6565730 CORBA Overview Developing Basic CORBA Applications Distributed Systems Frameworks

8/14/2019 6565730 CORBA Overview Developing Basic CORBA Applications Distributed Systems Frameworks

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CORBA Overview;

Developing Basic CORBA

ApplicationsDS 520 - Distributed Systems Frameworks


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Distributed Systems Frameworks 2

Review

Anatomy and Requirements of Distributed ComputingAdvantages and Features of DOC Systems

General Architecture of DOC Systems

Overview of Object Management Architecture and CORBA


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Distributed Computing

Can think of DC as: breaking down an application into individual computing agents distributed over a network

work together on a cooperative task

Motivation for DC:

parallel processing: can solve larger problems without larger computers

applications and data may be difficult to relocate

redundant processing agents for fault tolerant systems

Flavors of Distributed Programming

Messaging

Asynchronous, Open-loop: programmer must maintain context

Examples; socket programming, cgi (based on http), etc.

Remote Invocation

Synchronous (usually), Closed-loop, Location transparency (looks like a local call)

Examples: Remote Procedure Call (RPC), Distributed Objects


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General Pattern for Remote Invocation

Call:

marshal arguments convert to network format

locate server

transmit data

Client Code

Client Code

Stub

Server Code

Server Code

Skeleton

Infrastructure

Infrastructure

Serve:

receive data

convert & unmarshal

invoke methodmarshall return value

transmit data


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Anatomy of a Distributed Application

3 layers of a distributed application: network level (TCP/IP, network protocols) higher-level services (directory services, security protocols, etc.)

application level

At the application level:

processes

threads

objects: processes can be made up of one or more objects which can be accessed by one

or more threads within the process

agents: an independent functional element (e.g., in a banking application we may

have a customer agent, a transaction agent, an information brokerage agent)

Example (the customer agent): object1: running on client machine (2 threads: listening for data; updating display)

object2: running on the bank server (issuing queries; sending data back to client)


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Requirements for a Distributed Application

Partitioning and Distributing Data and Functions

data-driven distribution functional distribution

object-based distribution

Flexible, Extendible Communication Protocols

allocation of tasks to agents has a direct influence on the complexity of the communication

protocol (type of data, amount of data, persistence of connections)

may also be dictated by legacy systems that need to be incorporated

Multi-threading Requirements

server object may need to service multiple remote agents at once

effective way to optimize resources

Security Requirements

authentication of agent identities

define resource access levels

data encryption


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Features of DOC Systems Object Interface Specification

to allow clients to access objects regardless of implementation details Object Manager

The core of a distributed object system (e.g., ORB, or Registry in RMI)

Manages object skeletons and object references on the server

When a client requests a new object, the object manager

locates the skeleton for the class of the requested object

creates new instance based on skeleton; stores new object in the object storage

sends a reference to the new object back to the client

Registration / Naming Service

Acts as an intermediary between the object client and the object manager

Once the interface to an object is defined, an implementation of the interface must

be registered with the service so that it can be addressed by clients

Object Communication Protocol to handle remote object requests

Must support a means of transmitting and receiving object and method references,

and data in the form of objects or basic data types


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General Architecture for a DOC System

IDLCom

pilers

RegistrationService

ObjectSkeleton

ObjectStorage

Object Manager

Naming Service

Client Application

Server

Implementation

Client Stub

Interface

Object

Interface

Specification


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Remote Object Transactions at Runtime

Object

Stubs

Server ObjectImplementation

Object

Skeleton

Object Manager Naming Service

Client

Application

2.Resolve

Object

4. Object

Interactions

1.Request

Object

3. Object

Handle


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OMGs Mission

Develop a single architecture, using object technology, fordistributed application integration, guaranteeing: reusability of components; interoperability & portability;

basis in commercially available software

Consensus-based approach Focus on swiftly-developed, easily usable (off the shelf)

component standards:

Single terminology for object-orientation.

Common abstract framework.

Common reference model. Common interfaces & protocols


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Non-standardizedapplication-specific

interfaces

Verticaldomain-specific

interfaces

Horizontalfacility interfaces

Application Interfaces DomainInterfaces CORBAfacilities

General service interfaces

CORBAservices

Object Request Broker

Object Management Architecture


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Overview of CORBA Objects CORBA objects differ from typical programming language objects:

CORBA objects can be located anywhere on a network. CORBA objects (like Java objects) can run on any platform.

CORBA objects can be written in any of several languages. CORBA object developers need know nothing of where their clients willbe, what hardware or OS they will run on, or what language they will be

written in.

CORBA objects approach universal accessibility.

A client of an object has access to an object reference for the object, and

invokes operations on the object.

A client knows only the logical structure of the object according to its interface and

experiences the behavior of the object through invocations.

Client code has no knowledge of the implementation of the object or which ORB is used to

access the implementation.

An object implementation provides the semantics of the object, usually by

defining data for the object instance and code for the object's methods.


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ClientClient Object ImplementationObject Implementation

ORB

RequestRequest

A Request A request consists of:

Target object (target object identified by a unique object reference)

Operation

Parameters (the input, output and in-out parameters defined for the operation;

may be specified individually or as a list)

Optional request context

Results (the result values returned by the operation)

Skeletoncode

Skeleton

code

Client Proxy

(stub code)

Client Proxy

(stub code)


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CORBA Framework Elements

Object Request Broker (ORB)

This is the object manager in CORBA

Mechanisms for specifying interfaces

Interface Definition Language (IDL) - for static interface definitions

Dynamic Invocation Interface (DII) - lets clients access interfaces as first-classobjects at run-time from an Interface Repository.

Internet Inter-Orb Protocol (IIOP)

A binary protocol for communication between ORBs.

Was added in CORBA 2.0


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Today

CORBA Framework and Components

CORBA IDL

Steps in Developing CORBA Applications

Examples


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Object Request Broker (ORB)

The Object Manager in CORBA

On client side the ORB is responsible for accepting requests for a remote object

finding implementation of the object

accepting client-side reference to the remote object(converted to a language

specific form, e.g., a Java stub object)

routing client method calls through the object reference to the objectimplementation

On server side the ORB

lets object servers register new objects

receives requests from the client ORB

uses objects skeleton interface to invoke objects activation method

creates reference for new object and sends it back to client


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OMG IDLOMG Interface Definition Language (IDL):

mappings for many languages/compilers;

independent of any particular language/compiler;

multiple-inheritance, public interface-structured specification language;

not for implementation.

primary support for interoperability between static and dynamic requests

mechanisms.

IDL Structure

Module

a namespace Interface

abstract typemultiple inheritance

Struct

structured data

Module auction {exception NotAllowed {};

struct Sale {int price;string item;

}interface Auction {void bid (in long price)raises NotAllowed;

}}

Module auction {exception NotAllowed {};

struct Sale {int price;string item;

}

interface Auction {void bid (in long price)raises NotAllowed;

}}


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Internet Inter-Orb Protocol (IIOP)

CORBA specification is neutral with respect to network protocols the CORBA standard specifies what is known as the General Inter-ORB Protocol (GIOP)

GIOP is a high-level standard protocol for communication between ORBs

not used directly; instead, it is specialized by a particular protocol that would then be

used directly

Internet Inter-ORB Protocol (IIOP)

IIOP is the GIOP-based protocol for TCP/IP networks As of the 2.0 version of the CORBA specification, vendors are required to implement the

IIOP protocol

CORBA Networking Model

CORBA applications are built on top of GIOP-derived protocols such as IIOP

these protocols, in turn, rest on top of TCP/IP, DCE, or other underlying transport

protocol the network uses

an application architecture can be designed to use a bridge that would interconnect, for

instance, DCE-based application components with IIOP-based ones.


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Passing Objects by Reference

In a distributed application, there are two possible methods for

an application component to obtain access to an object in

another process:

When an object ispassed by reference, the object itself remains "in place"

while an object reference for that object is passed. Operations on the object

through the object reference are actually processed by the object itself.

When an object ispassed by value, the object's state is copied and passed to its

destination (via object serialization), where a new copy of the object is

instantiated. Operations on that object's copy are processed by the copy, not by

the original object.

Note: in CORBA, objects are generally passed by reference (however, CORBA

3.0 specification has now added pass-by-value semantics).


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Object References An Object Reference is the information needed to specify an object

within an ORB.

The representation of an object reference handed to a client is only valid for the lifetime

of that client.

The language mapping also provides additional ways to access object references in a

typed way for the convenience of the programmer.

There is a distinguished object reference, thenull reference, guaranteed to be differentfrom all object references, that denotes no object. In Java, this is a Javanull.

To invoke a CORBA object, you need a reference for the object. There

are two ways to get a reference for a CORBA object:

from another object, such as a factory or a name service

from a string that was specially created from an object reference

Interoperable Object References CORBA uses IOR as a pointer to a specific instance of a class in a distributed

environment

encodes host, port, object identity

may be externalized (using object_to_string)


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CORBA Components Client stub

Each stub represents (it is a proxy) an object operation (a possible request) which a client

invokes in a language-dependent manner (e.g., by calling a subroutine which represents the

operation).

The stubs make calls on the rest of the ORB using interfaces that are private to JavaIDL.

Alternatively, a client may dynamically construct and invoke request objects which can

represent any object operation.

Implementation Skeleton Each skeleton provides the interface through which a method receives a request (dynamic

and static skeletons)

Object Adapter

Purpose is to interface an object's implementation with its ORB

Each object adapter provides access to those services of an ORB (such as activation,

deactivation, object creation, object reference management) used by a particular type ofobject implementation.

ORB Interface

The interface to the small set of ORB operations common to all objects, e.g., the operation

which returns an object's interface type.


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Object

Adapter

Implementation

Skeletons

ORB Core

Client Object Implementation

Client

Stubs

ORB

Interface

Dynamic

Invocation

standard interface

One interface per object operation

One interface per object adaptor

Proprietary ORB interface

Normal call interfaceUp call interface

CORBA Components


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Client

ClientStubs

ORBInterface

DynamicInvocation

Clients perform requests using object references.

Clients may issue requests throughobject interface stubs (static) ordynamic invocation interface.

Clients may access general ORBservices:

Interface Repository. Context Management. List Management. Request Management.

Client Side


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Static v. Dynamic Invocation

Static Invocation

Static interfaces are generated in form of client stubs by the IDL (pre-)

compiler.

This means that the structure of the object has to be known before hand (at

compile time).

Allows for better type checking; less runtime overhead; self-documentation.

Dynamic Invocation

Dynamic Invocation Interface (DII) allows clients to invoke operations on

remote objects without having access to object stubs (another way to do this

without dynamic invocation is to download static client stubs via a Java

applet).

Clients must discover interface-related information at runtime (e.g., using the

interface repository)

Servers can offer new services anytime without the need for recompilation on

the client side.


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Dynamic Requests

The Dynamic Invocation Interface (DII) allows clients todynamically: discover objects; discover objects interfaces;

create requests;

invoke requests;

receive responses.

Major features of Dynamic Invocation Interface:

requests appear as objects themselves;

requests are reusable;

invocation may be synchronous or asynchronous; requests may be generated dynamically, statically or in combination approach.


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CORBA Interface Repository

The Interface Repository is a service that provides persistent

objects that represent the IDL information in a form availableat runtime.

Note: The JavaIDL runtime does not include an implementation of an Interface

Repository and one is not generally required by clients at runtime.

Using the IR, it is possible for a program to encounter an object whose

interface was not known at compile time, yet be able to determine whatoperations are valid on the object and make invocation on it.

Interface Repository provides:

Dynamic client access to interface definitions to construct a request.

Dynamic type-checking of request signatures.

Traversal of inheritance graphs.

ORB-to-ORB interoperability.


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CORBA Implementation Repository

The Implementation Repository contains information that allows the

ORB to locate and activate implementations of objects. Ordinarily, installation of implementations and control of policies

related to the activation and execution of object implementations is

done through operations on the Implementation Repository.

In addition to its role in the functioning of the ORB, the

Implementation Repository is a common place to store additionalinformation associated with implementations of ORB objects. (e.g.,

debugging information, administrative control, resource allocation,

security, etc)

The Implementation Repository supports the implementation of object

servers. It is not needed by clients in order to access servers.


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IDL InterfaceDefinitions

ImplementationInstallation

ClientStubs

InterfaceRepository

ImplementationRepositoryImplementation

Skeletons

Client Object Implementation

Accesses Includes DescribesIncludes

Summary of CORBA Interfaces

All objects are defined in IDL by specifying their interfaces.

Object definitions (interfaces) are manifested as objects in the InterfaceRepository, as client stubs, and as implementation skeletons.

Descriptions of object implementations are maintained as objects in the

Implementation Repository.


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Summary: CORBA Remote Method Invocation

Clients use object interfaces through language mapping

Java clients should work on any ORB that supports the Java language bindings. Clients can call any object instance remotely, so long as the object instance

implements the interface.

Clients can call remote objects statically or dynamically

The server cannot tell whether the client is using static or dynamic invocation.

Objects are identified using a unique id: Interoperable Object

Reference (IOR)

CORBA passes objects by reference

IOR was Introduced in CORBA 2.0

Object references can be converted to strings and back to live objects via

ORB interface functions.


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Steps in Developing CORBA

Applications

Write specification for each object using IDL

Use IDL Compiler (e.g., idl2java) to generate:

Client Stub code

Server Skeleton code

Write the client (in Java, can be applications or applets)

Write the server object implementation code (the servant)

Compile the client and server code

Start the server

Run the client application


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The Structure of CORBA IDL(See Section 2.3.4 of Brose, Vogel, Duddy)

Modules provide namespaces for a set of related class descriptions map to Java packages with the same name

Interfaces

specification of the operations a client can invoke on a remote object

in addition to operations, interfaces include constructs such as:

constant declarationsattributes (can be read/write orreadonly; implementation automatically createsget

andsetoperations for these attributes)

exceptions (raised if the operations do not perform successfully)

Operations

CORBA equivalent of methods in Java

IDL defines the operations signature: parameters and return values/types

parameters can be in, out, orinout

IDL also defines what exceptions can be raised by the operation


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Data Types in CORBA IDL

Basic Types short, long, unsigned long, unsigned short, float, double, long double, char, wchar,

boolean, string, octet, etc.

Constructed Types

structand union (similar to C++; can be used in conjunction with a typedef)

sequence (variable sized arrays of objects)

any (generic type which represents any possible IDL types; similar to the Java Object

type)

enum (enumerated type with named integer values)

arrays

valuetypes (similar to interfaces; preceded with keywordvaluetype to provide pass-

by-value semantics)

Each CORBA IDL data type gets mapped to a native data type via the

appropriate language binding (e.g, IDL-to-Java mapping).


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IDL Syntaxmodule {

;;

;

interface [:] {

;

;

;;

[]()

[raises ]

[]()

[raises ]

. . .

};

interface [:] {. . .};

. . .

};

module {

;

;

;

interface [:] {

;

;

;;

[]()

[raises ]

[]()

[raises ]

. . . };

interface [:] {. . .};

. . .

};


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An IDL Example

module MyAnimals {

interface Dog: Pet, Animal {attribute short age;

exception NotInterested{string explanation};

void Bark(in short how_long)

raises (NotInterested);

void Sit(in string where)


. . .

};

interface Cat: Animal {void Eat();

. . .

};

};

module MyAnimals {

interface Dog: Pet, Animal {attribute short age;

exception NotInterested{string explanation};

void Bark(in short how_long)


void Sit(in string where)


. . .

};

interface Cat: Animal {

void Eat();

. . .

};

};


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module RoomBooking {

interface Meeting {

readonly attribute string purpose;readonly attribute string participants;oneway void destroy();

};

interface MeetingFactory {Meeting CreateMeeting(in string purpose,in string participants);

};

interface Room {

// A Room provides methods to view, make,cancel bookings.

enum Slot { am9, am10, am11, pm12, pm1, pm2, pm3, pm4 };const short MaxSlots = 8;typedef Meeting Meetings[ MaxSlots ];

exception NoMeetingInThisSlot {};exception SlotAlreadyTaken {};

readonly attribute string name;

Meetings View();void Book( in Slot a_slot, in Meeting a_meeting )

raises(SlotAlreadyTaken);void Cancel( in Slot a_slot )

raises(NoMeetingInThisSlot);};

};

module RoomBooking {

interface Meeting {

readonly attribute string purpose;readonly attribute string participants;oneway void destroy();

};

interface MeetingFactory {Meeting CreateMeeting(in string purpose,in string participants);

};

interface Room {

// A Room provides methods to view, make,cancel bookings.enum Slot { am9, am10, am11, pm12, pm1, pm2, pm3, pm4 };const short MaxSlots = 8;typedef Meeting Meetings[ MaxSlots ];

exception NoMeetingInThisSlot {};exception SlotAlreadyTaken {};

readonly attribute string name;

Meetings View();void Book( in Slot a_slot, in Meeting a_meeting )

raises(SlotAlreadyTaken);void Cancel( in Slot a_slot )

raises(NoMeetingInThisSlot);};

};

Another IDL Example


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The CORBA Count Example

// Count.idl

module Counter

{

interface Count

{

attribute long sum;

long increment();

};

};

The Count Program

the client will invoke a methodincrement() on the remote object Count;increment() adds 1 to the value of the attributesumand returns the value

to the client program;the initial value ofsumis set by the client (sum is a read/write attribute, so the

client can use CORBAs built-in accessorfunctions to manipulate it.

First we must start

with an IDL

definition for the

Count object:


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The IDL Compiler

Before using the IDL compiler or running the program make sure thatthe PATH and CLASSPATH environment variables are properly setup:

Your PATH must point to the Java runtime environment directory as well asthe ORB runtime directory ( \inprise\vbroker\bin);

Your CLASSPATH variable must include the current directory (.), the usualJava classes and libraries (including the directory where your program classes

will be stored) as well as the following jar files required by Visibroker:

\inprise\vbroker\lib\vbjcosnm.jar\inprise\vbroker\lib\vbjorb.jar\inprise\vbroker\lib\vbjapp.jar\inprise\vbroker\lib\vbjtools.jar\inprise\vbroker\lib\vbjgk.jar

\inprise\vbroker\lib\vbjcosnm.jar\inprise\vbroker\lib\vbjorb.jar\inprise\vbroker\lib\vbjapp.jar\inprise\vbroker\lib\vbjtools.jar\inprise\vbroker\lib\vbjgk.jar

In Visibroker 3.x

\inprise\vbroker\lib\vbdev.jar\inprise\vbroker\lib\vbjdev.jar\inprise\vbroker\lib\vbjorb.jar\inprise\vbroker\lib\vbjmigration.jar\jdk1.2.2\lib\servlet.jar

\inprise\vbroker\lib\vbdev.jar\inprise\vbroker\lib\vbjdev.jar\inprise\vbroker\lib\vbjorb.jar\inprise\vbroker\lib\vbjmigration.jar\jdk1.2.2\lib\servlet.jar

In Visibroker 4.x


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The IDL Compiler

Now you can compile the IDL definition:> idl2java -no_tie Count.idl

Important Notes:

if you are using Visibroker 3.3, you need JDK 1.1.8; as VBJ 3.3 is not compatiblewith Java 2 platform

in VBJ 4.x, idl2java compiler generated code is based on the POA (portable object

adapter) semantics; in order to use BOA semantics, must use:

> idl2java -boa Count.idl

also some additional casting needs to be done in BOA

initialization (more on this later, but see Chapters 30 and 31 of

the VBJ 4.x Programmers Guide)

in VBJ 3.x, the idl2java compiler generated code is based on BOA semantics (also

the API for the stub and skeleton code is different than those in VBJ 4.x)


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What Does the IDL Compiler Generate?

idl2java

Count.idl

_st_Count.java

CountHelper.java CountHolder.java

_CountImplBase.java

Count.java _example_Count.java

Client-Side Server-Side

Client StubImplementation Skeleton

Note: these source files will be a part of the Java package Counter and will be placed ina directory with the same name.

VBJ 3.xVBJ 3.x


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What Does the IDL Compiler Generate?

idl2java

Count.idl

_CountStub.java

CountHelper.java CountHolder.java

CountPOA.java

Count.java

Client-Side Server-Side

Client StubImplementation Skeleton

Note: if-boa option is used with idl2java compiler,_CountImplBase.java is alsogenerated to be used in the object implementation.

VBJ 4.x using POAVBJ 4.x using POA


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Generated Classes & Interfaces Counter._st_Count: implements the client-side stub for the Count object; it provides

the marshaling functions for the client. [_CountStub in VBJ 4.x].

Counter._CountImplBase: implements the server-side skeleton forCount; itunmarshals the arguments passes by the client. [CountPOA in VBJ 4.x using POA].

Counter.CountHelper:provides some additional utility functions for the client,including the narrow operation for downcasting CORBA object references, and (in thiscase) the Visibroker specificbindoperation for finding the remote object.

Counter.CountHolder: it is used as a wrapper for passing outand inoutparameters of

type Count (Java only natively supports in parameters).Counter.Count: contains the Java interface corresponding to the IDL interface forCount; the object implementation forCount must implement this interface.

Counter._example_Count: a sample class for the Count object implementationwhich could be filled-in by the programmer. [not generated in VBJ 4.x].

package Counter;public interface Count extends org.omg.CORBA.Object {

public void sum(int sum);public int sum();public int increment();

}


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Class Hierarchy for BOA Count Interface

class

org.omg.CORBA.portable.Skeleton(provided by the ORB)

class

org.omg.CORBA.portable.Skeleton

(provided by the ORB)

abstract class

Counter._CountImplBase(generated by id2java)

abstract class

Counter._CountImplBase(generated by id2java)

class CountImpl(written by programmer

and used by the server)

class CountImpl(written by programmer

and used by the server)

interface

Counter.Count(generated by id2java)

interface

Counter.Count(generated by id2java)

Extends

Extends

Implements

class

org.omg.CORBA.portable.ObjectImpl(provided by the ORB)

class

org.omg.CORBA.portable.ObjectImpl

(provided by the ORB)

abstract class

Counter._st_Count(generated by id2java)

abstract class

Counter._st_Count(generated by id2java)

Extends

Note: in case of POA, the object skeleton CountPOA

extends org.omg.CORBA.PortableServer.Servant

Note: in case of POA, the object skeleton CountPOA

extends org.omg.CORBA.PortableServer.Servant


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Steps in Developing the Count Application

Write a client program in Java:

this can be an applet or an application; in this case we write a Java applicationCountClient.java.

Write the server-side code for the Count application: write a server application which creates and serves instance(s) of theCount object

(instances of the class CountImpl);

write the object implementation (CountImpl

).

Object Implementation:

CORBA inheritance model: the implementation class is always derived from the

corresponding_XXXImplBase class generated by IDL compiler (in this case from_CountImplBase; [Note: with POA this isXXXPOA, e.g., CountPOA]

this inheritance allows the servant class to obtain the properties of both CORBA and Java

object models;

the alternative to inheritance model is to use delegation (in CORBA terminology the Tie

method); if-no_tie option is not used with idl2java relevant classes will be

generated;

in this case we create ourCountImpl by modifying the file_example_Count.java.


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_example_Count.java

package Counter;

public class _example_Count extends Counter._CountImplBase {

public _example_Count(java.lang.String name) {

super(name);

}

public _example_Count() {

super();

}

public int increment() {

// implement operation...

return 0;

}

public void sum(int sum) {

// implement attribute writer...

}public int sum() {

// implement attribute reader...

return 0;

} }

package Counter;

public class _example_Count extends Counter._CountImplBase {

public _example_Count(java.lang.String name) {super(name);

}

public _example_Count() {

super();

}

public int increment() {// implement operation...

return 0;

}

public void sum(int sum) {

// implement attribute writer...

}public int sum() {

// implement attribute reader...

return 0;

} }

Th BOA C t Obj t I l t ti


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// CountImpl.java: The Count Implementation

class CountImpl extends Counter._CountImplBase

{ private int sum;

// ConstructorsCountImpl(String name){super(name);System.out.println("Count Object

Created");sum = 0;

}

// get sumpublic int sum() { return sum; }

// set sum

public void sum(int val) { sum = val; }

// increment methodpublic int increment() {sum++;return sum;

}}

The BOA Count Object Implementation

f S C


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Tasks Performed by the Main Server Class

Initialize the Object Request Broker done by creating an instance of the ORB pseudo-object; the static Java method init() on the class org.omg.CORBA.ORB returns

an instance of an ORB.

Initialize the Basic Object Adaptor

a reference to an instance of the BOA is obtained via the method BOA_init().

Create the object (an instance of the class implementation) in this case we create an instance ofCountImpl class

Activate the newly created object

in BOA this is done by calling the obj_is_ready() method of the ORBinstance on the object;

this action exports the object to the ORB.

Wait for incoming requests

in BOA this is done by calling the impl_is_ready() method of the ORBinstance on the object;


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Tasks Performed by the Client

Initialize the ORB

done the same way as for the server.

Locate the Remote Object

in this case client binds to the object via the Visibrokerbind() method.

Perform Operations via Remote Methods

set the remote sum attribute to zero;

calculate the start time;

invoke the increment method 1000 times;

calculate the elapsed time;print the results.

The BOA C t Client


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// CountClient.java Static Client, VisiBroker for Java

class CountClient{public static void main(String args[]) {try {// Initialize the ORBorg.omg.CORBA.ORB orb = org.omg.CORBA.ORB.init(args, null);

// Bind to the persistent Count Object referenceCounter.Count counter = Counter.CountHelper.bind(orb, "My Count");

// Set sum to initial value of 0

counter.sum((int)0);

// Calculate Start timelong startTime = System.currentTimeMillis();

// Increment 1000 timesfor (int i = 0 ; i < 1000 ; i++ ) { counter.increment();}

// Calculate stop time; print out statistics

long stopTime = System.currentTimeMillis();System.out.println("Avg Ping = " + ((stopTime-startTime)/1000f)+"

msecs");System.out.println("Sum = " + counter.sum());

}catch(org.omg.CORBA.SystemException e) {System.err.println("System Exception");

System.err.println(e); }} }

The BOA Count Client

C


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Building and Running the Count Example

Compile the client, server, and the implementation classesvbjc -d \CorbaJavaBook.2e\classes CountClient.java

vbjc -d \CorbaJavaBook.2e\classes CountServer.java

vbjc -d \CorbaJavaBook.2e\classes CountImpl.java

Note: \CorbaJavaBook.2e\classes is where the Java bytecode classes will

be stored (without -d option classes are generated in the current directory).

Start the Visibroker Smart Agent (OSAgent) osagent -c OR startosagent -c OSAgent may be installed as an NT Service or started using the icon in the program menu

Start the Count Server: vbj CountServer

Execute the Client Application: vbj CountClient


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The Count

Program in

Action


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More Examples of CORBA Applications

CORBA Object References

The POA version of Count Application

More on IDL elements

read/readonly attributes

oneway methods

parameter passing mechanisms

exceptions and exception handling

Discussion of Project Phase I

6565730 CORBA Overview Developing Basic CORBA Applications Distributed Systems Frameworks

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