springboot web - 启动(4) tomcat

2020-02-21 16:04:30来源：博客园阅读 ()

springboot web - 启动(4) tomcat

接第二篇

第二篇里面, 看到容器创建的是 AnnotationConfigServletWebServerApplicationContext 类型.

一 .类图

二. 构造

public GenericApplicationContext() {
　　//创建 bean 工厂
    this.beanFactory = new DefaultListableBeanFactory();
}

public AnnotationConfigServletWebServerApplicationContext() {
　　//创建读取器
    this.reader = new AnnotatedBeanDefinitionReader(this);
　　//创建扫描器
    this.scanner = new ClassPathBeanDefinitionScanner(this);
}

构造函数中, 创建了三个类, 并赋值给相应的属性.

三. 启动 tomcat

@Override
public void refresh() throws BeansException, IllegalStateException {
    synchronized (this.startupShutdownMonitor) {
        // Prepare this context for refreshing.
        prepareRefresh();

        // Tell the subclass to refresh the internal bean factory.
        ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

        // Prepare the bean factory for use in this context.
        prepareBeanFactory(beanFactory);

        try {
            // Allows post-processing of the bean factory in context subclasses.
            postProcessBeanFactory(beanFactory);

            // Invoke factory processors registered as beans in the context.
            invokeBeanFactoryPostProcessors(beanFactory);

            // Register bean processors that intercept bean creation.
            registerBeanPostProcessors(beanFactory);

            // Initialize message source for this context.
            initMessageSource();

            // Initialize event multicaster for this context.
            initApplicationEventMulticaster();

            // Initialize other special beans in specific context subclasses.
            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();
        }
    }
}

这里我主要是想要了解tomcat启动, 所以一些方法, 就先不看.

onRefresh() 方法执行的是 ServletWebServerApplicationContext 的方法.

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

createWebServer() 方法中, 会创建 Tomcat 类.

private void createWebServer() {
    WebServer webServer = this.webServer;
　　//当前进来, servletContext 为null
    ServletContext servletContext = getServletContext();
    if (webServer == null && servletContext == null) {
　　　　 //创建了 TomcatServletWebServerFactory 类
        ServletWebServerFactory factory = getWebServerFactory();
　　　　 //创建 Tomcat
        this.webServer = factory.getWebServer(getSelfInitializer());
    }
    else if (servletContext != null) {
        try {
            getSelfInitializer().onStartup(servletContext);
        }
        catch (ServletException ex) {
            throw new ApplicationContextException("Cannot initialize servlet context",
                    ex);
        }
    }
    initPropertySources();
}

getWebServer方法里面, 就创建了 Tomcat 类, 并对其进行一些配置操作.

@Override
public WebServer getWebServer(ServletContextInitializer... initializers) {
　　//创建 Tomcat 
    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);
　　//这里会创建 TomcatWebServer 实例, 并返回
    return getTomcatWebServer(tomcat);
}

这里的 protocol 是有一个默认值的:

public static final String DEFAULT_PROTOCOL = "org.apache.coyote.http11.Http11NioProtocol";

private String protocol = DEFAULT_PROTOCOL;

可以看到, 这里默认使用的是 同步非阻塞io协议


getTomcatWebServer()

protected TomcatWebServer getTomcatWebServer(Tomcat tomcat) {
    return new TomcatWebServer(tomcat, getPort() >= 0);
}

在创建 TomcatWebServer 的时候, 就会启动 Tomcat

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 {
    TomcatWebServer.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())) {
                    // Remove service connectors so that protocol binding doesn't
                    // happen when the service is started.
                    removeServiceConnectors();
                }
            });

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

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

            try {
                ContextBindings.bindClassLoader(context, context.getNamingToken(),
                        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) {
            stopSilently();
            throw new WebServerException("Unable to start embedded Tomcat", ex);
        }
    }
}