static {
        // Will always be non-null
        // 获取tomcat路径
        String userDir = System.getProperty("user.dir");

        // Home first
        // CATALINA_HOME_PROP=catalina.home
        String home = System.getProperty(Globals.CATALINA_HOME_PROP);
        File homeFile = null;

        if (home != null) {
            File f = new File(home);
            try {
                homeFile = f.getCanonicalFile();
            } catch (IOException ioe) {
                homeFile = f.getAbsoluteFile();
            }
        }

        // 第一次失败 先检查当前目录是否是在bin目录下
        if (homeFile == null) {
            // First fall-back. See if current directory is a bin directory
            // in a normal Tomcat install
            File bootstrapJar = new File(userDir, "bootstrap.jar");

            // 如果是在bin目录下，则去到上一级，并获取他的绝对路径
            if (bootstrapJar.exists()) {
                File f = new File(userDir, "..");
                try {
                    homeFile = f.getCanonicalFile();
                } catch (IOException ioe) {
                    homeFile = f.getAbsoluteFile();
                }
            }
        }

        // 第二次失败 直接使用当前路径
        if (homeFile == null) {
            // Second fall-back. Use current directory
            File f = new File(userDir);
            try {
                homeFile = f.getCanonicalFile();
            } catch (IOException ioe) {
                homeFile = f.getAbsoluteFile();
            }
        }

        // 将tomcat路径赋值到System中，供其他类调用
        catalinaHomeFile = homeFile;
        System.setProperty(
                Globals.CATALINA_HOME_PROP, catalinaHomeFile.getPath());

        // catalina.base路径，如果从脚本中获取为null
        // 则直接将catalina.home属性赋值给catalina.base
        String base = System.getProperty(Globals.CATALINA_BASE_PROP);
        if (base == null) {
            catalinaBaseFile = catalinaHomeFile;
        } else {
            File baseFile = new File(base);
            try {
                baseFile = baseFile.getCanonicalFile();
            } catch (IOException ioe) {
                baseFile = baseFile.getAbsoluteFile();
            }
            catalinaBaseFile = baseFile;
        }
        
        // 并保存到System属性中
        System.setProperty(
                Globals.CATALINA_BASE_PROP, catalinaBaseFile.getPath());
    }

public static void main(String args[]) {
        // 锁住当前实例 daemonLock是一个final static的Object对象
        synchronized (daemonLock) {
            // 线程安全的Bootstrap所持有的实例
            if (daemon == null) {
                // Don't set daemon until init() has completed
                Bootstrap bootstrap = new Bootstrap();
                try {
                    // 初始化ClassLoader
                    // 使用反射机制调用Catalina类中的setParentClassLoader方法将ClassLoader注入
                    bootstrap.init();
                } catch (Throwable t) {
                    handleThrowable(t);
                    t.printStackTrace();
                    return;
                }
                daemon = bootstrap;
            } else {
                 // 设置Catalina的ClassLoader到当前线程的上线文类加载器中
                 Thread.currentThread().setContextClassLoader(daemon.catalinaLoader);
            }
        }

        try {
            // 默认command为start，以防止没有传入action的参数
            String command = "start";
            if (args.length > 0) {
                // 从脚本中获取传来的action
                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")) {
                // 以下的三个方法全是反射调用的catalina
                // 调用catalina的setAwait方法，用于阻塞Server
                daemon.setAwait(true);
                // 使用Digester初始化容器实例，并执行容器的init
                daemon.load(args);
                // 启动容器
                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);
        }
    }