tomcat源码分析

tomcat整体架构

Server：代表整个服务，也可以理解为tomcat。
service:代表一个服务，它将若干个connector和contain连接起来。
connector：连接器，处理用户的web请求，支持三种协议：
AJP
HTTP
HTTPS

Container：容器，可以看做servelet容器。
engine：servelet引擎，一个container只能有一个engine，engine也可以看做是container本身。
host：虚拟主机，比如www.baidu.com，localhost，一个engine可以有多个host。
context：代表一个应用，比如订单服务order，url就为localhost/order,用户服务user，url就为localhost/user。一个host可以有多个context
Wrapper：servelet，比如订单信息，url就为localhost/order/detail/1，一个context可以有多个wrapper。

从配置文件server.xml更能感受分层结构：

tomcat初始化流程

启动流程：
BootStrap.main->
BootStrap.load->Catalina.load->Server.init->Service.init->engine.init->connector.init->

BootStrap.start->Server.start->service-start->engine.start->host.start（被engine异步启动）->context.start(被host异步启动)->connector.start

可以看到，主要分两步BootStrap的load和start方法，这两个方法里都是逐级调用下一级的init或start方法。

从我们启动tomcat的命令：./start.sh 入手：

#!/bin/sh

# Licensed to the Apache Software Foundation (ASF) under one or more
# contributor license agreements.  See the NOTICE file distributed with
# this work for additional information regarding copyright ownership.
# The ASF licenses this file to You under the Apache License, Version 2.0
# (the "License"); you may not use this file except in compliance with
# the License.  You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

# -----------------------------------------------------------------------------
# Start Script for the CATALINA Server
# -----------------------------------------------------------------------------

# Better OS/400 detection: see Bugzilla 31132
os400=false
case "`uname`" in
OS400*) os400=true;;
esac

# resolve links - $0 may be a softlink
PRG="$0"

while [ -h "$PRG" ] ; do
  ls=`ls -ld "$PRG"`
  link=`expr "$ls" : '.*-> \(.*\)$'`
  if expr "$link" : '/.*' > /dev/null; then
    PRG="$link"
  else
    PRG=`dirname "$PRG"`/"$link"
  fi
done

PRGDIR=`dirname "$PRG"`
#通过catalina.sh来执行
EXECUTABLE=catalina.sh

# Check that target executable exists
if $os400; then
  # -x will Only work on the os400 if the files are:
  # 1. owned by the user
  # 2. owned by the PRIMARY group of the user
  # this will not work if the user belongs in secondary groups
  eval
else
  if [ ! -x "$PRGDIR"/"$EXECUTABLE" ]; then
    echo "Cannot find $PRGDIR/$EXECUTABLE"
    echo "The file is absent or does not have execute permission"
    echo "This file is needed to run this program"
    exit 1
  fi
fi

exec "$PRGDIR"/"$EXECUTABLE" start "$@"

看看catalina.sh文件，代码太长，我们直接看启动部分：

 if [ "$1" = "-security" ] ; then
    if [ $have_tty -eq 1 ]; then
      echo "Using Security Manager"
    fi
    shift
    eval $_NOHUP "\"$_RUNJAVA\"" "\"$CATALINA_LOGGING_CONFIG\"" $LOGGING_MANAGER "$JAVA_OPTS" "$CATALINA_OPTS" \
      -D$ENDORSED_PROP="\"$JAVA_ENDORSED_DIRS\"" \
      -classpath "\"$CLASSPATH\"" \
      -Djava.security.manager \
      -Djava.security.policy=="\"$CATALINA_BASE/conf/catalina.policy\"" \
      -Dcatalina.base="\"$CATALINA_BASE\"" \
      -Dcatalina.home="\"$CATALINA_HOME\"" \
      -Djava.io.tmpdir="\"$CATALINA_TMPDIR\"" \
      # 启动Bootstrap类，并将start作为参数传进去
      org.apache.catalina.startup.Bootstrap "$@" start \
      >> "$CATALINA_OUT" 2>&1 "&"

现在进入java代码，BootStrap类：

 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Bootstrap
                    bootstrap.init();
                } catch (Throwable t) {
                    handleThrowable(t);
                    t.printStackTrace();
                    return;
                }
                // 初始化完成后再赋值给daemon
                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();
            }
            // 启动时走这里
            else if (command.equals("start")) {
                daemon.setAwait(true);
                // load并且start
                daemon.load(args);
                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);
        }
    }

首先初始化Bootstrap类，然后根据传入的参数执行不同操作，启动就是执行load和start方法，先看init方法做了什么：

 public void init() throws Exception {


        //初始化类加载器
        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];
        // 指定
        paramTypes[0] = Class.forName("java.lang.ClassLoader");
        Object paramValues[] = new Object[1];
        paramValues[0] = sharedLoader;
        Method method =
            startupInstance.getClass().getMethod(methodName, paramTypes);
        // Catalina的父类加载器设为sharedLoader
        method.invoke(startupInstance, paramValues);

        catalinaDaemon = startupInstance;  //Catalina实例
    }

initClassLoaders（）：

     
    private void initClassLoaders() {
        try {
            // 初始化common类加载器
            commonLoader = createClassLoader("common", null);
            if (commonLoader == null) {
                // no config file, default to this loader - we might be in a 'single' env.
                commonLoader = this.getClass().getClassLoader();
            }
            // 父类加载器为commonLoader
            catalinaLoader = createClassLoader("server", commonLoader);
            sharedLoader = createClassLoader("shared", commonLoader);
        } catch (Throwable t) {
            handleThrowable(t);
            log.error("Class loader creation threw exception", t);
            System.exit(1);
        }
    }


   private ClassLoader createClassLoader(String name, ClassLoader parent)
        throws Exception {

        //  catalinaLoader和sharedLoader的加路径为空，所以使用父类加载器
        String value = CatalinaProperties.getProperty(name + ".loader");
        if ((value == null) || (value.equals(""))) {
            return parent;
        }

        value = replace(value);

        List<Repository> repositories = new ArrayList<>();

        String[] repositoryPaths = getPaths(value);

        for (String repository : repositoryPaths) {
            // Check for a JAR URL repository
            try {
                @SuppressWarnings("unused")
                URL url = new URL(repository);
                repositories.add(new Repository(repository, RepositoryType.URL));
                continue;
            } catch (MalformedURLException e) {
                // Ignore
            }

            // 遍历指定目录下的jar包
            // Local repository
            if (repository.endsWith("*.jar")) {
                repository = repository.substring
                    (0, repository.length() - "*.jar".length());
                repositories.add(new Repository(repository, RepositoryType.GLOB));
            } else if (repository.endsWith(".jar")) {
                repositories.add(new Repository(repository, RepositoryType.JAR));
            } else {
                repositories.add(new Repository(repository, RepositoryType.DIR));
            }
        }

        return ClassLoaderFactory.createClassLoader(repositories, parent);
    }

initClassLoaders方法初始化了三个类加载器：commonLoader，catalinaLoader，sharedLoader，并将catalinaLoader，sharedLoader的父类加载器指定为commonLoader，初始化类加载器后又实例化了catalina实例，init方法结束，再看load方法：

    /**
     * Load daemon.
     */
    private void load(String[] arguments) throws Exception {

        // Call the load() method
        String methodName = "load";
        Object param[];
        Class<?> paramTypes[];
        if (arguments==null || arguments.length==0) {
            paramTypes = null;
            param = null;
        } else {
            paramTypes = new Class[1];
            paramTypes[0] = arguments.getClass();
            param = new Object[1];
            param[0] = arguments;
        }
        Method method =
            catalinaDaemon.getClass().getMethod(methodName, paramTypes);
        if (log.isDebugEnabled()) {
            log.debug("Calling startup class " + method);
        }
        // 调用了catalina的load方法
        method.invoke(catalinaDaemon, param);
    }

其实就是调用了Catalina的load方法:

 public void load() {

        if (loaded) {
            return;
        }
        loaded = true;

        long t1 = System.nanoTime();

        initDirs();

        // Before digester - it may be needed
        initNaming();

        // Create and execute our Digester
        //xml文件解析器，比如解析server.xml
        Digester digester = createStartDigester();

        InputSource inputSource = null;
        InputStream inputStream = null;
        File file = null;
        try {
            try {
                file = configFile();
                inputStream = new FileInputStream(file);
                inputSource = new InputSource(file.toURI().toURL().toString());
            } catch (Exception e) {
                if (log.isDebugEnabled()) {
                    log.debug(sm.getString("catalina.configFail", file), e);
                }
            }
            if (inputStream == null) {
                try {
                    inputStream = getClass().getClassLoader()
                        .getResourceAsStream(getConfigFile());
                    inputSource = new InputSource
                        (getClass().getClassLoader()
                         .getResource(getConfigFile()).toString());
                } catch (Exception e) {
                    if (log.isDebugEnabled()) {
                        log.debug(sm.getString("catalina.configFail",
                                getConfigFile()), e);
                    }
                }
            }

            // This should be included in catalina.jar
            // Alternative: don't bother with xml, just create it manually.
            if (inputStream == null) {
                try {
                    inputStream = getClass().getClassLoader()
                            .getResourceAsStream("server-embed.xml");
                    inputSource = new InputSource
                    (getClass().getClassLoader()
                            .getResource("server-embed.xml").toString());
                } catch (Exception e) {
                    if (log.isDebugEnabled()) {
                        log.debug(sm.getString("catalina.configFail",
                                "server-embed.xml"), e);
                    }
                }
            }


            if (inputStream == null || inputSource == null) {
                if  (file == null) {
                    log.warn(sm.getString("catalina.configFail",
                            getConfigFile() + "] or [server-embed.xml]"));
                } else {
                    log.warn(sm.getString("catalina.configFail",
                            file.getAbsolutePath()));
                    if (file.exists() && !file.canRead()) {
                        log.warn("Permissions incorrect, read permission is not allowed on the file.");
                    }
                }
                return;
            }

            try {
                inputSource.setByteStream(inputStream);
                digester.push(this);
                digester.parse(inputSource);
            } catch (SAXParseException spe) {
                log.warn("Catalina.start using " + getConfigFile() + ": " +
                        spe.getMessage());
                return;
            } catch (Exception e) {
                log.warn("Catalina.start using " + getConfigFile() + ": " , e);
                return;
            }
        } finally {
            if (inputStream != null) {
                try {
                    inputStream.close();
                } catch (IOException e) {
                    // Ignore
                }
            }
        }

        getServer().setCatalina(this);
        getServer().setCatalinaHome(Bootstrap.getCatalinaHomeFile());
        getServer().setCatalinaBase(Bootstrap.getCatalinaBaseFile());

        // Stream redirection
        initStreams();

        // Start the new server
        try {
            // 重点看init方法
            getServer().init();
        } catch (LifecycleException e) {
            if (Boolean.getBoolean("org.apache.catalina.startup.EXIT_ON_INIT_FAILURE")) {
                throw new java.lang.Error(e);
            } else {
                log.error("Catalina.start", e);
            }
        }

        long t2 = System.nanoTime();
        if(log.isInfoEnabled()) {
            log.info("Initialization processed in " + ((t2 - t1) / 1000000) + " ms");
        }
    }

getServer().init()会调用LifeCycleBase的init方法，LifeCycle是一个管理tomcat生命周期的接口，LifeCycleBase是它的实现类：

    @Override
    public final synchronized void init() throws LifecycleException {
        if (!state.equals(LifecycleState.NEW)) {
            invalidTransition(Lifecycle.BEFORE_INIT_EVENT);
        }

        try {
            setStateInternal(LifecycleState.INITIALIZING, null, false);
            // 进入这里
            initInternal();
            setStateInternal(LifecycleState.INITIALIZED, null, false);
        } catch (Throwable t) {
            handleSubClassException(t, "lifecycleBase.initFail", toString());
        }
    }

initInternal()是个抽象方法，由StandServer实现：

    @Override
    protected void initInternal() throws LifecycleException {

        super.initInternal();

        // Register global String cache
        // Note although the cache is global, if there are multiple Servers
        // present in the JVM (may happen when embedding) then the same cache
        // will be registered under multiple names
        onameStringCache = register(new StringCache(), "type=StringCache");

        // Register the MBeanFactory
        MBeanFactory factory = new MBeanFactory();
        factory.setContainer(this);
        onameMBeanFactory = register(factory, "type=MBeanFactory");

        // Register the naming resources
        globalNamingResources.init();

        // Populate the extension validator with JARs from common and shared
        // class loaders
        if (getCatalina() != null) {
            ClassLoader cl = getCatalina().getParentClassLoader();
            // Walk the class loader hierarchy. Stop at the system class loader.
            // This will add the shared (if present) and common class loaders
            while (cl != null && cl != ClassLoader.getSystemClassLoader()) {
                if (cl instanceof URLClassLoader) {
                    URL[] urls = ((URLClassLoader) cl).getURLs();
                    for (URL url : urls) {
                        if (url.getProtocol().equals("file")) {
                            try {
                                File f = new File (url.toURI());
                                if (f.isFile() &&
                                        f.getName().endsWith(".jar")) {
                                    ExtensionValidator.addSystemResource(f);
                                }
                            } catch (URISyntaxException | IOException e) {
                                // Ignore
                            }
                        }
                    }
                }
                cl = cl.getParent();
            }
        }
        // Initialize our defined Services
        for (Service service : services) {
            // 进入这里
            service.init();
        }
    }

service是StandService，但它的init是父类 LifeCycleBase的方法，又一次运行了这个方法：

    @Override
    public final synchronized void init() throws LifecycleException {
        if (!state.equals(LifecycleState.NEW)) {
            invalidTransition(Lifecycle.BEFORE_INIT_EVENT);
        }

        try {
            setStateInternal(LifecycleState.INITIALIZING, null, false);
            // 进入这里，这里由StandService实现
            initInternal();
            setStateInternal(LifecycleState.INITIALIZED, null, false);
        } catch (Throwable t) {
            handleSubClassException(t, "lifecycleBase.initFail", toString());
        }
    }

       @Override
    protected void initInternal() throws LifecycleException {

        super.initInternal();

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

        // Initialize any Executors
        for (Executor executor : findExecutors()) {
            if (executor instanceof JmxEnabled) {
                ((JmxEnabled) executor).setDomain(getDomain());
            }
            //初始化executor
            executor.init(); 
        }

        // Initialize mapper listener
        //初始化mapperListener
        mapperListener.init(); 

        // Initialize our defined Connectors
        synchronized (connectorsLock) {
            for (Connector connector : connectors) {
                try {
                    //初始化connector
                    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);
                    }
                }
            }
        }
    }

又一次调用了LifeCycleBase的init方法：

    @Override
    public final synchronized void init() throws LifecycleException {
        if (!state.equals(LifecycleState.NEW)) {
            invalidTransition(Lifecycle.BEFORE_INIT_EVENT);
        }

        try {
            setStateInternal(LifecycleState.INITIALIZING, null, false);
            // 进入这里，这次由Connect实现
            initInternal();
            setStateInternal(LifecycleState.INITIALIZED, null, false);
        } catch (Throwable t) {
            handleSubClassException(t, "lifecycleBase.initFail", toString());
        }
    }

    @Override
    protected void initInternal() throws LifecycleException {

        super.initInternal();

        // Initialize adapter
        adapter = new CoyoteAdapter(this);
        protocolHandler.setAdapter(adapter);

        // Make sure parseBodyMethodsSet has a default
        if (null == parseBodyMethodsSet) {
            setParseBodyMethods(getParseBodyMethods());
        }

        if (protocolHandler.isAprRequired() && !AprLifecycleListener.isInstanceCreated()) {
            throw new LifecycleException(sm.getString("coyoteConnector.protocolHandlerNoAprListener",
                    getProtocolHandlerClassName()));
        }
        if (protocolHandler.isAprRequired() && !AprLifecycleListener.isAprAvailable()) {
            throw new LifecycleException(sm.getString("coyoteConnector.protocolHandlerNoAprLibrary",
                    getProtocolHandlerClassName()));
        }
        if (AprLifecycleListener.isAprAvailable() && AprLifecycleListener.getUseOpenSSL() &&
                protocolHandler instanceof AbstractHttp11JsseProtocol) {
            AbstractHttp11JsseProtocol<?> jsseProtocolHandler =
                    (AbstractHttp11JsseProtocol<?>) protocolHandler;
            if (jsseProtocolHandler.isSSLEnabled() &&
                    jsseProtocolHandler.getSslImplementationName() == null) {
                // OpenSSL is compatible with the JSSE configuration, so use it if APR is available
                jsseProtocolHandler.setSslImplementationName(OpenSSLImplementation.class.getName());
            }
        }

        try {
            // 初始化ProtocolHandler
            protocolHandler.init();
        } catch (Exception e) {
            throw new LifecycleException(
                    sm.getString("coyoteConnector.protocolHandlerInitializationFailed"), e);
        }
    }

protocolHandler.init()由AbstractProtocol实现：

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

        if (oname == null) {
            // Component not pre-registered so register it
            oname = createObjectName();
            if (oname != null) {
                Registry.getRegistry(null, null).registerComponent(this, oname, null);
            }
        }

        if (this.domain != null) {
            ObjectName rgOname = new ObjectName(domain + ":type=GlobalRequestProcessor,name=" + getName());
            this.rgOname = rgOname;
            Registry.getRegistry(null, null).registerComponent(
                    getHandler().getGlobal(), rgOname, null);
        }

        String endpointName = getName();
        endpoint.setName(endpointName.substring(1, endpointName.length()-1));
        endpoint.setDomain(domain);
 
        // 初始化endPoint
        endpoint.init();
    }

endpoint.init()由AbstractEndPoint实现：

    public void init() throws Exception {
        if (bindOnInit) {
            // 重点在这里
            bindWithCleanup();
            bindState = BindState.BOUND_ON_INIT;
        }
        if (this.domain != null) {
            // Register endpoint (as ThreadPool - historical name)
            oname = new ObjectName(domain + ":type=ThreadPool,name=\"" + getName() + "\"");
            Registry.getRegistry(null, null).registerComponent(this, oname, null);

            ObjectName socketPropertiesOname = new ObjectName(domain +
                    ":type=SocketProperties,name=\"" + getName() + "\"");
            socketProperties.setObjectName(socketPropertiesOname);
            Registry.getRegistry(null, null).registerComponent(socketProperties, socketPropertiesOname, null);

            for (SSLHostConfig sslHostConfig : findSslHostConfigs()) {
                registerJmx(sslHostConfig);
            }
        }
    }



    private void bindWithCleanup() throws Exception {
        try {
            bind();
        } catch (Throwable t) {
            // Ensure open sockets etc. are cleaned up if something goes
            // wrong during bind
            ExceptionUtils.handleThrowable(t);
            unbind();
            throw t;
        }
    }

进入NioEndPoint：

      /**
     * Initialize the endpoint.
     */
    @Override
    public void bind() throws Exception {
        // 初始化ServerSocket
        initServerSocket();

        setStopLatch(new CountDownLatch(1));

        // Initialize SSL if needed
        initialiseSsl();
    }








    // Separated out to make it easier for folks that extend NioEndpoint to
    // implement custom [server]sockets
    protected void initServerSocket() throws Exception {
        if (getUseInheritedChannel()) {
            // Retrieve the channel provided by the OS
            Channel ic = System.inheritedChannel();
            if (ic instanceof ServerSocketChannel) {
                serverSock = (ServerSocketChannel) ic;
            }
            if (serverSock == null) {
                throw new IllegalArgumentException(sm.getString("endpoint.init.bind.inherited"));
            }
        } else {
            serverSock = ServerSocketChannel.open();
            socketProperties.setProperties(serverSock.socket());
            InetSocketAddress addr = new InetSocketAddress(getAddress(), getPortWithOffset());
            serverSock.socket().bind(addr,getAcceptCount());
        }
        serverSock.configureBlocking(true); //mimic APR behavior
    }

BootStrap的load方法完成，就是初始化了一些组件。
再来看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);
        // 调用Catalina的start方法
        method.invoke(catalinaDaemon, (Object [])null);
    }


 /**
     * Start a new server instance.
     */
    public void start() {

        if (getServer() == null) {
            load();
        }

        if (getServer() == null) {
            log.fatal("Cannot start server. Server instance is not configured.");
            return;
        }

        long t1 = System.nanoTime();

        // Start the new server
        try {
            // start
            getServer().start();
        } catch (LifecycleException e) {
            log.fatal(sm.getString("catalina.serverStartFail"), e);
            try {
                getServer().destroy();
            } catch (LifecycleException e1) {
                log.debug("destroy() failed for failed Server ", e1);
            }
            return;
        }

        long t2 = System.nanoTime();
        if(log.isInfoEnabled()) {
            log.info("Server startup in " + ((t2 - t1) / 1000000) + " ms");
        }

        // Register shutdown hook
        if (useShutdownHook) {
            if (shutdownHook == null) {
                shutdownHook = new CatalinaShutdownHook();
            }
            Runtime.getRuntime().addShutdownHook(shutdownHook);

            // If JULI is being used, disable JULI's shutdown hook since
            // shutdown hooks run in parallel and log messages may be lost
            // if JULI's hook completes before the CatalinaShutdownHook()
            LogManager logManager = LogManager.getLogManager();
            if (logManager instanceof ClassLoaderLogManager) {
                ((ClassLoaderLogManager) logManager).setUseShutdownHook(
                        false);
            }
        }

        if (await) {
            await();
            stop();
        }
    }

getServer().start()调用LifecycleBase的start方法：

    /**
     * {@inheritDoc}
     */
    @Override
    public final synchronized void start() throws LifecycleException {

        if (LifecycleState.STARTING_PREP.equals(state) || LifecycleState.STARTING.equals(state) ||
                LifecycleState.STARTED.equals(state)) {

            if (log.isDebugEnabled()) {
                Exception e = new LifecycleException();
                log.debug(sm.getString("lifecycleBase.alreadyStarted", toString()), e);
            } else if (log.isInfoEnabled()) {
                log.info(sm.getString("lifecycleBase.alreadyStarted", toString()));
            }

            return;
        }
       // start方法时，state为INITIALIZED
        if (state.equals(LifecycleState.NEW)) {
            init();
        } else if (state.equals(LifecycleState.FAILED)) {
            stop();
        } else if (!state.equals(LifecycleState.INITIALIZED) &&
                !state.equals(LifecycleState.STOPPED)) {
            invalidTransition(Lifecycle.BEFORE_START_EVENT);
        }

        try {
            setStateInternal(LifecycleState.STARTING_PREP, null, false);
            //进入这里，调用的是StandServer的startInternal（）
            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.
            handleSubClassException(t, "lifecycleBase.startFail", toString());
        }
    }


 @Override
    protected void startInternal() throws LifecycleException {

        fireLifecycleEvent(CONFIGURE_START_EVENT, null);
        setState(LifecycleState.STARTING);

        globalNamingResources.start();

        // Start our defined Services
        synchronized (servicesLock) {
            for (Service service : services) {
                // standService
                service.start();
            }
        }
    }

后面和load方法一样，都是调用了父类LifecycleBase的模板方法实现各个组件的start。