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 @java.io.Serial 118 private static final long serialVersionUID = -3042686055658047285L; 119 120 /** 121 * The JVM 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 /** 215 * The JVM code sets the depth of the backtrace for later retrieval 216 */ 217 private transient int depth; 218 219 // Setting this static field introduces an acceptable 220 // initialization dependency on a few java.util classes. 221 private static final List<Throwable> SUPPRESSED_SENTINEL = Collections.emptyList(); 222 223 /** 224 * The list of suppressed exceptions, as returned by {@link 225 * #getSuppressed()}. The list is initialized to a zero-element 226 * unmodifiable sentinel list. When a serialized Throwable is 227 * read in, if the {@code suppressedExceptions} field points to a 228 * zero-element list, the field is reset to the sentinel value. 229 * 230 * @serial 231 * @since 1.7 232 */ 233 @SuppressWarnings("serial") // Not statically typed as Serializable 234 private List<Throwable> suppressedExceptions = SUPPRESSED_SENTINEL; 235 236 /** Message for trying to suppress a null exception. */ 237 private static final String NULL_CAUSE_MESSAGE = "Cannot suppress a null exception."; 238 239 /** Message for trying to suppress oneself. */ 240 private static final String SELF_SUPPRESSION_MESSAGE = "Self-suppression not permitted"; 241 242 /** Caption for labeling causative exception stack traces */ 243 private static final String CAUSE_CAPTION = "Caused by: "; 244 245 /** Caption for labeling suppressed exception stack traces */ 246 private static final String SUPPRESSED_CAPTION = "Suppressed: "; 247 248 /** 249 * Constructs a new throwable with {@code null} as its detail message. 250 * The cause is not initialized, and may subsequently be initialized by a 251 * call to {@link #initCause}. 252 * 253 * <p>The {@link #fillInStackTrace()} method is called to initialize 254 * the stack trace data in the newly created throwable. 255 */ 256 public Throwable() { 257 fillInStackTrace(); 258 } 259 260 /** 261 * Constructs a new throwable with the specified detail message. The 262 * cause is not initialized, and may subsequently be initialized by 263 * a call to {@link #initCause}. 264 * 265 * <p>The {@link #fillInStackTrace()} method is called to initialize 266 * the stack trace data in the newly created throwable. 267 * 268 * @param message the detail message. The detail message is saved for 269 * later retrieval by the {@link #getMessage()} method. 270 */ 271 public Throwable(String message) { 272 fillInStackTrace(); 273 detailMessage = message; 274 } 275 276 /** 277 * Constructs a new throwable with the specified detail message and 278 * cause. <p>Note that the detail message associated with 279 * {@code cause} is <i>not</i> automatically incorporated in 280 * this throwable's detail message. 281 * 282 * <p>The {@link #fillInStackTrace()} method is called to initialize 283 * the stack trace data in the newly created throwable. 284 * 285 * @param message the detail message (which is saved for later retrieval 286 * by the {@link #getMessage()} method). 287 * @param cause the cause (which is saved for later retrieval by the 288 * {@link #getCause()} method). (A {@code null} value is 289 * permitted, and indicates that the cause is nonexistent or 290 * unknown.) 291 * @since 1.4 292 */ 293 public Throwable(String message, Throwable cause) { 294 fillInStackTrace(); 295 detailMessage = message; 296 this.cause = cause; 297 } 298 299 /** 300 * Constructs a new throwable with the specified cause and a detail 301 * message of {@code (cause==null ? null : cause.toString())} (which 302 * typically contains the class and detail message of {@code cause}). 303 * This constructor is useful for throwables that are little more than 304 * wrappers for other throwables (for example, {@link 305 * java.security.PrivilegedActionException}). 306 * 307 * <p>The {@link #fillInStackTrace()} method is called to initialize 308 * the stack trace data in the newly created throwable. 309 * 310 * @param cause the cause (which is saved for later retrieval by the 311 * {@link #getCause()} method). (A {@code null} value is 312 * permitted, and indicates that the cause is nonexistent or 313 * unknown.) 314 * @since 1.4 315 */ 316 public Throwable(Throwable cause) { 317 fillInStackTrace(); 318 detailMessage = (cause==null ? null : cause.toString()); 319 this.cause = cause; 320 } 321 322 /** 323 * Constructs a new throwable with the specified detail message, 324 * cause, {@linkplain #addSuppressed suppression} enabled or 325 * disabled, and writable stack trace enabled or disabled. If 326 * suppression is disabled, {@link #getSuppressed} for this object 327 * will return a zero-length array and calls to {@link 328 * #addSuppressed} that would otherwise append an exception to the 329 * suppressed list will have no effect. If the writable stack 330 * trace is false, this constructor will not call {@link 331 * #fillInStackTrace()}, a {@code null} will be written to the 332 * {@code stackTrace} field, and subsequent calls to {@code 333 * fillInStackTrace} and {@link 334 * #setStackTrace(StackTraceElement[])} will not set the stack 335 * trace. If the writable stack trace is false, {@link 336 * #getStackTrace} will return a zero length array. 337 * 338 * <p>Note that the other constructors of {@code Throwable} treat 339 * suppression as being enabled and the stack trace as being 340 * writable. Subclasses of {@code Throwable} should document any 341 * conditions under which suppression is disabled and document 342 * conditions under which the stack trace is not writable. 343 * Disabling of suppression should only occur in exceptional 344 * circumstances where special requirements exist, such as a 345 * virtual machine reusing exception objects under low-memory 346 * situations. Circumstances where a given exception object is 347 * repeatedly caught and rethrown, such as to implement control 348 * flow between two sub-systems, is another situation where 349 * immutable throwable objects would be appropriate. 350 * 351 * @param message the detail message. 352 * @param cause the cause. (A {@code null} value is permitted, 353 * and indicates that the cause is nonexistent or unknown.) 354 * @param enableSuppression whether or not suppression is enabled or disabled 355 * @param writableStackTrace whether or not the stack trace should be 356 * writable 357 * 358 * @see OutOfMemoryError 359 * @see NullPointerException 360 * @see ArithmeticException 361 * @since 1.7 362 */ 363 protected Throwable(String message, Throwable cause, 364 boolean enableSuppression, 365 boolean writableStackTrace) { 366 if (writableStackTrace) { 367 fillInStackTrace(); 368 } else { 369 stackTrace = null; 370 } 371 detailMessage = message; 372 this.cause = cause; 373 if (!enableSuppression) 374 suppressedExceptions = null; 375 } 376 377 /** 378 * Returns the detail message string of this throwable. 379 * 380 * @return the detail message string of this {@code Throwable} instance 381 * (which may be {@code null}). 382 */ 383 public String getMessage() { 384 return detailMessage; 385 } 386 387 /** 388 * Creates a localized description of this throwable. 389 * Subclasses may override this method in order to produce a 390 * locale-specific message. For subclasses that do not override this 391 * method, the default implementation returns the same result as 392 * {@code getMessage()}. 393 * 394 * @return The localized description of this throwable. 395 * @since 1.1 396 */ 397 public String getLocalizedMessage() { 398 return getMessage(); 399 } 400 401 /** 402 * Returns the cause of this throwable or {@code null} if the 403 * cause is nonexistent or unknown. (The cause is the throwable that 404 * caused this throwable to get thrown.) 405 * 406 * <p>This implementation returns the cause that was supplied via one of 407 * the constructors requiring a {@code Throwable}, or that was set after 408 * creation with the {@link #initCause(Throwable)} method. While it is 409 * typically unnecessary to override this method, a subclass can override 410 * it to return a cause set by some other means. This is appropriate for 411 * a "legacy chained throwable" that predates the addition of chained 412 * exceptions to {@code Throwable}. Note that it is <i>not</i> 413 * necessary to override any of the {@code PrintStackTrace} methods, 414 * all of which invoke the {@code getCause} method to determine the 415 * cause of a throwable. 416 * 417 * @return the cause of this throwable or {@code null} if the 418 * cause is nonexistent or unknown. 419 * @since 1.4 420 */ 421 public synchronized Throwable getCause() { 422 return (cause==this ? null : cause); 423 } 424 425 /** 426 * Initializes the <i>cause</i> of this throwable to the specified value. 427 * (The cause is the throwable that caused this throwable to get thrown.) 428 * 429 * <p>This method can be called at most once. It is generally called from 430 * within the constructor, or immediately after creating the 431 * throwable. If this throwable was created 432 * with {@link #Throwable(Throwable)} or 433 * {@link #Throwable(String,Throwable)}, this method cannot be called 434 * even once. 435 * 436 * <p>An example of using this method on a legacy throwable type 437 * without other support for setting the cause is: 438 * 439 * <pre> 440 * try { 441 * lowLevelOp(); 442 * } catch (LowLevelException le) { 443 * throw (HighLevelException) 444 * new HighLevelException().initCause(le); // Legacy constructor 445 * } 446 * </pre> 447 * 448 * @param cause the cause (which is saved for later retrieval by the 449 * {@link #getCause()} method). (A {@code null} value is 450 * permitted, and indicates that the cause is nonexistent or 451 * unknown.) 452 * @return a reference to this {@code Throwable} instance. 453 * @throws IllegalArgumentException if {@code cause} is this 454 * throwable. (A throwable cannot be its own cause.) 455 * @throws IllegalStateException if this throwable was 456 * created with {@link #Throwable(Throwable)} or 457 * {@link #Throwable(String,Throwable)}, or this method has already 458 * been called on this throwable. 459 * @since 1.4 460 */ 461 public synchronized Throwable initCause(Throwable cause) { 462 if (this.cause != this) 463 throw new IllegalStateException("Can't overwrite cause with " + 464 Objects.toString(cause, "a null"), this); 465 if (cause == this) 466 throw new IllegalArgumentException("Self-causation not permitted", this); 467 this.cause = cause; 468 return this; 469 } 470 471 /* 472 * This is called by readObject of a few exceptions such as 473 * ClassNotFoundException and ExceptionInInitializerError to deserialize 474 * a stream output from an older runtime version where the cause may 475 * have set to null. 476 */ 477 final void setCause(Throwable t) { 478 this.cause = t; 479 } 480 481 /** 482 * Returns a short description of this throwable. 483 * The result is the concatenation of: 484 * <ul> 485 * <li> the {@linkplain Class#getName() name} of the class of this object 486 * <li> ": " (a colon and a space) 487 * <li> the result of invoking this object's {@link #getLocalizedMessage} 488 * method 489 * </ul> 490 * If {@code getLocalizedMessage} returns {@code null}, then just 491 * the class name is returned. 492 * 493 * @return a string representation of this throwable. 494 */ 495 public String toString() { 496 String s = getClass().getName(); 497 String message = getLocalizedMessage(); 498 return (message != null) ? (s + ": " + message) : s; 499 } 500 501 /** 502 * Prints this throwable and its backtrace to the 503 * standard error stream. This method prints a stack trace for this 504 * {@code Throwable} object on the error output stream that is 505 * the value of the field {@code System.err}. The first line of 506 * output contains the result of the {@link #toString()} method for 507 * this object. Remaining lines represent data previously recorded by 508 * the method {@link #fillInStackTrace()}. The format of this 509 * information depends on the implementation, but the following 510 * example may be regarded as typical: 511 * <blockquote><pre> 512 * java.lang.NullPointerException 513 * at MyClass.mash(MyClass.java:9) 514 * at MyClass.crunch(MyClass.java:6) 515 * at MyClass.main(MyClass.java:3) 516 * </pre></blockquote> 517 * This example was produced by running the program: 518 * <pre> 519 * class MyClass { 520 * public static void main(String[] args) { 521 * crunch(null); 522 * } 523 * static void crunch(int[] a) { 524 * mash(a); 525 * } 526 * static void mash(int[] b) { 527 * System.out.println(b[0]); 528 * } 529 * } 530 * </pre> 531 * The backtrace for a throwable with an initialized, non-null cause 532 * should generally include the backtrace for the cause. The format 533 * of this information depends on the implementation, but the following 534 * example may be regarded as typical: 535 * <pre> 536 * HighLevelException: MidLevelException: LowLevelException 537 * at Junk.a(Junk.java:13) 538 * at Junk.main(Junk.java:4) 539 * Caused by: MidLevelException: LowLevelException 540 * at Junk.c(Junk.java:23) 541 * at Junk.b(Junk.java:17) 542 * at Junk.a(Junk.java:11) 543 * ... 1 more 544 * Caused by: LowLevelException 545 * at Junk.e(Junk.java:30) 546 * at Junk.d(Junk.java:27) 547 * at Junk.c(Junk.java:21) 548 * ... 3 more 549 * </pre> 550 * Note the presence of lines containing the characters {@code "..."}. 551 * These lines indicate that the remainder of the stack trace for this 552 * exception matches the indicated number of frames from the bottom of the 553 * stack trace of the exception that was caused by this exception (the 554 * "enclosing" exception). This shorthand can greatly reduce the length 555 * of the output in the common case where a wrapped exception is thrown 556 * from same method as the "causative exception" is caught. The above 557 * example was produced by running the program: 558 * <pre> 559 * public class Junk { 560 * public static void main(String args[]) { 561 * try { 562 * a(); 563 * } catch(HighLevelException e) { 564 * e.printStackTrace(); 565 * } 566 * } 567 * static void a() throws HighLevelException { 568 * try { 569 * b(); 570 * } catch(MidLevelException e) { 571 * throw new HighLevelException(e); 572 * } 573 * } 574 * static void b() throws MidLevelException { 575 * c(); 576 * } 577 * static void c() throws MidLevelException { 578 * try { 579 * d(); 580 * } catch(LowLevelException e) { 581 * throw new MidLevelException(e); 582 * } 583 * } 584 * static void d() throws LowLevelException { 585 * e(); 586 * } 587 * static void e() throws LowLevelException { 588 * throw new LowLevelException(); 589 * } 590 * } 591 * 592 * class HighLevelException extends Exception { 593 * HighLevelException(Throwable cause) { super(cause); } 594 * } 595 * 596 * class MidLevelException extends Exception { 597 * MidLevelException(Throwable cause) { super(cause); } 598 * } 599 * 600 * class LowLevelException extends Exception { 601 * } 602 * </pre> 603 * As of release 7, the platform supports the notion of 604 * <i>suppressed exceptions</i> (in conjunction with the {@code 605 * try}-with-resources statement). Any exceptions that were 606 * suppressed in order to deliver an exception are printed out 607 * beneath the stack trace. The format of this information 608 * depends on the implementation, but the following example may be 609 * regarded as typical: 610 * 611 * <pre> 612 * Exception in thread "main" java.lang.Exception: Something happened 613 * at Foo.bar(Foo.java:10) 614 * at Foo.main(Foo.java:5) 615 * Suppressed: Resource$CloseFailException: Resource ID = 0 616 * at Resource.close(Resource.java:26) 617 * at Foo.bar(Foo.java:9) 618 * ... 1 more 619 * </pre> 620 * Note that the "... n more" notation is used on suppressed exceptions 621 * just as it is used on causes. Unlike causes, suppressed exceptions are 622 * indented beyond their "containing exceptions." 623 * 624 * <p>An exception can have both a cause and one or more suppressed 625 * exceptions: 626 * <pre> 627 * Exception in thread "main" java.lang.Exception: Main block 628 * at Foo3.main(Foo3.java:7) 629 * Suppressed: Resource$CloseFailException: Resource ID = 2 630 * at Resource.close(Resource.java:26) 631 * at Foo3.main(Foo3.java:5) 632 * Suppressed: Resource$CloseFailException: Resource ID = 1 633 * at Resource.close(Resource.java:26) 634 * at Foo3.main(Foo3.java:5) 635 * Caused by: java.lang.Exception: I did it 636 * at Foo3.main(Foo3.java:8) 637 * </pre> 638 * Likewise, a suppressed exception can have a cause: 639 * <pre> 640 * Exception in thread "main" java.lang.Exception: Main block 641 * at Foo4.main(Foo4.java:6) 642 * Suppressed: Resource2$CloseFailException: Resource ID = 1 643 * at Resource2.close(Resource2.java:20) 644 * at Foo4.main(Foo4.java:5) 645 * Caused by: java.lang.Exception: Rats, you caught me 646 * at Resource2$CloseFailException.<init>(Resource2.java:45) 647 * ... 2 more 648 * </pre> 649 */ 650 public void printStackTrace() { 651 printStackTrace(System.err); 652 } 653 654 /** 655 * Prints this throwable and its backtrace to the specified print stream. 656 * 657 * @param s {@code PrintStream} to use for output 658 */ 659 public void printStackTrace(PrintStream s) { 660 printStackTrace(new WrappedPrintStream(s)); 661 } 662 663 private void printStackTrace(PrintStreamOrWriter s) { 664 // Guard against malicious overrides of Throwable.equals by 665 // using a Set with identity equality semantics. 666 Set<Throwable> dejaVu = Collections.newSetFromMap(new IdentityHashMap<>()); 667 dejaVu.add(this); 668 669 synchronized (s.lock()) { 670 // Print our stack trace 671 s.println(this); 672 StackTraceElement[] trace = getOurStackTrace(); 673 for (StackTraceElement traceElement : trace) 674 s.println("\tat " + traceElement); 675 676 // Print suppressed exceptions, if any 677 for (Throwable se : getSuppressed()) 678 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, "\t", dejaVu); 679 680 // Print cause, if any 681 Throwable ourCause = getCause(); 682 if (ourCause != null) 683 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, "", dejaVu); 684 } 685 } 686 687 /** 688 * Print our stack trace as an enclosed exception for the specified 689 * stack trace. 690 */ 691 private void printEnclosedStackTrace(PrintStreamOrWriter s, 692 StackTraceElement[] enclosingTrace, 693 String caption, 694 String prefix, 695 Set<Throwable> dejaVu) { 696 assert Thread.holdsLock(s.lock()); 697 if (dejaVu.contains(this)) { 698 s.println(prefix + caption + "[CIRCULAR REFERENCE: " + this + "]"); 699 } else { 700 dejaVu.add(this); 701 // Compute number of frames in common between this and enclosing trace 702 StackTraceElement[] trace = getOurStackTrace(); 703 int m = trace.length - 1; 704 int n = enclosingTrace.length - 1; 705 while (m >= 0 && n >=0 && trace[m].equals(enclosingTrace[n])) { 706 m--; n--; 707 } 708 int framesInCommon = trace.length - 1 - m; 709 710 // Print our stack trace 711 s.println(prefix + caption + this); 712 for (int i = 0; i <= m; i++) 713 s.println(prefix + "\tat " + trace[i]); 714 if (framesInCommon != 0) 715 s.println(prefix + "\t... " + framesInCommon + " more"); 716 717 // Print suppressed exceptions, if any 718 for (Throwable se : getSuppressed()) 719 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, 720 prefix +"\t", dejaVu); 721 722 // Print cause, if any 723 Throwable ourCause = getCause(); 724 if (ourCause != null) 725 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, prefix, dejaVu); 726 } 727 } 728 729 /** 730 * Prints this throwable and its backtrace to the specified 731 * print writer. 732 * 733 * @param s {@code PrintWriter} to use for output 734 * @since 1.1 735 */ 736 public void printStackTrace(PrintWriter s) { 737 printStackTrace(new WrappedPrintWriter(s)); 738 } 739 740 /** 741 * Wrapper class for PrintStream and PrintWriter to enable a single 742 * implementation of printStackTrace. 743 */ 744 private abstract static class PrintStreamOrWriter { 745 /** Returns the object to be locked when using this StreamOrWriter */ 746 abstract Object lock(); 747 748 /** Prints the specified string as a line on this StreamOrWriter */ 749 abstract void println(Object o); 750 } 751 752 private static class WrappedPrintStream extends PrintStreamOrWriter { 753 private final PrintStream printStream; 754 755 WrappedPrintStream(PrintStream printStream) { 756 this.printStream = printStream; 757 } 758 759 Object lock() { 760 return printStream; 761 } 762 763 void println(Object o) { 764 printStream.println(o); 765 } 766 } 767 768 private static class WrappedPrintWriter extends PrintStreamOrWriter { 769 private final PrintWriter printWriter; 770 771 WrappedPrintWriter(PrintWriter printWriter) { 772 this.printWriter = printWriter; 773 } 774 775 Object lock() { 776 return printWriter; 777 } 778 779 void println(Object o) { 780 printWriter.println(o); 781 } 782 } 783 784 /** 785 * Fills in the execution stack trace. This method records within this 786 * {@code Throwable} object information about the current state of 787 * the stack frames for the current thread. 788 * 789 * <p>If the stack trace of this {@code Throwable} {@linkplain 790 * Throwable#Throwable(String, Throwable, boolean, boolean) is not 791 * writable}, calling this method has no effect. 792 * 793 * @return a reference to this {@code Throwable} instance. 794 * @see java.lang.Throwable#printStackTrace() 795 */ 796 public synchronized Throwable fillInStackTrace() { 797 if (stackTrace != null || 798 backtrace != null /* Out of protocol state */ ) { 799 fillInStackTrace(0); 800 stackTrace = UNASSIGNED_STACK; 801 } 802 return this; 803 } 804 805 private native Throwable fillInStackTrace(int dummy); 806 807 /** 808 * Provides programmatic access to the stack trace information printed by 809 * {@link #printStackTrace()}. Returns an array of stack trace elements, 810 * each representing one stack frame. The zeroth element of the array 811 * (assuming the array's length is non-zero) represents the top of the 812 * stack, which is the last method invocation in the sequence. Typically, 813 * this is the point at which this throwable was created and thrown. 814 * The last element of the array (assuming the array's length is non-zero) 815 * represents the bottom of the stack, which is the first method invocation 816 * in the sequence. 817 * 818 * <p>Some virtual machines may, under some circumstances, omit one 819 * or more stack frames from the stack trace. In the extreme case, 820 * a virtual machine that has no stack trace information concerning 821 * this throwable is permitted to return a zero-length array from this 822 * method. Generally speaking, the array returned by this method will 823 * contain one element for every frame that would be printed by 824 * {@code printStackTrace}. Writes to the returned array do not 825 * affect future calls to this method. 826 * 827 * @return an array of stack trace elements representing the stack trace 828 * pertaining to this throwable. 829 * @since 1.4 830 */ 831 public StackTraceElement[] getStackTrace() { 832 return getOurStackTrace().clone(); 833 } 834 835 private synchronized StackTraceElement[] getOurStackTrace() { 836 // Initialize stack trace field with information from 837 // backtrace if this is the first call to this method 838 if (stackTrace == UNASSIGNED_STACK || 839 (stackTrace == null && backtrace != null) /* Out of protocol state */) { 840 stackTrace = StackTraceElement.of(this, depth); 841 } else if (stackTrace == null) { 842 return UNASSIGNED_STACK; 843 } 844 return stackTrace; 845 } 846 847 /** 848 * Sets the stack trace elements that will be returned by 849 * {@link #getStackTrace()} and printed by {@link #printStackTrace()} 850 * and related methods. 851 * 852 * This method, which is designed for use by RPC frameworks and other 853 * advanced systems, allows the client to override the default 854 * stack trace that is either generated by {@link #fillInStackTrace()} 855 * when a throwable is constructed or deserialized when a throwable is 856 * read from a serialization stream. 857 * 858 * <p>If the stack trace of this {@code Throwable} {@linkplain 859 * Throwable#Throwable(String, Throwable, boolean, boolean) is not 860 * writable}, calling this method has no effect other than 861 * validating its argument. 862 * 863 * @param stackTrace the stack trace elements to be associated with 864 * this {@code Throwable}. The specified array is copied by this 865 * call; changes in the specified array after the method invocation 866 * returns will have no affect on this {@code Throwable}'s stack 867 * trace. 868 * 869 * @throws NullPointerException if {@code stackTrace} is 870 * {@code null} or if any of the elements of 871 * {@code stackTrace} are {@code null} 872 * 873 * @since 1.4 874 */ 875 public void setStackTrace(StackTraceElement[] stackTrace) { 876 // Validate argument 877 StackTraceElement[] defensiveCopy = stackTrace.clone(); 878 for (int i = 0; i < defensiveCopy.length; i++) { 879 if (defensiveCopy[i] == null) 880 throw new NullPointerException("stackTrace[" + i + "]"); 881 } 882 883 synchronized (this) { 884 if (this.stackTrace == null && // Immutable stack 885 backtrace == null) // Test for out of protocol state 886 return; 887 this.stackTrace = defensiveCopy; 888 } 889 } 890 891 /** 892 * Reads a {@code Throwable} from a stream, enforcing 893 * well-formedness constraints on fields. Null entries and 894 * self-pointers are not allowed in the list of {@code 895 * suppressedExceptions}. Null entries are not allowed for stack 896 * trace elements. A null stack trace in the serial form results 897 * in a zero-length stack element array. A single-element stack 898 * trace whose entry is equal to {@code new StackTraceElement("", 899 * "", null, Integer.MIN_VALUE)} results in a {@code null} {@code 900 * stackTrace} field. 901 * 902 * Note that there are no constraints on the value the {@code 903 * cause} field can hold; both {@code null} and {@code this} are 904 * valid values for the field. 905 */ 906 @java.io.Serial 907 private void readObject(ObjectInputStream s) 908 throws IOException, ClassNotFoundException { 909 s.defaultReadObject(); // read in all fields 910 911 // Set suppressed exceptions and stack trace elements fields 912 // to marker values until the contents from the serial stream 913 // are validated. 914 List<Throwable> candidateSuppressedExceptions = suppressedExceptions; 915 suppressedExceptions = SUPPRESSED_SENTINEL; 916 917 StackTraceElement[] candidateStackTrace = stackTrace; 918 stackTrace = UNASSIGNED_STACK.clone(); 919 920 if (candidateSuppressedExceptions != null) { 921 int suppressedSize = validateSuppressedExceptionsList(candidateSuppressedExceptions); 922 if (suppressedSize > 0) { // Copy valid Throwables to new list 923 var suppList = new ArrayList<Throwable>(Math.min(100, suppressedSize)); 924 925 for (Throwable t : candidateSuppressedExceptions) { 926 // Enforce constraints on suppressed exceptions in 927 // case of corrupt or malicious stream. 928 Objects.requireNonNull(t, NULL_CAUSE_MESSAGE); 929 if (t == this) 930 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE); 931 suppList.add(t); 932 } 933 // If there are any invalid suppressed exceptions, 934 // implicitly use the sentinel value assigned earlier. 935 suppressedExceptions = suppList; 936 } 937 } else { 938 suppressedExceptions = null; 939 } 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 (candidateStackTrace != null) { 951 // Work from a clone of the candidateStackTrace to ensure 952 // consistency of checks. 953 candidateStackTrace = candidateStackTrace.clone(); 954 if (candidateStackTrace.length >= 1) { 955 if (candidateStackTrace.length == 1 && 956 // Check for the marker of an immutable stack trace 957 SentinelHolder.STACK_TRACE_ELEMENT_SENTINEL.equals(candidateStackTrace[0])) { 958 stackTrace = null; 959 } else { // Verify stack trace elements are non-null. 960 for (StackTraceElement ste : candidateStackTrace) { 961 Objects.requireNonNull(ste, "null StackTraceElement in serial stream."); 962 } 963 stackTrace = candidateStackTrace; 964 } 965 } 966 } 967 // A null stackTrace field in the serial form can result from 968 // an exception serialized without that field in older JDK 969 // releases; treat such exceptions as having empty stack 970 // traces by leaving stackTrace assigned to a clone of 971 // UNASSIGNED_STACK. 972 } 973 974 private int validateSuppressedExceptionsList(List<Throwable> deserSuppressedExceptions) 975 throws IOException { 976 if (!Object.class.getModule(). 977 equals(deserSuppressedExceptions.getClass().getModule())) { 978 throw new StreamCorruptedException("List implementation not in base module."); 979 } else { 980 int size = deserSuppressedExceptions.size(); 981 if (size < 0) { 982 throw new StreamCorruptedException("Negative list size reported."); 983 } 984 return size; 985 } 986 } 987 988 /** 989 * Write a {@code Throwable} object to a stream. 990 * 991 * A {@code null} stack trace field is represented in the serial 992 * form as a one-element array whose element is equal to {@code 993 * new StackTraceElement("", "", null, Integer.MIN_VALUE)}. 994 */ 995 @java.io.Serial 996 private synchronized void writeObject(ObjectOutputStream s) 997 throws IOException { 998 // Ensure that the stackTrace field is initialized to a 999 // non-null value, if appropriate. As of JDK 7, a null stack 1000 // trace field is a valid value indicating the stack trace 1001 // should not be set. 1002 getOurStackTrace(); 1003 1004 StackTraceElement[] oldStackTrace = stackTrace; 1005 try { 1006 if (stackTrace == null) 1007 stackTrace = SentinelHolder.STACK_TRACE_SENTINEL; 1008 s.defaultWriteObject(); 1009 } finally { 1010 stackTrace = oldStackTrace; 1011 } 1012 } 1013 1014 /** 1015 * Appends the specified exception to the exceptions that were 1016 * suppressed in order to deliver this exception. This method is 1017 * thread-safe and typically called (automatically and implicitly) 1018 * by the {@code try}-with-resources statement. 1019 * 1020 * <p>The suppression behavior is enabled <em>unless</em> disabled 1021 * {@linkplain #Throwable(String, Throwable, boolean, boolean) via 1022 * a constructor}. When suppression is disabled, this method does 1023 * nothing other than to validate its argument. 1024 * 1025 * <p>Note that when one exception {@linkplain 1026 * #initCause(Throwable) causes} another exception, the first 1027 * exception is usually caught and then the second exception is 1028 * thrown in response. In other words, there is a causal 1029 * connection between the two exceptions. 1030 * 1031 * In contrast, there are situations where two independent 1032 * exceptions can be thrown in sibling code blocks, in particular 1033 * in the {@code try} block of a {@code try}-with-resources 1034 * statement and the compiler-generated {@code finally} block 1035 * which closes the resource. 1036 * 1037 * In these situations, only one of the thrown exceptions can be 1038 * propagated. In the {@code try}-with-resources statement, when 1039 * there are two such exceptions, the exception originating from 1040 * the {@code try} block is propagated and the exception from the 1041 * {@code finally} block is added to the list of exceptions 1042 * suppressed by the exception from the {@code try} block. As an 1043 * exception unwinds the stack, it can accumulate multiple 1044 * suppressed exceptions. 1045 * 1046 * <p>An exception may have suppressed exceptions while also being 1047 * caused by another exception. Whether or not an exception has a 1048 * cause is semantically known at the time of its creation, unlike 1049 * whether or not an exception will suppress other exceptions 1050 * which is typically only determined after an exception is 1051 * thrown. 1052 * 1053 * <p>Note that programmer written code is also able to take 1054 * advantage of calling this method in situations where there are 1055 * multiple sibling exceptions and only one can be propagated. 1056 * 1057 * @param exception the exception to be added to the list of 1058 * suppressed exceptions 1059 * @throws IllegalArgumentException if {@code exception} is this 1060 * throwable; a throwable cannot suppress itself. 1061 * @throws NullPointerException if {@code exception} is {@code null} 1062 * @since 1.7 1063 */ 1064 public final synchronized void addSuppressed(Throwable exception) { 1065 if (exception == this) 1066 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE, exception); 1067 1068 Objects.requireNonNull(exception, NULL_CAUSE_MESSAGE); 1069 1070 if (suppressedExceptions == null) // Suppressed exceptions not recorded 1071 return; 1072 1073 if (suppressedExceptions == SUPPRESSED_SENTINEL) 1074 suppressedExceptions = new ArrayList<>(1); 1075 1076 suppressedExceptions.add(exception); 1077 } 1078 1079 private static final Throwable[] EMPTY_THROWABLE_ARRAY = new Throwable[0]; 1080 1081 /** 1082 * Returns an array containing all of the exceptions that were 1083 * suppressed, typically by the {@code try}-with-resources 1084 * statement, in order to deliver this exception. 1085 * 1086 * If no exceptions were suppressed or {@linkplain 1087 * #Throwable(String, Throwable, boolean, boolean) suppression is 1088 * disabled}, an empty array is returned. This method is 1089 * thread-safe. Writes to the returned array do not affect future 1090 * calls to this method. 1091 * 1092 * @return an array containing all of the exceptions that were 1093 * suppressed to deliver this exception. 1094 * @since 1.7 1095 */ 1096 public final synchronized Throwable[] getSuppressed() { 1097 if (suppressedExceptions == SUPPRESSED_SENTINEL || 1098 suppressedExceptions == null) 1099 return EMPTY_THROWABLE_ARRAY; 1100 else 1101 return suppressedExceptions.toArray(EMPTY_THROWABLE_ARRAY); 1102 } 1103 }