1. Fundamental Spring Boot:
Keep it Simple, Get it Right,
Be Productive and Have Fun
Wei Li
09/02/2020
SpringOne 2020

2. 22 2
About Me
Spring framework user
since version 1.0
Curious learner
Savvy runner
Problem solver
Wei Li​
Solutions Engineer,​
Liberty Mutual Insurance

3. 33 3
Spring Boot in a Nutshell
Dependency management
High productivity
Quality and cloud native
applications
Auto and conditional
configuration
Convention over
configuration
Rich non-functional
features and tooling
Happy developers

4. 44 4
About This Talk - Spring Boot Fundamental
Concepts
Application properties Manage beans
Bean scopeDependency injection
Post startup processingTroubleshooting tips
Be productive

5. 55 5
Application Properties
One property file per
environment Validate properties
Make properties type-safe
(properties => POJO)
Favor YAML file

6. 66 6
Application Properties – Favor YAML File
YAML Ain't Markup Language

7. 77 7
Application Properties – One File per Environment
Activate

8. 88 8
Application Properties – Default to Local Profile

9. 99 9
Application Properties – Avoid using @Value

10. 1010 10
Application Properties – Use Type-safe Properties
POJO

11. 1111 11
Application Properties – Use Type-safe Properties

12. 1212 12
Application Properties – Use Type-safe Properties

13. 1313 13
Application Properties – Use Type-safe Properties

14. 1414 14
Application Properties – We Can Validate Properties

15. 1515 15
Application Properties – We Can Validate Properties

16. 1616 16
Application Properties – We Can Validate Properties

17. 1717 17
Application Properties – Takeaway
If you define a set of configuration keys for your own components,
we recommend you group them in a POJO annotated with
@ConfigurationProperties. Doing so will provide you with structured,
type-safe object that you can inject into your own beans.
- https://docs.spring.io/spring-boot/docs/current/reference/html/
spring-boot-features.html#boot-features-external-config-vs-value

18. 1818 18
Dependency Injection
Preferred
Implicit constructor
injection
Lombok is our friend
Constructor Injection
Avoid if possible
Field Injection
Use wisely
Setter Injection

19. 1919 19
Dependency Injection – Avoid Field Injection
Hint: hard to unit test

20. 2020 20
Dependency Injection – Wisely Use Setter Injection

21. 2121 21
Dependency Injection – Prefer Constructor Injection

22. 2222 22
Dependency Injection – Implicit Constructor
Injection if Only One Constructor
Hint: test without Spring

23. 2323 23
Dependency Injection – Implicit Constructor with
Lombok
Lombok generates constructor

24. 2424 24
Dependency Injection – Takeaway
The Spring team generally advocates constructor injection, as it lets
you implement application components as immutable objects and
ensures that required dependencies are not null. Furthermore,
constructor-injected components are always returned to the client (calling)
code in a fully initialized state
- https://docs.spring.io/spring/docs/current/spring-framework-reference/core.html

25. 2525 25
Troubleshooting Tips
Turn on debug
• beans
• conditions
• configprops
• env
• loggers
• mappings
Tweak log level
Leverage Actuator endpoints

26. 2626 26
Troubleshooting Tips - Turn on Debug

27. 2727 27
Troubleshooting Tips - Tweak Log Levels

28. 2828 28
Troubleshooting Tips – Leverage Actuator Endpoints
http://localhost:8080/actuator/beans - all beans in the application
http://localhost:8080/actuator/conditions - conditions that were evaluated on
configuration and auto-configuration classes
http://localhost:8080/actuator/configprops - all @ConfigurationProperties
http://localhost:8080/actuator/env - properties from Spring’s ConfigurableEnvironment
http://localhost:8080/actuator/mappings - a list of all @RequestMapping paths
http://localhost:8080/actuator/loggers - the configuration of loggers in the application

29. 2929 29
Actuator Endpoints - beans

30. 3030 30
Actuator Endpoints - conditions

31. 3131 31
Actuator Endpoints – configprops

32. 3232 32
Actuator Endpoints - env

33. 3333 33
Actuator Endpoints - mappings

34. 3434 34
Actuator Endpoints - loggers

35. 3535 35
Be Productive
Lombok
DevTools
Boot Dashboard
H2 Console

36. 3636 36
Be Productive – Let Lombok Write Code For You
Hint: refactoring is easier

37. 3737 37
Be Productive – Let Lombok Write Code For You

38. 3838 38
Be Productive – Use DevTools
Automatic Application
Restart
Browser Refresh by
LiveReload

39. 3939 39
Be Productive – Use Boot Dashboard
Picture copyright - https://spring.io/blog/2015/10/08/the-spring-boot-dashboard-in-sts-part-1-local-boot-apps
Quick access to the
things you do all the
Time during
development

40. 4040 40
Be Productive – Use H2 Console

41. 4141 41
Manage Beans
@Component
@Service
@Repository
@Controller
@Configuration
@Bean
OthersSpring Built-in Stereotypes

42. 4242 42
Manage Beans - Stereotypes

43. 4343 43
Manage Beans - @Configuration and @Bean

44. 4444 44
Bean Scope
Mostly used • Prototype
• Request
• Session
…
Singleton is by default Other scopes

45. 4545 45
Bean Scope – Singleton is a given

46. 4646 46
Bean Scope – Other scopes

47. 4747 47
Post Startup Processing
CommandLineRunner ApplicationListener

48. 4848 48
Post Startup Processing – Use CommandLineRunner

49. 4949 49
Post Startup Processing – Use ApplicationListener

50. 5050 50
Summary
Don’t over engineer (YAGNI)
Up to date dependencies
Convention over configuration
Learn from the source