Breaking the Magician's Code

Diving deeper into Spring Boot internals

Transcript

1. Madhura Bhave @madhurabhave23 Breaking the Magician’s Code
2. DEMO start.spring.io
4. DEMO Starting from scratch
5. Embedded Servlet Container Tomcat WAR ServletContainerInitializer AbstractAnnotationConfigDispatcherServletInitializer WebApplicationContext Dispatcher Servlet
6. Embedded Servlet Container ServletWebServerApplicationContext ServletWebServerFactory WebServer getWebServer( ServletContextInitializer... initializers); WebServer start() stop() getPort()
7. DEMO Back to the CODE
8. Servlets ServletWebServerApplicationContext Servlet Filter ServletContextInitializer ServletRegistrationBean FilterRegistrationBean
9. Servlets ServletWebServerApplicationContext Servlet DispatcherServlet @RequestMapping(“/foo”) @RequestMapping(“/bar”)
10. DEMO Back to the CODE
11. Component scanning • @Componentscan • base Packages • base Package Classes • (default)
12. Component Scanning com.example.demo.core.* com.example.demo.domain.* com.example.demo.Application com.example.demo.config.*
13. Component Scanning example demo com config core domain
14. Component Scanning example demo com config core domain .Application
15. Component Scanning example demo com config core domain .Application
16. Component Scanning example demo com config core domain .Application
17. Component Scanning example demo com config core domain .Application
18. DEMO Back to the CODE
19. Meta-Annotations • Most Spring Annotations can be used as meta-annotations • Use in your own code • Used extensively in the framework: •@RestController •@GetMapping
20. 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 {};
21. DEMO Back to the CODE
22. Advanced Imports •@Import(Regular.class) •ImportSelector • Return String[] •ImportBeanDefinitionRegistrar • Direct registration
23. Spring Factories • Dirt simple way to discover implementations • Similar to Java Service Loader • Simple properties file •/META-INF/spring.factories
24. DEMO Back to the CODE
25. Conditions • @Conditional annotation • Condition interface public interface Condition { boolean matches( ConditionContext context, AnnotatedTypeMetadata metadata); }
26. Conditions • Spring Framework @Profile • Spring Boot (Bean,Class,Property) • Ordered so fastest run first
27. Spring Boot Code •ConditionalOnAClass -> ConditionalOnClass •MagicApplication -> SpringBootApplication •EnableMagicAutoConfiguration -> EnableAutoConfiguration •*Configuration -> *AutoConfiguration
28. Summary • There’s no such thing as magic • Follow the breadcrumbs • Annotations • Import Selectors • Spring Factories • Conditions • Use the source!
29. Madhura Bhave @madhurabhave23 Thanks! https://github.com/mbhave/non-magic-demo