Spring Boot2.X 启动配置原理

几个重要的事件回调机制

• 配置在META-INF/spring.factories

  • ApplicationContextInitializer

  • /**
     * Callback interface for initializing a Spring {@link ConfigurableApplicationContext}
     * prior to being {@linkplain ConfigurableApplicationContext#refresh() refreshed}.
     *
     * 
    Typically used within web applications that require some programmatic initialization
     * of the application context. For example, registering property sources or activating
     * profiles against the {@linkplain ConfigurableApplicationContext#getEnvironment()
     * context's environment}. See {@code ContextLoader} and {@code FrameworkServlet} support
     * for declaring a "contextInitializerClasses" context-param and init-param, respectively.
     *
     * 
    {@code ApplicationContextInitializer} processors are encouraged to detect
     * whether Spring's {@link org.springframework.core.Ordered Ordered} interface has been
     * implemented or if the @{@link org.springframework.core.annotation.Order Order}
     * annotation is present and to sort instances accordingly if so prior to invocation.
     *
     * @author Chris Beams
     * @since 3.1
     * @param  the application context type
     * @see org.springframework.web.context.ContextLoader#customizeContext
     * @see org.springframework.web.context.ContextLoader#CONTEXT_INITIALIZER_CLASSES_PARAM
     * @see org.springframework.web.servlet.FrameworkServlet#setContextInitializerClasses
     * @see org.springframework.web.servlet.FrameworkServlet#applyInitializers
     */
    public interface ApplicationContextInitializer {
    
    	/**
    	 * Initialize the given application context.
    	 * @param applicationContext the application to configure
    	 */
    	void initialize(C applicationContext);
    
    }

    • SpringApplicationRunListener

  • public interface SpringApplicationRunListener {
    
    	/**
    	 * 回调
         * Called once the {@link ApplicationContext} has been created and prepared, but
    	 * before sources have been loaded.
    	 * @param context the application context
    	 */
    	default void contextPrepared(ConfigurableApplicationContext context) {
    	}
    
    	/**
         * 回调
    	 * Called once the application context has been loaded but before it has been
    	 * refreshed.
    	 * @param context the application context
    	 */
    	default void contextLoaded(ConfigurableApplicationContext context) {
    	}
    
    }

• 只需要放在ioc容器中

  • ApplicationRunner

  • /**
     * Interface used to indicate that a bean should run when it is contained within
     * a {@link SpringApplication}. Multiple {@link ApplicationRunner} beans can be defined
     * within the same application context and can be ordered using the {@link Ordered}
     * interface or {@link Order @Order} annotation.
     *
     * @author Phillip Webb
     * @since 1.3.0
     * @see CommandLineRunner
     */
    @FunctionalInterface
    public interface ApplicationRunner {
    
    	/**
    	 * Callback used to run the bean.
    	 * @param args incoming application arguments
    	 * @throws Exception on error
    	 */
    	void run(ApplicationArguments args) throws Exception;
    
    }

  • CommandLineRunner

  • /**
     * Interface used to indicate that a bean should run when it is contained within
     * a {@link SpringApplication}. Multiple {@link CommandLineRunner} beans can be defined
     * within the same application context and can be ordered using the {@link Ordered}
     * interface or {@link Order @Order} annotation.
     * 
    
     * If you need access to {@link ApplicationArguments} instead of the raw String array
     * consider using {@link ApplicationRunner}.
     *
     * @author Dave Syer
     * @since 1.0.0
     * @see ApplicationRunner
     */
    @FunctionalInterface
    public interface CommandLineRunner {
    
    	/**
    	 * Callback used to run the bean.
    	 * @param args incoming main method arguments
    	 * @throws Exception on error
    	 */
    	void run(String... args) throws Exception;
    
    }

  • 测试：只要创建四个类分别实现四个接口即可
  • 
  • 还需要配置一个文件 resources/META-INF/spring.factories

  • # Initializers
    org.springframework.context.ApplicationContextInitializer=\
    com.atguigu.springboot07.listener.HelloApplicationContextInitializer
    
    org.springframework.boot.SpringApplicationRunListener=\
    com.atguigu.springboot07.listener.HelloSpringApplicationRunListener

  • public class HelloApplicationContextInitializer implements ApplicationContextInitializer {
        @Override
        public void initialize(ConfigurableApplicationContext applicationContext) {
            System.out.println("ApplicationContextInitializer...initialize"+applicationContext);
        }
    }
    
    public class HelloSpringApplicationRunListener implements SpringApplicationRunListener {
    
        /**
         * 如果没有这个有参构造,那么会报错,
         *  Exception in thread "main" java.lang.IllegalArgumentException: Cannot instantiate interface org.springframework.boot.SpringApplicationRunListener : com.atguigu.springboot07.listener.HelloSpringApplicationRunListener
         * 意思就是: 不能实例化这个类SpringApplicationRunListener,进入这个类发现这个类没有无参构造,只有有参构造
         */
        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...");
        }
    
        @Override
        public void failed(ConfigurableApplicationContext context, Throwable exception) {
            System.out.println("SpringApplicationRunListener...failed...");
        }
    }
    

  • HelloApplicationRunner 和 HelloCommandLineRunner 两个类都需要添加一个注解 @Component

  • @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));
        }
    }

  • 这里有个问题：

  • public class HelloSpringApplicationRunListener implements SpringApplicationRunListener {
    
        /**
         * 如果没有这个有参构造,那么会报错,
         *  Exception in thread "main" java.lang.IllegalArgumentException: Cannot instantiate interface org.springframework.boot.SpringApplicationRunListener : com.atguigu.springboot07.listener.HelloSpringApplicationRunListener
         * 意思就是: 不能实例化这个类SpringApplicationRunListener,进入这个类发现这个类没有无参构造,只有有参构造
         */
        public HelloSpringApplicationRunListener(SpringApplication application, String[] args){
    
        }

启动流程：

• Spring Boot 的入口类

• @SpringBootApplication
  public class SpringBootBestPracticeApplication {
      public static void main(String[] args) {
          SpringApplication.run(SpringBoot07Application.class, args);
      }
  }

• 做过 Spring Boot 项目的都知道，上面是 Spring Boot 最简单通用的入口类。入口类的要求是最顶层包下面第一个含有 main 方法的类，使用注解 @SpringBootApplication 来启用 Spring Boot 特性，使用 SpringApplication.run 方法来启动 Spring Boot 项目。

• 来看一下这个类的run方法调用关系源码：

• /**
   * Static helper that can be used to run a {@link SpringApplication} from the
   * specified source using default settings.
   * @param primarySource the primary source to load
   * @param args the application arguments (usually passed from a Java main method)
   * @return the running {@link ApplicationContext}
   */
  public static ConfigurableApplicationContext run(Class primarySource, String... args) {
      return run(new Class[] { primarySource }, args);
  }
  
  /**
   * Static helper that can be used to run a {@link SpringApplication} from the
   * specified sources using default settings and user supplied arguments.
   * @param primarySources the primary sources to load
   * @param args the application arguments (usually passed from a Java main method)
   * @return the running {@link ApplicationContext}
   */
  public static ConfigurableApplicationContext run(Class[] primarySources, String[] args) {
      return new SpringApplication(primarySources).run(args);
  }

• 第一个参数primarySource：加载的主要资源类

• 第二个参数 args：传递给应用的应用参数

• 先用主要资源类来实例化一个 SpringApplication 对象，再调用这个对象的 run 方法，所以我们分两步来分析这个启动源码。

• SpringApplication 的实例化过程：

  • 接着上面的 SpringApplication 构造方法进入以下源码：

  • /**
     * Create a new {@link SpringApplication} instance. The application context will load
     * beans from the specified primary sources (see {@link SpringApplication class-level}
     * documentation for details. The instance can be customized before calling
     * {@link #run(String...)}.
     * @param primarySources the primary bean sources
     * @see #run(Class, String[])
     * @see #SpringApplication(ResourceLoader, Class...)
     * @see #setSources(Set)
     */
    public SpringApplication(Class... primarySources) {
        this(null, primarySources);
    }
    
    
    /**
     * Create a new {@link SpringApplication} instance. The application context will load
     * beans from the specified primary sources (see {@link SpringApplication class-level}
     * documentation for details. The instance can be customized before calling
     * {@link #run(String...)}.
     * @param resourceLoader the resource loader to use
     * @param primarySources the primary bean sources
     * @see #run(Class, String[])
     * @see #setSources(Set)
     */
    public SpringApplication(ResourceLoader resourceLoader, Class... primarySources) {
        // 1、资源初始化资源加载器为 null
        this.resourceLoader = resourceLoader;
        // 2、断言主要加载资源类不能为 null，否则报错
        Assert.notNull(primarySources, "PrimarySources must not be null");
        // 3、初始化主要加载资源类集合并去重
        this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
        // 4、推断当前 WEB 应用类型（REACTIVE、NONE、SERVLET）
        /**
         * NONE: 非 WEB 项目
         * SERVLET: servlet WEB 项目
         * REACTIVE: 响应式 WEB 项目
         */
        this.webApplicationType = WebApplicationType.deduceFromClasspath();
        // 5、设置初始化器,得到Spring工厂实例
        setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));      
        // 6、设置监听器
        setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
        // 7、推断主入口应用类
        this.mainApplicationClass = deduceMainApplicationClass();
    
    }

• 调用这个对象的 run 方法：

  • 上面分析了 SpringApplication 实例对象构造方法初始化过程，下面继续来看下这个 SpringApplication 对象的 run 方法的源码和运行流程。

  • /**
     * 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) {
        // 1、创建并启动计时监控类
        StopWatch stopWatch = new StopWatch();
        stopWatch.start();
        // 2、初始化应用上下文和异常报告集合
        ConfigurableApplicationContext context = null;
        Collection exceptionReporters = new ArrayList<>();
        // 3、设置系统属性 `java.awt.headless` 的值，默认值为：true
        configureHeadlessProperty();
        // 4、创建所有 Spring 运行监听器并发布应用启动事件
        SpringApplicationRunListeners listeners = getRunListeners(args);
        listeners.starting();
        try {
            // 5、初始化默认应用参数类
            ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
            // 6、根据运行监听器和应用参数来准备 Spring 环境
            ConfigurableEnvironment environment = prepareEnvironment(listeners,applicationArguments);
            configureIgnoreBeanInfo(environment);
            // 7、创建 Banner 打印类
            Banner printedBanner = printBanner(environment);
            // 8、创建应用上下文
            context = createApplicationContext();
            // 9、准备异常报告器
            exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,
    			new Class[] { ConfigurableApplicationContext.class }, context);
            // 10、准备应用上下文
            prepareContext(context, environment, listeners, applicationArguments,printedBanner);
            // 11、刷新应用上下文
            refreshContext(context);
            // 12、应用上下文刷新后置处理
            afterRefresh(context, applicationArguments);
            // 13、停止计时监控类
            stopWatch.stop();
            // 14、输出日志记录执行主类名、时间信息
            if (this.logStartupInfo) {
                new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
            }
            // 15、发布应用上下文启动完成事件
            listeners.started(context);
            // 16、执行所有 Runner 运行器
            callRunners(context, applicationArguments);
        }
        catch (Throwable ex) {
            handleRunFailure(context, ex, exceptionReporters, listeners);
            throw new IllegalStateException(ex);
        }
        try {
            // 17、发布应用上下文就绪事件
            listeners.running(context);
        }
        catch (Throwable ex) {
            handleRunFailure(context, ex, exceptionReporters, null);
            throw new IllegalStateException(ex);
        }
        // 18、返回应用上下文
        return context;
    }

  • 这里只是描述的不详细没有深入方法进行说明，我找了一篇博客详细描述了整个方法调用

  • https://www.jianshu.com/p/414d3e2f04e9