SpringBoot应用启动流程源码解析
前言
Springboot应用在启动的时候分为两步:首先生成 SpringApplication 对象 ,运行 SpringApplication 的 run 方法,下面一一看一下每一步具体都干了什么
public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) { return new SpringApplication(primarySources).run(args); }
创建 SpringApplication 对象
public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) { this.resourceLoader = resourceLoader; Assert.notNull(primarySources, "PrimarySources must not be null"); //保存主配置类 this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources)); //判断当前是否一个web应用 this.webApplicationType = WebApplicationType.deduceFromClasspath(); //从类路径下找到META-INF/spring.factories配置的所有ApplicationContextInitializer;然后保存起来 setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class)); //从类路径下找到ETA-INF/spring.factories配置的所有ApplicationListener setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class)); //从多个配置类中找到有main方法的主配置类 this.mainApplicationClass = deduceMainApplicationClass(); }
其中从类路径下获取到META-INF/spring.factories配置的所有ApplicationContextInitializer和ApplicationListener的具体代码如下
public final class SpringFactoriesLoader { /**spring.factories的位置*/ public static final String FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories"; private static final Log logger = LogFactory.getLog(SpringFactoriesLoader.class); /** * 缓存扫描后的结果, 注意这个cache是static修饰的,说明是多个实例共享的 * 其中MultiValueMap的key就是spring.factories中的key(比如org.springframework.boot.autoconfigure.EnableAutoConfiguration), * 其值就是key对应的value以逗号分隔后得到的List集合(这里用到了MultiValueMap,他是guava的一键多值map, 类似Map<String, List<String>>) */ private static final Map<ClassLoader, MultiValueMap<String, String>> cache = new ConcurrentReferenceHashMap<>(); private SpringFactoriesLoader() { } /** * AutoConfigurationImportSelector及应用的初始化器和监听器里最终调用的就是这个方法, * 这里的factoryType是EnableAutoConfiguration.class、ApplicationContextInitializer.class、或ApplicationListener.class * classLoader是AutoConfigurationImportSelector、ApplicationContextInitializer、或ApplicationListener里的beanClassLoader */ public static List<String> loadFactoryNames(Class<?> factoryType, @Nullable ClassLoader classLoader) { String factoryTypeName = factoryType.getName(); return loadSpringFactories(classLoader).getOrDefault(factoryTypeName, Collections.emptyList()); } /** * 加载 spring.factories文件的核心实现 */ private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) { // 先从缓存获取,如果获取到了说明之前已经被加载过 MultiValueMap<String, String> result = cache.get(classLoader); if (result != null) { return result; } try { // 找到所有jar中的spring.factories文件的地址 Enumeration<URL> urls = (classLoader != null ? classLoader.getResources(FACTORIES_RESOURCE_LOCATION) : ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION)); result = new LinkedMultiValueMap<>(); // 循环处理每一个spring.factories文件 while (urls.hasMoreElements()) { URL url = urls.nextElement(); UrlResource resource = new UrlResource(url); // 加载spring.factories文件中的内容到Properties对象中 Properties properties = PropertiesLoaderUtils.loadProperties(resource); // 遍历spring.factories内容中的所有的键值对 for (Map.Entry<?, ?> entry : properties.entrySet()) { // 获得spring.factories内容中的key(比如org.springframework.boot.autoconfigure.EnableAutoConfiguratio) String factoryTypeName = ((String) entry.getKey()).trim(); // 获取value, 然后按英文逗号(,)分割得到value数组并遍历 for (String factoryImplementationName : StringUtils.commaDelimitedListToStringArray((String) entry.getValue())) { // 存储结果到上面的多值Map中(MultiValueMap<String, String>) result.add(factoryTypeName, factoryImplementationName.trim()); } } } cache.put(classLoader, result); return result; } catch (IOException ex) { throw new IllegalArgumentException("Unable to load factories from location [" + FACTORIES_RESOURCE_LOCATION + "]", ex); } } }
运行run方法
public ConfigurableApplicationContext run(String... args) { //开始停止的监听 StopWatch stopWatch = new StopWatch(); stopWatch.start(); //声明一个可配置的ioc容器 ConfigurableApplicationContext context = null; FailureAnalyzers analyzers = null; //配置awt相关的东西 configureHeadlessProperty(); //获取SpringApplicationRunListeners;从类路径下META-INF/spring.factories SpringApplicationRunListeners listeners = getRunListeners(args); //回调所有的获取SpringApplicationRunListener.starting()方法 listeners.starting(); try { //封装命令行参数 ApplicationArguments applicationArguments = new DefaultApplicationArguments( args); //准备环境 ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments); //创建环境完成后回调SpringApplicationRunListener.environmentPrepared();表示环境准备完成 Banner printedBanner = printBanner(environment); //创建ApplicationContext;决定创建web的ioc还是普通的ioc, //通过反射创建ioc容器((ConfigurableApplicationContext) BeanUtils.instantiateClass(contextClass);) context = createApplicationContext(); //出现异常之后做异常分析报告 analyzers = new FailureAnalyzers(context); //准备上下文环境;将environment保存到ioc中;而且applyInitializers(); //applyInitializers():回调之前保存的所有的ApplicationContextInitializer的initialize方法 //回调所有的SpringApplicationRunListener的contextPrepared(); // prepareContext(context, environment, listeners, applicationArguments, printedBanner); //prepareContext运行完成以后回调所有的SpringApplicationRunListener的contextLoaded(); //刷新容器;ioc容器初始化(如果是web应用还会创建嵌入式的Tomcat);Spring注解版 //扫描,创建,加载所有组件的地方;(配置类,组件,自动配置) refreshContext(context); //从ioc容器中获取所有的ApplicationRunner和CommandLineRunner进行回调 //ApplicationRunner先回调,CommandLineRunner再回调 afterRefresh(context, applicationArguments); //所有的SpringApplicationRunListener回调finished方法 listeners.finished(context, null); stopWatch.stop(); if (this.logStartupInfo) { new StartupInfoLogger(this.mainApplicationClass) .logStarted(getApplicationLog(), stopWatch); } //整个SpringBoot应用启动完成以后返回启动的ioc容器; return context; } catch (Throwable ex) { handleRunFailure(context, listeners, analyzers, ex); throw new IllegalStateException(ex); } }
几个重要的事件回调机制
配置在META-INF/spring.factories
ApplicationContextInitializer
SpringApplicationRunListener
只需要放在ioc容器中
ApplicationRunner
CommandLineRunner
以上就是本文的全部内容,希望对大家的学习有所帮助,也希望大家多多支持脚本之家。
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