How do I supply a custom exception to be thrown if the Preconditions reports a run time failure ?

[Rahul Agrawal]

Example if I had something to be verified as :


if (count <= 0) {
throw new mycustomRuntimeException("must be positive: " +
count);
}

and I want to use the Preconditions, how do I achieve the same.

This may even lead to another question as to if it really addes value
to introduce a custom runtime exception in such a scenario.

-rahul

[Robert Konigsberg]

In short, you don't. You can set up your own preconditions class that
has a similar structure to Preconditions if this is a common
occurrence.

I agree it addresses the value of a custom exception, but that's
something that can only be adequately answered in the context of your
project.

> --
> guava-...@googlegroups.com
> Project site: http://guava-libraries.googlecode.com
> This group: http://groups.google.com/group/guava-discuss
>
> This list is for general discussion.
> To report an issue: http://code.google.com/p/guava-libraries/issues/entry
> To get help: http://stackoverflow.com/questions/ask (use the tag "guava")
>

--
Robert Konigsberg
konig...@gmail.com

[Ricardo Redder]

I'm not sure if that helps you.... but can't you catch the Preconditions exception, and throw your custom exception, using the former as a your cause?

Something like:

try {

Preconditions.checkArgument(count > 0, "must be positive: %s", count);

} catch (IllegalArgumentException e) {

throw new MyCustomException(e);

}

ok... i agree it doesn't look nice, especially if you have multiple conditions to validate... but it might do the job.

Regards,

Redder

[Robert Konigsberg]

Given how little code is behind Preconditions, I'll just say that's
not worth it.

--
Robert Konigsberg
konig...@gmail.com

[Ricardo Redder]

hehe.... well pointed

--
Redder

[Benjamin Manes]

If you wanted something reusable and custom, I imagine it would be easy to whip something using Hamcrest such as:

checkThat(count, is(greaterThan(0)), elseThrow(MyCustomException.class));

[Robert Konigsberg]

Preconditions.throwIf(boolean b, RuntimeException e) {
if (!b) throw e;
}

throwIf(count > 0, new MyException());

Just kidding.

--
Robert Konigsberg
konig...@gmail.com

[Sam Berlin]

On Thu, Apr 14, 2011 at 4:46 PM, Robert Konigsberg <konig...@gmail.com> wrote:

Preconditions.throwIf(boolean b, RuntimeException e) {
 if (!b) throw e;
}

throwIf(count > 0, new MyException());

While gross, that actually has the kinda nice property that the first line in the stack trace is the code you care about, as opposed to the Preconditions lines.

 sam

[Colin Decker]

Another option:

public static void check(boolean b, Supplier<? extends RuntimeException> exceptionSupplier) {

  if (!b) {

    RuntimeException e = exceptionSupplier.get();

    e.fillInStackTrace();

    throw e;

  }

}

Could even make a version that took a Function<String, ? extends RuntimeException> to let Preconditions do its string building! (That might actually look half decent in Java 8 with constructor references.)

...seriously though, a simple "if (...) throw" seems best for less common exceptions.

-- 

Colin

[morten hattesen]

If you were to choose this solution, you'd better prevent new
Exceptions from being constructed for each test by pre-constructing
the exception in a constant, wherever possible.

private static final RuntimException MY_EX = new MyException();

Preconditions.throwIf(boolean b, RuntimeException e) {
  if (!b) throw e;
}

...
throwIf(count > 0, MY_EX);


On 14 Apr., 22:50, Sam Berlin <sber...@gmail.com> wrote:

> On Thu, Apr 14, 2011 at 4:46 PM, Robert Konigsberg <konigsb...@gmail.com>wrote:
>
> > Preconditions.throwIf(boolean b, RuntimeException e) {
> >  if (!b) throw e;
> > }
>
> > throwIf(count > 0, new MyException());
>
> While gross, that actually has the kinda nice property that the first line
> in the stack trace is the code you care about, as opposed to the
> Preconditions lines.
>
>  sam
>
> > Just kidding.
>
> > On Thu, Apr 14, 2011 at 4:23 PM, Benjamin Manes <bma...@google.com> wrote:
> > > If you wanted something reusable and custom, I imagine it would be easy
> > to
> > > whip something using Hamcrest such as:
> > > checkThat(count, is(greaterThan(0)), elseThrow(MyCustomException.class));
>

> > > On Thu, Apr 14, 2011 at 1:18 PM, Robert Konigsberg <konigsb...@gmail.com

>
> > > wrote:
>
> > >> Given how little code is behind Preconditions, I'll just say that's
> > >> not worth it.
>
> > >> On Thu, Apr 14, 2011 at 4:15 PM, Ricardo Redder
> > >> <ricardo.red...@gmail.com> wrote:
> > >> > I'm not sure if that helps you.... but can't you catch the
> > Preconditions
> > >> > exception, and throw your custom exception, using the former as a your
> > >> > cause?
> > >> > Something like:
> > >> > try {
> > >> > Preconditions.checkArgument(count > 0, "must be positive: %s", count);
> > >> > } catch (IllegalArgumentException e) {
> > >> > throw new MyCustomException(e);
> > >> > }
> > >> > ok... i agree it doesn't look nice, especially if you have multiple
> > >> > conditions to validate... but it might do the job.
> > >> > Regards,
>
> > >> > On Thu, Apr 14, 2011 at 8:59 AM, Robert Konigsberg

> > >> > <konigsb...@gmail.com>

> > >> > wrote:
>
> > >> >> In short, you don't. You can set up your own preconditions class that
> > >> >> has a similar structure to Preconditions if this is a common
> > >> >> occurrence.
>
> > >> >> I agree it addresses the value of a custom exception, but that's
> > >> >> something that can only be adequately answered in the context of your
> > >> >> project.
>
> > >> >> On Thu, Apr 14, 2011 at 7:41 AM, Rahul Agrawal <

> > rahulagra...@gmail.com>

> > >> >> wrote:
> > >> >> > Example if I had something to be verified as :
>
> > >> >> >  if (count <= 0) {
> > >> >> >       throw new mycustomRuntimeException("must be positive: " +
> > >> >> > count);
> > >> >> >     }
>
> > >> >> > and I want to use the Preconditions, how do I achieve the same.
>
> > >> >> > This may even lead to another question as to if it really addes
> > value
> > >> >> > to introduce a custom runtime exception in such a scenario.
>
> > >> >> > -rahul
>
> > >> >> > --
> > >> >> > guava-...@googlegroups.com
> > >> >> > Project site:http://guava-libraries.googlecode.com
> > >> >> > This group:http://groups.google.com/group/guava-discuss
>
> > >> >> > This list is for general discussion.
> > >> >> > To report an issue:
> > >> >> >http://code.google.com/p/guava-libraries/issues/entry

> > >> >> > To get help:http://stackoverflow.com/questions/ask(use the tag

> > >> >> > "guava")
>
> > >> >> --
> > >> >> Robert Konigsberg

> > >> >> konigsb...@gmail.com

>
> > >> >> --
> > >> >> guava-...@googlegroups.com
> > >> >> Project site:http://guava-libraries.googlecode.com
> > >> >> This group:http://groups.google.com/group/guava-discuss
>
> > >> >> This list is for general discussion.
> > >> >> To report an issue:
> > >> >>http://code.google.com/p/guava-libraries/issues/entry

> > >> >> To get help:http://stackoverflow.com/questions/ask(use the tag

> > >> >> "guava")
>
> > >> > --
> > >> > Redder
>
> > >> --
> > >> Robert Konigsberg

> > >> konigsb...@gmail.com

>
> > >> --
> > >> guava-...@googlegroups.com
> > >> Project site:http://guava-libraries.googlecode.com
> > >> This group:http://groups.google.com/group/guava-discuss
>
> > >> This list is for general discussion.
> > >> To report an issue:
> >http://code.google.com/p/guava-libraries/issues/entry

> > >> To get help:http://stackoverflow.com/questions/ask(use the tag

> > "guava")
>
> > --
> > Robert Konigsberg

> > konigsb...@gmail.com

[Robert Konigsberg]

Yes, I was making a joke (see the "just kidding" at the bottom.)

> To get help: http://stackoverflow.com/questions/ask (use the tag "guava")
>

--
Robert Konigsberg
konig...@gmail.com