SpringBoot之内嵌Tomcat

偏执的太偏执、 2022-10-31 05:23 150阅读 0赞

### 前言 ###

不得不说SpringBoot的开发者是在为大众程序猿某福利，把大家都惯成了懒汉，xml不配置了，连tomcat也懒的配置了，典型的一键启动系统，那么tomcat在springboot是怎么启动的呢？

### 内置tomcat ###

开发阶段对我们来说使用内置的tomcat是非常够用了，当然也可以使用jetty。

<dependency>
       <groupId>org.springframework.boot</groupId>
       <artifactId>spring-boot-starter-web</artifactId>
       <version>2.1.6.RELEASE</version>
    </dependency>
    复制代码

@SpringBootApplication
    public class MySpringbootTomcatStarter{
        public static void main(String[] args) {
            Long time=System.currentTimeMillis();
            SpringApplication.run(MySpringbootTomcatStarter.class);
            System.out.println("===应用启动耗时："+(System.currentTimeMillis()-time)+"===");
        }
    }
    复制代码

这里是main函数入口，两句代码最耀眼，分别是SpringBootApplication注解和SpringApplication.run()方法。

### 发布生产 ###

发布的时候，目前大多数的做法还是排除内置的tomcat，打瓦包（war）然后部署在生产的tomcat中，好吧，那打包的时候应该怎么处理？

<dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
        
        <exclusions>
            <exclusion>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-tomcat</artifactId>
            </exclusion>
        </exclusions>
    </dependency>
    
    <dependency>
        <groupId>javax.servlet</groupId>
        <artifactId>javax.servlet-api</artifactId>
        <version>3.1.0</version>
        <scope>provided</scope>
    </dependency>
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更新main函数，主要是继承SpringBootServletInitializer，并重写configure()方法。

@SpringBootApplication
    public class MySpringbootTomcatStarter extends SpringBootServletInitializer {
        public static void main(String[] args) {
            Long time=System.currentTimeMillis();
            SpringApplication.run(MySpringbootTomcatStarter.class);
            System.out.println("===应用启动耗时："+(System.currentTimeMillis()-time)+"===");
        }
    
        @Override
        protected SpringApplicationBuilder configure(SpringApplicationBuilder builder) {
            return builder.sources(this.getClass());
        }
    }
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### 从main函数说起 ###

public static ConfigurableApplicationContext run(Class<?> primarySource, String... args) {
        return run(new Class[]{primarySource}, args);
    }
    
    --这里run方法返回的是ConfigurableApplicationContext
    public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) {
    	return (new SpringApplication(primarySources)).run(args);
    }
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public ConfigurableApplicationContext run(String... args) {
    	ConfigurableApplicationContext context = null;
    	Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList();
    	this.configureHeadlessProperty();
    	SpringApplicationRunListeners listeners = this.getRunListeners(args);
    	listeners.starting();
    
    	Collection exceptionReporters;
    	try {
    		ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
    		ConfigurableEnvironment environment = this.prepareEnvironment(listeners, applicationArguments);
    		this.configureIgnoreBeanInfo(environment);
    		
    		//打印banner，这里你可以自己涂鸦一下，换成自己项目的logo
    		Banner printedBanner = this.printBanner(environment);
    		
    		//创建应用上下文
    		context = this.createApplicationContext();
    		exceptionReporters = this.getSpringFactoriesInstances(SpringBootExceptionReporter.class, new Class[]{ConfigurableApplicationContext.class}, context);
    
    		//预处理上下文
    		this.prepareContext(context, environment, listeners, applicationArguments, printedBanner);
    		
    		//刷新上下文
    		this.refreshContext(context);
    		
    		//再刷新上下文
    		this.afterRefresh(context, applicationArguments);
    		
    		listeners.started(context);
    		this.callRunners(context, applicationArguments);
    	} catch (Throwable var10) {
    		
    	}
    
    	try {
    		listeners.running(context);
    		return context;
    	} catch (Throwable var9) {
    		
    	}
    }
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既然我们想知道tomcat在SpringBoot中是怎么启动的，那么run方法中，重点关注创建应用上下文（**createApplicationContext**）和刷新上下文（**refreshContext**）。

创建上下文

//创建上下文
    protected ConfigurableApplicationContext createApplicationContext() {
    	Class<?> contextClass = this.applicationContextClass;
    	if (contextClass == null) {
    		try {
    			switch(this.webApplicationType) {
    				case SERVLET:
                        //创建AnnotationConfigServletWebServerApplicationContext
    				    contextClass = Class.forName("org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext");
    					break;
    				case REACTIVE:
    					contextClass = Class.forName("org.springframework.boot.web.reactive.context.AnnotationConfigReactiveWebServerApplicationContext");
    					break;
    				default:
    					contextClass = Class.forName("org.springframework.context.annotation.AnnotationConfigApplicationContext");
    			}
    		} catch (ClassNotFoundException var3) {
    			throw new IllegalStateException("Unable create a default ApplicationContext, please specify an ApplicationContextClass", var3);
    		}
    	}
    
    	return (ConfigurableApplicationContext)BeanUtils.instantiateClass(contextClass);
    }
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这里会创建AnnotationConfigServletWebServerApplicationContext类。 而AnnotationConfigServletWebServerApplicationContext类继承了ServletWebServerApplicationContext，而这个类是最终集成了AbstractApplicationContext。

刷新上下文

//SpringApplication.java
    //刷新上下文
    private void refreshContext(ConfigurableApplicationContext context) {
    	this.refresh(context);
    	if (this.registerShutdownHook) {
    		try {
    			context.registerShutdownHook();
    		} catch (AccessControlException var3) {
    		}
    	}
    }
    
    //这里直接调用最终父类AbstractApplicationContext.refresh()方法
    protected void refresh(ApplicationContext applicationContext) {
    	((AbstractApplicationContext)applicationContext).refresh();
    }
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//AbstractApplicationContext.java
    public void refresh() throws BeansException, IllegalStateException {
    	synchronized(this.startupShutdownMonitor) {
    		this.prepareRefresh();
    		ConfigurableListableBeanFactory beanFactory = this.obtainFreshBeanFactory();
    		this.prepareBeanFactory(beanFactory);
    
    		try {
    			this.postProcessBeanFactory(beanFactory);
    			this.invokeBeanFactoryPostProcessors(beanFactory);
    			this.registerBeanPostProcessors(beanFactory);
    			this.initMessageSource();
    			this.initApplicationEventMulticaster();
    			//调用各个子类的onRefresh()方法，也就说这里要回到子类：ServletWebServerApplicationContext，调用该类的onRefresh()方法
    			this.onRefresh();
    			this.registerListeners();
    			this.finishBeanFactoryInitialization(beanFactory);
    			this.finishRefresh();
    		} catch (BeansException var9) {
    			this.destroyBeans();
    			this.cancelRefresh(var9);
    			throw var9;
    		} finally {
    			this.resetCommonCaches();
    		}
    
    	}
    }
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//ServletWebServerApplicationContext.java
    //在这个方法里看到了熟悉的面孔，this.createWebServer，神秘的面纱就要揭开了。
    protected void onRefresh() {
    	super.onRefresh();
    	try {
    		this.createWebServer();
    	} catch (Throwable var2) {
    		
    	}
    }
    
    //ServletWebServerApplicationContext.java
    //这里是创建webServer，但是还没有启动tomcat，这里是通过ServletWebServerFactory创建，那么接着看下ServletWebServerFactory
    private void createWebServer() {
    	WebServer webServer = this.webServer;
    	ServletContext servletContext = this.getServletContext();
    	if (webServer == null && servletContext == null) {
    		ServletWebServerFactory factory = this.getWebServerFactory();
    		this.webServer = factory.getWebServer(new ServletContextInitializer[]{this.getSelfInitializer()});
    	} else if (servletContext != null) {
    		try {
    			this.getSelfInitializer().onStartup(servletContext);
    		} catch (ServletException var4) {
    		
    		}
    	}
    
    	this.initPropertySources();
    }
    
    //接口
    public interface ServletWebServerFactory {
        WebServer getWebServer(ServletContextInitializer... initializers);
    }
    
    //实现
    AbstractServletWebServerFactory
    JettyServletWebServerFactory
    TomcatServletWebServerFactory
    UndertowServletWebServerFactory
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这里ServletWebServerFactory接口有4个实现类

![QQ截图20190820132505.jpg][QQ_20190820132505.jpg]

而其中我们常用的有两个：TomcatServletWebServerFactory和JettyServletWebServerFactory。

//TomcatServletWebServerFactory.java
    //这里我们使用的tomcat，所以我们查看TomcatServletWebServerFactory。到这里总算是看到了tomcat的踪迹。
    @Override
    public WebServer getWebServer(ServletContextInitializer... initializers) {
    	Tomcat tomcat = new Tomcat();
    	File baseDir = (this.baseDirectory != null) ? this.baseDirectory : createTempDir("tomcat");
    	tomcat.setBaseDir(baseDir.getAbsolutePath());
        //创建Connector对象
    	Connector connector = new Connector(this.protocol);
    	tomcat.getService().addConnector(connector);
    	customizeConnector(connector);
    	tomcat.setConnector(connector);
    	tomcat.getHost().setAutoDeploy(false);
    	configureEngine(tomcat.getEngine());
    	for (Connector additionalConnector : this.additionalTomcatConnectors) {
    		tomcat.getService().addConnector(additionalConnector);
    	}
    	prepareContext(tomcat.getHost(), initializers);
    	return getTomcatWebServer(tomcat);
    }
    
    protected TomcatWebServer getTomcatWebServer(Tomcat tomcat) {
    	return new TomcatWebServer(tomcat, getPort() >= 0);
    }
    
    //Tomcat.java
    //返回Engine容器，看到这里，如果熟悉tomcat源码的话，对engine不会感到陌生。
    public Engine getEngine() {
        Service service = getServer().findServices()[0];
        if (service.getContainer() != null) {
            return service.getContainer();
        }
        Engine engine = new StandardEngine();
        engine.setName( "Tomcat" );
        engine.setDefaultHost(hostname);
        engine.setRealm(createDefaultRealm());
        service.setContainer(engine);
        return engine;
    }
    //Engine是最高级别容器，Host是Engine的子容器，Context是Host的子容器，Wrapper是Context的子容器
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getWebServer这个方法创建了Tomcat对象，并且做了两件重要的事情：把Connector对象添加到tomcat中，configureEngine(tomcat.getEngine());            getWebServer方法返回的是TomcatWebServer。

//TomcatWebServer.java
    //这里调用构造函数实例化TomcatWebServer
    public TomcatWebServer(Tomcat tomcat, boolean autoStart) {
    	Assert.notNull(tomcat, "Tomcat Server must not be null");
    	this.tomcat = tomcat;
    	this.autoStart = autoStart;
    	initialize();
    }
    
    private void initialize() throws WebServerException {
        //在控制台会看到这句日志
    	logger.info("Tomcat initialized with port(s): " + getPortsDescription(false));
    	synchronized (this.monitor) {
    		try {
    			addInstanceIdToEngineName();
    
    			Context context = findContext();
    			context.addLifecycleListener((event) -> {
    				if (context.equals(event.getSource()) && Lifecycle.START_EVENT.equals(event.getType())) {
    					removeServiceConnectors();
    				}
    			});
    
    			//===启动tomcat服务===
    			this.tomcat.start();
    
    			rethrowDeferredStartupExceptions();
    
    			try {
    				ContextBindings.bindClassLoader(context, context.getNamingToken(), getClass().getClassLoader());
    			}
    			catch (NamingException ex) {
                    
    			}
                
                //开启阻塞非守护进程
    			startDaemonAwaitThread();
    		}
    		catch (Exception ex) {
    			stopSilently();
    			destroySilently();
    			throw new WebServerException("Unable to start embedded Tomcat", ex);
    		}
    	}
    }
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//Tomcat.java
    public void start() throws LifecycleException {
    	getServer();
    	server.start();
    }
    //这里server.start又会回到TomcatWebServer的
    public void stop() throws LifecycleException {
    	getServer();
    	server.stop();
    }
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//TomcatWebServer.java
    //启动tomcat服务
    @Override
    public void start() throws WebServerException {
    	synchronized (this.monitor) {
    		if (this.started) {
    			return;
    		}
    		try {
    			addPreviouslyRemovedConnectors();
    			Connector connector = this.tomcat.getConnector();
    			if (connector != null && this.autoStart) {
    				performDeferredLoadOnStartup();
    			}
    			checkThatConnectorsHaveStarted();
    			this.started = true;
    			//在控制台打印这句日志，如果在yml设置了上下文，这里会打印
    			logger.info("Tomcat started on port(s): " + getPortsDescription(true) + " with context path '"
    					+ getContextPath() + "'");
    		}
    		catch (ConnectorStartFailedException ex) {
    			stopSilently();
    			throw ex;
    		}
    		catch (Exception ex) {
    			throw new WebServerException("Unable to start embedded Tomcat server", ex);
    		}
    		finally {
    			Context context = findContext();
    			ContextBindings.unbindClassLoader(context, context.getNamingToken(), getClass().getClassLoader());
    		}
    	}
    }
    
    //关闭tomcat服务
    @Override
    public void stop() throws WebServerException {
    	synchronized (this.monitor) {
    		boolean wasStarted = this.started;
    		try {
    			this.started = false;
    			try {
    				stopTomcat();
    				this.tomcat.destroy();
    			}
    			catch (LifecycleException ex) {
    				
    			}
    		}
    		catch (Exception ex) {
    			throw new WebServerException("Unable to stop embedded Tomcat", ex);
    		}
    		finally {
    			if (wasStarted) {
    				containerCounter.decrementAndGet();
    			}
    		}
    	}
    }
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[QQ_20190820132505.jpg]: /images/20221024/4457b326c30d4dcbb5d8a5699eba9ff5.png