo4.main(Foo4.java:5) 612 * Caused by: java.lang.Exception: Rats, you caught me 613 * at Resource2$CloseFailException.<init>(Resource2.java:45) 614 * ... 2 more 615 * </pre> 616 */ 617 public void printStackTrace() { 618 printStackTrace(System.err); 619 } 620 621 /** 622 * Prints this throwable and its backtrace to the specified print stream. 623 * 624 * @param s {@code PrintStream} to use for output 625 */ 626 public void printStackTrace(PrintStream s) { 627 printStackTrace(new WrappedPrintStream(s)); 628 } 629 630 private void printStackTrace(PrintStreamOrWriter s) { 631 // Guard against malicious overrides of Throwable.equals by 632 // using a Set with identity equality semantics. 633 Set<Throwable> dejaVu = 634 Collections.newSetFromMap(new IdentityHashMap<Throwable, Boolean>()); 635 dejaVu.add(this); 636 637 synchronized (s.lock()) { 638 // Print our stack trace 639 s.println(this); 640 StackTraceElement[] trace = getOurStackTrace(); 641 for (StackTraceElement traceElement : trace) 642 s.println("\tat " + traceElement); 643 644 // Print suppressed exceptions, if any 645 for (Throwable se : getSuppressed()) 646 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, "\t", dejaVu); 647 648 // Print cause, if any 649 Throwable ourCause = getCause(); 650 if (ourCause != null) 651 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, "", dejaVu); 652 } 653 } 654 655 /** 656 * Print our stack trace as an enclosed exception for the specified 657 * stack trace. 658 */ 659 private void printEnclosedStackTrace(PrintStreamOrWriter s, 660 StackTraceElement[] enclosingTrace, 661 String caption, 662 String prefix, 663 Set<Throwable> dejaVu) { 664 assert Thread.holdsLock(s.lock()); 665 if (dejaVu.contains(this)) { 666 s.println("\t[CIRCULAR REFERENCE:" + this + "]"); 667 } else { 668 dejaVu.add(this); 669 // Compute number of frames in common between this and enclosing trace 670 StackTraceElement[] trace = getOurStackTrace(); 671 int m = trace.length - 1; 672 int n = enclosingTrace.length - 1; 673 while (m >= 0 && n >=0 && trace[m].equals(enclosingTrace[n])) { 674 m--; n--; 675 } 676 int framesInCommon = trace.length - 1 - m; 677 678 // Print our stack trace 679 s.println(prefix + caption + this); 680 for (int i = 0; i <= m; i++) 681 s.println(prefix + "\tat " + trace[i]); 682 if (framesInCommon != 0) 683 s.println(prefix + "\t... " + framesInCommon + " more"); 684 685 // Print suppressed exceptions, if any 686 for (Throwable se : getSuppressed()) 687 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, 688 prefix +"\t", dejaVu); 689 690 // Print cause, if any 691 Throwable ourCause = getCause(); 692 if (ourCause != null) 693 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, prefix, dejaVu); 694 } 695 } 696 697 /** 698 * Prints this throwable and its backtrace to the specified 699 * print writer. 700 * 701 * @param s {@code PrintWriter} to use for output 702 * @since JDK1.1 703 */ 704 public void printStackTrace(PrintWriter s) { 705 printStackTrace(new WrappedPrintWriter(s)); 706 } 707 708 /** 709 * Wrapper class for PrintStream and PrintWriter to enable a single 710 * implementation of printStackTrace. 711 */ 712 private abstract static class PrintStreamOrWriter { 713 /** Returns the object to be locked when using this StreamOrWriter */ 714 abstract Object lock(); 715 716 /** Prints the specified string as a line on this StreamOrWriter */ 717 abstract void println(Object o); 718 } 719 720 private static class WrappedPrintStream extends PrintStreamOrWriter { 721 private final PrintStream printStream; 722 723 WrappedPrintStream(PrintStream printStream) { 724 this.printStream = printStream; 725 } 726 727 Object lock() { 728 return printStream; 729 } 730 731 void println(Object o) { 732 printStream.println(o); 733 } 734 } 735 736 private static class WrappedPrintWriter extends PrintStreamOrWriter { 737 private final PrintWriter printWriter; 738 739 WrappedPrintWriter(PrintWriter printWriter) { 740 this.printWriter = printWriter; 741 } 742 743 Object lock() { 744 return printWriter; 745 } 746 747 void println(Object o) { 748 printWriter.println(o); 749 } 750 } 751 752 /** 753 * Fills in the execution stack trace. This method records within this 754 * {@code Throwable} object information about the current state of 755 * the stack frames for the current thread. 756 * 757 * <p>If the stack trace of this {@code Throwable} {@linkplain 758 * Throwable#Throwable(String, Throwable, boolean, boolean) is not 759 * writable}, calling this method has no effect. 760 * 761 * @return a reference to this {@code Throwable} instance. 762 * @see java.lang.Throwable#printStackTrace() 763 */ 764 public synchronized Throwable fillInStackTrace() { 765 if (stackTrace != null) { 766 fillInStackTrace(0); 767 stackTrace = UNASSIGNED_STACK; 768 } 769 return this; 770 } 771 772 private native Throwable fillInStackTrace(int dummy); 773 774 /** 775 * Provides programmatic access to the stack trace information printed by 776 * {@link #printStackTrace()}. Returns an array of stack trace elements, 777 * each representing one stack frame. The zeroth element of the array 778 * (assuming the array's length is non-zero) represents the top of the 779 * stack, which is the last method invocation in the sequence. Typically, 780 * this is the point at which this throwable was created and thrown. 781 * The last element of the array (assuming the array's length is non-zero) 782 * represents the bottom of the stack, which is the first method invocation 783 * in the sequence. 784 * 785 * <p>Some virtual machines may, under some circumstances, omit one 786 * or more stack frames from the stack trace. In the extreme case, 787 * a virtual machine that has no stack trace information concerning 788 * this throwable is permitted to return a zero-length array from this 789 * method. Generally speaking, the array returned by this method will 790 * contain one element for every frame that would be printed by 791 * {@code printStackTrace}. 792 * 793 * @return an array of stack trace elements representing the stack trace 794 * pertaining to this throwable. 795 * @since 1.4 796 */ 797 public StackTraceElement[] getStackTrace() { 798 return getOurStackTrace().clone(); 799 } 800 801 private synchronized StackTraceElement[] getOurStackTrace() { 802 // Initialize stack trace field with information from 803 // backtrace if this is the first call to this method 804 if (stackTrace == UNASSIGNED_STACK) { 805 int depth = getStackTraceDepth(); 806 stackTrace = new StackTraceElement[depth]; 807 for (int i=0; i < depth; i++) 808 stackTrace[i] = getStackTraceElement(i); 809 } else if (stackTrace == null) { 810 return UNASSIGNED_STACK; 811 } 812 return stackTrace; 813 } 814 815 /** 816 * Sets the stack trace elements that will be returned by 817 * {@link #getStackTrace()} and printed by {@link #printStackTrace()} 818 * and related methods. 819 * 820 * This method, which is designed for use by RPC frameworks and other 821 * advanced systems, allows the client to override the default 822 * stack trace that is either generated by {@link #fillInStackTrace()} 823 * when a throwable is constructed or deserialized when a throwable is 824 * read from a serialization stream. 825 * 826 * <p>If the stack trace of this {@code Throwable} {@linkplain 827 * Throwable#Throwable(String, Throwable, boolean, boolean) is not 828 * writable}, calling this method has no effect other than 829 * validating its argument. 830 * 831 * @param stackTrace the stack trace elements to be associated with 832 * this {@code Throwable}. The specified array is copied by this 833 * call; changes in the specified array after the method invocation 834 * returns will have no affect on this {@code Throwable}'s stack 835 * trace. 836 * 837 * @throws NullPointerException if {@code stackTrace} is 838 * {@code null} or if any of the elements of 839 * {@code stackTrace} are {@code null} 840 * 841 * @since 1.4 842 */ 843 public void setStackTrace(StackTraceElement[] stackTrace) { 844 // Validate argument 845 StackTraceElement[] defensiveCopy = stackTrace.clone(); 846 for (int i = 0; i < defensiveCopy.length; i++) { 847 if (defensiveCopy[i] == null) 848 throw new NullPointerException("stackTrace[" + i + "]"); 849 } 850 851 if (this.stackTrace == null) // Immutable stack 852 return; 853 854 synchronized (this) { 855 this.stackTrace = defensiveCopy; 856 } 857 } 858 859 /** 860 * Returns the number of elements in the stack trace (or 0 if the stack 861 * trace is unavailable). 862 * 863 * package-protection for use by SharedSecrets. 864 */ 865 native int getStackTraceDepth(); 866 867 /** 868 * Returns the specified element of the stack trace. 869 * 870 * package-protection for use by SharedSecrets. 871 * 872 * @param index index of the element to return. 873 * @throws IndexOutOfBoundsException if {@code index < 0 || 874 * index >= getStackTraceDepth() } 875 */ 876 native StackTraceElement getStackTraceElement(int index); 877 878 /** 879 * Reads a {@code Throwable} from a stream, enforcing 880 * well-formedness constraints on fields. Null entries and 881 * self-pointers are not allowed in the list of {@code 882 * suppressedExceptions}. Null entries are not allowed for stack 883 * trace elements. A null stack trace in the serial form results 884 * in a zero-length stack element array. A single-element stack 885 * trace whose entry is equal to {@code new StackTraceElement("", 886 * "", null, Integer.MIN_VALUE)} results in a {@code null} {@code 887 * stackTrace} field. 888 * 889 * Note that there are no constraints on the value the {@code 890 * cause} field can hold; both {@code null} and {@code this} are 891 * valid values for the field. 892 */ 893 private void readObject(ObjectInputStream s) 894 throws IOException, ClassNotFoundException { 895 s.defaultReadObject(); // read in all fields 896 if (suppressedExceptions != null) { 897 List<Throwable> suppressed = null; 898 if (suppressedExceptions.isEmpty()) { 899 // Use the sentinel for a zero-length list 900 suppressed = SUPPRESSED_SENTINEL; 901 } else { // Copy Throwables to new list 902 suppressed = new ArrayList<>(1); 903 for (Throwable t : suppressedExceptions) { 904 // Enforce constraints on suppressed exceptions in 905 // case of corrupt or malicious stream. 906 if (t == null) 907 throw new NullPointerException(NULL_CAUSE_MESSAGE); 908 if (t == this) 909 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE); 910 suppressed.add(t); 911 } 912 } 913 suppressedExceptions = suppressed; 914 } // else a null suppressedExceptions field remains null 915 916 /* 917 * For zero-length stack traces, use a clone of 918 * UNASSIGNED_STACK rather than UNASSIGNED_STACK itself to 919 * allow identity comparison against UNASSIGNED_STACK in 920 * getOurStackTrace. The identity of UNASSIGNED_STACK in 921 * stackTrace indicates to the getOurStackTrace method that 922 * the stackTrace needs to be constructed from the information 923 * in backtrace. 924 */ 925 if (stackTrace != null) { 926 if (stackTrace.length == 0) { 927 stackTrace = UNASSIGNED_STACK.clone(); 928 } else if (stackTrace.length == 1 && 929 // Check for the marker of an immutable stack trace 930 SentinelHolder.STACK_TRACE_ELEMENT_SENTINEL.equals(stackTrace[0])) { 931 stackTrace = null; 932 } else { // Verify stack trace elements are non-null. 933 for(StackTraceElement ste : stackTrace) { 934 if (ste == null) 935 throw new NullPointerException("null StackTraceElement in serial stream. "); 936 } 937 } 938 } else { 939 // A null stackTrace field in the serial form can result 940 // from an exception serialized without that field in 941 // older JDK releases; treat such exceptions as having 942 // empty stack traces. 943 stackTrace = UNASSIGNED_STACK.clone(); 944 } 945 } 946 947 /** 948 * Write a {@code Throwable} object to a stream. 949 * 950 * A {@code null} stack trace field is represented in the serial 951 * form as a one-element array whose element is equal to {@code 952 * new StackTraceElement("", "", null, Integer.MIN_VALUE)}. 953 */ 954 private synchronized void writeObject(ObjectOutputStream s) 955 throws IOException { 956 // Ensure that the stackTrace field is initialized to a 957 // non-null value, if appropriate. As of JDK 7, a null stack 958 // trace field is a valid value indicating the stack trace 959 // should not be set. 960 getOurStackTrace(); 961 ObjectOutputStream.PutField fields = s.putFields(); 962 963 fields.put("detailMessage", detailMessage); 964 fields.put("cause", cause); 965 // Serialize a null stacktrace using the stack trace sentinel. 966 if (stackTrace == null) 967 fields.put("stackTrace", SentinelHolder.STACK_TRACE_SENTINEL); 968 else 969 fields.put("stackTrace", stackTrace); 970 fields.put("suppressedExceptions", suppressedExceptions); 971 972 s.writeFields(); 973 } 974 975 /** 976 * Appends the specified exception to the exceptions that were 977 * suppressed in order to deliver this exception. This method is 978 * typically called (automatically and implicitly) by the {@code 979 * try}-with-resources statement. 980 * 981 * <p>The suppression behavior is enabled <em>unless</em> disabled 982 * {@linkplain #Throwable(String, Throwable, boolean, boolean) via 983 * a constructor}. When suppression is disabled, this method does 984 * nothing other than to validate its argument. 985 * 986 * <p>Note that when one exception {@linkplain 987 * #initCause(Throwable) causes} another exception, the first 988 * exception is usually caught and then the second exception is 989 * thrown in response. In other words, there is a causal 990 * connection between the two exceptions. 991 * 992 * In contrast, there are situations where two independent 993 * exceptions can be thrown in sibling code blocks, in particular 994 * in the {@code try} block of a {@code try}-with-resources 995 * statement and the compiler-generated {@code finally} block 996 * which closes the resource. 997 * 998 * In these situations, only one of the thrown exceptions can be 999 * propagated. In the {@code try}-with-resources statement, when 1000 * there are two such exceptions, the exception originating from 1001 * the {@code try} block is propagated and the exception from the 1002 * {@code finally} block is added to the list of exceptions 1003 * suppressed by the exception from the {@code try} block. As an 1004 * exception unwinds the stack, it can accumulate multiple 1005 * suppressed exceptions. 1006 * 1007 * <p>An exception may have suppressed exceptions while also being 1008 * caused by another exception. Whether or not an exception has a 1009 * cause is semantically known at the time of its creation, unlike 1010 * whether or not an exception will suppress other exceptions 1011 * which is typically only determined after an exception is 1012 * thrown. 1013 * 1014 * <p>Note that programmer written code is also able to take 1015 * advantage of calling this method in situations where there are 1016 * multiple sibling exceptions and only one can be propagated. 1017 * 1018 * @param exception the exception to be added to the list of 1019 * suppressed exceptions 1020 * @throws IllegalArgumentException if {@code exception} is this 1021 * throwable; a throwable cannot suppress itself. 1022 * @throws NullPointerException if {@code exception} is {@code null} 1023 * @since 1.7 1024 */ 1025 public final synchronized void addSuppressed(Throwable exception) { 1026 if (exception == this) 1027 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE); 1028 1029 if (exception == null) 1030 throw new NullPointerException(NULL_CAUSE_MESSAGE); 1031 1032 if (suppressedExceptions == null) // Suppressed exceptions not recorded 1033 return; 1034 1035 if (suppressedExceptions == SUPPRESSED_SENTINEL) 1036 suppressedExceptions = new ArrayList<>(1); 1037 1038 suppressedExceptions.add(exception); 1039 } 1040 1041 private static final Throwable[] EMPTY_THROWABLE_ARRAY = new Throwable[0]; 1042 1043 /** 1044 * Returns an array containing all of the exceptions that were 1045 * suppressed, typically by the {@code try}-with-resources 1046 * statement, in order to deliver this exception. 1047 * 1048 * If no exceptions were suppressed or {@linkplain 1049 * #Throwable(String, Throwable, boolean, boolean) suppression is 1050 * disabled}, an empty array is returned. 1051 * 1052 * @return an array containing all of the exceptions that were 1053 * suppressed to deliver this exception. 1054 * @since 1.7 1055 */ 1056 public final synchronized Throwable[] getSuppressed() { 1057 if (suppressedExceptions == SUPPRESSED_SENTINEL || 1058 suppressedExceptions == null) 1059 return EMPTY_THROWABLE_ARRAY; 1060 else 1061 return suppressedExceptions.toArray(EMPTY_THROWABLE_ARRAY); 1062 } 1063 }