Clean, Pragmatic Architecture at Virtual JUG

In a mood for a closing brainstorm? Let’s have a critical review of the major decisions taken in a typical enterprise application architecture and learn to balance pragmatism with design goals. Find out how to do just-in-time design to keep as many use-cases as simple as possible (KISS).

We’ve all seen that without continuous refactoring simplistic design eventually degenerates into a Big Ball of Mud, under the assault of new features and bugfixes. At the other end, over-engineered code can burden the start-up of the development and then end up freezing the code in some rigid ‘a-priori’ design. It’s up to us to strike a balance that will preserve Developer Happiness™. To do that, we should regularly challenge the architecture of our system and seek ways to simplify it to fit our present needs, with a pragmatic mindset.

“Architecture is the art of postponing decisions”, said Uncle Bob. This session takes this idea further and explains how to Evolve a Pragmatic, Clean Architecture (aka Onion), guiding the design by what Genetic Programming would call a fitness function. It’s the philosophy Victor applied to design and develop 9 applications for IBM, and a key topic of the trainings he delivered at dozens of companies.

Along the way, you’ll also get a nice review of the fundamental data structure types, how to keep the logic simple by two types of extractions, enforcing boundaries using dependency directions, and crafting a testable design, all in a fun, dynamic and interactive session.

Transcript

2. When something is painful but you can't avoid doing it… postpone it
3. When something is painful but you can't avoid doing it… delegate it
4. When something is painful but you can't avoid doing it… Do It More Often! "Bring The Pain Forward!"
5. Continuous Integration Pair Programming Continuous Refactoring TDD XP "Bring The Pain Forward!"
6. Victor Rentea 14 years of Java Clean Code Evangelist VictorRentea.ro 30+ talks, 12 meetups .NET Lead Architect Tech Team Lead and Consultant Software Craftsman XP: Pair Programming, Refactoring, TDD
7. VictorRentea.ro @victorrentea victor.rentea@gmail.com Independent Technical Trainer & Coach Hibernate Spring Java 8 Architecture, DDD Design Patterns Clean Code Unit Testing, TDD Java Performance and much more… Scala 180+ days 1300 devs 6 years VictorRentea.ro victor.rentea@gmail.com 30 companies Posting daily on
12. 26 The most important principle in programming?
13. 27 Single Responsibility Principle EmployeeManager -read/persist -compute pay-roll -generate PDF report -manage projects vs
14. 28 Coupling vs
15. 29 Don’t Repeat Yourself
16. 30 Keep It Short & Simple Premature encapsulation is the root of all evil Overengineering – Adam Bien
17. 31 Keep It Short & Simple Premature encapsulation is the root of all evil Overengineering Simpler code Developer Happiness
18. 32 Invisible Magic to reduce effort and risk Protect the Developers ... Avoid building an intrusive Custom Framework (bugs to learn) Developer Comfort
19. 33 Request/Thread Scope @Autowired private MyRequestContext requestContext; ... { entity.setModifiedBy(requestContext.getCurrentUser()); } @Component @Scope(value = "request", proxyMode = TARGET_CLASS) class MyRequestContext { ... } Request Metadata
20. Fear Kills Creativity Simplify Unit Testing - Strong regression defense Protect the Developers 34 Developer Safety
21. Always Think Regular Brainstorming 35 Continuous Refactoring There are NO boring tasks automate them
23. 39 Keep Struggling for a Can you predict the future ? What features will grow super-complex in time? Simple Design At all times!
24. 40 - Kent Beck https://martinfowler.com/bliki/BeckDesignRules.html 2. Reveals Intention 3. No Duplication 4. Fewest Elements 1. Passes the Tests Rules of Simple Design
25. 41 A Simple Architecture that Evolves to Match the Growing Complexity This talk is about…
26. 42 Core Principles Modeling Data Organizing Logic The Onion Architecture Tests. Fear. Agenda VictorRentea.ro
27. You control them! Entities = your persistent data 43 Entity They simplify your logic
28. 44 Put small bits of highly reusable domain logic in your Domain Entities public class Customer { [...] public String getFullName() { return firstName + " " + lastName; } public void activate(User user) { if (status != Status.DRAFT) { throw new IllegalStateException(); } status = Status.ACTIVE; activatedBy = user; activatedDate = new Date(); } public boolean isActive() { return status == Status.ACTIVE; } public boolean canPlaceOrders() { return status == Status.ACTIVE && !isBann }
29. 45 activatedBy = user; activatedDate = new Date(); } public boolean isActive() { return status == Status.ACTIVE; } public boolean canPlaceOrders() { return status == Status.ACTIVE && !isBann } public void addAddress(Address address) { address.setCustomer(this); addresses.add(address); } public List<Address> getAddresses() { return Collections.unmodifiableList( addresses); } } public String toExportString() { return String.format("%s;%s;%d", firstName, lastName, isActive()?1:0); } BlOAt dAnGeR Fit Put small bits of highly reusable domain logic in your Domain Entities
30. Entity id 46 Small Immutable Lombok? No persistent ID unlike an Entity Equal by value of all fields Embeddable In larger entities Value Object: a grouping of domain data VO public class Money { private final Currency currency; private final BigDecimal amount; public Money(Currency currency, BigDecimal amount) { this.currency = currency; this.amount = amount; } public Currency getCurrency() { return currency; } public BigDecimal getAmount() { return amount; } public boolean equals(Object other) { ... } } validate();
31. Then, you start exposing data to UI (SPA, WS, JSF, desktop) UI has different goals They want data structures to match their screens. Never expose your Entities in your API 47 isDeletable: true (to show/hide the Delete button)
32. I like dumb DTOs (you'll see soon why) public fields ?! ! !.. VO Entity id Logic public class CustomerDto { private String fullName; private String phoneNumber; private Date birthDate; public final String getFullName return fullName; } public final void setFullName(S this.fullName = fullName; } public final String getPhoneNum return phoneNumber; } public final void setPhoneNumbe this.phoneNumber = phoneNumbe } public final Date getBirthDate( return birthDate; } public final void setBirthDate( this.birthDate = birthDate; } } 48 Form/Request View/Response DTO SearchCriteria/SearchResult Data Transfer Objects DTO Instead, expose in your API public class CustomerDto { public String fullName; public String phoneNumber; public Date birthDate; } dto.fullName = customer.getFullName();
33. 49 Core Principles Modeling Data Organizing Logic The Onion Architecture Tests. Fear. Agenda
34. 50 Complex Conversion? Extract Mappers VO Entity id DTO Mapper Logic API Domain CustomerDto dto = new CustomerDto(); dto.fullName = customer.getFullName(); dto.birthDate = customer.getBirthDate(); dto.phoneNumber = customer.getPhoneNumber(); CustomerDto dto = new CustomerDto(customer);
35. 61 Start implementing all domain logic in a Facade Mapper VO Entity id DTO Facade Facade Domain Service Domain Service Domain Services This approach is detailed in Java EE Patterns - Rethinking Best Practices, by Adam Bien Then extract logic into -To hide complexity: SRP -For Reuse: DRY ▪ (across Facades or Services) ≈ Application Service [DDD]
36. 63 Keep DTOs out! (parameters and return types) Mapper VO Entity id DTO Facade Facade Domain Service Domain Service Domain Services speak your Domain Model Convert them to your Domain Objects ASAP DTOs are fragile (under enemy control) * I like them dumb (no methods)
37. Fç Validate Data Façade Convert Data Implement Logic Aspects - Transactions - Logging - Exception Handling* - Access Control* 64 Facade Roles DTO Validator Mapper Domain Service VO Entity id
38. 65 What do you mean ? When a class grows too big (>~200 lines?) ➔ break it Extract when it Grows How? Look for a good class name to summarize some of its methods Huh? If I find a good name, I extract? That’s it? Exactly! Piece a cake! A Good Name He-he!☺ “There are only two things hard in programming: Cache Invalidation and Naming Things”
39. 66 CustomerFacade saveCustomer() getCustomer() searchCustomer() saveCustomerPreferences() getCustomerPreferences() validateAddress() resetPassword() checkPassworStrength() CustomerPreferecesFacade saveCustomerPreferences() getCustomerPreferences() validateAddress() resetPassword() checkPassworStrength() CustomerFacade saveCustomer() getCustomer() searchCustomer() Extract when it Grows at the same level of abstraction Horizontal Splitting > 300 lines
40. AlertService CompositeOrder Service 67 Separation by Layers of Abstraction OrderService DeliveryService Extract when it Grows Vertical Extraction more abstract, more higher-level
41. 69 Duplication Pair Programming Imposed repeat in .js the validations from .java Rush/Lazy Inadvertent you forget and implement it again Inter-developer you didn't knew that was already implemented bus factor =2
42. Practice Pair Programming
44. Developer Comfort is essential for Emerging Architectures
46. 75 Core Principles Modeling Data Organizing Logic The Onion Architecture Tests. Fear. Agenda VictorRentea.ro
47. 76 VO Entity id Domain Service Domain Service What code would you protect? Put it in the domain module Priceless Domain Logic Domain Objects domain
48. Façade DTO Validator Mapper F application 77 domain depends on domain VO Entity id Domain Service Domain Service
49. 78 External Service DTO Domain Service Domain Service domain
50. 79 External Service DTO Adapter Domain Service Domain Service <dependency> domain infrastructure A huge Adapter® Pattern - Hide their ugly API - Handle their Exceptions - Decouple their DTOs  your Entities - Validate their evil data
51. 80 External Service DTO IAdapter Adapter implements class OrderRepository implements IOrderRepo { public Order getById(id){ ... } } interface IOrderRepo { Order getById(id); } class OrderService { @Autowired IOrderRepository repo; ... { repo.getById(id); } } express your need in a domain interface… and implement it in a lower-level module… When you need to call outside… so nothing foreign enters your domain. Domain Service Domain Service <dependency> domain infrastructure
52. 81 calls Dependency Inversion Principle <dependency> higher-level module lower-level module "Best of OOP" - Uncle Bob Abstractions should not depend on details Low level classes are not visible
53. infra Adapter 83 External Service XML, JSON IAdapter <dependency> implements HTTP, RMI, … FTP JMS domain DB DTO
55. 85 BUT…
56. 86 VO Entity id Domain Service Domain Service IExtSrv Adapter IRepo What code would you protect? Put it in the domain module Interfaces for External Services you consume Interfaces for Repositories Priceless Domain Logic Domain Objects
57. infra ExtSrv Adapter Repo implem 87 Façade DTO Validator Mapper VO Entity id Domain Service Domain Service IExtSrv Adapter IRepo F application The Onion Architecture Behold, a.k.a. Clean, Hexagonal, Ports-and-Adapters
58. 98 Façade DTO Validator Mapper VO Entity id Domain Service Domain Service IRepo Repo implem F application infra IExtSrv Adapter Adapter WS Interface DTO
59. 99 Façade DTO Validator Mapper VO Entity id Domain Service Domain Service IRepo Repo implem F application IExtSrv Adapter Adapter WS Interface DTO domain Pragmatic for decent apps, 2 modules are enough
60. Use-case Optimal Query 100 CALLS DEPENDS Breaking into Bounded Contexts DTO Facade Infra Tip: Measure boundary violations com.myapp.order. … com.myapp.product. … EVENT TX FK? SELECT MICRO… "Light CQRS" consistency
62. 103 tardigrade
63. 104 fitness function
64. 105 coupling performance scalability fitness function security source code size
65. 108 Core Principles Modeling Data Organizing Logic The Onion Architecture Tests. Fear. Agenda VictorRentea.ro
66. 109 Lots of Unit Tests are Good ! A sense of confidence Developer Courage Continuous Refactoring (It’s still a single )
67. 110 As you fight to write Unit Tests, the Production code gets simpler
68. 112 First couple of unit tests : The most valuable Test no. difficulty
69. Maintainable Tests Pure Functions No side effects. No dependencies. Mock-based Less readable In-memory Emulation or JPQL tests on H2/* db Fragile data fixtures On Real Systems Eg: Connecting to a real DB 113 , = 2 + 2
70. infrastructure domain side effects 116 pure logic
71. ▪ 7 Virtutes of a Good Object ▪ NULL – the worst mistake in IT - https://dzone.com/articles/the-worst-mistake-of-computer-science-1 ▪ The Clean Architecture: - http://blog.8thlight.com/uncle-bob/2012/08/13/the-clean-architecture.html ▪ Some ☺ Programming Jargon - http://blog.codinghorror.com/new-programming-jargon/ ▪ Code quality: WTFs/minute - http://commadot.com/wtf-per-minute/ ▪ SOLID is WRONG - https://speakerdeck.com/tastapod/why-every-element-of-solid-is-wrong ▪ Good software is written 3 times - http://www.javaworld.com/article/2072651/becoming-a-great-programmer-- use-your-trash-can.html ▪ Prezi-like effect in PowerPoint 2016: “Morph” ▪ Value Objects vs Entity - http://enterprisecraftsmanship.com/2016/01/11/entity-vs-value-object-the- ultimate-list-of-differences/ ▪ Extends is bad - http://www.yegor256.com/2016/09/13/inheritance-is-procedural.html ▪ “Measure Don’t Ask” is TM of Kirk Pepperdine Further Reading 121
72. 122 Agenda VictorRentea.ro Core Principles Modeling Data Organizing Logic The Onion Architecture Tests. Fear.
73. 123 Core Principles VictorRentea.ro Modeling Data Organizing Logic The Onion Architecture Tests. Fear. Agenda Takeaways
74. 124 VictorRentea.ro Tests. Fear. Organizing Logic The Onion Architecture Modeling Data KISS: Avoid overengineering Magic to protect your Developers Takeaways
75. 125 VictorRentea.ro Tests. Fear. Organizing Logic The Onion Architecture Enemy data KISS: Avoid overengineering Magic to protect your Developers in your DTOs: keep them out Takeaways
76. 126 VictorRentea.ro Tests. Fear. Extract when it Grows The Onion Architecture KISS: Avoid overengineering Magic to protect your Developers : for SRP or DRY Enemy data in your DTOs: keep them out Takeaways
77. 127 VictorRentea.ro Extract when it Grows The Onion KISS: Avoid overengineering Magic to protect your Developers : for SRP or DRY Enemy data in your DTOs: keep them out , DIP: domain agnostic to externals Tests. Fear. Takeaways (Adapt® them)
78. 128 VictorRentea.ro Extract when it Grows The Onion KISS: Avoid overengineering Magic to protect your Developers : for SRP or DRY Enemy data in your DTOs: keep them out , DIP: domain agnostic to externals Tests: let them smash your design Takeaways (Adapt® them)
79. 129 KISS
80. 130 Keep It simple
81. 136 Put Passion In All That You Do!!
82. Thank You!!