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.

1. onRefresh()

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. 需要注意的是, 在 new Connector() 的时候对 Http11NioProtocol 进行了反射实例化.

public Http11NioProtocol() {
    super(new NioEndpoint());
}

在实例化的时候, new 了一个 NioEndpoint. 这个东西很重要, 后面会看到.


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);
        }
    }
}

2. finishRefresh()

ServletWebServerApplicationContext 重写了该方法.

@Override
protected void finishRefresh() {
　　//调用父类的 finishedRefresh 方法, 保证处理完整性
    super.finishRefresh();
　　//启动 TomcatWebServer
    WebServer webServer = startWebServer();
    if (webServer != null) {
        publishEvent(new ServletWebServerInitializedEvent(webServer, this));
    }
}

startWebServer()

private WebServer startWebServer() {
    WebServer webServer = this.webServer;
    if (webServer != null) {
        webServer.start();
    }
    return webServer;
}

@Override
public void start() throws WebServerException {
    synchronized (this.monitor) {
        if (this.started) {
            return;
        }
        try {
　　　　　　　//遍历service, 拿到service, 然后绑定 Connector
            addPreviouslyRemovedConnectors();
            Connector connector = this.tomcat.getConnector();
            if (connector != null && this.autoStart) {
                performDeferredLoadOnStartup();
            }
            checkThatConnectorsHaveStarted();
            this.started = true;
            TomcatWebServer.logger
                    .info("Tomcat started on port(s): " + getPortsDescription(true)
                            + " with context path '" + getContextPath() + "'");
      ......
}

addPreviouslyRemovedConnectors()

private void addPreviouslyRemovedConnectors() {
    Service[] services = this.tomcat.getServer().findServices();
    for (Service service : services) {
        Connector[] connectors = this.serviceConnectors.get(service);
        if (connectors != null) {
            for (Connector connector : connectors) {
                service.addConnector(connector);
                if (!this.autoStart) {
                    stopProtocolHandler(connector);
                }
            }
            this.serviceConnectors.remove(service);
        }
    }
}

service 在绑定 Connector 的时候, 会启动 Connector

 @Override
public void addConnector(Connector connector) {

    synchronized (connectorsLock) {
        connector.setService(this);
        Connector results[] = new Connector[connectors.length + 1];
        System.arraycopy(connectors, 0, results, 0, connectors.length);
        results[connectors.length] = connector;
        connectors = results;

        if (getState().isAvailable()) {
            try {
                connector.start();
            } catch (LifecycleException e) {
                log.error(sm.getString(
                        "standardService.connector.startFailed",
                        connector), e);
            }
        }

        // Report this property change to interested listeners
        support.firePropertyChange("connector", null, connector);
    }
}

看一下 connector.start() 方法.

@Override
public final synchronized void start() throws LifecycleException {

   ......try {
        setStateInternal(LifecycleState.STARTING_PREP, null, false);
        startInternal();
        if (state.equals(LifecycleState.FAILED)) {
            // This is a 'controlled' failure. The component put itself into the
            // FAILED state so call stop() to complete the clean-up.
            stop();
        } else if (!state.equals(LifecycleState.STARTING)) {
            // Shouldn't be necessary but acts as a check that sub-classes are
            // doing what they are supposed to.
            invalidTransition(Lifecycle.AFTER_START_EVENT);
        } else {
            setStateInternal(LifecycleState.STARTED, null, false);
        }
    } catch (Throwable t) {
        // This is an 'uncontrolled' failure so put the component into the
        // FAILED state and throw an exception.
        ExceptionUtils.handleThrowable(t);
        setStateInternal(LifecycleState.FAILED, null, false);
        throw new LifecycleException(sm.getString("lifecycleBase.startFail", toString()), t);
    }
}

startInternal() 是一个抽象方法, 其中的一个实现类 Connector

@Override
protected void startInternal() throws LifecycleException {
    // Validate settings before starting
    if (getPort() < 0) {
        throw new LifecycleException(sm.getString(
                "coyoteConnector.invalidPort", Integer.valueOf(getPort())));
    }
    setState(LifecycleState.STARTING);
    try {
        protocolHandler.start();
    } catch (Exception e) {
        throw new LifecycleException(
                sm.getString("coyoteConnector.protocolHandlerStartFailed"), e);
    }
}

接着进 start() 方法

@Override
public void start() throws Exception {
    if (getLog().isInfoEnabled()) {
        getLog().info(sm.getString("abstractProtocolHandler.start", getName()));
    }

    endpoint.start();

    // Start async timeout thread
    asyncTimeout = new AsyncTimeout();
    Thread timeoutThread = new Thread(asyncTimeout, getNameInternal() + "-AsyncTimeout");
    int priority = endpoint.getThreadPriority();
    if (priority < Thread.MIN_PRIORITY || priority > Thread.MAX_PRIORITY) {
        priority = Thread.NORM_PRIORITY;
    }
    timeoutThread.setPriority(priority);
    timeoutThread.setDaemon(true);
    timeoutThread.start();
}

endPoint.start() 方法:

public final void start() throws Exception {
    if (bindState == BindState.UNBOUND) {
        bind();
        bindState = BindState.BOUND_ON_START;
    }
    startInternal();
}

这个bind() 执行的是NioEndpoint 中的方法, 进行端口绑定监听.

 @Override
public void bind() throws Exception {

    serverSock = ServerSocketChannel.open();
    socketProperties.setProperties(serverSock.socket());
    InetSocketAddress addr = (getAddress()!=null?new InetSocketAddress(getAddress(),getPort()):new InetSocketAddress(getPort()));
    serverSock.socket().bind(addr,getAcceptCount());
    serverSock.configureBlocking(true); //mimic APR behavior

    // Initialize thread count defaults for acceptor, poller
    if (acceptorThreadCount == 0) {
        // FIXME: Doesn't seem to work that well with multiple accept threads
        acceptorThreadCount = 1;
    }
    if (pollerThreadCount <= 0) {
        //minimum one poller thread
        pollerThreadCount = 1;
    }
    setStopLatch(new CountDownLatch(pollerThreadCount));

    // Initialize SSL if needed
    initialiseSsl();

    selectorPool.open();
}

总结:

从执行流程上来看,

1. 在onRefresh() 中, 启动Tomcat

2. 在 finishBeanFactoryInitialization() 中进行了后台方法的路由映射(待续)

3. 在finishRefresh()中进行了端口绑定监听