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Activex & Component Object Model

Author: Gopalan Suresh Raj
Date Submitted: January 26th 2000
Level of Difficulty: Beginner
Subjects Covered: COM
Pre-required Reading: None

Introduction

Traditional operating systems only dealt with application binaries and not components. Hence, the benefits of good component-oriented design have till now never gone beyond the compilation step. In an object-centric world is’nt it still a puzzle why operating systems can’t recoganize objects? For a long time now, operating systems have been dealing only with application binaries a.k.a. EXEs. Objects in one process could not communicate with objects in another process using their own defined methods. The operating system defined certain mechanisms of inter-process communication like DDE, TCP/IP, Sockets, memory-mapped I/O or named pipes etc. These objects needed to use these OS defined mechanisms to communicate with each other.

ActiveX/COM - A Truly Distributed Object-Oriented Architecture

Components developed using Microsoft’s COM provide a way by which two objects in different object spaces or networks, could talk together by calling each other’s methods. This excellent technology forces the operating system to see applications as objects.

COM forces the OS to act as a central registry for objects. The OS takes the responsibility of creating objects when they are required, deleteing them when they are not, and handling communications between them, be it in the same or different processes or machines. One major advantage of this mechanism is versioning. If the COM object ever changes to a new version, the applications that use that object need not be recompiled.

The wonderful thing about COM components is that they are never linked to any application. The only thing that an application may know about a COM object is what functions it may or may not support. In fact, the object model is so flexible that applications can query the COM object at run-time as to what functionality it provides.

Garbage Collection is one other major advantage to using COM. When there are no outstanding references (a.k.a. pointers) to an object, the COM object destroys itself.

COM supports Marshalling. Distributed Computing purists will attest to the fact that marshalling is the process of packaging and transmitting data between different address spaces, automatically resolving pointer problems, preserving the data’s original form and integrity. Even though COM objects reside in separate processes or address spaces or even different machines, the operating system takes care of marshalling the call and calling objects running in a different application (or address space) on a different machine.

Over and above all this, COM is a binary standard. A fully compliant COM object can be written in any language that can produce binary compatible code. So you can write ‘em using C, C++, Java, J++ or Visual Basic. All of the Windows NT shell has been written using COM.

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Byte size articles:

COM Threading Models By Gopalan Suresh Raj, 070200
Gopalan explains the differences in COM and Win 32 threading models.
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ActiveX & COM By Gopalan Suresh Raj, 270100
Gopalan explains the basics of ActiveX / COM as a truly distributed Object Oriented Architecture.
Go To Article.

Full size articles:

COM Channel:

Java COM Integration - Use Visual J++ to implement COM Objects By Gopalan Suresh Raj.
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Developing an MSMQ Server Application using VJ++ By Gopalan Suresh Raj.
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Developing an MSMQ Client using VJ++ By Gopalan Suresh Raj.
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Coding a DCOM Server Component from IDL By Gopalan Suresh Raj.
Author: Gopalan Suresh Raj
Date Submitted: February 10th 2000
Level of Difficulty: Advanced
Subjects Covered: IDL, DCOM, J++
Pre-required Reading: Component Object Model

Coding a DCOM Client By Gopalan Suresh Raj.
Author: Gopalan Suresh Raj
Date Submitted: February 10th 2000
Level of Difficulty: Advanced
Subjects Covered: IDL, DCOM, J++
Pre-required Reading: Component Object Model, Coding a DCOM Server Component from IDL

Microsoft Transaction Server By Gopalan Suresh Raj.
Gopalans introductory article on Microsoft Transaction Server intorduces the basics to MTS, and leads in to the example articles included in the series.
Author: Gopalan Suresh Raj
Date Submitted: Jan 26 2000
Level of Difficulty: Beginners / Intermediate
Subjects Covered: MTS
Pre-required Reading: None

Developing a Simple MTS Server Component By Gopalan Suresh Raj.
Part 1 of a two part example.
Author: Gopalan Suresh Raj
Date Submitted: Jan 26 2000
Level of Difficulty: Beginners / Intermediate
Subjects Covered: MTS
Pre-required Reading: Microsoft Transaction Server

Developing a Simple MTS Client Application By Gopalan Suresh Raj.
Part 2 of a two part example.
Author: Gopalan Suresh Raj
Date Submitted: Jan 26 2000
Level of Difficulty: Beginners / Intermediate
Subjects Covered: MTS
Pre-required Reading: Microsoft Transaction Server, Developing a Simple MTS Server Component

Developing The Bank Account IDL By Gopalan Suresh Raj.
A Three-Tier Architecture for a Bank Checking Account - Developing The Bank Account IDL is part 1 of a 3 part example.
Author: Gopalan Suresh Raj
Date Submitted: Jan 26 2000
Level of Difficulty: Beginners / Intermediate
Subjects Covered: MTS
Pre-required Reading: Microsoft Transaction Server

MTS Server Component By Gopalan Suresh Raj.
A Three-Tier Architecture for a Bank Checking Account - MTS Server Component is the second part of this three part example.
Author: Gopalan Suresh Raj
Date Submitted: Jan 26 2000
Level of Difficulty: Beginners / Intermediate
Subjects Covered: MTS
Pre-required Reading: Microsoft Transaction Server, Developing The Bank Account IDL

MTS Client By Gopalan Suresh Raj.
A Three-Tier Architecture for a Bank Checking Account - MTS Server Component is the third part of this three part example.
Author: Gopalan Suresh Raj
Date Submitted: Jan 26 2000
Level of Difficulty: Beginners / Intermediate
Subjects Covered: MTS
Pre-required Reading: Microsoft Transaction Server, Developing The Bank Account IDL, MTS Server Component

Java Channel:

Enterprise Java Beans By Gopalan Suresh Raj.
In this introduction to Enterprise Java Beans, Gopalan covers the bases then goes on to demonstrate how to build server side business object components. This article is the introduction to Gopalan's series of Enterprise JavaBeans articles. (This series of articles is © Copyright 1997-2000 Gopalan Suresh Raj. Reproduced with Permission)
Author: Gopalan Suresh Raj
Date Submitted: January 6th 2000
Level of Difficulty: Advanced
Subjects Covered: Enterprise JavaBeans, EJB Server, EJB Architecture, Java Naming and Directory Interface, Java Transaction Service.
Pre-required Reading: None

Enterprise Java Beans Series - Components at the Server By Gopalan Suresh Raj.
Author: Gopalan Suresh Raj
Date Submitted: January 11th 2000
Level of Difficulty: Advanced
Subjects Covered: Server side components, CORBA
Pre-required Reading: Enterprise JavaBeans

Enterprise Java Beans Series - EJB Model By Gopalan Suresh Raj.
Author: Gopalan Suresh Raj
Date Submitted: January 11th 2000
Level of Difficulty: Advanced
Subjects Covered: Enterprise JavaBeans, EJB Server, EJB Containers, EJB Clients.
Pre-required Reading: Enterprise JavaBeans

Enterprise Java Beans Series - EJB Naming Services and JNDI By Gopalan Suresh Raj.
Author: Gopalan Suresh Raj
Date Submitted: January 11th 2000
Level of Difficulty: Advanced
Subjects Covered: Naming Services, Java Naming Directory Interface
Pre-required Reading: Enterprise JavaBeans

Enterprise Java Beans Series - EJB Transactions and JTS By Gopalan Suresh Raj.
Author: Gopalan Suresh Raj
Date Submitted: January 11th 2000
Level of Difficulty: Advanced
Subjects Covered: Java Transaction Service, Two-phase commits
Pre-required Reading: Enterprise JavaBeans

Enterprise Java Beans Series - EJB Lifecycle By Gopalan Suresh Raj.
Author: Gopalan Suresh Raj
Date Submitted: January 11th 2000
Level of Difficulty: Advanced
Subjects Covered: EJB server provider, EJB container provider, EJB developer, EJB deployer, Application developer.
Pre-required Reading: Enterprise JavaBeans

Enterprise Java Beans Series - EJB Servers By Gopalan Suresh Raj.
Author: Gopalan Suresh Raj
Date Submitted: January 11th 2000
Level of Difficulty: Advanced
Subjects Covered: Server Infrastructure
Pre-required Reading: Enterprise JavaBeans

Enterprise Java Beans Series - EJB Containers By Gopalan Suresh Raj.
Author: Gopalan Suresh Raj
Date Submitted: January 11th 2000
Level of Difficulty: Advanced
Subjects Covered: EJB Containers, EJB Servers
Pre-required Reading: Enterprise JavaBeans

Enterprise Java Beans Series - EJB Components By Gopalan Suresh Raj.
Author: Gopalan Suresh Raj
Date Submitted: January 11th 2000
Level of Difficulty: Advanced
Subjects Covered: EJB Object, Home Object, Remote Object
Pre-required Reading: Enterprise JavaBeans

Enterprise Java Beans Series - EJB Session Beans By Gopalan Suresh Raj.
Author: Gopalan Suresh Raj
Date Submitted: January 11th 2000
Level of Difficulty: Advanced
Subjects Covered: Stateful Session Beans, Stateless Session Beans
Pre-required Reading: Enterprise JavaBeans

Enterprise Java Beans Series - EJB Entity Beans By Gopalan Suresh Raj.
Author: Gopalan Suresh Raj
Date Submitted: January 11th 2000
Level of Difficulty: Advanced
Subjects Covered: Container-Managed Persistence, Bean-Managed Persistence
Pre-required Reading: Enterprise JavaBeans

Enterprise Java Beans Series - Writing an Entity Bean By Gopalan Suresh Raj.
Part 1 of a four part series: A four tier bank account example
Author: Gopalan Suresh Raj
Date Submitted: January 11th 2000
Level of Difficulty: Advanced
Subjects Covered: Developing Entity Beans, Home & Remote Interfaces, Data Sources.
Pre-required Reading: Enterprise JavaBeans

Enterprise Java Beans Series - Writing a Session Bean By Gopalan Suresh Raj.
Part 2 of a four part series: A four tier bank account example
Author: Gopalan Suresh Raj
Date Submitted: January 11th 2000
Level of Difficulty: Advanced
Subjects Covered: Developing Session Beans, Home & Remote Interfaces, Deployment Descriptors.
Pre-required Reading: Enterprise JavaBeans

Enterprise Java Beans Series - Writing an EJB Client By Gopalan Suresh Raj.
Part 3 of a four part series: A four tier bank account example
Author: Gopalan Suresh Raj
Date Submitted: January 11th 2000
Level of Difficulty: Advanced
Subjects Covered: EJB Clients.
Pre-required Reading: Enterprise JavaBeans

Enterprise Java Beans Series - Writing an EJB Servlet Client By Gopalan Suresh Raj.
Part 4 of a four part series: A four tier bank account example
Author: Gopalan Suresh Raj
Date Submitted: January 11th 2000
Level of Difficulty: Advanced
Subjects Covered: Servlet Clients.
Pre-required Reading: Enterprise JavaBeans