1. Service

public interface Service extends Lifecycle {

    // ------------------------------------------------------------- Properties
    public Engine getContainer();
    public void setContainer(Engine engine);

    public String getName();
    public void setName(String name);

    public Server getServer();
    public void setServer(Server server);

    public ClassLoader getParentClassLoader();
    public void setParentClassLoader(ClassLoader parent);

    public String getDomain();
    
    // --------------------------------------------------------- Public Methods
    public void addConnector(Connector connector);
    public Connector[] findConnectors();
    public void removeConnector(Connector connector);

    public void addExecutor(Executor ex);
    public Executor[] findExecutors();
    public Executor getExecutor(String name);
    public void removeExecutor(Executor ex);

    Mapper getMapper();
}

2. StandardService

StandardService是Service的实现类。
StandardService中关于Tomcat启动过程中重要的方法是initInternal()、startInternal()：

initInternal()：

protected void initInternal() throws LifecycleException {

    super.initInternal();

	// Engine init
    if (engine != null) {
        engine.init();
    }

    // Executor init
    for (Executor executor : findExecutors()) {
        if (executor instanceof JmxEnabled) {
            ((JmxEnabled) executor).setDomain(getDomain());
        }
        executor.init();
    }

    // MapperListener init
    mapperListener.init();

    // Connector init
    synchronized (connectorsLock) {
        for (Connector connector : connectors) {
            try {
                connector.init();
            } catch (Exception e) {
                String message = sm.getString("standardService.connector.initFailed", connector);
                log.error(message, e);
                if (Boolean.getBoolean("org.apache.catalina.startup.EXIT_ON_INIT_FAILURE"))
                    throw new LifecycleException(message);
            }
        }
    }
}

startInternal()：

protected void startInternal() throws LifecycleException {

    if(log.isInfoEnabled())
        log.info(sm.getString("standardService.start.name", this.name));
    setState(LifecycleState.STARTING);

    // Engine start
    if (engine != null) {
        synchronized (engine) {
            engine.start();
        }
    }
    
    // Executor start
    synchronized (executors) {
        for (Executor executor: executors) {
            executor.start();
        }
    }
    // MapperListener start
    mapperListener.start();

    // Connector start
    synchronized (connectorsLock) {
        for (Connector connector: connectors) {
            try {
                // If it has already failed, don't try and start it
                if (connector.getState() != LifecycleState.FAILED) {
                    connector.start();
                }
            } catch (Exception e) {
                log.error(sm.getString("standardService.connector.startFailed", connector), e);
            }
        }
    }
}