Add support to pass in message when using validate with boolean condition

[anjo-swe]

Currently there's no way to pass in String message when using a boolean condition.

public static <X extends Exception> void validate(boolean condition, ExceptionFactory<X> factory) throws X {
    if (!condition) {
      throw factory.newInstance(null);
    }
}

[helsing]

You could achieve it via creating a decorator class for the exception factory. Like this:

  private static <X extends Exception> ExceptionFactory<X> failWith(final ExceptionFactory<X> xFactory, final String message) {
    // (Obviously we could use a lambda expression instead, when in Java8)
    return new ExceptionFactory<X>() {
      @Override
      public X newInstance(String ignored) {
        return xFactory.newInstance(message);
      }
    };
  }

and then use it like this:

  import static org.valid4j.ExceptionFactories.exception;

  @Test
  public void shouldDescribeFailedValidation() {
    validate(false, failWith(exception(IllegalStateException.class), "failure message"));
  }

Would this work for you? Or would you suggest a better approach?