Applied Modularity
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Applied Modularity

Do we really need OSGi, Micro Services and the Java Module System?

About the Book

This book offers a general introduction into modularity in software engineering. The main part, however, represents an overview of five different approaches to modularity from a practical point of view. An example business domain is used to explain how the different modularity approaches work. When comparing the different approaches, similarities, differences, benefits and disadvantages between them become visible. To all implementations of the example business domain mentioned in the book code is available for you at GitHub. The book refers to this code that enables you to view, run, modify and rerun the implementations in your IDE. Finally, some projects reports are presented that provide some insight on how to cope with typical problems that you may face on the different ways to modularity.

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    • Java
    • Software Architecture
    • Software Engineering
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About the Author

Reik Oberrath
Reik Oberrath

Clean Code and efficient software development was the driving force throughout the author's working life. This force lead him to found the Clean Coding Cosmos in collaboration with his colleague Jörg Vollmer. Modularity is one major aspect of Clean Code which the author now illustrates with this book. This book’s experience is built on experience gained over 15 years as Java software developer, a number of publications in Journals about Clean Code topics in addition to series of several multi-year development projects in which different types of modularity have been applied.

Table of Contents

  • Preface
  • 1. What modularity is
    • 1.1 Why are many small pieces easier to maintain than one big one?
    • 1.2 How small or big can a piece of software be?
    • 1.3 How to structure pieces of software
    • 1.4 How to cut software into pieces?
    • 1.5 What kind of boundaries exist that separate pieces of software from each other?
    • 1.6 How to set up impermeable boundaries?
    • 1.7 What is modularity not good for?
    • Chapter Summary
  • 2. The example business domain HOO
    • 2.1 Requirements
    • 2.2 Implementation
    • 2.3 The search for alternative ways to modularity
  • 3. What OSGi is
    • 3.1 How does OSGi work?
    • 3.2 A real life OSGi example
    • 3.3 The HOO service as OSGi application
    • 3.4 What is OSGi good for?
  • 4. What micro-services are
    • 4.1 What is the relationship between SOA and micro-service architecture?
    • 4.2 How do micro-services work?
    • 4.3 A real life micro-service example
    • 4.4 The HOO Service as micro-service system
    • 4.5 What are micro-services good for?
  • 5. What a modular monolith is
    • 5.1 How does a classic monolith work?
    • 5.2 How does a pseudo-modular monolith work?
    • 5.3 How does a true modular monolith work?
    • 5.4 How is a true modular monolith built?
    • 5.5 A real life modular monolith example
    • 5.6 The HOO service as ODDM modular monolith
  • 6. What Java Modules are
    • 6.1 How do Java Modules work?
    • 6.2 The HOO service as a Java modulular monolith
    • 6.3 What are Java Modules good for?
  • 7. The HOO Service in Choreography Design
    • 7.1 Choreography with micro-services
    • 7.2 Choreography with OSGi
    • 7.3 Choreography with ODDM
    • 7.4 Choreography design with Java Modules
    • 7.5 Asynchronuous communication
  • 8. Comparing the different modularity approaches
    • 8.1 Implementation Details
    • 8.2 Dependency and Reference Types
    • 8.3 The degree of module coupling
    • 8.4 Costs and disadvantages
    • 8.5 Dependency levels, dependency cycles and dependency hell
    • 8.6 Asynchronous communication
  • 9. Conclusions
    • 9.1 Combining different modularity approaches
    • 9.2 Orchestration versus Choreography
    • 9.3 Transactionality and modularity
    • 9.4 Domain Driven Design (DDD) and modularity
    • 9.5 Towards a new modularity mind-set for developers
    • 9.6 Different ways to achieve the same goal
    • 9.7 How bad are monoliths?
  • Postface

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