day03-分析SpringBoot底层机制
分析SpringBoot底层机制
Tomcat启动分析,Spring容器初始化,Tomcat如何关联Spring容器?
1.创建SpringBoot环境
(1)创建Maven程序,创建SpringBoot环境
(2)pom.xml导入SpringBoot的父工程和依赖
<!--导入SpringBoot父工程-规定写法--> <parent> <artifactId>spring-boot-starter-parent</artifactId> <groupId>org.springframework.boot</groupId> <version>2.5.3</version> </parent> <dependencies> <!--导入web项目场景启动器:会自动导入和web开发相关的所有依赖[jar包]--> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> </dependency> </dependencies>
(3)创建主程序MainApp.java
package com.li.springboot; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; import org.springframework.context.ConfigurableApplicationContext; /** * @author 李 * @version 1.0 */ @SpringBootApplication//表示SpringBoot项目 public class MainApp { public static void main(String[] args) { //启动SpringBoot项目 ConfigurableApplicationContext ioc = SpringApplication.run(MainApp.class, args); } }
(4)启动项目,我们可以注意到Tomcat也随之启动了。

问题一:当我们执行run方法时,为什么会启动我们内置的tomcat?它的底层是如何实现的?
2.Spring容器初始化(@Configuration+@Bean)
我们知道,如果在一个类上添加了注解@Configuration,那么这个类就会变成配置类;配置类中通过@Bean注解,可以将方法中 new 出来的Bean对象注入到容器中,该bean对象的id默认为方法名。
配置类本身也会作为bean注入到容器中


容器初始化的底层机制仍然是我们之前分析的Spring容器的机制(IO/文件扫描+注解+反射+集合+映射)
对比:
- Spring通过@ComponentScan,指定要扫描的包;而SpringBoot默认从主程序所在的包开始扫描,同时也可以指定要扫描的包(scanBasePackages = {"xxx.xx"})。
- Spring通过xml或者注解,指定要注入的bean;SpringBoot通过扫描配置类(对应spring的xml)的@Bean或者注解,指定注入bean
3.SpringBoot怎样启动Tomcat,并能支持访问@Controller?
由前面的例子1中可以看到,当启动SpringBoot时,tomcat也会随之启动。那么问题来了:
- SpringBoot是怎么内嵌Tomcat,并启动Tomcat的?
- 而且底层是怎样让@Controller修饰的控制器也可以被访问的?
3.1源码分析SpringApplication.run()
SpringApplication.run()方法会完成两个重要任务:
- 创建容器
- 容器的刷新:包括参数的刷新+启动Tomcat
(1)创建一个控制器
package com.li.springboot.controller; import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.bind.annotation.RestController; /** * @author 李 * @version 1.0 * HiController被标注后,作为一个控制器注入容器中 */ @RestController//相当于@Controller+@ResponseBody public class HiController { @RequestMapping("/hi") public String hi() { return "hi,HiController"; } }
(2)启动主程序MainApp.java,进行debug

(3)首先进入SpringApplication.java的run方法

(4)点击step into,进入如下方法
public ConfigurableApplicationContext run(String... args) { ... try { ... context = this.createApplicationContext();//严重分析,创建容器 context.setApplicationStartup(this.applicationStartup); this.prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner); this.refreshContext(context);//刷新应用上下文,比如初始化默认设置/注入相关bean/启动Tomcat this.afterRefresh(context, applicationArguments); stopWatch.stop(); ... } catch (Throwable var10) {...} ... }
(5)分别对 **createApplicationContext() **和 refreshContext(context) 方法进行分析:
(5.1)step into 进入 **createApplicationContext() ** 方法中:
//springApplication.java //容器类型很多,会根据你的this.webApplicationType创建对应的容器,默认this.webApplicationType //的类型为SERVLET,也就是web容器(可以处理servlet) protected ConfigurableApplicationContext createApplicationContext() { return this.applicationContextFactory.create(this.webApplicationType); }

(5.2)点击进入下一层
//接口 ApplicationContextFactory.java //该方法根据webApplicationType创建不同的容器 ApplicationContextFactory DEFAULT = (webApplicationType) -> { try { switch(webApplicationType) { case SERVLET://默认进入这一分支,返回 //AnnotationConfigServletWebServerApplicationContext容器 return new AnnotationConfigServletWebServerApplicationContext(); case REACTIVE: return new AnnotationConfigReactiveWebServerApplicationContext(); default: return new AnnotationConfigApplicationContext(); } } catch (Exception var2) { throw new IllegalStateException("Unable create a default ApplicationContext instance, you may need a custom ApplicationContextFactory", var2); } };
总结:createApplicationContext()方法中创建了容器,但是还没有将bean注入到容器中。
(5.3)step into 进入 refreshContext(context) 方法中:
//springApplication.java private void refreshContext(ConfigurableApplicationContext context) { if (this.registerShutdownHook) { shutdownHook.registerApplicationContext(context); } this.refresh(context);//核心,真正执行相关任务 }
(5.4)在this.refresh(context);这一步进入下一层:
//springApplication.java protected void refresh(ConfigurableApplicationContext applicationContext) { applicationContext.refresh(); }
(5.5)继续进入下一层:
protected void refresh(ConfigurableApplicationContext applicationContext) { applicationContext.refresh(); }
(5.6)继续进入下一层:
//ServletWebServerApplicationContext.java public final void refresh() throws BeansException, IllegalStateException { try { super.refresh(); } catch (RuntimeException var3) { WebServer webServer = this.webServer; if (webServer != null) { webServer.stop(); } throw var3; } }
(5.7)在super.refresh();这一步进入下一层:
//AbstractApplicationContext.java @Override public void refresh() throws BeansException, IllegalStateException { synchronized (this.startupShutdownMonitor) { StartupStep contextRefresh = this.applicationStartup.start("spring.context.refresh"); ... try { ... // Initialize other special beans in specific context subclasses. //在上下文的子类初始化指定的bean onRefresh(); //当父类完成通用的工作后,再重新用动态绑定机制回到子类 ... } catch (BeansException ex) {...} finally {...} } }
(5.8)在onRefresh();这一步step into,会重新返回上一层:
//ServletWebServerApplicationContext.java protected void onRefresh() { super.onRefresh(); try { this.createWebServer();//创建一个webserver,可以理解成创建我们指定的web服务-Tomcat } catch (Throwable var2) { throw new ApplicationContextException("Unable to start web server", var2); } }
(5.9)在this.createWebServer();这一步step into:
//ServletWebServerApplicationContext.java private void createWebServer() { WebServer webServer = this.webServer; ServletContext servletContext = this.getServletContext(); if (webServer == null && servletContext == null) { StartupStep createWebServer = this.getApplicationStartup().start("spring.boot.webserver.create"); ServletWebServerFactory factory = this.getWebServerFactory(); createWebServer.tag("factory", factory.getClass().toString()); this.webServer = factory.getWebServer(new ServletContextInitializer[]{this.getSelfInitializer()});//使用TomcatServletWebServerFactory创建一个TomcatWebServer createWebServer.end(); this.getBeanFactory().registerSingleton("webServerGracefulShutdown", new WebServerGracefulShutdownLifecycle(this.webServer)); this.getBeanFactory().registerSingleton("webServerStartStop", new WebServerStartStopLifecycle(this, this.webServer)); } else if (servletContext != null) { try { this.getSelfInitializer().onStartup(servletContext); } catch (ServletException var5) { throw new ApplicationContextException("Cannot initialize servlet context", var5); } } this.initPropertySources(); }

(5.10)在this.webServer = factory.getWebServer(new ServletContextInitializer[]{this.getSelfInitializer()});这一步step into:
//TomcatServletWebServerFactory.java会创建Tomcat,并启动Tomcat public WebServer getWebServer(ServletContextInitializer... initializers) { if (this.disableMBeanRegistry) { Registry.disableRegistry(); } Tomcat tomcat = new Tomcat();//创建了Tomcat对象,下面是一系列的初始化任务 File baseDir = this.baseDirectory != null ? this.baseDirectory : this.createTempDir("tomcat"); tomcat.setBaseDir(baseDir.getAbsolutePath()); Connector connector = new Connector(this.protocol); connector.setThrowOnFailure(true); tomcat.getService().addConnector(connector); this.customizeConnector(connector); tomcat.setConnector(connector); tomcat.getHost().setAutoDeploy(false); this.configureEngine(tomcat.getEngine()); Iterator var5 = this.additionalTomcatConnectors.iterator(); while(var5.hasNext()) { Connector additionalConnector = (Connector)var5.next(); tomcat.getService().addConnector(additionalConnector); } this.prepareContext(tomcat.getHost(), initializers); return this.getTomcatWebServer(tomcat); }
(5.11)在return this.getTomcatWebServer(tomcat);这一步step into:
//TomcatServletWebServerFactory.java //这里做了端口校验,创建了TomcatWebServer protected TomcatWebServer getTomcatWebServer(Tomcat tomcat) { return new TomcatWebServer(tomcat, this.getPort() >= 0, this.getShutdown()); }
(5.12)继续step into进入下一层
//TomcatServletWebServerFactory.java public TomcatWebServer(Tomcat tomcat, boolean autoStart, Shutdown shutdown) { this.monitor = new Object(); this.serviceConnectors = new HashMap(); Assert.notNull(tomcat, "Tomcat Server must not be null"); this.tomcat = tomcat; this.autoStart = autoStart; this.gracefulShutdown = shutdown == Shutdown.GRACEFUL ? new GracefulShutdown(tomcat) : null; this.initialize();//进行初始化,并启动tomcat }
(5.13)this.initialize();继续step into:
//TomcatServletWebServerFactory.java private void initialize() throws WebServerException { logger.info("Tomcat initialized with port(s): " + this.getPortsDescription(false)); synchronized(this.monitor) { try { this.addInstanceIdToEngineName(); Context context = this.findContext(); context.addLifecycleListener((event) -> { if (context.equals(event.getSource()) && "start".equals(event.getType())) { this.removeServiceConnectors(); } }); this.tomcat.start();//启动Tomcat! this.rethrowDeferredStartupExceptions(); try { ContextBindings.bindClassLoader(context, context.getNamingToken(), this.getClass().getClassLoader()); } catch (NamingException var5) { } this.startDaemonAwaitThread(); } catch (Exception var6) { this.stopSilently(); this.destroySilently(); throw new WebServerException("Unable to start embedded Tomcat", var6); } } }
(6)一路返回上层,然后终于执行完refreshContext(context)方法,此时context为已经注入了bean

【推荐】编程新体验,更懂你的AI,立即体验豆包MarsCode编程助手
【推荐】凌霞软件回馈社区,博客园 & 1Panel & Halo 联合会员上线
【推荐】抖音旗下AI助手豆包,你的智能百科全书,全免费不限次数
【推荐】博客园社区专享云产品让利特惠,阿里云新客6.5折上折
【推荐】轻量又高性能的 SSH 工具 IShell:AI 加持,快人一步
· 微软正式发布.NET 10 Preview 1:开启下一代开发框架新篇章
· 没有源码,如何修改代码逻辑?
· PowerShell开发游戏 · 打蜜蜂
· 在鹅厂做java开发是什么体验
· WPF到Web的无缝过渡:英雄联盟客户端的OpenSilver迁移实战