SpringBoot 启动配置原理

发布于 2022-03-17 17:07:42

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代码可运行

springBoot 启动配置原理

springBoot 几个重要的事件回调机制
- 配置在 META_INF/spring.factories
  - ApplicationContextInitializer
  - SpringApplicationRunListener
- 只需要放在 ioc 容器中
  - ApplicationRunner
  - CommanLineRunner

启动流程：

一、创建 SpringApplication 对象（1.x 版本）

initialize(sources);
private void initialize(Object[] sources) {
    // 保存主配置类
	if (sources != null && sources.length > 0) {
		this.sources.addAll(Arrays.asList(sources));
	}
    // 判断当前是否一个web应用
	this.webEnvironment = deduceWebEnvironment();
    // 从类的路径下找到META-INF/spring.factories配置的所有ApplicationContextInitializer；然后保存起来
	setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
    // 从类路径下找到META-INF/spring.factories配置的所有ApplicationListener
	setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
    // 从多个配置类中找到有main方法的主配置类
	this.mainApplicationClass = deduceMainApplicationClass();
}

二、运行 run 方法(1.x 和 2.x)

public ConfigurableApplicationContext run(String... args) {
    StopWatch stopWatch = new StopWatch();
    stopWatch.start();
    ConfigurableApplicationContext context = null;
    Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList();
    this.configureHeadlessProperty();

    // 获取SpringApplicationRunListeners; 从类路径下META-INF/spring.factories
    SpringApplicationRunListeners listeners = this.getRunListeners(args);
    // 回调所有的获取SpringApplicationApplicationRunListener.starting()方法
    listeners.starting();

    Collection exceptionReporters;
    try {
        //封装命令行参数
        ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
        // 准备环境
        ConfigurableEnvironment environment = this.prepareEnvironment(listeners, applicationArguments);
        this.configureIgnoreBeanInfo(environment);
        // 创建环境完成后回调SpringApplicationRunListener.environmentPrepared();表示环境准备完成
        Banner printedBanner = this.printBanner(environment);

        // 创建ApplicationContext; 决定创建web的ioc还是普通的ioc
        context = this.createApplicationContext();
        exceptionReporters = this.getSpringFactoriesInstances(SpringBootExceptionReporter.class, new Class[]{ConfigurableApplicationContext.class}, context);
        // 准备上下文环境；将environment保存到ioc中；而且applyInitalizers();
        // applyInitalizers(): 回调之前保存的所有的ApplicationContextInitalizer的initze的方法
        // 回调所有的SpringApplicationRunListener的contextPrepared()
        this.prepareContext(context, environment, listeners, applicationArguments, printedBanner);
        // propareContext运行完成之后回调所有的SpringApplicationRunLitsener的contextLocaded();
        // 刷新容器； ioc容器初始化（如果是web应用还会创建嵌入式的Tomcat）;
        // 扫描,创建,加载所有组件的地方
        this.refreshContext(context);
        // 从ioc容器中获取所有的ApplicationRunner和CommandLineRunner进行回调
        // 所有的Application先回调，CommandLineRunner在回调
        this.afterRefresh(context, applicationArguments);
        stopWatch.stop();
        if (this.logStartupInfo) {
            (new StartupInfoLogger(this.mainApplicationClass)).logStarted(this.getApplicationLog(), stopWatch);
        }
		// 所有的SpringApplicationRunListener回调started方法
        listeners.started(context);
        this.callRunners(context, applicationArguments);
    } catch (Throwable var10) {
        this.handleRunFailure(context, var10, exceptionReporters, listeners);
        throw new IllegalStateException(var10);
    }

    try {
        listeners.running(context);
        // 整个SpringBoot应用启动完成以后返回启动的ioc容器
        return context;
    } catch (Throwable var9) {
        this.handleRunFailure(context, var9, exceptionReporters, (SpringApplicationRunListeners)null);
        throw new IllegalStateException(var9);
    }
}

三、事件监听机制

配置在 META-INF/spring.factories

ApplicationContextInitalizer

public class HelloApplicationContextInitializer implements ApplicationContextInitializer {

    @Override
    public void initialize(ConfigurableApplicationContext configurableApplicationContext) {
        System.out.println("ApplicationContextInitializer...initialize..."+configurableApplicationContext);
    }
}

SpringApplicationRunListener

public class HelloSpringApplicationRunListener implements SpringApplicationRunListener {

    // 必须要有构造器
    public HelloSpringApplicationRunListener(SpringApplication application, String[] args){

    }

    @Override
    public void environmentPrepared(ConfigurableEnvironment environment) {
        Object o = environment.getSystemProperties().get("os.name");
        System.out.println("SpringApplicationRunListener...environmentPrepared.."+o);
    }

    @Override
    public void contextPrepared(ConfigurableApplicationContext context) {
        System.out.println("SpringApplicationRunListener...contextPrepared...");
    }

    @Override
    public void contextLoaded(ConfigurableApplicationContext context) {
        System.out.println("SpringApplicationRunListener...contextLoaded...");
    }

    @Override
    public void started(ConfigurableApplicationContext context) {
        System.out.println("SpringApplicationRunListener...starting...");
    }

    @Override
    public void failed(ConfigurableApplicationContext context, Throwable exception) {
        System.out.println("SpringApplicationRunListener...finished...");
    }
}

配置（META-INFO/spring.factories）

org.springframework.context.ApplicationContextInitializer=\
com.oy.springboot.listener.HelloApplicationContextInitializer

org.springframework.boot.SpringApplicationRunListener=\
com.oy.springboot.listener.HelloSpringApplicationRunListener

只需要放在 ioc 容器中

ApplicationRunner

@Component
public class HelloApplicationRunner implements ApplicationRunner {
    @Override
    public void run(ApplicationArguments args) throws Exception {
        System.out.println("ApplicationRunner...run....");
    }
}

CommandLineRunner

@Component
public class HelloCommandLineRunner implements CommandLineRunner {
    @Override
    public void run(String... args) throws Exception {
        System.out.println("CommandLineRunner...run..."+ Arrays.asList(args));
    }
}

测试：

自定义 starter

starter:

1.编写自动配置

@Configuration //指定这个类是一个配置类
@ConditionalOnXXX //在指定条件成立的情况下自动配置类生效
@AutoConfigureAfter // 指定自动配置类的顺序
@Bean // 给容器中添加组件

@ConfigurationPropertie // 结合相关xxxProperties类来绑定相关的配置
@EnableConfigurationProperties // 让xxxProperties生效加入到容器中

自动配置类要能加载
将需要启动就能加载的自动配置类，配置在META-INF/spring.factories
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
org.springframework.boot.autoconfigure.admin.SpringApplicationAdminJmxAutoConfiguration,\
org.springframework.boot.autoconfigure.aop.AopAutoConfiguration,\

模式：

启动器只用来做依赖导入：
专门来写一个自动配置模块；
启动器依赖自动配置；别人只需要引入启动器（starter） eg: mybatis-spring-boot-starter; 自定义启动器名-spring-boot-starter

演示步骤（参考）：

项目结构

2. 先创建一个空项目，然后 oy-spring-boot-starter（用 maven 创建）和 oy-spring-boot-starter-autoconfigurer（spring Initializr 创建）

【oy-spring-boot-starter】 pom.xml 配置

<dependencies>
        <dependency>
            <groupId>com.oy.starter</groupId>
            <artifactId>oy-spring-boot-starter-autoconfigurer</artifactId>
            <version>0.0.1-SNAPSHOT</version>
</dependencies>

【oy-spring-boot-starter-autoconfigurer】 pom.xml 配置

<?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>
	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.3.3.RELEASE</version>
		<relativePath/> <!-- lookup parent from repository -->
	</parent>
	<groupId>com.oy.starter</groupId>
	<artifactId>oy-spring-boot-starter-autoconfigurer</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>oy-spring-boot-starter-autoconfigurer</name>
	<description>Demo project for Spring Boot</description>

	<properties>
		<java.version>1.8</java.version>
	</properties>

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

</project>

【HelloProperties】

@ConfigurationProperties(prefix = "oy.hello")
public class HelloProperties {
    private String prefix;
    private String suffix;

    public String getPrefix() {
        return prefix;
    }

    public void setPrefix(String prefix) {
        this.prefix = prefix;
    }

    public String getSuffix() {
        return suffix;
    }

    public void setSuffix(String suffix) {
        this.suffix = suffix;
    }
}

【HelloService】

public class HelloService {

    HelloProperties helloProperties;

    public HelloProperties getHelloProperties() {
        return helloProperties;
    }

    public void setHelloProperties(HelloProperties helloProperties) {
        this.helloProperties = helloProperties;
    }

    public String sayHellAtguigu(String name){
        return helloProperties.getPrefix()+"-" +name + helloProperties.getSuffix();
    }

【HelloServiceAutoConfiguration】

@Configuration
@ConditionalOnWebApplication // Web应用才生效
@EnableConfigurationProperties(HelloProperties.class)
public class HelloServiceAutoConfiguration {

    @Autowired
    HelloProperties helloProperties;

    @Bean
    public HelloService helloService(){
        HelloService service = new HelloService();
        service.setHelloProperties(helloProperties);
        return service;
    }
}

【spring.factories】

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
com.oy.starter.HelloServiceAutoConfiguration

测试：

**spring-boot-08-starter-test **项目结构

【pom.xml】

<dependency>
    <groupId>com.oy.stater</groupId>
    <artifactId>oy-spring-boot-starter</artifactId>
    <version>1.0-SNAPSHOT</version>
</dependency>

【HelloController.java】

@RestController
public class HelloController {

    @Autowired
    HelloService helloService;

    @GetMapping("/hello")
    public String hello(){
        return helloService.sayHellAtguigu("haha");
    }
}