SpringBoot是如何动起来的

ゝ一世哀愁。 2021-12-23 11:45 226阅读 0赞

## SpringBoot是如何动起来的 ##

### 程序入口 ###

SpringApplication.run(BeautyApplication.class, args);

#### 执行此方法来加载整个SpringBoot的环境。 ####

### 1. 从哪儿开始？ ###

*  SpringApplication.java

/**
         * 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) {
            //...
      }

#### 调用SpringApplication.java 中的 run 方法，目的是加载Spring Application，同时返回 ApplicationContext。 ####

### 2. 执行了什么？ ###

#### 2.1 计时 ####

##### 记录整个Spring Application的加载时间！ #####

StopWatch stopWatch = new StopWatch();
    stopWatch.start();
    // ...
    stopWatch.stop();
    if (this.logStartupInfo) {
        new StartupInfoLogger(this.mainApplicationClass)
                .logStarted(getApplicationLog(), stopWatch);
    }

#### 2.2 声明 ####

##### 指定 java.awt.headless，默认是true 一般是在程序开始激活headless模式，告诉程序，现在你要工作在Headless mode下，就不要指望硬件帮忙了，你得自力更生，依靠系统的计算能力模拟出这些特性来。 #####

private void configureHeadlessProperty() {
        System.setProperty(SYSTEM_PROPERTY_JAVA_AWT_HEADLESS, System.getProperty(
                SYSTEM_PROPERTY_JAVA_AWT_HEADLESS, Boolean.toString(this.headless)));
    }

#### 2.4 配置监听并发布应用启动事件 ####

##### SpringApplicationRunListener 负责加载 ApplicationListener事件。 #####

SpringApplicationRunListeners listeners = getRunListeners(args);
    // 开始
    listeners.starting();
    // 处理所有 property sources 配置和 profiles 配置，准备环境，分为标准 Servlet 环境和标准环境
    ConfigurableEnvironment environment = prepareEnvironment(listeners,applicationArguments);
    // 准备应用上下文
    prepareContext(context, environment, listeners, applicationArguments,printedBanner);
    // 完成
    listeners.started(context);
    // 异常
    handleRunFailure(context, ex, exceptionReporters, listeners);
    // 执行
    listeners.running(context);

##### getRunListeners 中根据 type = SpringApplicationRunListener.class 去拿到了所有的 Listener 并根据优先级排序。 #####

对应的就是 META-INF/spring.factories 文件中的 org.springframework.boot.SpringApplicationRunListener=org.springframework.boot.context.event.EventPublishingRunListener

private <T> Collection<T> getSpringFactoriesInstances(Class<T> type,
                Class<?>[] parameterTypes, Object... args) {
            ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
            // Use names and ensure unique to protect against duplicates
            Set<String> names = new LinkedHashSet<>(
                    SpringFactoriesLoader.loadFactoryNames(type, classLoader));
            List<T> instances = createSpringFactoriesInstances(type, parameterTypes,
                    classLoader, args, names);
            AnnotationAwareOrderComparator.sort(instances);
            return instances;
        }
    复制代码

##### 在 ApplicationListener 中 , 可以针对任何一个阶段插入处理代码。 #####

public interface SpringApplicationRunListener {
    
        /**
         * Called immediately when the run method has first started. Can be used for very
         * early initialization.
         */
        void starting();
    
        /**
         * Called once the environment has been prepared, but before the
         * {@link ApplicationContext} has been created.
         * @param environment the environment
         */
        void environmentPrepared(ConfigurableEnvironment environment);
    
        /**
         * Called once the {@link ApplicationContext} has been created and prepared, but
         * before sources have been loaded.
         * @param context the application context
         */
        void contextPrepared(ConfigurableApplicationContext context);
    
        /**
         * Called once the application context has been loaded but before it has been
         * refreshed.
         * @param context the application context
         */
        void contextLoaded(ConfigurableApplicationContext context);
    
        /**
         * The context has been refreshed and the application has started but
         * {@link CommandLineRunner CommandLineRunners} and {@link ApplicationRunner
         * ApplicationRunners} have not been called.
         * @param context the application context.
         * @since 2.0.0
         */
        void started(ConfigurableApplicationContext context);
    
        /**
         * Called immediately before the run method finishes, when the application context has
         * been refreshed and all {@link CommandLineRunner CommandLineRunners} and
         * {@link ApplicationRunner ApplicationRunners} have been called.
         * @param context the application context.
         * @since 2.0.0
         */
        void running(ConfigurableApplicationContext context);
    
        /**
         * Called when a failure occurs when running the application.
         * @param context the application context or {@code null} if a failure occurred before
         * the context was created
         * @param exception the failure
         * @since 2.0.0
         */
        void failed(ConfigurableApplicationContext context, Throwable exception);
    
    }

#### 3. 每个阶段执行的内容 ####

##### 3.1 listeners.starting(); #####

###### 在加载Spring Application之前执行，所有资源和环境未被加载。 ######

##### 3.2 prepareEnvironment(listeners, applicationArguments); #####

###### 创建 ConfigurableEnvironment； 将配置的环境绑定到Spring Application中； ######

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.webApplicationType == WebApplicationType.NONE) {
                environment = new EnvironmentConverter(getClassLoader())
                        .convertToStandardEnvironmentIfNecessary(environment);
            }
            ConfigurationPropertySources.attach(environment);
            return environment;
        }

##### 3.3 prepareContext #####

###### 配置忽略的Bean； ######

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());
            }
        }

###### 打印日志-加载的资源 ######

Banner printedBanner = printBanner(environment);

###### 根据不同的WebApplicationType创建Context ######

context = createApplicationContext();

##### 3.4 refreshContext #####

###### 支持定制刷新 ######

/**
         * Register a shutdown hook with the JVM runtime, closing this context
         * on JVM shutdown unless it has already been closed at that time.
         * <p>This method can be called multiple times. Only one shutdown hook
         * (at max) will be registered for each context instance.
         * @see java.lang.Runtime#addShutdownHook
         * @see #close()
         */
        void registerShutdownHook();

##### 3.5 afterRefresh #####

###### 刷新后的实现方法暂未实现 ######

/**
         * Called after the context has been refreshed.
         * @param context the application context
         * @param args the application arguments
         */
        protected void afterRefresh(ConfigurableApplicationContext context,
                ApplicationArguments args) {
        }

##### 3.6 listeners.started(context); #####

###### 到此为止， Spring Application的环境和资源都加载完毕了； 发布应用上下文启动完成事件； 执行所有 Runner 运行器 - 执行所有 ApplicationRunner 和 CommandLineRunner 这两种运行器 ######

// 启动
    callRunners(context, applicationArguments);

##### 3.7 listeners.running(context); #####

###### 触发所有 SpringApplicationRunListener 监听器的 running 事件方法 ######

转载于:https://www.cnblogs.com/rolandlee/p/10419685.html