CORBA - An Introduction to Network Programming with Java - page 155

environment to handle). To specify that a method may cause an exception to be
generated, the keyword raises is used. For example:
void myMethod(in dummy) raises (MyException);
(Note that brackets are required around the exception type.)

Obviously, raises maps to throws in Java.
One fi nal IDL keyword worth mentioning is typedef . This allows us to create
new types from existing ones. For example:

typedef sequence<long> IntSeq;
This creates a new type called IntSeq, which is equivalent to a sequence/array of
integers. This new type can then be used in data property declarations. For example:

attribute IntSeq numSeq;
N.B. If a structured type (array, sequence, etc.) is required as a data attribute or
parameter, then we cannot declare it directly as a structured type, but must use typedef
to create the new type and then use that new type. Thus, a declaration such as

attribute sequence<long> numSeq;
would be rejected.

6.3 The Java IDL Process

At the heart of Java IDL is a compiler that translates the programmer's IDL into
Java constructs, according to the IDL-to-Java mapping. Prior to J2SE 1.3, this com-
piler was called idltojava and was available as a separate download. As of J2SE 1.3,
the compiler is called idlj and is part of the core Java download. The stub and skel-
eton fi les (and a number of other fi les) are generated by the idlj compiler for each
object type that is specifi ed in the .idl fi le. Once these fi les have been generated, the
Java implementation fi les may be written, compiled and linked with the idlj -
generated fi les and the ORB library to create an object server, after which client
program(s) may be written to access the service provided.
Although the preceding two sentences summarise the basic procedure, there are
several steps required to set up a CORBA client/server application. These steps are
listed below.

1. Use the idlj compiler to compile the above fi le, generating up to six fi les for each
interface defi ned.
2. Implement each interface as a 'servant'.
3. Create the server (incorporating servants).
4. Compile the server and the idlj -generated fi les.
5. Create a client.
6. Compile the client.
7. Run the application.