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SpringBoot启动配置原理

SpringBoot启动流程

我们从SpringBoot的主方法的run方法进去一探究竟

@SpringBootApplication
public class SpringbootjpaApplication {

public static void main(String[] args) {
SpringApplication.run(SpringbootjpaApplication.class, args);
}

}

run方法进去以后做了两件事

  • 创建SpringApplication类
  • 执行run方法。
    public static ConfigurableApplicationContext run(Object[] sources, String[] args) {
    return new SpringApplication(sources).run(args);
    }

    创建SpringApplication对象

    调用initialize(sources)方法创建对象
    private void initialize(Object[] sources) {
    //保存主配置类
    if (sources != null && sources.length > 0) {
    this.sources.addAll(Arrays.asList(sources));
    }
    //判断当前应用是不是web应用
    this.webEnvironment = deduceWebEnvironment();
    //从类路径下找到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ETA-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,配置类可以是多个。
    this.mainApplicationClass = deduceMainApplicationClass();
    }//这样将SpringApplication对象创建出来

    运行run方法

    public ConfigurableApplicationContext run(String... args) {
    StopWatch stopWatch = new StopWatch();
    stopWatch.start();
    ConfigurableApplicationContext context = null;
    FailureAnalyzers analyzers = null;
    configureHeadlessProperty();
    //获取SpringApplicationRunListeners;从类路径下META-INF/spring.factories
    SpringApplicationRunListeners listeners = getRunListeners(args);
    //回调所有的获取SpringApplicationRunListener.starting()方法
    listeners.starting();
    try {
    //封装命令行参数
    ApplicationArguments applicationArguments = new DefaultApplicationArguments(
    args);
    //准备环境
    ConfigurableEnvironment environment = prepareEnvironment(listeners,
    applicationArguments);
    //prepareEnvironment中:listeners.environmentPrepared(environment);
    //创建环境完成后回调SpringApplicationRunListener.environmentPrepared();表示环境准备完成
    Banner printedBanner = printBanner(environment);//打印Spring的图标
    context = createApplicationContext();//创建IOC容器,决定创建web的ioc还是普通的ioc
    analyzers = new FailureAnalyzers(context);//出现异常做异常分析报告的
    //准备上下文环境;将environment保存到ioc中;而且applyInitializers();
    //applyInitializers():回调之前保存的所有的ApplicationContextInitializer的initialize方法
    //回调所有的SpringApplicationRunListener的contextPrepared();
    prepareContext(context, environment, listeners, applicationArguments,
    printedBanner);
    //prepareContext运行完成以后回调所有的SpringApplicationRunListener的contextLoaded();

    //s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;(配置类,组件,自动配置)
    refreshContext(context);
    //从ioc容器中获取所有的ApplicationRunner和CommandLineRunner进行回调
    //ApplicationRunner先回调,CommandLineRunner再回调
    afterRefresh(context, applicationArguments);
    listeners.finished(context, null);//所有的SpringApplicationRunListener回调finished方法
    stopWatch.stop();
    if (this.logStartupInfo) {
    new StartupInfoLogger(this.mainApplicationClass)
    .logStarted(getApplicationLog(), stopWatch);
    }
    //整个SpringBoot应用启动完成以后返回启动的ioc容器;
    return context;
    }
    catch (Throwable ex) {
    handleRunFailure(context, listeners, analyzers, ex);
    throw new IllegalStateException(ex);
    }
    }

关于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
CommandLineRunner

ApplicationContextInitializer

public class HelloApplicationContextInitializer implements ApplicationContextInitializer<ConfigurableApplicationContext> {
@Override
public void initialize(ConfigurableApplicationContext applicationContext) {
System.out.println("ApplicationContextInitializer...initialize..."+applicationContext);
}
}

SpringApplicationRunListener

public class HelloSpringApplicationRunListener implements SpringApplicationRunListener {

//必须有的构造器
public HelloSpringApplicationRunListener(SpringApplication application, String[] args){

}

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

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

配置让监听器起作用,在(META-INF/spring.factories)文件夹下进行配置,没有这个文件夹就在资源文件下新建一个。

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

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

ApplicationRunner

只需要放在ioc容器中

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

CommandLineRunner

只需要放在ioc容器中

@Component
public class HelloCommandLineRunner implements CommandLineRunner {
@Override
public void run(String... args) throws Exception {
System.out.println("CommandLineRunner...run..."+ Arrays.asList(args));
}
}
文章作者: zenshin
文章链接: https://zlh.giserhub.com/2020/04/23/springboot/startingprinciple/
版权声明: 本博客所有文章除特别声明外,均采用 CC BY-NC-SA 4.0 许可协议。转载请注明来自 zenshin's blog
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