org.apache.commons.lang.exception
Class ExceptionUtils

java.lang.Object
  org.apache.commons.lang.exception.ExceptionUtils

public class ExceptionUtils

extends Object

Provides utilities for manipulating and examining Throwable objects.

Since:

1.0

Version:

$Id: ExceptionUtils.java,v 1.34 2003/08/21 15:52:55 ggregory Exp $

Author:

Daniel Rall, Dmitri Plotnikov, Stephen Colebourne, Gary Gregory, Pete Gieser

Constructor Summary

ExceptionUtils()
Public constructor allows an instance of ExceptionUtils to be created, although that is not normally necessary.

Method Summary

static void	addCauseMethodName(String methodName) Adds to the list of method names used in the search for Throwable objects.
static Throwable	getCause(Throwable throwable) Introspects the Throwable to obtain the cause.
static Throwable	getCause(Throwable throwable, String[] methodNames) Introspects the Throwable to obtain the cause.
static String	getFullStackTrace(Throwable throwable) A way to get the entire nested stack-trace of an throwable.
static Throwable	getRootCause(Throwable throwable) Introspects the Throwable to obtain the root cause.
static String[]	getRootCauseStackTrace(Throwable throwable) Creates a compact stack trace for the root cause of the supplied Throwable.
static String[]	getStackFrames(Throwable throwable) Captures the stack trace associated with the specified Throwable object, decomposing it into a list of stack frames.
static String	getStackTrace(Throwable throwable) Gets the stack trace from a Throwable as a String.
static int	getThrowableCount(Throwable throwable) Counts the number of Throwable objects in the exception chain.
static Throwable[]	getThrowables(Throwable throwable) Returns the list of Throwable objects in the exception chain.
static int	indexOfThrowable(Throwable throwable, Class type) Returns the (zero based) index of the first Throwable that matches the specified type in the exception chain.
static int	indexOfThrowable(Throwable throwable, Class type, int fromIndex) Returns the (zero based) index of the first Throwable that matches the specified type in the exception chain from a specified index.
static boolean	isNestedThrowable(Throwable throwable) Checks whether this Throwable class can store a cause.
static boolean	isThrowableNested() Checks if the Throwable class has a getCause method.
static void	printRootCauseStackTrace(Throwable throwable) Prints a compact stack trace for the root cause of a throwable to System.err.
static void	printRootCauseStackTrace(Throwable throwable, PrintStream stream) Prints a compact stack trace for the root cause of a throwable.
static void	printRootCauseStackTrace(Throwable throwable, PrintWriter writer) Prints a compact stack trace for the root cause of a throwable.
static void	removeCommonFrames(List causeFrames, List wrapperFrames) Removes common frames from the cause trace given the two stack traces.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

ExceptionUtils

public ExceptionUtils()

Public constructor allows an instance of ExceptionUtils to be created, although that is not normally necessary.

Method Detail

addCauseMethodName

public static void addCauseMethodName(String methodName)

Adds to the list of method names used in the search for Throwable objects.

Parameters:

methodName - the methodName to add to the list, null and empty strings are ignored

Since:

2.0

getCause

public static Throwable getCause(Throwable throwable)

Introspects the Throwable to obtain the cause.

The method searches for methods with specific names that return a Throwable object. This will pick up most wrapping exceptions, including those from JDK 1.4, and NestableException. The method names can be added to using addCauseMethodName(String).

The default list searched for are:

• getCause()
• getNextException()
• getTargetException()
• getException()
• getSourceException()
• getRootCause()
• getCausedByException()
• getNested()

In the absence of any such method, the object is inspected for a detail field assignable to a Throwable.

If none of the above is found, returns null.

Parameters:

throwable - the throwable to introspect for a cause, may be null

Returns:

the cause of the Throwable, null if none found or null throwable input

getCause

public static Throwable getCause(Throwable throwable,
                                 String[] methodNames)

Introspects the Throwable to obtain the cause.

1. Try known exception types.
2. Try the supplied array of method names.
3. Try the field 'detail'.

A null set of method names means use the default set. A null in the set of method names will be ignored.

Parameters:

throwable - the throwable to introspect for a cause, may be null

methodNames - the method names, null treated as default set

Returns:

the cause of the Throwable, null if none found or null throwable input

getRootCause

public static Throwable getRootCause(Throwable throwable)

Introspects the Throwable to obtain the root cause.

This method walks through the exception chain to the last element, "root" of the tree, using getCause(Throwable), and returns that exception.

Parameters:

throwable - the throwable to get the root cause for, may be null

Returns:

the root cause of the Throwable, null if none found or null throwable input

isThrowableNested

public static boolean isThrowableNested()

Checks if the Throwable class has a getCause method.

This is true for JDK 1.4 and above.

Returns:

true if Throwable is nestable

Since:

2.0

isNestedThrowable

public static boolean isNestedThrowable(Throwable throwable)

Checks whether this Throwable class can store a cause.

This method does not check whether it actually does store a cause.

Parameters:

throwable - the Throwable to examine, may be null

Returns:

boolean true if nested otherwise false

Since:

2.0

getThrowableCount

public static int getThrowableCount(Throwable throwable)

Counts the number of Throwable objects in the exception chain.

A throwable without cause will return 1. A throwable with one cause will return 2 and so on. A null throwable will return 0.

Parameters:

throwable - the throwable to inspect, may be null

Returns:

the count of throwables, zero if null input

getThrowables

public static Throwable[] getThrowables(Throwable throwable)

Returns the list of Throwable objects in the exception chain.

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 null throwable will return an array size zero.

Parameters:

throwable - the throwable to inspect, may be null

Returns:

the array of throwables, never null

indexOfThrowable

public static int indexOfThrowable(Throwable throwable,
                                   Class type)

Returns the (zero based) index of the first Throwable that matches the specified type in the exception chain.

A null throwable returns -1. A null type returns -1. No match in the chain returns -1.

Parameters:

throwable - the throwable to inspect, may be null

type - the type to search for

Returns:

the index into the throwable chain, -1 if no match or null input

indexOfThrowable

public static int indexOfThrowable(Throwable throwable,
                                   Class type,
                                   int fromIndex)

Returns the (zero based) index of the first Throwable that matches the specified type in the exception chain from a specified index.

A null throwable returns -1. A null type returns -1. No match in the chain returns -1. A negative start index is treated as zero. A start index greater than the number of throwables returns -1.

Parameters:

throwable - the throwable to inspect, may be null

type - the type to search for

fromIndex - the (zero based) index of the starting position, negative treated as zero, larger than chain size returns -1

Returns:

the index into the throwable chain, -1 if no match or null input

printRootCauseStackTrace

public static void printRootCauseStackTrace(Throwable throwable)

Prints a compact stack trace for the root cause of a throwable to System.err.

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.

The method is equivalent to printStackTrace for throwables that don't have nested causes.

Parameters:

throwable - the throwable to output

Since:

2.0

printRootCauseStackTrace

public static void printRootCauseStackTrace(Throwable throwable,
                                            PrintStream stream)

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.

The method is equivalent to printStackTrace for throwables that don't have nested causes.

Parameters:

throwable - the throwable to output, may be null

stream - the stream to output to, may not be null

Throws:

IllegalArgumentException - if the stream is null

Since:

2.0

printRootCauseStackTrace

public static void printRootCauseStackTrace(Throwable throwable,
                                            PrintWriter writer)

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.

The method is equivalent to printStackTrace for throwables that don't have nested causes.

Parameters:

throwable - the throwable to output, may be null

writer - the writer to output to, may not be null

Throws:

IllegalArgumentException - if the writer is null

Since:

2.0

getRootCauseStackTrace

public static String[] getRootCauseStackTrace(Throwable throwable)

Creates a compact stack trace for the root cause of the supplied Throwable.

Parameters:

throwable - the throwable to examine, may be null

Returns:

an array of stack trace frames, never null

Since:

2.0

removeCommonFrames

public static void removeCommonFrames(List causeFrames,
                                      List wrapperFrames)

Removes common frames from the cause trace given the two stack traces.

Parameters:

causeFrames - stack trace of a cause throwable

wrapperFrames - stack trace of a wrapper throwable

Throws:

IllegalArgumentException - if either argument is null

Since:

2.0

getStackTrace

public static String getStackTrace(Throwable throwable)

Gets the stack trace from a Throwable as a String.

Parameters:

throwable - the Throwable to be examined

Returns:

the stack trace as generated by the exception's printStackTrace(PrintWriter) method

getFullStackTrace

public static String getFullStackTrace(Throwable throwable)

A way to get the entire nested stack-trace of an throwable.

Parameters:

throwable - the Throwable to be examined

Returns:

the nested stack trace, with the root cause first

Since:

2.0

getStackFrames

public static String[] getStackFrames(Throwable throwable)

Captures the stack trace associated with the specified Throwable object, decomposing it into a list of stack frames.

Parameters:

throwable - the Throwable to exaamine, may be null

Returns:

an array of strings describing each stack frame, never null