COM+ Programming: A Practical Guide Using Visual C++ and ATL
IntroductionEver since software development became an engineering discipline, software development teams everywhere in the world have faced similar development and deployment problems. Among other things, developers today are concerned about:Reusing code that has been tested and used in other applicationsDeveloping flexible applications that can be customized to the users needs, but not at the expense of overburdening the development teamAddressing anomalies and add features after the application has been shipped, while avoiding a complete rewrite of the applicationImproving application development time by leveraging against software code developed by third party software vendorsDeveloping distributed and non-distributed applications in a similar mannerAll of these challenges and many more are addressed by a single technology: the Microsoft Component Object Model, better known as COM. COM is a framework for developing software components, small binary executables, that provide services to applications and other components.The incredible explosion of the Internet has caused a revolution in the way information has to be made available to the users. In developing enterprise systems, the traditional client/server model has been replaced with a three-tier programming model, enhanced for Internet applications. Developing such enterprise systems is a time- and resource-consuming affair, as the system has to meet extra enterprise-level requirements such as scalability, robustness, security, transaction support, etc.COM+ is an advanced run-time environment that provides services to meet many of the above-mentioned enterprise-level requirements. It is an integral part of the Windows 2000 Operating System. Developers can leverage the services provided by COM+, instead of building the services themselves.This book focuses on understanding the COM+ architecture from a developer's perspective and building COM+ applications using Microsoft Visual C++ and the Active Template Library (ATL).COM+ is not a radical departure from COM--it is just the next stage in the evolution of the COM programming model. As a matter of fact, it is very difficult to determine where COM ends and where COM+ begins. In order to understand the COM+ architecture and the services provided by COM+, it is necessary to understand the fundamental component model at the heart of COM+. To this end, the book is divided in two parts. The first part builds the foundation that is COM and the second part explains the services provided by COM+ version 1.0.About This BookThe purpose of writing this book is twofold. To help you:Understand the COM/COM+ architecture, andExplore the services provided by COM+ 1.0.In order to achieve the stated goals, I have presented the material from a developer's perspective. I have illustrated the key concepts by writing some simple applications using Microsoft Visual C++ 6.0, Platform SDK (January 2000), and ATL 3.0. This book provides enough C++ code and tools to enable the readers to be more productive and to carry out further research.As we progress through unfolding the COM+ architecture and services, I first present one or more software-engineering problems at hand, and then discuss the solution that COM+ has to offer. Whenever applicable, code snippets are provided to illustrate and explain the concepts.In an attempt to focus on COM+ 1.0 architecture and services, I have refrained from including material that is not of any practical importance. Consequently, I do not discuss the origin and history of COM, or even Microsoft Transaction Server (MTS), a precursor to COM+ 1.0. However, whenever possible, I have touched upon the new services that are being planned for the future release of COM+ (COM+ 1.x).Choice of LanguageCOM+ is a specification. As such, it is language independent. However, most COM-based components are currently written in C++. This book uses C++ for almost all the server-side code. Client-side usage is shown in C++, VB, or in any other language that is appropriate for the given situation.PrerequisitesThe most important prerequisite for this book is your willingness to learn.The book is written for intermediate to advanced developers. It is assumed that the readers have a working knowledge of the following:Windows 2000 Operating SystemC++ programming languageVB programming languageC++ templates. In particular, familiarity with C++ Standard Template Library (STL) is helpfulDeveloping programs using Win32 APIWindows 2000 security modelStrictly speaking, many of these assumptions can be relaxed. For example, knowledge of Win32 API or C++ templates is helpful but not mandatory. As we go through developing sample code, I am confident readers will automatically pick up the missing information.Sample CodeAll the examples provided in the book are concise and complete. For brevity, I sometimes show only the relevant code snippet in the book. However, complete source code is available on the companion CD. All the examples and tools have been compiled under Visual C++ 6.0 SP3 and Platform SDK (January 2000), and have been tested with the release version of Windows 2000 OS.ReferencesThis book frequently refers to other books, Microsoft's Knowledge Base articles, articles from various journals and from Microsoft's Developers Network (MSDN) Library. All the references for a particular chapter are listed at the end of the chapter. Each reference is indexed by a keyword that uses a combination of author's last name and year the reference was published. For example, Don Box's book Essential COM, which was published in 1998, is indexed as Box-98. In the book, each time I have to refer to an article, I use the keyword index of the reference.Chapter OrganizationThe book is divided into two parts. The first part, The Foundation, consists of three chapters. It explains the fundamentals of Component Object Model and shows how to design and develop COM-based applications. Each chapter builds on the knowledge from the previous chapter.The second part, The Extension, focuses on COM+ architecture and services provided by COM+ 1.0. Each chapter focuses on a specific aspect of COM+. These chapters are largely independent of each other. Chapter five, however, explains the COM+ programming model, and should be read before looking into any other COM+ chapter.Companion CDThe companion CD contains the following:The source code for the C++ utility classes and tools developed in the book.The entire source code for all the examples arranged by chapters.More information about the contents of the CD can be found in the read-me file on the CD.