1 /* 2 * Copyright (c) 1994, 2016, 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 28 import java.io.*; 29 import java.util.*; 30 31 /** 32 * The {@code Throwable} class is the superclass of all errors and 33 * exceptions in the Java language. Only objects that are instances of this 34 * class (or one of its subclasses) are thrown by the Java Virtual Machine or 35 * can be thrown by the Java {@code throw} statement. Similarly, only 36 * this class or one of its subclasses can be the argument type in a 37 * {@code catch} clause. 38 * 39 * For the purposes of compile-time checking of exceptions, {@code 40 * Throwable} and any subclass of {@code Throwable} that is not also a 41 * subclass of either {@link RuntimeException} or {@link Error} are 42 * regarded as checked exceptions. 43 * 44 * <p>Instances of two subclasses, {@link java.lang.Error} and 45 * {@link java.lang.Exception}, are conventionally used to indicate 46 * that exceptional situations have occurred. Typically, these instances 47 * are freshly created in the context of the exceptional situation so 48 * as to include relevant information (such as stack trace data). 49 * 50 * <p>A throwable contains a snapshot of the execution stack of its 51 * thread at the time it was created. It can also contain a message 52 * string that gives more information about the error. Over time, a 53 * throwable can {@linkplain Throwable#addSuppressed suppress} other 54 * throwables from being propagated. Finally, the throwable can also 55 * contain a <i>cause</i>: another throwable that caused this 56 * throwable to be constructed. The recording of this causal information 57 * is referred to as the <i>chained exception</i> facility, as the 58 * cause can, itself, have a cause, and so on, leading to a "chain" of 59 * exceptions, each caused by another. 60 * 61 * <p>One reason that a throwable may have a cause is that the class that 62 * throws it is built atop a lower layered abstraction, and an operation on 63 * the upper layer fails due to a failure in the lower layer. It would be bad 64 * design to let the throwable thrown by the lower layer propagate outward, as 65 * it is generally unrelated to the abstraction provided by the upper layer. 66 * Further, doing so would tie the API of the upper layer to the details of 67 * its implementation, assuming the lower layer's exception was a checked 68 * exception. Throwing a "wrapped exception" (i.e., an exception containing a 69 * cause) allows the upper layer to communicate the details of the failure to 70 * its caller without incurring either of these shortcomings. It preserves 71 * the flexibility to change the implementation of the upper layer without 72 * changing its API (in particular, the set of exceptions thrown by its 73 * methods). 74 * 75 * <p>A second reason that a throwable may have a cause is that the method 76 * that throws it must conform to a general-purpose interface that does not 77 * permit the method to throw the cause directly. For example, suppose 78 * a persistent collection conforms to the {@link java.util.Collection 79 * Collection} interface, and that its persistence is implemented atop 80 * {@code java.io}. Suppose the internals of the {@code add} method 81 * can throw an {@link java.io.IOException IOException}. The implementation 82 * can communicate the details of the {@code IOException} to its caller 83 * while conforming to the {@code Collection} interface by wrapping the 84 * {@code IOException} in an appropriate unchecked exception. (The 85 * specification for the persistent collection should indicate that it is 86 * capable of throwing such exceptions.) 87 * 88 * <p>A cause can be associated with a throwable in two ways: via a 89 * constructor that takes the cause as an argument, or via the 90 * {@link #initCause(Throwable)} method. New throwable classes that 91 * wish to allow causes to be associated with them should provide constructors 92 * that take a cause and delegate (perhaps indirectly) to one of the 93 * {@code Throwable} constructors that takes a cause. 94 * 95 * Because the {@code initCause} method is public, it allows a cause to be 96 * associated with any throwable, even a "legacy throwable" whose 97 * implementation predates the addition of the exception chaining mechanism to 98 * {@code Throwable}. 99 * 100 * <p>By convention, class {@code Throwable} and its subclasses have two 101 * constructors, one that takes no arguments and one that takes a 102 * {@code String} argument that can be used to produce a detail message. 103 * Further, those subclasses that might likely have a cause associated with 104 * them should have two more constructors, one that takes a 105 * {@code Throwable} (the cause), and one that takes a 106 * {@code String} (the detail message) and a {@code Throwable} (the 107 * cause). 108 * 109 * @author unascribed 110 * @author Josh Bloch (Added exception chaining and programmatic access to 111 * stack trace in 1.4.) 112 * @jls 11.2 Compile-Time Checking of Exceptions 113 * @since 1.0 114 */ 115 public class Throwable implements Serializable { 116 /** use serialVersionUID from JDK 1.0.2 for interoperability */ 117 private static final long serialVersionUID = -3042686055658047285L; 118 119 /** 120 * The JVM saves some indication of the stack backtrace in this slot. 121 */ 122 private transient Object backtrace; 123 124 /** 125 * Specific details about the Throwable. For example, for 126 * {@code FileNotFoundException}, this contains the name of 127 * the file that could not be found. 128 * 129 * @serial 130 */ 131 private String detailMessage; 132 133 134 /** 135 * Holder class to defer initializing sentinel objects only used 136 * for serialization. 137 */ 138 private static class SentinelHolder { 139 /** 140 * {@linkplain #setStackTrace(StackTraceElement[]) Setting the 141 * stack trace} to a one-element array containing this sentinel 142 * value indicates future attempts to set the stack trace will be 143 * ignored. The sentinel is equal to the result of calling:<br> 144 * {@code new StackTraceElement("", "", null, Integer.MIN_VALUE)} 145 */ 146 public static final StackTraceElement STACK_TRACE_ELEMENT_SENTINEL = 147 new StackTraceElement("", "", null, Integer.MIN_VALUE); 148 149 /** 150 * Sentinel value used in the serial form to indicate an immutable 151 * stack trace. 152 */ 153 public static final StackTraceElement[] STACK_TRACE_SENTINEL = 154 new StackTraceElement[] {STACK_TRACE_ELEMENT_SENTINEL}; 155 } 156 157 /** 158 * A shared value for an empty stack. 159 */ 160 private static final StackTraceElement[] UNASSIGNED_STACK = new StackTraceElement[0]; 161 162 /* 163 * To allow Throwable objects to be made immutable and safely 164 * reused by the JVM, such as OutOfMemoryErrors, fields of 165 * Throwable that are writable in response to user actions, cause, 166 * stackTrace, and suppressedExceptions obey the following 167 * protocol: 168 * 169 * 1) The fields are initialized to a non-null sentinel value 170 * which indicates the value has logically not been set. 171 * 172 * 2) Writing a null to the field indicates further writes 173 * are forbidden 174 * 175 * 3) The sentinel value may be replaced with another non-null 176 * value. 177 * 178 * For example, implementations of the HotSpot JVM have 179 * preallocated OutOfMemoryError objects to provide for better 180 * diagnosability of that situation. These objects are created 181 * without calling the constructor for that class and the fields 182 * in question are initialized to null. To support this 183 * capability, any new fields added to Throwable that require 184 * being initialized to a non-null value require a coordinated JVM 185 * change. 186 */ 187 188 /** 189 * The throwable that caused this throwable to get thrown, or null if this 190 * throwable was not caused by another throwable, or if the causative 191 * throwable is unknown. If this field is equal to this throwable itself, 192 * it indicates that the cause of this throwable has not yet been 193 * initialized. 194 * 195 * @serial 196 * @since 1.4 197 */ 198 private Throwable cause = this; 199 200 /** 201 * The stack trace, as returned by {@link #getStackTrace()}. 202 * 203 * The field is initialized to a zero-length array. A {@code 204 * null} value of this field indicates subsequent calls to {@link 205 * #setStackTrace(StackTraceElement[])} and {@link 206 * #fillInStackTrace()} will be no-ops. 207 * 208 * @serial 209 * @since 1.4 210 */ 211 private StackTraceElement[] stackTrace = UNASSIGNED_STACK; 212 213 /** 214 * The JVM code sets the depth of the backtrace for later retrieval 215 */ 216 private transient int depth; 217 218 // Setting this static field introduces an acceptable 219 // initialization dependency on a few java.util classes. 220 private static final List<Throwable> SUPPRESSED_SENTINEL = Collections.emptyList(); 221 222 /** 223 * The list of suppressed exceptions, as returned by {@link 224 * #getSuppressed()}. The list is initialized to a zero-element 225 * unmodifiable sentinel list. When a serialized Throwable is 226 * read in, if the {@code suppressedExceptions} field points to a 227 * zero-element list, the field is reset to the sentinel value. 228 * 229 * @serial 230 * @since 1.7 231 */ 232 private List<Throwable> suppressedExceptions = SUPPRESSED_SENTINEL; 233 234 /** Message for trying to suppress a null exception. */ 235 private static final String NULL_CAUSE_MESSAGE = "Cannot suppress a null exception."; 236 237 /** Message for trying to suppress oneself. */ 238 private static final String SELF_SUPPRESSION_MESSAGE = "Self-suppression not permitted"; 239 240 /** Caption for labeling causative exception stack traces */ 241 private static final String CAUSE_CAPTION = "Caused by: "; 242 243 /** Caption for labeling suppressed exception stack traces */ 244 private static final String SUPPRESSED_CAPTION = "Suppressed: "; 245 246 /** 247 * Constructs a new throwable with {@code null} as its detail message. 248 * The cause is not initialized, and may subsequently be initialized by a 249 * call to {@link #initCause}. 250 * 251 * <p>The {@link #fillInStackTrace()} method is called to initialize 252 * the stack trace data in the newly created throwable. 253 */ 254 public Throwable() { 255 fillInStackTrace(); 256 } 257 258 /** 259 * Constructs a new throwable with the specified detail message. The 260 * cause is not initialized, and may subsequently be initialized by 261 * a call to {@link #initCause}. 262 * 263 * <p>The {@link #fillInStackTrace()} method is called to initialize 264 * the stack trace data in the newly created throwable. 265 * 266 * @param message the detail message. The detail message is saved for 267 * later retrieval by the {@link #getMessage()} method. 268 */ 269 public Throwable(String message) { 270 fillInStackTrace(); 271 detailMessage = message; 272 } 273 274 /** 275 * Constructs a new throwable with the specified detail message and 276 * cause. <p>Note that the detail message associated with 277 * {@code cause} is <i>not</i> automatically incorporated in 278 * this throwable's detail message. 279 * 280 * <p>The {@link #fillInStackTrace()} method is called to initialize 281 * the stack trace data in the newly created throwable. 282 * 283 * @param message the detail message (which is saved for later retrieval 284 * by the {@link #getMessage()} method). 285 * @param cause the cause (which is saved for later retrieval by the 286 * {@link #getCause()} method). (A {@code null} value is 287 * permitted, and indicates that the cause is nonexistent or 288 * unknown.) 289 * @since 1.4 290 */ 291 public Throwable(String message, Throwable cause) { 292 fillInStackTrace(); 293 detailMessage = message; 294 this.cause = cause; 295 } 296 297 /** 298 * Constructs a new throwable with the specified cause and a detail 299 * message of {@code (cause==null ? null : cause.toString())} (which 300 * typically contains the class and detail message of {@code cause}). 301 * This constructor is useful for throwables that are little more than 302 * wrappers for other throwables (for example, {@link 303 * java.security.PrivilegedActionException}). 304 * 305 * <p>The {@link #fillInStackTrace()} method is called to initialize 306 * the stack trace data in the newly created throwable. 307 * 308 * @param cause the cause (which is saved for later retrieval by the 309 * {@link #getCause()} method). (A {@code null} value is 310 * permitted, and indicates that the cause is nonexistent or 311 * unknown.) 312 * @since 1.4 313 */ 314 public Throwable(Throwable cause) { 315 fillInStackTrace(); 316 detailMessage = (cause==null ? null : cause.toString()); 317 this.cause = cause; 318 } 319 320 /** 321 * Constructs a new throwable with the specified detail message, 322 * cause, {@linkplain #addSuppressed suppression} enabled or 323 * disabled, and writable stack trace enabled or disabled. If 324 * suppression is disabled, {@link #getSuppressed} for this object 325 * will return a zero-length array and calls to {@link 326 * #addSuppressed} that would otherwise append an exception to the 327 * suppressed list will have no effect. If the writable stack 328 * trace is false, this constructor will not call {@link 329 * #fillInStackTrace()}, a {@code null} will be written to the 330 * {@code stackTrace} field, and subsequent calls to {@code 331 * fillInStackTrace} and {@link 332 * #setStackTrace(StackTraceElement[])} will not set the stack 333 * trace. If the writable stack trace is false, {@link 334 * #getStackTrace} will return a zero length array. 335 * 336 * <p>Note that the other constructors of {@code Throwable} treat 337 * suppression as being enabled and the stack trace as being 338 * writable. Subclasses of {@code Throwable} should document any 339 * conditions under which suppression is disabled and document 340 * conditions under which the stack trace is not writable. 341 * Disabling of suppression should only occur in exceptional 342 * circumstances where special requirements exist, such as a 343 * virtual machine reusing exception objects under low-memory 344 * situations. Circumstances where a given exception object is 345 * repeatedly caught and rethrown, such as to implement control 346 * flow between two sub-systems, is another situation where 347 * immutable throwable objects would be appropriate. 348 * 349 * @param message the detail message. 350 * @param cause the cause. (A {@code null} value is permitted, 351 * and indicates that the cause is nonexistent or unknown.) 352 * @param enableSuppression whether or not suppression is enabled or disabled 353 * @param writableStackTrace whether or not the stack trace should be 354 * writable 355 * 356 * @see OutOfMemoryError 357 * @see NullPointerException 358 * @see ArithmeticException 359 * @since 1.7 360 */ 361 protected Throwable(String message, Throwable cause, 362 boolean enableSuppression, 363 boolean writableStackTrace) { 364 if (writableStackTrace) { 365 fillInStackTrace(); 366 } else { 367 stackTrace = null; 368 } 369 detailMessage = message; 370 this.cause = cause; 371 if (!enableSuppression) 372 suppressedExceptions = null; 373 } 374 375 /** 376 * Returns the detail message string of this throwable. 377 * 378 * @return the detail message string of this {@code Throwable} instance 379 * (which may be {@code null}). 380 */ 381 public String getMessage() { 382 return detailMessage; 383 } 384 385 /** 386 * Creates a localized description of this throwable. 387 * Subclasses may override this method in order to produce a 388 * locale-specific message. For subclasses that do not override this 389 * method, the default implementation returns the same result as 390 * {@code getMessage()}. 391 * 392 * @return The localized description of this throwable. 393 * @since 1.1 394 */ 395 public String getLocalizedMessage() { 396 return getMessage(); 397 } 398 399 /** 400 * Returns the cause of this throwable or {@code null} if the 401 * cause is nonexistent or unknown. (The cause is the throwable that 402 * caused this throwable to get thrown.) 403 * 404 * <p>This implementation returns the cause that was supplied via one of 405 * the constructors requiring a {@code Throwable}, or that was set after 406 * creation with the {@link #initCause(Throwable)} method. While it is 407 * typically unnecessary to override this method, a subclass can override 408 * it to return a cause set by some other means. This is appropriate for 409 * a "legacy chained throwable" that predates the addition of chained 410 * exceptions to {@code Throwable}. Note that it is <i>not</i> 411 * necessary to override any of the {@code PrintStackTrace} methods, 412 * all of which invoke the {@code getCause} method to determine the 413 * cause of a throwable. 414 * 415 * @return the cause of this throwable or {@code null} if the 416 * cause is nonexistent or unknown. 417 * @since 1.4 418 */ 419 public synchronized Throwable getCause() { 420 return (cause==this ? null : cause); 421 } 422 423 /** 424 * Initializes the <i>cause</i> of this throwable to the specified value. 425 * (The cause is the throwable that caused this throwable to get thrown.) 426 * 427 * <p>This method can be called at most once. It is generally called from 428 * within the constructor, or immediately after creating the 429 * throwable. If this throwable was created 430 * with {@link #Throwable(Throwable)} or 431 * {@link #Throwable(String,Throwable)}, this method cannot be called 432 * even once. 433 * 434 * <p>An example of using this method on a legacy throwable type 435 * without other support for setting the cause is: 436 * 437 * <pre> 438 * try { 439 * lowLevelOp(); 440 * } catch (LowLevelException le) { 441 * throw (HighLevelException) 442 * new HighLevelException().initCause(le); // Legacy constructor 443 * } 444 * </pre> 445 * 446 * @param cause the cause (which is saved for later retrieval by the 447 * {@link #getCause()} method). (A {@code null} value is 448 * permitted, and indicates that the cause is nonexistent or 449 * unknown.) 450 * @return a reference to this {@code Throwable} instance. 451 * @throws IllegalArgumentException if {@code cause} is this 452 * throwable. (A throwable cannot be its own cause.) 453 * @throws IllegalStateException if this throwable was 454 * created with {@link #Throwable(Throwable)} or 455 * {@link #Throwable(String,Throwable)}, or this method has already 456 * been called on this throwable. 457 * @since 1.4 458 */ 459 public synchronized Throwable initCause(Throwable cause) { 460 if (this.cause != this) 461 throw new IllegalStateException("Can't overwrite cause with " + 462 Objects.toString(cause, "a null"), this); 463 if (cause == this) 464 throw new IllegalArgumentException("Self-causation not permitted", this); 465 this.cause = cause; 466 return this; 467 } 468 469 /** 470 * Returns a short description of this throwable. 471 * The result is the concatenation of: 472 * <ul> 473 * <li> the {@linkplain Class#getName() name} of the class of this object 474 * <li> ": " (a colon and a space) 475 * <li> the result of invoking this object's {@link #getLocalizedMessage} 476 * method 477 * </ul> 478 * If {@code getLocalizedMessage} returns {@code null}, then just 479 * the class name is returned. 480 * 481 * @return a string representation of this throwable. 482 */ 483 public String toString() { 484 String s = getClass().getName(); 485 String message = getLocalizedMessage(); 486 return (message != null) ? (s + ": " + message) : s; 487 } 488 489 /** 490 * Prints this throwable and its backtrace to the 491 * standard error stream. This method prints a stack trace for this 492 * {@code Throwable} object on the error output stream that is 493 * the value of the field {@code System.err}. The first line of 494 * output contains the result of the {@link #toString()} method for 495 * this object. Remaining lines represent data previously recorded by 496 * the method {@link #fillInStackTrace()}. The format of this 497 * information depends on the implementation, but the following 498 * example may be regarded as typical: 499 * <blockquote><pre> 500 * java.lang.NullPointerException 501 * at MyClass.mash(MyClass.java:9) 502 * at MyClass.crunch(MyClass.java:6) 503 * at MyClass.main(MyClass.java:3) 504 * </pre></blockquote> 505 * This example was produced by running the program: 506 * <pre> 507 * class MyClass { 508 * public static void main(String[] args) { 509 * crunch(null); 510 * } 511 * static void crunch(int[] a) { 512 * mash(a); 513 * } 514 * static void mash(int[] b) { 515 * System.out.println(b[0]); 516 * } 517 * } 518 * </pre> 519 * The backtrace for a throwable with an initialized, non-null cause 520 * should generally include the backtrace for the cause. The format 521 * of this information depends on the implementation, but the following 522 * example may be regarded as typical: 523 * <pre> 524 * HighLevelException: MidLevelException: LowLevelException 525 * at Junk.a(Junk.java:13) 526 * at Junk.main(Junk.java:4) 527 * Caused by: MidLevelException: LowLevelException 528 * at Junk.c(Junk.java:23) 529 * at Junk.b(Junk.java:17) 530 * at Junk.a(Junk.java:11) 531 * ... 1 more 532 * Caused by: LowLevelException 533 * at Junk.e(Junk.java:30) 534 * at Junk.d(Junk.java:27) 535 * at Junk.c(Junk.java:21) 536 * ... 3 more 537 * </pre> 538 * Note the presence of lines containing the characters {@code "..."}. 539 * These lines indicate that the remainder of the stack trace for this 540 * exception matches the indicated number of frames from the bottom of the 541 * stack trace of the exception that was caused by this exception (the 542 * "enclosing" exception). This shorthand can greatly reduce the length 543 * of the output in the common case where a wrapped exception is thrown 544 * from same method as the "causative exception" is caught. The above 545 * example was produced by running the program: 546 * <pre> 547 * public class Junk { 548 * public static void main(String args[]) { 549 * try { 550 * a(); 551 * } catch(HighLevelException e) { 552 * e.printStackTrace(); 553 * } 554 * } 555 * static void a() throws HighLevelException { 556 * try { 557 * b(); 558 * } catch(MidLevelException e) { 559 * throw new HighLevelException(e); 560 * } 561 * } 562 * static void b() throws MidLevelException { 563 * c(); 564 * } 565 * static void c() throws MidLevelException { 566 * try { 567 * d(); 568 * } catch(LowLevelException e) { 569 * throw new MidLevelException(e); 570 * } 571 * } 572 * static void d() throws LowLevelException { 573 * e(); 574 * } 575 * static void e() throws LowLevelException { 576 * throw new LowLevelException(); 577 * } 578 * } 579 * 580 * class HighLevelException extends Exception { 581 * HighLevelException(Throwable cause) { super(cause); } 582 * } 583 * 584 * class MidLevelException extends Exception { 585 * MidLevelException(Throwable cause) { super(cause); } 586 * } 587 * 588 * class LowLevelException extends Exception { 589 * } 590 * </pre> 591 * As of release 7, the platform supports the notion of 592 * <i>suppressed exceptions</i> (in conjunction with the {@code 593 * try}-with-resources statement). Any exceptions that were 594 * suppressed in order to deliver an exception are printed out 595 * beneath the stack trace. The format of this information 596 * depends on the implementation, but the following example may be 597 * regarded as typical: 598 * 599 * <pre> 600 * Exception in thread "main" java.lang.Exception: Something happened 601 * at Foo.bar(Foo.java:10) 602 * at Foo.main(Foo.java:5) 603 * Suppressed: Resource$CloseFailException: Resource ID = 0 604 * at Resource.close(Resource.java:26) 605 * at Foo.bar(Foo.java:9) 606 * ... 1 more 607 * </pre> 608 * Note that the "... n more" notation is used on suppressed exceptions 609 * just at it is used on causes. Unlike causes, suppressed exceptions are 610 * indented beyond their "containing exceptions." 611 * 612 * <p>An exception can have both a cause and one or more suppressed 613 * exceptions: 614 * <pre> 615 * Exception in thread "main" java.lang.Exception: Main block 616 * at Foo3.main(Foo3.java:7) 617 * Suppressed: Resource$CloseFailException: Resource ID = 2 618 * at Resource.close(Resource.java:26) 619 * at Foo3.main(Foo3.java:5) 620 * Suppressed: Resource$CloseFailException: Resource ID = 1 621 * at Resource.close(Resource.java:26) 622 * at Foo3.main(Foo3.java:5) 623 * Caused by: java.lang.Exception: I did it 624 * at Foo3.main(Foo3.java:8) 625 * </pre> 626 * Likewise, a suppressed exception can have a cause: 627 * <pre> 628 * Exception in thread "main" java.lang.Exception: Main block 629 * at Foo4.main(Foo4.java:6) 630 * Suppressed: Resource2$CloseFailException: Resource ID = 1 631 * at Resource2.close(Resource2.java:20) 632 * at Foo4.main(Foo4.java:5) 633 * Caused by: java.lang.Exception: Rats, you caught me 634 * at Resource2$CloseFailException.<init>(Resource2.java:45) 635 * ... 2 more 636 * </pre> 637 */ 638 public void printStackTrace() { 639 printStackTrace(System.err); 640 } 641 642 /** 643 * Prints this throwable and its backtrace to the specified print stream. 644 * 645 * @param s {@code PrintStream} to use for output 646 */ 647 public void printStackTrace(PrintStream s) { 648 printStackTrace(new WrappedPrintStream(s)); 649 } 650 651 private void printStackTrace(PrintStreamOrWriter s) { 652 // Guard against malicious overrides of Throwable.equals by 653 // using a Set with identity equality semantics. 654 Set<Throwable> dejaVu = Collections.newSetFromMap(new IdentityHashMap<>()); 655 dejaVu.add(this); 656 657 synchronized (s.lock()) { 658 // Print our stack trace 659 s.println(this); 660 StackTraceElement[] trace = getOurStackTrace(); 661 for (StackTraceElement traceElement : trace) 662 s.println("\tat " + traceElement); 663 664 // Print suppressed exceptions, if any 665 for (Throwable se : getSuppressed()) 666 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, "\t", dejaVu); 667 668 // Print cause, if any 669 Throwable ourCause = getCause(); 670 if (ourCause != null) 671 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, "", dejaVu); 672 } 673 } 674 675 /** 676 * Print our stack trace as an enclosed exception for the specified 677 * stack trace. 678 */ 679 private void printEnclosedStackTrace(PrintStreamOrWriter s, 680 StackTraceElement[] enclosingTrace, 681 String caption, 682 String prefix, 683 Set<Throwable> dejaVu) { 684 assert Thread.holdsLock(s.lock()); 685 if (dejaVu.contains(this)) { 686 s.println("\t[CIRCULAR REFERENCE:" + this + "]"); 687 } else { 688 dejaVu.add(this); 689 // Compute number of frames in common between this and enclosing trace 690 StackTraceElement[] trace = getOurStackTrace(); 691 int m = trace.length - 1; 692 int n = enclosingTrace.length - 1; 693 while (m >= 0 && n >=0 && trace[m].equals(enclosingTrace[n])) { 694 m--; n--; 695 } 696 int framesInCommon = trace.length - 1 - m; 697 698 // Print our stack trace 699 s.println(prefix + caption + this); 700 for (int i = 0; i <= m; i++) 701 s.println(prefix + "\tat " + trace[i]); 702 if (framesInCommon != 0) 703 s.println(prefix + "\t... " + framesInCommon + " more"); 704 705 // Print suppressed exceptions, if any 706 for (Throwable se : getSuppressed()) 707 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, 708 prefix +"\t", dejaVu); 709 710 // Print cause, if any 711 Throwable ourCause = getCause(); 712 if (ourCause != null) 713 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, prefix, dejaVu); 714 } 715 } 716 717 /** 718 * Prints this throwable and its backtrace to the specified 719 * print writer. 720 * 721 * @param s {@code PrintWriter} to use for output 722 * @since 1.1 723 */ 724 public void printStackTrace(PrintWriter s) { 725 printStackTrace(new WrappedPrintWriter(s)); 726 } 727 728 /** 729 * Wrapper class for PrintStream and PrintWriter to enable a single 730 * implementation of printStackTrace. 731 */ 732 private abstract static class PrintStreamOrWriter { 733 /** Returns the object to be locked when using this StreamOrWriter */ 734 abstract Object lock(); 735 736 /** Prints the specified string as a line on this StreamOrWriter */ 737 abstract void println(Object o); 738 } 739 740 private static class WrappedPrintStream extends PrintStreamOrWriter { 741 private final PrintStream printStream; 742 743 WrappedPrintStream(PrintStream printStream) { 744 this.printStream = printStream; 745 } 746 747 Object lock() { 748 return printStream; 749 } 750 751 void println(Object o) { 752 printStream.println(o); 753 } 754 } 755 756 private static class WrappedPrintWriter extends PrintStreamOrWriter { 757 private final PrintWriter printWriter; 758 759 WrappedPrintWriter(PrintWriter printWriter) { 760 this.printWriter = printWriter; 761 } 762 763 Object lock() { 764 return printWriter; 765 } 766 767 void println(Object o) { 768 printWriter.println(o); 769 } 770 } 771 772 /** 773 * Fills in the execution stack trace. This method records within this 774 * {@code Throwable} object information about the current state of 775 * the stack frames for the current thread. 776 * 777 * <p>If the stack trace of this {@code Throwable} {@linkplain 778 * Throwable#Throwable(String, Throwable, boolean, boolean) is not 779 * writable}, calling this method has no effect. 780 * 781 * @return a reference to this {@code Throwable} instance. 782 * @see java.lang.Throwable#printStackTrace() 783 */ 784 public synchronized Throwable fillInStackTrace() { 785 if (stackTrace != null || 786 backtrace != null /* Out of protocol state */ ) { 787 fillInStackTrace(0); 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 stackTrace = StackTraceElement.of(this, depth); 829 } else if (stackTrace == null) { 830 return UNASSIGNED_STACK; 831 } 832 return stackTrace; 833 } 834 835 /** 836 * This method is currently only called from the VM for instances of 837 * ExceptionInInitializerError which are stored for later chaining into a 838 * NoClassDefFoundError in order to prevent keeping classes from the native 839 * backtrace alive. 840 */ 841 private static void removeNativeBacktrace(Throwable throwable) { 842 Throwable t = throwable; 843 while ((t != null)) { 844 // Triggers the generation of the stack trace elements. 845 t.getOurStackTrace(); 846 if (t.suppressedExceptions != null) { 847 // If there are any suppressed exceptions, 848 // remove their native backtraces as well. 849 for (Throwable s : t.suppressedExceptions) { 850 removeNativeBacktrace(s); 851 } 852 } 853 // Now we don't need the native backtrace any more 854 t.backtrace = null; 855 t = t.getCause(); 856 } 857 } 858 859 /** 860 * Sets the stack trace elements that will be returned by 861 * {@link #getStackTrace()} and printed by {@link #printStackTrace()} 862 * and related methods. 863 * 864 * This method, which is designed for use by RPC frameworks and other 865 * advanced systems, allows the client to override the default 866 * stack trace that is either generated by {@link #fillInStackTrace()} 867 * when a throwable is constructed or deserialized when a throwable is 868 * read from a serialization stream. 869 * 870 * <p>If the stack trace of this {@code Throwable} {@linkplain 871 * Throwable#Throwable(String, Throwable, boolean, boolean) is not 872 * writable}, calling this method has no effect other than 873 * validating its argument. 874 * 875 * @param stackTrace the stack trace elements to be associated with 876 * this {@code Throwable}. The specified array is copied by this 877 * call; changes in the specified array after the method invocation 878 * returns will have no affect on this {@code Throwable}'s stack 879 * trace. 880 * 881 * @throws NullPointerException if {@code stackTrace} is 882 * {@code null} or if any of the elements of 883 * {@code stackTrace} are {@code null} 884 * 885 * @since 1.4 886 */ 887 public void setStackTrace(StackTraceElement[] stackTrace) { 888 // Validate argument 889 StackTraceElement[] defensiveCopy = stackTrace.clone(); 890 for (int i = 0; i < defensiveCopy.length; i++) { 891 if (defensiveCopy[i] == null) 892 throw new NullPointerException("stackTrace[" + i + "]"); 893 } 894 895 synchronized (this) { 896 if (this.stackTrace == null && // Immutable stack 897 backtrace == null) // Test for out of protocol state 898 return; 899 this.stackTrace = defensiveCopy; 900 } 901 } 902 903 /** 904 * Reads a {@code Throwable} from a stream, enforcing 905 * well-formedness constraints on fields. Null entries and 906 * self-pointers are not allowed in the list of {@code 907 * suppressedExceptions}. Null entries are not allowed for stack 908 * trace elements. A null stack trace in the serial form results 909 * in a zero-length stack element array. A single-element stack 910 * trace whose entry is equal to {@code new StackTraceElement("", 911 * "", null, Integer.MIN_VALUE)} results in a {@code null} {@code 912 * stackTrace} field. 913 * 914 * Note that there are no constraints on the value the {@code 915 * cause} field can hold; both {@code null} and {@code this} are 916 * valid values for the field. 917 */ 918 private void readObject(ObjectInputStream s) 919 throws IOException, ClassNotFoundException { 920 s.defaultReadObject(); // read in all fields 921 if (suppressedExceptions != null) { 922 List<Throwable> suppressed = null; 923 if (suppressedExceptions.isEmpty()) { 924 // Use the sentinel for a zero-length list 925 suppressed = SUPPRESSED_SENTINEL; 926 } else { // Copy Throwables to new list 927 suppressed = new ArrayList<>(1); 928 for (Throwable t : suppressedExceptions) { 929 // Enforce constraints on suppressed exceptions in 930 // case of corrupt or malicious stream. 931 if (t == null) 932 throw new NullPointerException(NULL_CAUSE_MESSAGE); 933 if (t == this) 934 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE); 935 suppressed.add(t); 936 } 937 } 938 suppressedExceptions = suppressed; 939 } // else a null suppressedExceptions field remains null 940 941 /* 942 * For zero-length stack traces, use a clone of 943 * UNASSIGNED_STACK rather than UNASSIGNED_STACK itself to 944 * allow identity comparison against UNASSIGNED_STACK in 945 * getOurStackTrace. The identity of UNASSIGNED_STACK in 946 * stackTrace indicates to the getOurStackTrace method that 947 * the stackTrace needs to be constructed from the information 948 * in backtrace. 949 */ 950 if (stackTrace != null) { 951 if (stackTrace.length == 0) { 952 stackTrace = UNASSIGNED_STACK.clone(); 953 } else if (stackTrace.length == 1 && 954 // Check for the marker of an immutable stack trace 955 SentinelHolder.STACK_TRACE_ELEMENT_SENTINEL.equals(stackTrace[0])) { 956 stackTrace = null; 957 } else { // Verify stack trace elements are non-null. 958 for(StackTraceElement ste : stackTrace) { 959 if (ste == null) 960 throw new NullPointerException("null StackTraceElement in serial stream. "); 961 } 962 } 963 } else { 964 // A null stackTrace field in the serial form can result 965 // from an exception serialized without that field in 966 // older JDK releases; treat such exceptions as having 967 // empty stack traces. 968 stackTrace = UNASSIGNED_STACK.clone(); 969 } 970 } 971 972 /** 973 * Write a {@code Throwable} object to a stream. 974 * 975 * A {@code null} stack trace field is represented in the serial 976 * form as a one-element array whose element is equal to {@code 977 * new StackTraceElement("", "", null, Integer.MIN_VALUE)}. 978 */ 979 private synchronized void writeObject(ObjectOutputStream s) 980 throws IOException { 981 // Ensure that the stackTrace field is initialized to a 982 // non-null value, if appropriate. As of JDK 7, a null stack 983 // trace field is a valid value indicating the stack trace 984 // should not be set. 985 getOurStackTrace(); 986 987 StackTraceElement[] oldStackTrace = stackTrace; 988 try { 989 if (stackTrace == null) 990 stackTrace = SentinelHolder.STACK_TRACE_SENTINEL; 991 s.defaultWriteObject(); 992 } finally { 993 stackTrace = oldStackTrace; 994 } 995 } 996 997 /** 998 * Appends the specified exception to the exceptions that were 999 * suppressed in order to deliver this exception. This method is 1000 * thread-safe and typically called (automatically and implicitly) 1001 * by the {@code try}-with-resources statement. 1002 * 1003 * <p>The suppression behavior is enabled <em>unless</em> disabled 1004 * {@linkplain #Throwable(String, Throwable, boolean, boolean) via 1005 * a constructor}. When suppression is disabled, this method does 1006 * nothing other than to validate its argument. 1007 * 1008 * <p>Note that when one exception {@linkplain 1009 * #initCause(Throwable) causes} another exception, the first 1010 * exception is usually caught and then the second exception is 1011 * thrown in response. In other words, there is a causal 1012 * connection between the two exceptions. 1013 * 1014 * In contrast, there are situations where two independent 1015 * exceptions can be thrown in sibling code blocks, in particular 1016 * in the {@code try} block of a {@code try}-with-resources 1017 * statement and the compiler-generated {@code finally} block 1018 * which closes the resource. 1019 * 1020 * In these situations, only one of the thrown exceptions can be 1021 * propagated. In the {@code try}-with-resources statement, when 1022 * there are two such exceptions, the exception originating from 1023 * the {@code try} block is propagated and the exception from the 1024 * {@code finally} block is added to the list of exceptions 1025 * suppressed by the exception from the {@code try} block. As an 1026 * exception unwinds the stack, it can accumulate multiple 1027 * suppressed exceptions. 1028 * 1029 * <p>An exception may have suppressed exceptions while also being 1030 * caused by another exception. Whether or not an exception has a 1031 * cause is semantically known at the time of its creation, unlike 1032 * whether or not an exception will suppress other exceptions 1033 * which is typically only determined after an exception is 1034 * thrown. 1035 * 1036 * <p>Note that programmer written code is also able to take 1037 * advantage of calling this method in situations where there are 1038 * multiple sibling exceptions and only one can be propagated. 1039 * 1040 * @param exception the exception to be added to the list of 1041 * suppressed exceptions 1042 * @throws IllegalArgumentException if {@code exception} is this 1043 * throwable; a throwable cannot suppress itself. 1044 * @throws NullPointerException if {@code exception} is {@code null} 1045 * @since 1.7 1046 */ 1047 public final synchronized void addSuppressed(Throwable exception) { 1048 if (exception == this) 1049 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE, exception); 1050 1051 if (exception == null) 1052 throw new NullPointerException(NULL_CAUSE_MESSAGE); 1053 1054 if (suppressedExceptions == null) // Suppressed exceptions not recorded 1055 return; 1056 1057 if (suppressedExceptions == SUPPRESSED_SENTINEL) 1058 suppressedExceptions = new ArrayList<>(1); 1059 1060 suppressedExceptions.add(exception); 1061 } 1062 1063 private static final Throwable[] EMPTY_THROWABLE_ARRAY = new Throwable[0]; 1064 1065 /** 1066 * Returns an array containing all of the exceptions that were 1067 * suppressed, typically by the {@code try}-with-resources 1068 * statement, in order to deliver this exception. 1069 * 1070 * If no exceptions were suppressed or {@linkplain 1071 * #Throwable(String, Throwable, boolean, boolean) suppression is 1072 * disabled}, an empty array is returned. This method is 1073 * thread-safe. Writes to the returned array do not affect future 1074 * calls to this method. 1075 * 1076 * @return an array containing all of the exceptions that were 1077 * suppressed to deliver this exception. 1078 * @since 1.7 1079 */ 1080 public final synchronized Throwable[] getSuppressed() { 1081 if (suppressedExceptions == SUPPRESSED_SENTINEL || 1082 suppressedExceptions == null) 1083 return EMPTY_THROWABLE_ARRAY; 1084 else 1085 return suppressedExceptions.toArray(EMPTY_THROWABLE_ARRAY); 1086 } 1087 }