[springboot] principle analysis

4. Principle of Spring Boot

Spring principle [ Spring annotation ], SpringMVC principle, automatic configuration principle , SpringBoot principle

1. SpringBoot startup process

• Create a SpringApplication

• • Save some info.
  • Determine the type of the current application. ClassUtils. Servlets
  • **bootstrappers****：初始启动引导器（**List<Bootstrapper>**）：去spring.factories文件中找** org.springframework.boot.**Bootstrapper**
  • 找 ApplicationContextInitializer；去spring.factories****找 ApplicationContextInitializer
• • • `List<ApplicationContextInitializer<?>> initializers
• • Find ApplicationListener; application listener. Go to spring.factories**** to find ApplicationListener
• • • `List<ApplicationListener<?>> listeners

• run SpringApplication

• • StopWatch
  • Record application startup time
  • **Create a bootstrap context (Context environment)** createBootstrapContext()
• • • Get all the previous bootstrappers and execute intitialize() one by one to complete the setting of the bootstrapper context
• • Let the current application enter headless mode. java.awt.headless
  • Get all RunListeners ** (running listeners) [in order to facilitate event awareness for all Listeners]**
• • • getSpringFactoriesInstances 去spring.factories****找 SpringApplicationRunListener.
• • Traverse the SpringApplicationRunListener to call the starting method;
• • • It is equivalent to notifying all interested people that the system is in the process of starting and that the project is starting.
• • Save command line arguments; ApplicationArguments
  • Prepare the environment prepareEnvironment();
• • • Return or create a basic environment information object. Standard Servlet Environment
    • Configuration environment information object.
• • • • Read configuration property values ​​for all configuration sources.
• • • Binding environment information
    • The listener calls listener.environmentPrepared(); notifies all listeners that the current environment is ready
• • Create an IOC container (createApplicationContext())
• • • Create container based on item type (Servlet),
    • AnnotationConfigServletWebServerApplicationContext is currently created
• • Prepare the basic information of the ApplicationContext IOC container prepareContext()
• • • Save environment information
    • The post-processing process of the IOC container.
    • apply initializers; applyInitializers;
• • • • Iterate over all ApplicationContextInitializers. Call initialize.. To initialize the extension function of the ioc container
      • Traverse all listeners and call contextPrepared. EventPublishRunListenr; notify all listeners ****contextPrepared
• • • All listeners call contextLoaded. Notify all listeners contextLoaded;
• • ** Refresh the IOC container. **refreshContext
• • • Create all components in the container (Spring annotations)
• • Work after container refresh is complete? after Refresh
  • All listeners call listeners.started ( context); notify all listeners started
  • **Call all runners; **callRunners()
• • • Get the ApplicationRunner in the container
    • Get the CommandLineRunner in the container
    • Merge all runners and sort by @Order
    • Traverse all runners. call run method
• • If the above is abnormal,
• • • Failed to call Listener
• • Call the running method listeners.running(context) of all listeners ; notify all listeners of running
  • **running if there is a problem. Continue to notify failed. ** call **failed of all Listeners ; ** notify all listeners of failed

public interface Bootstrapper {
    
    

	/**
	 * Initialize the given {@link BootstrapRegistry} with any required registrations.
	 * @param registry the registry to initialize
	 */
	void intitialize(BootstrapRegistry registry);

}

@FunctionalInterface
public interface ApplicationRunner {
    
    

	/**
	 * Callback used to run the bean.
	 * @param args incoming application arguments
	 * @throws Exception on error
	 */
	void run(ApplicationArguments args) throws Exception;

}
@FunctionalInterface
public interface CommandLineRunner {
    
    

	/**
	 * Callback used to run the bean.
	 * @param args incoming main method arguments
	 * @throws Exception on error
	 */
	void run(String... args) throws Exception;

}

2、Application Events and Listeners

https://docs.spring.io/spring-boot/docs/current/reference/html/spring-boot-features.html#boot-features-application-events-and-listeners

ApplicationContextInitializer

ApplicationListener

SpringApplicationRunListener

3、ApplicationRunner 与 CommandLineRunner