SpringBoot读取配置文件源码探究

1. SpringBoot读取配置文件源码探究 1.1. 概览

springboot的源码是再原来的Spring源码上又包了一层，看过spring源码都知道，当我们从入口debug进去的时候，原来的Spring源码都集中在refreshContext方法，SpringBoot的主要运行步骤，基本都包含在这个方法里了，而这个方法就是我们运行Springboot的主函数SpringApplication.run(Application.class, args);经过几步后到达的

public ConfigurableApplicationContext run(String... args) { StopWatch stopWatch = new StopWatch(); stopWatch.start(); ConfigurableApplicationContext context = null; FailureAnalyzers analyzers = null; configureHeadlessProperty(); SpringApplicationRunListeners listeners = getRunListeners(args); listeners.starting(); try { ApplicationArguments applicationArguments = new DefaultApplicationArguments( args); ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments); Banner printedBanner = printBanner(environment); context = createApplicationContext(); analyzers = new FailureAnalyzers(context); prepareContext(context, environment, listeners, applicationArguments, printedBanner); refreshContext(context); afterRefresh(context, applicationArguments); listeners.finished(context, null); stopWatch.stop(); if (this.logStartupInfo) { new StartupInfoLogger(this.mainApplicationClass) .logStarted(getApplicationLog(), stopWatch); } return context; } catch (Throwable ex) { handleRunFailure(context, listeners, analyzers, ex); throw new IllegalStateException(ex); } } 1.2. 配置读取步骤 1.2.1. prepareEnvironment

配置读取的步骤主要就在ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);这一步，我们继续深入

private ConfigurableEnvironment prepareEnvironment( SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments) { // Create and configure the environment ConfigurableEnvironment environment = getOrCreateEnvironment(); configureEnvironment(environment, applicationArguments.getSourceArgs()); //主要是这步 listeners.environmentPrepared(environment); if (!this.webEnvironment) { environment = new EnvironmentConverter(getClassLoader()) .convertToStandardEnvironmentIfNecessary(environment); } return environment; }

创建基本的环境容器后，进入listeners.environmentPrepared(environment);通过监听器来进行环境变量的初始化，同时读取配置也是一部分工作

1.2.2. environmentPrepared

下一步，看到对监听器进行循环处理，这里的listeners中，默认只有一个EventPublishRunListener

public void environmentPrepared(ConfigurableEnvironment environment) { for (SpringApplicationRunListener listener : this.listeners) { listener.environmentPrepared(environment); } }

继续如下，这一步它进行广播事件了

@Override public void environmentPrepared(ConfigurableEnvironment environment) { this.initialMulticaster.multicastEvent(new ApplicationEnvironmentPreparedEvent( this.application, this.args, environment)); } 1.2.3. multicastEvent @Override public void multicastEvent(ApplicationEvent event) { multicastEvent(event, resolveDefaultEventType(event)); }

继续，重点是invokeListener方法，去调用监听器事件，可以想象对配置文件来讲，这就是读取配置事件了。同时监听器有很多，读取配置文件的监听器是ConfigFileAplicationListener，看名字还是蛮明显的吧

@Override public void multicastEvent(final ApplicationEvent event, ResolvableType eventType) { ResolvableType type = (eventType != null ? eventType : resolveDefaultEventType(event)); for (final ApplicationListener<?> listener : getApplicationListeners(event, type)) { Executor executor = getTaskExecutor(); if (executor != null) { executor.execute(new Runnable() { @Override public void run() { invokeListener(listener, event); } }); } else { //重点 invokeListener(listener, event); } } }

继续，和上一步类似，do真正的事件了

protected void invokeListener(ApplicationListener<?> listener, ApplicationEvent event) { ErrorHandler errorHandler = getErrorHandler(); if (errorHandler != null) { try { doInvokeListener(listener, event); } catch (Throwable err) { errorHandler.handleError(err); } } else { //重点 doInvokeListener(listener, event); } } private void doInvokeListener(ApplicationListener listener, ApplicationEvent event) { try { // 入口 listener.onApplicationEvent(event); } catch (ClassCastException ex) { String msg = ex.getMessage(); if (msg == null || matchesClassCastMessage(msg, event.getClass())) { // Possibly a lambda-defined listener which we could not resolve the generic event type for // -> let's suppress the exception and just log a debug message. Log logger = LogFactory.getLog(getClass()); if (logger.isDebugEnabled()) { logger.debug("Non-matching event type for listener: " + listener, ex); } } else { throw ex; } } } 1.2.4. onApplicationEvent