Source code

001/*
002 * Copyright (C) 2007 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
005 * in compliance with the License. You may obtain a copy of the License at
006 *
007 * http://www.apache.org/licenses/LICENSE-2.0
008 *
009 * Unless required by applicable law or agreed to in writing, software distributed under the License
010 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
011 * or implied. See the License for the specific language governing permissions and limitations under
012 * the License.
013 */
014
015package com.google.common.base;
016
017import static com.google.common.base.Preconditions.checkNotNull;
018import static java.util.Arrays.asList;
019import static java.util.Collections.unmodifiableList;
020import static java.util.Objects.requireNonNull;
021
022import com.google.common.annotations.GwtCompatible;
023import com.google.common.annotations.GwtIncompatible;
024import com.google.common.annotations.VisibleForTesting;
025import com.google.errorprone.annotations.CanIgnoreReturnValue;
026import java.io.IOException;
027import java.io.PrintWriter;
028import java.io.StringWriter;
029import java.lang.reflect.InvocationTargetException;
030import java.lang.reflect.Method;
031import java.util.AbstractList;
032import java.util.ArrayList;
033import java.util.Collections;
034import java.util.List;
035import javax.annotation.CheckForNull;
036
037/**
038 * Static utility methods pertaining to instances of {@link Throwable}.
039 *
040 * <p>See the Guava User Guide entry on <a
041 * href="https://github.com/google/guava/wiki/ThrowablesExplained">Throwables</a>.
042 *
043 * @author Kevin Bourrillion
044 * @author Ben Yu
045 * @since 1.0
046 */
047@GwtCompatible(emulated = true)
048@ElementTypesAreNonnullByDefault
049public final class Throwables {
050  private Throwables() {}
051
052  /**
053   * Throws {@code throwable} if it is an instance of {@code declaredType}. Example usage:
054   *
055   * <pre>
056   * for (Foo foo : foos) {
057   *   try {
058   *     foo.bar();
059   *   } catch (BarException | RuntimeException | Error t) {
060   *     failure = t;
061   *   }
062   * }
063   * if (failure != null) {
064   *   throwIfInstanceOf(failure, BarException.class);
065   *   throwIfUnchecked(failure);
066   *   throw new AssertionError(failure);
067   * }
068   * </pre>
069   *
070   * @since 20.0
071   */
072  @GwtIncompatible // Class.cast, Class.isInstance
073  public static <X extends Throwable> void throwIfInstanceOf(
074      Throwable throwable, Class<X> declaredType) throws X {
075    checkNotNull(throwable);
076    if (declaredType.isInstance(throwable)) {
077      throw declaredType.cast(throwable);
078    }
079  }
080
081  /**
082   * Propagates {@code throwable} exactly as-is, if and only if it is an instance of {@code
083   * declaredType}. Example usage:
084   *
085   * <pre>
086   * try {
087   *   someMethodThatCouldThrowAnything();
088   * } catch (IKnowWhatToDoWithThisException e) {
089   *   handle(e);
090   * } catch (Throwable t) {
091   *   Throwables.propagateIfInstanceOf(t, IOException.class);
092   *   Throwables.propagateIfInstanceOf(t, SQLException.class);
093   *   throw Throwables.propagate(t);
094   * }
095   * </pre>
096   *
097   * @deprecated Use {@link #throwIfInstanceOf}, which has the same behavior but rejects {@code
098   *     null}.
099   */
100  @Deprecated
101  @GwtIncompatible // throwIfInstanceOf
102  public static <X extends Throwable> void propagateIfInstanceOf(
103      @CheckForNull Throwable throwable, Class<X> declaredType) throws X {
104    if (throwable != null) {
105      throwIfInstanceOf(throwable, declaredType);
106    }
107  }
108
109  /**
110   * Throws {@code throwable} if it is a {@link RuntimeException} or {@link Error}. Example usage:
111   *
112   * <pre>
113   * for (Foo foo : foos) {
114   *   try {
115   *     foo.bar();
116   *   } catch (RuntimeException | Error t) {
117   *     failure = t;
118   *   }
119   * }
120   * if (failure != null) {
121   *   throwIfUnchecked(failure);
122   *   throw new AssertionError(failure);
123   * }
124   * </pre>
125   *
126   * @since 20.0
127   */
128  public static void throwIfUnchecked(Throwable throwable) {
129    checkNotNull(throwable);
130    if (throwable instanceof RuntimeException) {
131      throw (RuntimeException) throwable;
132    }
133    if (throwable instanceof Error) {
134      throw (Error) throwable;
135    }
136  }
137
138  /**
139   * Propagates {@code throwable} exactly as-is, if and only if it is an instance of {@link
140   * RuntimeException} or {@link Error}. Example usage:
141   *
142   * <pre>
143   * try {
144   *   someMethodThatCouldThrowAnything();
145   * } catch (IKnowWhatToDoWithThisException e) {
146   *   handle(e);
147   * } catch (Throwable t) {
148   *   Throwables.propagateIfPossible(t);
149   *   throw new RuntimeException("unexpected", t);
150   * }
151   * </pre>
152   *
153   * @deprecated Use {@link #throwIfUnchecked}, which has the same behavior but rejects {@code
154   *     null}.
155   */
156  @Deprecated
157  @GwtIncompatible
158  public static void propagateIfPossible(@CheckForNull Throwable throwable) {
159    if (throwable != null) {
160      throwIfUnchecked(throwable);
161    }
162  }
163
164  /**
165   * Propagates {@code throwable} exactly as-is, if and only if it is an instance of {@link
166   * RuntimeException}, {@link Error}, or {@code declaredType}. Example usage:
167   *
168   * <pre>
169   * try {
170   *   someMethodThatCouldThrowAnything();
171   * } catch (IKnowWhatToDoWithThisException e) {
172   *   handle(e);
173   * } catch (Throwable t) {
174   *   Throwables.propagateIfPossible(t, OtherException.class);
175   *   throw new RuntimeException("unexpected", t);
176   * }
177   * </pre>
178   *
179   * @param throwable the Throwable to possibly propagate
180   * @param declaredType the single checked exception type declared by the calling method
181   */
182  @GwtIncompatible // propagateIfInstanceOf
183  public static <X extends Throwable> void propagateIfPossible(
184      @CheckForNull Throwable throwable, Class<X> declaredType) throws X {
185    propagateIfInstanceOf(throwable, declaredType);
186    propagateIfPossible(throwable);
187  }
188
189  /**
190   * Propagates {@code throwable} exactly as-is, if and only if it is an instance of {@link
191   * RuntimeException}, {@link Error}, {@code declaredType1}, or {@code declaredType2}. In the
192   * unlikely case that you have three or more declared checked exception types, you can handle them
193   * all by invoking these methods repeatedly. See usage example in {@link
194   * #propagateIfPossible(Throwable, Class)}.
195   *
196   * @param throwable the Throwable to possibly propagate
197   * @param declaredType1 any checked exception type declared by the calling method
198   * @param declaredType2 any other checked exception type declared by the calling method
199   */
200  @GwtIncompatible // propagateIfInstanceOf
201  public static <X1 extends Throwable, X2 extends Throwable> void propagateIfPossible(
202      @CheckForNull Throwable throwable, Class<X1> declaredType1, Class<X2> declaredType2)
203      throws X1, X2 {
204    checkNotNull(declaredType2);
205    propagateIfInstanceOf(throwable, declaredType1);
206    propagateIfPossible(throwable, declaredType2);
207  }
208
209  /**
210   * Propagates {@code throwable} as-is if it is an instance of {@link RuntimeException} or {@link
211   * Error}, or else as a last resort, wraps it in a {@code RuntimeException} and then propagates.
212   *
213   * <p>This method always throws an exception. The {@code RuntimeException} return type allows
214   * client code to signal to the compiler that statements after the call are unreachable. Example
215   * usage:
216   *
217   * <pre>
218   * T doSomething() {
219   *   try {
220   *     return someMethodThatCouldThrowAnything();
221   *   } catch (IKnowWhatToDoWithThisException e) {
222   *     return handle(e);
223   *   } catch (Throwable t) {
224   *     throw Throwables.propagate(t);
225   *   }
226   * }
227   * </pre>
228   *
229   * @param throwable the Throwable to propagate
230   * @return nothing will ever be returned; this return type is only for your convenience, as
231   *     illustrated in the example above
232   * @deprecated Use {@code throw e} or {@code throw new RuntimeException(e)} directly, or use a
233   *     combination of {@link #throwIfUnchecked} and {@code throw new RuntimeException(e)}. For
234   *     background on the deprecation, read <a href="https://goo.gl/Ivn2kc">Why we deprecated
235   *     {@code Throwables.propagate}</a>.
236   */
237  @CanIgnoreReturnValue
238  @GwtIncompatible
239  @Deprecated
240  public static RuntimeException propagate(Throwable throwable) {
241    throwIfUnchecked(throwable);
242    throw new RuntimeException(throwable);
243  }
244
245  /**
246   * Returns the innermost cause of {@code throwable}. The first throwable in a chain provides
247   * context from when the error or exception was initially detected. Example usage:
248   *
249   * <pre>
250   * assertEquals("Unable to assign a customer id", Throwables.getRootCause(e).getMessage());
251   * </pre>
252   *
253   * @throws IllegalArgumentException if there is a loop in the causal chain
254   */
255  public static Throwable getRootCause(Throwable throwable) {
256    // Keep a second pointer that slowly walks the causal chain. If the fast pointer ever catches
257    // the slower pointer, then there's a loop.
258    Throwable slowPointer = throwable;
259    boolean advanceSlowPointer = false;
260
261    Throwable cause;
262    while ((cause = throwable.getCause()) != null) {
263      throwable = cause;
264
265      if (throwable == slowPointer) {
266        throw new IllegalArgumentException("Loop in causal chain detected.", throwable);
267      }
268      if (advanceSlowPointer) {
269        slowPointer = slowPointer.getCause();
270      }
271      advanceSlowPointer = !advanceSlowPointer; // only advance every other iteration
272    }
273    return throwable;
274  }
275
276  /**
277   * Gets a {@code Throwable} cause chain as a list. The first entry in the list will be {@code
278   * throwable} followed by its cause hierarchy. Note that this is a snapshot of the cause chain and
279   * will not reflect any subsequent changes to the cause chain.
280   *
281   * <p>Here's an example of how it can be used to find specific types of exceptions in the cause
282   * chain:
283   *
284   * <pre>
285   * Iterables.filter(Throwables.getCausalChain(e), IOException.class));
286   * </pre>
287   *
288   * @param throwable the non-null {@code Throwable} to extract causes from
289   * @return an unmodifiable list containing the cause chain starting with {@code throwable}
290   * @throws IllegalArgumentException if there is a loop in the causal chain
291   */
292  public static List<Throwable> getCausalChain(Throwable throwable) {
293    checkNotNull(throwable);
294    List<Throwable> causes = new ArrayList<>(4);
295    causes.add(throwable);
296
297    // Keep a second pointer that slowly walks the causal chain. If the fast pointer ever catches
298    // the slower pointer, then there's a loop.
299    Throwable slowPointer = throwable;
300    boolean advanceSlowPointer = false;
301
302    Throwable cause;
303    while ((cause = throwable.getCause()) != null) {
304      throwable = cause;
305      causes.add(throwable);
306
307      if (throwable == slowPointer) {
308        throw new IllegalArgumentException("Loop in causal chain detected.", throwable);
309      }
310      if (advanceSlowPointer) {
311        slowPointer = slowPointer.getCause();
312      }
313      advanceSlowPointer = !advanceSlowPointer; // only advance every other iteration
314    }
315    return Collections.unmodifiableList(causes);
316  }
317
318  /**
319   * Returns {@code throwable}'s cause, cast to {@code expectedCauseType}.
320   *
321   * <p>Prefer this method instead of manually casting an exception's cause. For example, {@code
322   * (IOException) e.getCause()} throws a {@link ClassCastException} that discards the original
323   * exception {@code e} if the cause is not an {@link IOException}, but {@code
324   * Throwables.getCauseAs(e, IOException.class)} keeps {@code e} as the {@link
325   * ClassCastException}'s cause.
326   *
327   * @throws ClassCastException if the cause cannot be cast to the expected type. The {@code
328   *     ClassCastException}'s cause is {@code throwable}.
329   * @since 22.0
330   */
331  @GwtIncompatible // Class.cast(Object)
332  @CheckForNull
333  public static <X extends Throwable> X getCauseAs(
334      Throwable throwable, Class<X> expectedCauseType) {
335    try {
336      return expectedCauseType.cast(throwable.getCause());
337    } catch (ClassCastException e) {
338      e.initCause(throwable);
339      throw e;
340    }
341  }
342
343  /**
344   * Returns a string containing the result of {@link Throwable#toString() toString()}, followed by
345   * the full, recursive stack trace of {@code throwable}. Note that you probably should not be
346   * parsing the resulting string; if you need programmatic access to the stack frames, you can call
347   * {@link Throwable#getStackTrace()}.
348   */
349  @GwtIncompatible // java.io.PrintWriter, java.io.StringWriter
350  public static String getStackTraceAsString(Throwable throwable) {
351    StringWriter stringWriter = new StringWriter();
352    throwable.printStackTrace(new PrintWriter(stringWriter));
353    return stringWriter.toString();
354  }
355
356  /**
357   * Returns the stack trace of {@code throwable}, possibly providing slower iteration over the full
358   * trace but faster iteration over parts of the trace. Here, "slower" and "faster" are defined in
359   * comparison to the normal way to access the stack trace, {@link Throwable#getStackTrace()
360   * throwable.getStackTrace()}. Note, however, that this method's special implementation is not
361   * available for all platforms and configurations. If that implementation is unavailable, this
362   * method falls back to {@code getStackTrace}. Callers that require the special implementation can
363   * check its availability with {@link #lazyStackTraceIsLazy()}.
364   *
365   * <p>The expected (but not guaranteed) performance of the special implementation differs from
366   * {@code getStackTrace} in one main way: The {@code lazyStackTrace} call itself returns quickly
367   * by delaying the per-stack-frame work until each element is accessed. Roughly speaking:
368   *
369   * <ul>
370   *   <li>{@code getStackTrace} takes {@code stackSize} time to return but then negligible time to
371   *       retrieve each element of the returned list.
372   *   <li>{@code lazyStackTrace} takes negligible time to return but then {@code 1/stackSize} time
373   *       to retrieve each element of the returned list (probably slightly more than {@code
374   *       1/stackSize}).
375   * </ul>
376   *
377   * <p>Note: The special implementation does not respect calls to {@link Throwable#setStackTrace
378   * throwable.setStackTrace}. Instead, it always reflects the original stack trace from the
379   * exception's creation.
380   *
381   * @since 19.0
382   * @deprecated This method is equivalent to {@link Throwable#getStackTrace()} on JDK versions past
383   *     JDK 8 and on all Android versions. Use {@link Throwable#getStackTrace()} directly, or where
384   *     possible use the {@code java.lang.StackWalker.walk} method introduced in JDK 9.
385   */
386  @Deprecated
387  @GwtIncompatible // lazyStackTraceIsLazy, jlaStackTrace
388  public static List<StackTraceElement> lazyStackTrace(Throwable throwable) {
389    return lazyStackTraceIsLazy()
390        ? jlaStackTrace(throwable)
391        : unmodifiableList(asList(throwable.getStackTrace()));
392  }
393
394  /**
395   * Returns whether {@link #lazyStackTrace} will use the special implementation described in its
396   * documentation.
397   *
398   * @since 19.0
399   * @deprecated This method always returns false on JDK versions past JDK 8 and on all Android
400   *     versions.
401   */
402  @Deprecated
403  @GwtIncompatible // getStackTraceElementMethod
404  public static boolean lazyStackTraceIsLazy() {
405    return getStackTraceElementMethod != null && getStackTraceDepthMethod != null;
406  }
407
408  @GwtIncompatible // invokeAccessibleNonThrowingMethod
409  private static List<StackTraceElement> jlaStackTrace(Throwable t) {
410    checkNotNull(t);
411    /*
412     * TODO(cpovirk): Consider optimizing iterator() to catch IOOBE instead of doing bounds checks.
413     *
414     * TODO(cpovirk): Consider the UnsignedBytes pattern if it performs faster and doesn't cause
415     * AOSP grief.
416     */
417    return new AbstractList<StackTraceElement>() {
418      /*
419       * The following requireNonNull calls are safe because we use jlaStackTrace() only if
420       * lazyStackTraceIsLazy() returns true.
421       */
422      @Override
423      public StackTraceElement get(int n) {
424        return (StackTraceElement)
425            invokeAccessibleNonThrowingMethod(
426                requireNonNull(getStackTraceElementMethod), requireNonNull(jla), t, n);
427      }
428
429      @Override
430      public int size() {
431        return (Integer)
432            invokeAccessibleNonThrowingMethod(
433                requireNonNull(getStackTraceDepthMethod), requireNonNull(jla), t);
434      }
435    };
436  }
437
438  @GwtIncompatible // java.lang.reflect
439  private static Object invokeAccessibleNonThrowingMethod(
440      Method method, Object receiver, Object... params) {
441    try {
442      return method.invoke(receiver, params);
443    } catch (IllegalAccessException e) {
444      throw new RuntimeException(e);
445    } catch (InvocationTargetException e) {
446      throw propagate(e.getCause());
447    }
448  }
449
450  /** JavaLangAccess class name to load using reflection */
451  @GwtIncompatible // not used by GWT emulation
452  private static final String JAVA_LANG_ACCESS_CLASSNAME = "sun.misc.JavaLangAccess";
453
454  /** SharedSecrets class name to load using reflection */
455  @GwtIncompatible // not used by GWT emulation
456  @VisibleForTesting
457  static final String SHARED_SECRETS_CLASSNAME = "sun.misc.SharedSecrets";
458
459  /** Access to some fancy internal JVM internals. */
460  @GwtIncompatible // java.lang.reflect
461  @CheckForNull
462  private static final Object jla = getJLA();
463
464  /**
465   * The "getStackTraceElementMethod" method, only available on some JDKs so we use reflection to
466   * find it when available. When this is null, use the slow way.
467   */
468  @GwtIncompatible // java.lang.reflect
469  @CheckForNull
470  private static final Method getStackTraceElementMethod = (jla == null) ? null : getGetMethod();
471
472  /**
473   * The "getStackTraceDepth" method, only available on some JDKs so we use reflection to find it
474   * when available. When this is null, use the slow way.
475   */
476  @GwtIncompatible // java.lang.reflect
477  @CheckForNull
478  private static final Method getStackTraceDepthMethod = (jla == null) ? null : getSizeMethod(jla);
479
480  /**
481   * Returns the JavaLangAccess class that is present in all Sun JDKs. It is not allowed in
482   * AppEngine, and not present in non-Sun JDKs.
483   */
484  @GwtIncompatible // java.lang.reflect
485  @CheckForNull
486  private static Object getJLA() {
487    try {
488      /*
489       * We load sun.misc.* classes using reflection since Android doesn't support these classes and
490       * would result in compilation failure if we directly refer to these classes.
491       */
492      Class<?> sharedSecrets = Class.forName(SHARED_SECRETS_CLASSNAME, false, null);
493      Method langAccess = sharedSecrets.getMethod("getJavaLangAccess");
494      return langAccess.invoke(null);
495    } catch (ThreadDeath death) {
496      throw death;
497    } catch (Throwable t) {
498      /*
499       * This is not one of AppEngine's allowed classes, so even in Sun JDKs, this can fail with
500       * a NoClassDefFoundError. Other apps might deny access to sun.misc packages.
501       */
502      return null;
503    }
504  }
505
506  /**
507   * Returns the Method that can be used to resolve an individual StackTraceElement, or null if that
508   * method cannot be found (it is only to be found in fairly recent JDKs).
509   */
510  @GwtIncompatible // java.lang.reflect
511  @CheckForNull
512  private static Method getGetMethod() {
513    return getJlaMethod("getStackTraceElement", Throwable.class, int.class);
514  }
515
516  /**
517   * Returns the Method that can be used to return the size of a stack, or null if that method
518   * cannot be found (it is only to be found in fairly recent JDKs). Tries to test method {@link
519   * sun.misc.JavaLangAccess#getStackTraceDepth(Throwable)} getStackTraceDepth} prior to return it
520   * (might fail some JDKs).
521   *
522   * <p>See <a href="https://github.com/google/guava/issues/2887">Throwables#lazyStackTrace throws
523   * UnsupportedOperationException</a>.
524   */
525  @GwtIncompatible // java.lang.reflect
526  @CheckForNull
527  private static Method getSizeMethod(Object jla) {
528    try {
529      Method getStackTraceDepth = getJlaMethod("getStackTraceDepth", Throwable.class);
530      if (getStackTraceDepth == null) {
531        return null;
532      }
533      getStackTraceDepth.invoke(jla, new Throwable());
534      return getStackTraceDepth;
535    } catch (UnsupportedOperationException | IllegalAccessException | InvocationTargetException e) {
536      return null;
537    }
538  }
539
540  @GwtIncompatible // java.lang.reflect
541  @CheckForNull
542  private static Method getJlaMethod(String name, Class<?>... parameterTypes) throws ThreadDeath {
543    try {
544      return Class.forName(JAVA_LANG_ACCESS_CLASSNAME, false, null).getMethod(name, parameterTypes);
545    } catch (ThreadDeath death) {
546      throw death;
547    } catch (Throwable t) {
548      /*
549       * Either the JavaLangAccess class itself is not found, or the method is not supported on the
550       * JVM.
551       */
552      return null;
553    }
554  }
555}