ExceptionUtils.java

package org.codehaus.plexus.util;

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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;

/**
 * <p>
 * <code>ExceptionUtils</code> provides utilities for manipulating <code>Throwable</code> objects.
 * </p>
 *
 * @author <a href="mailto:dlr@finemaltcoding.com">Daniel Rall</a>
 * @author Dmitri Plotnikov
 * @author Stephen Colebourne
 * @since 1.0
 *
 */
public class ExceptionUtils
{
    /**
     * Used when printing stack frames to denote the start of a wrapped exception. Package private for accessibility by
     * test suite.
     */
    static final String WRAPPED_MARKER = " [wrapped] ";

    /**
     * The names of methods commonly used to access a wrapped exception.
     */
    protected static String[] CAUSE_METHOD_NAMES = { "getCause", "getNextException", "getTargetException",
        "getException", "getSourceException", "getRootCause", "getCausedByException", "getNested" };

    /**
     * Constructs a new <code>ExceptionUtils</code>. Protected to discourage instantiation.
     */
    protected 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, null and empty strings are ignored
     */
    public static void addCauseMethodName( String methodName )
    {
        if ( methodName != null && methodName.length() > 0 )
        {
            List<String> list = new ArrayList<String>( Arrays.asList( CAUSE_METHOD_NAMES ) );
            list.add( methodName );
            CAUSE_METHOD_NAMES = list.toArray( new String[list.size()] );
        }
    }

    /**
     * <p>
     * Introspects the specified <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 The method names can be added to using
     * {@link #addCauseMethodName(String)}. The default list searched for are:
     * </p>
     * <ul>
     * <li><code>getCause()</code>
     * <li><code>getNextException()</code>
     * <li><code>getTargetException()</code>
     * <li><code>getException()</code>
     * <li><code>getSourceException()</code>
     * <li><code>getRootCause()</code>
     * <li><code>getCausedByException()</code>
     * <li><code>getNested()</code>
     * </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 exception to introspect for a cause.
     * @return The cause of the <code>Throwable</code>.
     * @throws NullPointerException if the throwable is null
     */
    public static Throwable getCause( Throwable throwable )
    {
        return getCause( throwable, CAUSE_METHOD_NAMES );
    }

    /**
     * <p>
     * Introspects the specified <code>Throwable</code> to obtain the cause using a supplied array of method names.
     * </p>
     *
     * @param throwable The exception to introspect for a cause.
     * @param methodNames the methods names to match
     * @return The cause of the <code>Throwable</code>.
     * @throws NullPointerException if the method names array is null or contains null
     * @throws NullPointerException if the throwable is null
     */
    public static Throwable getCause( Throwable throwable, String[] methodNames )
    {
        Throwable cause = getCauseUsingWellKnownTypes( throwable );
        if ( cause == null )
        {
            for ( String methodName : methodNames )
            {
                cause = getCauseUsingMethodName( throwable, methodName );
                if ( cause != null )
                {
                    break;
                }
            }

            if ( cause == null )
            {
                cause = getCauseUsingFieldName( throwable, "detail" );
            }
        }
        return cause;
    }

    /**
     * <p>
     * Walks through the exception chain to the last element -- the "root" of the tree -- using
     * {@link #getCause(Throwable)}, and returns that exception.
     * </p>
     *
     * @param throwable the throwable to get the root cause for
     * @return The root cause of the <code>Throwable</code>.
     */
    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>
     * 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 SQLException )
        {
            return ( (SQLException) throwable ).getNextException();
        }
        else if ( throwable instanceof InvocationTargetException )
        {
            return ( (InvocationTargetException) throwable ).getTargetException();
        }
        else
        {
            return null;
        }
    }

    /**
     * <p>
     * Find a throwable 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, new Object[0] );
            }
            catch ( IllegalAccessException ignored )
            {
            }
            catch ( IllegalArgumentException ignored )
            {
            }
            catch ( InvocationTargetException ignored )
            {
            }
        }
        return null;
    }

    /**
     * <p>
     * Find a throwable 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>
     * Returns the number of <code>Throwable</code> objects in the exception chain.
     * </p>
     *
     * @param throwable the exception to inspect
     * @return The throwable count.
     */
    public static int getThrowableCount( Throwable throwable )
    {
        // Count the number of throwables
        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>
     *
     * @param throwable the exception to inspect
     * @return The list of <code>Throwable</code> objects.
     */
    public static Throwable[] getThrowables( Throwable throwable )
    {
        List<Throwable> list = new ArrayList<>();
        while ( throwable != null )
        {
            list.add( throwable );
            throwable = getCause( throwable );
        }
        return list.toArray( new Throwable[list.size()] );
    }

    /**
     * <p>
     * Delegates to {@link #indexOfThrowable(Throwable, Class, int)}, starting the search at the beginning of the
     * exception chain.
     * </p>
     * @param throwable the exception to inspect
     * @param type <code>Class</code> to look for
     * @return index of the stack matching the type
     * @see #indexOfThrowable(Throwable, Class, int)
     */
    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 of <code>Throwable</code> objects with an index greater than or equal to the specified index, or
     * <code>-1</code> if the type is not found.
     * </p>
     *
     * @param throwable the exception to inspect
     * @param type <code>Class</code> to look for
     * @param fromIndex the (zero based) index of the starting position in the chain to be searched
     * @return the first occurrence of the type in the chain, or <code>-1</code> if the type is not found
     * @throws IndexOutOfBoundsException If the <code>fromIndex</code> argument is negative or not less than the count
     *             of <code>Throwable</code>s in the chain.
     */
    public static int indexOfThrowable( Throwable throwable, Class type, int fromIndex )
    {
        if ( fromIndex < 0 )
        {
            throw new IndexOutOfBoundsException( "Throwable index out of range: " + fromIndex );
        }
        Throwable[] throwables = ExceptionUtils.getThrowables( throwable );
        if ( fromIndex >= throwables.length )
        {
            throw new IndexOutOfBoundsException( "Throwable index out of range: " + fromIndex );
        }
        for ( int i = fromIndex; i < throwables.length; i++ )
        {
            if ( throwables[i].getClass().equals( type ) )
            {
                return i;
            }
        }
        return -1;
    }

    /**
     * Prints a compact stack trace for the root cause of a throwable. 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>
     * The method is equivalent to t.printStackTrace() for throwables that don't have nested causes.
     * @param t the exception
     * @param stream the stream
     */
    public static void printRootCauseStackTrace( Throwable t, PrintStream stream )
    {
        String trace[] = getRootCauseStackTrace( t );
        for ( String aTrace : trace )
        {
            stream.println( aTrace );
        }
        stream.flush();
    }

    /**
     * Equivalent to printRootCauseStackTrace(t, System.err)
     * @param t the exception
     */
    public static void printRootCauseStackTrace( Throwable t )
    {
        printRootCauseStackTrace( t, System.err );
    }

    /**
     * Same as printRootCauseStackTrace(t, stream), except it takes a PrintWriter as an argument.
     * @param t the cause
     * @param writer the writer
     */
    public static void printRootCauseStackTrace( Throwable t, PrintWriter writer )
    {
        String trace[] = getRootCauseStackTrace( t );
        for ( String aTrace : trace )
        {
            writer.println( aTrace );
        }
        writer.flush();
    }

    /**
     * Creates a compact stack trace for the root cause of the supplied throwable. See
     * <code>printRootCauseStackTrace(Throwable t, PrintStream s)</code>
     * @param t the cause
     * @return the Stack
     */
    public static String[] getRootCauseStackTrace( Throwable t )
    {
        Throwable[] throwables = getThrowables( t );
        int count = throwables.length;
        ArrayList<String> frames = new ArrayList<>();
        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 ( String aTrace : trace )
            {
                frames.add( aTrace );
            }
        }
        return frames.toArray( new String[frames.size()] );
    }

    /**
     * Given two stack traces, removes common frames from the cause trace.
     *
     * @param causeFrames stack trace of a cause throwable
     * @param wrapperFrames stack trace of a wrapper throwable
     */
    private static void removeCommonFrames( List<String> causeFrames, List<String> wrapperFrames )
    {
        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 = causeFrames.get( causeFrameIndex );
            String wrapperFrame = wrapperFrames.get( wrapperFrameIndex );
            if ( causeFrame.equals( wrapperFrame ) )
            {
                causeFrames.remove( causeFrameIndex );
            }
            causeFrameIndex--;
            wrapperFrameIndex--;
        }
    }

    /**
     * A convenient way of extracting the stack trace from an exception.
     *
     * @param t The <code>Throwable</code>.
     * @return The stack trace as generated by the exception's <code>printStackTrace(PrintWriter)</code> method.
     */
    public static String getStackTrace( Throwable t )
    {
        StringWriter sw = new StringWriter();
        PrintWriter pw = new PrintWriter( sw, true );
        t.printStackTrace( pw );
        return sw.getBuffer().toString();
    }

    /**
     * A way to get the entire nested stack-trace of an throwable.
     *
     * @param t The <code>Throwable</code>.
     * @return The nested stack trace, with the root cause first.
     */
    public static String getFullStackTrace( Throwable t )
    {
        StringWriter sw = new StringWriter();
        PrintWriter pw = new PrintWriter( sw, true );
        Throwable[] ts = getThrowables( t );
        for ( Throwable t1 : ts )
        {
            t1.printStackTrace( pw );
            if ( isNestedThrowable( t1 ) )
            {
                break;
            }
        }
        return sw.getBuffer().toString();
    }

    /**
     * Whether an Throwable is considered nested or not.
     *
     * @param throwable The <code>Throwable</code>.
     * @return boolean true/false
     */
    public static boolean isNestedThrowable( Throwable throwable )
    {
        if ( throwable == null )
        {
            return false;
        }

        if ( throwable instanceof SQLException )
        {
            return true;
        }
        else if ( throwable instanceof InvocationTargetException )
        {
            return true;
        }

        for ( String CAUSE_METHOD_NAME : CAUSE_METHOD_NAMES )
        {
            try
            {
                Method method = throwable.getClass().getMethod( CAUSE_METHOD_NAME, null );
                if ( method != null )
                {
                    return true;
                }
            }
            catch ( NoSuchMethodException ignored )
            {
            }
            catch ( SecurityException ignored )
            {
            }
        }

        try
        {
            Field field = throwable.getClass().getField( "detail" );
            if ( field != null )
            {
                return true;
            }
        }
        catch ( NoSuchFieldException ignored )
        {
        }
        catch ( SecurityException ignored )
        {
        }

        return false;
    }

    /**
     * Captures the stack trace associated with the specified <code>Throwable</code> object, decomposing it into a list
     * of stack frames.
     *
     * @param t The <code>Throwable</code>.
     * @return An array of strings describing each stack frame.
     */
    public static String[] getStackFrames( Throwable t )
    {
        return getStackFrames( getStackTrace( t ) );
    }

    /**
     * Functionality shared between the <code>getStackFrames(Throwable)</code> methods of this and the classes.
     */
    static String[] getStackFrames( String stackTrace )
    {
        String linebreak = System.getProperty( "line.separator" );
        StringTokenizer frames = new StringTokenizer( stackTrace, linebreak );
        List<String> list = new LinkedList<String>();
        while ( frames.hasMoreTokens() )
        {
            list.add( frames.nextToken() );
        }
        return list.toArray( new String[list.size()] );
    }

    /**
     * Produces a List of stack frames - the message is not included. This works in most cases - it will only fail if
     * the exception message contains a line that starts with: " at".
     *
     * @param t is any throwable
     * @return List of stack frames
     */
    static List<String> getStackFrameList( Throwable t )
    {
        String stackTrace = getStackTrace( t );
        String linebreak = System.getProperty( "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;
    }
}