TOMCAT启动流程

TOMCAT/bin/catalina.bat（或者catalina.sh）中，指定了启动类

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TOMCAT源码工程中，打开Bootstrap.java，找到main方法

    /**
     * Main method and entry point when starting Tomcat via the provided
     * scripts.
     *
     * @param args Command line arguments to be processed
     */
    public static void main(String args[]) {

        synchronized (daemonLock) {
            if (daemon == null) {
                // Don't set daemon until init() has completed
                Bootstrap bootstrap = new Bootstrap();
                try {
                    // 初始化类加载器
                    bootstrap.init();
                } catch (Throwable t) {
                    handleThrowable(t);
                    t.printStackTrace();
                    return;
                }
                daemon = bootstrap;
            } else {
                // When running as a service the call to stop will be on a new
                // thread so make sure the correct class loader is used to
                // prevent a range of class not found exceptions.
                Thread.currentThread().setContextClassLoader(daemon.catalinaLoader);
            }
        }

        try {
            String command = "start";
            if (args.length > 0) {
                command = args[args.length - 1];
            }

            if (command.equals("startd")) {
                args[args.length - 1] = "start";
                daemon.load(args);
                daemon.start();
            } else if (command.equals("stopd")) {
                args[args.length - 1] = "stop";
                daemon.stop();
            } else if (command.equals("start")) {
                daemon.setAwait(true);
                daemon.load(args);

                // 调用org.apache.catalina.startup.Catalina.start()
                daemon.start();
                if (null == daemon.getServer()) {
                    System.exit(1);
                }
            } else if (command.equals("stop")) {
                daemon.stopServer(args);
            } else if (command.equals("configtest")) {
                daemon.load(args);
                if (null == daemon.getServer()) {
                    System.exit(1);
                }
                System.exit(0);
            } else {
                log.warn("Bootstrap: command \"" + command + "\" does not exist.");
            }
        } catch (Throwable t) {
            // Unwrap the Exception for clearer error reporting
            if (t instanceof InvocationTargetException &&
                    t.getCause() != null) {
                t = t.getCause();
            }
            handleThrowable(t);
            t.printStackTrace();
            System.exit(1);
        }
    }

Bootstrap.init方法：

    /**
     * Initialize daemon.
     * @throws Exception Fatal initialization error
     */
    public void init() throws Exception {
        // 初始化classLoader
        initClassLoaders();

        Thread.currentThread().setContextClassLoader(catalinaLoader);

        SecurityClassLoad.securityClassLoad(catalinaLoader);

        // Load our startup class and call its process() method
        if (log.isDebugEnabled()) {
            log.debug("Loading startup class");
        }
        Class<?> startupClass = catalinaLoader.loadClass("org.apache.catalina.startup.Catalina");
        Object startupInstance = startupClass.getConstructor().newInstance();

        // Set the shared extensions class loader
        if (log.isDebugEnabled()) {
            log.debug("Setting startup class properties");
        }
        String methodName = "setParentClassLoader";
        Class<?> paramTypes[] = new Class[1];
        paramTypes[0] = Class.forName("java.lang.ClassLoader");
        Object paramValues[] = new Object[1];
        paramValues[0] = sharedLoader;
        Method method =
            startupInstance.getClass().getMethod(methodName, paramTypes);
        method.invoke(startupInstance, paramValues);

        catalinaDaemon = startupInstance;
    }

初始化类加载器，
创建Catalina实例，并赋值给catalinaDeamon, 将bootstrap实例赋值给deamon,后续对deamon调用了start方法，所以此处实质上执行的的是bootstrap.start()。
Bootstrap.java中start方法

/**
     * Start the Catalina daemon.
     * @throws Exception Fatal start error
     */
    public void start() throws Exception {
        if (catalinaDaemon == null) {
            init();
        }

        Method method = catalinaDaemon.getClass().getMethod("start", (Class [])null);
        method.invoke(catalinaDaemon, (Object [])null);
    }

bootstrap start方法实质上调用了Catalina的start方法

Catalina中start方法调用自身load方法开始初始化流程：
创建了StandardServer,通过Digester解析配置文件conf/server.xml,然后调用server.initInternal方法
server.initInternal中调用了service的init,
service.initInternal中调用了engine,executor,listener,connector的init
connector.initInternal中创建乐CoyoteAdapter，调用了protocolHanlder的init
AbstractProtocol.init中调用了endpoint的init,
Endpoint.init中创建Socket等

catalina start中执行完load, 会调用server.start开始启动流程：
Service.startInternal调用了service.start调用了engine,executor,listener,connector的start
Connector.startInternal调用protocolHandler的start
ProtocolHandler.startInternal调用了endpoint的start
endpoint中创建线程来监听请求