启动流程
1、创建SpringApplication对象（springboot2.x是通过构造器创造的）
1 @SuppressWarnings({ "unchecked", "rawtypes" })
2 public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
3 this.resourceLoader = resourceLoader;
//先判断主配置类是否为空
4 Assert.notNull(primarySources, "PrimarySources must not be null");
//不为空保存主配置类
5 this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
// 判断当前是否是一个Web应用
6 this.webApplicationType = WebApplicationType.deduceFromClasspath();
// 从类路径下META-INF/spring.factories配置的所有ApplicationContextInitializer；然后保存起来
7 setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
// 从类路径下META-INF/spring.factories配置所有的ApplicationListener
8 setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
// 从多个配置类中找到有main方法的主配置类
9 this.mainApplicationClass = deduceMainApplicationClass();
10 }
2、运行run方法
1 /**
2 * Run the Spring application, creating and refreshing a new
3 * {@link ApplicationContext}.
4 * @param args the application arguments (usually passed from a Java main method)
5 * @return a running {@link ApplicationContext}
6 */
7 public ConfigurableApplicationContext run(String... args) {
8 StopWatch stopWatch = new StopWatch();
9 stopWatch.start();
10 ConfigurableApplicationContext context = null;
11 Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
12 configureHeadlessProperty();
// 获取SpringApplicationRunListeners；从类路径下META-INF/spring.factories
13 SpringApplicationRunListeners listeners = getRunListeners(args);
14 listeners.starting();
15 try {
//封装命令行参数
16 ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
// 准备环境
17 ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);
18 configureIgnoreBeanInfo(environment);
// 打印图标
19 Banner printedBanner = printBanner(environment);
// 创建ApplicationContext 决定创建web的ioc还是普通的ioc 底层用的反射创建
20 context = createApplicationContext();
21 exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,
22 new Class[] { ConfigurableApplicationContext.class }, context);
// 准备上下文环境
23 prepareContext(context, environment, listeners, applicationArguments, printedBanner);
// 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、加载所有的组件
24 refreshContext(context);
25 afterRefresh(context, applicationArguments);
26 stopWatch.stop();
27 if (this.logStartupInfo) {
28 new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
29 }
30 listeners.started(context);
31 callRunners(context, applicationArguments);
32 }
33 catch (Throwable ex) {
34 handleRunFailure(context, ex, exceptionReporters, listeners);
35 throw new IllegalStateException(ex);
36 }
37
38 try {
39 listeners.running(context);
40 }
41 catch (Throwable ex) {
42 handleRunFailure(context, ex, exceptionReporters, null);
43 throw new IllegalStateException(ex);
44 }
// 启动完成之后，返回ioc容器
45 return context;
46 }