Exception not catched but program exit and finally is executed

Question

I am doing a pressure test on linux server.But I find that my java app always exit without any error message.So I use try-catch-finally and want to get some information about the exit reason.Code like:

try{
// the code which make my program exit without any error log
}catch(Throwable e){
//print some log
}finally{
// print some log
}

I find that the catch clause is never executed but the finally log is executed when my program exit.Anyone could tell my how could this happen?I am quite sure the code in try{} exit with some problem instead of normal exit. Since the code in try{} is doing a while loop and consume very much memory , so , could the reason is that jvm exit because memory is used up?

`I am quite sure the code in try{} exit with some problem instead of normal exit`. "Quite sure" doesn't instill much confidence. — Kon, Jan 18 '16 at 03:19
Why not manually throw exceptions? or add debugging methods to the java app that are enabled based on an argument passed in at run time? are you actually printing to the correct location/window as well? you haven't given enough code to really show us the issue. — Byren Higgin, Jan 18 '16 at 03:21

score 2 · Answer 1 · answered Jan 18 '16 at 03:25

I see two possibilities:

You are mistaken that the try-block is throwing an exception: maybe no exception is being thrown, or maybe there is an exception being thrown, but it's being caught before the end of the try-block.
- You can double-check by adding logging statements at the end of the try-block and immediately before any return or break or continue statement that could exit the try-block prematurely.
The exception-type you are catching is not the usual java.lang.Throwable, but rather, some other Throwable class that you have explicitly defined and/or imported.
- You can double-check by changing Throwable to the more-explicit java.lang.Throwable.

Stephen C · Answer 2 · 2016-01-18T05:41:27.747

I find that the catch clause is never executed but the finally log is executed when my program exit.

That would mean that the try block is NOT throwing an exception¹.

The finally block will be executed irrespective of how the try block and the chosen catch block (if any) terminates.

However, it could also be that your "finding" about the catch clause is incorrect.

Anyone could tell my how could this happen?

See above.

I am quite sure the code in try{} exit with some problem instead of normal exit.

On what evidence?

Since the code in try{} is doing a while loop and consume very much memory, so could the reason is that jvm exit because memory is used up?

That would result in an OutOfMemoryError and the catch block for Throwable should catch that.

The only case where it is possible that the try block throws an exception and the catch for Throwable doesn't appear to work is if the catch itself throws another exception ... before it does what you were trying to do (i.e. log the error). That scenario is possible if the first exception was OutOfMemoryError. If the GC was unable to free any memory when the scope of the try block exited, then a second OOME might be thrown if the logging code needed to create objects.

It should be noted that catching Throwable is dangerous. It catches various Error exceptions that should not be caught because they are not recoverable. Bad things can happen.

^{1 - It is also theoretically possible that Throwable in your code is not java.lang.Throwable, but only a crazy person would write and use their own Throwable exception class .... and then forget that they had done that :-).}

Exception not catched but program exit and finally is executed

2 Answers2