Workshop Guide for Java Hexagonal Applications using Spring Boot

1. Java Development
HEXAGONAL
ARCHITECTURE
for Java Applications

2. 01 Concepts
Software Architecture

3. 01 What drives the software architecture?
• High Maintainability
• Low Technical Debt: The cost payed by bad decisions
• Lack of understanding
• Lack of tests
• Lack of documentation
• Lack of collaboration
• Lack of process

4. 01 Common multi-layer architecture
!
"
#
"
! UI Layer
" Application Layer
# Data
" Crosscutting
Dependency

5. 01 Multi-tier architecture
Web Application Tier
! !
" "
"
# # #
" "
"
!
"
Client Tier
Browsers, Frontend App
Mobile devices, PC$Q
%
!
+
Data / Integration Tier
Database, File Storage,
External Systems, Cloud
&

ERP
CRM
DOCs
Dependency

6. 01 Dependency inversion principle
Reference: http://blog.ploeh.dk/2013/12/03/layers-onions-ports-adapters-its-all-the-same
Dependency
DANGER -
Possible business
logic leaks

7. 02 Hexagonal
Architecture
The Pattern

8. 02 Intent
• Alternative names
• Ports & Adapters
• Onion Architecture / Onion Layers
“Allow an application to equally be driven by users,
programs, automated test or batch scripts, and to be
developed and tested in isolation from its eventual run-
time devices and databases.”
Alistair Cockburn

9. 02 Key Concepts
Ports are interfaces
Adapters are implementations

10. The big picture: Ports & Adapters02
"Application
Port Port
Port
Mock
DB
DB
Integration
Test
Agent
UI
Adapter
Adapter
Adapter
Adapter
Use Case
Boundary
‘’driven’’ adapters
‘’driver’’ adapters

11. Overview02

In-Memory
"Application
# Database
( Web Services
)
) Enterprise Integration
*

SQL Server
REST
Adapter
* Configuration
+
Test Agent
!
HTML5 App
Environment
Adapter
File Source
Adapter
,
SQL
Adapter
#
NoSQL
Adapter
- MQ Service
MQ
Adapter
.
. Messaging Queue
&ERP
CRM
DOCs
EI
Adapter
(SOAP
Adapter
TEST
Adapter

12. 03 Application
Keeping it simple

13. 03
• Organizing Concerns and Code with Domains
• Well defined boundaries between domains
• Simple event-driven components
• Life Preserver diagram
Life preserver approach by Russ Miles

14. Life Preserver diagram03
Integration
Core
Domain Event
Service
Domain
Boundary

15. Notes03
• Core
• Single purpose
• Focus on unit testing
• No side-effects
• Integration
• Side effects

16. 04 Practice
Ticket System

17. Kick-off04
github.com/fabricioepa/lab-
springboot-rest-sample
Lets start from the sample project and
then create the ports and adapters

18. 05 Core
Use Case as service

19. Implementing the Use Case as Service05
• Domain model
• Entities
• Repositories
• Well defined interface
• Input/Output Events
• Event Handlers & Translators
• Service composition
• Unit Testing

20. Life Preserver
Services
Domain
Event
Repository
D
atabase
Test
UnitTest
Framework
0405

21. 06 Controllers

22. Implementing passive controllers
• Dummy service invokers
• Do not perform multiple service calls
• It does not make any workflow decision
• REST Domain translator
0305
• UC
• Service
• Services
• Domain
• Controller
REST
Domain
06

23. Life Preserver
Services
Domain
Event
Repository
D
atabase
Test
UnitTest
Framework
Domain
Controller
R
EST
030506

24. 07
Configuration

25. Externalized configuration
• External files
• Environment variables
• Configuration profiles
• Services
030507

26. MySQL
Life Preserver
Services
Domain
Event
Repository
D
atabase
Test
UnitTest
Framework
Domain
Controller
R
EST
C
onfiguration
App
Settings
Test
Client
H2
in-memory
Environment
030507

27. Comments
• How many ports?
• The hexagon is a metaphor
• Abstractions
• Use Case as port
• Module as port: Notification, Administration,
Public API, Database
0303
• Services

28. See more…
• RESTful API with Spring Boot
• Securing REST APIs
• References:
[1] alistair.cockburn.us/Hexagonal+architecture
[2] www.infoq.com/news/2013/08/hexagonal-lifepreserver-spring
[3] github.com/russmiles/life-preserver-introductory-article-developer-magazine/
blob/master/README.md
[4] github.com/spring-guides/deprecate-tut-rest
[5] blog.ploeh.dk/2013/12/03/layers-onions-ports-adapters-its-all-the-same
/ fabricioepa.wordpress.com

29. Contact
FABRICIO EPAMINONDAS
0 linkedin.com/in/fabricioepa
/ fabricioepa.wordpress.com
1 @fabricioepa