Java tutorial
package com.free.exception; /* ==================================================================== * The Apache Software License, Version 1.1 * * Copyright (c) 2002-2003 The Apache Software Foundation. All rights * reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in * the documentation and/or other materials provided with the * distribution. * * 3. The end-user documentation included with the redistribution, if * any, must include the following acknowledgement: * "This product includes software developed by the * Apache Software Foundation (http://www.apache.org/)." * Alternately, this acknowledgement may appear in the software itself, * if and wherever such third-party acknowledgements normally appear. * * 4. The names "The Jakarta Project", "Commons", and "Apache Software * Foundation" must not be used to endorse or promote products derived * from this software without prior written permission. For written * permission, please contact apache@apache.org. * * 5. Products derived from this software may not be called "Apache" * nor may "Apache" appear in their names without prior written * permission of the Apache Software Foundation. * * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE * DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. * ==================================================================== * * This software consists of voluntary contributions made by many * individuals on behalf of the Apache Software Foundation. For more * information on the Apache Software Foundation, please see * <http://www.apache.org/>. */ import java.io.PrintStream; import java.io.PrintWriter; import java.io.StringWriter; import java.lang.reflect.Field; import java.lang.reflect.InvocationTargetException; import java.lang.reflect.Method; import java.sql.SQLException; import java.util.ArrayList; import java.util.LinkedList; import java.util.List; import java.util.StringTokenizer; /** * <p> * Provides utilities for manipulating and examining <code>Throwable</code> * objects. * </p> * * @author <a href="mailto:dlr@finemaltcoding.com">Daniel Rall</a> * @author Dmitri Plotnikov * @author Stephen Colebourne * @author <a href="mailto:ggregory@seagullsw.com">Gary Gregory</a> * @author Pete Gieser * @version $Id: ExceptionUtils.java,v 1.2 2004/11/21 00:11:27 pgmjsd Exp $ * @since 1.0 */ final class ExceptionHelper { private static final String LINE_SEPARATOR = System.getProperty("line.separator"); private static final String[] EMPTY_STRING_ARRAY = {}; private static final Object[] EMPTY_OBJECT_ARRAY = {}; /** * <p> * Used when printing stack frames to denote the start of a wrapped exception. * </p> * <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> */ private static final String[] CAUSE_METHOD_NAMES = { "getCause", "getNextException", "getTargetException", "getException", "getSourceException", "getRootCause", "getCausedByException", "getNested" }; /** * <p> * The Method object for JDK1.4 getCause. * </p> */ private static final Method THROWABLE_CAUSE_METHOD; static { Method getCauseMethod; try { getCauseMethod = Throwable.class.getMethod("getCause", (Class[]) null); } catch (Exception e) { getCauseMethod = null; } THROWABLE_CAUSE_METHOD = getCauseMethod; } private ExceptionHelper() { } // ----------------------------------------------------------------------- /** * <p> * Adds to the list of method names used in the search for * <code>Throwable</code> objects. * </p> * * @param methodName * the methodName to add to the list, <code>null</code> and empty * strings are ignored * @since 2.0 */ /* * public static void addCauseMethodName(String methodName) { if ( * StringHelper.isNotEmpty(methodName) ) { List list = new ArrayList( * Arrays.asList(CAUSE_METHOD_NAMES ); list.add(methodName); * CAUSE_METHOD_NAMES = (String[]) list.toArray(new String[list.size()]); } } */ /** * <p> * Introspects the <code>Throwable</code> to obtain the cause. * </p> * <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, and * {@link org.apache.commons.lang.exception.NestableException * NestableException}. The method names can be added to using * {@link #addCauseMethodName(String)}. * </p> * <p/> * <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/> * <p> * In the absence of any such method, the object is inspected for a * <code>detail</code> field assignable to a <code>Throwable</code>. * </p> * <p/> * <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 */ public static Throwable getCause(Throwable throwable) { return getCause(throwable, CAUSE_METHOD_NAMES); } /** * <p> * Introspects the <code>Throwable</code> to obtain the cause. * </p> * <p/> * <ol> * <li>Try known exception types.</li> * <li>Try the supplied array of method names.</li> * <li>Try the field 'detail'.</li> * </ol> * <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 */ public static Throwable getCause(Throwable throwable, String[] methodNames) { if (throwable == null) { return null; } Throwable cause = getCauseUsingWellKnownTypes(throwable); if (cause == null) { if (methodNames == null) { methodNames = CAUSE_METHOD_NAMES; } for (int i = 0; i < methodNames.length; i++) { String methodName = methodNames[i]; if (methodName != null) { cause = getCauseUsingMethodName(throwable, methodName); if (cause != null) { break; } } } if (cause == null) { cause = getCauseUsingFieldName(throwable, "detail"); } } return cause; } /** * <p> * Introspects the <code>Throwable</code> to obtain the root cause. * </p> * <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> * * @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(Throwable throwable) { Throwable cause = getCause(throwable); if (cause != null) { throwable = cause; while ((throwable = getCause(throwable)) != null) { cause = throwable; } } return cause; } /** * <p> * Finds a <code>Throwable</code> for known types. * </p> * <p/> * <p> * Uses <code>instanceof</code> checks to examine the exception, looking for * well known types which could contain chained or wrapped exceptions. * </p> * * @param throwable * the exception to examine * @return the wrapped exception, or <code>null</code> if not found */ private static Throwable getCauseUsingWellKnownTypes(Throwable throwable) { if (throwable instanceof Nestable) { return ((Nestable) throwable).getCause(); } else if (throwable instanceof SQLException) { return ((SQLException) throwable).getNextException(); } else if (throwable instanceof InvocationTargetException) { return ((InvocationTargetException) throwable).getTargetException(); } else { return null; } } /** * <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 */ private static Throwable getCauseUsingMethodName(Throwable throwable, String methodName) { Method method = null; try { method = throwable.getClass().getMethod(methodName, (Class[]) null); } catch (NoSuchMethodException ignored) { } catch (SecurityException ignored) { } if (method != null && Throwable.class.isAssignableFrom(method.getReturnType())) { try { return (Throwable) method.invoke(throwable, EMPTY_OBJECT_ARRAY); } catch (IllegalAccessException ignored) { } catch (IllegalArgumentException ignored) { } catch (InvocationTargetException ignored) { } } return null; } /** * <p> * Finds a <code>Throwable</code> by field name. * </p> * * @param throwable * the exception to examine * @param fieldName * the name of the attribute to examine * @return the wrapped exception, or <code>null</code> if not found */ private static Throwable getCauseUsingFieldName(Throwable throwable, String fieldName) { Field field = null; try { field = throwable.getClass().getField(fieldName); } catch (NoSuchFieldException ignored) { } catch (SecurityException ignored) { } if (field != null && Throwable.class.isAssignableFrom(field.getType())) { try { return (Throwable) field.get(throwable); } catch (IllegalAccessException ignored) { } catch (IllegalArgumentException ignored) { } } return null; } // ----------------------------------------------------------------------- /** * <p> * Checks if the Throwable class has a <code>getCause</code> method. * </p> * <p/> * <p> * This is true for JDK 1.4 and above. * </p> * * @return true if Throwable is nestable * @since 2.0 */ public static boolean isThrowableNested() { return (THROWABLE_CAUSE_METHOD != null); } /** * <p> * Checks whether this <code>Throwable</code> class can store a cause. * </p> * <p/> * <p> * This method does <b>not</b> check whether it actually does store a cause. * <p> * * @param throwable * the <code>Throwable</code> to examine, may be null * @return boolean <code>true</code> if nested otherwise <code>false</code> * @since 2.0 */ public static boolean isNestedThrowable(Throwable throwable) { if (throwable == null) { return false; } if (throwable instanceof Nestable) { return true; } else if (throwable instanceof SQLException) { return true; } else if (throwable instanceof InvocationTargetException) { return true; } else if (isThrowableNested()) { return true; } Class<?> cls = throwable.getClass(); for (int i = 0, isize = CAUSE_METHOD_NAMES.length; i < isize; i++) { try { Method method = cls.getMethod(CAUSE_METHOD_NAMES[i], (Class[]) null); if (method != null && Throwable.class.isAssignableFrom(method.getReturnType())) { return true; } } catch (NoSuchMethodException ignored) { } catch (SecurityException ignored) { } } try { Field field = cls.getField("detail"); if (field != null) { return true; } } catch (NoSuchFieldException ignored) { } catch (SecurityException ignored) { } return false; } // ----------------------------------------------------------------------- /** * <p> * Counts the number of <code>Throwable</code> objects in the exception chain. * </p> * <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> * * @param throwable * the throwable to inspect, may be null * @return the count of throwables, zero if null input */ public static int getThrowableCount(Throwable throwable) { int count = 0; while (throwable != null) { count++; throwable = ExceptionHelper.getCause(throwable); } return count; } /** * <p> * Returns the list of <code>Throwable</code> objects in the exception chain. * </p> * <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 size zero. * </p> * * @param throwable * the throwable to inspect, may be null * @return the array of throwables, never null */ public static Throwable[] getThrowables(Throwable throwable) { List<Throwable> list = new ArrayList<Throwable>(); while (throwable != null) { list.add(throwable); throwable = ExceptionHelper.getCause(throwable); } return (Throwable[]) list.toArray(new Throwable[list.size()]); } // ----------------------------------------------------------------------- /** * <p> * Returns the (zero based) index of the first <code>Throwable</code> that * matches the specified type in the exception chain. * </p> * <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 * @return the index into the throwable chain, -1 if no match or null input */ public static int indexOfThrowable(Throwable throwable, Class<?> type) { return indexOfThrowable(throwable, type, 0); } /** * <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. * </p> * <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 * @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(Throwable throwable, Class<?> type, int fromIndex) { if (throwable == null) { return -1; } if (fromIndex < 0) { fromIndex = 0; } Throwable[] throwables = ExceptionHelper.getThrowables(throwable); if (fromIndex >= throwables.length) { return -1; } for (int i = fromIndex; i < throwables.length; i++) { if (throwables[i].getClass().equals(type)) { return i; } } return -1; } // ----------------------------------------------------------------------- /** * <p> * Prints a compact stack trace for the root cause of a throwable to * <code>System.err</code>. * </p> * <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/> * <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(Throwable throwable) { printRootCauseStackTrace(throwable, System.err); } /** * <p> * Prints a compact stack trace for the root cause of a throwable. * </p> * <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/> * <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(Throwable throwable, PrintStream stream) { if (throwable == null) { return; } if (stream == null) { throw new IllegalArgumentException("The PrintStream must not be null"); } String trace[] = getRootCauseStackTrace(throwable); for (int i = 0; i < trace.length; i++) { stream.println(trace[i]); } stream.flush(); } /** * <p> * Prints a compact stack trace for the root cause of a throwable. * </p> * <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/> * <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(Throwable throwable, PrintWriter writer) { if (throwable == null) { return; } if (writer == null) { throw new IllegalArgumentException("The PrintWriter must not be null"); } String trace[] = getRootCauseStackTrace(throwable); for (int i = 0; i < trace.length; i++) { writer.println(trace[i]); } writer.flush(); } // ----------------------------------------------------------------------- /** * <p> * Creates a compact stack trace for the root cause of the supplied * <code>Throwable</code>. * </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(Throwable throwable) { if (throwable == null) { return EMPTY_STRING_ARRAY; } Throwable throwables[] = getThrowables(throwable); int count = throwables.length; ArrayList<String> frames = new ArrayList<String>(); List<String> nextTrace = getStackFrameList(throwables[count - 1]); for (int i = count; --i >= 0;) { 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 (String[]) frames.toArray(new String[0]); } /** * <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(List<String> causeFrames, 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 String causeFrame = (String) causeFrames.get(causeFrameIndex); String wrapperFrame = (String) wrapperFrames.get(wrapperFrameIndex); if (causeFrame.equals(wrapperFrame)) { causeFrames.remove(causeFrameIndex); } causeFrameIndex--; wrapperFrameIndex--; } } // ----------------------------------------------------------------------- /** * <p> * Gets the stack trace from a Throwable as a String. * </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(Throwable throwable) { StringWriter sw = new StringWriter(); PrintWriter pw = new PrintWriter(sw, true); throwable.printStackTrace(pw); return sw.getBuffer().toString(); } /** * <p> * A way to get the entire nested stack-trace of an throwable. * </p> * * @param throwable * the <code>Throwable</code> to be examined * @return the nested stack trace, with the root cause first * @since 2.0 */ public static String getFullStackTrace(Throwable throwable) { StringWriter sw = new StringWriter(); PrintWriter pw = new PrintWriter(sw, true); Throwable[] ts = getThrowables(throwable); for (int i = 0; i < ts.length; i++) { ts[i].printStackTrace(pw); if (isNestedThrowable(ts[i])) { break; } } 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> * * @param throwable * the <code>Throwable</code> to exaamine, may be null * @return an array of strings describing each stack frame, never null */ public static String[] getStackFrames(Throwable throwable) { if (throwable == null) { return EMPTY_STRING_ARRAY; } return getStackFrames(getStackTrace(throwable)); } /** * <p> * Functionality shared between the <code>getStackFrames(Throwable)</code> * methods of this and the * {@link org.apache.commons.lang.exception.NestableDelegate} classes. * </p> */ static String[] getStackFrames(String stackTrace) { String linebreak = LINE_SEPARATOR; StringTokenizer frames = new StringTokenizer(stackTrace, linebreak); List<String> list = new LinkedList<String>(); while (frames.hasMoreTokens()) { list.add(frames.nextToken()); } return (String[]) list.toArray(new String[list.size()]); } /** * <p> * Produces a <code>List</code> of stack frames - the message is not included. * </p> * <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(Throwable t) { String stackTrace = getStackTrace(t); String linebreak = LINE_SEPARATOR; StringTokenizer frames = new StringTokenizer(stackTrace, linebreak); List<String> list = new LinkedList<String>(); boolean traceStarted = false; while (frames.hasMoreTokens()) { String token = frames.nextToken(); // Determine if the line starts with <whitespace>at int at = token.indexOf("at"); if (at != -1 && token.substring(0, at).trim().length() == 0) { traceStarted = true; list.add(token); } else if (traceStarted) { break; } } return list; } }