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NJIT

Creando Archivos CORBA IDL

Preethi Balasubramanian

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Contents

The CORBA Interface Definition Language

(IDL)

Declaring data members, methods, andparameters

The interface compiler

Separating client and server on differentmachines

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CORBA IDL

La CORBA Idioma de Definicin Interfaces (IDL)

Declarando miembros de datos, mtodos, y

parmetros

El compilador de la interfaz

Separando al cliente y el servidor en mquinas

diferentes

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The Interface Definition

The interface is the syntax part of thecontract that the server object offers to theclients that invoke it.

Clients access objects only through theiradvertised interface, invoking only thoseoperations that the object exposes through its

IDL interface, with only those parameters(input and output) that are included in theinvocation.

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The Interface Definition

The IDL interface definition is independent

of programming language.

It is mapped to programming languagesusing the interface compiler.

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Example - Calc.idl

module Calc{

interface Calculator {

float calculate(in float val1, in

float val2, in char operator);

}

}

This is an interface for a Calculator with one

methodcalculate. A module can have many

interfaces.

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Mapping IDL to Java, C++

IDL Java C++

module package namespace

interface interface abstract class

operation method member function

attribute pair of methods pair of functionsexception exception exception

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Declaring Data Members

Data members are declared using theattributekeyword. The declaration must include a name and a

type. Attributes are readable and writable by default. To

make a readonly attribute, use thereadonlykeyword.IDL compiler generates public read and write methods

for the data member as required.

For example,attribute long assignable ;

generates,int assignable();void assignable (int i);

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Declaring Data Members

CORBA const values declared in an IDL map to

public static finalfields in the correspondingJava interface. Constants not declared inside theinterface are mapped topublic interface with

the same name containing a field value.const float sample = 2.3;

It is also possible to define your own types usingthe typedef keyword.

typedef string name;

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Declaring Methods (contd.)

module Calc{interface Calculator{

//User-defined exception

exception MyException{};

//synchronous methodfloat calculate(in float val1, in float

val2, in char operator) raises (MyException);

//asynchronous method

oneway void set_value(in long val);};

};

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More on Exceptions

System Exceptionsare thrown when

something goes wrong with the system.User Exceptionsare generated if somethinggoes wrong inside the execution of the remote

method. They are declared inside the IDL

definition for the object, and are automaticallygenerated by the IDL compiler. Implementation

of these exceptions depends on the language

mapping.

There are two types of CORBA exceptions:

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Declaring Parameters

Parameters can be of following types: Basic (char,

long,short,float,bool, etc.), Constructed (struct,

union,array,sequence), Typed objects, orany.

Parameters can be declared asin,out, orinout.

inparameters are copied from client to server

outparameters are copied from server to clientinoutparameters are used both for incoming and

outgoing information and are copied both ways.

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Declaring Parameters(contd.)

CORBA 2.0 supports only pass-by-value for

non-object data types. Objects are passed by

reference.

CORBA 3.0 supports pass-by-value for

objects by using the valuetypekeyword.

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Interface Compilers

IDL Compilers implement languagemappings in software.

They compile the interface definition(defined using IDL) to produce output thatcan be compiled and linked with an objectimplementation and its clients.

Every ORB comes with one or more IDLcompilers, one for each language that itsupports.

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Interface Compilers (contd.)

Many vendors supply their IDL compilers.Because the compilers implement mappingstandards, every vendor's IDL compilerproduces language code with the samemappings, making the code vendorindependent.

Suns JDK provides the idlj compiler.VisiBroker provides idl2cpp and idl2javacompilers.

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Need for Interface Compiler

The interface compiler converts the languageindependent IDL to language specific code thatC++, Java or other language clients and servers

can understand.For example, theidljcompiler compiles the IDLto Java code.

IDL allows an object implementer to choose the

appropriate programming language for the object.Client and server can be developed in parallel.

Clients depend only on the interface and not theimplementation of the server code.

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Need for Interface Compiler

By using IDL and interface compiler, thefollowing can be defined independent of theprogramming language :

Modularized object interfaces

Operations and attributes that an objectsupports

Exceptions raised by an operation Data types of an operation return value, its

parameters, and an object's attributes

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The idlj compiler

To compile the IDL to java usingidlj,

idlj -fall

Thefalloption creates both server and

client files.

-fclient generates client files only (default).

fservergenerates server files only.

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Files created by idlj(contd.)

Calc.CalculatorOperations The interfacethat defines the exposed remote methods.

Calc._CalculatorStub- The client stub.Implements a local object representing theremote CORBA object. This object forwardsall requests to the remote object. The client

does not use this class directly. Calc._CalculatorImplBase- An abstract

class that implements the Calculatorinterface. It is the server skeleton.

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Separating client and server

_CalculatorStub

Calculator

CalculatorHelper

CalculatorHolder CalculatorOperations

_CalculatorImplBase

Calculator

CalculatorOperations

Client Server

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Running the ApplicationDefine Interface

Compile Interface (idlj)

javac

Holder

Helper Implement Interface

Client stub

Operations

Server Skeleton

Operations

Start ORBjavac

Start Client Start Server

Implement Client

Client Server

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References

Client/Server Programming with Java and

CORBA Robert Orfali and Dan Harkey

http://developer.java.sun.com http://www.omg.org

http://www.infosys.tuwien.ac.at/Research/

Corba

http://www.objs.com