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】[上]

搭建SpringBoot 底层机制开发环境

1、创建Maven 项目nlc-springboot

2、修改nlc-springboot\pom.xml , 导入相关依赖

<groupId>com.nlc</groupId>
<artifactId>nlc-springboot</artifactId>
<version>1.0-SNAPSHOT</version>
<!-- 导入springboot 父工程，规定的写法-->
<parent><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-parent</artifactId><version>2.5.3</version>
</parent>
<!-- 导入web 项目场景启动器,会自动导入和web 开发相关依赖,非常方便-->
<dependencies><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId></dependency>
</dependencies>

3 、创建nlc-springboot\src\main\java\com\nlc\springboot\MainApp.java

@SpringBootApplication
public class MainApp {public static void main(String[] args) {//启动SpringBoot 应用程序ConfigurableApplicationContext run = SpringApplication.run(MainApp.class, args);}
}

4、启动项目ok, 大家注意Tomcat 也启动了

@Configuration + @Bean 会发生什么，并分析机制

1 、创建nlc-springboot\src\main\java\com\nlc\springboot\bean\Dog.java

public class Dog {
}

2 、创建nlc-springboot\src\main\java\com\nlc\springboot\config\Config.java

@Configuration
public class Config {/*** 1. 通过@Bean 的方式, 将new 出来的Bean 对象, 放入到Spring 容器* 2. 该bean 在Spring 容器的name 就是方法名* 3. 通过方法名, 可以得到new Dog()* @return*/@Beanpublic Dog dog() {return new Dog();}
}

3 、Debug：nlc-springboot\src\main\java\com\nlc\springboot\MainApp.java, 看看容器中是否已经注入了dog 实例

4、底层机制分析: 仍然是我们实现Spring 容器那一套机制IO/文件扫描+注解+反射+集合+映射

提出问题：SpringBoot 是怎么启动Tomcat ，并可以支持访问@Controller

1 、创建nlc-springboot\src\main\java\com\nlc\springboot\controller\HiController.java

@RestController
public class HiController {@RequestMapping("/hi")public String hi() {System.out.println("hi i am HiController");return "hi i am HiController";}
}

2、完成测试, 浏览器输入http://localhost:8080/hi

3、问题: SpringBoot 是怎么内嵌Tomcat, 并启动Tomcat 的? =>追踪源码

源码分析: SpringApplication.run()

1、Debug SpringApplication.run(MainApp.class, args) 看看SpringBoot 是如何启动Tomcat 的.
2、我们的Debug 目标: 紧抓一条线, 就是看到tomcat 被启动的代码. 比如tomcat.start()

public class MainApp {public static void main(String[] args) {//启动springboot应用程序/项目//当我们执行run方法时，怎么就启动我们的内置的tomcat?//在分析run方法的底层机制的基础上，我们自己尝试实现ConfigurableApplicationContext ioc =SpringApplication.run(MainApp.class, args);/** 开始debug SpringApplication.run()* 1.SpringApplication.java* public static ConfigurableApplicationContext run(Class<?> primarySource, String... args) {return run(new Class[]{primarySource}, args);}** 2.SpringApplication.java:创建返回 ConfigurableApplicationContext 对象*  public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) {*     return (new SpringApplication(primarySources)).run(args);*   }** 3.SpringApplication.java*   public ConfigurableApplicationContext run(String... args) {StopWatch stopWatch = new StopWatch();stopWatch.start();DefaultBootstrapContext bootstrapContext = this.createBootstrapContext();ConfigurableApplicationContext context = null;this.configureHeadlessProperty();SpringApplicationRunListeners listeners = this.getRunListeners(args);listeners.starting(bootstrapContext, this.mainApplicationClass);try {ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);ConfigurableEnvironment environment = this.prepareEnvironment(listeners, bootstrapContext, applicationArguments);this.configureIgnoreBeanInfo(environment);Banner printedBanner = this.printBanner(environment);context = this.createApplicationContext();//创建容器，严重分析context.setApplicationStartup(this.applicationStartup);this.prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner);this.refreshContext(context);//严重分析，刷新应用程序上下文，比如：初始化默认配置/注入相关Bean/启动tomcatthis.afterRefresh(context, applicationArguments);stopWatch.stop();if (this.logStartupInfo) {(new StartupInfoLogger(this.mainApplicationClass)).logStarted(this.getApplicationLog(), stopWatch);}listeners.started(context);this.callRunners(context, applicationArguments);} catch (Throwable var10) {this.handleRunFailure(context, var10, listeners);throw new IllegalStateException(var10);}try {listeners.running(context);return context;} catch (Throwable var9) {this.handleRunFailure(context, var9, (SpringApplicationRunListeners)null);throw new IllegalStateException(var9);}}* 4.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 是SERVLET也就是web容器/可以处理servlet* protected ConfigurableApplicationContext createApplicationContext() {return this.applicationContextFactory.create(this.webApplicationType);}** 5.ApplicationContextFactory.java*   ApplicationContextFactory DEFAULT = (webApplicationType) -> {try {switch (webApplicationType) {//如果想要更改可以通过配置文件更改想要创建的容器种类，但是目前本身就是web开发，没必要去改case SERVLET://默认进入这个分支，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);}};** 6.SpringApplication.java* private void refreshContext(ConfigurableApplicationContext context) {if (this.registerShutdownHook) {shutdownHook.registerApplicationContext(context);}this.refresh(context);//严重分析，真正执行相关任务}** 7.SpringApplication.java*  protected void refresh(ConfigurableApplicationContext applicationContext) {applicationContext.refresh();}**8.ServletWebServerApplicationContext.java*    public final void refresh() throws BeansException, IllegalStateException {try {super.refresh();//容器类型很多，走一下父类} catch (RuntimeException var3) {WebServer webServer = this.webServer;if (webServer != null) {webServer.stop();//如果出现异常就关闭服务，所以 super.refresh()里面肯定存在tomcat启动代码}throw var3;}}** 9.AbstractApplicationContext.java*   public void refresh() throws BeansException, IllegalStateException {synchronized(this.startupShutdownMonitor) {StartupStep contextRefresh = this.applicationStartup.start("spring.context.refresh");this.prepareRefresh();ConfigurableListableBeanFactory beanFactory = this.obtainFreshBeanFactory();this.prepareBeanFactory(beanFactory);try {this.postProcessBeanFactory(beanFactory);StartupStep beanPostProcess = this.applicationStartup.start("spring.context.beans.post-process");this.invokeBeanFactoryPostProcessors(beanFactory);this.registerBeanPostProcessors(beanFactory);beanPostProcess.end();this.initMessageSource();this.initApplicationEventMulticaster();this.onRefresh();//有点像模板模式，先回到父类做一些共同的工作，因为下面有很多容器都会做共同的工作，到真正要刷新的时候又通过动态绑定机制回到子类，再开始进行具体的刷新任务this.registerListeners();this.finishBeanFactoryInitialization(beanFactory);this.finishRefresh();} catch (BeansException var10) {if (this.logger.isWarnEnabled()) {this.logger.warn("Exception encountered during context initialization - cancelling refresh attempt: " + var10);}this.destroyBeans();this.cancelRefresh(var10);throw var10;} finally {this.resetCommonCaches();contextRefresh.end();}}}**10.ServletWebServerApplicationContext.Java* protected void onRefresh() {super.onRefresh();try {this.createWebServer();//创建webservlet 可以理解成创建指定 web服务-Tomcat} catch (Throwable var2) {throw new ApplicationContextException("Unable to start web server", var2);}}**11.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()});//严重分析，使用TomcatServletWebServerFactory创建一个TomcatWebServletcreateWebServer.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();}* 12.TomcatServletWebServerFactory.java*    public WebServer getWebServer(ServletContextInitializer... initializers) {if (this.disableMBeanRegistry) {Registry.disableRegistry();}Tomcat tomcat = new Tomcat();//创建Tomcat对象File baseDir = this.baseDirectory != null ? this.baseDirectory : this.createTempDir("tomcat");//做了一系列的设置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);//严重分析}* 13.TomcatServletWebServerFactory.java//做了一个校验创建TomcatWebServer*   protected TomcatWebServer getTomcatWebServer(Tomcat tomcat) {return new TomcatWebServer(tomcat, this.getPort() >= 0, this.getShutdown());}** 14.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();//分析方法，进行初始化和相应的启动}** 15.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监听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);}}}*执行到this.tomcat.start();我们可以返回如下图位置查看context容器值*/System.out.println("hello ioc");

当我们刷新整个上下文时像config的配置类进去了，包括我们的Bean也进去了