001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.lang3.exception;
018
019import java.io.PrintStream;
020import java.io.PrintWriter;
021import java.io.StringWriter;
022import java.lang.reflect.InvocationTargetException;
023import java.lang.reflect.Method;
024import java.lang.reflect.UndeclaredThrowableException;
025import java.util.ArrayList;
026import java.util.List;
027import java.util.StringTokenizer;
028
029import org.apache.commons.lang3.ArrayUtils;
030import org.apache.commons.lang3.ClassUtils;
031import org.apache.commons.lang3.StringUtils;
032import org.apache.commons.lang3.Validate;
033
034/**
035 * <p>Provides utilities for manipulating and examining
036 * <code>Throwable</code> objects.</p>
037 *
038 * @since 1.0
039 */
040public class ExceptionUtils {
041
042    /**
043     * <p>Used when printing stack frames to denote the start of a
044     * wrapped exception.</p>
045     *
046     * <p>Package private for accessibility by test suite.</p>
047     */
048    static final String WRAPPED_MARKER = " [wrapped] ";
049
050    /**
051     * <p>The names of methods commonly used to access a wrapped exception.</p>
052     */
053    // TODO: Remove in Lang 4.0
054    private static final String[] CAUSE_METHOD_NAMES = {
055        "getCause",
056        "getNextException",
057        "getTargetException",
058        "getException",
059        "getSourceException",
060        "getRootCause",
061        "getCausedByException",
062        "getNested",
063        "getLinkedException",
064        "getNestedException",
065        "getLinkedCause",
066        "getThrowable",
067    };
068
069    /**
070     * <p>
071     * Public constructor allows an instance of <code>ExceptionUtils</code> to be created, although that is not
072     * normally necessary.
073     * </p>
074     */
075    public ExceptionUtils() {
076        super();
077    }
078
079    //-----------------------------------------------------------------------
080    /**
081     * <p>Returns the default names used when searching for the cause of an exception.</p>
082     *
083     * <p>This may be modified and used in the overloaded getCause(Throwable, String[]) method.</p>
084     *
085     * @return cloned array of the default method names
086     * @since 3.0
087     * @deprecated This feature will be removed in Lang 4.0
088     */
089    @Deprecated
090    public static String[] getDefaultCauseMethodNames() {
091        return ArrayUtils.clone(CAUSE_METHOD_NAMES);
092    }
093
094    //-----------------------------------------------------------------------
095    /**
096     * <p>Introspects the <code>Throwable</code> to obtain the cause.</p>
097     *
098     * <p>The method searches for methods with specific names that return a
099     * <code>Throwable</code> object. This will pick up most wrapping exceptions,
100     * including those from JDK 1.4.
101     *
102     * <p>The default list searched for are:</p>
103     * <ul>
104     *  <li><code>getCause()</code></li>
105     *  <li><code>getNextException()</code></li>
106     *  <li><code>getTargetException()</code></li>
107     *  <li><code>getException()</code></li>
108     *  <li><code>getSourceException()</code></li>
109     *  <li><code>getRootCause()</code></li>
110     *  <li><code>getCausedByException()</code></li>
111     *  <li><code>getNested()</code></li>
112     * </ul>
113     *
114     * <p>If none of the above is found, returns <code>null</code>.</p>
115     *
116     * @param throwable  the throwable to introspect for a cause, may be null
117     * @return the cause of the <code>Throwable</code>,
118     *  <code>null</code> if none found or null throwable input
119     * @since 1.0
120     * @deprecated This feature will be removed in Lang 4.0, use {@link Throwable#getCause} instead
121     */
122    @Deprecated
123    public static Throwable getCause(final Throwable throwable) {
124        return getCause(throwable, null);
125    }
126
127    /**
128     * <p>Introspects the <code>Throwable</code> to obtain the cause.</p>
129     *
130     * <p>A <code>null</code> set of method names means use the default set.
131     * A <code>null</code> in the set of method names will be ignored.</p>
132     *
133     * @param throwable  the throwable to introspect for a cause, may be null
134     * @param methodNames  the method names, null treated as default set
135     * @return the cause of the <code>Throwable</code>,
136     *  <code>null</code> if none found or null throwable input
137     * @since 1.0
138     * @deprecated This feature will be removed in Lang 4.0, use {@link Throwable#getCause} instead
139     */
140    @Deprecated
141    public static Throwable getCause(final Throwable throwable, String[] methodNames) {
142        if (throwable == null) {
143            return null;
144        }
145
146        if (methodNames == null) {
147            final Throwable cause = throwable.getCause();
148            if (cause != null) {
149                return cause;
150            }
151
152            methodNames = CAUSE_METHOD_NAMES;
153        }
154
155        for (final String methodName : methodNames) {
156            if (methodName != null) {
157                final Throwable legacyCause = getCauseUsingMethodName(throwable, methodName);
158                if (legacyCause != null) {
159                    return legacyCause;
160                }
161            }
162        }
163
164        return null;
165    }
166
167    /**
168     * <p>Introspects the <code>Throwable</code> to obtain the root cause.</p>
169     *
170     * <p>This method walks through the exception chain to the last element,
171     * "root" of the tree, using {@link Throwable#getCause()}, and
172     * returns that exception.</p>
173     *
174     * <p>From version 2.2, this method handles recursive cause structures
175     * that might otherwise cause infinite loops. If the throwable parameter
176     * has a cause of itself, then null will be returned. If the throwable
177     * parameter cause chain loops, the last element in the chain before the
178     * loop is returned.</p>
179     *
180     * @param throwable  the throwable to get the root cause for, may be null
181     * @return the root cause of the <code>Throwable</code>,
182     *  <code>null</code> if null throwable input
183     */
184    public static Throwable getRootCause(final Throwable throwable) {
185        final List<Throwable> list = getThrowableList(throwable);
186        return list.isEmpty() ? null : list.get(list.size() - 1);
187    }
188
189    /**
190     * <p>Finds a <code>Throwable</code> by method name.</p>
191     *
192     * @param throwable  the exception to examine
193     * @param methodName  the name of the method to find and invoke
194     * @return the wrapped exception, or <code>null</code> if not found
195     */
196    // TODO: Remove in Lang 4.0
197    private static Throwable getCauseUsingMethodName(final Throwable throwable, final String methodName) {
198        Method method = null;
199        try {
200            method = throwable.getClass().getMethod(methodName);
201        } catch (final NoSuchMethodException | SecurityException ignored) { // NOPMD
202            // exception ignored
203        }
204
205        if (method != null && Throwable.class.isAssignableFrom(method.getReturnType())) {
206            try {
207                return (Throwable) method.invoke(throwable);
208            } catch (final IllegalAccessException | IllegalArgumentException | InvocationTargetException ignored) { // NOPMD
209                // exception ignored
210            }
211        }
212        return null;
213    }
214
215    //-----------------------------------------------------------------------
216    /**
217     * <p>Counts the number of <code>Throwable</code> objects in the
218     * exception chain.</p>
219     *
220     * <p>A throwable without cause will return <code>1</code>.
221     * A throwable with one cause will return <code>2</code> and so on.
222     * A <code>null</code> throwable will return <code>0</code>.</p>
223     *
224     * <p>From version 2.2, this method handles recursive cause structures
225     * that might otherwise cause infinite loops. The cause chain is
226     * processed until the end is reached, or until the next item in the
227     * chain is already in the result set.</p>
228     *
229     * @param throwable  the throwable to inspect, may be null
230     * @return the count of throwables, zero if null input
231     */
232    public static int getThrowableCount(final Throwable throwable) {
233        return getThrowableList(throwable).size();
234    }
235
236    /**
237     * <p>Returns the list of <code>Throwable</code> objects in the
238     * exception chain.</p>
239     *
240     * <p>A throwable without cause will return an array containing
241     * one element - the input throwable.
242     * A throwable with one cause will return an array containing
243     * two elements. - the input throwable and the cause throwable.
244     * A <code>null</code> throwable will return an array of size zero.</p>
245     *
246     * <p>From version 2.2, this method handles recursive cause structures
247     * that might otherwise cause infinite loops. The cause chain is
248     * processed until the end is reached, or until the next item in the
249     * chain is already in the result set.</p>
250     *
251     * @see #getThrowableList(Throwable)
252     * @param throwable  the throwable to inspect, may be null
253     * @return the array of throwables, never null
254     */
255    public static Throwable[] getThrowables(final Throwable throwable) {
256        final List<Throwable> list = getThrowableList(throwable);
257        return list.toArray(new Throwable[list.size()]);
258    }
259
260    /**
261     * <p>Returns the list of <code>Throwable</code> objects in the
262     * exception chain.</p>
263     *
264     * <p>A throwable without cause will return a list containing
265     * one element - the input throwable.
266     * A throwable with one cause will return a list containing
267     * two elements. - the input throwable and the cause throwable.
268     * A <code>null</code> throwable will return a list of size zero.</p>
269     *
270     * <p>This method handles recursive cause structures that might
271     * otherwise cause infinite loops. The cause chain is processed until
272     * the end is reached, or until the next item in the chain is already
273     * in the result set.</p>
274     *
275     * @param throwable  the throwable to inspect, may be null
276     * @return the list of throwables, never null
277     * @since 2.2
278     */
279    public static List<Throwable> getThrowableList(Throwable throwable) {
280        final List<Throwable> list = new ArrayList<>();
281        while (throwable != null && !list.contains(throwable)) {
282            list.add(throwable);
283            throwable = throwable.getCause();
284        }
285        return list;
286    }
287
288    //-----------------------------------------------------------------------
289    /**
290     * <p>Returns the (zero based) index of the first <code>Throwable</code>
291     * that matches the specified class (exactly) in the exception chain.
292     * Subclasses of the specified class do not match - see
293     * {@link #indexOfType(Throwable, Class)} for the opposite.</p>
294     *
295     * <p>A <code>null</code> throwable returns <code>-1</code>.
296     * A <code>null</code> type returns <code>-1</code>.
297     * No match in the chain returns <code>-1</code>.</p>
298     *
299     * @param throwable  the throwable to inspect, may be null
300     * @param clazz  the class to search for, subclasses do not match, null returns -1
301     * @return the index into the throwable chain, -1 if no match or null input
302     */
303    public static int indexOfThrowable(final Throwable throwable, final Class<?> clazz) {
304        return indexOf(throwable, clazz, 0, false);
305    }
306
307    /**
308     * <p>Returns the (zero based) index of the first <code>Throwable</code>
309     * that matches the specified type in the exception chain from
310     * a specified index.
311     * Subclasses of the specified class do not match - see
312     * {@link #indexOfType(Throwable, Class, int)} for the opposite.</p>
313     *
314     * <p>A <code>null</code> throwable returns <code>-1</code>.
315     * A <code>null</code> type returns <code>-1</code>.
316     * No match in the chain returns <code>-1</code>.
317     * A negative start index is treated as zero.
318     * A start index greater than the number of throwables returns <code>-1</code>.</p>
319     *
320     * @param throwable  the throwable to inspect, may be null
321     * @param clazz  the class to search for, subclasses do not match, null returns -1
322     * @param fromIndex  the (zero based) index of the starting position,
323     *  negative treated as zero, larger than chain size returns -1
324     * @return the index into the throwable chain, -1 if no match or null input
325     */
326    public static int indexOfThrowable(final Throwable throwable, final Class<?> clazz, final int fromIndex) {
327        return indexOf(throwable, clazz, fromIndex, false);
328    }
329
330    //-----------------------------------------------------------------------
331    /**
332     * <p>Returns the (zero based) index of the first <code>Throwable</code>
333     * that matches the specified class or subclass in the exception chain.
334     * Subclasses of the specified class do match - see
335     * {@link #indexOfThrowable(Throwable, Class)} for the opposite.</p>
336     *
337     * <p>A <code>null</code> throwable returns <code>-1</code>.
338     * A <code>null</code> type returns <code>-1</code>.
339     * No match in the chain returns <code>-1</code>.</p>
340     *
341     * @param throwable  the throwable to inspect, may be null
342     * @param type  the type to search for, subclasses match, null returns -1
343     * @return the index into the throwable chain, -1 if no match or null input
344     * @since 2.1
345     */
346    public static int indexOfType(final Throwable throwable, final Class<?> type) {
347        return indexOf(throwable, type, 0, true);
348    }
349
350    /**
351     * <p>Returns the (zero based) index of the first <code>Throwable</code>
352     * that matches the specified type in the exception chain from
353     * a specified index.
354     * Subclasses of the specified class do match - see
355     * {@link #indexOfThrowable(Throwable, Class)} for the opposite.</p>
356     *
357     * <p>A <code>null</code> throwable returns <code>-1</code>.
358     * A <code>null</code> type returns <code>-1</code>.
359     * No match in the chain returns <code>-1</code>.
360     * A negative start index is treated as zero.
361     * A start index greater than the number of throwables returns <code>-1</code>.</p>
362     *
363     * @param throwable  the throwable to inspect, may be null
364     * @param type  the type to search for, subclasses match, null returns -1
365     * @param fromIndex  the (zero based) index of the starting position,
366     *  negative treated as zero, larger than chain size returns -1
367     * @return the index into the throwable chain, -1 if no match or null input
368     * @since 2.1
369     */
370    public static int indexOfType(final Throwable throwable, final Class<?> type, final int fromIndex) {
371        return indexOf(throwable, type, fromIndex, true);
372    }
373
374    /**
375     * <p>Worker method for the <code>indexOfType</code> methods.</p>
376     *
377     * @param throwable  the throwable to inspect, may be null
378     * @param type  the type to search for, subclasses match, null returns -1
379     * @param fromIndex  the (zero based) index of the starting position,
380     *  negative treated as zero, larger than chain size returns -1
381     * @param subclass if <code>true</code>, compares with {@link Class#isAssignableFrom(Class)}, otherwise compares
382     * using references
383     * @return index of the <code>type</code> within throwables nested within the specified <code>throwable</code>
384     */
385    private static int indexOf(final Throwable throwable, final Class<?> type, int fromIndex, final boolean subclass) {
386        if (throwable == null || type == null) {
387            return -1;
388        }
389        if (fromIndex < 0) {
390            fromIndex = 0;
391        }
392        final Throwable[] throwables = getThrowables(throwable);
393        if (fromIndex >= throwables.length) {
394            return -1;
395        }
396        if (subclass) {
397            for (int i = fromIndex; i < throwables.length; i++) {
398                if (type.isAssignableFrom(throwables[i].getClass())) {
399                    return i;
400                }
401            }
402        } else {
403            for (int i = fromIndex; i < throwables.length; i++) {
404                if (type.equals(throwables[i].getClass())) {
405                    return i;
406                }
407            }
408        }
409        return -1;
410    }
411
412    //-----------------------------------------------------------------------
413    /**
414     * <p>Prints a compact stack trace for the root cause of a throwable
415     * to <code>System.err</code>.</p>
416     *
417     * <p>The compact stack trace starts with the root cause and prints
418     * stack frames up to the place where it was caught and wrapped.
419     * Then it prints the wrapped exception and continues with stack frames
420     * until the wrapper exception is caught and wrapped again, etc.</p>
421     *
422     * <p>The output of this method is consistent across JDK versions.
423     * Note that this is the opposite order to the JDK1.4 display.</p>
424     *
425     * <p>The method is equivalent to <code>printStackTrace</code> for throwables
426     * that don't have nested causes.</p>
427     *
428     * @param throwable  the throwable to output
429     * @since 2.0
430     */
431    public static void printRootCauseStackTrace(final Throwable throwable) {
432        printRootCauseStackTrace(throwable, System.err);
433    }
434
435    /**
436     * <p>Prints a compact stack trace for the root cause of a throwable.</p>
437     *
438     * <p>The compact stack trace starts with the root cause and prints
439     * stack frames up to the place where it was caught and wrapped.
440     * Then it prints the wrapped exception and continues with stack frames
441     * until the wrapper exception is caught and wrapped again, etc.</p>
442     *
443     * <p>The output of this method is consistent across JDK versions.
444     * Note that this is the opposite order to the JDK1.4 display.</p>
445     *
446     * <p>The method is equivalent to <code>printStackTrace</code> for throwables
447     * that don't have nested causes.</p>
448     *
449     * @param throwable  the throwable to output, may be null
450     * @param stream  the stream to output to, may not be null
451     * @throws IllegalArgumentException if the stream is <code>null</code>
452     * @since 2.0
453     */
454    public static void printRootCauseStackTrace(final Throwable throwable, final PrintStream stream) {
455        if (throwable == null) {
456            return;
457        }
458        Validate.isTrue(stream != null, "The PrintStream must not be null");
459        final String trace[] = getRootCauseStackTrace(throwable);
460        for (final String element : trace) {
461            stream.println(element);
462        }
463        stream.flush();
464    }
465
466    /**
467     * <p>Prints a compact stack trace for the root cause of a throwable.</p>
468     *
469     * <p>The compact stack trace starts with the root cause and prints
470     * stack frames up to the place where it was caught and wrapped.
471     * Then it prints the wrapped exception and continues with stack frames
472     * until the wrapper exception is caught and wrapped again, etc.</p>
473     *
474     * <p>The output of this method is consistent across JDK versions.
475     * Note that this is the opposite order to the JDK1.4 display.</p>
476     *
477     * <p>The method is equivalent to <code>printStackTrace</code> for throwables
478     * that don't have nested causes.</p>
479     *
480     * @param throwable  the throwable to output, may be null
481     * @param writer  the writer to output to, may not be null
482     * @throws IllegalArgumentException if the writer is <code>null</code>
483     * @since 2.0
484     */
485    public static void printRootCauseStackTrace(final Throwable throwable, final PrintWriter writer) {
486        if (throwable == null) {
487            return;
488        }
489        Validate.isTrue(writer != null, "The PrintWriter must not be null");
490        final String trace[] = getRootCauseStackTrace(throwable);
491        for (final String element : trace) {
492            writer.println(element);
493        }
494        writer.flush();
495    }
496
497    //-----------------------------------------------------------------------
498    /**
499     * <p>Creates a compact stack trace for the root cause of the supplied
500     * <code>Throwable</code>.</p>
501     *
502     * <p>The output of this method is consistent across JDK versions.
503     * It consists of the root exception followed by each of its wrapping
504     * exceptions separated by '[wrapped]'. Note that this is the opposite
505     * order to the JDK1.4 display.</p>
506     *
507     * @param throwable  the throwable to examine, may be null
508     * @return an array of stack trace frames, never null
509     * @since 2.0
510     */
511    public static String[] getRootCauseStackTrace(final Throwable throwable) {
512        if (throwable == null) {
513            return ArrayUtils.EMPTY_STRING_ARRAY;
514        }
515        final Throwable throwables[] = getThrowables(throwable);
516        final int count = throwables.length;
517        final List<String> frames = new ArrayList<>();
518        List<String> nextTrace = getStackFrameList(throwables[count - 1]);
519        for (int i = count; --i >= 0;) {
520            final List<String> trace = nextTrace;
521            if (i != 0) {
522                nextTrace = getStackFrameList(throwables[i - 1]);
523                removeCommonFrames(trace, nextTrace);
524            }
525            if (i == count - 1) {
526                frames.add(throwables[i].toString());
527            } else {
528                frames.add(WRAPPED_MARKER + throwables[i].toString());
529            }
530            frames.addAll(trace);
531        }
532        return frames.toArray(new String[frames.size()]);
533    }
534
535    /**
536     * <p>Removes common frames from the cause trace given the two stack traces.</p>
537     *
538     * @param causeFrames  stack trace of a cause throwable
539     * @param wrapperFrames  stack trace of a wrapper throwable
540     * @throws IllegalArgumentException if either argument is null
541     * @since 2.0
542     */
543    public static void removeCommonFrames(final List<String> causeFrames, final List<String> wrapperFrames) {
544        if (causeFrames == null || wrapperFrames == null) {
545            throw new IllegalArgumentException("The List must not be null");
546        }
547        int causeFrameIndex = causeFrames.size() - 1;
548        int wrapperFrameIndex = wrapperFrames.size() - 1;
549        while (causeFrameIndex >= 0 && wrapperFrameIndex >= 0) {
550            // Remove the frame from the cause trace if it is the same
551            // as in the wrapper trace
552            final String causeFrame = causeFrames.get(causeFrameIndex);
553            final String wrapperFrame = wrapperFrames.get(wrapperFrameIndex);
554            if (causeFrame.equals(wrapperFrame)) {
555                causeFrames.remove(causeFrameIndex);
556            }
557            causeFrameIndex--;
558            wrapperFrameIndex--;
559        }
560    }
561
562    //-----------------------------------------------------------------------
563    /**
564     * <p>Gets the stack trace from a Throwable as a String.</p>
565     *
566     * <p>The result of this method vary by JDK version as this method
567     * uses {@link Throwable#printStackTrace(java.io.PrintWriter)}.
568     * On JDK1.3 and earlier, the cause exception will not be shown
569     * unless the specified throwable alters printStackTrace.</p>
570     *
571     * @param throwable  the <code>Throwable</code> to be examined
572     * @return the stack trace as generated by the exception's
573     *  <code>printStackTrace(PrintWriter)</code> method
574     */
575    public static String getStackTrace(final Throwable throwable) {
576        final StringWriter sw = new StringWriter();
577        final PrintWriter pw = new PrintWriter(sw, true);
578        throwable.printStackTrace(pw);
579        return sw.getBuffer().toString();
580    }
581
582    /**
583     * <p>Captures the stack trace associated with the specified
584     * <code>Throwable</code> object, decomposing it into a list of
585     * stack frames.</p>
586     *
587     * <p>The result of this method vary by JDK version as this method
588     * uses {@link Throwable#printStackTrace(java.io.PrintWriter)}.
589     * On JDK1.3 and earlier, the cause exception will not be shown
590     * unless the specified throwable alters printStackTrace.</p>
591     *
592     * @param throwable  the <code>Throwable</code> to examine, may be null
593     * @return an array of strings describing each stack frame, never null
594     */
595    public static String[] getStackFrames(final Throwable throwable) {
596        if (throwable == null) {
597            return ArrayUtils.EMPTY_STRING_ARRAY;
598        }
599        return getStackFrames(getStackTrace(throwable));
600    }
601
602    //-----------------------------------------------------------------------
603    /**
604     * <p>Returns an array where each element is a line from the argument.</p>
605     *
606     * <p>The end of line is determined by the value of {@link System#lineSeparator()}.</p>
607     *
608     * @param stackTrace  a stack trace String
609     * @return an array where each element is a line from the argument
610     */
611    static String[] getStackFrames(final String stackTrace) {
612        final String linebreak = System.lineSeparator();
613        final StringTokenizer frames = new StringTokenizer(stackTrace, linebreak);
614        final List<String> list = new ArrayList<>();
615        while (frames.hasMoreTokens()) {
616            list.add(frames.nextToken());
617        }
618        return list.toArray(new String[list.size()]);
619    }
620
621    /**
622     * <p>Produces a <code>List</code> of stack frames - the message
623     * is not included. Only the trace of the specified exception is
624     * returned, any caused by trace is stripped.</p>
625     *
626     * <p>This works in most cases - it will only fail if the exception
627     * message contains a line that starts with:
628     * <code>&quot;&nbsp;&nbsp;&nbsp;at&quot;.</code></p>
629     *
630     * @param t is any throwable
631     * @return List of stack frames
632     */
633    static List<String> getStackFrameList(final Throwable t) {
634        final String stackTrace = getStackTrace(t);
635        final String linebreak = System.lineSeparator();
636        final StringTokenizer frames = new StringTokenizer(stackTrace, linebreak);
637        final List<String> list = new ArrayList<>();
638        boolean traceStarted = false;
639        while (frames.hasMoreTokens()) {
640            final String token = frames.nextToken();
641            // Determine if the line starts with <whitespace>at
642            final int at = token.indexOf("at");
643            if (at != -1 && token.substring(0, at).trim().isEmpty()) {
644                traceStarted = true;
645                list.add(token);
646            } else if (traceStarted) {
647                break;
648            }
649        }
650        return list;
651    }
652
653    //-----------------------------------------------------------------------
654    /**
655     * Gets a short message summarising the exception.
656     * <p>
657     * The message returned is of the form
658     * {ClassNameWithoutPackage}: {ThrowableMessage}
659     *
660     * @param th  the throwable to get a message for, null returns empty string
661     * @return the message, non-null
662     * @since 2.2
663     */
664    public static String getMessage(final Throwable th) {
665        if (th == null) {
666            return StringUtils.EMPTY;
667        }
668        final String clsName = ClassUtils.getShortClassName(th, null);
669        final String msg = th.getMessage();
670        return clsName + ": " + StringUtils.defaultString(msg);
671    }
672
673    //-----------------------------------------------------------------------
674    /**
675     * Gets a short message summarising the root cause exception.
676     * <p>
677     * The message returned is of the form
678     * {ClassNameWithoutPackage}: {ThrowableMessage}
679     *
680     * @param th  the throwable to get a message for, null returns empty string
681     * @return the message, non-null
682     * @since 2.2
683     */
684    public static String getRootCauseMessage(final Throwable th) {
685        Throwable root = getRootCause(th);
686        root = root == null ? th : root;
687        return getMessage(root);
688    }
689
690    /**
691     * Throw a checked exception without adding the exception to the throws
692     * clause of the calling method. This method prevents throws clause
693     * pollution and reduces the clutter of "Caused by" exceptions in the
694     * stacktrace.
695     * <p>
696     * The use of this technique may be controversial, but exceedingly useful to
697     * library developers.
698     * <code>
699     *  public int propagateExample { // note that there is no throws clause
700     *      try {
701     *          return invocation(); // throws IOException
702     *      } catch (Exception e) {
703     *          return ExceptionUtils.rethrow(e);  // propagates a checked exception
704     *      }
705     *  }
706     * </code>
707     * <p>
708     * This is an alternative to the more conservative approach of wrapping the
709     * checked exception in a RuntimeException:
710     * <code>
711     *  public int wrapExample { // note that there is no throws clause
712     *      try {
713     *          return invocation(); // throws IOException
714     *      } catch (Error e) {
715     *          throw e;
716     *      } catch (RuntimeException e) {
717     *          throw e;  // wraps a checked exception
718     *      } catch (Exception e) {
719     *          throw new UndeclaredThrowableException(e);  // wraps a checked exception
720     *      }
721     *  }
722     * </code>
723     * <p>
724     * One downside to using this approach is that the java compiler will not
725     * allow invoking code to specify a checked exception in a catch clause
726     * unless there is some code path within the try block that has invoked a
727     * method declared with that checked exception. If the invoking site wishes
728     * to catch the shaded checked exception, it must either invoke the shaded
729     * code through a method re-declaring the desired checked exception, or
730     * catch Exception and use the instanceof operator. Either of these
731     * techniques are required when interacting with non-java jvm code such as
732     * Jython, Scala, or Groovy, since these languages do not consider any
733     * exceptions as checked.
734     *
735     * @param throwable
736     *            The throwable to rethrow.
737     * @param <R> The type of the returned value.
738     * @return Never actually returned, this generic type matches any type
739     *         which the calling site requires. "Returning" the results of this
740     *         method, as done in the propagateExample above, will satisfy the
741     *         java compiler requirement that all code paths return a value.
742     * @since 3.5
743     * @see #wrapAndThrow(Throwable)
744     */
745    public static <R> R rethrow(final Throwable throwable) {
746        // claim that the typeErasure invocation throws a RuntimeException
747        return ExceptionUtils.<R, RuntimeException> typeErasure(throwable);
748    }
749
750    /**
751     * Claim a Throwable is another Exception type using type erasure. This
752     * hides a checked exception from the java compiler, allowing a checked
753     * exception to be thrown without having the exception in the method's throw
754     * clause.
755     */
756    @SuppressWarnings("unchecked")
757    private static <R, T extends Throwable> R typeErasure(final Throwable throwable) throws T {
758        throw (T) throwable;
759    }
760
761    /**
762     * Throw a checked exception without adding the exception to the throws
763     * clause of the calling method. For checked exceptions, this method throws
764     * an UndeclaredThrowableException wrapping the checked exception. For
765     * Errors and RuntimeExceptions, the original exception is rethrown.
766     * <p>
767     * The downside to using this approach is that invoking code which needs to
768     * handle specific checked exceptions must sniff up the exception chain to
769     * determine if the caught exception was caused by the checked exception.
770     *
771     * @param throwable
772     *            The throwable to rethrow.
773     * @param <R> The type of the returned value.
774     * @return Never actually returned, this generic type matches any type
775     *         which the calling site requires. "Returning" the results of this
776     *         method will satisfy the java compiler requirement that all code
777     *         paths return a value.
778     * @since 3.5
779     * @see #rethrow(Throwable)
780     * @see #hasCause(Throwable, Class)
781     */
782    public static <R> R wrapAndThrow(final Throwable throwable) {
783        if (throwable instanceof RuntimeException) {
784            throw (RuntimeException) throwable;
785        }
786        if (throwable instanceof Error) {
787            throw (Error) throwable;
788        }
789        throw new UndeclaredThrowableException(throwable);
790    }
791
792    /**
793     * Does the throwable's causal chain have an immediate or wrapped exception
794     * of the given type?
795     *
796     * @param chain
797     *            The root of a Throwable causal chain.
798     * @param type
799     *            The exception type to test.
800     * @return true, if chain is an instance of type or is an
801     *         UndeclaredThrowableException wrapping a cause.
802     * @since 3.5
803     * @see #wrapAndThrow(Throwable)
804     */
805    public static boolean hasCause(Throwable chain,
806            final Class<? extends Throwable> type) {
807        if (chain instanceof UndeclaredThrowableException) {
808            chain = chain.getCause();
809        }
810        return type.isInstance(chain);
811    }
812}