Tomcat - 启动过程：初始化和启动流程

Bootstrap主入口？

Tomcat源码就从它的main方法开始。Tomcat的main方法在org.apache.catalina.startup.Bootstrap 里。如下代码我们就是创建一个 Bootstrap 对象，调用它的 init 方法初始化，然后根据启动参数，分别调用 Bootstrap 对象的不同方法。

php 复制代码

    /**
     * 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) {
//        创建一个Bootstrap对象，调用它的init方法初始化
        synchronized (daemonLock) {
            if (daemon == null) {
                // Don't set daemon until init() has completed
                Bootstrap bootstrap = new Bootstrap();
                try {
                    bootstrap.init();
                } catch (Throwable t) {
                    handleThrowable(t);
                    log.error("Init exception", t);
                    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);
            }
        }

//        根据启动参数，分别调用BootStrap对象的不同方法
        try {
            String command = "start";
            if (args.length > 0) {
                command = args[args.length - 1];
            }

            switch (command) {
                case "startd":
                    args[args.length - 1] = "start";
                    daemon.load(args);
                    daemon.start();
                    break;
                case "stopd":
                    args[args.length - 1] = "stop";
                    daemon.stop();
                    break;
                case "start":
                    daemon.setAwait(true);
                    daemon.load(args);
                    daemon.start();
                    if (null == daemon.getServer()) {
                        System.exit(1);
                    }
                    break;
                case "stop":
                    daemon.stopServer(args);
                    break;
                case "configtest":
                    daemon.load(args);
                    if (null == daemon.getServer()) {
                        System.exit(1);
                    }
                    System.exit(0);
                    break;
                default:
                    log.warn("Bootstrap: command "" + command + "" does not exist.");
                    break;
            }
        } catch (Throwable t) {
            // Unwrap the Exception for clearer error reporting
            Throwable throwable = t;
            if (throwable instanceof InvocationTargetException && throwable.getCause() != null) {
                throwable = throwable.getCause();
            }
            handleThrowable(throwable);
            log.error("Error running command", throwable);
            System.exit(1);
        }
    }

Catalina是如何初始化的

ini 复制代码

 /**
     * Initialize daemon.
     * 初始化守护进程
     *
     * @throws Exception Fatal initialization error
     */
    public void init() throws Exception {

//        初始化classloader(包括catalinaLoader）
        initClassLoaders();

//        设置当前的线程的contextClassLoader为catalinaLoader
        Thread.currentThread().setContextClassLoader(catalinaLoader);

        // 通过catalinaLoader加载Catalina，并初始化startupInstance 对象
        // Load our startup class and call its process() method
        if (log.isTraceEnabled()) {
            log.trace("Loading startup class");
        }
        Class<?> startupClass = catalinaLoader.loadClass("org.apache.catalina.startup.Catalina");
        Object startupInstance = startupClass.getConstructor().newInstance();

        // 通过反射调用了setParentClassLoader 方法
        // Set the shared extensions class loader
        if (log.isTraceEnabled()) {
            log.trace("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;
    }