Best way to check whether a certain exception type was the cause (of a cause, etc ...) in a nested exception?
Solution 1
Why would you want to avoid getCause
. You can, of course, write yourself a method to perform the task, something like:
public static boolean isCause(
Class<? extends Throwable> expected,
Throwable exc
) {
return expected.isInstance(exc) || (
exc != null && isCause(expected, exc.getCause())
);
}
Solution 2
If you are using Apache Commons Lang, then you can use the following:
(1) When the cause should be exactly of the specified type
if (ExceptionUtils.indexOfThrowable(exception, ExpectedException.class) != -1) {
// exception is or has a cause of type ExpectedException.class
}
(2) When the cause should be either of the specified type or its subclass type
if (ExceptionUtils.indexOfType(exception, ExpectedException.class) != -1) {
// exception is or has a cause of type ExpectedException.class or its subclass
}
Solution 3
I don't think you have any choice but to call through the layers of getCause. If you look at the source code for the Spring NestedRuntimeException that you mention that is how it is implemented.
Solution 4
Imitation is the sincerest form of flattery. Based on a quick inspection of the source, this is exactly what NestedRuntimeException does:
/**
* Check whether this exception contains an exception of the given type:
* either it is of the given class itself or it contains a nested cause
* of the given type.
* @param exType the exception type to look for
* @return whether there is a nested exception of the specified type
*/
public boolean contains(Class exType) {
if (exType == null) {
return false;
}
if (exType.isInstance(this)) {
return true;
}
Throwable cause = getCause();
if (cause == this) {
return false;
}
if (cause instanceof NestedRuntimeException) {
return ((NestedRuntimeException) cause).contains(exType);
}
else {
while (cause != null) {
if (exType.isInstance(cause)) {
return true;
}
if (cause.getCause() == cause) {
break;
}
cause = cause.getCause();
}
return false;
}
}
CAVEAT: The above is the code as of 4 March 2009 so, if you really want to know what Spring is doing right now, you should research the code as it exists today (whenever that is).
Solution 5
Based on Patrick Boos answer: If you using Apache Commons Lang 3 you can check:
indexOfThrowable: Returns the (zero based) index of the first Throwable that matches the specified class (exactly) in the exception chain. Subclasses of the specified class do not match
if (ExceptionUtils.indexOfThrowable(e, clazz) != -1) {
// your code
}
or
indexOfType: Returns the (zero based) index of the first Throwable that matches the specified class or subclass in the exception chain. Subclasses of the specified class do match
if (ExceptionUtils.indexOfType(e, clazz) != -1) {
// your code
}
Example for multiple types with Java 8:
Class<? extends Throwable>[] classes = {...}
boolean match = Arrays.stream(classes)
.anyMatch(clazz -> ExceptionUtils.indexOfType(e, clazz) != -1);
Yang Meyer
iOS Craftsman. Creating delightful user interfaces through high-quality code.
Updated on July 28, 2022Comments
-
Yang Meyer almost 2 years
I am writing some JUnit tests that verify that an exception of type
MyCustomException
is thrown. However, this exception is wrapped in other exceptions a number of times, e.g. in an InvocationTargetException, which in turn is wrapped in a RuntimeException.What's the best way to determine whether MyCustomException somehow caused the exception that I actually catch? I would like to do something like this (see underlined):
try { doSomethingPotentiallyExceptional(); fail("Expected an exception."); } catch (RuntimeException e) { if (!e.
wasCausedBy(MyCustomException.class) fail("Expected a different kind of exception."); }
I would like to avoid calling
getCause()
a few "layers" deep, and similar ugly work-arounds. Is there a nicer way?(Apparently, Spring has NestedRuntimeException.contains(Class), which does what I want - but I'm not using Spring.)
CLOSED: OK, I guess there's really no getting around a utility method :-) Thanks to everybody who replied!
-
DavidS about 7 yearsNote that this algorithm may cause an infinite loop if the cause has a loop, which can happen in some cases like EclipseLink DB exceptions. Apache Commons Lang ExceptionUtils::getRootCause handles this case, so probably
indexOfThrowable
from Patrick's answer does as well. -
Brett about 7 years@DavidS Not an infinite loop - it'd quick throw
StackOverflowError
. If you've got a breakdown in causality like that then you've got bigger problems (probably trying to reuse exception objects even though they are strangely mutable). -
DavidS about 7 yearsA StackOverflowError then, thanks. Regardless, this isn't a problem with code I've written; it's a problem in some common libraries, including some Oracle jdbc drivers. It's a common enough problem that Apache Commons chose to handle it in
getRootCause
, Oracle chose to handle it in printStackTrace, and Guava considered handling it in Throwables. My comment was intended to warn of this, not recommend how best to construct Exceptions. -
Brett about 7 years@DavidS I'm disappointed libraries have shipped with predestination paradoxes. Interesting the OpenJDK
printStackTace
source makes a suggestion about guarding against malicious exceptions, but fails in more than one way. P4 bug - I'd be more worried about the library than attempting to deal with every possible DoS bug. Code that is susceptible to this sort of this is ubiquitous - usesequals
for instance. -
Joshua Goldberg about 5 yearsI think this might also cause an infinite loop in some circumstances, like some other answers. (I've seen such a chain in getCause() for NoClassDefFound exceptions, for example.) To avoid would require the check like the
cause.getCause() == cause
in the answer based on Spring from @BobCross. -
Joshua Goldberg about 5 yearsI've also seen infinite loops in pure-JDK
NoClassDefFound
errors (arising from another exception getting triggered during a static initialization block.) -
Tharindu Sathischandra almost 4 yearsThen how can we return our expected cause exception?
-
Tharindu Sathischandra almost 4 years
public static Throwable getCauseException( Class<? extends Throwable> expected, Throwable e ) { if(e == null) return null; if(expected.isInstance(e)){ return e; } return getCauseException(expected, e.getCause());}
For getting the cause error. -
Gabriel over 3 yearsor
ExceptionUtils.hasCause(e, ExpectedException.class)
-
M. Justin over 2 years@JoshuaGoldberg This has been safe against infinite loops since 23.0, released in 2017, per guava#2866. More specifically, it will throw an
IllegalArgumentException
in this case. -
Joshua Goldberg over 2 yearsJust to note, hasCause is in apache's ExceptionUtils (There are some other packages with ExceptionUtils classes.)
-
Joshua Goldberg over 2 years@M.Justin, when the chain is recursive and getCausalChain throws the IllegalArgumentException, does that prevent it from being used to check for a particular exception type in the cause chain?
-
M. Justin over 2 yearsCorrect, you couldn't use this method to check for a particular exception if there's a loop. What it does do in this scenario is protect you from the code blocking forever due to an infinite loop.