本博客通过debug方式简单跟一下Springboot application启动的源码,Springboot的启动源码是比较复杂的,本博客只是简单梳理一下源码,浅析其原理
为了方便跟源码,先找个Application类,打个断点,进行调试,如图所示:
step into,run方法调用了SpringApplication的run方法
通过debug,Springboot启动过程,会先执行如下关键的构造函数
分析构造函数源码:
public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) { this.resourceLoader = resourceLoader; Assert.notNull(primarySources, "PrimarySources must not be null"); this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources)); // 判断当前的web类型 this.webApplicationType = WebApplicationType.deduceFromClasspath(); //设置初始化的ApplicationInitializer类,从类路径下面的META-INF/spring.factories配置文件获取所有的ApplicationInitializer保存起来 setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class)); //同理,从类路径下面的META-INF/spring.factories配置文件获取所有的ApplicationListener保存起来 setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class)); //从多个配置类中找到有main方法的主配置类 this.mainApplicationClass = deduceMainApplicationClass(); }
注意:上面过程其实就是创建Springboot的Application启动类的过程
deduceFromClasspath方法是判断web类型的
继续debug ApplicationContextInitializer这些Initializer类,可以说是初始化类的设置过程
SpringFactoriesLoader.loadFactoryNames(type, classLoader)获取所有的Initializer类的类名
Evaluate可以看出扫描到如下的类
继续debug,这个是Spring框架的底层类
找到主要的源码,loadSpringFactories方法也是从如下的位置获取配置信息的
从META-INF/spring.factories获取对应的配置信息
框架的文件位置在autoconfiguration工程里,显然如果要自定义Initializer类的话,自己新建一些Initializer类,然后自己写个META-INF/spring.factories类,也是可以被扫描到的
private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) { //用一个ConcurrentReferenceHashMap来缓存信息 MultiValueMap<String, String> result = cache.get(classLoader); if (result != null) { //缓存读取到配置信息,返回缓存数据 return result; } // 缓存读取不到的情况,重新从META-INF/spring.factories配置文件读取 try { Enumeration<URL> urls = (classLoader != null ? classLoader.getResources(FACTORIES_RESOURCE_LOCATION) : ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION)); result = new LinkedMultiValueMap<>(); // 遍历循环读取配置信息 while (urls.hasMoreElements()) { URL url = urls.nextElement(); UrlResource resource = new UrlResource(url); // 用PropertiesLoaderUtils工具类读取资源文件 Properties properties = PropertiesLoaderUtils.loadProperties(resource); for (Map.Entry<?, ?> entry : properties.entrySet()) { //获取到Initializer对应的全类名 String factoryTypeName = ((String) entry.getKey()).trim(); for (String factoryImplementationName : StringUtils.commaDelimitedListToStringArray((String) entry.getValue())) { result.add(factoryTypeName, factoryImplementationName.trim()); } } } // 重新放在缓存里 cache.put(classLoader, result); return result; } catch (IOException ex) { throw new IllegalArgumentException("Unable to load factories from location [" + FACTORIES_RESOURCE_LOCATION + "]", ex); } }
ApplicationInitializer类的全类名都被扫描到之后,返回刚才的源码,继续看看,如图,从命名看应该是进行类的实例化过程
step into,果然是的,还是调用了Spring框架的底层工具类,BeanUtils进行类的实例化过程
setListeners方法的过程同理,本文就不详细分析:
继续往下debug,deduceMainApplicationClass方法
private Class<?> deduceMainApplicationClass() { try { //获取运行时的堆栈属性数组 StackTraceElement[] stackTrace = new RuntimeException().getStackTrace(); for (StackTraceElement stackTraceElement : stackTrace) { //有main方法的Application类返回 if ("main".equals(stackTraceElement.getMethodName())) { return Class.forName(stackTraceElement.getClassName()); } } } catch (ClassNotFoundException ex) { // Swallow and continue } return null; }
获取到的就是创建Springboot工程时的Application类
Springboot的Application类创建成功之后,才真正开始执行run方法
public ConfigurableApplicationContext run(String... args) { StopWatch stopWatch = new StopWatch(); stopWatch.start(); ConfigurableApplicationContext context = null; Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>(); //校验java.awt.headless的 configureHeadlessProperty(); //从META-INF/spring.factories获取SpringApplicationRunListeners,和前面的分析同理,本文就不详细介绍 SpringApplicationRunListeners listeners = getRunListeners(args); //回调SpringApplicationRunListeners 的starting方法 listeners.starting(); try { //封装命令行参数 ApplicationArguments applicationArguments = new DefaultApplicationArguments(args); //准备环境,环境创建完成之后,再回调SpringApplicationRunListeners 的environmentPrepared方法,表示环境准备好 ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments); configureIgnoreBeanInfo(environment); //控制台打印Banner信息的,后面再简单分析 Banner printedBanner = printBanner(environment); // 创建Spring的IOC容器,创建过程比较复杂,会分析是web类型的ioc容器,还是普通的ioc容器等等 context = createApplicationContext(); exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class, new Class[] { ConfigurableApplicationContext.class }, context); //将environment保存到ioc,执行applyInitializers方法,applyInitializers方法执行完成之后,再回调SpringApplicationRunListeners的contextPrepared方法 //applyInitializers方法作用:回调之前保存的所有的ApplicationContextInitializer的initialize方法 prepareContext(context, environment, listeners, applicationArguments, printedBanner); //刷新ioc容器,其实就是ioc容器的初始化过程,还没进行属性设置,后置处理器,仅仅是扫描、创建、加载所有组件等等过程 refreshContext(context); afterRefresh(context, applicationArguments); stopWatch.stop(); if (this.logStartupInfo) { new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch); } //回调所有SpringApplicationRunListener的started方法 listeners.started(context); //从ioc容器中获取所有的ApplicationRunner和CommandLineRunner进行回调,ApplicationRunner先回调,CommandLineRunner再回调 callRunners(context, applicationArguments); } catch (Throwable ex) { handleRunFailure(context, ex, exceptionReporters, listeners); throw new IllegalStateException(ex); } try { //回调所有SpringApplicationRunListener的running方法 listeners.running(context); } catch (Throwable ex) { handleRunFailure(context, ex, exceptionReporters, null); throw new IllegalStateException(ex); } //Springboot应用启动成功后,才返回启动的ioc容器 return context; }
回顾一下前面源码的环境准备方法,找重点代码,如图,可以看出环境准备完成后会回调SpringApplicationRunListener的environmentPrepared方法,表示环境准备完成
banner打印的方法,如图,执行完成,控制台的banner信息就打印出来了:
ioc初始化之前,会执行applyInitializers方法,执行完成后,再回调SpringApplicationRunListener的contextPrepared方法
applyInitializers():回调之前保存的所有的ApplicationContextInitializer的initialize方法
从ioc容器中获取所有的ApplicationRunner和CommandLineRunner进行回调
ok,从源码的简单分析,可以看出有几个重要的事件监听机制,下面引用尚硅谷视频的例子:
只需要放在ioc容器中的有:
@Component public class HelloApplicationRunner implements ApplicationRunner { @Override public void run(ApplicationArguments args) throws Exception { System.out.println("ApplicationRunner...run...."); } }
@Component public class HelloCommandLineRunner implements CommandLineRunner { @Override public void run(String... args) throws Exception { System.out.println("CommandLineRunner...run..."+ Arrays.asList(args)); } }
配置在META-INF/spring.factories的有:
public class HelloApplicationContextInitializer implements ApplicationContextInitializer<ConfigurableApplicationContext> { @Override public void initialize(ConfigurableApplicationContext applicationContext) { System.out.println("ApplicationContextInitializer...initialize..."+applicationContext); } }
package com.example.springboot.web.listener; import org.springframework.boot.SpringApplication; import org.springframework.boot.SpringApplicationRunListener; import org.springframework.context.ConfigurableApplicationContext; import org.springframework.core.env.ConfigurableEnvironment; public class HelloSpringApplicationRunListener implements SpringApplicationRunListener { //必须有的构造器 public HelloSpringApplicationRunListener(SpringApplication application, String[] args){ } @Override public void starting() { System.out.println("SpringApplicationRunListener...starting..."); } @Override public void environmentPrepared(ConfigurableEnvironment environment) { Object o = environment.getSystemProperties().get("os.name"); System.out.println("SpringApplicationRunListener...environmentPrepared.."+o); } @Override public void contextPrepared(ConfigurableApplicationContext context) { System.out.println("SpringApplicationRunListener...contextPrepared..."); } @Override public void contextLoaded(ConfigurableApplicationContext context) { System.out.println("SpringApplicationRunListener...contextLoaded..."); } }
配置(META-INF/spring.factories)
org.springframework.context.ApplicationContextInitializer=/ com.example.springboot.web.listener.HelloApplicationContextInitializer org.springframework.boot.SpringApplicationRunListener=/ com.example.springboot.web.listener.HelloSpringApplicationRunListener
例子下载: github下载链接