OpenCard Framework 1.2 Programmer's Guide - OpenSCDP

Obtaining a card service
Handling exceptions
Card services are the means by which smart card functions are made available to
the application. Thus, the next step is to obtain the proper instance of a given card
service.
The actions you have to take depend on the nature of the application. We
distinguish between two types of applications: (1) the ones that are prepared to
work with only one particular card-resident application, and (2) the ones that can
interact with a variety of different (at least two) card-resident applications.
In the first situation, you have probably specified the CardService class that you
already required at the time you issued the waitForCard call. The code fragment to
obtain e.g. FileAccessCardService looks like this:
FileAccessCardService facs = null;
try {
facs = (FileAccessCardService)
card.getCardService(FileAccessCardService, true);
} catch OpenCard Exceptions {
// handle error...
}
You’re now ready to start working with the requested card service. We’ll show you
how to work with some of the available card services in subsequent sections.
In the situation where your application can interact with several different
card-resident applications, you will have to find out what card-resident
applications are present. For that purpose, you must obtain
AppletAccessCardService, which has a list method that lets you obtain the list of
applications on the card. In this case, the code looks something like this:
AppletAccessCardService aacs = null;
try {
aacs = (AppletAccessCardService)
card.getCardService(AppletAccessCardService, true);
} catch OpenCard Exceptions {
// handle error...
}
You’re now ready to write the code to select a particular application in the card.
We’ll show you how to do that in the next section.
It is important that provisions be made in every code for dealing with exceptional
circumstances, and OPENCARD FRAMEWORK features a number of corresponding
methods for responding appropriately to unusual situations.
At the root of OCF’s exception hierarchy are two classes:
opencard.core.OpenCardException and opencard.core.OpenCardRuntimeException.
The first is a subclass of JAVA’s IOException and is therefore checked, while the
second is a subclass of RuntimeException and is thus unchecked. The distinction is
that the latter need not be caught or declared to be thrown (i.e. the compiler does
not force you to handle these exceptions - hence the term ’unchecked exception’).
The rationale behind this concept is that exceptions of this kind disrupt the normal
program flow so severely that continuing would not make much sense. Further,
from a pragmatic point of view, it would often be impractical to check for these
conditions (an example of this is OutOfMemoryError, which can be thrown
Chapter 4. Programming with OCF 21