我们知道，springBoot项目只需运行main函数即可，那么tomcat是怎么启动的，springmvc又是如何和tomcat绑定的呢？
1.如何启动tomcat
从SpringBoot主类run方法进入，看context = createApplicationContext();
/**
* Run the Spring application, creating and refreshing a new
* {@link ApplicationContext}.
* @param args the application arguments (usually passed from a Java main method)
* @return a running {@link ApplicationContext}
*/
public ConfigurableApplicationContext run(String... args) {
long startTime = System.nanoTime();
DefaultBootstrapContext bootstrapContext = createBootstrapContext();
ConfigurableApplicationContext context = null;
configureHeadlessProperty();
SpringApplicationRunListeners listeners = getRunListeners(args);
listeners.starting(bootstrapContext, this.mainApplicationClass);
try {
ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
ConfigurableEnvironment environment = prepareEnvironment(listeners, bootstrapContext, applicationArguments);
configureIgnoreBeanInfo(environment);
Banner printedBanner = printBanner(environment);
//创建web环境
context = createApplicationContext();
context.setApplicationStartup(this.applicationStartup);
prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner);
refreshContext(context);
afterRefresh(context, applicationArguments);
Duration timeTakenToStartup = Duration.ofNanos(System.nanoTime() - startTime);
if (this.logStartupInfo) {
new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), timeTakenToStartup);
}
listeners.started(context, timeTakenToStartup);
callRunners(context, applicationArguments);
}
catch (Throwable ex) {
handleRunFailure(context, ex, listeners);
throw new IllegalStateException(ex);
}
try {
Duration timeTakenToReady = Duration.ofNanos(System.nanoTime() - startTime);
listeners.ready(context, timeTakenToReady);
}
catch (Throwable ex) {
handleRunFailure(context, ex, null);
throw new IllegalStateException(ex);
}
return context;
}
/**
* Strategy method used to create the {@link ApplicationContext}. By default this
* method will respect any explicitly set application context class or factory before
* falling back to a suitable default.
* @return the application context (not yet refreshed)
* @see #setApplicationContextFactory(ApplicationContextFactory)
*/
protected ConfigurableApplicationContext createApplicationContext() {
return this.applicationContextFactory.create(this.webApplicationType);
}
private ApplicationContextFactory applicationContextFactory = ApplicationContextFactory.DEFAULT;
@FunctionalInterface
public interface ApplicationContextFactory {
/**
* A default {@link ApplicationContextFactory} implementation that will create an
* appropriate context for the {@link WebApplicationType}.
*/
ApplicationContextFactory DEFAULT = (webApplicationType) -> {
try {
// 从spring.factories中获取ApplicationFactory的实现类
for (ApplicationContextFactory candidate : SpringFactoriesLoader
.loadFactories(ApplicationContextFactory.class, ApplicationContextFactory.class.getClassLoader())) {
//获取到AnnotationConfigServletWebServerApplicationContext对象
ConfiguraAnnotationConfigServletWebServerApplicationContext对象bleApplicationContext context = candidate.create(webApplicationType);
if (context != null) {
return context;
}
}
return new AnnotationConfigApplicationContext();
}
catch (Exception ex) {
throw new IllegalStateException("Unable create a default ApplicationContext instance, "
+ "you may need a custom ApplicationContextFactory", ex);
}
};可以看到ApplicationContextFactory是一个函数式接口，那么applicationContextFactory.create的时候会调用lambda表达式，lamdba表达式里从spring.factories中获取ApplicationFactory的实现类，那么candidate.create(webApplicationType)只能获取到AnnotationConfigServletWebServerApplicationContext
再回到前面，看refreshContext(context)->refresh(context)->applicationContext.refresh();;
AnnotationConfigServletWebServerApplicationContext没有refresh方法，调用的是父类ServletWebServerApplicationContext的refresh方法：
@Override
public final void refresh() throws BeansException, IllegalStateException {
try {
super.refresh();
}
catch (RuntimeException ex) {
WebServer webServer = this.webServer;
if (webServer != null) {
webServer.stop();
}
throw ex;
}
}
ServletWebServerApplicationContext调用的也是父类AbstractApplicationContext的refresh方法：
@Override
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
StartupStep contextRefresh = this.applicationStartup.start("spring.context.refresh");
// Prepare this context for refreshing.
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
postProcessBeanFactory(beanFactory);
StartupStep beanPostProcess = this.applicationStartup.start("spring.context.beans.post-process");
// Invoke factory processors registered as beans in the context.
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
registerBeanPostProcessors(beanFactory);
beanPostProcess.end();
// Initialize message source for this context.
initMessageSource();
// Initialize event multicaster for this context.
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
onRefresh();
// Check for listener beans and register them.
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
finishRefresh();
}
catch (BeansException ex) {
if (logger.isWarnEnabled()) {
logger.warn("Exception encountered during context initialization - " +
"cancelling refresh attempt: " + ex);
}
// Destroy already created singletons to avoid dangling resources.
destroyBeans();
// Reset 'active' flag.
cancelRefresh(ex);
// Propagate exception to caller.
throw ex;
}
finally {
// Reset common introspection caches in Spring's core, since we
// might not ever need metadata for singleton beans anymore...
resetCommonCaches();
contextRefresh.end();
}
}
}
看onRefresh()方法：
/**
* Template method which can be overridden to add context-specific refresh work.
* Called on initialization of special beans, before instantiation of singletons.
* This implementation is empty.
* @throws BeansException in case of errors
* @see #refresh()
*/
protected void onRefresh() throws BeansException {
// For subclasses: do nothing by default.
}
空方法，交由子类实现，也就是ServletWebServerApplicationContext：
@Override
protected void onRefresh() {
//父类方法初始化了web项目的ui主题
super.onRefresh();
try {
//创建web容器
createWebServer();
}
catch (Throwable ex) {
throw new ApplicationContextException("Unable to start web server", ex);
}
}
private void createWebServer() {
WebServer webServer = this.webServer;
ServletContext servletContext = getServletContext();
//进入这里
if (webServer == null && servletContext == null) {
//创建一个DefaultStartupStep
StartupStep createWebServer = this.getApplicationStartup().start("spring.boot.webserver.create");
//获取TomcatServletWebServerFactory
ServletWebServerFactory factory = getWebServerFactory();
createWebServer.tag("factory", factory.getClass().toString());
//获取TomcatWebServer
this.webServer = factory.getWebServer(getSelfInitializer());
createWebServer.end();
getBeanFactory().registerSingleton("webServerGracefulShutdown",
new WebServerGracefulShutdownLifecycle(this.webServer));
getBeanFactory().registerSingleton("webServerStartStop",
new WebServerStartStopLifecycle(this, this.webServer));
}
else if (servletContext != null) {
try {
getSelfInitializer().onStartup(servletContext);
}
catch (ServletException ex) {
throw new ApplicationContextException("Cannot initialize servlet context", ex);
}
}
initPropertySources();
}
首先看getWebServerFactory是如何获取TomcatServletWebServerFactory的：
/**
* Returns the {@link ServletWebServerFactory} that should be used to create the
* embedded {@link WebServer}. By default this method searches for a suitable bean in
* the context itself.
* @return a {@link ServletWebServerFactory} (never {@code null})
*/
protected ServletWebServerFactory getWebServerFactory() {
// Use bean names so that we don't consider the hierarchy
//从beanFactory获取ServletWebServerFactory的名称
String[] beanNames = getBeanFactory().getBeanNamesForType(ServletWebServerFactory.class);
//只能有一个
if (beanNames.length == 0) {
throw new MissingWebServerFactoryBeanException(getClass(), ServletWebServerFactory.class,
WebApplicationType.SERVLET);
}
if (beanNames.length > 1) {
throw new ApplicationContextException("Unable to start ServletWebServerApplicationContext due to multiple "
+ "ServletWebServerFactory beans : " + StringUtils.arrayToCommaDelimitedString(beanNames));
}
//获取该beanFactory
return getBeanFactory().getBean(beanNames[0], ServletWebServerFactory.class);
}可以看到ServletWebServerFactory的实现类有很多个，springBoot默认的实现是TomcatServletWebServerFactory，
它是什么时候加入bean工厂的呢？通过搜索得知它是在ServletWebServerFactoryConfiguration中被注册的：
我们再看this.webServer = factory.getWebServer(getSelfInitializer());
@Override
public WebServer getWebServer(ServletContextInitializer... initializers) {
if (this.disableMBeanRegistry) {
Registry.disableRegistry();
}
Tomcat tomcat = new Tomcat();
File baseDir = (this.baseDirectory != null) ? this.baseDirectory : createTempDir("tomcat");
tomcat.setBaseDir(baseDir.getAbsolutePath());
for (LifecycleListener listener : this.serverLifecycleListeners) {
tomcat.getServer().addLifecycleListener(listener);
}
Connector connector = new Connector(this.protocol);
connector.setThrowOnFailure(true);
tomcat.getService().addConnector(connector);
customizeConnector(connector);
tomcat.setConnector(connector);
tomcat.getHost().setAutoDeploy(false);
configureEngine(tomcat.getEngine());
for (Connector additionalConnector : this.additionalTomcatConnectors) {
tomcat.getService().addConnector(additionalConnector);
}
prepareContext(tomcat.getHost(), initializers);
return getTomcatWebServer(tomcat);
}
/**
* Factory method called to create the {@link TomcatWebServer}. Subclasses can
* override this method to return a different {@link TomcatWebServer} or apply
* additional processing to the Tomcat server.
* @param tomcat the Tomcat server.
* @return a new {@link TomcatWebServer} instance
*/
protected TomcatWebServer getTomcatWebServer(Tomcat tomcat) {
return new TomcatWebServer(tomcat, getPort() >= 0);
}
/**
* Create a new {@link TomcatWebServer} instance.
* @param tomcat the underlying Tomcat server
* @param autoStart if the server should be started
*/
public TomcatWebServer(Tomcat tomcat, boolean autoStart) {
Assert.notNull(tomcat, "Tomcat Server must not be null");
this.tomcat = tomcat;
this.autoStart = autoStart;
initialize();
}
private void initialize() throws WebServerException {
logger.info("Tomcat initialized with port(s): " + getPortsDescription(false));
synchronized (this.monitor) {
try {
addInstanceIdToEngineName();
Context context = findContext();
context.addLifecycleListener((event) -> {
if (context.equals(event.getSource())
&& Lifecycle.START_EVENT.equals(event.getType())) {
// Remove service connectors so that protocol binding doesn't
// happen when the service is started.
removeServiceConnectors();
}
});
// Start the server to trigger initialization listeners
// 启动tomcat
this.tomcat.start();
// We can re-throw failure exception directly in the main thread
rethrowDeferredStartupExceptions();
try {
ContextBindings.bindClassLoader(context, context.getNamingToken(),
getClass().getClassLoader());
}
catch (NamingException ex) {
// Naming is not enabled. Continue
}
// Unlike Jetty, all Tomcat threads are daemon threads. We create a
// blocking non-daemon to stop immediate shutdown
startDaemonAwaitThread();
}
catch (Exception ex) {
stopSilently();
throw new WebServerException("Unable to start embedded Tomcat", ex);
}
}
}
初始化了一个tomcat并启动。
2.tomcat如何注册DispatchServlet
回到this.webServer = factory.getWebServer(getSelfInitializer());
这行代码，看getSelfInitializer()；
/**
* Returns the {@link ServletContextInitializer} that will be used to complete the
* setup of this {@link WebApplicationContext}.
* @return the self initializer
* @see #prepareWebApplicationContext(ServletContext)
*/
private org.springframework.boot.web.servlet.ServletContextInitializer getSelfInitializer() {
return this::selfInitialize;
}
private void selfInitialize(ServletContext servletContext) throws ServletException {
prepareWebApplicationContext(servletContext);
ConfigurableListableBeanFactory beanFactory = getBeanFactory();
ExistingWebApplicationScopes existingScopes = new ExistingWebApplicationScopes(
beanFactory);
WebApplicationContextUtils.registerWebApplicationScopes(beanFactory,
getServletContext());
existingScopes.restore();
WebApplicationContextUtils.registerEnvironmentBeans(beanFactory,
getServletContext());
// 获取ServletContextInitializer实现类
for (ServletContextInitializer beans : getServletContextInitializerBeans()) {
// 注册dispatchServlet
beans.onStartup(servletContext);
}
}
@SafeVarargs
public ServletContextInitializerBeans(ListableBeanFactory beanFactory,
Class... initializerTypes) {
this.initializers = new LinkedMultiValueMap<>();
this.initializerTypes = (initializerTypes.length != 0)
? Arrays.asList(initializerTypes)
: Collections.singletonList(ServletContextInitializer.class);
// 这里实例化了dispatchServlet
addServletContextInitializerBeans(beanFactory);
addAdaptableBeans(beanFactory);
List sortedInitializers = this.initializers.values()
.stream()
.flatMap((value) -> value.stream()
.sorted(AnnotationAwareOrderComparator.INSTANCE))
.collect(Collectors.toList());
this.sortedList = Collections.unmodifiableList(sortedInitializers);
}
private void addServletContextInitializerBeans(ListableBeanFactory beanFactory) {
// 实例化ServletContextInitializer的实现类
for (Entry initializerBean : getOrderedBeansOfType(
beanFactory, ServletContextInitializer.class)) {
addServletContextInitializerBean(initializerBean.getKey(),
initializerBean.getValue(), beanFactory);
}
}
ServletContextInitializer的实现类中有个dispatcherServletRegistration，就是讲dispatchServlet注册到tomcat的；
再回到initializer.onStartup方法：
@Override
public void onStartup(Set> classes, ServletContext servletContext)
throws ServletException {
try {
for (ServletContextInitializer initializer : this.initializers) {
//注册dispatchServlet
initializer.onStartup(servletContext);
}
}
catch (Exception ex) {
this.startUpException = ex;
// Prevent Tomcat from logging and re-throwing when we know we can
// deal with it in the main thread, but log for information here.
if (logger.isErrorEnabled()) {
logger.error("Error starting Tomcat context. Exception: "
+ ex.getClass().getName() + ". Message: " + ex.getMessage());
}
}
}
这里的initializer就是dispatcherServletRegistration，但是他没有onStartup方法，它调用的是它的父类RegistrationBean这个实现类：
@Override
public final void onStartup(ServletContext servletContext) throws ServletException {
String description = getDescription();
if (!isEnabled()) {
logger.info(StringUtils.capitalize(description) + " was not registered (disabled)");
return;
}
//注册
register(description, servletContext);
}由子类DynamicRegistrationBean实现：
@Override
protected final void register(String description, ServletContext servletContext) {
//注册
D registration = addRegistration(description, servletContext);
if (registration == null) {
logger.info(StringUtils.capitalize(description) + " was not registered (possibly already registered?)");
return;
}
configure(registration);
}addRegistration由子类ServletRegistrationBean实现：
可以看到，这里将dispatchServlet注册进了tomcat的servlet。