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.isis.core.commons.exceptions; 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.List; /** * <p>Provides utilities for manipulating and examining * <code>Throwable</code> objects.</p> * * @author Daniel L. Rall * @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 594278 2007-11-12 19:58:30Z bayard $ */ // portions copied in from commons-lang 2.6 public class ExceptionUtils { /** * <p>The names of methods commonly used to access a wrapped exception.</p> */ private static String[] CAUSE_METHOD_NAMES = { "getCause", "getNextException", "getTargetException", "getException", "getSourceException", "getRootCause", "getCausedByException", "getNested", "getLinkedException", "getNestedException", "getLinkedCause", "getThrowable", }; /** * <p>The Method object for Java 1.4 getCause.</p> */ private static final Method THROWABLE_CAUSE_METHOD; /** * <p>The Method object for Java 1.4 initCause.</p> */ private static final Method THROWABLE_INITCAUSE_METHOD; static { Method causeMethod; try { causeMethod = Throwable.class.getMethod("getCause", null); } catch (Exception e) { causeMethod = null; } THROWABLE_CAUSE_METHOD = causeMethod; try { causeMethod = Throwable.class.getMethod("initCause", new Class[] { Throwable.class }); } catch (Exception e) { causeMethod = null; } THROWABLE_INITCAUSE_METHOD = causeMethod; } /** * <p> * Public constructor allows an instance of <code>ExceptionUtils</code> to be created, although that is not * normally necessary. * </p> */ public ExceptionUtils() { super(); } //----------------------------------------------------------------------- /** * <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 * @since 1.0 */ public static Throwable getCause(Throwable throwable) { synchronized (CAUSE_METHOD_NAMES) { 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 * @since 1.0 */ public static Throwable getCause(Throwable throwable, String[] methodNames) { if (throwable == null) { return null; } Throwable cause = getCauseUsingWellKnownTypes(throwable); if (cause == null) { if (methodNames == null) { synchronized (CAUSE_METHOD_NAMES) { 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>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) { // exception ignored } catch (SecurityException ignored) { // exception ignored } if (method != null && Throwable.class.isAssignableFrom(method.getReturnType())) { try { return (Throwable) method.invoke(throwable, /*ArrayUtils.*/EMPTY_OBJECT_ARRAY); } catch (IllegalAccessException ignored) { // exception ignored } catch (IllegalArgumentException ignored) { // exception ignored } catch (InvocationTargetException ignored) { // exception ignored } } return null; } private static final Object[] EMPTY_OBJECT_ARRAY = new Object[0]; /** * <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) { // exception ignored } catch (SecurityException ignored) { // exception ignored } if (field != null && Throwable.class.isAssignableFrom(field.getType())) { try { return (Throwable) field.get(throwable); } catch (IllegalAccessException ignored) { // exception ignored } catch (IllegalArgumentException ignored) { // exception 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(); synchronized (CAUSE_METHOD_NAMES) { 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) { // exception ignored } catch (SecurityException ignored) { // exception ignored } } } try { Field field = cls.getField("detail"); if (field != null) { return true; } } catch (NoSuchFieldException ignored) { // exception ignored } catch (SecurityException ignored) { // exception ignored } return false; } /** * <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(Throwable throwable) { List list = getThrowableList(throwable); return (Throwable[]) 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 getThrowableList(Throwable throwable) { List list = new ArrayList(); while (throwable != null && list.contains(throwable) == false) { list.add(throwable); throwable = ExceptionUtils.getCause(throwable); } return list; } //----------------------------------------------------------------------- /** * <p>A way to get the entire nested stack-trace of an throwable.</p> * * <p>The result of this method is highly dependent on the JDK version * and whether the exceptions override printStackTrace or not.</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(); } }