1 /* 2 * Copyright (c) 1994, 2013, 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 sun.misc.VM; 28 29 import java.io.*; 30 import java.util.*; 31 32 /** 33 * The {@code Throwable} class is the superclass of all errors and 34 * exceptions in the Java language. Only objects that are instances of this 35 * class (or one of its subclasses) are thrown by the Java Virtual Machine or 36 * can be thrown by the Java {@code throw} statement. Similarly, only 37 * this class or one of its subclasses can be the argument type in a 38 * {@code catch} clause. 39 * 40 * For the purposes of compile-time checking of exceptions, {@code 41 * Throwable} and any subclass of {@code Throwable} that is not also a 42 * subclass of either {@link RuntimeException} or {@link Error} are 43 * regarded as checked exceptions. 44 * 45 * <p>Instances of two subclasses, {@link java.lang.Error} and 46 * {@link java.lang.Exception}, are conventionally used to indicate 47 * that exceptional situations have occurred. Typically, these instances 48 * are freshly created in the context of the exceptional situation so 49 * as to include relevant information (such as stack trace data). 50 * 51 * <p>A throwable contains a snapshot of the execution stack of its 52 * thread at the time it was created. It can also contain a message 53 * string that gives more information about the error. Over time, a 54 * throwable can {@linkplain Throwable#addSuppressed suppress} other 55 * throwables from being propagated. Finally, the throwable can also 56 * contain a <i>cause</i>: another throwable that caused this 57 * throwable to be constructed. The recording of this causal information 58 * is referred to as the <i>chained exception</i> facility, as the 59 * cause can, itself, have a cause, and so on, leading to a "chain" of 60 * exceptions, each caused by another. 61 * 62 * <p>One reason that a throwable may have a cause is that the class that 63 * throws it is built atop a lower layered abstraction, and an operation on 64 * the upper layer fails due to a failure in the lower layer. It would be bad 65 * design to let the throwable thrown by the lower layer propagate outward, as 66 * it is generally unrelated to the abstraction provided by the upper layer. 67 * Further, doing so would tie the API of the upper layer to the details of 68 * its implementation, assuming the lower layer's exception was a checked 69 * exception. Throwing a "wrapped exception" (i.e., an exception containing a 70 * cause) allows the upper layer to communicate the details of the failure to 71 * its caller without incurring either of these shortcomings. It preserves 72 * the flexibility to change the implementation of the upper layer without 73 * changing its API (in particular, the set of exceptions thrown by its 74 * methods). 75 * 76 * <p>A second reason that a throwable may have a cause is that the method 77 * that throws it must conform to a general-purpose interface that does not 78 * permit the method to throw the cause directly. For example, suppose 79 * a persistent collection conforms to the {@link java.util.Collection 80 * Collection} interface, and that its persistence is implemented atop 81 * {@code java.io}. Suppose the internals of the {@code add} method 82 * can throw an {@link java.io.IOException IOException}. The implementation 83 * can communicate the details of the {@code IOException} to its caller 84 * while conforming to the {@code Collection} interface by wrapping the 85 * {@code IOException} in an appropriate unchecked exception. (The 86 * specification for the persistent collection should indicate that it is 87 * capable of throwing such exceptions.) 88 * 89 * <p>A cause can be associated with a throwable in two ways: via a 90 * constructor that takes the cause as an argument, or via the 91 * {@link #initCause(Throwable)} method. New throwable classes that 92 * wish to allow causes to be associated with them should provide constructors 93 * that take a cause and delegate (perhaps indirectly) to one of the 94 * {@code Throwable} constructors that takes a cause. 95 * 96 * Because the {@code initCause} method is public, it allows a cause to be 97 * associated with any throwable, even a "legacy throwable" whose 98 * implementation predates the addition of the exception chaining mechanism to 99 * {@code Throwable}. 100 * 101 * <p>By convention, class {@code Throwable} and its subclasses have two 102 * constructors, one that takes no arguments and one that takes a 103 * {@code String} argument that can be used to produce a detail message. 104 * Further, those subclasses that might likely have a cause associated with 105 * them should have two more constructors, one that takes a 106 * {@code Throwable} (the cause), and one that takes a 107 * {@code String} (the detail message) and a {@code Throwable} (the 108 * cause). 109 * 110 * @author unascribed 111 * @author Josh Bloch (Added exception chaining and programmatic access to 112 * stack trace in 1.4.) 113 * @jls 11.2 Compile-Time Checking of Exceptions 114 * @since 1.0 115 */ 116 public class Throwable implements Serializable { 117 /** use serialVersionUID from JDK 1.0.2 for interoperability */ 118 private static final long serialVersionUID = -3042686055658047285L; 119 120 /** 121 * Native code saves some indication of the stack backtrace in this slot. 122 */ 123 private transient Object backtrace; 124 125 /** 126 * Specific details about the Throwable. For example, for 127 * {@code FileNotFoundException}, this contains the name of 128 * the file that could not be found. 129 * 130 * @serial 131 */ 132 private String detailMessage; 133 134 135 /** 136 * Holder class to defer initializing sentinel objects only used 137 * for serialization. 138 */ 139 private static class SentinelHolder { 140 /** 141 * {@linkplain #setStackTrace(StackTraceElement[]) Setting the 142 * stack trace} to a one-element array containing this sentinel 143 * value indicates future attempts to set the stack trace will be 144 * ignored. The sentinel is equal to the result of calling:<br> 145 * {@code new StackTraceElement("", "", null, Integer.MIN_VALUE)} 146 */ 147 public static final StackTraceElement STACK_TRACE_ELEMENT_SENTINEL = 148 new StackTraceElement("", "", null, Integer.MIN_VALUE); 149 150 /** 151 * Sentinel value used in the serial form to indicate an immutable 152 * stack trace. 153 */ 154 public static final StackTraceElement[] STACK_TRACE_SENTINEL = 155 new StackTraceElement[] {STACK_TRACE_ELEMENT_SENTINEL}; 156 } 157 158 /** 159 * A shared value for an empty stack. 160 */ 161 private static final StackTraceElement[] UNASSIGNED_STACK = new StackTraceElement[0]; 162 163 /* 164 * To allow Throwable objects to be made immutable and safely 165 * reused by the JVM, such as OutOfMemoryErrors, fields of 166 * Throwable that are writable in response to user actions, cause, 167 * stackTrace, and suppressedExceptions obey the following 168 * protocol: 169 * 170 * 1) The fields are initialized to a non-null sentinel value 171 * which indicates the value has logically not been set. 172 * 173 * 2) Writing a null to the field indicates further writes 174 * are forbidden 175 * 176 * 3) The sentinel value may be replaced with another non-null 177 * value. 178 * 179 * For example, implementations of the HotSpot JVM have 180 * preallocated OutOfMemoryError objects to provide for better 181 * diagnosability of that situation. These objects are created 182 * without calling the constructor for that class and the fields 183 * in question are initialized to null. To support this 184 * capability, any new fields added to Throwable that require 185 * being initialized to a non-null value require a coordinated JVM 186 * change. 187 */ 188 189 /** 190 * The throwable that caused this throwable to get thrown, or null if this 191 * throwable was not caused by another throwable, or if the causative 192 * throwable is unknown. If this field is equal to this throwable itself, 193 * it indicates that the cause of this throwable has not yet been 194 * initialized. 195 * 196 * @serial 197 * @since 1.4 198 */ 199 private Throwable cause = this; 200 201 /** 202 * The stack trace, as returned by {@link #getStackTrace()}. 203 * 204 * The field is initialized to a zero-length array. A {@code 205 * null} value of this field indicates subsequent calls to {@link 206 * #setStackTrace(StackTraceElement[])} and {@link 207 * #fillInStackTrace()} will be no-ops. 208 * 209 * @serial 210 * @since 1.4 211 */ 212 private StackTraceElement[] stackTrace = UNASSIGNED_STACK; 213 214 // Setting this static field introduces an acceptable 215 // initialization dependency on a few java.util classes. 216 private static final List<Throwable> SUPPRESSED_SENTINEL = Collections.emptyList(); 217 218 /** 219 * The list of suppressed exceptions, as returned by {@link 220 * #getSuppressed()}. The list is initialized to a zero-element 221 * unmodifiable sentinel list. When a serialized Throwable is 222 * read in, if the {@code suppressedExceptions} field points to a 223 * zero-element list, the field is reset to the sentinel value. 224 * 225 * @serial 226 * @since 1.7 227 */ 228 private List<Throwable> suppressedExceptions = SUPPRESSED_SENTINEL; 229 230 /** Message for trying to suppress a null exception. */ 231 private static final String NULL_CAUSE_MESSAGE = "Cannot suppress a null exception."; 232 233 /** Message for trying to suppress oneself. */ 234 private static final String SELF_SUPPRESSION_MESSAGE = "Self-suppression not permitted"; 235 236 /** Caption for labeling causative exception stack traces */ 237 private static final String CAUSE_CAPTION = "Caused by: "; 238 239 /** Caption for labeling suppressed exception stack traces */ 240 private static final String SUPPRESSED_CAPTION = "Suppressed: "; 241 242 /** 243 * Constructs a new throwable with {@code null} as its detail message. 244 * The cause is not initialized, and may subsequently be initialized by a 245 * call to {@link #initCause}. 246 * 247 * <p>The {@link #fillInStackTrace()} method is called to initialize 248 * the stack trace data in the newly created throwable. 249 */ 250 public Throwable() { 251 fillInStackTrace(); 252 } 253 254 /** 255 * Constructs a new throwable with the specified detail message. The 256 * cause is not initialized, and may subsequently be initialized by 257 * a call to {@link #initCause}. 258 * 259 * <p>The {@link #fillInStackTrace()} method is called to initialize 260 * the stack trace data in the newly created throwable. 261 * 262 * @param message the detail message. The detail message is saved for 263 * later retrieval by the {@link #getMessage()} method. 264 */ 265 public Throwable(String message) { 266 fillInStackTrace(); 267 detailMessage = message; 268 } 269 270 /** 271 * Constructs a new throwable with the specified detail message and 272 * cause. <p>Note that the detail message associated with 273 * {@code cause} is <i>not</i> automatically incorporated in 274 * this throwable's detail message. 275 * 276 * <p>The {@link #fillInStackTrace()} method is called to initialize 277 * the stack trace data in the newly created throwable. 278 * 279 * @param message the detail message (which is saved for later retrieval 280 * by the {@link #getMessage()} method). 281 * @param cause the cause (which is saved for later retrieval by the 282 * {@link #getCause()} method). (A {@code null} value is 283 * permitted, and indicates that the cause is nonexistent or 284 * unknown.) 285 * @since 1.4 286 */ 287 public Throwable(String message, Throwable cause) { 288 fillInStackTrace(); 289 detailMessage = message; 290 this.cause = cause; 291 } 292 293 /** 294 * Constructs a new throwable with the specified cause and a detail 295 * message of {@code (cause==null ? null : cause.toString())} (which 296 * typically contains the class and detail message of {@code cause}). 297 * This constructor is useful for throwables that are little more than 298 * wrappers for other throwables (for example, {@link 299 * java.security.PrivilegedActionException}). 300 * 301 * <p>The {@link #fillInStackTrace()} method is called to initialize 302 * the stack trace data in the newly created throwable. 303 * 304 * @param cause the cause (which is saved for later retrieval by the 305 * {@link #getCause()} method). (A {@code null} value is 306 * permitted, and indicates that the cause is nonexistent or 307 * unknown.) 308 * @since 1.4 309 */ 310 public Throwable(Throwable cause) { 311 fillInStackTrace(); 312 detailMessage = (cause==null ? null : cause.toString()); 313 this.cause = cause; 314 } 315 316 /** 317 * Constructs a new throwable with the specified detail message, 318 * cause, {@linkplain #addSuppressed suppression} enabled or 319 * disabled, and writable stack trace enabled or disabled. If 320 * suppression is disabled, {@link #getSuppressed} for this object 321 * will return a zero-length array and calls to {@link 322 * #addSuppressed} that would otherwise append an exception to the 323 * suppressed list will have no effect. If the writable stack 324 * trace is false, this constructor will not call {@link 325 * #fillInStackTrace()}, a {@code null} will be written to the 326 * {@code stackTrace} field, and subsequent calls to {@code 327 * fillInStackTrace} and {@link 328 * #setStackTrace(StackTraceElement[])} will not set the stack 329 * trace. If the writable stack trace is false, {@link 330 * #getStackTrace} will return a zero length array. 331 * 332 * <p>Note that the other constructors of {@code Throwable} treat 333 * suppression as being enabled and the stack trace as being 334 * writable. Subclasses of {@code Throwable} should document any 335 * conditions under which suppression is disabled and document 336 * conditions under which the stack trace is not writable. 337 * Disabling of suppression should only occur in exceptional 338 * circumstances where special requirements exist, such as a 339 * virtual machine reusing exception objects under low-memory 340 * situations. Circumstances where a given exception object is 341 * repeatedly caught and rethrown, such as to implement control 342 * flow between two sub-systems, is another situation where 343 * immutable throwable objects would be appropriate. 344 * 345 * @param message the detail message. 346 * @param cause the cause. (A {@code null} value is permitted, 347 * and indicates that the cause is nonexistent or unknown.) 348 * @param enableSuppression whether or not suppression is enabled or disabled 349 * @param writableStackTrace whether or not the stack trace should be 350 * writable 351 * 352 * @see OutOfMemoryError 353 * @see NullPointerException 354 * @see ArithmeticException 355 * @since 1.7 356 */ 357 protected Throwable(String message, Throwable cause, 358 boolean enableSuppression, 359 boolean writableStackTrace) { 360 if (writableStackTrace) { 361 fillInStackTrace(); 362 } else { 363 stackTrace = null; 364 } 365 detailMessage = message; 366 this.cause = cause; 367 if (!enableSuppression) 368 suppressedExceptions = null; 369 } 370 371 /** 372 * Returns the detail message string of this throwable. 373 * 374 * @return the detail message string of this {@code Throwable} instance 375 * (which may be {@code null}). 376 */ 377 public String getMessage() { 378 return detailMessage; 379 } 380 381 /** 382 * Creates a localized description of this throwable. 383 * Subclasses may override this method in order to produce a 384 * locale-specific message. For subclasses that do not override this 385 * method, the default implementation returns the same result as 386 * {@code getMessage()}. 387 * 388 * @return The localized description of this throwable. 389 * @since 1.1 390 */ 391 public String getLocalizedMessage() { 392 return getMessage(); 393 } 394 395 /** 396 * Returns the cause of this throwable or {@code null} if the 397 * cause is nonexistent or unknown. (The cause is the throwable that 398 * caused this throwable to get thrown.) 399 * 400 * <p>This implementation returns the cause that was supplied via one of 401 * the constructors requiring a {@code Throwable}, or that was set after 402 * creation with the {@link #initCause(Throwable)} method. While it is 403 * typically unnecessary to override this method, a subclass can override 404 * it to return a cause set by some other means. This is appropriate for 405 * a "legacy chained throwable" that predates the addition of chained 406 * exceptions to {@code Throwable}. Note that it is <i>not</i> 407 * necessary to override any of the {@code PrintStackTrace} methods, 408 * all of which invoke the {@code getCause} method to determine the 409 * cause of a throwable. 410 * 411 * @return the cause of this throwable or {@code null} if the 412 * cause is nonexistent or unknown. 413 * @since 1.4 414 */ 415 public synchronized Throwable getCause() { 416 return (cause==this ? null : cause); 417 } 418 419 /** 420 * Initializes the <i>cause</i> of this throwable to the specified value. 421 * (The cause is the throwable that caused this throwable to get thrown.) 422 * 423 * <p>This method can be called at most once. It is generally called from 424 * within the constructor, or immediately after creating the 425 * throwable. If this throwable was created 426 * with {@link #Throwable(Throwable)} or 427 * {@link #Throwable(String,Throwable)}, this method cannot be called 428 * even once. 429 * 430 * <p>An example of using this method on a legacy throwable type 431 * without other support for setting the cause is: 432 * 433 * <pre> 434 * try { 435 * lowLevelOp(); 436 * } catch (LowLevelException le) { 437 * throw (HighLevelException) 438 * new HighLevelException().initCause(le); // Legacy constructor 439 * } 440 * </pre> 441 * 442 * @param cause the cause (which is saved for later retrieval by the 443 * {@link #getCause()} method). (A {@code null} value is 444 * permitted, and indicates that the cause is nonexistent or 445 * unknown.) 446 * @return a reference to this {@code Throwable} instance. 447 * @throws IllegalArgumentException if {@code cause} is this 448 * throwable. (A throwable cannot be its own cause.) 449 * @throws IllegalStateException if this throwable was 450 * created with {@link #Throwable(Throwable)} or 451 * {@link #Throwable(String,Throwable)}, or this method has already 452 * been called on this throwable. 453 * @since 1.4 454 */ 455 public synchronized Throwable initCause(Throwable cause) { 456 if (this.cause != this) 457 throw new IllegalStateException("Can't overwrite cause with " + 458 Objects.toString(cause, "a null"), this); 459 if (cause == this) 460 throw new IllegalArgumentException("Self-causation not permitted", this); 461 this.cause = cause; 462 return this; 463 } 464 465 /** 466 * Returns a short description of this throwable. 467 * The result is the concatenation of: 468 * <ul> 469 * <li> the {@linkplain Class#getName() name} of the class of this object 470 * <li> ": " (a colon and a space) 471 * <li> the result of invoking this object's {@link #getLocalizedMessage} 472 * method 473 * </ul> 474 * If {@code getLocalizedMessage} returns {@code null}, then just 475 * the class name is returned. 476 * 477 * @return a string representation of this throwable. 478 */ 479 public String toString() { 480 String s = getClass().getName(); 481 String message = getLocalizedMessage(); 482 return (message != null) ? (s + ": " + message) : s; 483 } 484 485 /** 486 * Prints this throwable and its backtrace to the 487 * standard error stream. This method prints a stack trace for this 488 * {@code Throwable} object on the error output stream that is 489 * the value of the field {@code System.err}. The first line of 490 * output contains the result of the {@link #toString()} method for 491 * this object. Remaining lines represent data previously recorded by 492 * the method {@link #fillInStackTrace()}. The format of this 493 * information depends on the implementation, but the following 494 * example may be regarded as typical: 495 * <blockquote><pre> 496 * java.lang.NullPointerException 497 * at MyClass.mash(MyClass.java:9) 498 * at MyClass.crunch(MyClass.java:6) 499 * at MyClass.main(MyClass.java:3) 500 * </pre></blockquote> 501 * This example was produced by running the program: 502 * <pre> 503 * class MyClass { 504 * public static void main(String[] args) { 505 * crunch(null); 506 * } 507 * static void crunch(int[] a) { 508 * mash(a); 509 * } 510 * static void mash(int[] b) { 511 * System.out.println(b[0]); 512 * } 513 * } 514 * </pre> 515 * The backtrace for a throwable with an initialized, non-null cause 516 * should generally include the backtrace for the cause. The format 517 * of this information depends on the implementation, but the following 518 * example may be regarded as typical: 519 * <pre> 520 * HighLevelException: MidLevelException: LowLevelException 521 * at Junk.a(Junk.java:13) 522 * at Junk.main(Junk.java:4) 523 * Caused by: MidLevelException: LowLevelException 524 * at Junk.c(Junk.java:23) 525 * at Junk.b(Junk.java:17) 526 * at Junk.a(Junk.java:11) 527 * ... 1 more 528 * Caused by: LowLevelException 529 * at Junk.e(Junk.java:30) 530 * at Junk.d(Junk.java:27) 531 * at Junk.c(Junk.java:21) 532 * ... 3 more 533 * </pre> 534 * Note the presence of lines containing the characters {@code "..."}. 535 * These lines indicate that the remainder of the stack trace for this 536 * exception matches the indicated number of frames from the bottom of the 537 * stack trace of the exception that was caused by this exception (the 538 * "enclosing" exception). This shorthand can greatly reduce the length 539 * of the output in the common case where a wrapped exception is thrown 540 * from same method as the "causative exception" is caught. The above 541 * example was produced by running the program: 542 * <pre> 543 * public class Junk { 544 * public static void main(String args[]) { 545 * try { 546 * a(); 547 * } catch(HighLevelException e) { 548 * e.printStackTrace(); 549 * } 550 * } 551 * static void a() throws HighLevelException { 552 * try { 553 * b(); 554 * } catch(MidLevelException e) { 555 * throw new HighLevelException(e); 556 * } 557 * } 558 * static void b() throws MidLevelException { 559 * c(); 560 * } 561 * static void c() throws MidLevelException { 562 * try { 563 * d(); 564 * } catch(LowLevelException e) { 565 * throw new MidLevelException(e); 566 * } 567 * } 568 * static void d() throws LowLevelException { 569 * e(); 570 * } 571 * static void e() throws LowLevelException { 572 * throw new LowLevelException(); 573 * } 574 * } 575 * 576 * class HighLevelException extends Exception { 577 * HighLevelException(Throwable cause) { super(cause); } 578 * } 579 * 580 * class MidLevelException extends Exception { 581 * MidLevelException(Throwable cause) { super(cause); } 582 * } 583 * 584 * class LowLevelException extends Exception { 585 * } 586 * </pre> 587 * As of release 7, the platform supports the notion of 588 * <i>suppressed exceptions</i> (in conjunction with the {@code 589 * try}-with-resources statement). Any exceptions that were 590 * suppressed in order to deliver an exception are printed out 591 * beneath the stack trace. The format of this information 592 * depends on the implementation, but the following example may be 593 * regarded as typical: 594 * 595 * <pre> 596 * Exception in thread "main" java.lang.Exception: Something happened 597 * at Foo.bar(Foo.java:10) 598 * at Foo.main(Foo.java:5) 599 * Suppressed: Resource$CloseFailException: Resource ID = 0 600 * at Resource.close(Resource.java:26) 601 * at Foo.bar(Foo.java:9) 602 * ... 1 more 603 * </pre> 604 * Note that the "... n more" notation is used on suppressed exceptions 605 * just at it is used on causes. Unlike causes, suppressed exceptions are 606 * indented beyond their "containing exceptions." 607 * 608 * <p>An exception can have both a cause and one or more suppressed 609 * exceptions: 610 * <pre> 611 * Exception in thread "main" java.lang.Exception: Main block 612 * at Foo3.main(Foo3.java:7) 613 * Suppressed: Resource$CloseFailException: Resource ID = 2 614 * at Resource.close(Resource.java:26) 615 * at Foo3.main(Foo3.java:5) 616 * Suppressed: Resource$CloseFailException: Resource ID = 1 617 * at Resource.close(Resource.java:26) 618 * at Foo3.main(Foo3.java:5) 619 * Caused by: java.lang.Exception: I did it 620 * at Foo3.main(Foo3.java:8) 621 * </pre> 622 * Likewise, a suppressed exception can have a cause: 623 * <pre> 624 * Exception in thread "main" java.lang.Exception: Main block 625 * at Foo4.main(Foo4.java:6) 626 * Suppressed: Resource2$CloseFailException: Resource ID = 1 627 * at Resource2.close(Resource2.java:20) 628 * at Foo4.main(Foo4.java:5) 629 * Caused by: java.lang.Exception: Rats, you caught me 630 * at Resource2$CloseFailException.<init>(Resource2.java:45) 631 * ... 2 more 632 * </pre> 633 */ 634 public void printStackTrace() { 635 printStackTrace(System.err); 636 } 637 638 /** 639 * Prints this throwable and its backtrace to the specified print stream. 640 * 641 * @param s {@code PrintStream} to use for output 642 */ 643 public void printStackTrace(PrintStream s) { 644 printStackTrace(new WrappedPrintStream(s)); 645 } 646 647 private void printStackTrace(PrintStreamOrWriter s) { 648 // Guard against malicious overrides of Throwable.equals by 649 // using a Set with identity equality semantics. 650 Set<Throwable> dejaVu = Collections.newSetFromMap(new IdentityHashMap<>()); 651 dejaVu.add(this); 652 653 synchronized (s.lock()) { 654 // Print our stack trace 655 s.println(this); 656 StackTraceElement[] trace = getOurStackTrace(); 657 for (StackTraceElement traceElement : trace) 658 s.println("\tat " + traceElement); 659 660 // Print suppressed exceptions, if any 661 for (Throwable se : getSuppressed()) 662 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, "\t", dejaVu); 663 664 // Print cause, if any 665 Throwable ourCause = getCause(); 666 if (ourCause != null) 667 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, "", dejaVu); 668 } 669 } 670 671 /** 672 * Print our stack trace as an enclosed exception for the specified 673 * stack trace. 674 */ 675 private void printEnclosedStackTrace(PrintStreamOrWriter s, 676 StackTraceElement[] enclosingTrace, 677 String caption, 678 String prefix, 679 Set<Throwable> dejaVu) { 680 assert Thread.holdsLock(s.lock()); 681 if (dejaVu.contains(this)) { 682 s.println("\t[CIRCULAR REFERENCE:" + this + "]"); 683 } else { 684 dejaVu.add(this); 685 // Compute number of frames in common between this and enclosing trace 686 StackTraceElement[] trace = getOurStackTrace(); 687 int m = trace.length - 1; 688 int n = enclosingTrace.length - 1; 689 while (m >= 0 && n >=0 && trace[m].equals(enclosingTrace[n])) { 690 m--; n--; 691 } 692 int framesInCommon = trace.length - 1 - m; 693 694 // Print our stack trace 695 s.println(prefix + caption + this); 696 for (int i = 0; i <= m; i++) 697 s.println(prefix + "\tat " + trace[i]); 698 if (framesInCommon != 0) 699 s.println(prefix + "\t... " + framesInCommon + " more"); 700 701 // Print suppressed exceptions, if any 702 for (Throwable se : getSuppressed()) 703 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, 704 prefix +"\t", dejaVu); 705 706 // Print cause, if any 707 Throwable ourCause = getCause(); 708 if (ourCause != null) 709 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, prefix, dejaVu); 710 } 711 } 712 713 /** 714 * Prints this throwable and its backtrace to the specified 715 * print writer. 716 * 717 * @param s {@code PrintWriter} to use for output 718 * @since 1.1 719 */ 720 public void printStackTrace(PrintWriter s) { 721 printStackTrace(new WrappedPrintWriter(s)); 722 } 723 724 /** 725 * Wrapper class for PrintStream and PrintWriter to enable a single 726 * implementation of printStackTrace. 727 */ 728 private abstract static class PrintStreamOrWriter { 729 /** Returns the object to be locked when using this StreamOrWriter */ 730 abstract Object lock(); 731 732 /** Prints the specified string as a line on this StreamOrWriter */ 733 abstract void println(Object o); 734 } 735 736 private static class WrappedPrintStream extends PrintStreamOrWriter { 737 private final PrintStream printStream; 738 739 WrappedPrintStream(PrintStream printStream) { 740 this.printStream = printStream; 741 } 742 743 Object lock() { 744 return printStream; 745 } 746 747 void println(Object o) { 748 printStream.println(o); 749 } 750 } 751 752 private static class WrappedPrintWriter extends PrintStreamOrWriter { 753 private final PrintWriter printWriter; 754 755 WrappedPrintWriter(PrintWriter printWriter) { 756 this.printWriter = printWriter; 757 } 758 759 Object lock() { 760 return printWriter; 761 } 762 763 void println(Object o) { 764 printWriter.println(o); 765 } 766 } 767 768 /** 769 * Fills in the execution stack trace. This method records within this 770 * {@code Throwable} object information about the current state of 771 * the stack frames for the current thread. 772 * 773 * <p>If the stack trace of this {@code Throwable} {@linkplain 774 * Throwable#Throwable(String, Throwable, boolean, boolean) is not 775 * writable}, calling this method has no effect. 776 * 777 * @return a reference to this {@code Throwable} instance. 778 * @see java.lang.Throwable#printStackTrace() 779 */ 780 public synchronized Throwable fillInStackTrace() { 781 if (stackTrace != null || 782 backtrace != null /* Out of protocol state */ ) { 783 if (backtrace == null && StackStreamFactory.useStackTrace(this)) { 784 backtrace = StackStreamFactory.makeStackTrace(this); 785 } else { 786 fillInStackTrace(0); 787 } 788 stackTrace = UNASSIGNED_STACK; 789 } 790 return this; 791 } 792 793 private native Throwable fillInStackTrace(int dummy); 794 795 /** 796 * Provides programmatic access to the stack trace information printed by 797 * {@link #printStackTrace()}. Returns an array of stack trace elements, 798 * each representing one stack frame. The zeroth element of the array 799 * (assuming the array's length is non-zero) represents the top of the 800 * stack, which is the last method invocation in the sequence. Typically, 801 * this is the point at which this throwable was created and thrown. 802 * The last element of the array (assuming the array's length is non-zero) 803 * represents the bottom of the stack, which is the first method invocation 804 * in the sequence. 805 * 806 * <p>Some virtual machines may, under some circumstances, omit one 807 * or more stack frames from the stack trace. In the extreme case, 808 * a virtual machine that has no stack trace information concerning 809 * this throwable is permitted to return a zero-length array from this 810 * method. Generally speaking, the array returned by this method will 811 * contain one element for every frame that would be printed by 812 * {@code printStackTrace}. Writes to the returned array do not 813 * affect future calls to this method. 814 * 815 * @return an array of stack trace elements representing the stack trace 816 * pertaining to this throwable. 817 * @since 1.4 818 */ 819 public StackTraceElement[] getStackTrace() { 820 return getOurStackTrace().clone(); 821 } 822 823 private synchronized StackTraceElement[] getOurStackTrace() { 824 // Initialize stack trace field with information from 825 // backtrace if this is the first call to this method 826 if (stackTrace == UNASSIGNED_STACK || 827 (stackTrace == null && backtrace != null) /* Out of protocol state */) { 828 if (backtrace instanceof StackStreamFactory.StackTrace) { 829 stackTrace = ((StackStreamFactory.StackTrace)backtrace).getStackTraceElements(); 830 } else { 831 int depth = getStackTraceDepth(); 832 stackTrace = new StackTraceElement[depth]; 833 for (int i = 0; i < depth; i++) 834 stackTrace[i] = getStackTraceElement(i); 835 } 836 } else if (stackTrace == null) { 837 return UNASSIGNED_STACK; 838 } 839 return stackTrace; 840 } 841 842 /** 843 * Sets the stack trace elements that will be returned by 844 * {@link #getStackTrace()} and printed by {@link #printStackTrace()} 845 * and related methods. 846 * 847 * This method, which is designed for use by RPC frameworks and other 848 * advanced systems, allows the client to override the default 849 * stack trace that is either generated by {@link #fillInStackTrace()} 850 * when a throwable is constructed or deserialized when a throwable is 851 * read from a serialization stream. 852 * 853 * <p>If the stack trace of this {@code Throwable} {@linkplain 854 * Throwable#Throwable(String, Throwable, boolean, boolean) is not 855 * writable}, calling this method has no effect other than 856 * validating its argument. 857 * 858 * @param stackTrace the stack trace elements to be associated with 859 * this {@code Throwable}. The specified array is copied by this 860 * call; changes in the specified array after the method invocation 861 * returns will have no affect on this {@code Throwable}'s stack 862 * trace. 863 * 864 * @throws NullPointerException if {@code stackTrace} is 865 * {@code null} or if any of the elements of 866 * {@code stackTrace} are {@code null} 867 * 868 * @since 1.4 869 */ 870 public void setStackTrace(StackTraceElement[] stackTrace) { 871 // Validate argument 872 StackTraceElement[] defensiveCopy = stackTrace.clone(); 873 for (int i = 0; i < defensiveCopy.length; i++) { 874 if (defensiveCopy[i] == null) 875 throw new NullPointerException("stackTrace[" + i + "]"); 876 } 877 878 synchronized (this) { 879 if (this.stackTrace == null && // Immutable stack 880 backtrace == null) // Test for out of protocol state 881 return; 882 this.stackTrace = defensiveCopy; 883 } 884 } 885 886 /** 887 * Returns the number of elements in the stack trace (or 0 if the stack 888 * trace is unavailable). 889 * 890 * package-protection for use by SharedSecrets. 891 */ 892 native int getStackTraceDepth(); 893 894 /** 895 * Returns the specified element of the stack trace. 896 * 897 * package-protection for use by SharedSecrets. 898 * 899 * @param index index of the element to return. 900 * @throws IndexOutOfBoundsException if {@code index < 0 || 901 * index >= getStackTraceDepth() } 902 */ 903 native StackTraceElement getStackTraceElement(int index); 904 905 /** 906 * Reads a {@code Throwable} from a stream, enforcing 907 * well-formedness constraints on fields. Null entries and 908 * self-pointers are not allowed in the list of {@code 909 * suppressedExceptions}. Null entries are not allowed for stack 910 * trace elements. A null stack trace in the serial form results 911 * in a zero-length stack element array. A single-element stack 912 * trace whose entry is equal to {@code new StackTraceElement("", 913 * "", null, Integer.MIN_VALUE)} results in a {@code null} {@code 914 * stackTrace} field. 915 * 916 * Note that there are no constraints on the value the {@code 917 * cause} field can hold; both {@code null} and {@code this} are 918 * valid values for the field. 919 */ 920 private void readObject(ObjectInputStream s) 921 throws IOException, ClassNotFoundException { 922 s.defaultReadObject(); // read in all fields 923 if (suppressedExceptions != null) { 924 List<Throwable> suppressed = null; 925 if (suppressedExceptions.isEmpty()) { 926 // Use the sentinel for a zero-length list 927 suppressed = SUPPRESSED_SENTINEL; 928 } else { // Copy Throwables to new list 929 suppressed = new ArrayList<>(1); 930 for (Throwable t : suppressedExceptions) { 931 // Enforce constraints on suppressed exceptions in 932 // case of corrupt or malicious stream. 933 if (t == null) 934 throw new NullPointerException(NULL_CAUSE_MESSAGE); 935 if (t == this) 936 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE); 937 suppressed.add(t); 938 } 939 } 940 suppressedExceptions = suppressed; 941 } // else a null suppressedExceptions field remains null 942 943 /* 944 * For zero-length stack traces, use a clone of 945 * UNASSIGNED_STACK rather than UNASSIGNED_STACK itself to 946 * allow identity comparison against UNASSIGNED_STACK in 947 * getOurStackTrace. The identity of UNASSIGNED_STACK in 948 * stackTrace indicates to the getOurStackTrace method that 949 * the stackTrace needs to be constructed from the information 950 * in backtrace. 951 */ 952 if (stackTrace != null) { 953 if (stackTrace.length == 0) { 954 stackTrace = UNASSIGNED_STACK.clone(); 955 } else if (stackTrace.length == 1 && 956 // Check for the marker of an immutable stack trace 957 SentinelHolder.STACK_TRACE_ELEMENT_SENTINEL.equals(stackTrace[0])) { 958 stackTrace = null; 959 } else { // Verify stack trace elements are non-null. 960 for(StackTraceElement ste : stackTrace) { 961 if (ste == null) 962 throw new NullPointerException("null StackTraceElement in serial stream. "); 963 } 964 } 965 } else { 966 // A null stackTrace field in the serial form can result 967 // from an exception serialized without that field in 968 // older JDK releases; treat such exceptions as having 969 // empty stack traces. 970 stackTrace = UNASSIGNED_STACK.clone(); 971 } 972 } 973 974 /** 975 * Write a {@code Throwable} object to a stream. 976 * 977 * A {@code null} stack trace field is represented in the serial 978 * form as a one-element array whose element is equal to {@code 979 * new StackTraceElement("", "", null, Integer.MIN_VALUE)}. 980 */ 981 private synchronized void writeObject(ObjectOutputStream s) 982 throws IOException { 983 // Ensure that the stackTrace field is initialized to a 984 // non-null value, if appropriate. As of JDK 7, a null stack 985 // trace field is a valid value indicating the stack trace 986 // should not be set. 987 getOurStackTrace(); 988 989 StackTraceElement[] oldStackTrace = stackTrace; 990 try { 991 if (stackTrace == null) 992 stackTrace = SentinelHolder.STACK_TRACE_SENTINEL; 993 s.defaultWriteObject(); 994 } finally { 995 stackTrace = oldStackTrace; 996 } 997 } 998 999 /** 1000 * Appends the specified exception to the exceptions that were 1001 * suppressed in order to deliver this exception. This method is 1002 * thread-safe and typically called (automatically and implicitly) 1003 * by the {@code try}-with-resources statement. 1004 * 1005 * <p>The suppression behavior is enabled <em>unless</em> disabled 1006 * {@linkplain #Throwable(String, Throwable, boolean, boolean) via 1007 * a constructor}. When suppression is disabled, this method does 1008 * nothing other than to validate its argument. 1009 * 1010 * <p>Note that when one exception {@linkplain 1011 * #initCause(Throwable) causes} another exception, the first 1012 * exception is usually caught and then the second exception is 1013 * thrown in response. In other words, there is a causal 1014 * connection between the two exceptions. 1015 * 1016 * In contrast, there are situations where two independent 1017 * exceptions can be thrown in sibling code blocks, in particular 1018 * in the {@code try} block of a {@code try}-with-resources 1019 * statement and the compiler-generated {@code finally} block 1020 * which closes the resource. 1021 * 1022 * In these situations, only one of the thrown exceptions can be 1023 * propagated. In the {@code try}-with-resources statement, when 1024 * there are two such exceptions, the exception originating from 1025 * the {@code try} block is propagated and the exception from the 1026 * {@code finally} block is added to the list of exceptions 1027 * suppressed by the exception from the {@code try} block. As an 1028 * exception unwinds the stack, it can accumulate multiple 1029 * suppressed exceptions. 1030 * 1031 * <p>An exception may have suppressed exceptions while also being 1032 * caused by another exception. Whether or not an exception has a 1033 * cause is semantically known at the time of its creation, unlike 1034 * whether or not an exception will suppress other exceptions 1035 * which is typically only determined after an exception is 1036 * thrown. 1037 * 1038 * <p>Note that programmer written code is also able to take 1039 * advantage of calling this method in situations where there are 1040 * multiple sibling exceptions and only one can be propagated. 1041 * 1042 * @param exception the exception to be added to the list of 1043 * suppressed exceptions 1044 * @throws IllegalArgumentException if {@code exception} is this 1045 * throwable; a throwable cannot suppress itself. 1046 * @throws NullPointerException if {@code exception} is {@code null} 1047 * @since 1.7 1048 */ 1049 public final synchronized void addSuppressed(Throwable exception) { 1050 if (exception == this) 1051 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE, exception); 1052 1053 if (exception == null) 1054 throw new NullPointerException(NULL_CAUSE_MESSAGE); 1055 1056 if (suppressedExceptions == null) // Suppressed exceptions not recorded 1057 return; 1058 1059 if (suppressedExceptions == SUPPRESSED_SENTINEL) 1060 suppressedExceptions = new ArrayList<>(1); 1061 1062 suppressedExceptions.add(exception); 1063 } 1064 1065 private static final Throwable[] EMPTY_THROWABLE_ARRAY = new Throwable[0]; 1066 1067 /** 1068 * Returns an array containing all of the exceptions that were 1069 * suppressed, typically by the {@code try}-with-resources 1070 * statement, in order to deliver this exception. 1071 * 1072 * If no exceptions were suppressed or {@linkplain 1073 * #Throwable(String, Throwable, boolean, boolean) suppression is 1074 * disabled}, an empty array is returned. This method is 1075 * thread-safe. Writes to the returned array do not affect future 1076 * calls to this method. 1077 * 1078 * @return an array containing all of the exceptions that were 1079 * suppressed to deliver this exception. 1080 * @since 1.7 1081 */ 1082 public final synchronized Throwable[] getSuppressed() { 1083 if (suppressedExceptions == SUPPRESSED_SENTINEL || 1084 suppressedExceptions == null) 1085 return EMPTY_THROWABLE_ARRAY; 1086 else 1087 return suppressedExceptions.toArray(EMPTY_THROWABLE_ARRAY); 1088 } 1089 }