SpringOne 2020 Wei Li: Solutions Engineer, Liberty Mutual Insurance

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

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

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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

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

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

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Application Properties – Favor YAML File
YAML Ain't Markup Language

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Application Properties – One File per Environment
Activate

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Application Properties – Default to Local Profile

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Application Properties – Avoid using @Value

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Application Properties – Use Type-safe Properties
POJO

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Application Properties – Use Type-safe Properties

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Application Properties – Use Type-safe Properties

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Application Properties – Use Type-safe Properties

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Application Properties – We Can Validate Properties

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Application Properties – We Can Validate Properties

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Application Properties – We Can Validate Properties

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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

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

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Dependency Injection – Avoid Field Injection
Hint: hard to unit test

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Dependency Injection – Wisely Use Setter Injection

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Dependency Injection – Prefer Constructor Injection

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

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Dependency Injection – Implicit Constructor with
Lombok
Lombok generates constructor

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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

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

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Troubleshooting Tips - Turn on Debug

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Troubleshooting Tips - Tweak Log Levels

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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

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Actuator Endpoints - beans

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Actuator Endpoints - conditions

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Actuator Endpoints – configprops

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Actuator Endpoints - env

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Actuator Endpoints - mappings

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Actuator Endpoints - loggers

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Be Productive
Lombok
DevTools
Boot Dashboard
H2 Console

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

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Be Productive – Let Lombok Write Code For You

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

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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

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Be Productive – Use H2 Console

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

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Manage Beans - Stereotypes

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Manage Beans - @Configuration and @Bean

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

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Bean Scope – Singleton is a given

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Bean Scope – Other scopes

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Post Startup Processing
CommandLineRunner ApplicationListener

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Post Startup Processing – Use CommandLineRunner

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Post Startup Processing – Use ApplicationListener

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