死磕源码系列【SpringApplicationRunListener监听器源码及加载过程解析】

以你之姓@ 2022-12-14 12:27 116阅读 0赞

> springboot提供了两个类SpringApplicationRunListeners、SpringApplicationRunListener（EventPublishingRunListener），spring框架还提供了一个ApplicationListener接口，那么这几个类或接口的关系又是如何呢？首先SpringApplicationRunListeners类是SpringApplicationRunListener接口的代理类，可以批量调用SpringApplicationRunListener接口方法，SpringApplicationRunListener接口只有一个实现类EventPublishingRunListener，其有一个属性SimpleApplicationEventMulticaster，SimpleApplicationEventMulticaster即是一个ApplicationListener监听器接口的代理实现类，可以批量的执行监听器的onApplicationEvent方法。

##### 1.SpringApplicationRunListener接口源码 #####

SpringApplicationRunListener是对org.springframework.boot.SpringApplication类的run方法进行监听，SpringApplicationRunListener实现类是通过SpringFactoriesLoader类加载（即springboot SPI）;并且需要声明一个包含SpringApplication实例及String\[\]的参数构造方法。

public interface SpringApplicationRunListener { 
    
    	/** * 当run方法第一次启动时立即调用，可用于非常早期的初始化 */
    	default void starting() { 
    	}
    
    	/** * 在ApplicationContext创建之前，一旦环境environment准备好就调用。 * @param environment the environment */
    	default void environmentPrepared(ConfigurableEnvironment environment) { 
    	}
    
    	/** * 在资源（可以理解为配置主类）被加载完成之前，一旦ApplicationContext被创建并准备好就立马调用， * @param context the application context */
    	default void contextPrepared(ConfigurableApplicationContext context) { 
    	}
    
    	/** * 在资源加载完成之后，但在刷新之前调用 * @param context the application context */
    	default void contextLoaded(ConfigurableApplicationContext context) { 
    	}
    
    	/** * 上下文已刷新，应用程序已启动，但是CommandLineRunner和ApplicationRunner尚未调用。 * @param context the application context. * @since 2.0.0 */
    	default void started(ConfigurableApplicationContext context) { 
    	}
    
    	/** * 当ApplicationContext已经refresh且所有的CommandLineRunner和ApplicationRunner都已被调用时，在run方法完成之前立即调用。 * @param context the application context. * @since 2.0.0 */
    	default void running(ConfigurableApplicationContext context) { 
    	}
    
    	/** * 在运行应用程序时发生故障时调用 * @param context 应用程序上下文，可能为null(在应用程序上下文创建之前) * @param exception the failure * @since 2.0.0 */
    	default void failed(ConfigurableApplicationContext context, Throwable exception) { 
    	}

##### 2.SpringApplicationRunListener接口唯一实现类EventPublishingRunListener #####

public class EventPublishingRunListener implements SpringApplicationRunListener, Ordered { 
    	//启动类实例对象
    	private final SpringApplication application;
    	//参数
    	private final String[] args;
    	//ApplicationListener监听器接口代理广播类
    	private final SimpleApplicationEventMulticaster initialMulticaster;
    
    	public EventPublishingRunListener(SpringApplication application, String[] args) { 
    		this.application = application;
    		this.args = args;
    		this.initialMulticaster = new SimpleApplicationEventMulticaster();
        //获取应用程序的监听器类，并循环添加到代理类的监听器助手属性对象中
    		for (ApplicationListener<?> listener : application.getListeners()) { 
    			this.initialMulticaster.addApplicationListener(listener);
    		}
    	}
    }

其中application.getListeners()获取通过SPI方式定义的所有ApplicationListener监听器接口定义的监听器类，其初始化是在SpringApplication类中通过构造函数的方式，如下：

//监听器对象集合
    private List<ApplicationListener<?>> listeners;
    
    public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) { 
    		this.resourceLoader = resourceLoader;
    		Assert.notNull(primarySources, "PrimarySources must not be null");
    		this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
    		this.webApplicationType = WebApplicationType.deduceFromClasspath();
      	//通过SPI方式初始化应用程序初始化器
    		setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
    		//通过SPI方式获取ApplicationListener监听器
    		setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
    		this.mainApplicationClass = deduceMainApplicationClass();
    	}

spring.factories配置文件：

# Application Listeners
    org.springframework.context.ApplicationListener=\
    org.springframework.boot.ClearCachesApplicationListener,\
    org.springframework.boot.builder.ParentContextCloserApplicationListener,\
    org.springframework.boot.cloud.CloudFoundryVcapEnvironmentPostProcessor,\
    org.springframework.boot.context.FileEncodingApplicationListener,\
    org.springframework.boot.context.config.AnsiOutputApplicationListener,\
    org.springframework.boot.context.config.ConfigFileApplicationListener,\
    org.springframework.boot.context.config.DelegatingApplicationListener,\
    org.springframework.boot.context.logging.ClasspathLoggingApplicationListener,\
    org.springframework.boot.context.logging.LoggingApplicationListener,\
    org.springframework.boot.liquibase.LiquibaseServiceLocatorApplicationListener

##### 3.SpringApplicationRunListener接口实现类集合类SpringApplicationRunListeners #####

class SpringApplicationRunListeners { 
    
    	private final Log log;
    	//存储SpringApplicationRunListener监听器集合
    	private final List<SpringApplicationRunListener> listeners;
    
    	SpringApplicationRunListeners(Log log, Collection<? extends SpringApplicationRunListener> listeners) { 
    		this.log = log;
    		this.listeners = new ArrayList<>(listeners);
    	}
    }

##### 4.org.springframework.boot.SpringApplication\#run(java.lang.String…)方法中通过SPI方式获取SpringApplicationRunListeners对象 #####

public ConfigurableApplicationContext run(String... args) { 
    		StopWatch stopWatch = new StopWatch();
    		stopWatch.start();
    		ConfigurableApplicationContext context = null;
    		Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
    		configureHeadlessProperty();
        //通过SPI方式获取SpringApplicationRunListener监听器对象集合
    		SpringApplicationRunListeners listeners = getRunListeners(args);
        //启动监听器，传递ApplicationStartingEvent事件
    		listeners.starting();
    		try { 
    			ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
          //environment准备好之后调用监听器environmentPrepared方法
          //传递ApplicationEnvironmentPreparedEvent事件
    			ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);
    			configureIgnoreBeanInfo(environment);
    			Banner printedBanner = printBanner(environment);
    			context = createApplicationContext();
    			exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,
    					new Class[] {  ConfigurableApplicationContext.class }, context);
          //资源加载之前调用监听器的contextPrepared方法，传递ApplicationContextInitializedEvent事件
          //资源加载之后，refresh方法调用之前调用监听器的contextLoaded方法，传递ApplicationPreparedEvent事件
    			prepareContext(context, environment, listeners, applicationArguments, printedBanner);
    			refreshContext(context);
    			afterRefresh(context, applicationArguments);
    			stopWatch.stop();
    			if (this.logStartupInfo) { 
    				new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
    			}
          //应用程序refresh之后调用，传递ApplicationStartedEvent事件
    			listeners.started(context);
    			callRunners(context, applicationArguments);
    		}
    		catch (Throwable ex) { 
          //应用程序启动过程中出现异常调用failed方法
          //传递ApplicationFailedEvent事件
    			handleRunFailure(context, ex, exceptionReporters, listeners);
    			throw new IllegalStateException(ex);
    		}
    
    		try { 
          //在应用程序run方法运行结束之前调用，传递ApplicationReadyEvent事件
    			listeners.running(context);
    		}
    		catch (Throwable ex) { 
    			handleRunFailure(context, ex, exceptionReporters, null);
    			throw new IllegalStateException(ex);
    		}
    		return context;
    	}
    	//通过SPI方式获取SpringApplicationRunListener接口实现类，并创建SpringApplicationRunListeners集合类
    	private SpringApplicationRunListeners getRunListeners(String[] args) { 
    		Class<?>[] types = new Class<?>[] {  SpringApplication.class, String[].class };
    		return new SpringApplicationRunListeners(logger,
    				getSpringFactoriesInstances(SpringApplicationRunListener.class, types, this, args));
    	}

spring.factories配置文件如下：

# Run Listeners
    org.springframework.boot.SpringApplicationRunListener=\
    org.springframework.boot.context.event.EventPublishingRunListener

GitHub地址：[https://github.com/mingyang66/spring-parent][https_github.com_mingyang66_spring-parent]

[https_github.com_mingyang66_spring-parent]: https://github.com/mingyang66/spring-parent