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SpringBoot版本为:2.1.1.RELEASE
在上一篇文章中,我们讲到了SpringApplication对象的创建,接下来将会分析SpringApplication创建之后run()方法的执行。
通过debug的方式,我们可以进入run方法,源代码如下:
/** * 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) { <1>: StopWatch stopWatch = new StopWatch(); stopWatch.start(); ConfigurableApplicationContext context = null; CollectionexceptionReporters = new ArrayList<>(); configureHeadlessProperty(); <2>: SpringApplicationRunListeners listeners = getRunListeners(args); listeners.starting(); try { <3>: ApplicationArguments applicationArguments = new DefaultApplicationArguments( args); <4>: ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments); configureIgnoreBeanInfo(environment); <5>: Banner printedBanner = printBanner(environment); <6>: context = createApplicationContext(); exceptionReporters = getSpringFactoriesInstances( SpringBootExceptionReporter.class, new Class[] { ConfigurableApplicationContext.class }, context); <7>: prepareContext(context, environment, listeners, applicationArguments, printedBanner); <8>: refreshContext(context); <9>: afterRefresh(context, applicationArguments); stopWatch.stop(); if (this.logStartupInfo) { new StartupInfoLogger(this.mainApplicationClass) .logStarted(getApplicationLog(), stopWatch); } <10>: listeners.started(context); <11>: callRunners(context, applicationArguments); } catch (Throwable ex) { handleRunFailure(context, ex, exceptionReporters, listeners); throw new IllegalStateException(ex); } try { <12>: listeners.running(context); } catch (Throwable ex) { handleRunFailure(context, ex, exceptionReporters, null); throw new IllegalStateException(ex); } <13>: return context; }
下面我们逐一分析:
<1> : StopWatch stopWatch = new StopWatch(); stopWatch.start();这段代码功能很简单,创建一个StopWatch对象,开始记录run()启动过程时长;
<2>: 先来看这个方法:SpringApplicationRunListeners listeners = getRunListeners(args);
private SpringApplicationRunListeners getRunListeners(String[] args) { Class [] types = new Class [] { SpringApplication.class, String[].class }; return new SpringApplicationRunListeners(logger, getSpringFactoriesInstances( SpringApplicationRunListener.class, types, this, args)); }
在这段代码里,我们又看见了熟悉的 getSpringFactoriesInstances(),原理还是一样,就是 getSpringFactoriesInstances()方法会从类路径下的 META-INF/spring.factories文件中找 对应SpringApplicationRunListener的全路径数组,并通过createSpringFactoriesInstances()方法实例化成对象返回;
再看 listeners.starting() 方法:public void starting() { for (SpringApplicationRunListener listener : this.listeners) { listener.starting(); } }
所以这个方法就是回调之前获得的所有SpringApplicationRunListener对象的starting()方法,启动监听。我们可以继续再深入看一下这个监听对象的其他方法:
SpringApplicationRunListener 接口中共有上面几个方法,这几个方法将会贯穿run()方法的运行。<3>:这个方法的作用也很简单,即使封装命令行参数。
<4>: ConfigurableEnvironment environment = prepareEnvironment(listeners,
applicationArguments)其实这是环境准备阶段,我们可以看一下它的实现过程:
private ConfigurableEnvironment prepareEnvironment( SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments) { // Create and configure the environment ConfigurableEnvironment environment = getOrCreateEnvironment(); configureEnvironment(environment, applicationArguments.getSourceArgs()); listeners.environmentPrepared(environment); bindToSpringApplication(environment); if (!this.isCustomEnvironment) { environment = new EnvironmentConverter(getClassLoader()) .convertEnvironmentIfNecessary(environment, deduceEnvironmentClass()); } ConfigurationPropertySources.attach(environment); return environment; }
这个方法表示创建环境,并且environment 的属性都会加载进来,包括 application.properties 和外部的属性配置,具体实现有兴趣的同学可以研究一下。其中listeners.environmentPrepared(environment)方法表示环境准备完成
<5>:功能为打印Banner,也可以自定义启动logo,比如在resources路径下创建一个banner.txt文件,将你想打印的图标放入其中
<6>:创建ApplicationContext容器,根据类型决定是创建普通WEB容器还是REACTIVE容器还是普通Annotation的ioc 容器
<7>:prepareContext(context, environment, listeners, applicationArguments,
printedBanner); 这个方法的具体实现:private void prepareContext(ConfigurableApplicationContext context, ConfigurableEnvironment environment, SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments, Banner printedBanner) { context.setEnvironment(environment); postProcessApplicationContext(context); 7.1: applyInitializers(context); 7.2: listeners.contextPrepared(context); if (this.logStartupInfo) { logStartupInfo(context.getParent() == null); logStartupProfileInfo(context); } // Add boot specific singleton beans ConfigurableListableBeanFactory beanFactory = context.getBeanFactory(); beanFactory.registerSingleton("springApplicationArguments", applicationArguments); if (printedBanner != null) { beanFactory.registerSingleton("springBootBanner", printedBanner); } if (beanFactory instanceof DefaultListableBeanFactory) { ((DefaultListableBeanFactory) beanFactory) .setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding); } // Load the sources Set
7.1: 从initializers集合中遍历所有的ApplicationContextInitializer,并通过initializer.initialize( )方法初始化
7,2:回调SpringApplicationRunListener对象的contextPrepared()方法,表示容器已准备
<8>:refreshContext(context)
刷新容器,初始化ioc容器,向容器中加入配置类、组件,并且可以出发自动配置功能,具体原理可以参考SpringBoot的自动配置原理和Spring注解版容器的加载<9>: afterRefresh(context, applicationArguments);
执行Spring容器初始化的后置处理,默认为空protected void afterRefresh(ConfigurableApplicationContext context, ApplicationArguments args) { }
<10>: listeners.started(context);
回调所有的SpringApplicationRunListener对象的started()方法<11>: callRunners(context, applicationArguments)
private void callRunners(ApplicationContext context, ApplicationArguments args) { List
调用ApplicationRunner或者CommandLineRunner 的运行方法,其中ApplicationRunner的优先级要比CommandLineRunner要高。
在我们日常的项目里,经常需要初始化一些资源,比如线程池或者数据库数据等,我们就可以实现这两个接口,在实现方法里写具体的处理逻辑,也可以在实现类上加上@Order(value) 注解来指定优先级(ps:该实现类要加上@Component)<12>:listeners.running(context);
回调所有SpringApplicationRunListener对象的running()方法<13>:return context
返回容器至此,SpringBoot的启动过程已全部完毕,下一篇文章将会讲解SpringBoot的事件监听机制!
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