SpringBoot-startup configuration principle

1. Startup process:

Several important event callback mechanisms

The following two are configured in META-INF/spring.factories:

ApplicationContextInitializer
SpringApplicationRunListener

The following two are configured in the ioc container

ApplicationRunner
CommandLineRunner

1. Create SpringApplication:

Starting a SpringBoot application will first create a SpringApplication, and then call the run method.
Insert picture description here
new SpringApplication (main program class)

Determine whether web application
Load and save all ApplicationContextInitializer (META-INF/spring.factories),
Load and save all ApplicationListener
Get the main program class

Creating SpringApplication is actually calling the constructor of SpringApplication, and completing the application type judgment and loading of Initializers, Listeners, etc. in it.
Insert picture description here
(1) webApplicationType: returns the type of the current web application.
None: non-web application starts
SERVLET: servlet-based web application and uses embedded server
REACTIVE: non-blocking

(2) Initializer and listener loading
setInitializers : load the initializer
setListenersfrom META-INF/spring.factories: load the listener from META-INF/spring.factories
Insert picture description here
Many packages have spring.factories, the following is an example of the autoconfiguration package:

After startup, the initializer and listener successfully loaded

(3) deduceMainApplicationClass()

Look at the passed class, which class has a main method, and which class is the main program.
Insert picture description here

2、run

run()

Call back all the starting of SpringApplicationRunListener (META-INF/spring.factories)
Get ApplicationArguments
Prepare environment & callback environmentPrepared of all listeners (SpringApplicationRunListener)
Print banner information
Create ioc container object (web environment container or ordinary environment container)
Prepare the environment
执行ApplicationContextInitializer. initialize()
Listener SpringApplicationRunListener callback contextPrepared
Load main configuration class definition information
Listener SpringApplicationRunListener callback contextLoaded
Refresh and start the IOC container;
Scan and load components in all containers (including all EnableAutoConfiguration components obtained from META-INF/spring.factories)
Call back all the run methods of ApplicationRunner and CommandLineRunner in the container
Listener SpringApplicationRunListener callback started method and running method