springboot2.2.6 启动配置流程

1、主程序启动

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

2、先创建springApplication

SprinigApplication.java
​
//先创建SpringApplication,在调用run()方法
public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) {
  return new SpringApplication(primarySources).run(args);
}
​
//创建springApplication
public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
  this.resourceLoader = resourceLoader;
  Assert.notNull(primarySources, "PrimarySources must not be null");
  this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
  //判断是否是一个web应用
  this.webApplicationType = WebApplicationType.deduceFromClasspath();
  //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));
  //类路径下找到META-INF/spring.factiores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()
}

3、再运行run()方法

SprinigApplication.java
​
/**
     * 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) {
  StopWatch stopWatch = new StopWatch();
  stopWatch.start();
  //定义上下文（ico容器）对象
  ConfigurableApplicationContext context = null;
  Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
  configureHeadlessProperty();
  //获取SpringApplicationRunListener，从类路径下MEAT-INF/spring.factories
  SpringApplicationRunListeners listeners = getRunListeners(args);
  //回调所有SpringApplicationRunListener的starting()方法
  listeners.starting();
  try {
  //封装命令行参数
    ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
    //准备环境  创建环境完成后，回调SpringApplicationRunListener的 prepareEnvironment方法，表示环境准备完成
    ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);
    //处理需要忽略的bean
    configureIgnoreBeanInfo(environment);
    //打印SpringBoot标志图像
    Banner printedBanner = printBanner(environment);
    //创建ApplicationContext;决定是创建web IOC还是普通IOC
    context = createApplicationContext();
    exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,
                                                     new Class[] { ConfigurableApplicationContext.class }, context);
    
    //准备上下文环境，将environment保存在IOC中，而且调用applyInitializers(context)方法；
    //applyInitializers()方法中，回调之前保存的所有的ApplicationContextInitializer的initialize()方法,然后回调所有SpringApplicationRunListener的contextPrepared()方法；然后调用所有SpringApplicationRunListener的contextLoaded()方法
    
    prepareContext(context,environment,listeners,applicationArguments, printedBanner);
    //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（配置类，自建，自动配置）
    refreshContext(context);
    //
    afterRefresh(context, applicationArguments);
    stopWatch.stop();
    if (this.logStartupInfo) {
      new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
    }
    //所有的SpringApplicationRunListener回调started()方法
    listeners.started(context);
    //从IOC中获取所有的ApplicationRunner，CommandLineRunner进行回调，ApplicationRunner先回调，CommandLineRunner后回调
    callRunners(context, applicationArguments);
  }
  catch (Throwable ex) {
    handleRunFailure(context, ex, exceptionReporters, listeners);
    throw new IllegalStateException(ex);
  }
​
  try {
  //回调所有SpringApplicationRunListener的running()方法
    listeners.running(context);
  }
  catch (Throwable ex) {
    handleRunFailure(context, ex, exceptionReporters, null);
    throw new IllegalStateException(ex);
  }
  //整个SpringBoot应用启动完成之后，返回启动的IOC容器
  return context;
}

 

4、主要类：

配置在META-INF/spring.factories下的

ApplicationContextInitializer.java //用于初始化ConfigurableApplicationContext

SpringApplicationRunListener.java //在ConfigurableApplicationContext初始化过程中用SpringApplicationRunListener接口回调各种函数，用于实现用户自己的逻辑

只需要放在IOC容器中的

ApplicationRunner.java

CommandLineRunner.java

//项目启动后初始化一些信息，如数据库连接，自定义配置等