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Tomcat是一款我们平时开发过程中最常用到的Servlet容器。本系列博客会记录Tomcat的整体架构、主要组件、IO线程模型、请求在Tomcat内部的流转过程以及一些Tomcat调优的相关知识。
力求达到以下几个目的：
在前面分析Tomcat启动脚本的过程中，我们最后发现startup.bat最后是通过调用Bootstrap这个类的main方法来启动Tomcat的，所以先去看下Bootstrap这个类。
public static void main(String args[]) {
synchronized (daemonLock) {
if (daemon == null) {
// Don‘t set daemon until init() has completed
Bootstrap bootstrap = new Bootstrap();
try {
//创建Bootstrap对象，代用init方法
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")) {
//一般情况下会进入这步，调用Bootstrap对象的load和start方法。
//将Catalina启动设置成block模式
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);
}
}
上面的代码逻辑比较简单，如果我们正常启动tomcat，会顺序执行Bootstrap对象的init()方法， daemon.setAwait(true)、daemon.load(args)和daemon.start()方法。我们先看下Bootstrap对象的init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;
}
这个方法主要做了以下几件事：
执行完init()方法，就开始执行bootstrap对象的load和start方法;
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);
method.invoke(catalinaDaemon, param);
}
调用catalinaDaemon对象的load方法，catalinaDaemon这个对象的类型是org.apache.catalina.startup.Catalina。strat方法也是类似的，最后都是调用Catalina的start方法。
总结下Bootstrap的启动方法最主要干的事情就是创建了Catalina对象，并调用它的load和start方法。
第一节分析到Bootstrap会触发调用Catalina的load和start方法。
/**
* 从注释可以看出这个方法的作用是创建一个Server实例
* Start a new server instance.
*/
public void load() {
if (loaded) {
return;
}
loaded = true;
long t1 = System.nanoTime();
//检查临时目录
initDirs();
// Before digester - it may be needed
initNaming();
// Create and execute our Digester
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 {
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");
}
}
将上面的代码精简下：
Digester digester = createStartDigester();
inputSource.setByteStream(inputStream);
digester.push(this);
digester.parse(inputSource);
getServer().setCatalina(this);
getServer().init();
做的事情就两个：
临时总结下：Catalina的load方法的作用主要是解析conf/server.xml，生成StandardServer对象，再触发StandardServer的init方法。
第一节中还分析到Bootstrap会触发调用Catalina的start方法。那么我们看看start方法中干了什么。
/**
* 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 {
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();
}
}
这段代码最主要的作用就是调用StandardServer对象的start方法。
总结下：Catalina对象的laod和start方法的作用是解析conf/server.xml，生成StandardServer对象，再触发StandardServer的init方法和start方法。
到这边为止我们可以看到Tomcat的启动流程还是很清晰的，下面继续看StandardServer的init方法和start到底干了些什么。
通过寻找StandardServer的init方法，我们发现StandardServer本身没有实现这个方法，这个方法是它从父类LifecycleBase中继承过来的：
@Override
public final synchronized void init() throws LifecycleException {
if (!state.equals(LifecycleState.NEW)) {
invalidTransition(Lifecycle.BEFORE_INIT_EVENT);
}
try {
//发布初始化容器时间，对应的listener做相应处理
setStateInternal(LifecycleState.INITIALIZING, null, false);
//调用子类的initInternal（）
initInternal();
//发布容器已经初始化事件，对应的listener做相应处理
setStateInternal(LifecycleState.INITIALIZED, null, false);
} catch (Throwable t) {
handleSubClassException(t, "lifecycleBase.initFail", toString());
}
}
所以调用StandardServer的init方法，其实是促发了容器初始化事件发布，然后又调到了StandardServer的initInternal方法。那么我们看看StandardServer的start方法的逻辑是什么。
代码点进去，发现StandardServer的start方法也是调的父类LifecycleBase中的方法。
@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;
}
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 {
//发布事件
setStateInternal(LifecycleState.STARTING_PREP, null, false);
//调用子类的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 {
//发布容器启动事件
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());
}
}
从以上init和start方法的定义可以看到这两个方法最终将会调用StandardServer中定义的initInternal和startInternal。
先来看initInternal方法
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 e) {
// Ignore
} catch (IOException e) {
// Ignore
}
}
}
}
cl = cl.getParent();
}
}
// Initialize our defined Services
for (int i = 0; i < services.length; i++) {
services[i].init();
}
}
重点代码在最后，循环调用了Service组件的init方法。
再来看StandardServer的startInternal方法
@Override
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();
}
}
}
也是循环调用了Service组件的start方法。这边的Service组件就是在从conf/server.xml中解析出来的StandardService对象，查看下这个类的继承体系：
LifecycleBase (org.apache.catalina.util)
LifecycleMBeanBase (org.apache.catalina.util)
StandardService (org.apache.catalina.core)
我们发现这个类继承体系和StandardServer是一样的。其实我们再观察的仔细一点会发现从conf/server.xml解析胡来的类的继承体系都是一样的。所以我们调用这些类的init和start方法最后还是会调用到他们的initInternal和startInternal方法。
先看下StandardService的initInternal方法
@Override
protected void initInternal() throws LifecycleException {
super.initInternal();
//调用engine的initInternal方法，这个方法中也没做特别重要的操作，只是做了一个getReal操作
if (engine != null) {
engine.init();
}
//StandardThreadExecutor的initInternal方法中没没干什么事情
// Initialize any Executors
for (Executor executor : findExecutors()) {
if (executor instanceof JmxEnabled) {
((JmxEnabled) executor).setDomain(getDomain());
}
executor.init();
}
// Initialize mapper listener
//这步也没做什么重要操作
mapperListener.init();
// Initialize our defined Connectors
// 连接器主键的初始化，主要是检查连接器的protocolHandler的主键，并将其初始化.
synchronized (connectorsLock) {
for (Connector connector : connectors) {
connector.init();
}
}
}
看了上面的代码，觉得Tomcat源码逻辑还是很清晰的。之前在分析Tomcat组件的文章中讲到Service组件是有Connector组件、engine组件和一个可选的线程池组成。上面的代码中正好对应了这三个组件的初始化话。
Connector组件和engine组件的初始化又会触发他们各自子组件的初始化，所以StandardService的initInternal方法会触发Tomcat下各类组件的初始化。这边大致记录下各个组件初始化话的顺序：
然后再看StandardService的startInternal方法
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();
}
}
}
}
逻辑依然很清楚，StandardService会依次触发各个子组件的start方法。
Engine组件的start：Engine组件的start方法组要作用还是触发了Host组件的start方法，具体代码见
protected synchronized void startInternal() throws LifecycleException {
// Start our subordinate components, if any
if ((loader != null) && (loader instanceof Lifecycle))
((Lifecycle) loader).start();
logger = null;
getLogger();
if ((manager != null) && (manager instanceof Lifecycle))
((Lifecycle) manager).start();
if ((cluster != null) && (cluster instanceof Lifecycle))
((Lifecycle) cluster).start();
Realm realm = getRealmInternal();
if ((realm != null) && (realm instanceof Lifecycle))
((Lifecycle) realm).start();
if ((resources != null) && (resources instanceof Lifecycle))
((Lifecycle) resources).start();
// 找出Engine的子容器，也就是Host容器
Container children[] = findChildren();
List<Future<Void>> results = new ArrayList<Future<Void>>();
//利用线程池调用Host的start方法
for (int i = 0; i < children.length; i++) {
results.add(startStopExecutor.submit(new StartChild(children[i])));
}
boolean fail = false;
for (Future<Void> result : results) {
try {
result.get();
} catch (Exception e) {
log.error(sm.getString("containerBase.threadedStartFailed"), e);
fail = true;
}
}
if (fail) {
throw new LifecycleException(
sm.getString("containerBase.threadedStartFailed"));
}
// Start the Valves in our pipeline (including the basic), if any
if (pipeline instanceof Lifecycle)
((Lifecycle) pipeline).start();
setState(LifecycleState.STARTING);
// Start our thread
threadStart();
}
Host组件的start：经过前面介绍，我们知道Host组件的start方法最后还是会调用自己startInternal方法；
Context组件的start:触发Wrapper的start，加载filter、Servlet等；
Wrapper组件的start:
这边我们重点看下StandardContext的startInternal，这个方法干的事情比较多：
protected synchronized void startInternal() throws LifecycleException {
if(log.isDebugEnabled())
log.debug("Starting " + getBaseName());
// Send j2ee.state.starting notification
if (this.getObjectName() != null) {
Notification notification = new Notification("j2ee.state.starting",
this.getObjectName(), sequenceNumber.getAndIncrement());
broadcaster.sendNotification(notification);
}
setConfigured(false);
boolean ok = true;
// Currently this is effectively a NO-OP but needs to be called to
// ensure the NamingResources follows the correct lifecycle
if (namingResources != null) {
namingResources.start();
}
// Post work directory
postWorkDirectory();
// Add missing components as necessary
if (getResources() == null) { // (1) Required by Loader
if (log.isDebugEnabled())
log.debug("Configuring default Resources");
try {
setResources(new StandardRoot(this));
} catch (IllegalArgumentException e) {
log.error(sm.getString("standardContext.resourcesInit"), e);
ok = false;
}
}
if (ok) {
resourcesStart();
}
if (getLoader() == null) {
WebappLoader webappLoader = new WebappLoader(getParentClassLoader());
webappLoader.setDelegate(getDelegate());
setLoader(webappLoader);
}
// An explicit cookie processor hasn‘t been specified; use the default
if (cookieProcessor == null) {
cookieProcessor = new Rfc6265CookieProcessor();
}
// Initialize character set mapper
getCharsetMapper();
// Validate required extensions
boolean dependencyCheck = true;
try {
dependencyCheck = ExtensionValidator.validateApplication
(getResources(), this);
} catch (IOException ioe) {
log.error(sm.getString("standardContext.extensionValidationError"), ioe);
dependencyCheck = false;
}
if (!dependencyCheck) {
// do not make application available if dependency check fails
ok = false;
}
// Reading the "catalina.useNaming" environment variable
String useNamingProperty = System.getProperty("catalina.useNaming");
if ((useNamingProperty != null)
&& (useNamingProperty.equals("false"))) {
useNaming = false;
}
if (ok && isUseNaming()) {
if (getNamingContextListener() == null) {
NamingContextListener ncl = new NamingContextListener();
ncl.setName(getNamingContextName());
ncl.setExceptionOnFailedWrite(getJndiExceptionOnFailedWrite());
addLifecycleListener(ncl);
setNamingContextListener(ncl);
}
}
// Standard container startup
if (log.isDebugEnabled())
log.debug("Processing standard container startup");
// Binding thread
ClassLoader oldCCL = bindThread();
try {
if (ok) {
// Start our subordinate components, if any
Loader loader = getLoader();
if (loader instanceof Lifecycle) {
((Lifecycle) loader).start();
}
// since the loader just started, the webapp classloader is now
// created.
setClassLoaderProperty("clearReferencesRmiTargets",
getClearReferencesRmiTargets());
setClassLoaderProperty("clearReferencesStopThreads",
getClearReferencesStopThreads());
setClassLoaderProperty("clearReferencesStopTimerThreads",
getClearReferencesStopTimerThreads());
setClassLoaderProperty("clearReferencesHttpClientKeepAliveThread",
getClearReferencesHttpClientKeepAliveThread());
setClassLoaderProperty("clearReferencesObjectStreamClassCaches",
getClearReferencesObjectStreamClassCaches());
setClassLoaderProperty("skipMemoryLeakChecksOnJvmShutdown",
getSkipMemoryLeakChecksOnJvmShutdown());
// By calling unbindThread and bindThread in a row, we setup the
// current Thread CCL to be the webapp classloader
unbindThread(oldCCL);
oldCCL = bindThread();
// Initialize logger again. Other components might have used it
// too early, so it should be reset.
logger = null;
getLogger();
Realm realm = getRealmInternal();
if(null != realm) {
if (realm instanceof Lifecycle) {
((Lifecycle) realm).start();
}
// Place the CredentialHandler into the ServletContext so
// applications can have access to it. Wrap it in a "safe"
// handler so application‘s can‘t modify it.
CredentialHandler safeHandler = new CredentialHandler() {
@Override
public boolean matches(String inputCredentials, String storedCredentials) {
return getRealmInternal().getCredentialHandler().matches(inputCredentials, storedCredentials);
}
@Override
public String mutate(String inputCredentials) {
return getRealmInternal().getCredentialHandler().mutate(inputCredentials);
}
};
context.setAttribute(Globals.CREDENTIAL_HANDLER, safeHandler);
}
// Notify our interested LifecycleListeners
fireLifecycleEvent(Lifecycle.CONFIGURE_START_EVENT, null);
// Start our child containers, if not already started
for (Container child : findChildren()) {
if (!child.getState().isAvailable()) {
child.start();
}
}
// Start the Valves in our pipeline (including the basic),
// if any
if (pipeline instanceof Lifecycle) {
((Lifecycle) pipeline).start();
}
// Acquire clustered manager
Manager contextManager = null;
Manager manager = getManager();
if (manager == null) {
if (log.isDebugEnabled()) {
log.debug(sm.getString("standardContext.cluster.noManager",
Boolean.valueOf((getCluster() != null)),
Boolean.valueOf(distributable)));
}
if ( (getCluster() != null) && distributable) {
try {
contextManager = getCluster().createManager(getName());
} catch (Exception ex) {
log.error("standardContext.clusterFail", ex);
ok = false;
}
} else {
contextManager = new StandardManager();
}
}
// Configure default manager if none was specified
if (contextManager != null) {
if (log.isDebugEnabled()) {
log.debug(sm.getString("standardContext.manager",
contextManager.getClass().getName()));
}
setManager(contextManager);
}
if (manager!=null && (getCluster() != null) && distributable) {
//let the cluster know that there is a context that is distributable
//and that it has its own manager
getCluster().registerManager(manager);
}
}
if (!getConfigured()) {
log.error(sm.getString("standardContext.configurationFail"));
ok = false;
}
// We put the resources into the servlet context
if (ok)
getServletContext().setAttribute
(Globals.RESOURCES_ATTR, getResources());
if (ok ) {
if (getInstanceManager() == null) {
javax.naming.Context context = null;
if (isUseNaming() && getNamingContextListener() != null) {
context = getNamingContextListener().getEnvContext();
}
Map<String, Map<String, String>> injectionMap = buildInjectionMap(
getIgnoreAnnotations() ? new NamingResourcesImpl(): getNamingResources());
setInstanceManager(new DefaultInstanceManager(context,
injectionMap, this, this.getClass().getClassLoader()));
}
getServletContext().setAttribute(
InstanceManager.class.getName(), getInstanceManager());
InstanceManagerBindings.bind(getLoader().getClassLoader(), getInstanceManager());
}
// Create context attributes that will be required
if (ok) {
getServletContext().setAttribute(
JarScanner.class.getName(), getJarScanner());
}
// Set up the context init params
mergeParameters();
// Call ServletContainerInitializers
for (Map.Entry<ServletContainerInitializer, Set<Class<?>>> entry :
initializers.entrySet()) {
try {
entry.getKey().onStartup(entry.getValue(),
getServletContext());
} catch (ServletException e) {
log.error(sm.getString("standardContext.sciFail"), e);
ok = false;
break;
}
}
// Configure and call application event listeners
if (ok) {
if (!listenerStart()) {
log.error(sm.getString("standardContext.listenerFail"));
ok = false;
}
}
// Check constraints for uncovered HTTP methods
// Needs to be after SCIs and listeners as they may programmatically
// change constraints
if (ok) {
checkConstraintsForUncoveredMethods(findConstraints());
}
try {
// Start manager
Manager manager = getManager();
if (manager instanceof Lifecycle) {
((Lifecycle) manager).start();
}
} catch(Exception e) {
log.error(sm.getString("standardContext.managerFail"), e);
ok = false;
}
// Configure and call application filters
if (ok) {
if (!filterStart()) {
log.error(sm.getString("standardContext.filterFail"));
ok = false;
}
}
// Load and initialize all "load on startup" servlets
if (ok) {
if (!loadOnStartup(findChildren())){
log.error(sm.getString("standardContext.servletFail"));
ok = false;
}
}
// Start ContainerBackgroundProcessor thread
super.threadStart();
} finally {
// Unbinding thread
unbindThread(oldCCL);
}
// Set available status depending upon startup success
if (ok) {
if (log.isDebugEnabled())
log.debug("Starting completed");
} else {
log.error(sm.getString("standardContext.startFailed", getName()));
}
startTime=System.currentTimeMillis();
// Send j2ee.state.running notification
if (ok && (this.getObjectName() != null)) {
Notification notification =
new Notification("j2ee.state.running", this.getObjectName(),
sequenceNumber.getAndIncrement());
broadcaster.sendNotification(notification);
}
// The WebResources implementation caches references to JAR files. On
// some platforms these references may lock the JAR files. Since web
// application start is likely to have read from lots of JARs, trigger
// a clean-up now.
getResources().gc();
// Reinitializing if something went wrong
if (!ok) {
setState(LifecycleState.FAILED);
} else {
setState(LifecycleState.STARTING);
}
}
上面的代码有4处重点：调用ServletContainerInitializers、启用Listener、启用Filter和启用startup的Servlet。这个和我们平时对Tomcat启动流程的认知是一致的。
到这里整个Container组件（包括Engine、Host、Context和Wrapper组件）的start方法调用就结束了。接下来是Connector和Mapper组件的start。
//MapperListenner的startInternal
public void startInternal() throws LifecycleException {
setState(LifecycleState.STARTING);
Engine engine = service.getContainer();
if (engine == null) {
return;
}
findDefaultHost();
addListeners(engine);
Container[] conHosts = engine.findChildren();
for (Container conHost : conHosts) {
Host host = (Host) conHost;
if (!LifecycleState.NEW.equals(host.getState())) {
// Registering the host will register the context and wrappers
registerHost(host);
}
}
}
以上方法的主要作用是将Host组件和域名映射起来。
最后看下Connector组件的start：
protected void startInternal() throws LifecycleException {
// Validate settings before starting
if (getPortWithOffset() < 0) {
throw new LifecycleException(sm.getString(
"coyoteConnector.invalidPort", Integer.valueOf(getPortWithOffset())));
}
setState(LifecycleState.STARTING);
try {
//促发protocolHandler组件的start，最后促发endpoint组件的start
//触发endpoint时会建立exceutor线程池，默认的话核心线程数10，最大线程数200
//建立poller线程，最大是2个线程，如果你机器cpu的核数小于2的话就建立1个
//建立accetpor线程，默认是1个（可以看看Acceptor这个类的源代码，了解下怎么接收请求的）
protocolHandler.start();
} catch (Exception e) {
throw new LifecycleException(
sm.getString("coyoteConnector.protocolHandlerStartFailed"), e);
}
}
通过以上一些列复杂的调用过程，最终执行完所有在server.xml里配置的节点的实现类中initInternal和startInternal方法。上面提到的org.apache.catalina.core.StandardServer、org.apache.catalina.core.StandardService、org.apache.catalina.connector.Connector、org.apache.catalina.core.StandardEngine、org.apache.catalina.core.StandardHost、org.apache.catalina.core.StandardContext等等组件的这两个方法都会调用到。
至此，Tomcat已经能开始响应浏览器发过来的请求了。至于具体的Tomcat响应请求流程会在后续博客中介绍。
看了整个启动流程，虽然逻辑是比较清楚的，但是流程比较上，所以有必要做下总结：
step1：Bootstrap作为整个Tomcat主启动类，最主要的功能是创建Catalina对象，并调用它的load和start方法；
step2：Catalina的load方法的作用主要是解析conf/server.xml，生成StandardServer对象（此时生成StandardServer对象中已经包含了各种子组件，比如StandardService、StandardEngine等），再触发StandardServer的init方法；Catalina的start方法又触发了StandardServer的start方法；
step3：StandardServer的init方法和start方法会依次触发各个子组件的initInternal和startInternal方法。大致的触发顺序是：
Engine组件的initInternal（这边要注意的是Engine组件并没有触发它的子组件Host、Context和Wrapper的initInternal）-->Executor组件initInternal（处理请求的工作线程池）-->Mapper组件初始化（mapper组件初始化也没干什么重要的操作，也没触发其他子组件初始化）-->Connector组件初始化（检查连接器的protocolHandler的子组件，并触发其初始化）-->ProtocolHandler组件初始化(触发Endpoint组件初始化)?
? Engine组件的startInternal（主要作用是触发Host组件的start）-->Host组件的startInternal（主要作用是触发Context组件的startInternal）-->Contextz组件的startInternal（加载调用ServletContainerInitializers、加载Listener、加载filtr和startup的Servlet，并且触发Wrapper组件的startInternal）-->Wrapper组件的startInternal（加载映射Servlet）-->Mapper组件的startInternal（将域名和Host组件映射起来）-->Connector组件的startInternal（protocolHandler组件的start，最后促发endpoint组件的start）
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原文地址：https://www.cnblogs.com/54chensongxia/p/13236745.html
