Java tutorial
/* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You under the Apache License, Version 2.0 * (the "License"); you may not use this file except in compliance with * the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.apache.commons.lang3.exception; import java.io.PrintStream; import java.io.PrintWriter; import java.io.StringWriter; import java.lang.reflect.InvocationTargetException; import java.lang.reflect.Method; import java.util.ArrayList; import java.util.List; import java.util.StringTokenizer; import org.apache.commons.lang3.ArrayUtils; import org.apache.commons.lang3.ClassUtils; import org.apache.commons.lang3.StringUtils; import org.apache.commons.lang3.SystemUtils; /** * <p>Provides utilities for manipulating and examining * <code>Throwable</code> objects.</p> * * @since 1.0 * @version $Id$ */ public class ExceptionUtils { /** * <p>Used when printing stack frames to denote the start of a * wrapped exception.</p> * * <p>Package private for accessibility by test suite.</p> */ static final String WRAPPED_MARKER = " [wrapped] "; /** * <p>The names of methods commonly used to access a wrapped exception.</p> */ // TODO: Remove in Lang 4.0 private static final String[] CAUSE_METHOD_NAMES = { "getCause", "getNextException", "getTargetException", "getException", "getSourceException", "getRootCause", "getCausedByException", "getNested", "getLinkedException", "getNestedException", "getLinkedCause", "getThrowable", }; /** * <p> * Public constructor allows an instance of <code>ExceptionUtils</code> to be created, although that is not * normally necessary. * </p> */ public ExceptionUtils() { super(); } //----------------------------------------------------------------------- /** * <p>Returns the default names used when searching for the cause of an exception.</p> * * <p>This may be modified and used in the overloaded getCause(Throwable, String[]) method.</p> * * @return cloned array of the default method names * @since 3.0 * @deprecated This feature will be removed in Lang 4.0 */ @Deprecated public static String[] getDefaultCauseMethodNames() { return ArrayUtils.clone(CAUSE_METHOD_NAMES); } //----------------------------------------------------------------------- /** * <p>Introspects the <code>Throwable</code> to obtain the cause.</p> * * <p>The method searches for methods with specific names that return a * <code>Throwable</code> object. This will pick up most wrapping exceptions, * including those from JDK 1.4. * * <p>The default list searched for are:</p> * <ul> * <li><code>getCause()</code></li> * <li><code>getNextException()</code></li> * <li><code>getTargetException()</code></li> * <li><code>getException()</code></li> * <li><code>getSourceException()</code></li> * <li><code>getRootCause()</code></li> * <li><code>getCausedByException()</code></li> * <li><code>getNested()</code></li> * </ul> * * <p>If none of the above is found, returns <code>null</code>.</p> * * @param throwable the throwable to introspect for a cause, may be null * @return the cause of the <code>Throwable</code>, * <code>null</code> if none found or null throwable input * @since 1.0 * @deprecated This feature will be removed in Lang 4.0 */ @Deprecated public static Throwable getCause(final Throwable throwable) { return getCause(throwable, CAUSE_METHOD_NAMES); } /** * <p>Introspects the <code>Throwable</code> to obtain the cause.</p> * * <p>A <code>null</code> set of method names means use the default set. * A <code>null</code> in the set of method names will be ignored.</p> * * @param throwable the throwable to introspect for a cause, may be null * @param methodNames the method names, null treated as default set * @return the cause of the <code>Throwable</code>, * <code>null</code> if none found or null throwable input * @since 1.0 * @deprecated This feature will be removed in Lang 4.0 */ @Deprecated public static Throwable getCause(final Throwable throwable, String[] methodNames) { if (throwable == null) { return null; } if (methodNames == null) { methodNames = CAUSE_METHOD_NAMES; } for (final String methodName : methodNames) { if (methodName != null) { final Throwable cause = getCauseUsingMethodName(throwable, methodName); if (cause != null) { return cause; } } } return null; } /** * <p>Introspects the <code>Throwable</code> to obtain the root cause.</p> * * <p>This method walks through the exception chain to the last element, * "root" of the tree, using {@link #getCause(Throwable)}, and * returns that exception.</p> * * <p>From version 2.2, this method handles recursive cause structures * that might otherwise cause infinite loops. If the throwable parameter * has a cause of itself, then null will be returned. If the throwable * parameter cause chain loops, the last element in the chain before the * loop is returned.</p> * * @param throwable the throwable to get the root cause for, may be null * @return the root cause of the <code>Throwable</code>, * <code>null</code> if none found or null throwable input */ public static Throwable getRootCause(final Throwable throwable) { final List<Throwable> list = getThrowableList(throwable); return list.size() < 2 ? null : (Throwable) list.get(list.size() - 1); } /** * <p>Finds a <code>Throwable</code> by method name.</p> * * @param throwable the exception to examine * @param methodName the name of the method to find and invoke * @return the wrapped exception, or <code>null</code> if not found */ // TODO: Remove in Lang 4.0 private static Throwable getCauseUsingMethodName(final Throwable throwable, final String methodName) { Method method = null; try { method = throwable.getClass().getMethod(methodName); } catch (final NoSuchMethodException ignored) { // NOPMD // exception ignored } catch (final SecurityException ignored) { // NOPMD // exception ignored } if (method != null && Throwable.class.isAssignableFrom(method.getReturnType())) { try { return (Throwable) method.invoke(throwable); } catch (final IllegalAccessException ignored) { // NOPMD // exception ignored } catch (final IllegalArgumentException ignored) { // NOPMD // exception ignored } catch (final InvocationTargetException ignored) { // NOPMD // exception ignored } } return null; } //----------------------------------------------------------------------- /** * <p>Counts the number of <code>Throwable</code> objects in the * exception chain.</p> * * <p>A throwable without cause will return <code>1</code>. * A throwable with one cause will return <code>2</code> and so on. * A <code>null</code> throwable will return <code>0</code>.</p> * * <p>From version 2.2, this method handles recursive cause structures * that might otherwise cause infinite loops. The cause chain is * processed until the end is reached, or until the next item in the * chain is already in the result set.</p> * * @param throwable the throwable to inspect, may be null * @return the count of throwables, zero if null input */ public static int getThrowableCount(final Throwable throwable) { return getThrowableList(throwable).size(); } /** * <p>Returns the list of <code>Throwable</code> objects in the * exception chain.</p> * * <p>A throwable without cause will return an array containing * one element - the input throwable. * A throwable with one cause will return an array containing * two elements. - the input throwable and the cause throwable. * A <code>null</code> throwable will return an array of size zero.</p> * * <p>From version 2.2, this method handles recursive cause structures * that might otherwise cause infinite loops. The cause chain is * processed until the end is reached, or until the next item in the * chain is already in the result set.</p> * * @see #getThrowableList(Throwable) * @param throwable the throwable to inspect, may be null * @return the array of throwables, never null */ public static Throwable[] getThrowables(final Throwable throwable) { final List<Throwable> list = getThrowableList(throwable); return list.toArray(new Throwable[list.size()]); } /** * <p>Returns the list of <code>Throwable</code> objects in the * exception chain.</p> * * <p>A throwable without cause will return a list containing * one element - the input throwable. * A throwable with one cause will return a list containing * two elements. - the input throwable and the cause throwable. * A <code>null</code> throwable will return a list of size zero.</p> * * <p>This method handles recursive cause structures that might * otherwise cause infinite loops. The cause chain is processed until * the end is reached, or until the next item in the chain is already * in the result set.</p> * * @param throwable the throwable to inspect, may be null * @return the list of throwables, never null * @since Commons Lang 2.2 */ public static List<Throwable> getThrowableList(Throwable throwable) { final List<Throwable> list = new ArrayList<Throwable>(); while (throwable != null && list.contains(throwable) == false) { list.add(throwable); throwable = ExceptionUtils.getCause(throwable); } return list; } //----------------------------------------------------------------------- /** * <p>Returns the (zero based) index of the first <code>Throwable</code> * that matches the specified class (exactly) in the exception chain. * Subclasses of the specified class do not match - see * {@link #indexOfType(Throwable, Class)} for the opposite.</p> * * <p>A <code>null</code> throwable returns <code>-1</code>. * A <code>null</code> type returns <code>-1</code>. * No match in the chain returns <code>-1</code>.</p> * * @param throwable the throwable to inspect, may be null * @param clazz the class to search for, subclasses do not match, null returns -1 * @return the index into the throwable chain, -1 if no match or null input */ public static int indexOfThrowable(final Throwable throwable, final Class<?> clazz) { return indexOf(throwable, clazz, 0, false); } /** * <p>Returns the (zero based) index of the first <code>Throwable</code> * that matches the specified type in the exception chain from * a specified index. * Subclasses of the specified class do not match - see * {@link #indexOfType(Throwable, Class, int)} for the opposite.</p> * * <p>A <code>null</code> throwable returns <code>-1</code>. * A <code>null</code> type returns <code>-1</code>. * No match in the chain returns <code>-1</code>. * A negative start index is treated as zero. * A start index greater than the number of throwables returns <code>-1</code>.</p> * * @param throwable the throwable to inspect, may be null * @param clazz the class to search for, subclasses do not match, null returns -1 * @param fromIndex the (zero based) index of the starting position, * negative treated as zero, larger than chain size returns -1 * @return the index into the throwable chain, -1 if no match or null input */ public static int indexOfThrowable(final Throwable throwable, final Class<?> clazz, final int fromIndex) { return indexOf(throwable, clazz, fromIndex, false); } //----------------------------------------------------------------------- /** * <p>Returns the (zero based) index of the first <code>Throwable</code> * that matches the specified class or subclass in the exception chain. * Subclasses of the specified class do match - see * {@link #indexOfThrowable(Throwable, Class)} for the opposite.</p> * * <p>A <code>null</code> throwable returns <code>-1</code>. * A <code>null</code> type returns <code>-1</code>. * No match in the chain returns <code>-1</code>.</p> * * @param throwable the throwable to inspect, may be null * @param type the type to search for, subclasses match, null returns -1 * @return the index into the throwable chain, -1 if no match or null input * @since 2.1 */ public static int indexOfType(final Throwable throwable, final Class<?> type) { return indexOf(throwable, type, 0, true); } /** * <p>Returns the (zero based) index of the first <code>Throwable</code> * that matches the specified type in the exception chain from * a specified index. * Subclasses of the specified class do match - see * {@link #indexOfThrowable(Throwable, Class)} for the opposite.</p> * * <p>A <code>null</code> throwable returns <code>-1</code>. * A <code>null</code> type returns <code>-1</code>. * No match in the chain returns <code>-1</code>. * A negative start index is treated as zero. * A start index greater than the number of throwables returns <code>-1</code>.</p> * * @param throwable the throwable to inspect, may be null * @param type the type to search for, subclasses match, null returns -1 * @param fromIndex the (zero based) index of the starting position, * negative treated as zero, larger than chain size returns -1 * @return the index into the throwable chain, -1 if no match or null input * @since 2.1 */ public static int indexOfType(final Throwable throwable, final Class<?> type, final int fromIndex) { return indexOf(throwable, type, fromIndex, true); } /** * <p>Worker method for the <code>indexOfType</code> methods.</p> * * @param throwable the throwable to inspect, may be null * @param type the type to search for, subclasses match, null returns -1 * @param fromIndex the (zero based) index of the starting position, * negative treated as zero, larger than chain size returns -1 * @param subclass if <code>true</code>, compares with {@link Class#isAssignableFrom(Class)}, otherwise compares * using references * @return index of the <code>type</code> within throwables nested within the specified <code>throwable</code> */ private static int indexOf(final Throwable throwable, final Class<?> type, int fromIndex, final boolean subclass) { if (throwable == null || type == null) { return -1; } if (fromIndex < 0) { fromIndex = 0; } final Throwable[] throwables = ExceptionUtils.getThrowables(throwable); if (fromIndex >= throwables.length) { return -1; } if (subclass) { for (int i = fromIndex; i < throwables.length; i++) { if (type.isAssignableFrom(throwables[i].getClass())) { return i; } } } else { for (int i = fromIndex; i < throwables.length; i++) { if (type.equals(throwables[i].getClass())) { return i; } } } return -1; } //----------------------------------------------------------------------- /** * <p>Prints a compact stack trace for the root cause of a throwable * to <code>System.err</code>.</p> * * <p>The compact stack trace starts with the root cause and prints * stack frames up to the place where it was caught and wrapped. * Then it prints the wrapped exception and continues with stack frames * until the wrapper exception is caught and wrapped again, etc.</p> * * <p>The output of this method is consistent across JDK versions. * Note that this is the opposite order to the JDK1.4 display.</p> * * <p>The method is equivalent to <code>printStackTrace</code> for throwables * that don't have nested causes.</p> * * @param throwable the throwable to output * @since 2.0 */ public static void printRootCauseStackTrace(final Throwable throwable) { printRootCauseStackTrace(throwable, System.err); } /** * <p>Prints a compact stack trace for the root cause of a throwable.</p> * * <p>The compact stack trace starts with the root cause and prints * stack frames up to the place where it was caught and wrapped. * Then it prints the wrapped exception and continues with stack frames * until the wrapper exception is caught and wrapped again, etc.</p> * * <p>The output of this method is consistent across JDK versions. * Note that this is the opposite order to the JDK1.4 display.</p> * * <p>The method is equivalent to <code>printStackTrace</code> for throwables * that don't have nested causes.</p> * * @param throwable the throwable to output, may be null * @param stream the stream to output to, may not be null * @throws IllegalArgumentException if the stream is <code>null</code> * @since 2.0 */ public static void printRootCauseStackTrace(final Throwable throwable, final PrintStream stream) { if (throwable == null) { return; } if (stream == null) { throw new IllegalArgumentException("The PrintStream must not be null"); } final String trace[] = getRootCauseStackTrace(throwable); for (final String element : trace) { stream.println(element); } stream.flush(); } /** * <p>Prints a compact stack trace for the root cause of a throwable.</p> * * <p>The compact stack trace starts with the root cause and prints * stack frames up to the place where it was caught and wrapped. * Then it prints the wrapped exception and continues with stack frames * until the wrapper exception is caught and wrapped again, etc.</p> * * <p>The output of this method is consistent across JDK versions. * Note that this is the opposite order to the JDK1.4 display.</p> * * <p>The method is equivalent to <code>printStackTrace</code> for throwables * that don't have nested causes.</p> * * @param throwable the throwable to output, may be null * @param writer the writer to output to, may not be null * @throws IllegalArgumentException if the writer is <code>null</code> * @since 2.0 */ public static void printRootCauseStackTrace(final Throwable throwable, final PrintWriter writer) { if (throwable == null) { return; } if (writer == null) { throw new IllegalArgumentException("The PrintWriter must not be null"); } final String trace[] = getRootCauseStackTrace(throwable); for (final String element : trace) { writer.println(element); } writer.flush(); } //----------------------------------------------------------------------- /** * <p>Creates a compact stack trace for the root cause of the supplied * <code>Throwable</code>.</p> * * <p>The output of this method is consistent across JDK versions. * It consists of the root exception followed by each of its wrapping * exceptions separated by '[wrapped]'. Note that this is the opposite * order to the JDK1.4 display.</p> * * @param throwable the throwable to examine, may be null * @return an array of stack trace frames, never null * @since 2.0 */ public static String[] getRootCauseStackTrace(final Throwable throwable) { if (throwable == null) { return ArrayUtils.EMPTY_STRING_ARRAY; } final Throwable throwables[] = getThrowables(throwable); final int count = throwables.length; final List<String> frames = new ArrayList<String>(); List<String> nextTrace = getStackFrameList(throwables[count - 1]); for (int i = count; --i >= 0;) { final List<String> trace = nextTrace; if (i != 0) { nextTrace = getStackFrameList(throwables[i - 1]); removeCommonFrames(trace, nextTrace); } if (i == count - 1) { frames.add(throwables[i].toString()); } else { frames.add(WRAPPED_MARKER + throwables[i].toString()); } for (int j = 0; j < trace.size(); j++) { frames.add(trace.get(j)); } } return frames.toArray(new String[frames.size()]); } /** * <p>Removes common frames from the cause trace given the two stack traces.</p> * * @param causeFrames stack trace of a cause throwable * @param wrapperFrames stack trace of a wrapper throwable * @throws IllegalArgumentException if either argument is null * @since 2.0 */ public static void removeCommonFrames(final List<String> causeFrames, final List<String> wrapperFrames) { if (causeFrames == null || wrapperFrames == null) { throw new IllegalArgumentException("The List must not be null"); } int causeFrameIndex = causeFrames.size() - 1; int wrapperFrameIndex = wrapperFrames.size() - 1; while (causeFrameIndex >= 0 && wrapperFrameIndex >= 0) { // Remove the frame from the cause trace if it is the same // as in the wrapper trace final String causeFrame = causeFrames.get(causeFrameIndex); final String wrapperFrame = wrapperFrames.get(wrapperFrameIndex); if (causeFrame.equals(wrapperFrame)) { causeFrames.remove(causeFrameIndex); } causeFrameIndex--; wrapperFrameIndex--; } } //----------------------------------------------------------------------- /** * <p>Gets the stack trace from a Throwable as a String.</p> * * <p>The result of this method vary by JDK version as this method * uses {@link Throwable#printStackTrace(java.io.PrintWriter)}. * On JDK1.3 and earlier, the cause exception will not be shown * unless the specified throwable alters printStackTrace.</p> * * @param throwable the <code>Throwable</code> to be examined * @return the stack trace as generated by the exception's * <code>printStackTrace(PrintWriter)</code> method */ public static String getStackTrace(final Throwable throwable) { final StringWriter sw = new StringWriter(); final PrintWriter pw = new PrintWriter(sw, true); throwable.printStackTrace(pw); return sw.getBuffer().toString(); } /** * <p>Captures the stack trace associated with the specified * <code>Throwable</code> object, decomposing it into a list of * stack frames.</p> * * <p>The result of this method vary by JDK version as this method * uses {@link Throwable#printStackTrace(java.io.PrintWriter)}. * On JDK1.3 and earlier, the cause exception will not be shown * unless the specified throwable alters printStackTrace.</p> * * @param throwable the <code>Throwable</code> to examine, may be null * @return an array of strings describing each stack frame, never null */ public static String[] getStackFrames(final Throwable throwable) { if (throwable == null) { return ArrayUtils.EMPTY_STRING_ARRAY; } return getStackFrames(getStackTrace(throwable)); } //----------------------------------------------------------------------- /** * <p>Returns an array where each element is a line from the argument.</p> * * <p>The end of line is determined by the value of {@link SystemUtils#LINE_SEPARATOR}.</p> * * @param stackTrace a stack trace String * @return an array where each element is a line from the argument */ static String[] getStackFrames(final String stackTrace) { final String linebreak = SystemUtils.LINE_SEPARATOR; final StringTokenizer frames = new StringTokenizer(stackTrace, linebreak); final List<String> list = new ArrayList<String>(); while (frames.hasMoreTokens()) { list.add(frames.nextToken()); } return list.toArray(new String[list.size()]); } /** * <p>Produces a <code>List</code> of stack frames - the message * is not included. Only the trace of the specified exception is * returned, any caused by trace is stripped.</p> * * <p>This works in most cases - it will only fail if the exception * message contains a line that starts with: * <code>" at".</code></p> * * @param t is any throwable * @return List of stack frames */ static List<String> getStackFrameList(final Throwable t) { final String stackTrace = getStackTrace(t); final String linebreak = SystemUtils.LINE_SEPARATOR; final StringTokenizer frames = new StringTokenizer(stackTrace, linebreak); final List<String> list = new ArrayList<String>(); boolean traceStarted = false; while (frames.hasMoreTokens()) { final String token = frames.nextToken(); // Determine if the line starts with <whitespace>at final int at = token.indexOf("at"); if (at != -1 && token.substring(0, at).trim().isEmpty()) { traceStarted = true; list.add(token); } else if (traceStarted) { break; } } return list; } //----------------------------------------------------------------------- /** * Gets a short message summarising the exception. * <p> * The message returned is of the form * {ClassNameWithoutPackage}: {ThrowableMessage} * * @param th the throwable to get a message for, null returns empty string * @return the message, non-null * @since Commons Lang 2.2 */ public static String getMessage(final Throwable th) { if (th == null) { return ""; } final String clsName = ClassUtils.getShortClassName(th, null); final String msg = th.getMessage(); return clsName + ": " + StringUtils.defaultString(msg); } //----------------------------------------------------------------------- /** * Gets a short message summarising the root cause exception. * <p> * The message returned is of the form * {ClassNameWithoutPackage}: {ThrowableMessage} * * @param th the throwable to get a message for, null returns empty string * @return the message, non-null * @since Commons Lang 2.2 */ public static String getRootCauseMessage(final Throwable th) { Throwable root = ExceptionUtils.getRootCause(th); root = root == null ? th : root; return getMessage(root); } }