SpringBoot源码分析(二)启动原理

2019/04/10 10:10
阅读数 78

Springboot的jar启动方式,是通过IOC容器启动 带动了Web容器的启动

而Springboot的war启动方式,是通过Web容器(如Tomcat)的启动 带动了IOC容器相关的启动

一、不可不说的Web容器(如Tomcat)

不管是jar启动还是war包启动,都绕不开web容器相关。先了解这个怎么工作的,以Tomcat为例,

看看Springboot 怎么来自动装配tomcat 相关的组件?

1.1 相关类

相关包org.springframework.boot.autoconfigure.web,在springboot的自动配置包的web下(自动配置功能都在这个autoconfigure包下)。

embedded(内嵌)里面四个类一个A四B,一个:

<strong>EmbeddedWebServerFactoryCustomizerAutoConfiguration(内嵌web容器工厂自定义定制器装配类)</strong>

四个具体容器相关:

JettyWebServerFactoryCustomizer、NettyWebServerFactoryCustomizer、TomcatWebServerFactoryCustomizer、UndertowWebServerFactoryCustomizer

<strong>一个自动配置类+四个常用web容器定制器</strong>

1.2.工作流程

以Tomcat定制器切入,断点落在构造器上,启动。

总结出它的工作流程:

1.启动=》2.createWebServer=》

3.拿TomcatServletWebServerFactory(tomcatWeb容器工厂)=》

4.拿WebServerFactoryCustomizer(工厂定制器)

也就是拿工厂定制器获取工厂,再拿工厂获取web容器,这么个流程

1.3.具体工作

可以仔细看下相关工厂是如何配置创建容器运行的

TomcatServletWebServerFactory的创建Tomcat方法

	public WebServer getWebServer(ServletContextInitializer... initializers) {
		Tomcat tomcat = new Tomcat();
		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);
		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);
	}

创建Tocmat类并设置相关这些组件,应该很熟悉(以后出Tomcat源码分析)。

TomcatWebServerFactoryCustomizer的customize定制方法,通过类serverProperties配置文件设置工厂的属性

二、SpringBoot的jar启动方式

来自:

    public static void main(String[] args) {
        SpringApplication.run(StudySpringbootApplication.class, args);
    }

打开源码:

	public static ConfigurableApplicationContext run(Class<?>[] primarySources,
			String[] args) {
		return new SpringApplication(primarySources).run(args);
	}

其实两步,一步创建SpringApplication ,一步run运行。

创建类做的事情比较简单,主要包括判断web应用类型、用SpringFactories技术从 spring.factories 文件里获取ApplicationContextInitializer 对应类和ApplicationListener,最后获取当前应用的启动类的类对象。

2.1 run方法

	public ConfigurableApplicationContext run(String... args) {
        //StopWatch是记录时间的工具,为了打印那句SpringBoot启动耗时的
		StopWatch stopWatch = new StopWatch();
		stopWatch.start();
		ConfigurableApplicationContext context = null;
		Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
        //系统设置,在缺失显示屏、鼠标或者键盘时也让这个java应用相关正常工作
		configureHeadlessProperty();
        //去meta-info/spring.factories中获取SpringApplicationRunListener 监听器(事件发布监听器)
		SpringApplicationRunListeners listeners = getRunListeners(args);
        //发布容器 starting事件(for循环一个个调用,通过spring的事件多播器)
		listeners.starting();
		try {
            //封装命令行参数
			ApplicationArguments applicationArguments = new DefaultApplicationArguments(
					args);
            //准备容器环境
            //1:获取或者创建环境
            //2:把命令行参数设置到环境中
            //3:通过监听器发布环境准备事件
			ConfigurableEnvironment environment = prepareEnvironment(listeners,
					applicationArguments);
            //配置是否跳过搜索BeanInfo类,默认忽略跳过
			configureIgnoreBeanInfo(environment);
            //打印控制台那个SpringBoot图标
			Banner printedBanner = printBanner(environment);
            //根据类型(servlet或者reactive?)创建应用上下文ApplicationContext
			context = createApplicationContext();
            //到spring.factoris文件里拿springboot异常报告类的集合
			exceptionReporters = getSpringFactoriesInstances(
					SpringBootExceptionReporter.class,
					new Class[] { ConfigurableApplicationContext.class }, context);
            //准备环境
            //1:把应用上下文ApplicationContext环境设置到容器中
            //2:循环调用AppplicationInitnazlier 进行容器初始化工作
            //3:发布 容器上下文准备 完成事件
            //4:注册关于springboot特定特性的相关单例Bean
            //5:BeanDefinitionLoader加载资源源码,将启动类注入容器
            //6:发布 容器上下文加载 完毕事件
			prepareContext(context, environment, listeners, applicationArguments,
					printedBanner);
            //IOC容器refresh,见以前IOC源码分析
			refreshContext(context);
            //springboot2.x已经改成空方法,以前里面是后面的callRunners
			afterRefresh(context, applicationArguments);
            //计时(耗时统计)停止
			stopWatch.stop();
            //打印那句springboot在多少秒内启动了
			if (this.logStartupInfo) {
				new StartupInfoLogger(this.mainApplicationClass)
						.logStarted(getApplicationLog(), stopWatch);
			}
            //发布容器启动事件
			listeners.started(context);
            //运行 ApplicationRunner 和CommandLineRunner
			callRunners(context, applicationArguments);
		}
		catch (Throwable ex) {
			handleRunFailure(context, ex, exceptionReporters, listeners);
			throw new IllegalStateException(ex);
		}

		try {
            //发布容器运行事件
			listeners.running(context);
		}
		catch (Throwable ex) {
			handleRunFailure(context, ex, exceptionReporters, null);
			throw new IllegalStateException(ex);
		}
		return context;
	}

其实大多是准备、工具、事件等,最核心的还是里面的refreshContext(context);带动了IOC容器启动

2.2 refreshContext(context)

其实大部分内容在之前IOC容器源码写过,唯一的区别在于:

<strong>SpringIOC的refresh方法里的onRefresh方法是空的,而SpringBoot继承重写了这个方法!</strong>

SpringBoot的onRefresh:

	@Override
	protected void onRefresh() {
		super.onRefresh();
		try {
			createWebServer();
		}
		catch (Throwable ex) {
			throw new ApplicationContextException("Unable to start web server", ex);
		}
	}

SpringBoot里应用上下文是用的新的ServletWebServerApplicationContext类(更具体实现之一是AnnotationConfigServletWebServerApplicationContext)

这里就开始和上面说过的Web容器相关知识衔接上了,这里进行的Web容器(Tomcat)的创建运行!

createWebServer:

	private void createWebServer() {
		WebServer webServer = this.webServer;
		ServletContext servletContext = getServletContext();
		if (webServer == null && servletContext == null) {
			ServletWebServerFactory factory = getWebServerFactory();
			this.webServer = factory.getWebServer(getSelfInitializer());
		}
		else if (servletContext != null) {
			try {
				getSelfInitializer().onStartup(servletContext);
			}
			catch (ServletException ex) {
				//...
			}
		}
		initPropertySources();
	}

这里就是判断有没有Server以及环境,没有的话就获取web容器制造工厂,最后通过工厂获取Tomcat赋值。

实际上获取Tomcat创建的时候,此时构造器最后的代码就是启动,TomcatWebServer类构造器如下:

	public TomcatWebServer(Tomcat tomcat, boolean autoStart) {
		Assert.notNull(tomcat, "Tomcat Server must not be null");
		this.tomcat = tomcat;
		this.autoStart = autoStart;
		initialize();
	}

TomcatWebServer的initialize:

private void initialize() throws WebServerException {
		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();
					}
				});
				this.tomcat.start();
				rethrowDeferredStartupExceptions();
				try {
					ContextBindings.bindClassLoader(context, context.getNamingToken(),
							getClass().getClassLoader());
				}
				catch (NamingException ex) {
				}
				startDaemonAwaitThread();
			}
			catch (Exception ex) {
				stopSilently();
				throw new WebServerException("Unable to start embedded Tomcat", ex);
			}
		}
	}

<strong>最终在IOC 容器中的 org.springframework.context.support.AbstractApplicationContext的refresh 的 onReFresh方法带动了Tomcat启动 </strong>

三、SpringBoot的war包启动方式

@SpringBootApplication
public class StudySpringbootApplication extends SpringBootServletInitializer {
    @Override
    protected SpringApplicationBuilder configure(SpringApplicationBuilder builder) {
        return builder.sources(StudySpringbootApplication.class);
    }
}

<strong>Springboot的war启动方式,是通过Web容器(如Tomcat)的启动 带动了IOC容器相关的启动</strong>

3.1 Tomcat加载war

要说Tomcat怎么加载war包就不得不从servlet3.0的特性说起:

1.web应用启动,会创建当前Web应用<strong>导入jar包中的 ServletContainerInitializer类的实例</strong>

2.ServletContainerInitializer 类必须放在jar包的 META-INF/services目录下,文件名称为<strong>javax.servlet.ServletContainerInitializer </strong>

3.文件的内容指向ServletContainerInitializer实现类的全路径 4.ServletContainerInitializer实现类使用<strong>@HandlesTypes注解</strong>, 在我们<strong>应用启动的时候,加载注解指定的的类 </strong>

3.2 Spring中的ServletContainerInitializer

Spring中实现ServletContainerInitializer的类是SpringServletContainerInitializer

@HandlesTypes(WebApplicationInitializer.class)
public class SpringServletContainerInitializer implements ServletContainerInitializer {
	@Override
	public void onStartup(@Nullable Set<Class<?>> webAppInitializerClasses, ServletContext servletContext) {
		//创建保存需要加载的类的集合
		List<WebApplicationInitializer> initializers = new LinkedList<>();
        
		if (webAppInitializerClasses != null) {
			for (Class<?> waiClass : webAppInitializerClasses) {
                //判断需要加载的类不是接口不是抽象类
				if (!waiClass.isInterface() && !Modifier.isAbstract(waiClass.getModifiers()) &&
						WebApplicationInitializer.class.isAssignableFrom(waiClass)) {
					try {
                        //通过反射创建实例并且加入到集合中
						initializers.add((WebApplicationInitializer)
						ReflectionUtils.accessibleConstructor(waiClass).newInstance());
					}
					catch (Throwable ex) {
						//...
					}
				}
			}
		}

		if (initializers.isEmpty()) {
			return;
		}
		AnnotationAwareOrderComparator.sort(initializers);
        //循环调用集合中的感兴趣类对象的onstartup的方法
		for (WebApplicationInitializer initializer : initializers) {
			initializer.onStartup(servletContext);
		}
	}
}

总结:HandlesTypes指定了WebApplicationInitializer类,并在onStartup方法中,创建这些需要加载的类的实例,并且循环调用他们的onStartup方法。

3.2 工作过程

1.Tomcat启动,war包应用的jar包里找ServletContainerInitializer 文件,然后找到spring-web-5.1.2.RELEASE.jar这个jar包里的META-INF\services\javax.servlet.ServletContainerInitializer 文件指向自己实现的SpringServletContainerInitializer并执行它

2.将@HandlesTypes标注的类(WebApplicationInitializer)都传入到 onStartup()的方法中Set<Class<?>>参数中 ,通过 ReflectionUtils.accessibleConstructor(waiClass).newInstance());,为这些类创建实例

3.调用WebApplicationInitializer的onStartup方法

4.而Springboot启动类继承了SpringBootServletInitializer(实现了接口WebApplicationInitializer)

5.而我们的启动类StudySpringbootApplication没有重写onStartup,调的SpringBootServletInitializer的onStartup

6.而SpringBootServletInitializer的onStartup方法调了我们重写的configure方法,加载启动。

4.1 实战调试细节

@SpringBootApplication
public class StudySpringbootApplication extends SpringBootServletInitializer {
    @Override
    protected SpringApplicationBuilder configure(SpringApplicationBuilder builder) {
        return builder.sources(StudySpringbootApplication.class);
    }
}

可以把断点打到第六行里builder.sources,通过断点一看调用栈和代码,逻辑就全出来了:

StudySpringbootApplication.configure <<==== 父类SpringBootServletInitializer(主类继继承的这个类).createRootApplicationContext

父类SpringBootServletInitializer.createRootApplicationContext:

	protected WebApplicationContext createRootApplicationContext(
			ServletContext servletContext) {
        //创建spring应用的构建器
		SpringApplicationBuilder builder = createSpringApplicationBuilder();
		builder.main(getClass());
        //设置环境
		ApplicationContext parent = getExistingRootWebApplicationContext(servletContext);
		if (parent != null) {
			servletContext.setAttribute(
					WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, null);
			builder.initializers(new ParentContextApplicationContextInitializer(parent));
		}
		builder.initializers(
				new ServletContextApplicationContextInitializer(servletContext));
		builder.contextClass(AnnotationConfigServletWebServerApplicationContext.class);
        //调用我们自己启动类上的confiure方法 传入我们自己的主启动类
		builder = configure(builder);
		builder.listeners(new WebEnvironmentPropertySourceInitializer(servletContext));
		SpringApplication application = builder.build();
		if (application.getAllSources().isEmpty() && AnnotationUtils
				.findAnnotation(getClass(), Configuration.class) != null) {
			application.addPrimarySources(Collections.singleton(getClass()));
		}
	
		if (this.registerErrorPageFilter) {
			application.addPrimarySources(
					Collections.singleton(ErrorPageFilterConfiguration.class));
		}
        //调用我们类上的run方法
		return run(application);
	}

注意重点是 调用了自己的方法(传入主类)和 run方法 run源码:

	protected WebApplicationContext run(SpringApplication application) {
		return (WebApplicationContext) application.run();
	}

继续打开run源码:

	public ConfigurableApplicationContext run(String... args) {
		StopWatch stopWatch = new StopWatch();
		stopWatch.start();
		ConfigurableApplicationContext context = null;
		Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
		configureHeadlessProperty();
		SpringApplicationRunListeners listeners = getRunListeners(args);
		listeners.starting();
		try {
			ApplicationArguments applicationArguments = new DefaultApplicationArguments(
					args);
			ConfigurableEnvironment environment = prepareEnvironment(listeners,
					applicationArguments);
			configureIgnoreBeanInfo(environment);
			Banner printedBanner = printBanner(environment);
			context = createApplicationContext();
			exceptionReporters = getSpringFactoriesInstances(
					SpringBootExceptionReporter.class,
					new Class[] { ConfigurableApplicationContext.class }, context);
			prepareContext(context, environment, listeners, applicationArguments,
					printedBanner);
			refreshContext(context);
			afterRefresh(context, applicationArguments);
			stopWatch.stop();
			if (this.logStartupInfo) {
				new StartupInfoLogger(this.mainApplicationClass)
						.logStarted(getApplicationLog(), stopWatch);
			}
			listeners.started(context);
			callRunners(context, applicationArguments);
		}
		catch (Throwable ex) {
			handleRunFailure(context, ex, exceptionReporters, listeners);
			throw new IllegalStateException(ex);
		}

		try {
			listeners.running(context);
		}
		catch (Throwable ex) {
			handleRunFailure(context, ex, exceptionReporters, null);
			throw new IllegalStateException(ex);
		}
		return context;
	}

是不是很熟悉,和jar启动的run IOC一样!所以最终还是殊途同归,还是走了application.run()方法,走了IOC容器启动Refresh!

原文出处:https://www.cnblogs.com/chz-blogs/p/12595734.html

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