1、背景
SpringBoot是一个框架,一种全新的编程标准,他的产生简化了框架的应用,同时也提供了很多便捷的性能,比方内置tomcat就是其中一项,他让咱们省去了搭建tomcat容器,生成war,部署,启动tomcat。因为内置了启动容器,应用程序能够间接通过Maven命令将我的项目编译成可执行的jar包,通过java-jar命令间接启动,不须要再像以前一样,打包成War包,而后部署在Tomcat中,那么内置tomcat是如何实现的呢?
2、tomcat启动过程及原理
2.1、下载一个springboot我的项目
在这里下载一个我的项目https://start.spring.io/也能够在idea新建SpringBoot-Web工程。
<dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> </dependency>
点击pom.xml会有tomcat依赖
<dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-tomcat</artifactId> <version>2.1.2.RELEASE</version> <scope>compile</scope> </dependency>
2.2、从启动入口开始一步步摸索
点击进入run办法
public static ConfigurableApplicationContext run(Class<?> primarySource, String... args) { return run(new Class<?>[] { primarySource }, args); } //持续点击进入run办法 public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) { return new SpringApplication(primarySources).run(args); }
进入到这个run办法之后就能够看到,咱们意识的一些初始化事件。次要的过程也是在这里实现的。
2.3、源码代码流程大抵是这样
/** * Run the Spring application, creating and refreshing a new * {@link ApplicationContext}. * @param args the application arguments (usually passed from a Java main method) * @return a running {@link ApplicationContext} */ public ConfigurableApplicationContext run(String... args) { StopWatch stopWatch = new StopWatch(); stopWatch.start(); ConfigurableApplicationContext context = null; Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>(); /**1、配置零碎属性*/ configureHeadlessProperty(); /**2.获取监听器*/ SpringApplicationRunListeners listeners = getRunListeners(args); /**公布利用开始启动事件 */ listeners.starting(); try { /** 3.初始化参数 */ ApplicationArguments applicationArguments = new DefaultApplicationArguments( args); /** 4.配置环境*/ ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments); configureIgnoreBeanInfo(environment); Banner printedBanner = printBanner(environment); /**5.创立利用上下文*/ context = createApplicationContext(); exceptionReporters = getSpringFactoriesInstances( SpringBootExceptionReporter.class, new Class[] { ConfigurableApplicationContext.class }, context); /**6.预处理上下文*/ prepareContext(context, environment, listeners, applicationArguments, printedBanner); /**6.刷新上下文*/ refreshContext(context); afterRefresh(context, applicationArguments); stopWatch.stop(); if (this.logStartupInfo) { new StartupInfoLogger(this.mainApplicationClass) .logStarted(getApplicationLog(), stopWatch); } /** 8.公布利用曾经启动事件 */ listeners.started(context); callRunners(context, applicationArguments); } catch (Throwable ex) { handleRunFailure(context, ex, exceptionReporters, listeners); throw new IllegalStateException(ex); } try { /** 9.公布利用曾经启动实现的监听事件 */ listeners.running(context); } catch (Throwable ex) { handleRunFailure(context, ex, exceptionReporters, null); throw new IllegalStateException(ex); } return context; }
代码中次要就是通过switch语句,依据webApplicationType的类型来创立不同的ApplicationContext:
●DEFAULT_SERVLET_WEB_CONTEXT_CLASS:Web类型,实例化AnnotationConfigServletWebServerApplicationContext
●DEFAULT_REACTIVE_WEB_CONTEXT_CLASS:响应式Web类型,实例化AnnotationConfigReactiveWebServerApplicationContext
●DEFAULT_CONTEXT_CLASS:非Web类型,实例化AnnotationConfigApplicationContext
2.4、创立完利用上下文之后,咱们在看刷新上下文办法
一步步通过断点点击办法进去查看,咱们看到很相熟代码spring的相干代码。
@Override public void refresh() throws BeansException, IllegalStateException { synchronized (this.startupShutdownMonitor) { // Prepare this context for refreshing. //初始化前的筹备工作,次要是一些零碎属性、环境变量的校验,比方Spring启动须要某些环境变量,能够在这个中央进行设置和校验 prepareRefresh(); // Tell the subclass to refresh the internal bean factory. ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory(); // Prepare the bean factory for use in this context. //筹备bean工厂 注册了局部类 prepareBeanFactory(beanFactory); try { // Allows post-processing of the bean factory in context subclasses. postProcessBeanFactory(beanFactory); // Invoke factory processors registered as beans in the context. //注册bean工厂后置处理器,并解析java代码配置bean定义 invokeBeanFactoryPostProcessors(beanFactory); // Register bean processors that intercept bean creation. //注册bean后置处理器,并不会执行后置处理器,在前面实例化的时候执行 registerBeanPostProcessors(beanFactory); // Initialize message source for this context. initMessageSource(); // Initialize event multicaster for this context. //初始化事件监听多路播送器 initApplicationEventMulticaster(); // Initialize other special beans in specific context subclasses. //待子类实现,springBoot在这里实现创立内置的tomact容器 onRefresh(); // Check for listener beans and register them. registerListeners(); // Instantiate all remaining (non-lazy-init) singletons. finishBeanFactoryInitialization(beanFactory); // Last step: publish corresponding event. finishRefresh(); } catch (BeansException ex) { if (logger.isWarnEnabled()) { logger.warn("Exception encountered during context initialization - " + "cancelling refresh attempt: " + ex); } // Destroy already created singletons to avoid dangling resources. destroyBeans(); // Reset 'active' flag. cancelRefresh(ex); // Propagate exception to caller. throw ex; } finally { // Reset common introspection caches in Spring's core, since we // might not ever need metadata for singleton beans anymore... resetCommonCaches(); } } }
2.5、onRefresh()办法是调用其子类实现的
也就是ServletWebServerApplicationContext
/** 失去Servlet工厂 **/ this.webServer = factory.getWebServer(getSelfInitializer());
其中createWebServer()办法是用来启动web服务的,然而还没有真正启动Tomcat,只是通过ServletWebServerFactory创立了一个WebServer,持续来看这个ServletWebServerFactory:
this.webServer=factory.getWebServer(getSelfInitializer());这个办法能够看出TomcatServletWebServerFactory的实现。相干Tomcat的实现。
2.6、TomcatServletWebServerFactory的getWebServer()办法
清晰的看到new进去了一个Tomcat.
2.7、Tomcat创立之后,持续剖析Tomcat的相干设置和参数
@Override public WebServer getWebServer(ServletContextInitializer... initializers) { /** 1、创立Tomcat实例 **/ Tomcat tomcat = new Tomcat(); //创立Tomcat工作目录 File baseDir = (this.baseDirectory != null) ? this.baseDirectory : createTempDir("tomcat"); tomcat.setBaseDir(baseDir.getAbsolutePath()); Connector connector = new Connector(this.protocol); tomcat.getService().addConnector(connector); customizeConnector(connector); /** 2、给创立好的tomcat设置连接器connector **/ tomcat.setConnector(connector); /** 3.设置不主动部署 **/ tomcat.getHost().setAutoDeploy(false); /** 4.配置Tomcat容器引擎 **/ configureEngine(tomcat.getEngine()); for (Connector additionalConnector : this.additionalTomcatConnectors) { tomcat.getService().addConnector(additionalConnector); } /**筹备Tomcat的StandardContext,并增加到Tomcat中*/ prepareContext(tomcat.getHost(), initializers); /** 将创立好的Tomcat包装成WebServer返回**/ return getTomcatWebServer(tomcat); }
2.8、持续点击getTomcatWebServer办法,找到initialize()办法,能够看到tomcat.start();启动tomcat服务办法。
// Start the server to trigger initialization listeners //启动tomcat服务 this.tomcat.start(); //开启阻塞非守护过程 startDaemonAwaitThread();
2.9、TomcatWebServer.java控制台会打印这句话
Tomcat started on port(s):8080(http)with context path
3、总结
SpringBoot的启动次要是通过实例化SpringApplication来启动的,启动过程次要做了如下几件事件:
配置零碎属性、获取监听器,公布利用开始启动事件、初始化参数、配置环境、创立利用上下文、预处理上下文、刷新上下文、再次刷新上下文、公布利用曾经启动事件、公布利用启动实现事件。而启动Tomcat是刷新上下文这一步。
Spring Boot创立Tomcat时,会先创立一个上下文,将WebApplicationContext传给Tomcat;
启动Web容器,须要调用getWebserver(),因为默认的Web环境就是TomcatServletWebServerFactory,所以会创立Tomcat的Webserver,这里会把根上下文作为参数给TomcatServletWebServerFactory的getWebServer();启动Tomcat,调用Tomcat中Host、Engine的启动办法。