SpringApplication的启动过程

参考视频：

https://www.ixigua.com/7090148232243708446?wid_try=1

public class SpringApplication {......单参数构造方法public SpringApplication(Class... primarySources) {调用双参构造方法this((ResourceLoader)null, primarySources);}双参数构造方法public SpringApplication(ResourceLoader resourceLoader, Class... primarySources) {这个构造函数相当于初始化各种属性参数等操作.......在1.0之前这个构造函数是作为init方法存在.........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 = Collections.emptySet();this.isCustomEnvironment = false;this.lazyInitialization = false;this.applicationContextFactory = ApplicationContextFactory.DEFAULT;this.applicationStartup = ApplicationStartup.DEFAULT;this.resourceLoader = resourceLoader;断言你传过来的字节码文件不能为空，如果为空就给你打印后面这句话Assert.notNull(primarySources, "PrimarySources must not be null");this.primarySources = new LinkedHashSet(Arrays.asList(primarySources));this.webApplicationType = WebApplicationType.deduceFromClasspath();this.bootstrapRegistryInitializers = this.getBootstrapRegistryInitializersFromSpringFactories();this.setInitializers(this.getSpringFactoriesInstances(ApplicationContextInitializer.class));this.setListeners(this.getSpringFactoriesInstances(ApplicationListener.class));this.mainApplicationClass = this.deduceMainApplicationClass();}......run方法public static ConfigurableApplicationContext run(Class<?> primarySource, String... args) {生成一个新的数组,数组里存的是Class类型，这些class从哪来，从字节码文件中来。return run(new Class[]{primarySource}, args);}......另一个run方法public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) {这里调用了SpringApplication的第一个构造函数return (new SpringApplication(primarySources)).run(args);}......另另一个run方法public ConfigurableApplicationContext run(String... args) {StopWatch stopWatch = new StopWatch();stopWatch.start();springboot当中用到的最早的一个配置文件类型，它优先加载于application.propertiesDefaultBootstrapContext bootstrapContext = this.createBootstrapContext();ConfigurableApplicationContext context = null;this.configureHeadlessProperty();SpringApplicationRunListeners listeners = this.getRunListeners(args);listeners.starting(bootstrapContext, this.mainApplicationClass);try {ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);加载环境变量，运行起来控制台会输出类似的Starting Application using Java 1.8.0_131 on PC-202032 with PID 5060(D://.......)ConfigurableEnvironment environment = this.prepareEnvironment(listeners, bootstrapContext, applicationArguments);this.configureIgnoreBeanInfo(environment);控制台打印的花式文字Banner printedBanner = this.printBanner(environment);创建了spring的核心容器context = this.createApplicationContext();让你的核心容器跑起来context.setApplicationStartup(this.applicationStartup);预处理this.prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner);刷新整理this.refreshContext(context);最后刷新this.afterRefresh(context, applicationArguments);stopWatch.stop();if (this.logStartupInfo) {(new StartupInfoLogger(this.mainApplicationClass)).logStarted(this.getApplicationLog(), stopWatch);}listeners.started(context);this.callRunners(context, applicationArguments);} catch (Throwable var10) {this.handleRunFailure(context, var10, listeners);throw new IllegalStateException(var10);}try {listeners.running(context);return context;} catch (Throwable var9) {this.handleRunFailure(context, var9, (SpringApplicationRunListeners)null);throw new IllegalStateException(var9);}}}

@SpringBootApplication
public class Application {public static void main(String[] args) {SpringApplication.run(Application.class, args);}
}public static ConfigurableApplicationContext run(Class<?> primarySource, String... args) {// 调用了当前类下的另一个run方法return run(new Class[]{primarySource}, args);
}public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) {// 在当前类下的另一个run方法中 调用了当前类的单参构造方法return (new SpringApplication(primarySources)).run(args);
}public SpringApplication(Class... primarySources) {// 单参构造方法中，又去调用了双参构造方法this((ResourceLoader)null, primarySources);
}

// 在双参构造方法中有这么一个ApplicationContextFactory
this.applicationContextFactory = ApplicationContextFactory.DEFAULT;

public class StopWatch {

        ......public void start(String taskName) throws IllegalStateException {if (this.currentTaskName != null) {throw new IllegalStateException("Can't start StopWatch: it's already running");} else {this.currentTaskName = taskName;this.startTimeNanos = System.nanoTime();}}}

它这个run要这个类的字节码有什么用呢？它这个类上面的注解@SpringBootApplication

SpringUtils中的setApplicationContext到底什么时候被执行了？今天我们研究一下。

参考链接：ApplicationContextAware接口的setApplicationContext方法调用过程_大家说的博客-CSDN博客_setapplicationcontext方法


@Component
public class SpringUtils implements ApplicationContextAware {.........private ApplicationContext applicationContext;private BeanDefinitionBuilder beanDefinitionBuilder = BeanDefinitionBuilder.genericBeanDefinition();private DefaultListableBeanFactory autowireCapableBeanFactory;@Overridepublic void setApplicationContext(ApplicationContext applicationContext) throws BeansException {if (this.applicationContext == null) {this.applicationContext = applicationContext;}}......
}

SpringApplication.java:

public class SpringApplication {....../*** Refresh the underlying {@link ApplicationContext}.* @param applicationContext the application context to refresh*/protected void refresh(ConfigurableApplicationContext applicationContext) {applicationContext.refresh();}......
}

点击refresh进入ConfigurableApplicationContext 接口

public interface ConfigurableApplicationContext extends ApplicationContext, Lifecycle, Closeable {........void refresh() throws BeansException, IllegalStateException;........
}

点击抽象方法refresh() ，进入实现类AbstractApplicationContext.java

在refresh()方法中点击this.prepareBeanFactory(beanFactory);// 点击进入查看prepareBeanFactory()

public abstract class AbstractApplicationContext extends DefaultResourceLoader implements ConfigurableApplicationContext {......public void refresh() throws BeansException, IllegalStateException {Object var1 = this.startupShutdownMonitor;synchronized(this.startupShutdownMonitor) {StartupStep contextRefresh = this.applicationStartup.start("spring.context.refresh");this.prepareRefresh();ConfigurableListableBeanFactory beanFactory = this.obtainFreshBeanFactory();1这里---->this.prepareBeanFactory(beanFactory);//---->beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));---->ApplicationContextAwareProcessor.javatry {this.postProcessBeanFactory(beanFactory);StartupStep beanPostProcess = this.applicationStartup.start("spring.context.beans.post-process");this.invokeBeanFactoryPostProcessors(beanFactory);this.registerBeanPostProcessors(beanFactory);beanPostProcess.end();this.initMessageSource();this.initApplicationEventMulticaster();this.onRefresh();this.registerListeners();4这里---->this.finishBeanFactoryInitialization(beanFactory);this.finishRefresh();} catch (BeansException var10) {if (this.logger.isWarnEnabled()) {this.logger.warn("Exception encountered during context initialization - cancelling refresh attempt: " + var10);}this.destroyBeans();this.cancelRefresh(var10);throw var10;} finally {this.resetCommonCaches();contextRefresh.end();}}}.........protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {beanFactory.setBeanClassLoader(this.getClassLoader());if (!shouldIgnoreSpel) {beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));}beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, this.getEnvironment()));
2这里---->beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
3这里---->ApplicationContextAwareProcessor.javabeanFactory.ignoreDependencyInterface(EnvironmentAware.class);beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class);beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);beanFactory.ignoreDependencyInterface(MessageSourceAware.class);beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);beanFactory.ignoreDependencyInterface(ApplicationStartupAware.class);beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);beanFactory.registerResolvableDependency(ResourceLoader.class, this);beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);beanFactory.registerResolvableDependency(ApplicationContext.class, this);beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));if (!NativeDetector.inNativeImage() && beanFactory.containsBean("loadTimeWeaver")) {beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));}if (!beanFactory.containsLocalBean("environment")) {beanFactory.registerSingleton("environment", this.getEnvironment());}if (!beanFactory.containsLocalBean("systemProperties")) {beanFactory.registerSingleton("systemProperties", this.getEnvironment().getSystemProperties());}if (!beanFactory.containsLocalBean("systemEnvironment")) {beanFactory.registerSingleton("systemEnvironment", this.getEnvironment().getSystemEnvironment());}if (!beanFactory.containsLocalBean("applicationStartup")) {beanFactory.registerSingleton("applicationStartup", this.getApplicationStartup());}}........
5这里---->protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {if (beanFactory.containsBean("conversionService") && beanFactory.isTypeMatch("conversionService", ConversionService.class)) {beanFactory.setConversionService((ConversionService)beanFactory.getBean("conversionService", ConversionService.class));}if (!beanFactory.hasEmbeddedValueResolver()) {beanFactory.addEmbeddedValueResolver((strVal) -> {return this.getEnvironment().resolvePlaceholders(strVal);});}String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);String[] var3 = weaverAwareNames;int var4 = weaverAwareNames.length;for(int var5 = 0; var5 < var4; ++var5) {String weaverAwareName = var3[var5];this.getBean(weaverAwareName);}beanFactory.setTempClassLoader((ClassLoader)null);beanFactory.freezeConfiguration();
6这里---->beanFactory.preInstantiateSingletons();}....
}

在AbstractApplicationContext .java的refresh()的prepareBeanFactory()中查看：beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));

我们看到一个new ApplicationContextAwareProcessor(this)类，这个类是一个BeanPostProcessor类型的类。OK，我们先在这里有一个印象，就是在BeanFactory里面加入了一个 ApplicationContextAwareProcessor。
这个过程就是ApplicationContextAwareProcessor的装配过程。

---------------------------------------------------------------------------

AbstractApplicationContext.java的refresh()方法中继续往下执行，执行到AbstractApplicationContext .java的实例化bean的方法
// Instantiate all remaining (non-lazy-init) singletons.
finishBeanFactoryInitialization(beanFactory);
代码执行到这个方法。

protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory)

在AbstractApplicationContext.java的finishBeanFactoryInitialization()方法中：

会执行beanFactory.preInstantiateSingletons();

最终会执行到：

AbstractAutowireCapableBeanFactory#doCreateBean方法

方法当中：

Object exposedObject = bean;
       try {
           populateBean(beanName, mbd, instanceWrapper);
           if (exposedObject != null) {
               exposedObject = initializeBean(beanName, exposedObject, mbd);
           }
       }
点进去

这个方法就是调用 ApplicationContextAwareProcessor的地方，我们进去看看。

我们可以看到，确实在BeanPostProcessors容器中有一个ApplicationContextAwareProcessor类。那么我们进到ApplicationContextAwareProcessor这个类的postProcessBeforeInitialization方法中。

根据这个源码，我们知道了，确实调用到了setApplicationContext()方法。

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