SpringBoot 源码解析 （六）----- Spring Boot的核心能力 - 内置Servlet容器源码分析（Tomcat）

<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-web</artifactId>
</dependency>

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
    <exclusions>
        <exclusion>
            <!--移除spring-boot-starter-web中的tomcat-->
            <artifactId>spring-boot-starter-tomcat</artifactId>
            <groupId>org.springframework.boot</groupId>
        </exclusion>
    </exclusions>
</dependency>

<dependency>
    <groupId>org.springframework.boot</groupId>
    <!--引入jetty-->
    <artifactId>spring-boot-starter-jetty</artifactId>
</dependency>

@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@Configuration
@ConditionalOnWebApplication// 在Web环境下才会起作用
@Import(BeanPostProcessorsRegistrar.class)// 会Import一个内部类BeanPostProcessorsRegistrar
public class EmbeddedServletContainerAutoConfiguration {

    @Configuration
    // Tomcat类和Servlet类必须在classloader中存在
    // 文章开头我们已经导入了web的starter，其中包含tomcat和SpringMvc
    // 那么classPath下会存在Tomcat.class和Servlet.class
    @ConditionalOnClass({ Servlet.class, Tomcat.class })
    // 当前Spring容器中不存在EmbeddedServletContainerFactory类型的实例
    @ConditionalOnMissingBean(value = EmbeddedServletContainerFactory.class, search = SearchStrategy.CURRENT)
    public static class EmbeddedTomcat {

        @Bean
        public TomcatEmbeddedServletContainerFactory tomcatEmbeddedServletContainerFactory() {
            // 上述条件注解成立的话就会构造TomcatEmbeddedServletContainerFactory这个EmbeddedServletContainerFactory
            return new TomcatEmbeddedServletContainerFactory();
        }
    }
    
    @Configuration
    @ConditionalOnClass({ Servlet.class, Server.class, Loader.class,
            WebAppContext.class })
    @ConditionalOnMissingBean(value = EmbeddedServletContainerFactory.class, search = SearchStrategy.CURRENT)
    public static class EmbeddedJetty {

        @Bean
        public JettyEmbeddedServletContainerFactory jettyEmbeddedServletContainerFactory() {
            return new JettyEmbeddedServletContainerFactory();
        }

    }
    
    @Configuration
    @ConditionalOnClass({ Servlet.class, Undertow.class, SslClientAuthMode.class })
    @ConditionalOnMissingBean(value = EmbeddedServletContainerFactory.class, search = SearchStrategy.CURRENT)
    public static class EmbeddedUndertow {

        @Bean
        public UndertowEmbeddedServletContainerFactory undertowEmbeddedServletContainerFactory() {
            return new UndertowEmbeddedServletContainerFactory();
        }

    }
    
    //other code...
}

public interface EmbeddedServletContainerFactory {

    EmbeddedServletContainer getEmbeddedServletContainer( ServletContextInitializer... initializers);
}

public class TomcatEmbeddedServletContainerFactory extends AbstractEmbeddedServletContainerFactory implements ResourceLoaderAware {
    
    //other code...
    
    @Override
    public EmbeddedServletContainer getEmbeddedServletContainer( ServletContextInitializer... initializers) {
        //创建一个Tomcat
        Tomcat tomcat = new Tomcat();
        
       //配置Tomcat的基本环节
        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);
        
        //包装tomcat对象，返回一个嵌入式Tomcat容器，内部会启动该tomcat容器
        return getTomcatEmbeddedServletContainer(tomcat);
    }
}

protected TomcatEmbeddedServletContainer getTomcatEmbeddedServletContainer(
    Tomcat tomcat) {
    return new TomcatEmbeddedServletContainer(tomcat, getPort() >= 0);
}

public class TomcatEmbeddedServletContainer implements EmbeddedServletContainer {

    public TomcatEmbeddedServletContainer(Tomcat tomcat, boolean autoStart) {
        Assert.notNull(tomcat, "Tomcat Server must not be null");
        this.tomcat = tomcat;
        this.autoStart = autoStart;
        
        //初始化嵌入式Tomcat容器，并启动Tomcat
        initialize();
    }
    
    private void initialize() throws EmbeddedServletContainerException {
        TomcatEmbeddedServletContainer.logger
                .info("Tomcat initialized with port(s): " + getPortsDescription(false));
        synchronized (this.monitor) {
            try {
                addInstanceIdToEngineName();
                try {
                    final Context context = findContext();
                    context.addLifecycleListener(new LifecycleListener() {

                        @Override
                        public void lifecycleEvent(LifecycleEvent event) {
                            if (context.equals(event.getSource())
                                    && Lifecycle.START_EVENT.equals(event.getType())) {
                                // Remove service connectors so that protocol
                                // binding doesn‘t happen when the service is
                                // started.
                                removeServiceConnectors();
                            }
                        }

                    });

                    // Start the server to trigger initialization listeners
                    //启动tomcat
                    this.tomcat.start();

                    // We can re-throw failure exception directly in the main thread
                    rethrowDeferredStartupExceptions();

                    try {
                        ContextBindings.bindClassLoader(context, getNamingToken(context),
                                getClass().getClassLoader());
                    }
                    catch (NamingException ex) {
                        // Naming is not enabled. Continue
                    }

                    // Unlike Jetty, all Tomcat threads are daemon threads. We create a
                    // blocking non-daemon to stop immediate shutdown
                    startDaemonAwaitThread();
                }
                catch (Exception ex) {
                    containerCounter.decrementAndGet();
                    throw ex;
                }
            }
            catch (Exception ex) {
                stopSilently();
                throw new EmbeddedServletContainerException(
                        "Unable to start embedded Tomcat", ex);
            }
        }
    }
}

public ConfigurableApplicationContext run(String... args) {
    // 计时工具
    StopWatch stopWatch = new StopWatch();
    stopWatch.start();

    ConfigurableApplicationContext context = null;
    Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();

    configureHeadlessProperty();

    // 第一步：获取并启动监听器
    SpringApplicationRunListeners listeners = getRunListeners(args);
    listeners.starting();
    
    try {
        ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);

        // 第二步：根据SpringApplicationRunListeners以及参数来准备环境
        ConfigurableEnvironment environment = prepareEnvironment(listeners,applicationArguments);
        configureIgnoreBeanInfo(environment);

        // 准备Banner打印器 - 就是启动Spring Boot的时候打印在console上的ASCII艺术字体
        Banner printedBanner = printBanner(environment);

        // 第三步：创建Spring容器
        context = createApplicationContext();

        exceptionReporters = getSpringFactoriesInstances(
                SpringBootExceptionReporter.class,
                new Class[] { ConfigurableApplicationContext.class }, context);

        // 第四步：Spring容器前置处理
        prepareContext(context, environment, listeners, applicationArguments,printedBanner);

        // 第五步：刷新容器
        refreshContext(context);

　　　　 // 第六步：Spring容器后置处理
        afterRefresh(context, applicationArguments);

  　　　 // 第七步：发出结束执行的事件
        listeners.started(context);
        // 第八步：执行Runners
        this.callRunners(context, applicationArguments);
        stopWatch.stop();
        // 返回容器
        return context;
    }
    catch (Throwable ex) {
        handleRunFailure(context, listeners, exceptionReporters, ex);
        throw new IllegalStateException(ex);
    }
}

public static final String DEFAULT_CONTEXT_CLASS = "org.springframework.context."
            + "annotation.AnnotationConfigApplicationContext";

public static final String DEFAULT_WEB_CONTEXT_CLASS = "org.springframework."
            + "boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext";

protected ConfigurableApplicationContext createApplicationContext() {
    Class<?> contextClass = this.applicationContextClass;
    if (contextClass == null) {
        try {
            //根据应用环境，创建不同的IOC容器
            contextClass = Class.forName(this.webEnvironment
                                         ? DEFAULT_WEB_CONTEXT_CLASS : DEFAULT_CONTEXT_CLASS);
        }
    }
    return (ConfigurableApplicationContext) BeanUtils.instantiate(contextClass);
}

 1 public void refresh() throws BeansException, IllegalStateException {
 2     synchronized (this.startupShutdownMonitor) {
 3         /**
 4          * 刷新上下文环境
 5          */
 6         prepareRefresh();
 7 
 8         /**
 9          * 初始化BeanFactory，解析XML，相当于之前的XmlBeanFactory的操作，
10          */
11         ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
12 
13         /**
14          * 为上下文准备BeanFactory，即对BeanFactory的各种功能进行填充，如常用的注解@Autowired @Qualifier等
15          * 添加ApplicationContextAwareProcessor处理器
16          * 在依赖注入忽略实现*Aware的接口，如EnvironmentAware、ApplicationEventPublisherAware等
17          * 注册依赖，如一个bean的属性中含有ApplicationEventPublisher(beanFactory)，则会将beanFactory的实例注入进去
18          */
19         prepareBeanFactory(beanFactory);
20 
21         try {
22             /**
23              * 提供子类覆盖的额外处理，即子类处理自定义的BeanFactoryPostProcess
24              */
25             postProcessBeanFactory(beanFactory);
26 
27             /**
28              * 激活各种BeanFactory处理器,包括BeanDefinitionRegistryBeanFactoryPostProcessor和普通的BeanFactoryPostProcessor
29              * 执行对应的postProcessBeanDefinitionRegistry方法 和  postProcessBeanFactory方法
30              */
31             invokeBeanFactoryPostProcessors(beanFactory);
32 
33             /**
34              * 注册拦截Bean创建的Bean处理器，即注册BeanPostProcessor，不是BeanFactoryPostProcessor，注意两者的区别
35              * 注意，这里仅仅是注册，并不会执行对应的方法，将在bean的实例化时执行对应的方法
36              */
37             registerBeanPostProcessors(beanFactory);
38 
39             /**
40              * 初始化上下文中的资源文件，如国际化文件的处理等
41              */
42             initMessageSource();
43 
44             /**
45              * 初始化上下文事件广播器，并放入applicatioEventMulticaster,如ApplicationEventPublisher
46              */
47             initApplicationEventMulticaster();
48 
49             /**
50              * 给子类扩展初始化其他Bean
51              */
52             onRefresh();
53 
54             /**
55              * 在所有bean中查找listener bean，然后注册到广播器中
56              */
57             registerListeners();
58 
59             /**
60              * 设置转换器
61              * 注册一个默认的属性值解析器
62              * 冻结所有的bean定义，说明注册的bean定义将不能被修改或进一步的处理
63              * 初始化剩余的非惰性的bean，即初始化非延迟加载的bean
64              */
65             finishBeanFactoryInitialization(beanFactory);
66 
67             /**
68              * 通过spring的事件发布机制发布ContextRefreshedEvent事件，以保证对应的监听器做进一步的处理
69              * 即对那种在spring启动后需要处理的一些类，这些类实现了ApplicationListener<ContextRefreshedEvent>，
70              * 这里就是要触发这些类的执行(执行onApplicationEvent方法)
71              * spring的内置Event有ContextClosedEvent、ContextRefreshedEvent、ContextStartedEvent、ContextStoppedEvent、RequestHandleEvent
72              * 完成初始化，通知生命周期处理器lifeCycleProcessor刷新过程，同时发出ContextRefreshEvent通知其他人
73              */
74             finishRefresh();
75         }
76 
77         finally {
78     
79             resetCommonCaches();
80         }
81     }
82 }

protected void onRefresh() throws BeansException {

}

public class AnnotationConfigEmbeddedWebApplicationContext extends EmbeddedWebApplicationContext {

@Override
protected void onRefresh() {
    super.onRefresh();
    try {
        //核心方法：会获取嵌入式的Servlet容器工厂，并通过工厂来获取Servlet容器
        createEmbeddedServletContainer();
    }
    catch (Throwable ex) {
        throw new ApplicationContextException("Unable to start embedded container", ex);
    }
}

 1 private void createEmbeddedServletContainer() {
 2     EmbeddedServletContainer localContainer = this.embeddedServletContainer;
 3     ServletContext localServletContext = getServletContext();
 4     if (localContainer == null && localServletContext == null) {
 5         //先获取嵌入式Servlet容器工厂
 6         EmbeddedServletContainerFactory containerFactory = getEmbeddedServletContainerFactory();
 7         //根据容器工厂来获取对应的嵌入式Servlet容器
 8         this.embeddedServletContainer = containerFactory.getEmbeddedServletContainer(getSelfInitializer());
 9     }
10     else if (localServletContext != null) {
11         try {
12             getSelfInitializer().onStartup(localServletContext);
13         }
14         catch (ServletException ex) {
15             throw new ApplicationContextException("Cannot initialize servlet context",ex);
16         }
17     }
18     initPropertySources();
19 }

protected EmbeddedServletContainerFactory getEmbeddedServletContainerFactory() {
    //从Spring的IOC容器中获取EmbeddedServletContainerFactory.class类型的Bean
    String[] beanNames = getBeanFactory().getBeanNamesForType(EmbeddedServletContainerFactory.class);
    //调用getBean实例化EmbeddedServletContainerFactory.class
    return getBeanFactory().getBean(beanNames[0], EmbeddedServletContainerFactory.class);
}

private ServletContextInitializer getSelfInitializer() {
    //创建一个ServletContextInitializer对象，并重写onStartup方法，很明显是一个回调方法
    return new ServletContextInitializer() {
        public void onStartup(ServletContext servletContext) throws ServletException {
            EmbeddedWebApplicationContext.this.selfInitialize(servletContext);
        }
    };
}