Question

SpringBoot 启动方法

• Author: HuiFer
• 源码阅读仓库: SourceHot-spring-boot

入口

• 通常一个简单的 SpringBoot 基础项目我们会有如下代码

@SpringBootApplication
@RestController
@RequestMapping("/")
public class Application {

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

}

• 值得关注的有SpringApplication.run以及注解@SpringBootApplication

run 方法

    public ConfigurableApplicationContext run(String... args) {
        // 秒表
        StopWatch stopWatch = new StopWatch();
        stopWatch.start();
        ConfigurableApplicationContext context = null;
        Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
        configureHeadlessProperty();
        // 获取监听器
        SpringApplicationRunListeners listeners = getRunListeners(args);
        // 监听器启动
        listeners.starting();
        try {
            // application 启动参数列表
            ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
            ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);
            // 配置忽略的bean信息
            configureIgnoreBeanInfo(environment);
            Banner printedBanner = printBanner(environment);
            // 创建应用上下文
            context = createApplicationContext();
            exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,
                    new Class[] { ConfigurableApplicationContext.class }, context);
            // 准备上下文，装配bean
            prepareContext(context, environment, listeners, applicationArguments, printedBanner);
            // 上下文刷新
            refreshContext(context);
            // 刷新后做什么
            afterRefresh(context, applicationArguments);
            stopWatch.stop();
            if (this.logStartupInfo) {
                new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
            }
            // 监听器开始了
            listeners.started(context);
            // 唤醒
            callRunners(context, applicationArguments);
        }
        catch (Throwable ex) {
            handleRunFailure(context, ex, exceptionReporters, listeners);
            throw new IllegalStateException(ex);
        }

        try {
            // 监听器正式运行
            listeners.running(context);
        }
        catch (Throwable ex) {
            handleRunFailure(context, ex, exceptionReporters, null);
            throw new IllegalStateException(ex);
        }
        return context;
    }

getRunListeners

• 获取监听器

    private SpringApplicationRunListeners getRunListeners(String[] args) {
        Class<?>[] types = new Class<?>[] { SpringApplication.class, String[].class };
        // 获取  Spring Factory 实例对象
        return new SpringApplicationRunListeners(logger,
                getSpringFactoriesInstances(SpringApplicationRunListener.class, types, this, args));
    }


    private <T> Collection<T> getSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes, Object... args) {
        ClassLoader classLoader = getClassLoader();
        // Use names and ensure unique to protect against duplicates
        // 读取 spring.factories
        Set<String> names = new LinkedHashSet<>(SpringFactoriesLoader.loadFactoryNames(type, classLoader));
        // 创建SpringFactory实例
        List<T> instances = createSpringFactoriesInstances(type, parameterTypes, classLoader, args, names);
        /**
         * 排序 {@link Ordered}
         */
        AnnotationAwareOrderComparator.sort(instances);
        return instances;
    }

createSpringFactoriesInstances

@SuppressWarnings("unchecked")
private <T> List<T> createSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes,
        ClassLoader classLoader, Object[] args, Set<String> names) {
    // 初始化
    List<T> instances = new ArrayList<>(names.size());
    for (String name : names) {
        try {
            // 通过名字创建类的class对象
            Class<?> instanceClass = ClassUtils.forName(name, classLoader);
            Assert.isAssignable(type, instanceClass);
            // 构造器获取
            Constructor<?> constructor = instanceClass.getDeclaredConstructor(parameterTypes);
            // 创建具体实例
            T instance = (T) BeanUtils.instantiateClass(constructor, args);
            // 加入实例表中
            instances.add(instance);
        }
        catch (Throwable ex) {
            throw new IllegalArgumentException("Cannot instantiate " + type + " : " + name, ex);
        }
    }
    return instances;
}

• SpringFactoriesLoader.loadFactoryNames(type, classLoader) 是 spring 提供的方法，主要目的是读取spring.factories文件
  • 读取需要创建的内容

• 创建完成

  

• AnnotationAwareOrderComparator.sort(instances)排序

  • 通过 spring 的源码我们知道这个方法是根据order的数字大小进行排序，观察

    SharedMetadataReaderFactoryContextInitializer

    

  • 同样的再找一个DelegatingApplicationContextInitializer

    

• 下图中的所有类都有 Order 数值返回

  排序前:

排序后：

listeners.starting()

• SpringApplicationRunListeners : org.springframework.boot.SpringApplicationRunListeners 这个类是org.springframework.boot.SpringApplicationRunListener的集合表现形式

  class SpringApplicationRunListeners {
  
      private final List<SpringApplicationRunListener> listeners;
  SpringApplicationRunListeners(Log log, Collection<? extends SpringApplicationRunListener> listeners) {
          this.log = log;
          this.listeners = new ArrayList<>(listeners);
      }
  
      void starting() {
          for (SpringApplicationRunListener listener : this.listeners) {
              listener.starting();
          }
      }
  
  }
  

  • 这里主要是启动org.springframework.boot.SpringApplicationRunListener#starting方法，只有一个实现org.springframework.boot.context.event.EventPublishingRunListener#starting

prepareEnvironment

    private ConfigurableEnvironment prepareEnvironment(SpringApplicationRunListeners listeners,
            ApplicationArguments applicationArguments) {
        // Create and configure the environment
        // 得到一个环境
        ConfigurableEnvironment environment = getOrCreateEnvironment();
        // 配置环境
        configureEnvironment(environment, applicationArguments.getSourceArgs());
        ConfigurationPropertySources.attach(environment);
        listeners.environmentPrepared(environment);
        // 绑定springBoot应用
        bindToSpringApplication(environment);
        // 是否创建自定义环境
        if (!this.isCustomEnvironment) {
            environment = new EnvironmentConverter(getClassLoader()).convertEnvironmentIfNecessary(environment,
                    deduceEnvironmentClass());
        }
        ConfigurationPropertySources.attach(environment);
        return environment;
    }

configureIgnoreBeanInfo

• 获取spring.beaninfo.ignore并且设置到环境信息中

    private void configureIgnoreBeanInfo(ConfigurableEnvironment environment) {
        if (System.getProperty(CachedIntrospectionResults.IGNORE_BEANINFO_PROPERTY_NAME) == null) {
            Boolean ignore = environment.getProperty("spring.beaninfo.ignore", Boolean.class, Boolean.TRUE);
            System.setProperty(CachedIntrospectionResults.IGNORE_BEANINFO_PROPERTY_NAME, ignore.toString());
        }
    }

printBanner

    private Banner printBanner(ConfigurableEnvironment environment) {
        if (this.bannerMode == Banner.Mode.OFF) {
            return null;
        }
        ResourceLoader resourceLoader = (this.resourceLoader != null) ? this.resourceLoader
                : new DefaultResourceLoader(getClassLoader());
        // 创建打印器
        SpringApplicationBannerPrinter bannerPrinter = new SpringApplicationBannerPrinter(resourceLoader, this.banner);
        if (this.bannerMode == Mode.LOG) {
            // 输出
            return bannerPrinter.print(environment, this.mainApplicationClass, logger);
        }
        // 输出
        return bannerPrinter.print(environment, this.mainApplicationClass, System.out);
    }

    Banner print(Environment environment, Class<?> sourceClass, PrintStream out) {
        Banner banner = getBanner(environment);
        banner.printBanner(environment, sourceClass, out);
        return new PrintedBanner(banner, sourceClass);
    }

• 最终输出内容类：org.springframework.boot.SpringBootBanner

  class SpringBootBanner implements Banner {
  
      private static final String[] BANNER = { "", "  .   ____          _            __ _ _",
              " /\\\\ / ___'_ __ _ _(_)_ __  __ _ \\ \\ \\ \\", "( ( )\\___ | '_ | '_| | '_ \\/ _` | \\ \\ \\ \\",
              " \\\\/  ___)| |_)| | | | | || (_| |  ) ) ) )", "  '  |____| .__|_| |_|_| |_\\__, | / / / /",
              " =========|_|==============|___/=/_/_/_/" };
  
      private static final String SPRING_BOOT = " :: Spring Boot :: ";
  
      private static final int STRAP_LINE_SIZE = 42;
  
      @Override
      public void printBanner(Environment environment, Class<?> sourceClass, PrintStream printStream) {
          for (String line : BANNER) {
              printStream.println(line);
          }
          String version = SpringBootVersion.getVersion();
          version = (version != null) ? " (v" + version + ")" : "";
          StringBuilder padding = new StringBuilder();
          while (padding.length() < STRAP_LINE_SIZE - (version.length() + SPRING_BOOT.length())) {
              padding.append(" ");
          }
  
          printStream.println(AnsiOutput.toString(AnsiColor.GREEN, SPRING_BOOT, AnsiColor.DEFAULT, padding.toString(),
                  AnsiStyle.FAINT, version));
          printStream.println();
      }
  
  }
  

createApplicationContext

    protected ConfigurableApplicationContext createApplicationContext() {
        // 获取上下文类
        Class<?> contextClass = this.applicationContextClass;
        if (contextClass == null) {
            try {
                // 根据不同类型选择创建的实例
                switch (this.webApplicationType) {
                case SERVLET:
                    contextClass = Class.forName(DEFAULT_SERVLET_WEB_CONTEXT_CLASS);
                    break;
                case REACTIVE:
                    contextClass = Class.forName(DEFAULT_REACTIVE_WEB_CONTEXT_CLASS);
                    break;
                default:
                    contextClass = Class.forName(DEFAULT_CONTEXT_CLASS);
                }
            }
            catch (ClassNotFoundException ex) {
                throw new IllegalStateException(
                        "Unable create a default ApplicationContext, please specify an ApplicationContextClass", ex);
            }
        }
        return (ConfigurableApplicationContext) BeanUtils.instantiateClass(contextClass);
    }

• this.applicationContextClass 初始化方法

    public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
        this.resourceLoader = resourceLoader;
        Assert.notNull(primarySources, "PrimarySources must not be null");
        this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
        // 设置 web应用类型
        this.webApplicationType = WebApplicationType.deduceFromClasspath();
        setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
        setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
        this.mainApplicationClass = deduceMainApplicationClass();
    }

• org.springframework.boot.WebApplicationType#deduceFromClasspath

    static WebApplicationType deduceFromClasspath() {
        if (ClassUtils.isPresent(WEBFLUX_INDICATOR_CLASS, null) && !ClassUtils.isPresent(WEBMVC_INDICATOR_CLASS, null)
                && !ClassUtils.isPresent(JERSEY_INDICATOR_CLASS, null)) {
            return WebApplicationType.REACTIVE;
        }
        for (String className : SERVLET_INDICATOR_CLASSES) {
            if (!ClassUtils.isPresent(className, null)) {
                return WebApplicationType.NONE;
            }
        }
        return WebApplicationType.SERVLET;
    }

exceptionReporters

prepareContext

    private void prepareContext(ConfigurableApplicationContext context, ConfigurableEnvironment environment,
            SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments, Banner printedBanner) {
        // 上下文中设置环境
        context.setEnvironment(environment);
        // 上下文处理
        postProcessApplicationContext(context);
        // 初始化
        applyInitializers(context);
        // 监听器中放入上下文
        listeners.contextPrepared(context);
        if (this.logStartupInfo) {
            logStartupInfo(context.getParent() == null);
            logStartupProfileInfo(context);
        }
        // Add boot specific singleton beans
        ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
        // 单例对象注册
        beanFactory.registerSingleton("springApplicationArguments", applicationArguments);
        if (printedBanner != null) {
            beanFactory.registerSingleton("springBootBanner", printedBanner);
        }
        if (beanFactory instanceof DefaultListableBeanFactory) {
            ((DefaultListableBeanFactory) beanFactory)
                    .setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);
        }
        if (this.lazyInitialization) {
            context.addBeanFactoryPostProcessor(new LazyInitializationBeanFactoryPostProcessor());
        }
        // Load the sources
        Set<Object> sources = getAllSources();
        Assert.notEmpty(sources, "Sources must not be empty");
        // 加载上下文
        load(context, sources.toArray(new Object[0]));
        // 监听器做加载上下文操作
        listeners.contextLoaded(context);
    }

• set方法就不说了

postProcessApplicationContext

    protected void postProcessApplicationContext(ConfigurableApplicationContext context) {
        if (this.beanNameGenerator != null) {
            // 注册 beanName 的生成器
            context.getBeanFactory().registerSingleton(AnnotationConfigUtils.CONFIGURATION_BEAN_NAME_GENERATOR,
                    this.beanNameGenerator);
        }
        if (this.resourceLoader != null) {
            if (context instanceof GenericApplicationContext) {
                // 设置资源加载器
                ((GenericApplicationContext) context).setResourceLoader(this.resourceLoader);
            }
            if (context instanceof DefaultResourceLoader) {
                // 设置类加载器
                ((DefaultResourceLoader) context).setClassLoader(this.resourceLoader.getClassLoader());
            }
        }
        if (this.addConversionService) {
            // 转换服务
            context.getBeanFactory().setConversionService(ApplicationConversionService.getSharedInstance());
        }
    }

• 看一下最终设置完成后的 context

  context.getBeanFactory().setConversionService(ApplicationConversionService.getSharedInstance());
  

applyInitializers

• 初始化应用上下文

    @SuppressWarnings({ "rawtypes", "unchecked" })
    protected void applyInitializers(ConfigurableApplicationContext context) {
        for (ApplicationContextInitializer initializer : getInitializers()) {
            Class<?> requiredType = GenericTypeResolver.resolveTypeArgument(initializer.getClass(),
                    ApplicationContextInitializer.class);
            Assert.isInstanceOf(requiredType, context, "Unable to call initializer.");
            initializer.initialize(context);
        }
    }

• 初始化 List<ApplicationListener<?>> listeners: setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));

• 获取 List<ApplicationListener<?>> listeners: public Set<ApplicationListener<?>> getListeners() { return asUnmodifiableOrderedSet(this.listeners);}

• 数据结果

• 子类的具体实现不展开了

getAllSources

    public Set<Object> getAllSources() {
        Set<Object> allSources = new LinkedHashSet<>();
        if (!CollectionUtils.isEmpty(this.primarySources)) {
            allSources.addAll(this.primarySources);
        }
        if (!CollectionUtils.isEmpty(this.sources)) {
            allSources.addAll(this.sources);
        }
        return Collections.unmodifiableSet(allSources);
    }

• primarySources 就是我们的项目启动类，在SpringApplication的构造器中有this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources))

load

• 加载 bean 到应用上下文

    protected void load(ApplicationContext context, Object[] sources) {
        if (logger.isDebugEnabled()) {
            logger.debug("Loading source " + StringUtils.arrayToCommaDelimitedString(sources));
        }
        // bean定义加载器
        BeanDefinitionLoader loader = createBeanDefinitionLoader(getBeanDefinitionRegistry(context), sources);
        if (this.beanNameGenerator != null) {
            // 设置 beanName生成器
            loader.setBeanNameGenerator(this.beanNameGenerator);
        }
        if (this.resourceLoader != null) {
            // 设置 资源加载器
            loader.setResourceLoader(this.resourceLoader);
        }
        if (this.environment != null) {
            // 设置环境
            loader.setEnvironment(this.environment);
        }
        // 加载
        loader.load();
    }

    int load() {
        int count = 0;
        for (Object source : this.sources) {
            count += load(source);
        }
        return count;
    }

private int load(Object source) {
        Assert.notNull(source, "Source must not be null");
        if (source instanceof Class<?>) {
            return load((Class<?>) source);
        }
        if (source instanceof Resource) {
            return load((Resource) source);
        }
        if (source instanceof Package) {
            return load((Package) source);
        }
        if (source instanceof CharSequence) {
            return load((CharSequence) source);
        }
        throw new IllegalArgumentException("Invalid source type " + source.getClass());
    }

• 通过前文我们已经知道 source就是一个 class

  

    private int load(Class<?> source) {
        if (isGroovyPresent() && GroovyBeanDefinitionSource.class.isAssignableFrom(source)) {
            // Any GroovyLoaders added in beans{} DSL can contribute beans here
            GroovyBeanDefinitionSource loader = BeanUtils.instantiateClass(source, GroovyBeanDefinitionSource.class);
            load(loader);
        }
        // 是否为组件
        if (isComponent(source)) {
            this.annotatedReader.register(source);
            return 1;
        }
        return 0;
    }

• 我们的启动类是一个组件，直接注册完成返回 1

listeners.contextLoaded(context)

• 监听器行为: 在上下文资源加载后做一些事情

refreshContext

• 上下文刷新

    private void refreshContext(ConfigurableApplicationContext context) {
        refresh(context);
        if (this.registerShutdownHook) {
            try {
                context.registerShutdownHook();
            }
            catch (AccessControlException ex) {
                // Not allowed in some environments.
            }
        }
    }

    /**
     * Refresh the underlying {@link ApplicationContext}.
     * @param applicationContext the application context to refresh
     */
    protected void refresh(ApplicationContext applicationContext) {
        Assert.isInstanceOf(AbstractApplicationContext.class, applicationContext);
        ((AbstractApplicationContext) applicationContext).refresh();
    }

• 最终来到了org.springframework.context.support.AbstractApplicationContext#refresh方法，此方法是 spring 的一个方法，此处不在阐述

afterRefresh

• 刷新上下文之后做的事情,空的没有实现

      protected void afterRefresh(ConfigurableApplicationContext context, ApplicationArguments args) {
      }
  

stopWatch.stop()

• 秒表结束

listeners.started(context)

• 各类监听器启动

callRunners

• 两种 runner 启动ApplicationRunner 和 CommandLineRunner

    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);
        for (Object runner : new LinkedHashSet<>(runners)) {
            if (runner instanceof ApplicationRunner) {
                callRunner((ApplicationRunner) runner, args);
            }
            if (runner instanceof CommandLineRunner) {
                callRunner((CommandLineRunner) runner, args);
            }
        }
    }

private void callRunner(ApplicationRunner runner, ApplicationArguments args) {
        try {
            (runner).run(args);
        }
        catch (Exception ex) {
            throw new IllegalStateException("Failed to execute ApplicationRunner", ex);
        }
    }

listeners.running(context)

• 监听器正式开始工作