Questions about rethrowing exceptions

[Jon]

Hello,

I am relatively new to the Java language and am working on a
communications API. This API will read and write to streams derived
from a socket. Naturally, there is the possibility that a socket
failure could occur. My API internally catches exceptions of type
IOException because this needs to change the state of my network
object. However, I also need to propogate the error back out to the
calling application. I am currently attempting to do so as shown
below:

try
{
...
}
catch(IOException e)
{
// do my own processing here
throw e;
}

My question is whether this is an appropriate use of exceptions and
whether it will have the intended consequences of propogating the
exception to the application?

Regards,

Jon Trauntvein

 

[Christopher Benson-Manica]

(I am not a guru, but...)

try
{
...
}
catch(IOException e)
{
// do my own processing here
throw e;
}

My question is whether this is an appropriate use of exceptions and
whether it will have the intended consequences of propogating the
exception to the application?

Yes, IME it's common to re-throw exceptions in this manner, and it
will do what you intend.

 

[Thomas Fritsch]

I am relatively new to the Java language and am working on a
communications API. This API will read and write to streams derived
from a socket. Naturally, there is the possibility that a socket
failure could occur. My API internally catches exceptions of type
IOException because this needs to change the state of my network
object. However, I also need to propogate the error back out to the
calling application. I am currently attempting to do so as shown
below:

try
{
...
}
catch(IOException e)
{
// do my own processing here
throw e;
}

My question is whether this is an appropriate use of exceptions and
whether it will have the intended consequences of propogating the
exception to the application?

Your approach is OK as long as your try/catch is inside a method which
is declared with "throws IOException".

Another approach (which is possible since Java 1.4) is to wrap the
caught IOException into your own Exception object like below:

void yourMethod(...) throws YourException
{
try
{
...
}
catch(IOException e)
{
// do my own processing here
YourException e2 = new YourException("...");
e2.initCause(e);
throw e2;
}
}

See also the API docs of Throwable#initCause and Throwable#printStackTrace.