CORBA_1/001 Department of Computer Science Southern Illinois University Edwardsville Spring, 2010...

CORBA_1/001

Department of Computer ScienceSouthern Illinois University Edwardsville

Spring, 2010

Dr. Hiroshi FujinokiE-mail: [email protected]

CORBA: Concept and Programming (2)

CS 547/CS490-003 Advanced Network Programming

CORBA_2/002

CS 547 Advanced Network Programming

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

Presentation Agenda


CORBA Broker

Request (What time?) Request

Reply

CORBA/003

CORBA Time Server and Client Overview

Time Client Time Server

Reply (Current Time)

• CORBA Time Client requests the current time

• CORBA broker forwards the client request to the time server


CORBA Broker

Request (What time?)

Reply

CORBA/004

CORBA Time Server and Client Overview (continued)

Time Client Time Server

• CORBA Time Client requests the current time

• CORBA broker forwards the client request to the time server

• Put the CORBA Broker at the server host

CORBA_2/005


The CORBA ORB we are going to use

• Java 2 SDK

• Java IDL assumes JAVA for its programming language

• Java 2 contains a free CORBA ORB

• Java 2 SDK for Win32 environment is available

- the CORBA ORB developed by Sun Microsystems

- Posted in CS547/CS490-003 Home

• Java 2 SDK Standard Edition v.1.4.0, rev. 01 (v.1.4.0_01)

- A little bit big (about 32MB)

- Sample server/client source will be posted

CORBA_2/006


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_2/007


Time Client

11:01:58

Time Server

ORB

IIOP

TCP/IP

ORB

IIOP

TCP/IP

Internet

Time Client CORBA program

Time Server CORBA program

CORBA

CORBA Interface(IDL)

Current_Time();Current_Time();


CORBA_2/008


Time Client

What_time(); 11:01:58

Time Server

11:01:58

ORB

IIOP

TCP/IP

ORB

IIOP

TCP/IP

Internet

CORBA Interface(IDL)


CORBA_2/009


Time Client

ORB

IIOP

TCP/IP

Time Server

ORB

IIOP

TCP/IP


CORBA IDL

• CORBA IDL to define the interface for the caller function

• IDL file is not a function implementation but a definition of the function


CORBA_2/010


Time Client

ORB

IIOP

TCP/IP

Time Server

ORB

IIOP

TCP/IP


CORBA IDL

• After a CORBA IDL is compiled, the client stub and server skeleton are created

“Stub”“Skeleton”

• Client stub and server skeleton are the interface between your programming language and a CORBA ORB

CORBA_2/011


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_2/012


Client Stub • A client stub is a proxy object

localobject

localobject

localobject

Host A

Local object callCORBA Client Process

Remote object callthrough CORBA

ORB

Network

remoteobject

ORB

Host B

CORBA_2/013


Client Stub

localobject

localobject

localobject

remoteobject

ORB

Host A

Local object call

ORB


Network

clientstub

CORBA Client Process

Local object call

Client stub talks toORB on behalf of

a calling client

Host B

CORBA_2/014


Server Skeleton

• A server skeleton is an ORB – remote method interface

• There must be a translator program between an ORB and a remote object

• The translator must know how to call the remote object

• A remote method is implemented in some high-level programming language (such as C++, Java, COBOL, FORTLAN, CGI…)

(1) Type of programming language

(2) Input parameters (parameter types)

(3) Output parameters (parameter types)

CORBA_2/015


remoteobject

ORB

Network

localobject

localobject

localobject

Host A

Local object call

ORB


clientstub

CORBA Client Process

Local object call

Host B

remoteobject

ORB

Skeleton


CORBA_2/016

CORBA BrokerToday Client Today Server

Request

CORBA Today Server/Client Development procedures

18:01 July 9, 2002

Reply (“18:01 July 9, 2002)

CORBA_2/017


Example of Time Server/Client IDL:

This IDL file is assumed to be saved as “Today.IDL”

module TodayApp{ interface Today { string which_day(); oneway void shutdown(); };};


CORBA_2/018


IDL Syntax

IDL is a language to define interface for Java and the following termsare defined:

(1) Module

(2) Interface

(3) Operation

(4) Parameter

(5) Attribute

(6) Constant

(7) Exception

(8) Type

: declares an object

: defines a name of an object

: declares a method in an object

: defines parameters in a method

: defines attributes in an object

: declares constant(s) in an object

: defines operations for exception

: data type definition

CORBA_2/019


CORBA Time Server/Client Development procedures

Example of Time Server/Client IDL:

module TodayApp{ interface Today { string which_day(); oneway void shutdown(); };};

Module Object Name

Object Methods

CORBA_2/020


CORBA Time Server/Client Development procedures

CORBA IDLCORBA IDL

Compiler

POA File

Stub File

(= function prototypes)

Interface File in the target programming language

Helper File

Holder File

Operations File

If no error, six files will be generated

CORBA_2/021


Compiling IDL file by JAVA IDL compiler

Go to a command line prompt in Windows’ DOS box

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)

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_2/022


• This file contains the abstract class for stream-based (connection-oriented) server skeleton

POA (Portable Object Adapter) File

• The server class (the server object) is implemented by extending this class

• POA file provides basic CORBA functionality for a CORBA server (an object)

This file is a skeleton (for CORBA server)

• File name: “TodayPOA.java”, if the name of IDL is “Today.idl”

CORBA_2/023


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_2/024


Describe the last 3 output files from the IDL compiler

Interface File

CORBA_2/025


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

• File name: “TodayHolder.java”, if the IDL file is “Today.idl”

• Delegates to the methods in the Helper class for reading and writing

CORBA_2/026


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_2/027


CORBA IDLCORBA IDL

Compiler

Time Server Source Code JAVACompiler

JAVACompiler

Time Server Executable

Time Client Executable

Time Client Source Code

CORBA_2/057


CORBA IDLCORBA IDL

Compiler

Today Server Source Code

Today Client Source Code

Compiler

Compiler

Today Server Executable

Today Client Executable

Server ProgramCORBA_2/030


Coding Time Server Program: Program Organization

The CORBA server program consists of three sections:

(3) Server Body Section

(1) Server Setup Section

(2) Servant Section

CORBA_2/031


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_2/032


Section 2: Servant Section 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"); }}

Implementation of “which_day” method

CORBA_2/028


Servant

• Servant is a CORBA server service registered to an ORB

• An ORB creates an object (= activates a servant) based on a servant when a CORBA client makes a request to it

= implementation of your CORBA server object

CORBA_2/029


Object Adapter

• When a CORBA server is started, CORBA object may not be created

• When a CORBA server is started, the operations are registered to its ORB

• OA creates (instantiates) and deletes local CORBA objects

• Most popular OA is POA (Portable Object Adapter)


ORB POA

CORBA Server

CORBAObject

Servant

Register

Create

Object Adapter

What is OA (Object Adapter)?

• OA manages (creates and deletes) local CORBA objects

• OA (Object Adapter) is an ORB component

CORBA_2/029

CORBA_2/033


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_2/034


Initialize the local ORB

ORB orb = ORB.init (args, null);

• 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

“args” in main () can be passed here

• Special ORB properties can be specified

Pointer to ORBproperties (default = NULL)

CORBA_2/035


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_2/036


Get reference to the RootPOA & activate the POAManager

ORB

Root POA

POA1

CORBA Server

Servant

Register

CORBAObject

Create

POAn

CORBA Server

Servant

Register

POA Manager

CORBA_2/037


Create a servant and register it with the ORB created at

1. TodayImpl todayImpl = new TodayImpl ();

2. today_impl.setORB(orb);

There are two steps to perform

CORBA_2/038



TodayImpl todayImpl = new TodayImpl ();

The Servant Class Name(“TodayImpl” class)

Object (= the instantiation of “TodayImpl” class)

The constructor of the “TodayImpl” class

Step #1

CORBA_2/039



todayImpl.setORB (orb);

Servant object name (not servant class name)

setORB method registers this object to ORB (POA)

Register an object to ORB (POA) Step #2

CORBA_2/040


Get object reference for the servant created at

remoteobject

ORB

Host B

CORBAclient

ORB

Host A

CORBABroker

ORB

Host C

TCP/IPInterne

t

Object Reference= a set of information that physically identify a target CORBA remote object

Object Reference

• IP address• Port #

• Protocol = TCP

=

CORBA_2/041


ORB

Root POA

POA1

CORBA Server

Servant

Register

CORBA Broker

Network


CORBAObject

CreateGet objectreference

Created

CORBA_2/042



• 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_2/043


ORB

Root POA

POA1

CORBA Server

Servant

Register

CORBA Broker

Network


CORBAObject

CreateGet objectreference

ObjectReference

ServerName

CORBA_2/044



Class name of naming contextObject name (instantiation) of naming context

orb.omg.CORBA.Object objRef =

orb.resolve_initial_references (“NameService”);

“resolve_initial_references” advertises POAs in an ORB

Constant “NameService” required

CORBA_2/045



NamingContextExt ncRef =


NamingContextHelper.narrow(objRef);



ORB

Root POA

POA1

CORBA Server

Servant

Register

CORBA_2/046


CORBA Broker

Network

CORBAObject

Create


Get objectreference

Advertise the servant object by “Server Name”

BindServerName

ObjectReference

CORBA_2/047



String name = “Today”;

NameComponentPath path [ ] = ncRef.to_name (name);

ncRef.rebind (path, href);

The server name to be advertisedto a CORBA broker

CORBA_2/048


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

Client Program

CORBA_2/049


Coding Time Client Program: Program Organization

The CORBA client program consists of two sections:

(2) Client Body Section

(1) Client Setup Section

CORBA_2/050


Section 1: Client Setup Section

import TodayApp.*; import org.omg.CosNaming.*; import org.omg.CosNaming.NamingContextPackage.*; import org.omg.CORBA.*;

CORBA_2/051


Section 2: Client Body Section

Create and instantiate the local ORB

Resolve the object reference in Naming


Invoke a remote CORBA object

CORBA_2/052


ORB orb = ORB.init (args, null);

“args” in main ( ) can be passed here

Pointer to ORBproperties (default = NULL)

Initialize the local ORB = same as the one in the server side

CORBA_2/053


orb.omg.CORBA.Object objRef =


orb.resolve_initial_references (“NameService”);



Get the root naming context = This is the fifth step () in the server

CORBA_2/054


CORBA Broker

Network

ServerName

ORB

Client

Server name = “Today”

CORBA Client


CORBA_2/055



String name = “Today”;

todayImpl = TodayHelper.narrow (ncRef.resolve_str(name));

static Today todayImpl;Object name(the one specified by “interface” keyword in IDL)

Call a CORBA Broker to find this object

CORBA_2/056


Invoke a remote CORBA object

System.out.println (todayImpl.whcih_day());

You can call a remote CORBA objectas if it were an ordinary local JAVA object

Class name of your CORBA object

(remote) CORBA method

A method defined in Java library

CORBA_2/057


CORBA IDLCORBA IDL

Compiler

Today Server Source Code

Today Client Source Code

Compiler

Compiler

Today Server Executable

Today Client Executable

CORBA_2/058



(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_2/059


Execute the programs: Procedures

Step1: Start the CORBA Broker

Step2: Start the server program

start ordb –ORBInitialPort 1050 –ORBInitialHost localhost

start java TodayServer –ORBInitialPort 1050 –ORBInitialHost localhost

Port# the CORBA Broker is listening to

IP address of a machineto start a CORBA broker

Port# the CORBA Broker is listing to

IP address of a machine where the CORBA broker is running

CORBA_2/060


Execute the programs: Procedures

Step3: Start the client program

java TodayClient –ORBInitialPort 1050 –ORBInitialHost <IP of the broker>

Port# the CORBA Broker is listing to

IP address of a machine where the CORBA broker is running


CORBA/061


Execute the programs: Procedures (continued)

Request

Reply


CORBA/062


Execute the programs: Procedures (continued)

Expected output:

18:01 July 9, 2002


CORBA/063

CORBA Today Server and Client Overview (continued)

Time Client

11:01:58

Time Server

ORB

IIOP

TCP/IP

ORB

IIOP

TCP/IP

Internet

Time Client CORBA program

Time Server CORBA program


Data transfer “pass by value”

CORBA_1/001 Department of Computer Science Southern Illinois University Edwardsville Spring, 2010...

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