1 /* 2 * Copyright (c) 1994, 2019, 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 * This is called by readObject of a few exceptions such as 471 * ClassNotFoundException and ExceptionInInitializerError to deserialize 472 * a stream output from an older runtime version where the cause may 473 * have set to null. 474 */ 475 final void setCause(Throwable t) { 476 this.cause = t; 477 } 478 479 /** 480 * Returns a short description of this throwable. 481 * The result is the concatenation of: 482 * <ul> 483 * <li> the {@linkplain Class#getName() name} of the class of this object 484 * <li> ": " (a colon and a space) 485 * <li> the result of invoking this object's {@link #getLocalizedMessage} 486 * method 487 * </ul> 488 * If {@code getLocalizedMessage} returns {@code null}, then just 489 * the class name is returned. 490 * 491 * @return a string representation of this throwable. 492 */ 493 public String toString() { 494 String s = getClass().getName(); 495 String message = getLocalizedMessage(); 496 return (message != null) ? (s + ": " + message) : s; 497 } 498 499 /** 500 * Prints this throwable and its backtrace to the 501 * standard error stream. This method prints a stack trace for this 502 * {@code Throwable} object on the error output stream that is 503 * the value of the field {@code System.err}. The first line of 504 * output contains the result of the {@link #toString()} method for 505 * this object. Remaining lines represent data previously recorded by 506 * the method {@link #fillInStackTrace()}. The format of this 507 * information depends on the implementation, but the following 508 * example may be regarded as typical: 509 * <blockquote><pre> 510 * java.lang.NullPointerException 511 * at MyClass.mash(MyClass.java:9) 512 * at MyClass.crunch(MyClass.java:6) 513 * at MyClass.main(MyClass.java:3) 514 * </pre></blockquote> 515 * This example was produced by running the program: 516 * <pre> 517 * class MyClass { 518 * public static void main(String[] args) { 519 * crunch(null); 520 * } 521 * static void crunch(int[] a) { 522 * mash(a); 523 * } 524 * static void mash(int[] b) { 525 * System.out.println(b[0]); 526 * } 527 * } 528 * </pre> 529 * The backtrace for a throwable with an initialized, non-null cause 530 * should generally include the backtrace for the cause. The format 531 * of this information depends on the implementation, but the following 532 * example may be regarded as typical: 533 * <pre> 534 * HighLevelException: MidLevelException: LowLevelException 535 * at Junk.a(Junk.java:13) 536 * at Junk.main(Junk.java:4) 537 * Caused by: MidLevelException: LowLevelException 538 * at Junk.c(Junk.java:23) 539 * at Junk.b(Junk.java:17) 540 * at Junk.a(Junk.java:11) 541 * ... 1 more 542 * Caused by: LowLevelException 543 * at Junk.e(Junk.java:30) 544 * at Junk.d(Junk.java:27) 545 * at Junk.c(Junk.java:21) 546 * ... 3 more 547 * </pre> 548 * Note the presence of lines containing the characters {@code "..."}. 549 * These lines indicate that the remainder of the stack trace for this 550 * exception matches the indicated number of frames from the bottom of the 551 * stack trace of the exception that was caused by this exception (the 552 * "enclosing" exception). This shorthand can greatly reduce the length 553 * of the output in the common case where a wrapped exception is thrown 554 * from same method as the "causative exception" is caught. The above 555 * example was produced by running the program: 556 * <pre> 557 * public class Junk { 558 * public static void main(String args[]) { 559 * try { 560 * a(); 561 * } catch(HighLevelException e) { 562 * e.printStackTrace(); 563 * } 564 * } 565 * static void a() throws HighLevelException { 566 * try { 567 * b(); 568 * } catch(MidLevelException e) { 569 * throw new HighLevelException(e); 570 * } 571 * } 572 * static void b() throws MidLevelException { 573 * c(); 574 * } 575 * static void c() throws MidLevelException { 576 * try { 577 * d(); 578 * } catch(LowLevelException e) { 579 * throw new MidLevelException(e); 580 * } 581 * } 582 * static void d() throws LowLevelException { 583 * e(); 584 * } 585 * static void e() throws LowLevelException { 586 * throw new LowLevelException(); 587 * } 588 * } 589 * 590 * class HighLevelException extends Exception { 591 * HighLevelException(Throwable cause) { super(cause); } 592 * } 593 * 594 * class MidLevelException extends Exception { 595 * MidLevelException(Throwable cause) { super(cause); } 596 * } 597 * 598 * class LowLevelException extends Exception { 599 * } 600 * </pre> 601 * As of release 7, the platform supports the notion of 602 * <i>suppressed exceptions</i> (in conjunction with the {@code 603 * try}-with-resources statement). Any exceptions that were 604 * suppressed in order to deliver an exception are printed out 605 * beneath the stack trace. The format of this information 606 * depends on the implementation, but the following example may be 607 * regarded as typical: 608 * 609 * <pre> 610 * Exception in thread "main" java.lang.Exception: Something happened 611 * at Foo.bar(Foo.java:10) 612 * at Foo.main(Foo.java:5) 613 * Suppressed: Resource$CloseFailException: Resource ID = 0 614 * at Resource.close(Resource.java:26) 615 * at Foo.bar(Foo.java:9) 616 * ... 1 more 617 * </pre> 618 * Note that the "... n more" notation is used on suppressed exceptions 619 * just as it is used on causes. Unlike causes, suppressed exceptions are 620 * indented beyond their "containing exceptions." 621 * 622 * <p>An exception can have both a cause and one or more suppressed 623 * exceptions: 624 * <pre> 625 * Exception in thread "main" java.lang.Exception: Main block 626 * at Foo3.main(Foo3.java:7) 627 * Suppressed: Resource$CloseFailException: Resource ID = 2 628 * at Resource.close(Resource.java:26) 629 * at Foo3.main(Foo3.java:5) 630 * Suppressed: Resource$CloseFailException: Resource ID = 1 631 * at Resource.close(Resource.java:26) 632 * at Foo3.main(Foo3.java:5) 633 * Caused by: java.lang.Exception: I did it 634 * at Foo3.main(Foo3.java:8) 635 * </pre> 636 * Likewise, a suppressed exception can have a cause: 637 * <pre> 638 * Exception in thread "main" java.lang.Exception: Main block 639 * at Foo4.main(Foo4.java:6) 640 * Suppressed: Resource2$CloseFailException: Resource ID = 1 641 * at Resource2.close(Resource2.java:20) 642 * at Foo4.main(Foo4.java:5) 643 * Caused by: java.lang.Exception: Rats, you caught me 644 * at Resource2$CloseFailException.<init>(Resource2.java:45) 645 * ... 2 more 646 * </pre> 647 */ 648 public void printStackTrace() { 649 printStackTrace(System.err); 650 } 651 652 /** 653 * Prints this throwable and its backtrace to the specified print stream. 654 * 655 * @param s {@code PrintStream} to use for output 656 */ 657 public void printStackTrace(PrintStream s) { 658 printStackTrace(new WrappedPrintStream(s)); 659 } 660 661 private void printStackTrace(PrintStreamOrWriter s) { 662 // Guard against malicious overrides of Throwable.equals by 663 // using a Set with identity equality semantics. 664 Set<Throwable> dejaVu = Collections.newSetFromMap(new IdentityHashMap<>()); 665 dejaVu.add(this); 666 667 synchronized (s.lock()) { 668 // Print our stack trace 669 s.println(this); 670 StackTraceElement[] trace = getOurStackTrace(); 671 for (StackTraceElement traceElement : trace) 672 s.println("\tat " + traceElement); 673 674 // Print suppressed exceptions, if any 675 for (Throwable se : getSuppressed()) 676 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, "\t", dejaVu); 677 678 // Print cause, if any 679 Throwable ourCause = getCause(); 680 if (ourCause != null) 681 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, "", dejaVu); 682 } 683 } 684 685 /** 686 * Print our stack trace as an enclosed exception for the specified 687 * stack trace. 688 */ 689 private void printEnclosedStackTrace(PrintStreamOrWriter s, 690 StackTraceElement[] enclosingTrace, 691 String caption, 692 String prefix, 693 Set<Throwable> dejaVu) { 694 assert Thread.holdsLock(s.lock()); 695 if (dejaVu.contains(this)) { 696 s.println(prefix + caption + "[CIRCULAR REFERENCE: " + this + "]"); 697 } else { 698 dejaVu.add(this); 699 // Compute number of frames in common between this and enclosing trace 700 StackTraceElement[] trace = getOurStackTrace(); 701 int m = trace.length - 1; 702 int n = enclosingTrace.length - 1; 703 while (m >= 0 && n >=0 && trace[m].equals(enclosingTrace[n])) { 704 m--; n--; 705 } 706 int framesInCommon = trace.length - 1 - m; 707 708 // Print our stack trace 709 s.println(prefix + caption + this); 710 for (int i = 0; i <= m; i++) 711 s.println(prefix + "\tat " + trace[i]); 712 if (framesInCommon != 0) 713 s.println(prefix + "\t... " + framesInCommon + " more"); 714 715 // Print suppressed exceptions, if any 716 for (Throwable se : getSuppressed()) 717 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, 718 prefix +"\t", dejaVu); 719 720 // Print cause, if any 721 Throwable ourCause = getCause(); 722 if (ourCause != null) 723 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, prefix, dejaVu); 724 } 725 } 726 727 /** 728 * Prints this throwable and its backtrace to the specified 729 * print writer. 730 * 731 * @param s {@code PrintWriter} to use for output 732 * @since 1.1 733 */ 734 public void printStackTrace(PrintWriter s) { 735 printStackTrace(new WrappedPrintWriter(s)); 736 } 737 738 /** 739 * Wrapper class for PrintStream and PrintWriter to enable a single 740 * implementation of printStackTrace. 741 */ 742 private abstract static class PrintStreamOrWriter { 743 /** Returns the object to be locked when using this StreamOrWriter */ 744 abstract Object lock(); 745 746 /** Prints the specified string as a line on this StreamOrWriter */ 747 abstract void println(Object o); 748 } 749 750 private static class WrappedPrintStream extends PrintStreamOrWriter { 751 private final PrintStream printStream; 752 753 WrappedPrintStream(PrintStream printStream) { 754 this.printStream = printStream; 755 } 756 757 Object lock() { 758 return printStream; 759 } 760 761 void println(Object o) { 762 printStream.println(o); 763 } 764 } 765 766 private static class WrappedPrintWriter extends PrintStreamOrWriter { 767 private final PrintWriter printWriter; 768 769 WrappedPrintWriter(PrintWriter printWriter) { 770 this.printWriter = printWriter; 771 } 772 773 Object lock() { 774 return printWriter; 775 } 776 777 void println(Object o) { 778 printWriter.println(o); 779 } 780 } 781 782 /** 783 * Fills in the execution stack trace. This method records within this 784 * {@code Throwable} object information about the current state of 785 * the stack frames for the current thread. 786 * 787 * <p>If the stack trace of this {@code Throwable} {@linkplain 788 * Throwable#Throwable(String, Throwable, boolean, boolean) is not 789 * writable}, calling this method has no effect. 790 * 791 * @return a reference to this {@code Throwable} instance. 792 * @see java.lang.Throwable#printStackTrace() 793 */ 794 public synchronized Throwable fillInStackTrace() { 795 if (stackTrace != null || 796 backtrace != null /* Out of protocol state */ ) { 797 fillInStackTrace(0); 798 stackTrace = UNASSIGNED_STACK; 799 } 800 return this; 801 } 802 803 private native Throwable fillInStackTrace(int dummy); 804 805 /** 806 * Provides programmatic access to the stack trace information printed by 807 * {@link #printStackTrace()}. Returns an array of stack trace elements, 808 * each representing one stack frame. The zeroth element of the array 809 * (assuming the array's length is non-zero) represents the top of the 810 * stack, which is the last method invocation in the sequence. Typically, 811 * this is the point at which this throwable was created and thrown. 812 * The last element of the array (assuming the array's length is non-zero) 813 * represents the bottom of the stack, which is the first method invocation 814 * in the sequence. 815 * 816 * <p>Some virtual machines may, under some circumstances, omit one 817 * or more stack frames from the stack trace. In the extreme case, 818 * a virtual machine that has no stack trace information concerning 819 * this throwable is permitted to return a zero-length array from this 820 * method. Generally speaking, the array returned by this method will 821 * contain one element for every frame that would be printed by 822 * {@code printStackTrace}. Writes to the returned array do not 823 * affect future calls to this method. 824 * 825 * @return an array of stack trace elements representing the stack trace 826 * pertaining to this throwable. 827 * @since 1.4 828 */ 829 public StackTraceElement[] getStackTrace() { 830 return getOurStackTrace().clone(); 831 } 832 833 private synchronized StackTraceElement[] getOurStackTrace() { 834 // Initialize stack trace field with information from 835 // backtrace if this is the first call to this method 836 if (stackTrace == UNASSIGNED_STACK || 837 (stackTrace == null && backtrace != null) /* Out of protocol state */) { 838 stackTrace = StackTraceElement.of(this, depth); 839 } else if (stackTrace == null) { 840 return UNASSIGNED_STACK; 841 } 842 return stackTrace; 843 } 844 845 /** 846 * Sets the stack trace elements that will be returned by 847 * {@link #getStackTrace()} and printed by {@link #printStackTrace()} 848 * and related methods. 849 * 850 * This method, which is designed for use by RPC frameworks and other 851 * advanced systems, allows the client to override the default 852 * stack trace that is either generated by {@link #fillInStackTrace()} 853 * when a throwable is constructed or deserialized when a throwable is 854 * read from a serialization stream. 855 * 856 * <p>If the stack trace of this {@code Throwable} {@linkplain 857 * Throwable#Throwable(String, Throwable, boolean, boolean) is not 858 * writable}, calling this method has no effect other than 859 * validating its argument. 860 * 861 * @param stackTrace the stack trace elements to be associated with 862 * this {@code Throwable}. The specified array is copied by this 863 * call; changes in the specified array after the method invocation 864 * returns will have no affect on this {@code Throwable}'s stack 865 * trace. 866 * 867 * @throws NullPointerException if {@code stackTrace} is 868 * {@code null} or if any of the elements of 869 * {@code stackTrace} are {@code null} 870 * 871 * @since 1.4 872 */ 873 public void setStackTrace(StackTraceElement[] stackTrace) { 874 // Validate argument 875 StackTraceElement[] defensiveCopy = stackTrace.clone(); 876 for (int i = 0; i < defensiveCopy.length; i++) { 877 if (defensiveCopy[i] == null) 878 throw new NullPointerException("stackTrace[" + i + "]"); 879 } 880 881 synchronized (this) { 882 if (this.stackTrace == null && // Immutable stack 883 backtrace == null) // Test for out of protocol state 884 return; 885 this.stackTrace = defensiveCopy; 886 } 887 } 888 889 /** 890 * Reads a {@code Throwable} from a stream, enforcing 891 * well-formedness constraints on fields. Null entries and 892 * self-pointers are not allowed in the list of {@code 893 * suppressedExceptions}. Null entries are not allowed for stack 894 * trace elements. A null stack trace in the serial form results 895 * in a zero-length stack element array. A single-element stack 896 * trace whose entry is equal to {@code new StackTraceElement("", 897 * "", null, Integer.MIN_VALUE)} results in a {@code null} {@code 898 * stackTrace} field. 899 * 900 * Note that there are no constraints on the value the {@code 901 * cause} field can hold; both {@code null} and {@code this} are 902 * valid values for the field. 903 */ 904 private void readObject(ObjectInputStream s) 905 throws IOException, ClassNotFoundException { 906 s.defaultReadObject(); // read in all fields 907 908 // Set suppressed exceptions and stack trace elements fields 909 // to marker values until the contents from the serial stream 910 // are validated. 911 List<Throwable> candidateSuppressedExceptions = suppressedExceptions; 912 suppressedExceptions = SUPPRESSED_SENTINEL; 913 914 StackTraceElement[] candidateStackTrace = stackTrace; 915 stackTrace = UNASSIGNED_STACK.clone(); 916 917 if (candidateSuppressedExceptions != null) { 918 int suppressedSize = validateSuppressedExceptionsList(candidateSuppressedExceptions); 919 if (suppressedSize > 0) { // Copy valid Throwables to new list 920 var suppList = new ArrayList<Throwable>(Math.min(100, suppressedSize)); 921 922 for (Throwable t : candidateSuppressedExceptions) { 923 // Enforce constraints on suppressed exceptions in 924 // case of corrupt or malicious stream. 925 Objects.requireNonNull(t, NULL_CAUSE_MESSAGE); 926 if (t == this) 927 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE); 928 suppList.add(t); 929 } 930 // If there are any invalid suppressed exceptions, 931 // implicitly use the sentinel value assigned earlier. 932 suppressedExceptions = suppList; 933 } 934 } else { 935 suppressedExceptions = null; 936 } 937 938 /* 939 * For zero-length stack traces, use a clone of 940 * UNASSIGNED_STACK rather than UNASSIGNED_STACK itself to 941 * allow identity comparison against UNASSIGNED_STACK in 942 * getOurStackTrace. The identity of UNASSIGNED_STACK in 943 * stackTrace indicates to the getOurStackTrace method that 944 * the stackTrace needs to be constructed from the information 945 * in backtrace. 946 */ 947 if (candidateStackTrace != null) { 948 // Work from a clone of the candidateStackTrace to ensure 949 // consistency of checks. 950 candidateStackTrace = candidateStackTrace.clone(); 951 if (candidateStackTrace.length >= 1) { 952 if (candidateStackTrace.length == 1 && 953 // Check for the marker of an immutable stack trace 954 SentinelHolder.STACK_TRACE_ELEMENT_SENTINEL.equals(candidateStackTrace[0])) { 955 stackTrace = null; 956 } else { // Verify stack trace elements are non-null. 957 for (StackTraceElement ste : candidateStackTrace) { 958 Objects.requireNonNull(ste, "null StackTraceElement in serial stream."); 959 } 960 stackTrace = candidateStackTrace; 961 } 962 } 963 } 964 // A null stackTrace field in the serial form can result from 965 // an exception serialized without that field in older JDK 966 // releases; treat such exceptions as having empty stack 967 // traces by leaving stackTrace assigned to a clone of 968 // UNASSIGNED_STACK. 969 } 970 971 private int validateSuppressedExceptionsList(List<Throwable> deserSuppressedExceptions) 972 throws IOException { 973 if (!Object.class.getModule(). 974 equals(deserSuppressedExceptions.getClass().getModule())) { 975 throw new StreamCorruptedException("List implementation not in base module."); 976 } else { 977 int size = deserSuppressedExceptions.size(); 978 if (size < 0) { 979 throw new StreamCorruptedException("Negative list size reported."); 980 } 981 return size; 982 } 983 } 984 985 /** 986 * Write a {@code Throwable} object to a stream. 987 * 988 * A {@code null} stack trace field is represented in the serial 989 * form as a one-element array whose element is equal to {@code 990 * new StackTraceElement("", "", null, Integer.MIN_VALUE)}. 991 */ 992 private synchronized void writeObject(ObjectOutputStream s) 993 throws IOException { 994 // Ensure that the stackTrace field is initialized to a 995 // non-null value, if appropriate. As of JDK 7, a null stack 996 // trace field is a valid value indicating the stack trace 997 // should not be set. 998 getOurStackTrace(); 999 1000 StackTraceElement[] oldStackTrace = stackTrace; 1001 try { 1002 if (stackTrace == null) 1003 stackTrace = SentinelHolder.STACK_TRACE_SENTINEL; 1004 s.defaultWriteObject(); 1005 } finally { 1006 stackTrace = oldStackTrace; 1007 } 1008 } 1009 1010 /** 1011 * Appends the specified exception to the exceptions that were 1012 * suppressed in order to deliver this exception. This method is 1013 * thread-safe and typically called (automatically and implicitly) 1014 * by the {@code try}-with-resources statement. 1015 * 1016 * <p>The suppression behavior is enabled <em>unless</em> disabled 1017 * {@linkplain #Throwable(String, Throwable, boolean, boolean) via 1018 * a constructor}. When suppression is disabled, this method does 1019 * nothing other than to validate its argument. 1020 * 1021 * <p>Note that when one exception {@linkplain 1022 * #initCause(Throwable) causes} another exception, the first 1023 * exception is usually caught and then the second exception is 1024 * thrown in response. In other words, there is a causal 1025 * connection between the two exceptions. 1026 * 1027 * In contrast, there are situations where two independent 1028 * exceptions can be thrown in sibling code blocks, in particular 1029 * in the {@code try} block of a {@code try}-with-resources 1030 * statement and the compiler-generated {@code finally} block 1031 * which closes the resource. 1032 * 1033 * In these situations, only one of the thrown exceptions can be 1034 * propagated. In the {@code try}-with-resources statement, when 1035 * there are two such exceptions, the exception originating from 1036 * the {@code try} block is propagated and the exception from the 1037 * {@code finally} block is added to the list of exceptions 1038 * suppressed by the exception from the {@code try} block. As an 1039 * exception unwinds the stack, it can accumulate multiple 1040 * suppressed exceptions. 1041 * 1042 * <p>An exception may have suppressed exceptions while also being 1043 * caused by another exception. Whether or not an exception has a 1044 * cause is semantically known at the time of its creation, unlike 1045 * whether or not an exception will suppress other exceptions 1046 * which is typically only determined after an exception is 1047 * thrown. 1048 * 1049 * <p>Note that programmer written code is also able to take 1050 * advantage of calling this method in situations where there are 1051 * multiple sibling exceptions and only one can be propagated. 1052 * 1053 * @param exception the exception to be added to the list of 1054 * suppressed exceptions 1055 * @throws IllegalArgumentException if {@code exception} is this 1056 * throwable; a throwable cannot suppress itself. 1057 * @throws NullPointerException if {@code exception} is {@code null} 1058 * @since 1.7 1059 */ 1060 public final synchronized void addSuppressed(Throwable exception) { 1061 if (exception == this) 1062 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE, exception); 1063 1064 Objects.requireNonNull(exception, NULL_CAUSE_MESSAGE); 1065 1066 if (suppressedExceptions == null) // Suppressed exceptions not recorded 1067 return; 1068 1069 if (suppressedExceptions == SUPPRESSED_SENTINEL) 1070 suppressedExceptions = new ArrayList<>(1); 1071 1072 suppressedExceptions.add(exception); 1073 } 1074 1075 private static final Throwable[] EMPTY_THROWABLE_ARRAY = new Throwable[0]; 1076 1077 /** 1078 * Returns an array containing all of the exceptions that were 1079 * suppressed, typically by the {@code try}-with-resources 1080 * statement, in order to deliver this exception. 1081 * 1082 * If no exceptions were suppressed or {@linkplain 1083 * #Throwable(String, Throwable, boolean, boolean) suppression is 1084 * disabled}, an empty array is returned. This method is 1085 * thread-safe. Writes to the returned array do not affect future 1086 * calls to this method. 1087 * 1088 * @return an array containing all of the exceptions that were 1089 * suppressed to deliver this exception. 1090 * @since 1.7 1091 */ 1092 public final synchronized Throwable[] getSuppressed() { 1093 if (suppressedExceptions == SUPPRESSED_SENTINEL || 1094 suppressedExceptions == null) 1095 return EMPTY_THROWABLE_ARRAY; 1096 else 1097 return suppressedExceptions.toArray(EMPTY_THROWABLE_ARRAY); 1098 } 1099 }