ExceptionUtils.java

/*
 * Copyright 2002-2005 The Apache Software Foundation.
 * 
 * Licensed 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.lang.exception;

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.Arrays;
import java.util.LinkedList;
import java.util.List;
import java.util.StringTokenizer;

import org.apache.commons.lang.ArrayUtils;
import org.apache.commons.lang.StringUtils;
import org.apache.commons.lang.SystemUtils;

/**
 * <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 $Id$
 */
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>
     */
    private static String[] CAUSE_METHOD_NAMES = {
        "getCause",
        "getNextException",
        "getTargetException",
        "getException",
        "getSourceException",
        "getRootCause",
        "getCausedByException",
        "getNested",
        "getLinkedException",
        "getNestedException",
        "getLinkedCause",
        "getThrowable",
    };

    /**
     * <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;
    }
    
    /**
     * <p>Public constructor allows an instance of <code>ExceptionUtils</code>
     * to be created, although that is not normally necessary.</p>
     */
    public 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 (StringUtils.isNotEmpty(methodName) && !isCauseMethodName(methodName)) {            
            List list = getCauseMethodNameList();
            if (list.add(methodName)) {
                CAUSE_METHOD_NAMES = toArray(list);
            }
        }
    }

    /**
     * <p>Removes from the list of method names used in the search for <code>Throwable</code>
     * objects.</p>
     * 
     * @param methodName  the methodName to remove from the list, <code>null</code>
     *  and empty strings are ignored
     * @since 2.1
     */
    public static void removeCauseMethodName(String methodName) {
        if (StringUtils.isNotEmpty(methodName)) {
            List list = getCauseMethodNameList();
            if (list.remove(methodName)) {
                CAUSE_METHOD_NAMES = toArray(list);
            }
        }
    }

    /**
     * Returns the given list as a <code>String[]</code>.
     * @param list a list to transform.
     * @return the given list as a <code>String[]</code>.
     */
    private static String[] toArray(List list) {
        return (String[]) list.toArray(new String[list.size()]);
    }

    /**
     * Returns {@link #CAUSE_METHOD_NAMES} as a List.
     * @return {@link #CAUSE_METHOD_NAMES} as a List.
     */
    private static ArrayList getCauseMethodNameList() {
        return new ArrayList(Arrays.asList(CAUSE_METHOD_NAMES));
    }

    /**
     * <p>Tests if the list of method names used in the search for <code>Throwable</code>
     * objects include the given name.</p>
     * 
     * @param methodName  the methodName to search in the list.
     * @return if the list of method names used in the search for <code>Throwable</code>
     *  objects include the given name.
     * @since 2.1
     */
    public static boolean isCauseMethodName(String methodName) {
        return ArrayUtils.indexOf(CAUSE_METHOD_NAMES, methodName) >= 0;
    }

    /**
     * <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) {
        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) {
                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, ArrayUtils.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 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(Throwable throwable, 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(Throwable throwable, Class clazz, 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(Throwable throwable, 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(Throwable throwable, Class type, int fromIndex) {
        return indexOf(throwable, type, fromIndex, true);
    }

    private static int indexOf(Throwable throwable, Class type, int fromIndex, boolean subclass) {
        if (throwable == null || type == null) {
            return -1;
        }
        if (fromIndex < 0) {
            fromIndex = 0;
        }
        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 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 ArrayUtils.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 examine, may be null
     * @return an array of strings describing each stack frame, never null
     */
    public static String[] getStackFrames(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>
     *  
     * <p>Functionality shared between the
     * <code>getStackFrames(Throwable)</code> methods of this and the
     * {@link org.apache.commons.lang.exception.NestableDelegate}
     * classes.</p>
     * @param stackTrace A stack trace String.
     * @return an array where each element is a line from the argument.
     */
    static String[] getStackFrames(String stackTrace) {
        String linebreak = SystemUtils.LINE_SEPARATOR;
        StringTokenizer frames = new StringTokenizer(stackTrace, linebreak);
        List list = new LinkedList();
        while (frames.hasMoreTokens()) {
            list.add(frames.nextToken());
        }
        return toArray(list);
    }

    /**
     * <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>&quot;&nbsp;&nbsp;&nbsp;at&quot;.</code></p>
     * 
     * @param t is any throwable
     * @return List of stack frames
     */
    static List getStackFrameList(Throwable t) {
        String stackTrace = getStackTrace(t);
        String linebreak = SystemUtils.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;
    }
    
}