Premanand Chandrasekaran - Domain-Driven Design with Java - A Practitioners Guide: Create simple, elegant, and valuable software solutions for complex business problems

Create simple, elegant, and valuable software solutions for complex business problems

Premanand Chandrasekaran

Karthik Krishnan

BIRMINGHAMMUMBAI

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To my mother, Bhanumathy, for all her sacrifices and for exemplifying the power of determination. To my wife, Vidya, for being my loving partner throughout our joint life journey and to our son, Siddharth, for being a constant source of joy and pride.

Prem

To my late mother, Visalam, and my father, Krishnan, for inculcating the value of hard work and perseverance. To my loving wife, Suja, for being the patient partner and providing a lot of encouragement, and to my daughter, Ananya, for being the source of cheer and happiness in our family.

Karthik

The ideas behind Domain-driven Design (DDD) have an outsized influence on software architecture and the way we think about software projects. Ubiquitous Language is a term defined by DDD, describing the practice of creating a more precise language when discussing design in software projects. However, DDD itself has provided a ubiquitous language for software architecture: most discussions around microservices touch on terms originating in the DDD world.

However, the book that started it all, Domain-driven Design by Eric Evans, falls into the category of what Mark Twain called a classic: a book that everyone wants to have read. The truth of the matter is that, while the book is packed full of influential ideas, it is quite abstract for readers looking for advice on how to build software. That doesnt indicate a deficiency in the sourceit is designed to cover broad concepts, which encompasses many different facets of design, including but not limited to software development.

However, when developers need to utilize these ideas in a practical sense, such as in a concrete project, the abstract doesnt helpthey need a practitioners guide, which readers now hold in their hands. This book does an excellent job translating the concepts of DDD into useful overviews and concrete advice on how to implement the ideas. For example, a pertinent question that developers have that is unanswered in the DDD book: which is better to implement a project, imperative or functional programming style? Each has trade-offs; this book helps teams make those kinds of implementation decisions. This book covers multiple perspectives on applying DDD to Java projects, including foundational material about how DDD and agile engineering practices intersect in modern projects.

While many books exist that cover DDD and software architecture independently, this book does an excellent job mapping one to another, describing how the design influence of DDD maps to a number of different architecture topologies. For example, it describes how teams can reconcile bounded contexts with layered and other architecture styles.

Part one of this book covers many foundational details of the book, including technical and design details. Part two covers Real World DDD, covering how to apply the abstract ideas in a more concrete realm. It covers everything from how to discover and document the domain, to how to map real-world concepts into DDD concepts. For example, it does an excellent job describing aggregates, their design, and relationships.

Part three covers a topic dear to my heart as the author of Building Evolutionary Architectures, which is the evolution of software. Software products constantly evolve, including new features and capabilities. Therefore, software development isnt a static processit must evolve along multiple dimensions to remain successful. This book contains a number of useful evolution patterns, covering both the domain and architecture characteristics.

Towards the ideal of creating a practitioners guide, the book also covers engineering practicalities such as logging, testing, versioning, and a host of other practical considerations. Though these areas may fall outside the scope of the DDD book, teams need them.

DDD offers a host of conceptual ideas but lacks implementation details. This book serves as an excellent bridge between abstract and implementation. While the focus is on Java, the content is broad enough for any practitioner to get a good overview of the many important considerations for DDD projects. In fact, each specific technology stack would benefit from having a practitioners guide such as this one.

- Neal Ford

Director/Software Architect / Meme Wrangler

Thoughtworks, Inc.

The early 2000s were a dynamic time in the software industry. A number of luminaries were exploring lightweight agile processes that had the effect of converting software engineering from a paint-by-numbers activity into first-class knowledge work. Agile methodologies such as eXtreme Programming were natural extensions of arguments put forth by Jack Reeves in his 1992 C++ Journal article What is Software Design, which claimed that source code not design docs or architecture diagrams was the only equivalent to design specifications found in other engineering disciplines. The split between design and manufacturing still exists, of course, but with software, we dont need people for manufacturing. The compiler does it for us, which means that all work the people do is design work, and agile processes pushed the new generation of software engineers into messy design conversations with the business.

The turn of the century also corresponded with the dotcom boom (and subsequent bust) as user interactions shifted from desktop applications to the web, creating technical scaling problems that were orders of magnitude beyond what the industry had faced up to that point. Distributed technologies werent exactly new, but the ever-increasing technical complexity needed to solve problems of scale required new architectural approaches and created a demand for software engineering talent.