spring-: spring-boot-bootstrapping-behind-the-scenes

Spring Boot applications are behind many steps behind the startup. This article will gradually analyze its logical execution order.

I. Spring Boot Application Step

<.> 1.1 JVM startup and the main class load

Java virtual machine (JVM) starts and loads the main class containing the

method.

• public static void main(String[] args) <.> 1.2 Execution
Method

SpringApplication.run() Execute the method to start the Spring Boot application. This is the entrance point for all Spring Boot applications.

<.> 1.3 Initialization
• SpringApplication.run()

Initialization, including: SpringApplication Judgment application type (web or non -web).

Load application configuration and environmental attributes.

• Prepare for the context. SpringApplication
  • <.> 1.4 Prepare
Create the context of the Spring application, as a container management bean, configuration and dependencies.

If it is a web application, use the context based on the service (such as ). ApplicationContext

<.> 1.5 load

• AnnotationConfigServletWebServerApplicationContext Load the registered
Bean (modify the context before the context was started).

<.> 1.6 Detect and apply ApplicationContextInitializer

• Spring scan and load any ApplicationContextInitializer implementation, allowing external listeners to receive application startup notifications.

<.> 1.7 Preparing the environment (attributes, configuration files and configuration) SpringApplicationRunListener

Load environmental variables,

or
• and command line parameters. SpringApplicationRunListener
Determine the activity and the default configuration file.

<.> 1.8 Refresh the context

• The context is completely refreshed, including: application.properties application.yml Scanning belt includes categories of
,
• ,
and

annotations.

instantiated bean and manage its life cycle.

Application dependency injection and analytical dependence relationship.

• • @Component <.> 1.9 Start the embedded web server (if applicable) @Service @Repository @Controller
  If it is a web application, Spring Boot automatically starts the embedded Web server (Tomcat, Jetty or Undertow).
  Web server monitor the passing request of the specified port.
  <.> 1.10 execute
and

bean

If there is a bean of

or
• , they execute them.
• These beans are used to run the initialization logic after the application starts.

<.> 1.11 triggers Incident CommandLineRunner ApplicationRunner

• Trigger event, indicating that the application has been completely started and prepared for the request. ApplicationReadyEvent

<.> 1.12 Keep application operation (for web applications)

For web applications, the application keeps running, waiting for the HTTP request to be introduced.

• For non -web applications, exit after running the logic of initialization.
2. Logic execution order: Brief overview

In order to remember the startup process, it can be regarded as three main stages:

1️🎜 During the guidance stage

JVM start the application.

Execute .

• Prepare environment and configuration.
• SpringApplication.run() 2️🎜 The initialization stage of the context

Create and refresh the context.

Scan, create and inject bean.

If it is a web application, start the embedded server.

3️🎜 After starting,
execute and

.

The application is fully running and waiting for the request. ?

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