Get Your Hands Dirty on Clean Architecture
Get Your Hands Dirty on Clean Architecture
A Hands-on Guide to Creating Clean Web Applications with Code Examples in Java
About the Book
Looking for inspiration on how to build a web application with a clean, maintainable architecture can be frustrating. Many web sources and books do a great job of explaining the concepts of a clean architecture, but fall short in giving hands-on advice on how to implement them.
This book fills this void by converting the concepts of a Hexagonal Architecture into actual code. It concentrates on one of the most common forms of applications we're building today - a web application with an underlying database.
The book starts with a discussion about the conventional layered architecture style and which advantages the domain-centric architecture styles of Robert C. Martin's Clean Architecture and Alistair Cockburn's Hexagonal Architecture bring to the table. It then quickly dives into hands-on chapters that show a way of how to manifest a Hexagonal Architecture in actual code.
After discussing each of the layers in a hexagonal architecture style, the book goes into detail about different mapping strategies between those layers, how to assemble the architecture elements to an application, how to enforce the architecture boundaries, which shortcuts produce which technical debt, and when we might willingly take on this technical debt anyways.
If you prefer a print version of the book, you can get it on Amazon.
About the Author
Reader Testimonials
Gernot Starke
Co-founder of arc42.org and founding member of iSAQB (International Software Architecture Qualification Board).
Tom Hombergs has done a terrific job in explaining clean architecture - from concepts to code. Really wish more technical books would be as clear as that one!
Marten Deinum
Spring Framework contributor and author of "Spring 5 Recipes" and "Spring Boot 2 Recipes"
Love your book. One of the most practical books on hexagonal architecture I have seen/read so far.
Sebastian Kempken
Software architect at Adcubum
A book taken right out of the machine room of software development. Tom talks straight from his experience and guides you through the day-to-day trade-offs necessary to deliver clean architecture.
Table of Contents
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Preface
- What Is the Goal of This Book?
- Who Should Read This Book?
- The Example Application
- A Note on Code Examples
- Print Version
- Feedback
-
1. What’s Wrong With Layers?
- It Promotes Database-Driven Design
- It’s Prone to Shortcuts
- It Grows Hard to Test
- It Hides the Use Cases
- It Makes Parallel Work Difficult
- How Does This Help Me Build Maintainable Software?
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2. Inverting Dependencies
- The Single Responsibility Principle
- A Tale about Side Effects
- The Dependency Inversion Principle
- Clean Architecture
- Hexagonal Architecture
- How Does This Help Me Build Maintainable Software?
-
3. Organizing Code
- Organizing By Layer
- Organizing By Feature
- An Architecturally Expressive Package Structure
- The Role of Dependency Injection
- How Does This Help Me Build Maintainable Software?
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4. Implementing a Use Case
- Implementing the Domain Model
- A Use Case in a Nutshell
- Validating Input
- The Power of Constructors
- Different Input Models for Different Use Cases
- Validating Business Rules
- Rich vs. Anemic Domain Model
- Different Output Models for Different Use Cases
- What About Read-Only Use Cases?
- How Does This Help Me Build Maintainable Software?
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5. Implementing a Web Adapter
- Dependency Inversion
- Responsibilities of a Web Adapter
- Slicing Controllers
- How Does This Help Me Build Maintainable Software?
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6. Implementing a Persistence Adapter
- Dependency Inversion
- Responsibilities of a Persistence Adapter
- Slicing Port Interfaces
- Slicing Persistence Adapters
- Example with Spring Data JPA
- What about Database Transactions?
- How Does This Help Me Build Maintainable Software?
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7. Testing Architecture Elements
- The Test Pyramid
- Testing a Domain Entity with Unit Tests
- Testing a Use Case with Unit Tests
- Testing a Web Adapter with Integration Tests
- Testing a Persistence Adapter with Integration Tests
- Testing Main Paths with System Tests
- How Much Testing is Enough?
- How Does This Help Me Build Maintainable Software?
-
8. Mapping Between Boundaries
- The “No Mapping” Strategy
- The “Two-Way” Mapping Strategy
- The “Full” Mapping Strategy
- The “One-Way” Mapping Strategy
- When to use which Mapping Strategy?
- How Does This Help Me Build Maintainable Software?
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9. Assembling the Application
- Why Even Care About Assembly?
- Assembling via Plain Code
- Assembling via Spring’s Classpath Scanning
- Assembling via Spring’s Java Config
- How Does This Help Me Build Maintainable Software?
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10. Enforcing Architecture Boundaries
- Boundaries and Dependencies
- Visibility Modifiers
- Post-Compile Checks
- Build Artifacts
- How Does This Help Me Build Maintainable Software?
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11. Taking Shortcuts Consciously
- Why Shortcuts Are Like Broken Windows
- The Responsibility of Starting Clean
- Sharing Models between Use Cases
- Using Domain Entities as Input or Output Model
- Skipping Incoming Ports
- Skipping Application Services
- How Does This Help Me Build Maintainable Software?
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12. Deciding on an Architecture Style
- The Domain is King
- Experience is Queen
- It Depends
- Changelog
- Notes
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