Breaking the Magician's Code - Diving deeper into Spring Boot internals

Presented @DevNexus '17

Transcript

1. Breaking the Magician's Code
   Diving deeper into Spring Boot internals
   

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2. @phillip_webb
   @madhurabhave23
   

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4. DEMO
   start.spring.io
   

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5. DEMO
   Starting from scratch
   

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6. Embedded Servlet Container
   Tomcat
   WAR ServletContainerInitializer
   AbstractAnnotationConfigDispatcherServletInitializer
   WebApplicationContext
   Dispatcher
   Servlet
   

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7. Embedded Servlet Container
   WebApplicationContext
   Embedded
   EmbeddedServletContainerFactory
   EmbeddedServletContainer getEmbeddedServletContainer(
   ServletContextInitializer... initializers);
   EmbeddedServletContainer
   start()
   stop()
   getPort()
   

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8. DEMO
   Back to the CODE
   

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9. Servlets
   WebApplicationContext
   Embedded
   Servlet
   Filter
   ServletContextInitializer
   ServletRegistrationBean
   FilterRegistrationBean
   

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10. Servlets
    WebApplicationContext
    Embedded
    Servlet
    DispatcherServlet
    @RequestMapping(“/foo”)
    @RequestMapping(“/bar”)
    

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11. DEMO
    Back to the CODE
    

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12. Component scanning
    • @Componentscan
    • base Packages
    • base Package Classes
    • (default)
    

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13. Component Scanning
    com.example.demo.core.*
    com.example.demo.domain.*
    com.example.demo.Application
    com.example.demo.config.*
    

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14. Component Scanning
    example
    demo
    com
    config
    core
    domain
    

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15. Component Scanning
    example
    demo
    com
    config
    core
    domain
    .Application
    

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16. Component Scanning
    example
    demo
    com
    config
    core
    domain
    .Application
    

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17. Component Scanning
    example
    demo
    com
    config
    core
    domain
    .Application
    

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18. Component Scanning
    example
    demo
    com
    config
    core
    domain
    .Application
    

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19. DEMO
    Back to the CODE
    

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20. Meta-Annotations
    • Most Spring Annotations can be used as
    meta-annotations
    • Use in your own code
    • Used extensively in the framework:
    •@RestController
    •@GetMapping
    

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21. META-Annotations
    • @AliasFor for advanced mappings:
    @SpringBootConfiguration
    @EnableAutoConfiguration
    @ComponentScan
    public @interface SpringBootApplication {
    @AliasFor(annotation = EnableAutoConfiguration.class,
    attribute = "exclude")
    Class>[] exclude() default {};
    @AliasFor(annotation = ComponentScan.class,
    attribute = "basePackages")
    String[] scanBasePackages() default {};
    

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22. DEMO
    Back to the CODE
    

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23. Advanced ImportS
    • @Import(Regular.class)
    • ImportSelector
    • Return String[]
    • ImportBeanDefinitionRegistrar
    • Direct registration
    

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24. Spring Factories
    • Dirt simple way to discover
    implementations
    • Similar to Java Service Loader
    • Simple properties file
    • /META-INF/spring.factories
    

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25. DEMO
    Back to the CODE
    

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26. Conditions
    • @Conditional annotation
    • Condition interface
    public interface Condition {
    boolean matches(
    ConditionContext context,
    AnnotatedTypeMetadata metadata);
    }
    

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27. Conditions
    • Spring Framework @Profile
    • Spring Boot (Bean,Class,Property)
    • Ordered so fastest run first
    

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28. DEMO
    Back to the CODE
    

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29. Spring Boot Code
    •ConditionalOnAClass ->
    ConditionalOnClass
    • MagicApplication ->
    SpringBootApplication
    • EnableMagicAutoConfiguration ->
    EnableAutoConfiguration
    • EnableMagicProperties ->
    EnableConfigurationProperties
    • *Configuration -> *AutoConfiguration
    

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30. Summary
    • There’s no such thing as magic
    • Follow the breadcrumbs
    • Annotations
    • Import Selectors
    • Spring Factories
    • Conditions
    • Use the source!
    

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31. Thanks!
    Questions?
    @madhurabhave23 @phillip_webb
    speakerdeck.com/philwebb
    https://github.com/mbhave/non-magic-demo
    

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