1 /* 2 * Copyright (C) 2014 The Android Open Source Project 3 * Copyright (c) 1994, 2013, Oracle and/or its affiliates. All rights reserved. 4 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 5 * 6 * This code is free software; you can redistribute it and/or modify it 7 * under the terms of the GNU General Public License version 2 only, as 8 * published by the Free Software Foundation. Oracle designates this 9 * particular file as subject to the "Classpath" exception as provided 10 * by Oracle in the LICENSE file that accompanied this code. 11 * 12 * This code is distributed in the hope that it will be useful, but WITHOUT 13 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 14 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 15 * version 2 for more details (a copy is included in the LICENSE file that 16 * accompanied this code). 17 * 18 * You should have received a copy of the GNU General Public License version 19 * 2 along with this work; if not, write to the Free Software Foundation, 20 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 21 * 22 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 23 * or visit www.oracle.com if you need additional information or have any 24 * questions. 25 */ 26 27 package java.lang; 28 import dalvik.annotation.optimization.FastNative; 29 import java.io.*; 30 import java.util.*; 31 32 /** 33 * The {@code Throwable} class is the superclass of all errors and 34 * exceptions in the Java language. Only objects that are instances of this 35 * class (or one of its subclasses) are thrown by the Java Virtual Machine or 36 * can be thrown by the Java {@code throw} statement. Similarly, only 37 * this class or one of its subclasses can be the argument type in a 38 * {@code catch} clause. 39 * 40 * For the purposes of compile-time checking of exceptions, {@code 41 * Throwable} and any subclass of {@code Throwable} that is not also a 42 * subclass of either {@link RuntimeException} or {@link Error} are 43 * regarded as checked exceptions. 44 * 45 * <p>Instances of two subclasses, {@link java.lang.Error} and 46 * {@link java.lang.Exception}, are conventionally used to indicate 47 * that exceptional situations have occurred. Typically, these instances 48 * are freshly created in the context of the exceptional situation so 49 * as to include relevant information (such as stack trace data). 50 * 51 * <p>A throwable contains a snapshot of the execution stack of its 52 * thread at the time it was created. It can also contain a message 53 * string that gives more information about the error. Over time, a 54 * throwable can {@linkplain Throwable#addSuppressed suppress} other 55 * throwables from being propagated. Finally, the throwable can also 56 * contain a <i>cause</i>: another throwable that caused this 57 * throwable to be constructed. The recording of this causal information 58 * is referred to as the <i>chained exception</i> facility, as the 59 * cause can, itself, have a cause, and so on, leading to a "chain" of 60 * exceptions, each caused by another. 61 * 62 * <p>One reason that a throwable may have a cause is that the class that 63 * throws it is built atop a lower layered abstraction, and an operation on 64 * the upper layer fails due to a failure in the lower layer. It would be bad 65 * design to let the throwable thrown by the lower layer propagate outward, as 66 * it is generally unrelated to the abstraction provided by the upper layer. 67 * Further, doing so would tie the API of the upper layer to the details of 68 * its implementation, assuming the lower layer's exception was a checked 69 * exception. Throwing a "wrapped exception" (i.e., an exception containing a 70 * cause) allows the upper layer to communicate the details of the failure to 71 * its caller without incurring either of these shortcomings. It preserves 72 * the flexibility to change the implementation of the upper layer without 73 * changing its API (in particular, the set of exceptions thrown by its 74 * methods). 75 * 76 * <p>A second reason that a throwable may have a cause is that the method 77 * that throws it must conform to a general-purpose interface that does not 78 * permit the method to throw the cause directly. For example, suppose 79 * a persistent collection conforms to the {@link java.util.Collection 80 * Collection} interface, and that its persistence is implemented atop 81 * {@code java.io}. Suppose the internals of the {@code add} method 82 * can throw an {@link java.io.IOException IOException}. The implementation 83 * can communicate the details of the {@code IOException} to its caller 84 * while conforming to the {@code Collection} interface by wrapping the 85 * {@code IOException} in an appropriate unchecked exception. (The 86 * specification for the persistent collection should indicate that it is 87 * capable of throwing such exceptions.) 88 * 89 * <p>A cause can be associated with a throwable in two ways: via a 90 * constructor that takes the cause as an argument, or via the 91 * {@link #initCause(Throwable)} method. New throwable classes that 92 * wish to allow causes to be associated with them should provide constructors 93 * that take a cause and delegate (perhaps indirectly) to one of the 94 * {@code Throwable} constructors that takes a cause. 95 * 96 * Because the {@code initCause} method is public, it allows a cause to be 97 * associated with any throwable, even a "legacy throwable" whose 98 * implementation predates the addition of the exception chaining mechanism to 99 * {@code Throwable}. 100 * 101 * <p>By convention, class {@code Throwable} and its subclasses have two 102 * constructors, one that takes no arguments and one that takes a 103 * {@code String} argument that can be used to produce a detail message. 104 * Further, those subclasses that might likely have a cause associated with 105 * them should have two more constructors, one that takes a 106 * {@code Throwable} (the cause), and one that takes a 107 * {@code String} (the detail message) and a {@code Throwable} (the 108 * cause). 109 * 110 * @author unascribed 111 * @author Josh Bloch (Added exception chaining and programmatic access to 112 * stack trace in 1.4.) 113 * @jls 11.2 Compile-Time Checking of Exceptions 114 * @since JDK1.0 115 */ 116 public class Throwable implements Serializable { 117 /** use serialVersionUID from JDK 1.0.2 for interoperability */ 118 private static final long serialVersionUID = -3042686055658047285L; 119 120 /** 121 * Native code saves some indication of the stack backtrace in this slot. 122 */ 123 private transient volatile 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 sentinal 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 * To allow Throwable objects to be made immutable and safely 160 * reused by the JVM, such as OutOfMemoryErrors, fields of 161 * Throwable that are writable in response to user actions, cause, 162 * stackTrace, and suppressedExceptions obey the following 163 * protocol: 164 * 165 * 1) The fields are initialized to a non-null sentinel value 166 * which indicates the value has logically not been set. 167 * 168 * 2) Writing a null to the field indicates further writes 169 * are forbidden 170 * 171 * 3) The sentinel value may be replaced with another non-null 172 * value. 173 * 174 * For example, implementations of the HotSpot JVM have 175 * preallocated OutOfMemoryError objects to provide for better 176 * diagnosability of that situation. These objects are created 177 * without calling the constructor for that class and the fields 178 * in question are initialized to null. To support this 179 * capability, any new fields added to Throwable that require 180 * being initialized to a non-null value require a coordinated JVM 181 * change. 182 */ 183 184 /** 185 * The throwable that caused this throwable to get thrown, or null if this 186 * throwable was not caused by another throwable, or if the causative 187 * throwable is unknown. If this field is equal to this throwable itself, 188 * it indicates that the cause of this throwable has not yet been 189 * initialized. 190 * 191 * @serial 192 * @since 1.4 193 */ 194 private Throwable cause = this; 195 196 /** 197 * The stack trace, as returned by {@link #getStackTrace()}. 198 * 199 * The field is initialized to a zero-length array. A {@code 200 * null} value of this field indicates subsequent calls to {@link 201 * #setStackTrace(StackTraceElement[])} and {@link 202 * #fillInStackTrace()} will be be no-ops. 203 * 204 * @serial 205 * @since 1.4 206 */ 207 // Android-changed. 208 private StackTraceElement[] stackTrace = libcore.util.EmptyArray.STACK_TRACE_ELEMENT; 209 210 /** 211 * The list of suppressed exceptions, as returned by {@link 212 * #getSuppressed()}. The list is initialized to a zero-element 213 * unmodifiable sentinel list. When a serialized Throwable is 214 * read in, if the {@code suppressedExceptions} field points to a 215 * zero-element list, the field is reset to the sentinel value. 216 * 217 * @serial 218 * @since 1.7 219 */ 220 private List<Throwable> suppressedExceptions = Collections.emptyList(); 221 222 /** Message for trying to suppress a null exception. */ 223 private static final String NULL_CAUSE_MESSAGE = "Cannot suppress a null exception."; 224 225 /** Message for trying to suppress oneself. */ 226 private static final String SELF_SUPPRESSION_MESSAGE = "Self-suppression not permitted"; 227 228 /** Caption for labeling causative exception stack traces */ 229 private static final String CAUSE_CAPTION = "Caused by: "; 230 231 /** Caption for labeling suppressed exception stack traces */ 232 private static final String SUPPRESSED_CAPTION = "Suppressed: "; 233 234 /** 235 * Constructs a new throwable with {@code null} as its detail message. 236 * The cause is not initialized, and may subsequently be initialized by a 237 * call to {@link #initCause}. 238 * 239 * <p>The {@link #fillInStackTrace()} method is called to initialize 240 * the stack trace data in the newly created throwable. 241 */ Throwable()242 public Throwable() { 243 fillInStackTrace(); 244 } 245 246 /** 247 * Constructs a new throwable with the specified detail message. The 248 * cause is not initialized, and may subsequently be initialized by 249 * a 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 * @param message the detail message. The detail message is saved for 255 * later retrieval by the {@link #getMessage()} method. 256 */ Throwable(String message)257 public Throwable(String message) { 258 fillInStackTrace(); 259 detailMessage = message; 260 } 261 262 /** 263 * Constructs a new throwable with the specified detail message and 264 * cause. <p>Note that the detail message associated with 265 * {@code cause} is <i>not</i> automatically incorporated in 266 * this throwable's detail message. 267 * 268 * <p>The {@link #fillInStackTrace()} method is called to initialize 269 * the stack trace data in the newly created throwable. 270 * 271 * @param message the detail message (which is saved for later retrieval 272 * by the {@link #getMessage()} method). 273 * @param cause the cause (which is saved for later retrieval by the 274 * {@link #getCause()} method). (A {@code null} value is 275 * permitted, and indicates that the cause is nonexistent or 276 * unknown.) 277 * @since 1.4 278 */ Throwable(String message, Throwable cause)279 public Throwable(String message, Throwable cause) { 280 fillInStackTrace(); 281 detailMessage = message; 282 this.cause = cause; 283 } 284 285 /** 286 * Constructs a new throwable with the specified cause and a detail 287 * message of {@code (cause==null ? null : cause.toString())} (which 288 * typically contains the class and detail message of {@code cause}). 289 * This constructor is useful for throwables that are little more than 290 * wrappers for other throwables (for example, {@link 291 * java.security.PrivilegedActionException}). 292 * 293 * <p>The {@link #fillInStackTrace()} method is called to initialize 294 * the stack trace data in the newly created throwable. 295 * 296 * @param cause the cause (which is saved for later retrieval by the 297 * {@link #getCause()} method). (A {@code null} value is 298 * permitted, and indicates that the cause is nonexistent or 299 * unknown.) 300 * @since 1.4 301 */ Throwable(Throwable cause)302 public Throwable(Throwable cause) { 303 fillInStackTrace(); 304 detailMessage = (cause==null ? null : cause.toString()); 305 this.cause = cause; 306 } 307 308 /** 309 * Constructs a new throwable with the specified detail message, 310 * cause, {@linkplain #addSuppressed suppression} enabled or 311 * disabled, and writable stack trace enabled or disabled. If 312 * suppression is disabled, {@link #getSuppressed} for this object 313 * will return a zero-length array and calls to {@link 314 * #addSuppressed} that would otherwise append an exception to the 315 * suppressed list will have no effect. If the writable stack 316 * trace is false, this constructor will not call {@link 317 * #fillInStackTrace()}, a {@code null} will be written to the 318 * {@code stackTrace} field, and subsequent calls to {@code 319 * fillInStackTrace} and {@link 320 * #setStackTrace(StackTraceElement[])} will not set the stack 321 * trace. If the writable stack trace is false, {@link 322 * #getStackTrace} will return a zero length array. 323 * 324 * <p>Note that the other constructors of {@code Throwable} treat 325 * suppression as being enabled and the stack trace as being 326 * writable. Subclasses of {@code Throwable} should document any 327 * conditions under which suppression is disabled and document 328 * conditions under which the stack trace is not writable. 329 * Disabling of suppression should only occur in exceptional 330 * circumstances where special requirements exist, such as a 331 * virtual machine reusing exception objects under low-memory 332 * situations. Circumstances where a given exception object is 333 * repeatedly caught and rethrown, such as to implement control 334 * flow between two sub-systems, is another situation where 335 * immutable throwable objects would be appropriate. 336 * 337 * @param message the detail message. 338 * @param cause the cause. (A {@code null} value is permitted, 339 * and indicates that the cause is nonexistent or unknown.) 340 * @param enableSuppression whether or not suppression is enabled or disabled 341 * @param writableStackTrace whether or not the stack trace should be 342 * writable 343 * 344 * @see OutOfMemoryError 345 * @see NullPointerException 346 * @see ArithmeticException 347 * @since 1.7 348 */ Throwable(String message, Throwable cause, boolean enableSuppression, boolean writableStackTrace)349 protected Throwable(String message, Throwable cause, 350 boolean enableSuppression, 351 boolean writableStackTrace) { 352 if (writableStackTrace) { 353 fillInStackTrace(); 354 } else { 355 stackTrace = null; 356 } 357 detailMessage = message; 358 this.cause = cause; 359 if (!enableSuppression) 360 suppressedExceptions = null; 361 } 362 363 /** 364 * Returns the detail message string of this throwable. 365 * 366 * @return the detail message string of this {@code Throwable} instance 367 * (which may be {@code null}). 368 */ getMessage()369 public String getMessage() { 370 return detailMessage; 371 } 372 373 /** 374 * Creates a localized description of this throwable. 375 * Subclasses may override this method in order to produce a 376 * locale-specific message. For subclasses that do not override this 377 * method, the default implementation returns the same result as 378 * {@code getMessage()}. 379 * 380 * @return The localized description of this throwable. 381 * @since JDK1.1 382 */ getLocalizedMessage()383 public String getLocalizedMessage() { 384 return getMessage(); 385 } 386 387 /** 388 * Returns the cause of this throwable or {@code null} if the 389 * cause is nonexistent or unknown. (The cause is the throwable that 390 * caused this throwable to get thrown.) 391 * 392 * <p>This implementation returns the cause that was supplied via one of 393 * the constructors requiring a {@code Throwable}, or that was set after 394 * creation with the {@link #initCause(Throwable)} method. While it is 395 * typically unnecessary to override this method, a subclass can override 396 * it to return a cause set by some other means. This is appropriate for 397 * a "legacy chained throwable" that predates the addition of chained 398 * exceptions to {@code Throwable}. Note that it is <i>not</i> 399 * necessary to override any of the {@code PrintStackTrace} methods, 400 * all of which invoke the {@code getCause} method to determine the 401 * cause of a throwable. 402 * 403 * @return the cause of this throwable or {@code null} if the 404 * cause is nonexistent or unknown. 405 * @since 1.4 406 */ getCause()407 public synchronized Throwable getCause() { 408 return (cause==this ? null : cause); 409 } 410 411 /** 412 * Initializes the <i>cause</i> of this throwable to the specified value. 413 * (The cause is the throwable that caused this throwable to get thrown.) 414 * 415 * <p>This method can be called at most once. It is generally called from 416 * within the constructor, or immediately after creating the 417 * throwable. If this throwable was created 418 * with {@link #Throwable(Throwable)} or 419 * {@link #Throwable(String,Throwable)}, this method cannot be called 420 * even once. 421 * 422 * <p>An example of using this method on a legacy throwable type 423 * without other support for setting the cause is: 424 * 425 * <pre> 426 * try { 427 * lowLevelOp(); 428 * } catch (LowLevelException le) { 429 * throw (HighLevelException) 430 * new HighLevelException().initCause(le); // Legacy constructor 431 * } 432 * </pre> 433 * 434 * @param cause the cause (which is saved for later retrieval by the 435 * {@link #getCause()} method). (A {@code null} value is 436 * permitted, and indicates that the cause is nonexistent or 437 * unknown.) 438 * @return a reference to this {@code Throwable} instance. 439 * @throws IllegalArgumentException if {@code cause} is this 440 * throwable. (A throwable cannot be its own cause.) 441 * @throws IllegalStateException if this throwable was 442 * created with {@link #Throwable(Throwable)} or 443 * {@link #Throwable(String,Throwable)}, or this method has already 444 * been called on this throwable. 445 * @since 1.4 446 */ initCause(Throwable cause)447 public synchronized Throwable initCause(Throwable cause) { 448 if (this.cause != this) 449 throw new IllegalStateException("Can't overwrite cause with " + 450 Objects.toString(cause, "a null"), this); 451 if (cause == this) 452 throw new IllegalArgumentException("Self-causation not permitted", this); 453 this.cause = cause; 454 return this; 455 } 456 457 /** 458 * Returns a short description of this throwable. 459 * The result is the concatenation of: 460 * <ul> 461 * <li> the {@linkplain Class#getName() name} of the class of this object 462 * <li> ": " (a colon and a space) 463 * <li> the result of invoking this object's {@link #getLocalizedMessage} 464 * method 465 * </ul> 466 * If {@code getLocalizedMessage} returns {@code null}, then just 467 * the class name is returned. 468 * 469 * @return a string representation of this throwable. 470 */ toString()471 public String toString() { 472 String s = getClass().getName(); 473 String message = getLocalizedMessage(); 474 return (message != null) ? (s + ": " + message) : s; 475 } 476 477 /** 478 * Prints this throwable and its backtrace to the 479 * standard error stream. This method prints a stack trace for this 480 * {@code Throwable} object on the error output stream that is 481 * the value of the field {@code System.err}. The first line of 482 * output contains the result of the {@link #toString()} method for 483 * this object. Remaining lines represent data previously recorded by 484 * the method {@link #fillInStackTrace()}. The format of this 485 * information depends on the implementation, but the following 486 * example may be regarded as typical: 487 * <blockquote><pre> 488 * java.lang.NullPointerException 489 * at MyClass.mash(MyClass.java:9) 490 * at MyClass.crunch(MyClass.java:6) 491 * at MyClass.main(MyClass.java:3) 492 * </pre></blockquote> 493 * This example was produced by running the program: 494 * <pre> 495 * class MyClass { 496 * public static void main(String[] args) { 497 * crunch(null); 498 * } 499 * static void crunch(int[] a) { 500 * mash(a); 501 * } 502 * static void mash(int[] b) { 503 * System.out.println(b[0]); 504 * } 505 * } 506 * </pre> 507 * The backtrace for a throwable with an initialized, non-null cause 508 * should generally include the backtrace for the cause. The format 509 * of this information depends on the implementation, but the following 510 * example may be regarded as typical: 511 * <pre> 512 * HighLevelException: MidLevelException: LowLevelException 513 * at Junk.a(Junk.java:13) 514 * at Junk.main(Junk.java:4) 515 * Caused by: MidLevelException: LowLevelException 516 * at Junk.c(Junk.java:23) 517 * at Junk.b(Junk.java:17) 518 * at Junk.a(Junk.java:11) 519 * ... 1 more 520 * Caused by: LowLevelException 521 * at Junk.e(Junk.java:30) 522 * at Junk.d(Junk.java:27) 523 * at Junk.c(Junk.java:21) 524 * ... 3 more 525 * </pre> 526 * Note the presence of lines containing the characters {@code "..."}. 527 * These lines indicate that the remainder of the stack trace for this 528 * exception matches the indicated number of frames from the bottom of the 529 * stack trace of the exception that was caused by this exception (the 530 * "enclosing" exception). This shorthand can greatly reduce the length 531 * of the output in the common case where a wrapped exception is thrown 532 * from same method as the "causative exception" is caught. The above 533 * example was produced by running the program: 534 * <pre> 535 * public class Junk { 536 * public static void main(String args[]) { 537 * try { 538 * a(); 539 * } catch(HighLevelException e) { 540 * e.printStackTrace(); 541 * } 542 * } 543 * static void a() throws HighLevelException { 544 * try { 545 * b(); 546 * } catch(MidLevelException e) { 547 * throw new HighLevelException(e); 548 * } 549 * } 550 * static void b() throws MidLevelException { 551 * c(); 552 * } 553 * static void c() throws MidLevelException { 554 * try { 555 * d(); 556 * } catch(LowLevelException e) { 557 * throw new MidLevelException(e); 558 * } 559 * } 560 * static void d() throws LowLevelException { 561 * e(); 562 * } 563 * static void e() throws LowLevelException { 564 * throw new LowLevelException(); 565 * } 566 * } 567 * 568 * class HighLevelException extends Exception { 569 * HighLevelException(Throwable cause) { super(cause); } 570 * } 571 * 572 * class MidLevelException extends Exception { 573 * MidLevelException(Throwable cause) { super(cause); } 574 * } 575 * 576 * class LowLevelException extends Exception { 577 * } 578 * </pre> 579 * As of release 7, the platform supports the notion of 580 * <i>suppressed exceptions</i> (in conjunction with the {@code 581 * try}-with-resources statement). Any exceptions that were 582 * suppressed in order to deliver an exception are printed out 583 * beneath the stack trace. The format of this information 584 * depends on the implementation, but the following example may be 585 * regarded as typical: 586 * 587 * <pre> 588 * Exception in thread "main" java.lang.Exception: Something happened 589 * at Foo.bar(Foo.java:10) 590 * at Foo.main(Foo.java:5) 591 * Suppressed: Resource$CloseFailException: Resource ID = 0 592 * at Resource.close(Resource.java:26) 593 * at Foo.bar(Foo.java:9) 594 * ... 1 more 595 * </pre> 596 * Note that the "... n more" notation is used on suppressed exceptions 597 * just at it is used on causes. Unlike causes, suppressed exceptions are 598 * indented beyond their "containing exceptions." 599 * 600 * <p>An exception can have both a cause and one or more suppressed 601 * exceptions: 602 * <pre> 603 * Exception in thread "main" java.lang.Exception: Main block 604 * at Foo3.main(Foo3.java:7) 605 * Suppressed: Resource$CloseFailException: Resource ID = 2 606 * at Resource.close(Resource.java:26) 607 * at Foo3.main(Foo3.java:5) 608 * Suppressed: Resource$CloseFailException: Resource ID = 1 609 * at Resource.close(Resource.java:26) 610 * at Foo3.main(Foo3.java:5) 611 * Caused by: java.lang.Exception: I did it 612 * at Foo3.main(Foo3.java:8) 613 * </pre> 614 * Likewise, a suppressed exception can have a cause: 615 * <pre> 616 * Exception in thread "main" java.lang.Exception: Main block 617 * at Foo4.main(Foo4.java:6) 618 * Suppressed: Resource2$CloseFailException: Resource ID = 1 619 * at Resource2.close(Resource2.java:20) 620 * at Foo4.main(Foo4.java:5) 621 * Caused by: java.lang.Exception: Rats, you caught me 622 * at Resource2$CloseFailException.<init>(Resource2.java:45) 623 * ... 2 more 624 * </pre> 625 */ printStackTrace()626 public void printStackTrace() { 627 printStackTrace(System.err); 628 } 629 630 /** 631 * Prints this throwable and its backtrace to the specified print stream. 632 * 633 * @param s {@code PrintStream} to use for output 634 */ printStackTrace(PrintStream s)635 public void printStackTrace(PrintStream s) { 636 printStackTrace(new WrappedPrintStream(s)); 637 } 638 printStackTrace(PrintStreamOrWriter s)639 private void printStackTrace(PrintStreamOrWriter s) { 640 // Guard against malicious overrides of Throwable.equals by 641 // using a Set with identity equality semantics. 642 Set<Throwable> dejaVu = 643 Collections.newSetFromMap(new IdentityHashMap<Throwable, Boolean>()); 644 dejaVu.add(this); 645 646 synchronized (s.lock()) { 647 // Print our stack trace 648 s.println(this); 649 StackTraceElement[] trace = getOurStackTrace(); 650 for (StackTraceElement traceElement : trace) 651 s.println("\tat " + traceElement); 652 653 // Print suppressed exceptions, if any 654 for (Throwable se : getSuppressed()) 655 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, "\t", dejaVu); 656 657 // Print cause, if any 658 Throwable ourCause = getCause(); 659 if (ourCause != null) 660 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, "", dejaVu); 661 } 662 } 663 664 /** 665 * Print our stack trace as an enclosed exception for the specified 666 * stack trace. 667 */ printEnclosedStackTrace(PrintStreamOrWriter s, StackTraceElement[] enclosingTrace, String caption, String prefix, Set<Throwable> dejaVu)668 private void printEnclosedStackTrace(PrintStreamOrWriter s, 669 StackTraceElement[] enclosingTrace, 670 String caption, 671 String prefix, 672 Set<Throwable> dejaVu) { 673 if (dejaVu.contains(this)) { 674 s.println("\t[CIRCULAR REFERENCE:" + this + "]"); 675 } else { 676 dejaVu.add(this); 677 // Compute number of frames in common between this and enclosing trace 678 StackTraceElement[] trace = getOurStackTrace(); 679 int m = trace.length - 1; 680 int n = enclosingTrace.length - 1; 681 while (m >= 0 && n >=0 && trace[m].equals(enclosingTrace[n])) { 682 m--; n--; 683 } 684 int framesInCommon = trace.length - 1 - m; 685 686 // Print our stack trace 687 s.println(prefix + caption + this); 688 for (int i = 0; i <= m; i++) 689 s.println(prefix + "\tat " + trace[i]); 690 if (framesInCommon != 0) 691 s.println(prefix + "\t... " + framesInCommon + " more"); 692 693 // Print suppressed exceptions, if any 694 for (Throwable se : getSuppressed()) 695 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, 696 prefix +"\t", dejaVu); 697 698 // Print cause, if any 699 Throwable ourCause = getCause(); 700 if (ourCause != null) 701 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, prefix, dejaVu); 702 } 703 } 704 705 /** 706 * Prints this throwable and its backtrace to the specified 707 * print writer. 708 * 709 * @param s {@code PrintWriter} to use for output 710 * @since JDK1.1 711 */ printStackTrace(PrintWriter s)712 public void printStackTrace(PrintWriter s) { 713 printStackTrace(new WrappedPrintWriter(s)); 714 } 715 716 /** 717 * Wrapper class for PrintStream and PrintWriter to enable a single 718 * implementation of printStackTrace. 719 */ 720 private abstract static class PrintStreamOrWriter { 721 /** Returns the object to be locked when using this StreamOrWriter */ lock()722 abstract Object lock(); 723 724 /** Prints the specified string as a line on this StreamOrWriter */ println(Object o)725 abstract void println(Object o); 726 } 727 728 private static class WrappedPrintStream extends PrintStreamOrWriter { 729 private final PrintStream printStream; 730 WrappedPrintStream(PrintStream printStream)731 WrappedPrintStream(PrintStream printStream) { 732 this.printStream = printStream; 733 } 734 lock()735 Object lock() { 736 return printStream; 737 } 738 println(Object o)739 void println(Object o) { 740 printStream.println(o); 741 } 742 } 743 744 private static class WrappedPrintWriter extends PrintStreamOrWriter { 745 private final PrintWriter printWriter; 746 WrappedPrintWriter(PrintWriter printWriter)747 WrappedPrintWriter(PrintWriter printWriter) { 748 this.printWriter = printWriter; 749 } 750 lock()751 Object lock() { 752 return printWriter; 753 } 754 println(Object o)755 void println(Object o) { 756 printWriter.println(o); 757 } 758 } 759 760 /** 761 * Fills in the execution stack trace. This method records within this 762 * {@code Throwable} object information about the current state of 763 * the stack frames for the current thread. 764 * 765 * <p>If the stack trace of this {@code Throwable} {@linkplain 766 * Throwable#Throwable(String, Throwable, boolean, boolean) is not 767 * writable}, calling this method has no effect. 768 * 769 * @return a reference to this {@code Throwable} instance. 770 * @see java.lang.Throwable#printStackTrace() 771 */ fillInStackTrace()772 public synchronized Throwable fillInStackTrace() { 773 if (stackTrace != null || 774 backtrace != null /* Out of protocol state */ ) { 775 backtrace = nativeFillInStackTrace(); 776 stackTrace = libcore.util.EmptyArray.STACK_TRACE_ELEMENT; 777 } 778 return this; 779 } 780 781 @FastNative nativeFillInStackTrace()782 private static native Object nativeFillInStackTrace(); 783 784 /** 785 * Provides programmatic access to the stack trace information printed by 786 * {@link #printStackTrace()}. Returns an array of stack trace elements, 787 * each representing one stack frame. The zeroth element of the array 788 * (assuming the array's length is non-zero) represents the top of the 789 * stack, which is the last method invocation in the sequence. Typically, 790 * this is the point at which this throwable was created and thrown. 791 * The last element of the array (assuming the array's length is non-zero) 792 * represents the bottom of the stack, which is the first method invocation 793 * in the sequence. 794 * 795 * <p>Some virtual machines may, under some circumstances, omit one 796 * or more stack frames from the stack trace. In the extreme case, 797 * a virtual machine that has no stack trace information concerning 798 * this throwable is permitted to return a zero-length array from this 799 * method. Generally speaking, the array returned by this method will 800 * contain one element for every frame that would be printed by 801 * {@code printStackTrace}. Writes to the returned array do not 802 * affect future calls to this method. 803 * 804 * @return an array of stack trace elements representing the stack trace 805 * pertaining to this throwable. 806 * @since 1.4 807 */ getStackTrace()808 public StackTraceElement[] getStackTrace() { 809 return getOurStackTrace().clone(); 810 } 811 getOurStackTrace()812 private synchronized StackTraceElement[] getOurStackTrace() { 813 // Initialize stack trace field with information from 814 // backtrace if this is the first call to this method 815 // 816 // Android-changed: test explicitly for equality with 817 // STACK_TRACE_ELEMENT 818 if (stackTrace == libcore.util.EmptyArray.STACK_TRACE_ELEMENT || 819 (stackTrace == null && backtrace != null) /* Out of protocol state */) { 820 stackTrace = nativeGetStackTrace(backtrace); 821 backtrace = null; 822 } 823 824 // Android-changed: Return an empty element both when the stack trace 825 // isn't writeable and also when nativeGetStackTrace returns null. 826 if (stackTrace == null) { 827 return libcore.util.EmptyArray.STACK_TRACE_ELEMENT; 828 } 829 830 return stackTrace; 831 } 832 833 /** 834 * Sets the stack trace elements that will be returned by 835 * {@link #getStackTrace()} and printed by {@link #printStackTrace()} 836 * and related methods. 837 * 838 * This method, which is designed for use by RPC frameworks and other 839 * advanced systems, allows the client to override the default 840 * stack trace that is either generated by {@link #fillInStackTrace()} 841 * when a throwable is constructed or deserialized when a throwable is 842 * read from a serialization stream. 843 * 844 * <p>If the stack trace of this {@code Throwable} {@linkplain 845 * Throwable#Throwable(String, Throwable, boolean, boolean) is not 846 * writable}, calling this method has no effect other than 847 * validating its argument. 848 * 849 * @param stackTrace the stack trace elements to be associated with 850 * this {@code Throwable}. The specified array is copied by this 851 * call; changes in the specified array after the method invocation 852 * returns will have no affect on this {@code Throwable}'s stack 853 * trace. 854 * 855 * @throws NullPointerException if {@code stackTrace} is 856 * {@code null} or if any of the elements of 857 * {@code stackTrace} are {@code null} 858 * 859 * @since 1.4 860 */ setStackTrace(StackTraceElement[] stackTrace)861 public void setStackTrace(StackTraceElement[] stackTrace) { 862 // Validate argument 863 StackTraceElement[] defensiveCopy = stackTrace.clone(); 864 for (int i = 0; i < defensiveCopy.length; i++) { 865 if (defensiveCopy[i] == null) 866 throw new NullPointerException("stackTrace[" + i + "]"); 867 } 868 869 synchronized (this) { 870 if (this.stackTrace == null && // Immutable stack 871 backtrace == null) // Test for out of protocol state 872 return; 873 this.stackTrace = defensiveCopy; 874 } 875 } 876 877 /** 878 * Returns the specified element of the stack trace. 879 * 880 * package-protection for use by SharedSecrets. 881 * 882 * @param index index of the element to return. 883 * @throws IndexOutOfBoundsException if {@code index < 0 || 884 * index >= getStackTraceDepth() } 885 */ 886 @FastNative nativeGetStackTrace(Object stackState)887 private static native StackTraceElement[] nativeGetStackTrace(Object stackState); 888 889 890 /** 891 * Reads a {@code Throwable} from a stream, enforcing 892 * well-formedness constraints on fields. Null entries and 893 * self-pointers are not allowed in the list of {@code 894 * suppressedExceptions}. Null entries are not allowed for stack 895 * trace elements. A null stack trace in the serial form results 896 * in a zero-length stack element array. A single-element stack 897 * trace whose entry is equal to {@code new StackTraceElement("", 898 * "", null, Integer.MIN_VALUE)} results in a {@code null} {@code 899 * stackTrace} field. 900 * 901 * Note that there are no constraints on the value the {@code 902 * cause} field can hold; both {@code null} and {@code this} are 903 * valid values for the field. 904 */ readObject(ObjectInputStream s)905 private void readObject(ObjectInputStream s) 906 throws IOException, ClassNotFoundException { 907 s.defaultReadObject(); // read in all fields 908 if (suppressedExceptions != null) { 909 List<Throwable> suppressed = null; 910 if (suppressedExceptions.isEmpty()) { 911 // Use the sentinel for a zero-length list 912 suppressed = Collections.emptyList(); 913 } else { // Copy Throwables to new list 914 suppressed = new ArrayList<>(1); 915 for (Throwable t : suppressedExceptions) { 916 // Enforce constraints on suppressed exceptions in 917 // case of corrupt or malicious stream. 918 if (t == null) 919 throw new NullPointerException(NULL_CAUSE_MESSAGE); 920 if (t == this) 921 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE); 922 suppressed.add(t); 923 } 924 } 925 suppressedExceptions = suppressed; 926 } // else a null suppressedExceptions field remains null 927 928 /* 929 * For zero-length stack traces, use a clone of 930 * UNASSIGNED_STACK rather than UNASSIGNED_STACK itself to 931 * allow identity comparison against UNASSIGNED_STACK in 932 * getOurStackTrace. The identity of UNASSIGNED_STACK in 933 * stackTrace indicates to the getOurStackTrace method that 934 * the stackTrace needs to be constructed from the information 935 * in backtrace. 936 */ 937 if (stackTrace != null) { 938 if (stackTrace.length == 0) { 939 } else if (stackTrace.length == 1 && 940 // Check for the marker of an immutable stack trace 941 SentinelHolder.STACK_TRACE_ELEMENT_SENTINEL.equals(stackTrace[0])) { 942 stackTrace = null; 943 } else { // Verify stack trace elements are non-null. 944 for(StackTraceElement ste : stackTrace) { 945 if (ste == null) 946 throw new NullPointerException("null StackTraceElement in serial stream. "); 947 } 948 } 949 } else { 950 // A null stackTrace field in the serial form can result 951 // from an exception serialized without that field in 952 // older JDK releases; treat such exceptions as having 953 // empty stack traces. 954 stackTrace = new StackTraceElement[0]; 955 } 956 } 957 958 /** 959 * Write a {@code Throwable} object to a stream. 960 * 961 * A {@code null} stack trace field is represented in the serial 962 * form as a one-element array whose element is equal to {@code 963 * new StackTraceElement("", "", null, Integer.MIN_VALUE)}. 964 */ writeObject(ObjectOutputStream s)965 private synchronized void writeObject(ObjectOutputStream s) 966 throws IOException { 967 // Ensure that the stackTrace field is initialized to a 968 // non-null value, if appropriate. As of JDK 7, a null stack 969 // trace field is a valid value indicating the stack trace 970 // should not be set. 971 getOurStackTrace(); 972 973 StackTraceElement[] oldStackTrace = stackTrace; 974 try { 975 if (stackTrace == null) 976 stackTrace = SentinelHolder.STACK_TRACE_SENTINEL; 977 s.defaultWriteObject(); 978 } finally { 979 stackTrace = oldStackTrace; 980 } 981 } 982 983 /** 984 * Appends the specified exception to the exceptions that were 985 * suppressed in order to deliver this exception. This method is 986 * thread-safe and typically called (automatically and implicitly) 987 * by the {@code try}-with-resources statement. 988 * 989 * <p>The suppression behavior is enabled <em>unless</em> disabled 990 * {@linkplain #Throwable(String, Throwable, boolean, boolean) via 991 * a constructor}. When suppression is disabled, this method does 992 * nothing other than to validate its argument. 993 * 994 * <p>Note that when one exception {@linkplain 995 * #initCause(Throwable) causes} another exception, the first 996 * exception is usually caught and then the second exception is 997 * thrown in response. In other words, there is a causal 998 * connection between the two exceptions. 999 * 1000 * In contrast, there are situations where two independent 1001 * exceptions can be thrown in sibling code blocks, in particular 1002 * in the {@code try} block of a {@code try}-with-resources 1003 * statement and the compiler-generated {@code finally} block 1004 * which closes the resource. 1005 * 1006 * In these situations, only one of the thrown exceptions can be 1007 * propagated. In the {@code try}-with-resources statement, when 1008 * there are two such exceptions, the exception originating from 1009 * the {@code try} block is propagated and the exception from the 1010 * {@code finally} block is added to the list of exceptions 1011 * suppressed by the exception from the {@code try} block. As an 1012 * exception unwinds the stack, it can accumulate multiple 1013 * suppressed exceptions. 1014 * 1015 * <p>An exception may have suppressed exceptions while also being 1016 * caused by another exception. Whether or not an exception has a 1017 * cause is semantically known at the time of its creation, unlike 1018 * whether or not an exception will suppress other exceptions 1019 * which is typically only determined after an exception is 1020 * thrown. 1021 * 1022 * <p>Note that programmer written code is also able to take 1023 * advantage of calling this method in situations where there are 1024 * multiple sibling exceptions and only one can be propagated. 1025 * 1026 * @param exception the exception to be added to the list of 1027 * suppressed exceptions 1028 * @throws IllegalArgumentException if {@code exception} is this 1029 * throwable; a throwable cannot suppress itself. 1030 * @throws NullPointerException if {@code exception} is {@code null} 1031 * @since 1.7 1032 */ addSuppressed(Throwable exception)1033 public final synchronized void addSuppressed(Throwable exception) { 1034 if (exception == this) 1035 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE, exception); 1036 1037 if (exception == null) 1038 throw new NullPointerException(NULL_CAUSE_MESSAGE); 1039 1040 if (suppressedExceptions == null) // Suppressed exceptions not recorded 1041 return; 1042 1043 if (suppressedExceptions.isEmpty()) 1044 suppressedExceptions = new ArrayList<>(1); 1045 1046 suppressedExceptions.add(exception); 1047 } 1048 1049 private static Throwable[] EMPTY_THROWABLE_ARRAY; 1050 1051 /** 1052 * Returns an array containing all of the exceptions that were 1053 * suppressed, typically by the {@code try}-with-resources 1054 * statement, in order to deliver this exception. 1055 * 1056 * If no exceptions were suppressed or {@linkplain 1057 * #Throwable(String, Throwable, boolean, boolean) suppression is 1058 * disabled}, an empty array is returned. This method is 1059 * thread-safe. Writes to the returned array do not affect future 1060 * calls to this method. 1061 * 1062 * @return an array containing all of the exceptions that were 1063 * suppressed to deliver this exception. 1064 * @since 1.7 1065 */ getSuppressed()1066 public final synchronized Throwable[] getSuppressed() { 1067 if (EMPTY_THROWABLE_ARRAY == null) { 1068 EMPTY_THROWABLE_ARRAY = new Throwable[0]; 1069 } 1070 1071 if (suppressedExceptions == null || suppressedExceptions.isEmpty()) 1072 return EMPTY_THROWABLE_ARRAY; 1073 else 1074 return suppressedExceptions.toArray(EMPTY_THROWABLE_ARRAY); 1075 } 1076 } 1077