Tomcat啟動和停止
很明顯，我們啟動或停止Tomcat，一般呼叫的是bin下的startup.sh或shutdown.sh(以Linux為例，以下涉及到平臺，若無特殊說明，一般都指Linux)。我們看看startup.sh的指令碼是什麼？
# ----------------------------------------------------------------------------- # 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"` 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 "$@"
最後一行，它執行的是"/"$EXECUTABLE，那它是什麼呢？參看前面的一行
EXECUTABLE=catalina.sh
是的，啟動指令碼還是呼叫的catalina.sh.
接下來我們看看catalina.sh指令碼有什麼內容。
程式碼比較長，為了看的更明白，刪除一些不必要的，完整的指令碼大家可以參看catalina.sh
#!/bin/sh # Control Script for the CATALINA Server # # Environment Variable Prerequisites # # Do not set the variables in this script. Instead put them into a script # setenv.sh in CATALINA_BASE/bin to keep your customizations separate. # # CATALINA_HOME May point at your Catalina "build" directory. # # CATALINA_BASE (Optional) Base directory for resolving dynamic portions # of a Catalina installation. If not present, resolves to # the same directory that CATALINA_HOME points to. # # CATALINA_OUT (Optional) Full path to a file where stdout and stderr # will be redirected. # Default is $CATALINA_BASE/logs/catalina.out # # # JAVA_HOME Must point at your Java Development Kit installation. # Required to run the with the "debug" argument. # # JRE_HOME Must point at your Java Runtime installation. # Defaults to JAVA_HOME if empty. If JRE_HOME and JAVA_HOME # are both set, JRE_HOME is used. # # JAVA_OPTS (Optional) Java runtime options used when any command # is executed. # Include here and not in CATALINA_OPTS all options, that # should be used by Tomcat and also by the stop process, # the version command etc. # Most options should go into CATALINA_OPTS. # Djava.util.logging.config.file=$CATALINA_BASE/conf/logging.properties" ## ----------------------------------------------------------------------------- # ----- Execute The Requested Command ----------------------------------------- elif [ "$1" = "start" ] ; then if [ -z "$CATALINA_OUT_CMD" ] ; then touch "$CATALINA_OUT" catalina_out_command=">> \"$CATALINA_OUT\" 2>&1" else catalina_out_command="| $CATALINA_OUT_CMD" fi if [ ! -z "$CATALINA_PID" ]; then catalina_pid_file="$CATALINA_PID" else catalina_pid_file=/dev/null fi if [ "$1" = "-security" ] ; then if [ $have_tty -eq 1 ]; then echo "Using Security Manager" fi shift eval \{ $_NOHUP "\"$_RUNJAVA\"" "\"$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\"" \ org.apache.catalina.startup.Bootstrap "$@" start \ 2\>\&1 \& echo \$! \>\"$catalina_pid_file\" \; \} $catalina_out_command "&" else eval \{ $_NOHUP "\"$_RUNJAVA\"" "\"$LOGGING_CONFIG\"" $LOGGING_MANAGER $JAVA_OPTS $CATALINA_OPTS \ -D$ENDORSED_PROP="\"$JAVA_ENDORSED_DIRS\"" \ -classpath "\"$CLASSPATH\"" \ -Dcatalina.base="\"$CATALINA_BASE\"" \ -Dcatalina.home="\"$CATALINA_HOME\"" \ -Djava.io.tmpdir="\"$CATALINA_TMPDIR\"" \ org.apache.catalina.startup.Bootstrap "$@" start \ 2\>\&1 \& echo \$! \>\"$catalina_pid_file\" \; \} $catalina_out_command "&" fi echo "Tomcat started." elif [ "$1" = "stop" ] ; then eval "\"$_RUNJAVA\"" $JAVA_OPTS \ -D$ENDORSED_PROP="\"$JAVA_ENDORSED_DIRS\"" \ -classpath "\"$CLASSPATH\"" \ -Dcatalina.base="\"$CATALINA_BASE\"" \ -Dcatalina.home="\"$CATALINA_HOME\"" \ -Djava.io.tmpdir="\"$CATALINA_TMPDIR\"" \ org.apache.catalina.startup.Bootstrap "$@" stop elif [ "$1" = "version" ] ; then "$_RUNJAVA" \ -classpath "$CATALINA_HOME/lib/catalina.jar" \ org.apache.catalina.util.ServerInfo else echo "Usage: catalina.sh ( commands ... )" echo "commands:" if $os400; then echo " debug Start Catalina in a debugger (not available on OS400)" echo " debug -security Debug Catalina with a security manager (not available on OS400)" else echo " debug Start Catalina in a debugger" echo " debug -security Debug Catalina with a security manager" fi echo " jpda start Start Catalina under JPDA debugger" echo " run Start Catalina in the current window" echo " run -security Start in the current window with security manager" echo " start Start Catalina in a separate window" echo " start -security Start in a separate window with security manager" echo " stop Stop Catalina, waiting up to 5 seconds for the process to end" echo " stop n Stop Catalina, waiting up to n seconds for the process to end" echo " stop -force Stop Catalina, wait up to 5 seconds and then use kill -KILL if still running" echo " stop n -force Stop Catalina, wait up to n seconds and then use kill -KILL if still running" echo " configtest Run a basic syntax check on server.xml - check exit code for result" echo " version What version of tomcat are you running?" echo "Note: Waiting for the process to end and use of the -force option require that \$CATALINA_PID is defined" exit 1
從以上指令碼可以看出，無論是start還是stop，其實呼叫的都是org.apache.catalina.startup.Bootstrap 這個類。
整理一下，Tomcat整個程式的入口在Boostrap這個類這裡。
OK，我們看看Bootstrap的啟動過程。
Bootstrap的啟動過程
Bootstrap這個類在以下package裡
org.apache.catalina.startup
Bootstrap類有個main方法，這是Tomcat的入口。
public static void main(String args[]) { 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); 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); 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); } }
程式碼比較簡單，也比較直觀。
首先建立一個Bootstrap的例項，然後呼叫init方法。接著處理main方法的傳入引數，是start還是stop等，當然預設是start了。
再看看init的方法
public void init() throws Exception { 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; }
我們可以看到初始化ClassLoader，接著會建立一個startupClass的類，就是這段程式碼：
Class<?> startupClass = catalinaLoader.loadClass("org.apache.catalina.startup.Catalina");
Object startupInstance = startupClass.getConstructor().newInstance();
我們看到startup的類其實就是org.apache.catalina.startup.Catalina，最後建立了另外一個例項catalinaDaemon。Tomcat的啟動，停止都是呼叫它。
我們看看start方法啟動Tomcat
public void start() throws Exception { if( catalinaDaemon==null ) init(); Method method = catalinaDaemon.getClass().getMethod("start", (Class [] )null); method.invoke(catalinaDaemon, (Object [])null); }
這裡首先判斷有沒有初始化，如果沒有，呼叫init並對其初始化，然後使用Method進行反射呼叫Catalina的start方法。
注：Method是java.lang.reflect包裡的類，代表了一個具體的方法，在這裡，只是start方法。Method.invoke方法是指執行該方法，它有2個引數，第一個引數是方法名，第二個是該方法的引數。
Catalina的啟動
追本溯源，最後Tomcat的管理落到了Catalina這個類了，所以Catalina才是最重要的類。
先看看Catalina的方法。
我們可以清晰看到幾個重要的方法：
- await
- load
- start
- stop
- usage
對於這幾個方法，也算是直觀。那麼我們從簡單的開始說起。
方法usage
見以下程式碼，其實就是顯示catalina的用法。
/** * Print usage information for this application. */ protected void usage() { System.out.println(sm.getString("catalina.usage")); }
方法await
程式碼如下
/** * Await and shutdown. */ public void await() { getServer().await(); }
這個方法搭配setAwait來用，setAwait方法用於設定Server啟動完成後是否進入等待狀態，如果為true，則進入，否則不進入。
方法load
/** * Start a new server instance. */ public void load() { if (loaded) { return; } loaded = true; long t1 = System.nanoTime(); initDirs(); // Before digester - it may be needed initNaming(); // Set configuration source ConfigFileLoader.setSource(new CatalinaBaseConfigurationSource(Bootstrap.getCatalinaBaseFile(), getConfigFile())); File file = configFile(); // Create and execute our Digester Digester digester = createStartDigester(); try (ConfigurationSource.Resource resource = ConfigFileLoader.getSource().getServerXml()) { InputStream inputStream = resource.getInputStream(); InputSource inputSource = new InputSource(resource.getURI().toURL().toString()); inputSource.setByteStream(inputStream); digester.push(this); digester.parse(inputSource); } catch (Exception e) { if (file == null) { log.warn(sm.getString("catalina.configFail", getConfigFile() + "] or [server-embed.xml"), e); } else { log.warn(sm.getString("catalina.configFail", file.getAbsolutePath()), e); if (file.exists() && !file.canRead()) { log.warn(sm.getString("catalina.incorrectPermissions")); } } return; } getServer().setCatalina(this); getServer().setCatalinaHome(Bootstrap.getCatalinaHomeFile()); getServer().setCatalinaBase(Bootstrap.getCatalinaBaseFile()); // Stream redirection initStreams(); // Start the new server try { 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(sm.getString("catalina.initError"), e); } } long t2 = System.nanoTime(); if(log.isInfoEnabled()) { log.info(sm.getString("catalina.init", Long.valueOf((t2 - t1) / 1000000))); } }
這個方法會載入conf/server.xml這個配置檔案，並且將我們前面描述到的Server，Listener，Service，Engine等逐一載入。而且Server例項已經由Digester建立，以下是createStartDigester的實現，部分程式碼刪除。
protected Digester createStartDigester() { long t1=System.currentTimeMillis(); // Initialize the digester Digester digester = new Digester(); digester.setValidating(false); digester.setRulesValidation(true); Map<Class<?>, List<String>> fakeAttributes = new HashMap<>(); // Ignore className on all elements List<String> objectAttrs = new ArrayList<>(); objectAttrs.add("className"); fakeAttributes.put(Object.class, objectAttrs); // Ignore attribute added by Eclipse for its internal tracking List<String> contextAttrs = new ArrayList<>(); contextAttrs.add("source"); fakeAttributes.put(StandardContext.class, contextAttrs); // Ignore Connector attribute used internally but set on Server List<String> connectorAttrs = new ArrayList<>(); connectorAttrs.add("portOffset"); fakeAttributes.put(Connector.class, connectorAttrs); digester.setFakeAttributes(fakeAttributes); digester.setUseContextClassLoader(true); // Configure the actions we will be using digester.addObjectCreate("Server", "org.apache.catalina.core.StandardServer", "className"); digester.addSetProperties("Server"); digester.addSetNext("Server", "setServer", "org.apache.catalina.Server"); digester.addObjectCreate("Server/GlobalNamingResources", "org.apache.catalina.deploy.NamingResourcesImpl"); digester.addSetProperties("Server/GlobalNamingResources"); digester.addSetNext("Server/GlobalNamingResources", "setGlobalNamingResources", "org.apache.catalina.deploy.NamingResourcesImpl"); digester.addObjectCreate("Server/Listener", null, // MUST be specified in the element "className"); digester.addSetProperties("Server/Listener"); digester.addSetNext("Server/Listener", "addLifecycleListener", "org.apache.catalina.LifecycleListener"); digester.addObjectCreate("Server/Service", "org.apache.catalina.core.StandardService", "className"); digester.addSetProperties("Server/Service"); digester.addSetNext("Server/Service", "addService", "org.apache.catalina.Service"); digester.addObjectCreate("Server/Service/Listener", null, // MUST be specified in the element "className"); digester.addSetProperties("Server/Service/Listener"); digester.addSetNext("Server/Service/Listener", "addLifecycleListener", "org.apache.catalina.LifecycleListener"); //Executor digester.addObjectCreate("Server/Service/Executor", "org.apache.catalina.core.StandardThreadExecutor", "className"); digester.addSetProperties("Server/Service/Executor"); digester.addSetNext("Server/Service/Executor", "addExecutor", "org.apache.catalina.Executor"); digester.addRule("Server/Service/Connector", new ConnectorCreateRule()); digester.addRule("Server/Service/Connector", new SetAllPropertiesRule( new String[]{"executor", "sslImplementationName", "protocol"})); digester.addSetNext("Server/Service/Connector", "addConnector", "org.apache.catalina.connector.Connector"); digester.addRule("Server/Service/Connector", new AddPortOffsetRule()); digester.addObjectCreate("Server/Service/Connector/SSLHostConfig", "org.apache.tomcat.util.net.SSLHostConfig"); digester.addSetProperties("Server/Service/Connector/SSLHostConfig"); digester.addSetNext("Server/Service/Connector/SSLHostConfig", "addSslHostConfig", "org.apache.tomcat.util.net.SSLHostConfig"); digester.addObjectCreate("Server/Service/Connector/Listener", null, // MUST be specified in the element "className"); digester.addSetProperties("Server/Service/Connector/Listener"); digester.addSetNext("Server/Service/Connector/Listener", "addLifecycleListener", "org.apache.catalina.LifecycleListener"); digester.addObjectCreate("Server/Service/Connector/UpgradeProtocol", null, // MUST be specified in the element "className"); digester.addSetProperties("Server/Service/Connector/UpgradeProtocol"); digester.addSetNext("Server/Service/Connector/UpgradeProtocol", "addUpgradeProtocol", "org.apache.coyote.UpgradeProtocol"); // Add RuleSets for nested elements digester.addRuleSet(new NamingRuleSet("Server/GlobalNamingResources/")); digester.addRuleSet(new EngineRuleSet("Server/Service/")); digester.addRuleSet(new HostRuleSet("Server/Service/Engine/")); digester.addRuleSet(new ContextRuleSet("Server/Service/Engine/Host/")); addClusterRuleSet(digester, "Server/Service/Engine/Host/Cluster/"); digester.addRuleSet(new NamingRuleSet("Server/Service/Engine/Host/Context/")); // When the 'engine' is found, set the parentClassLoader. digester.addRule("Server/Service/Engine", new SetParentClassLoaderRule(parentClassLoader)); addClusterRuleSet(digester, "Server/Service/Engine/Cluster/"); long t2=System.currentTimeMillis(); if (log.isDebugEnabled()) { log.debug("Digester for server.xml created " + ( t2-t1 )); } return digester; }
方法start
start用來啟動一個Server，具體程式碼如下
/** * Start a new server instance. */ public void start() { if (getServer() == null) { load(); } if (getServer() == null) { log.fatal(sm.getString("catalina.noServer")); return; } long t1 = System.nanoTime(); // Start the new server try { 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(sm.getString("catalina.startup", Long.valueOf((t2 - t1) / 1000000))); } // 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(); } }
首先判斷Server是否存在，如果不存在，呼叫load初始化一下。接著呼叫Server的start方法啟動它。最後如果啟用關閉的鉤子，還要註冊一下該鉤子。在末尾，如果如果await設定為true的話，需要呼叫await和stop。Await會直接呼叫Server的await方法，Server內部會進入一個while迴圈，以下程式碼是Server的await方法的實現。當await裡while結束，執行stop方法，停止伺服器。
public void await() { // Set up a server socket to wait on try { awaitSocket = new ServerSocket(getPortWithOffset(), 1, InetAddress.getByName(address)); } catch (IOException e) { log.error(sm.getString("standardServer.awaitSocket.fail", address, String.valueOf(getPortWithOffset()), String.valueOf(getPort()), String.valueOf(getPortOffset())), e); return; } try { awaitThread = Thread.currentThread(); // Loop waiting for a connection and a valid command while (!stopAwait) { ServerSocket serverSocket = awaitSocket; if (serverSocket == null) { break; } // Wait for the next connection Socket socket = null; StringBuilder command = new StringBuilder(); try { InputStream stream; long acceptStartTime = System.currentTimeMillis(); try { socket = serverSocket.accept(); socket.setSoTimeout(10 * 1000); // Ten seconds stream = socket.getInputStream(); } catch (SocketTimeoutException ste) { // This should never happen but bug 56684 suggests that // it does. log.warn(sm.getString("standardServer.accept.timeout", Long.valueOf(System.currentTimeMillis() - acceptStartTime)), ste); continue; } catch (AccessControlException ace) { log.warn(sm.getString("standardServer.accept.security"), ace); continue; } catch (IOException e) { if (stopAwait) { // Wait was aborted with socket.close() break; } log.error(sm.getString("standardServer.accept.error"), e); break; } // Read a set of characters from the socket int expected = 1024; // Cut off to avoid DoS attack while (expected < shutdown.length()) { if (random == null) random = new Random(); expected += (random.nextInt() % 1024); } while (expected > 0) { int ch = -1; try { ch = stream.read(); } catch (IOException e) { log.warn(sm.getString("standardServer.accept.readError"), e); ch = -1; } // Control character or EOF (-1) terminates loop if (ch < 32 || ch == 127) { break; } command.append((char) ch); expected--; } } finally { // Close the socket now that we are done with it try { if (socket != null) { socket.close(); } } catch (IOException e) { // Ignore } } // Match against our command string boolean match = command.toString().equals(shutdown); if (match) { log.info(sm.getString("standardServer.shutdownViaPort")); break; } else log.warn(sm.getString("standardServer.invalidShutdownCommand", command.toString())); } } finally { ServerSocket serverSocket = awaitSocket; awaitThread = null; awaitSocket = null; // Close the server socket and return if (serverSocket != null) { try { serverSocket.close(); } catch (IOException e) { // Ignore } } } }
Server的啟動
前面也提到了Catalina的start其實呼叫的是Server的start方法，我們看看Server的start的方法怎麼實現的。在深入前，我們看看Server的方法列表等資訊。
Server是一個介面，繼承了LifeCycle這個介面。
Server提供了2個方法addService（）以及removeService（），分別用來增加或刪除Service。在前面我們講過，一個Server是可以包含多個Service的。
在Server 啟動前，Server包含的幾個Service也需要初始化，其實每個Service的初始化也是用Service本身的init方法來初始化。
Server的預設實現是org.apache.catalina.core.StandardServer，StandardServer又繼承了LifeCycleMBeanBase，
public final class StandardServer extends LifecycleMBeanBase implements Server
LifeCycleMBeanBase又繼承了LifecycleBase
public abstract class LifecycleMBeanBase extends LifecycleBase
LifeCycleBase又實現了LifeCycle
public abstract class LifecycleBase implements Lifecycle
因為init和start都是LifeCycleBase裡，這也是tomcat的生命週期重要的方法。Init和start也分別呼叫了initInternal和startInternal。至於怎麼實現，還得看子類的具體邏輯，前面說到StandardServer是預設的實現，那我們看看StandardServer的具體實現邏輯。繼續上程式碼：
protected void initInternal() throws LifecycleException { super.initInternal(); //… … // Initialize our defined Services for (int i = 0; i < services.length; i++) { services[i].init(); } }
上面是initInternal的程式碼，我們發現其實就是呼叫Server包含的Service的init方法。
下面是startInternal的程式碼。
protected void startInternal() throws LifecycleException { fireLifecycleEvent(CONFIGURE_START_EVENT, null); setState(LifecycleState.STARTING); globalNamingResources.start(); // Start our defined Services synchronized (servicesLock) { for (int i = 0; i < services.length; i++) { services[i].start(); } } if (periodicEventDelay > 0) { monitorFuture = getUtilityExecutor().scheduleWithFixedDelay( new Runnable() { @Override public void run() { startPeriodicLifecycleEvent(); } }, 0, 60, TimeUnit.SECONDS); } }
首先需要啟動各個Service，這也是通過Service 的start方法來實現。
Service的啟動過程
前面已經說到，Server會呼叫Service的start方法來啟動各個Service，我們繼續看Service的啟動。Service的預設實現是org.apache.catalina.core.StandardService，StandardService也繼承了LifeCycleMBeanBase類，所以init和start最終也會呼叫initInternal和startInternal這兩個方法。還是先看StandardService的方法列表。
和StandardServer類似，一個Service可能包含多個Connector，所以我們看到了addConnector和removeConnector這兩個方法。
我們可以看到initInternal和startInternal兩個方法，我們抽取核心的程式碼在這裡展示一下:
@Override protected void initInternal() throws LifecycleException { super.initInternal(); if (engine != null) { engine.init(); } // Initialize any Executors for (Executor executor : findExecutors()) { if (executor instanceof JmxEnabled) { ((JmxEnabled) executor).setDomain(getDomain()); } executor.init(); } // Initialize mapper listener mapperListener.init(); // Initialize our defined Connectors synchronized (connectorsLock) { for (Connector connector : connectors) { connector.init(); } } } protected void startInternal() throws LifecycleException { if(log.isInfoEnabled()) log.info(sm.getString("standardService.start.name", this.name)); setState(LifecycleState.STARTING); // Start our defined Container first if (engine != null) { synchronized (engine) { engine.start(); } } synchronized (executors) { for (Executor executor: executors) { executor.start(); } } mapperListener.start(); // Start our defined Connectors second synchronized (connectorsLock) { for (Connector connector: connectors) { // If it has already failed, don't try and start it if (connector.getState() != LifecycleState.FAILED) { connector.start(); } }
根據以上程式碼可以看出，無論是initInternal還是startInternal，都涉及到了Engine，Executor，Listener以及Connector。
這裡需要說明的是Executor，前面並未提及，因為Tomcat預設把它註釋掉了，其實它就是Connector中管理執行緒的執行緒池。
<!--The connectors can use a shared executor, you can define one or more named thread pools--> <Executor name="tomcatThreadPool" namePrefix="catalina-exec-" maxThreads="150" minSpareThreads="4"/>
如何使用Executor？只需要在Connector加上executor這個屬性，並指向定義的Executor。
<Connector executor = “tomcatThreadPool” port="8080" protocol="HTTP/1.1" connectionTimeout="20000" redirectPort="8443" />
綜合上述，現在我們可以瞭解Tomcat的啟動過程了，先初始化，然後在啟動。
Startup.sh -> Bootstrap的main -> Catalina -> StandardServer -> StandardService->Container->Executor->Connector