SpringBoot加载原理流程以及Spring事件机制简单概述Springboot自动装配

上一篇提到了Spring注解Compoent原理，这次简单介绍一下，什么是Spring事件驱动，Springboot如何利用事物驱动进行加载.

@SpringBootApplication
public class DemoApplication {

	public static void main(String[] args) {
		//10分钟
		SpringApplication springApplication = new SpringApplication(DemoApplication.class);
		Properties defaultProperties = new Properties();
		defaultProperties.put("server.port",0);
		springApplication.setDefaultProperties(defaultProperties);
		springApplication.addListeners(System.err::println);
		springApplication.run(args);
//		new SpringApplicationBuilder(DemoApplication.class)
//				.properties("server.port=0").run(args);
	}

}

代码来自start.spring.io.官网。我们今天重点关注的是run方法。

public class SpringApplication {


    .....        


    public ConfigurableApplicationContext run(String... args) {
        //时间启动时间锚点
		StopWatch stopWatch = new StopWatch();
        //开始启动
		stopWatch.start();
        //定义上下文边界
		ConfigurableApplicationContext context = null;
        //设置异常
		Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
        //设置系统环境变量
		configureHeadlessProperty();
        //获取事件发布器 其实就是SimpleApplicationEventMulticaster的Spring发布器，用来发布消息
		SpringApplicationRunListeners listeners = getRunListeners(args);
        //发布一个ApplicationStartingEvent事件
		listeners.starting();
		try {
            //启动参数
			ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
            //获取系统参数 发布ApplicationEnvironmentPreparedEvent
			ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);
			configureIgnoreBeanInfo(environment);
            //输出benner
			Banner printedBanner = printBanner(environment);
            //根据参数设置创建不同的Springboot上下文有server,webflux，mvc等，并初始化ioc容器(DefaultListableBeanFactory) (AnnotationConfigApplicationContext)这个是默认的Context,并设置过滤器
			context = createApplicationContext();
            //创建异常
			exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,
					new Class[] { ConfigurableApplicationContext.class }, context);
            //创建多个监听器
            //发布 ApplicationContextInitializedEvent()初始化事件
            //打印log日志 此时ioc容器还未有Bean
            //将spring applicationArguments  printedBanner 设置成单例级别
            //增加 Component 过滤器(includeFilters)
            //准备 BeanDefinitionLoader  Bean的载入器
            //发布 ApplicationPreparedEvent 事件应用预处理完毕
			prepareContext(context, environment, listeners, applicationArguments, printedBanner);
            //那么到这里准备开始载入Bean了
            //ComponentScan在此处被调用，获取包扫描的基础路径进行（ComponentScanAnnotationParser类 parse 方法 return  
scanner.doScan(StringUtils.toStringArray(basePackages));
            // 解析加载bean 并且处理自动装配 import机制 SpringBoot spi机制（andidate.isAssignable(ImportSelector.class)），
//所有的逻辑 所有的逻辑在这里完成parser.parse(candidates);
//ContextRefreshedEvent 发布事件
			refreshContext(context);
			afterRefresh(context, applicationArguments);
			stopWatch.stop();
			if (this.logStartupInfo) {
				new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
			}
			listeners.started(context);
			callRunners(context, applicationArguments);
		}
		catch (Throwable ex) {
			handleRunFailure(context, ex, exceptionReporters, listeners);
			throw new IllegalStateException(ex);
		}

		try {
			listeners.running(context);
		}
		catch (Throwable ex) {
			handleRunFailure(context, ex, exceptionReporters, null);
			throw new IllegalStateException(ex);
		}
		return context;
	}

    ...

}

class ComponentScanAnnotationParser {

    ...
	public Set<BeanDefinitionHolder> parse(AnnotationAttributes componentScan, final String declaringClass) {
		ClassPathBeanDefinitionScanner scanner = new ClassPathBeanDefinitionScanner(this.registry,
				componentScan.getBoolean("useDefaultFilters"), this.environment, this.resourceLoader);

		Class<? extends BeanNameGenerator> generatorClass = componentScan.getClass("nameGenerator");
		boolean useInheritedGenerator = (BeanNameGenerator.class == generatorClass);
		scanner.setBeanNameGenerator(useInheritedGenerator ? this.beanNameGenerator :
				BeanUtils.instantiateClass(generatorClass));

		ScopedProxyMode scopedProxyMode = componentScan.getEnum("scopedProxy");
		if (scopedProxyMode != ScopedProxyMode.DEFAULT) {
			scanner.setScopedProxyMode(scopedProxyMode);
		}
		else {
			Class<? extends ScopeMetadataResolver> resolverClass = componentScan.getClass("scopeResolver");
			scanner.setScopeMetadataResolver(BeanUtils.instantiateClass(resolverClass));
		}

		scanner.setResourcePattern(componentScan.getString("resourcePattern"));

		for (AnnotationAttributes filter : componentScan.getAnnotationArray("includeFilters")) {
			for (TypeFilter typeFilter : typeFiltersFor(filter)) {
				scanner.addIncludeFilter(typeFilter);
			}
		}
		for (AnnotationAttributes filter : componentScan.getAnnotationArray("excludeFilters")) {
			for (TypeFilter typeFilter : typeFiltersFor(filter)) {
				scanner.addExcludeFilter(typeFilter);
			}
		}

		boolean lazyInit = componentScan.getBoolean("lazyInit");
		if (lazyInit) {
			scanner.getBeanDefinitionDefaults().setLazyInit(true);
		}

		Set<String> basePackages = new LinkedHashSet<>();
		String[] basePackagesArray = componentScan.getStringArray("basePackages");
		for (String pkg : basePackagesArray) {
			String[] tokenized = StringUtils.tokenizeToStringArray(this.environment.resolvePlaceholders(pkg),
					ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
			Collections.addAll(basePackages, tokenized);
		}
		for (Class<?> clazz : componentScan.getClassArray("basePackageClasses")) {
			basePackages.add(ClassUtils.getPackageName(clazz));
		}
		if (basePackages.isEmpty()) {
			basePackages.add(ClassUtils.getPackageName(declaringClass));
		}

		scanner.addExcludeFilter(new AbstractTypeHierarchyTraversingFilter(false, false) {
			@Override
			protected boolean matchClassName(String className) {
				return declaringClass.equals(className);
			}
		});
		return scanner.doScan(StringUtils.toStringArray(basePackages));
	}
    ...
}

 

5.0新特性 Components 可从配置文件META-INF/spring.components 写入 , 不需要带注解

public final class CandidateComponentsIndexLoader {

	/**
	 * The location to look for components.
	 * <p>Can be present in multiple JAR files.
	 */
	public static final String COMPONENTS_RESOURCE_LOCATION = "META-INF/spring.components";

	/**
	 * System property that instructs Spring to ignore the index, i.e.
	 * to always return {@code null} from {@link #loadIndex(ClassLoader)}.
	 * <p>The default is "false", allowing for regular use of the index. Switching this
	 * flag to {@code true} fulfills a corner case scenario when an index is partially
	 * available for some libraries (or use cases) but couldn't be built for the whole
	 * application. In this case, the application context fallbacks to a regular
	 * classpath arrangement (i.e. as no index was present at all).
	 */
	public static final String IGNORE_INDEX = "spring.index.ignore";


	private static final boolean shouldIgnoreIndex = SpringProperties.getFlag(IGNORE_INDEX);

	private static final Log logger = LogFactory.getLog(CandidateComponentsIndexLoader.class);

	private static final ConcurrentMap<ClassLoader, CandidateComponentsIndex> cache =
			new ConcurrentReferenceHashMap<>();


	private CandidateComponentsIndexLoader() {
	}


	/**
	 * Load and instantiate the {@link CandidateComponentsIndex} from
	 * {@value #COMPONENTS_RESOURCE_LOCATION}, using the given class loader. If no
	 * index is available, return {@code null}.
	 * @param classLoader the ClassLoader to use for loading (can be {@code null} to use the default)
	 * @return the index to use or {@code null} if no index was found
	 * @throws IllegalArgumentException if any module index cannot
	 * be loaded or if an error occurs while creating {@link CandidateComponentsIndex}
	 */
	@Nullable
	public static CandidateComponentsIndex loadIndex(@Nullable ClassLoader classLoader) {
		ClassLoader classLoaderToUse = classLoader;
		if (classLoaderToUse == null) {
			classLoaderToUse = CandidateComponentsIndexLoader.class.getClassLoader();
		}
		return cache.computeIfAbsent(classLoaderToUse, CandidateComponentsIndexLoader::doLoadIndex);
	}

	@Nullable
	private static CandidateComponentsIndex doLoadIndex(ClassLoader classLoader) {
		if (shouldIgnoreIndex) {
			return null;
		}

		try {
			Enumeration<URL> urls = classLoader.getResources(COMPONENTS_RESOURCE_LOCATION);
			if (!urls.hasMoreElements()) {
				return null;
			}
			List<Properties> result = new ArrayList<>();
			while (urls.hasMoreElements()) {
				URL url = urls.nextElement();
				Properties properties = PropertiesLoaderUtils.loadProperties(new UrlResource(url));
				result.add(properties);
			}
			if (logger.isDebugEnabled()) {
				logger.debug("Loaded " + result.size() + "] index(es)");
			}
			int totalCount = result.stream().mapToInt(Properties::size).sum();
			return (totalCount > 0 ? new CandidateComponentsIndex(result) : null);
		}
		catch (IOException ex) {
			throw new IllegalStateException("Unable to load indexes from location [" +
					COMPONENTS_RESOURCE_LOCATION + "]", ex);
		}
	}

}


protected Set<BeanDefinitionHolder> doScan(String... basePackages) {
		Assert.notEmpty(basePackages, "At least one base package must be specified");
		Set<BeanDefinitionHolder> beanDefinitions = new LinkedHashSet<>();
		for (String basePackage : basePackages) {
                        //此方法过滤
			Set<BeanDefinition> candidates = findCandidateComponents(basePackage);
			for (BeanDefinition candidate : candidates) {
				ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(candidate);
				candidate.setScope(scopeMetadata.getScopeName());
				String beanName = this.beanNameGenerator.generateBeanName(candidate, this.registry);
				if (candidate instanceof AbstractBeanDefinition) {
					postProcessBeanDefinition((AbstractBeanDefinition) candidate, beanName);
				}
				if (candidate instanceof AnnotatedBeanDefinition) {
					AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition) candidate);
				}
				if (checkCandidate(beanName, candidate)) {
					BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName);
					definitionHolder =
							AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
					beanDefinitions.add(definitionHolder);
					registerBeanDefinition(definitionHolder, this.registry);
				}
			}
		}
		return beanDefinitions;
	}

 

还有一个类， SpringApplicationRunListeners 此类贯穿上下文生命周期发布不同的事件,

class SpringApplicationRunListeners {

	private final Log log;

	private final List<SpringApplicationRunListener> listeners;

	SpringApplicationRunListeners(Log log, Collection<? extends SpringApplicationRunListener> listeners) {
		this.log = log;
		this.listeners = new ArrayList<>(listeners);
	}

	public void starting() {
		for (SpringApplicationRunListener listener : this.listeners) {
			listener.starting();
		}
	}

	public void environmentPrepared(ConfigurableEnvironment environment) {
		for (SpringApplicationRunListener listener : this.listeners) {
			listener.environmentPrepared(environment);
		}
	}

	public void contextPrepared(ConfigurableApplicationContext context) {
		for (SpringApplicationRunListener listener : this.listeners) {
			listener.contextPrepared(context);
		}
	}

	public void contextLoaded(ConfigurableApplicationContext context) {
		for (SpringApplicationRunListener listener : this.listeners) {
			listener.contextLoaded(context);
		}
	}

	public void started(ConfigurableApplicationContext context) {
		for (SpringApplicationRunListener listener : this.listeners) {
			listener.started(context);
		}
	}

	public void running(ConfigurableApplicationContext context) {
		for (SpringApplicationRunListener listener : this.listeners) {
			listener.running(context);
		}
	}

	public void failed(ConfigurableApplicationContext context, Throwable exception) {
		for (SpringApplicationRunListener listener : this.listeners) {
			callFailedListener(listener, context, exception);
		}
	}

	private void callFailedListener(SpringApplicationRunListener listener, ConfigurableApplicationContext context,
			Throwable exception) {
		try {
			listener.failed(context, exception);
		}
		catch (Throwable ex) {
			if (exception == null) {
				ReflectionUtils.rethrowRuntimeException(ex);
			}
			if (this.log.isDebugEnabled()) {
				this.log.error("Error handling failed", ex);
			}
			else {
				String message = ex.getMessage();
				message = (message != null) ? message : "no error message";
				this.log.warn("Error handling failed (" + message + ")");
			}
		}
	}

}

下图是所有的Spring以及SpringBoot的监听器 根据事件来处理不同的逻辑，所以说spring boot是一个基于spring事件处理的集成框架