老师找学生做网站是什么心态,网站建设-应酷,恒网做的网站,旅游投资公司网站建设关键词#xff1a;Spring Boot、启动流程、源码解析、IoC容器、自动配置 摘要#xff1a;本文深入分析Spring Boot的启动流程#xff0c;结合核心源码详解从run()方法到嵌入式服务器启动的每一步操作#xff0c;揭秘自动配置原理及扩展点。 一、为什么需要掌握启动流程Spring Boot、启动流程、源码解析、IoC容器、自动配置 摘要本文深入分析Spring Boot的启动流程结合核心源码详解从run()方法到嵌入式服务器启动的每一步操作揭秘自动配置原理及扩展点。 一、为什么需要掌握启动流程
Spring Boot以其约定大于配置、快速启动的特性成为Java微服务开发的首选框架。理解其启动流程能帮助我们 定制化扩展自定义启动加载过程⚡ 性能优化加速应用启动大型项目启动耗时从分钟级降到秒级 故障排查解决初始化阶段的诡异Bug 深入理解框架打通Spring Boot任督二脉
下面我们将结合源码深入剖析Spring Boot启动的每一个关键步骤。
二、启动流程总览10步图解
flowchart TBA[SpringApplication.run()] -- B[初始化SpringApplicationRunListeners]B -- C[准备环境Environment]C -- D[打印Banner]D -- E[创建ApplicationContext]E -- F[准备上下文]F -- G[刷新上下文brfont color#FF0000最核心/font]G -- H[加载自动配置]G -- I[实例化单例Bean]I -- J[启动嵌入式服务器]J -- K[发布Ready事件]三、启动流程源码级分解
步骤1: SpringApplication初始化
// 源码位置SpringApplication.java
public SpringApplication(Class?... primarySources) {this.primarySources new LinkedHashSet(Arrays.asList(primarySources));this.webApplicationType WebApplicationType.deduceFromClasspath(); // 1.推断应用类型this.bootstrappers new ArrayList(getSpringFactoriesInstances(Bootstrapper.class)); setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class)); // 2.加载InitializersetListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class)); // 3.加载Listenerthis.mainApplicationClass deduceMainApplicationClass(); // 4.推断主类
}作用说明 推断应用类型Servlet/Reactive/None通过检测类路径是否存在 javax.servlet.Servlet和org.springframework.web.context.ConfigurableWebApplicationContext → SERVLETorg.springframework.web.reactive.DispatcherHandler → REACTIVE否则 → NONE 通过SPI机制加载META-INF/spring.factories中定义的拓展组件
步骤2: 执行run()方法
// 源码位置SpringApplication.java
public ConfigurableApplicationContext run(String... args) {// 1. 启动计时器StopWatch stopWatch new StopWatch();stopWatch.start();// 2. 初始化SpringApplicationRunListenersSpringApplicationRunListeners listeners getRunListeners(args);listeners.starting(); // 发布ApplicationStartingEvent// 3. 准备环境ConfigurableEnvironment environment prepareEnvironment(listeners, applicationArguments);// 4. 打印BannerBanner printedBanner printBanner(environment);// 5. 创建ApplicationContextcontext createApplicationContext();// 6. 准备上下文prepareContext(context, environment, listeners, applicationArguments, printedBanner);// 7. 刷新上下文核心refreshContext(context);// 8. 执行RunnercallRunners(context, applicationArguments);// 9. 完成启动listeners.started(context);return context;
}步骤3: 环境准备Environment
private ConfigurableEnvironment prepareEnvironment(...) {// 创建环境对象Servlet环境或标准环境ConfigurableEnvironment environment getOrCreateEnvironment();// 加载配置源application.properties/ymlconfigureEnvironment(environment, applicationArguments.getSourceArgs());// 发布ApplicationEnvironmentPreparedEventlisteners.environmentPrepared(environment);// 绑定SpringApplication配置bindToSpringApplication(environment);return environment;
}步骤4: 创建IoC容器
根据应用类型创建不同类型的上下文
// 源码位置SpringApplication.java
protected ConfigurableApplicationContext createApplicationContext() {return this.applicationContextFactory.create(this.webApplicationType);
}// 默认实现
ApplicationContextFactory DEFAULT (webApplicationType) - {switch (webApplicationType) {case SERVLET:return new AnnotationConfigServletWebServerApplicationContext();case REACTIVE:return new AnnotationConfigReactiveWebServerApplicationContext();default:return new AnnotationConfigApplicationContext();}
};步骤5: 刷新上下文最核心步骤
// 源码位置SpringApplication.java
private void refreshContext(ConfigurableApplicationContext context) {// 调用AbstractApplicationContext.refresh()refresh(context);
}// 源码位置AbstractApplicationContext.java
public void refresh() throws BeansException, IllegalStateException {synchronized (this.startupShutdownMonitor) {// [1] 准备刷新工作prepareRefresh();// [2] 获取新的BeanFactoryConfigurableListableBeanFactory beanFactory obtainFreshBeanFactory();// [3] 配置BeanFactory注册环境等组件prepareBeanFactory(beanFactory);try {// [4] 后处理BeanFactorypostProcessBeanFactory(beanFactory);// [5] 执行BeanFactoryPostProcessorinvokeBeanFactoryPostProcessors(beanFactory);// [6] 注册BeanPostProcessorregisterBeanPostProcessors(beanFactory);// [7] 初始化MessageSource国际化initMessageSource();// [8] 初始化事件广播器initApplicationEventMulticaster();// [9] 初始化特殊BeanonRefresh();// [10] 注册监听器registerListeners();// [11] 实例化非懒加载的单例BeanfinishBeanFactoryInitialization(beanFactory);// [12] 完成刷新finishRefresh();}}
}关键子步骤自动配置生效过程
// 源码位置PostProcessorRegistrationDelegate.java
public static void invokeBeanFactoryPostProcessors(...) {// 处理BeanDefinitionRegistryPostProcessorprocessConfigBeanDefinitions(registry);
}private static void processConfigBeanDefinitions(...) {// 创建ConfigurationClassParser解析Configuration类parser.parse(candidates);// 加载自动配置类SetString candidates new LinkedHashSet(configCandidates);AutoConfigurationImportSelector.selectImports() // 关键方法
}自动配置选择器核心逻辑
// 源码位置AutoConfigurationImportSelector.java
protected ListString getCandidateConfigurations(...) {// 从META-INF/spring.factories加载配置ListString configurations SpringFactoriesLoader.loadFactoryNames(EnableAutoConfiguration.class, getBeanClassLoader());// 应用条件过滤ConditionalOnClass等configurations filter(configurations, autoConfigurationMetadata);return configurations;
}四、关键扩展点实战
扩展点1自定义ApplicationRunner
Component
Order(1) // 控制执行顺序
public class CacheInitializer implements ApplicationRunner {Overridepublic void run(ApplicationArguments args) {System.out.println(初始化缓存数据...);// 实际业务逻辑}
}扩展点2自定义事件监听
Component
public class StartupMonitorListener implements ApplicationListenerApplicationReadyEvent {Overridepublic void onApplicationEvent(ApplicationReadyEvent event) {System.out.println(应用启动完成耗时 TimeUnit.NANOSECONDS.toMillis(event.getTimestamp()) ms);}
}扩展点3自定义BeanPostProcessor
Component
public class CustomBeanPostProcessor implements BeanPostProcessor {Overridepublic Object postProcessAfterInitialization(Object bean, String beanName) {if(bean instanceof Controller) {System.out.println(Controller初始化完成: beanName);}return bean;}
}五、性能优化实践
减少组件扫描范围
SpringBootApplication(scanBasePackages com.example.core)排除不必要的自动配置
EnableAutoConfiguration(exclude {DataSourceAutoConfiguration.class, KafkaAutoConfiguration.class
})启用懒初始化慎用
spring.main.lazy-initializationtrue关闭JMX监控节省30-50ms
spring.jmx.enabledfalse六、常见面试题
Q1: SpringBootApplication注解做了哪些事
A: 该注解是三个核心注解的组合
SpringBootConfiguration标识为配置类EnableAutoConfiguration启用自动配置ComponentScan组件扫描默认当前包
Q2: 自动配置是如何实现的
A: 通过EnableAutoConfiguration引入AutoConfigurationImportSelector该选择器
从META-INF/spring.factories加载配置类过滤掉缺少依赖的配置通过ConditionalOnClass等条件注解应用排序规则
Q3: 如何加速Spring Boot启动
优化方案
减小ComponentScan范围排除不必要的自动配置使用Lazy延迟初始化关闭JMX、actuator等非必要模块
七、总结
Spring Boot的启动过程本质上是IoC容器的初始化过程核心亮点在于
事件驱动架构通过11种启动事件解耦各阶段条件化自动配置按需加载超过300自动配置类嵌入式容器无缝集成Tomcat/Jetty等服务器SPI扩展机制通过spring.factories实现插件化
掌握启动流程后你可以
定制自己的启动初始化逻辑解决Bean初始化顺序问题实现秒级启动的微服务深度优化Spring Boot应用
