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When something is painful but you can't avoid doing it… postpone it

When something is painful but you can't avoid doing it… delegate it

When something is painful but you can't avoid doing it… Do It More Often! "Bring The Pain Forward!"

Continuous Integration Pair Programming Continuous Refactoring TDD XP "Bring The Pain Forward!"

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

VictorRentea.ro @victorrentea [email protected] 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 [email protected] 30 companies Posting daily on

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26 The most important principle in programming?

27 Single Responsibility Principle EmployeeManager -read/persist -compute pay-roll -generate PDF report -manage projects vs

28 Coupling vs

29 Don’t Repeat Yourself

30 Keep It Short & Simple Premature encapsulation is the root of all evil Overengineering – Adam Bien

31 Keep It Short & Simple Premature encapsulation is the root of all evil Overengineering Simpler code Developer Happiness

32 Invisible Magic to reduce effort and risk Protect the Developers ... Avoid building an intrusive Custom Framework (bugs to learn) Developer Comfort

33 Request/Thread Scope @Autowired private MyRequestContext requestContext; ... { entity.setModifiedBy(requestContext.getCurrentUser()); } @Component @Scope(value = "request", proxyMode = TARGET_CLASS) class MyRequestContext { ... } Request Metadata

Fear Kills Creativity Simplify Unit Testing - Strong regression defense Protect the Developers 34 Developer Safety

Always Think Regular Brainstorming 35 Continuous Refactoring There are NO boring tasks automate them

36

39 Keep Struggling for a Can you predict the future ? What features will grow super-complex in time? Simple Design At all times!

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

41 A Simple Architecture that Evolves to Match the Growing Complexity This talk is about…

42 Core Principles Modeling Data Organizing Logic The Onion Architecture Tests. Fear. Agenda VictorRentea.ro

You control them! Entities = your persistent data 43 Entity They simplify your logic

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 }

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

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

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();

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)

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();

49 Core Principles Modeling Data Organizing Logic The Onion Architecture Tests. Fear. Agenda

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);

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]

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)

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

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”

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

AlertService CompositeOrder Service 67 Separation by Layers of Abstraction OrderService DeliveryService Extract when it Grows Vertical Extraction more abstract, more higher-level

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

Practice Pair Programming

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Developer Comfort is essential for Emerging Architectures

74

75 Core Principles Modeling Data Organizing Logic The Onion Architecture Tests. Fear. Agenda VictorRentea.ro

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

Façade DTO Validator Mapper F application 77 domain depends on domain VO Entity id Domain Service Domain Service

78 External Service DTO Domain Service Domain Service domain

79 External Service DTO Adapter Domain Service Domain Service domain infrastructure A huge Adapter® Pattern - Hide their ugly API - Handle their Exceptions - Decouple their DTOs  your Entities - Validate their evil data

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 domain infrastructure

81 calls Dependency Inversion Principle higher-level module lower-level module "Best of OOP" - Uncle Bob Abstractions should not depend on details Low level classes are not visible

infra Adapter 83 External Service XML, JSON IAdapter implements HTTP, RMI, … FTP JMS domain DB DTO

84

85 BUT…

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

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

98 Façade DTO Validator Mapper VO Entity id Domain Service Domain Service IRepo Repo implem F application infra IExtSrv Adapter Adapter WS Interface DTO

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

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

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103 tardigrade

104 fitness function

105 coupling performance scalability fitness function security source code size

108 Core Principles Modeling Data Organizing Logic The Onion Architecture Tests. Fear. Agenda VictorRentea.ro

109 Lots of Unit Tests are Good ! A sense of confidence Developer Courage Continuous Refactoring (It’s still a single )

110 As you fight to write Unit Tests, the Production code gets simpler

112 First couple of unit tests : The most valuable Test no. difficulty

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

infrastructure domain side effects 116 pure logic

▪ 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

122 Agenda VictorRentea.ro Core Principles Modeling Data Organizing Logic The Onion Architecture Tests. Fear.

123 Core Principles VictorRentea.ro Modeling Data Organizing Logic The Onion Architecture Tests. Fear. Agenda Takeaways

124 VictorRentea.ro Tests. Fear. Organizing Logic The Onion Architecture Modeling Data KISS: Avoid overengineering Magic to protect your Developers Takeaways

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

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

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)

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)

129 KISS

130 Keep It simple

136 Put Passion In All That You Do!!

Thank You!!