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CS 547/CS490-003 Advanced Network Programming
CORBA: Concept and Programming (2)
Department of Computer Science
Southern Illinois University Edwardsville
Spring, 2010
Dr. Hiroshi Fujinoki
E-mail: [email protected]
CORBA_1/001
CS 547 Advanced Network Programming
Presentation Agenda
1. Overview for a simple CORBA application: CORBA Time Server and Client
2. CORBA Programming Concept
3. Coding IDL
4. Coding CORBA Time Server and Client
5. Executing the CORBA server and client
CORBA_2/002
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CORBA Time Server and Client Overview
• CORBA Time Client requests the current time
• CORBA broker forwards the client request to the time server
Time Client
Time Server
Request
Request (What time?)
Reply
Reply (Current Time)
CORBA Broker
CORBA/003
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CORBA Time Server and Client Overview (continued)
• CORBA Time Client requests the current time
• CORBA broker forwards the client request to the time server
CORBA Broker
Time Server
Time Client
Request (What time?)
Reply
• Put the CORBA Broker at the server host
CORBA/004
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The CORBA ORB we are going to use
• Java 2 SDK - the CORBA ORB developed by Sun Microsystems
• Java 2 SDK Standard Edition v.1.4.0, rev. 01 (v.1.4.0_01)
• Java IDL assumes JAVA for its programming language
• Java 2 contains a free CORBA ORB
• Java 2 SDK for Win32 environment is available
- Posted in CS547/CS490-003 Home
- A little bit big (about 32MB)
- Sample server/client source will be posted
CORBA_2/005
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Installing Java 2 SDK
• Download java-2 SDK standard Edition for Win32 environment
• Can be downloaded from the Sun web site for J2SE
(http://java.sun.com/j2se/1.4/)
J2SE
J2SE CORBA
Java IDL
ORB
CORBA_2/006
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CORBA Time Server and Client Overview (continued)
Time Client
CORBA program
CORBA
Time Client
Time Server
Current_Time(); 11:01:58
Current_Time();
ORB
ORB
IIOP
IIOP
TCP/IP
TCP/IP
Internet
CORBA_2/007
Time Server
CORBA program
CORBA Interface
(IDL)
CS 547 Advanced Network Programming
CORBA Time Server and Client Overview (continued)
Time Client
What_time(); 11:01:58
Time Server
11:01:58
ORB
ORB
IIOP
IIOP
TCP/IP
TCP/IP
Internet
CORBA_2/008
CORBA Interface
(IDL)
CS 547 Advanced Network Programming
CORBA Time Server and Client Overview (continued)
Time Client
Time Server
Current_Time();
Current_Time();
ORB
ORB
IIOP
TCP/IP
IIOP
CORBA IDL
TCP/IP
• CORBA IDL to define the interface for the caller function
• IDL file is not a function implementation but a definition of the function
CORBA_2/009
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CORBA Time Server and Client Overview (continued)
Time Client
“Stub”
“Skeleton”
Time Server
Current_Time();
Current_Time();
ORB
ORB
IIOP
TCP/IP
CORBA IDL
IIOP
TCP/IP
• After a CORBA IDL is compiled, the client stub and server skeleton
are created
• Client stub and server skeleton are the interface between your
programming language and a CORBA ORB
CORBA_2/010
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Client Stub
1. A client stub has exactly the same interface as the remote object
a CORBA client is trying to call
2. The client stub communicates with the local ORB to talk to
the actual remote object
3. The client stub also performs data marshaling/unmarshaling between
a CORBA client and the local ORB
Marshaling/unmarshaling = convert the format of data
CORBA_2/011
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Client Stub
• A client stub is a proxy object
Host A
CORBA Client Process
Local object call
local
object
local
object
local
object
Remote object call
through CORBA
ORB
Host B
remote
object
ORB
Network
CORBA_2/012
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Client Stub
Host A
CORBA Client Process
local
object
Local object call
local
object
Local object call
client
stub
local
object
Remote object call
through CORBA
ORB
Host B
Client stub talks to
ORB on behalf of
a calling client
remote
object
ORB
Network
CORBA_2/013
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Server Skeleton
• A server skeleton is an ORB – remote method interface
• A remote method is implemented in some high-level
programming language (such as C++, Java, COBOL, FORTLAN, CGI…)
• There must be a translator program between an ORB and a remote object
• The translator must know how to call the remote object
(1) Type of programming language
(2) Input parameters (parameter types)
(3) Output parameters (parameter types)
CORBA_2/014
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Host A
remote
CORBA Client Process
object
local
object
Local object call
local
object
Local object call
client
Skeleton
stub
local
object
ORB
ORB
Host B
remote
object
ORB
Network
CORBA_2/015
Remote object call
through CORBA
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CORBA Today Server/Client Development procedures
18:01 July 9, 2002
CORBA Broker
Today Server
Today Client
Request
Reply (“18:01 July 9, 2002)
CORBA_2/016
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CORBA Today Server/Client Development procedures
Example of Time Server/Client IDL:
module TodayApp
{
interface Today
{
string which_day();
oneway void shutdown();
};
};
This IDL file is assumed to be saved as “Today.IDL”
CORBA_2/017

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IDL Syntax
IDL is a language to define interface for Java and the following terms
are defined:
(1) Module: declares an object
(2) Interface: defines a name of an object
(3) Operation: declares a method in an object
(4) Parameter: defines parameters in a method
(5) Attribute: defines attributes in an object
(6) Constant: declares constant(s) in an object
(7) Exception: defines operations for exception
(8) Type: data type definition
CORBA_2/018
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CORBA Time Server/Client Development procedures
Example of Time Server/Client IDL:
Module
module TodayApp
{
interface Today
{
string which_day();
oneway void shutdown();
};
};
CORBA_2/019
Object Name
Object Methods
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CORBA Time Server/Client Development procedures
 POA File
If no error, six files
will be generated
 Stub File
 Interface File in the target
programming language
(= function prototypes)
 Helper File
CORBA IDL
CORBA IDL
Compiler
 Holder File
 Operations File
CORBA_2/020
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Compiling IDL file by JAVA IDL compiler
 Make sure that the j2sdk/bin directory (or the directory of idlj, java, javac,
and orbd) are in your path
• You can make sure your current path setting by typing “PATH”
at DOS command prompt
• If the current path does not include a path to j2sdk/bin, you can
include a path by modifying config.sys (a hidden Windows system file)
 Go to a command line prompt in Windows’ DOS box
 Change to the directory that contains your IDL file (*.idl file)
 Compile your IDL by: “idlj -fall Hello.idl”
 On success, the IDL output directory will be created with six files
CORBA_2/021
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POA (Portable Object Adapter) File
• This file contains the abstract class for stream-based (connection-oriented)
server skeleton
• POA file provides basic CORBA functionality for a CORBA server (an object)
• The server class (the server object) is implemented by extending this class
• File name: “TodayPOA.java”, if the name of IDL is “Today.idl”
This file is a skeleton (for CORBA server)
CORBA_2/022
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Stub File
• This is the client stub
• The stub file provides basic CORBA functionality for a CORBA client
• File name: “_TodayStub.java”, if the name of IDL is “Today.idl”
CORBA_2/023
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Interface File
Describe the last 3 output files from the IDL compiler
CORBA_2/024
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Helper File
• Contains the class that convert JAVA data types to/from CORBA data types
• File name: “TodayHelper.java”, if the IDL file is “Today.idl”
Holder File
• Contains public functions and variables in the resulting JAVA program
• Delegates to the methods in the Helper class for reading and writing
• File name: “TodayHolder.java”, if the IDL file is “Today.idl”
CORBA_2/025
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Operations File
• Contains the methods in the client process
• This file defines the signatures (the interface) of all methods
• Shared by the stub and the skeleton
• File name: “TodayOperations.java”, if the IDL is “Today.idl”
CORBA_2/026
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Time Server Source Code
JAVA
Compiler
Time Server Executable
CORBA IDL
CORBA IDL
Compiler
Time Client Source Code
CORBA_2/027
Time Client Executable
JAVA
Compiler
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Today Server Source Code
Compiler




Today Server Executable


CORBA IDL
Compiler
CORBA IDL


Today Client Source Code
CORBA_2/057
Today Client Executable

Compiler
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Coding Time Server Program: Program Organization
The CORBA server program consists of three sections:
(1) Server Setup Section
(2) Servant Section
(3) Server Body Section
Server Program
CORBA_2/030
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Section 1: Server Setup Section
// TodayServer.java
import TodayApp.*;
import org.omg.CosNaming.*;
import org.omg.CosNaming.NamingContextPackage.*;
import org.omg.CORBA.*;
import org.omg.PortableServer.*;
import org.omg.PortableServer.POA;
import java.util.Properties;
CORBA_2/031

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Section 2: Servant Section
Implementation of
“which_day” method
class TodayImpl extends TodayPOA
{
private ORB orb;
public void setORB(ORB orb_val)
{ orb = orb_val; }
public String which_day()
{
return ("\n18:01 July 9, 2002");
}
}
CORBA_2/032

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Servant
• An ORB creates an object (= activates a servant) based on a servant
when a CORBA client makes a request to it
• Servant is a CORBA server service registered to an ORB
= implementation of your CORBA server object
CORBA_2/028
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Object Adapter
• When a CORBA server is started, CORBA object may not be created
• OA creates (instantiates) and deletes local CORBA objects
• Most popular OA is POA (Portable Object Adapter)
• When a CORBA server is started, the operations are registered to its ORB
CORBA_2/029
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Object Adapter
What is OA (Object Adapter)?
• OA (Object Adapter) is an ORB component
• OA manages (creates and deletes) local CORBA objects
CORBA Server
Servant
Create
Register
ORB
CORBA_2/029
POA
CORBA
Object
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Section 3: Server Body Section
 Initialize the local ORB
 Get reference to RootPOA & activate the POAmanager
 Create an ORB servant and register it with the ORB setup at 
 Get object reference from the servant created at 
 Get the root naming context
 Bind the object reference in naming
 Wait for invocation from clients
CORBA_2/033

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 Initialize the local ORB
Pointer to ORB
properties (default = NULL)
ORB orb = ORB.init (args, null);
“args” in main () can be passed here
• ORB.init initializes the local ORB and needs to be called
at the beginning
• The call to the ORB’s init () method passes in the server’s command
line arguments, allowing you to set certain properties at runtime
• Special ORB properties can be specified
CORBA_2/034
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 Get reference to the RootPOA & activate the POAManager
POA rootpoa = POAHelper.narrow (orb.resolve_initial_references(“RootPOA”);
Rootpoa.the POAManager().activate();
• The reference to the root POA is retrieved in the first line
• The POA Manager is activated
CORBA_2/035
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 Get reference to the RootPOA & activate the POAManager
CORBA Server
CORBA Server
Servant
Servant
Create
Register
Register
POA1
POAn
Root POA
ORB
CORBA_2/036
CORBA
Object
POA Manager
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 Create a servant and register it with the ORB created at 
There are two steps to perform 
1. TodayImpl todayImpl = new TodayImpl ();
2. today_impl.setORB(orb);
CORBA_2/037
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 Create a servant and register it with the ORB created at 
Step #1
The constructor of
the “TodayImpl” class
TodayImpl todayImpl = new TodayImpl ();
Object (= the instantiation of
“TodayImpl” class)
The Servant Class Name
(“TodayImpl” class)
CORBA_2/038
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 Create a servant and register it with the ORB created at 
Step #2
Register an object to ORB (POA)
todayImpl.setORB (orb);
setORB method registers this object to
ORB (POA)
Servant object name (not servant class name)
CORBA_2/039
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 Get object reference for the servant created at 
Host C
CORBA
Broker
• IP address
• Port #
ORB
CORBA
client
ORB
=
• Protocol = TCP
Host A
Object Reference
Host B
remote
object
ORB
CORBA_2/040
TCP/IP
Internet
Object Reference
= a set of information
that physically identify
a target CORBA remote
object
CS 547 Advanced Network Programming
 Get the root naming context
CORBA Server
CORBA
Object
Get object
reference
Servant
Register
POA1
Root POA
ORB
CORBA Broker
CORBA_2/041
Network
Create
Created
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 Get the root naming context
• It is not a good idea to let a CORBA client to identify
each CORBA server by the object reference
• In CORBA, a CORBA client can call a CORBA server
by its server name
• We have to give a CORBA server a name to a CORBA Broker
CORBA_2/042
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 Get the root naming context
CORBA Server
Server
Name
CORBA
Object
Object
Reference
Servant
Register
POA1
Root POA
ORB
CORBA Broker
CORBA_2/043
Network
Create
Get object
reference
CS 547 Advanced Network Programming
 Get the root naming context
orb.omg.CORBA.Object objRef =
Object name (instantiation) of naming
Class name of naming context
context
orb.resolve_initial_references (“NameService”);
“resolve_initial_references” advertises POAs in an ORB
Constant “NameService” required
CORBA_2/044
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 Get the root naming context
NamingContextExt ncRef =
Object name (instantiation) of naming
Class name of naming context
context
NamingContextHelper.narrow(objRef);
“resolve_initial_references” advertises POAs in an ORB
Constant “NameService” required
CORBA_2/045
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 Bind the object reference in naming
Server
Name
Bind
CORBA Server
CORBA
Object
Object
Reference
Servant
Register
POA1
Root POA
CORBA Broker
ORB
Network
Advertise the servant object by “Server Name”
CORBA_2/046
Create
Get object
reference
CS 547 Advanced Network Programming
 Bind the object reference in naming
String name = “Today”;
The server name to be advertised
to a CORBA broker
NameComponentPath path [ ] = ncRef.to_name (name);
ncRef.rebind (path, href);
CORBA_2/047
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 Wait for invocation from a client
orb.run ();
After this, “Today” CORBA object (= Today CORBA Server)
is up and running, waiting for a CORBA client
CORBA_2/048
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Coding Time Client Program: Program Organization
The CORBA client program consists of two sections:
(1) Client Setup Section
(2) Client Body Section
Client Program
CORBA_2/049
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Section 1: Client Setup Section
import TodayApp.*;
import org.omg.CosNaming.*;
import org.omg.CosNaming.NamingContextPackage.*;
import org.omg.CORBA.*;
CORBA_2/050

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Section 2: Client Body Section
 Create and instantiate the local ORB
 Get the root naming context
 Resolve the object reference in Naming
 Invoke a remote CORBA object
CORBA_2/051

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 Initialize the local ORB
= same as the one in the server side
Pointer to ORB
properties (default = NULL)
ORB orb = ORB.init (args, null);
“args” in main ( ) can be passed here
CORBA_2/052
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 Get the root naming context = This is the fifth step () in the server
orb.omg.CORBA.Object objRef =
Object name (instantiation) of naming
Class name of naming context
context
orb.resolve_initial_references (“NameService”);
“resolve_initial_references” advertises POAs in an ORB
Constant “NameService” required
CORBA_2/053
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 Resolve the object reference in Naming
CORBA Client
Client
ORB
Server
Name
CORBA Broker
Network
Server name = “Today”
CORBA_2/054
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 Resolve the object reference in Naming
static Today todayImpl;
Object name
(the one specified by
“interface” keyword in IDL)
String name = “Today”;
todayImpl = TodayHelper.narrow (ncRef.resolve_str(name));
Call a CORBA Broker to find this object
CORBA_2/055
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 Invoke a remote CORBA object
Class name of your CORBA object
System.out.println (todayImpl.whcih_day());
You can call a remote CORBA object
as if it were an ordinary local JAVA object
(remote) CORBA method
A method defined in Java library
CORBA_2/056
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Today Server Source Code
Compiler




Today Server Executable


CORBA IDL
Compiler
CORBA IDL


Today Client Source Code
CORBA_2/057
Today Client Executable

Compiler
CS 547 Advanced Network Programming
CORBA Today Server/Client Development procedures
(1) Create a project directory (such as “Time”)
(2) Create the IDL file and save it in the directory created at (1)
(3) Compile the IDL file (: “idlj –fall Today.idl” in the directory
(4) If no error, a subdirectory, “TodayApp” will be created and the
six output files from IDL compiler will be placed in the subdirectory
(5) Create a server source code file in “Time” directory (TodayServer.java)
(6) Compile the server program (: “javac TodayServer.java TodayApp/*.java”)
(7) Create a client source code file in “Time” directory (TodayClient.java)
(8) Compile the client program (: “javac TodayClient.java TodayApp/*.java”)
CORBA_2/058
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Execute the programs: Procedures
Port# the CORBA Broker
is listening to
Step1: Start the CORBA Broker
start ordb –ORBInitialPort 1050 –ORBInitialHost localhost
Step2: Start the server program
IP address of a machine
to start a CORBA broker
Port# the CORBA Broker is listing to
start java TodayServer –ORBInitialPort 1050 –ORBInitialHost localhost
IP address of a machine where the CORBA broker is running
CORBA_2/059
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Execute the programs: Procedures
Step3: Start the client program
Port# the CORBA Broker is listing to
java TodayClient –ORBInitialPort 1050 –ORBInitialHost <IP of the broker>
IP address of a machine where the CORBA broker is running
CORBA_2/060
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Execute the programs: Procedures (continued)
CORBA Broker
Today Server
Today Client
Request
Reply
CORBA/061
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Execute the programs: Procedures (continued)
Expected output:
18:01 July 9, 2002
Today Client
CORBA/062
CORBA Broker
Today Server
CS 547 Advanced Network Programming
CORBA Today Server and Client Overview (continued)
Time Client
CORBA program
Time Client
Time Server
Current_Time(); 11:01:58
Current_Time();
ORB
ORB
IIOP
IIOP
TCP/IP
TCP/IP
Internet
Data transfer “pass by value”
CORBA/063
Time Server
CORBA program