创建SpringBoot项目

pom.xml 文件

xml 复制代码

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
		 xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<groupId>com.example</groupId>
	<artifactId>demo</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>demo</name>
	<description>Demo project for Spring Boot</description>

	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>3.1.2</version>
		<relativePath/> <!-- lookup parent from repository -->
	</parent>

	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>
	</dependencies>

	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
				<version>3.1.0</version>
				<configuration>
					<excludes>
						<exclude>
							<groupId>org.projectlombok</groupId>
							<artifactId>lombok</artifactId>
						</exclude>
					</excludes>
				</configuration>
			</plugin>
		</plugins>
	</build>
</project>

启动程序类【DemoApplication】

java 复制代码

package com.example.demo;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class DemoApplication {
	public static void main(String[] args) {
	    // @param args JAR运行时传入的自定义参数
		SpringApplication.run(DemoApplication.class, args);
	}
}

java 复制代码

public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) {
	return new SpringApplication(primarySources).run(args);
}

SpringBootApplication复合注解

【自动配置Bean】@EnableAutoConfiguration，对start依赖包中被@Configuration注解修饰的类进行自动装配

【自动扫描Bean】@ComponentScan自动扫描DemoApplication启动类同级目录下的所有符合条件的组件

【基于JavaConfig创建Bean】@SpringBootConfiguration等同于@Configuration，将当前类标记为配置类并加载到容器

创建 SpringApplication 对象
初始化 SpringApplication对象的相关变量

java 复制代码

public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
	// 【添加资源加载器】ResourceLoader接口实例对象 
	this.resourceLoader = resourceLoader;

    // 【设置主方法类】当前SpringBoot应用启动类的class对象
	Assert.notNull(primarySources, "PrimarySources must not be null");
	this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
	
	// 推断应用类型：SERVLET、REACTIVE、NONE，默认SERVLET类型
	this.webApplicationType = WebApplicationType.deduceFromClasspath();
	
	// 初始化bootstrapRegistryInitializers变量
	// private final List<BootstrapRegistryInitializer> bootstrapRegistryInitializers;
	this.bootstrapRegistryInitializers = 
		new ArrayList<>(getSpringFactoriesInstances(BootstrapRegistryInitializer.class));

    // 初始initializers变量
    // private List<ApplicationContextInitializer<?>> initializers;
	setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
	
    // 初始化listeners变量
    // private List<ApplicationListener<?>> listeners;
	setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
	
	// 推断当前main方法所属的类的类型：SpringBoot启动类 
	this.mainApplicationClass = deduceMainApplicationClass();
}

通过run方法创建 ConfigurableApplicationContext 对象

java 复制代码

/**
 * Run the Spring application, creating and refreshing a new {@link ApplicationContext}.
 * @param args the application arguments (usually passed from a Java main method)
 * @return a running {@link ApplicationContext}
 */
public ConfigurableApplicationContext run(String... args) {
	long startTime = System.nanoTime();

	// 创建 启动上下文 对象
	DefaultBootstrapContext bootstrapContext = createBootstrapContext();

	// 允许无输入设备也可以启动服务
	configureHeadlessProperty();

    // 获取 SpringApplicationRunListeners 监听器并启动，启动流程中接收不同执行事件通知的监听者
    // SpringApplicationRunListener接口规定了SpringBoot的生命周期，在各个生命周期广播相应事件，调用实际的ApplicationListener类
	SpringApplicationRunListeners listeners = getRunListeners(args);
	listeners.starting(bootstrapContext, this.mainApplicationClass);

    ConfigurableApplicationContext context = null;
	try {
        // 初始化自定义启动参数
		ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
		// 准备运行环境
		ConfigurableEnvironment environment = prepareEnvironment(listeners, bootstrapContext, applicationArguments);
		Banner printedBanner = printBanner(environment); 

		// 创建Spring容器
		context = createApplicationContext();
		context.setApplicationStartup(this.applicationStartup);
        // Spring容器前置处理
		prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner);
		// 刷新Spring容器
		refreshContext(context);
        // Spring容器后置处理
		afterRefresh(context, applicationArguments);
		
		Duration timeTakenToStartup = Duration.ofNanos(System.nanoTime() - startTime);
		if (this.logStartupInfo) {
			new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), timeTakenToStartup);
		}

		// 启动完成事件
		listeners.started(context, timeTakenToStartup);
		
        // 回调自定义实现的Runner接口，处理一些执行后的定制化需求
		callRunners(context, applicationArguments);
	} catch (Throwable ex) {
		if (ex instanceof AbandonedRunException) {
			throw ex;
		}
		handleRunFailure(context, ex, listeners);
		throw new IllegalStateException(ex);
	}
	try {
		if (context.isRunning()) {
			Duration timeTakenToReady = Duration.ofNanos(System.nanoTime() - startTime);
			listeners.ready(context, timeTakenToReady);
		}
	} catch (Throwable ex) {
		if (ex instanceof AbandonedRunException) {
			throw ex;
		}
		handleRunFailure(context, ex, null);
		throw new IllegalStateException(ex);
	}
	return context;
}