Java tutorial
package com.kamuda.common.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. 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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; import org.hibernate.util.ArrayHelper; /** * <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 * @since 1.0 * @version $Id: ExceptionUtils.java,v 1.6 2004/06/04 05:43:45 steveebersole Exp $ */ public final class ExceptionUtils { private static final String LINE_SEPARATOR = System.getProperty("line.separator"); /** * <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> */ 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", null); } catch (Exception e) { getCauseMethod = null; } THROWABLE_CAUSE_METHOD = getCauseMethod; } private ExceptionUtils() { } //----------------------------------------------------------------------- /** * <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>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>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>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>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> * * <ol> * <li>Try known exception types.</li> * <li>Try the supplied array of method names.</li> * <li>Try the field 'detail'.</li> * </ol> * * <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>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>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, null); } catch (NoSuchMethodException ignored) { } catch (SecurityException ignored) { } if (method != null && Throwable.class.isAssignableFrom(method.getReturnType())) { try { return (Throwable) method.invoke(throwable, ArrayHelper.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>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>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], 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>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 = ExceptionUtils.getCause(throwable); } return count; } /** * <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 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 list = new ArrayList(); while (throwable != null) { list.add(throwable); throwable = ExceptionUtils.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>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>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 = ExceptionUtils.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>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 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>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 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>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 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 ArrayHelper.EMPTY_STRING_ARRAY; } Throwable throwables[] = getThrowables(throwable); int count = throwables.length; ArrayList frames = new ArrayList(); List nextTrace = getStackFrameList(throwables[count - 1]); for (int i = count; --i >= 0;) { List 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 causeFrames, List 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 ArrayHelper.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 list = new LinkedList(); 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>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 getStackFrameList(Throwable t) { String stackTrace = getStackTrace(t); String linebreak = LINE_SEPARATOR; StringTokenizer frames = new StringTokenizer(stackTrace, linebreak); List list = new LinkedList(); 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; } }