Spring Boot run方法执行流程
SpringApplication的run方法的实现是启动原理探寻的起点,该方法的主要流程大体可以归纳如下:
1、如果我们使用的是SpringApplication的静态run方法,那么,这个方法里面首先要创建一个SpringApplication对象实例,然后调用这个创建好的SpringApplication的实例方法。在SpringApplication实例初始化的时候,它会提前做几件事情:
public static ConfigurableApplicationContext run(Class<?>[] primarySources,
String[] args) {
return (new SpringApplication(primarySources)).run(args);
}
- 根据classpath里面是否存在某个特征类
(org.springframework.web.context.ConfigurableWebApplicationContext)来决定是否应该创建一个为
Web应用使用的ApplicationContext类型。
- 使用SpringFactoriesLoader在应用的classpath中查找并加载所有可用ApplicationContextInitializer。
- 使用SpringFactoriesLoader在应用的classpath中查找并加载所有可用的ApplicationListener。
- 推断并设置main方法的定义类。
public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
this.sources = new LinkedHashSet();
this.bannerMode = Mode.CONSOLE;
this.logStartupInfo = true;
this.addCommandLineProperties = true;
this.addConversionService = true;
this.headless = true;
this.registerShutdownHook = true;
this.additionalProfiles = new HashSet();
this.isCustomEnvironment = false;
this.lazyInitialization = false;
this.resourceLoader = resourceLoader;
Assert.notNull(primarySources, "PrimarySources must not be null");
//把SpringdemoApplication.class设置为属性存储起来
this.primarySources = new LinkedHashSet(Arrays.asList(primarySources));
//设置应用类型为Standard还是Web
this.webApplicationType = WebApplicationType.deduceFromClasspath();
//设置初始化器(Initializer),最后会调用这些初始化器
this.setInitializers(this.getSpringFactoriesInstances(ApplicationContextInitializer.class));
//设置监听器(Listener)
this.setListeners(this.getSpringFactoriesInstances(ApplicationListener.class));
this.mainApplicationClass = this.deduceMainApplicationClass();
}
2、SpringApplication实例初始化完成并且完成设置后,就开始执行run方法的逻辑了,方法执行依次,首先遍
历执行所有通过SpringFactoriesLoader可以查找到并加载的SpringApplicationRunListener。调用它们的
started()方法,告诉这些SpringApplicationRunListener,“嘿,SpringBoot应用要开始执行咯!”。
/*从run方法进来*/
public ConfigurableApplicationContext run(String... args) {
//计时工具
StopWatch stopWatch = new StopWatch();
stopWatch.start();
ConfigurableApplicationContext context = null;
Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList();
this.configureHeadlessProperty();
//第一步,获取并启动监听器
SpringApplicationRunListeners listeners = this.getRunListeners(args);
listeners.starting();
Collection exceptionReporters;
try {
ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
//第二步,根据SpringApplicationRunListeners以及参数来准备环境
ConfigurableEnvironment environment = this.prepareEnvironment(listeners, applicationArguments);
this.configureIgnoreBeanInfo(environment);
//准备Banner打印器‐就是启动Spring Boot的时候在console上的ASCII艺术字体
Banner printedBanner = this.printBanner(environment);
//第三步:创建Spring容器
context = this.createApplicationContext();
exceptionReporters = this.getSpringFactoriesInstances(SpringBootExceptionReporter.class, new Class[]{ConfigurableApplicationContext.class}, context);
//第四步:Spring容器前置处理
this.prepareContext(context, environment, listeners, applicationArguments, printedBanner);
//第五步:刷新容器
this.refreshContext(context);
//第六步:Spring容器后置处理
this.afterRefresh(context, applicationArguments);
stopWatch.stop();
if (this.logStartupInfo) {
(new StartupInfoLogger(this.mainApplicationClass)).logStarted(this.getApplicationLog(), stopWatch);
}
//第七步:发出结束执行的事件
listeners.started(context);
//第八步:执行Runners
this.callRunners(context, applicationArguments);
} catch (Throwable var10) {
this.handleRunFailure(context, var10, exceptionReporters, listeners);
throw new IllegalStateException(var10);
}
try {
listeners.running(context);
//返回容器
return context;
} catch (Throwable var9) {
this.handleRunFailure(context, var9, exceptionReporters, (SpringApplicationRunListeners)null);
throw new IllegalStateException(var9);
}
}
3、创建并配置当前Spring Boot应用将要使用的Environment(包括配置要使用的PropertySource以及Profile)。
private ConfigurableEnvironment prepareEnvironment(SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments) {
ConfigurableEnvironment environment = this.getOrCreateEnvironment();
this.configureEnvironment((ConfigurableEnvironment)environment, applicationArguments.getSourceArgs());
ConfigurationPropertySources.attach((Environment)environment);
listeners.environmentPrepared((ConfigurableEnvironment)environment);
this.bindToSpringApplication((ConfigurableEnvironment)environment);
if (!this.isCustomEnvironment) {
environment = (new EnvironmentConverter(this.getClassLoader())).convertEnvironmentIfNecessary((ConfigurableEnvironment)environment, this.deduceEnvironmentClass());
}
ConfigurationPropertySources.attach((Environment)environment);
return (ConfigurableEnvironment)environment;
}
4、遍历调用所有SpringApplicationRunListener的environmentPrepared()的方法,告诉他们:“当前SpringBoot应用使用的Environment准备好了咯!”。
void environmentPrepared(ConfigurableEnvironment environment) {
Iterator var2 = this.listeners.iterator();
while(var2.hasNext()) {
SpringApplicationRunListener listener = (SpringApplicationRunListener)var2.next();
listener.environmentPrepared(environment);
}
}
5、如果SpringApplication的showBanner属性被设置为true,则打印banner。
public interface Banner {
void printBanner(Environment environment, Class<?> sourceClass, PrintStream out);
public static enum Mode {
OFF,
CONSOLE,
LOG;
private Mode() {
}
}
}
6、根据用户是否明确设置了applicationContextClass类型以及初始化阶段的推断结果,决定该为当前SpringBoot应用创建什么类型的ApplicationContext并创建完成,然后根据条件决定是否添ShutdownHook,决定是否使用自定义的BeanNameGenerator,决定是否使用自定义的ResourceLoader,当然,最重要的,将之前准备好的Environment设置给创建好的ApplicationContext使用。
7、ApplicationContext创建好之后,SpringApplication会再次借助Spring-FactoriesLoader,查找并加载classpath中所有可用的ApplicationContext-Initializer,然后遍历调用这些ApplicationContextInitializer的initialize(applicationContext)方法来对已经创建好的ApplicationContext进行进一步的处理。
protected void applyInitializers(ConfigurableApplicationContext context) {
Iterator var2 = this.getInitializers().iterator();
while(var2.hasNext()) {
ApplicationContextInitializer initializer = (ApplicationContextInitializer)var2.next();
Class<?> requiredType = GenericTypeResolver.resolveTypeArgument(initializer.getClass(), ApplicationContextInitializer.class);
Assert.isInstanceOf(requiredType, context, "Unable to call initializer.");
initializer.initialize(context);
}
}
8、遍历调用所有SpringApplicationRunListener的contextPrepared()方法。
9、最核心的一步,将之前通过@EnableAutoConfiguration获取的所有配置以及其他形式的IoC容器配置加载到已经准备完毕的ApplicationContext
10、遍历调用所有SpringApplicationRunListener的contextLoaded()方法。
void contextLoaded(ConfigurableApplicationContext context) {
for (SpringApplicationRunListener listener : this.listeners) {
listener.contextLoaded(context);
}
}
11、调用ApplicationContext的refresh()方法,完成IoC容器可用的最后一道工序。
private void refreshContext(ConfigurableApplicationContext context) {
this.refresh(context);
if (this.registerShutdownHook) {
try {
context.registerShutdownHook();
} catch (AccessControlException var3) {
}
}
}
12、查找当前ApplicationContext中是否注册有CommandLineRunner,如果有,则遍历执行它们。
private void callRunners(ApplicationContext context, ApplicationArguments args) {
List<Object> runners = new ArrayList();
runners.addAll(context.getBeansOfType(ApplicationRunner.class).values());
runners.addAll(context.getBeansOfType(CommandLineRunner.class).values());
AnnotationAwareOrderComparator.sort(runners);
Iterator var4 = (new LinkedHashSet(runners)).iterator();
while(var4.hasNext()) {
Object runner = var4.next();
if (runner instanceof ApplicationRunner) {
this.callRunner((ApplicationRunner)runner, args);
}
if (runner instanceof CommandLineRunner) {
this.callRunner((CommandLineRunner)runner, args);
}
}
}
13、正常情况下,遍历执行SpringApplicationRunListener的finished()方法、(如果整个过程出现异常,则依然调用所有SpringApplicationRunListener的finished()方法,只不过这种情况下会将异常信息一并传入处理) 去除事件通知点后,整个流程如下:
void failed(ConfigurableApplicationContext context, Throwable exception) {
for (SpringApplicationRunListener listener : this.listeners) {
callFailedListener(listener, context, exception);
}
}
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