今天小编给大家分享一下ServletWebServerApplicationContext如何创建Web容器Tomcat的相关知识点，内容详细，逻辑清晰，相信大部分人都还太了解这方面的知识，所以分享这篇文章给大家参考一下，希望大家阅读完这篇文章后有所收获，下面我们一起来了解一下吧。
正文
ServletWebServerApplicationContext实现了父类AbstractApplicationContext的onRefresh模板方法，在这里进行了拓展创建了Web容器。
@Override
protected void onRefresh() {
super.onRefresh();
try {
createWebServer();
}
catch (Throwable ex) {
throw new ApplicationContextException("Unable to start web server", ex);
}
}创建Web服务
private void createWebServer() {
WebServer webServer = this.webServer;
ServletContext servletContext = getServletContext();
if (webServer == null && servletContext == null) {
//一、获取Web服务器工厂
ServletWebServerFactory factory = getWebServerFactory();
//二、获取Web服务
this.webServer = factory.getWebServer(getSelfInitializer());
//三、注册Bean生命周期（在容器启动和销毁时调用）
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);
}
}
//四、初始化上下文环境
initPropertySources();
}一、获取Web服务器工厂
protected ServletWebServerFactory getWebServerFactory() {
// Use bean names so that we don't consider the hierarchy
//获取Web服务器工厂名称
String[] beanNames = getBeanFactory().getBeanNamesForType(ServletWebServerFactory.class);
if (beanNames.length == 0) {
throw new ApplicationContextException("Unable to start ServletWebServerApplicationContext due to missing "
+ "ServletWebServerFactory bean.");
}
if (beanNames.length > 1) {
throw new ApplicationContextException("Unable to start ServletWebServerApplicationContext due to multiple "
+ "ServletWebServerFactory beans : " + StringUtils.arrayToCommaDelimitedString(beanNames));
}
//从容器中获取Web服务器工厂实例
return getBeanFactory().getBean(beanNames[0], ServletWebServerFactory.class);
}这里的Web服务器工厂是通过
ServletWebServerFactoryAutoConfiguration@Configuration(proxyBeanMethods = false)
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@ConditionalOnClass(ServletRequest.class)
//Web启动环境
@ConditionalOnWebApplication(type = Type.SERVLET)
@EnableConfigurationProperties(ServerProperties.class)
//2.1导入Web工厂
@Import({ ServletWebServerFactoryAutoConfiguration.BeanPostProcessorsRegistrar.class,
ServletWebServerFactoryConfiguration.EmbeddedTomcat.class,
ServletWebServerFactoryConfiguration.EmbeddedJetty.class,
ServletWebServerFactoryConfiguration.EmbeddedUndertow.class })
public class ServletWebServerFactoryAutoConfiguration {
//导入Web服务器工厂自定义程序
@Bean
public ServletWebServerFactoryCustomizer servletWebServerFactoryCustomizer(ServerProperties serverProperties) {
return new ServletWebServerFactoryCustomizer(serverProperties);
}
//如果是Tomcat则导入Tomcat自定义程序
@Bean
@ConditionalOnClass(name = "org.apache.catalina.startup.Tomcat")
public TomcatServletWebServerFactoryCustomizer tomcatServletWebServerFactoryCustomizer(
ServerProperties serverProperties) {
return new TomcatServletWebServerFactoryCustomizer(serverProperties);
}
@Bean
@ConditionalOnMissingFilterBean(ForwardedHeaderFilter.class)
@ConditionalOnProperty(value = "server.forward-headers-strategy", havingValue = "framework")
public FilterRegistrationBean<ForwardedHeaderFilter> forwardedHeaderFilter() {
ForwardedHeaderFilter filter = new ForwardedHeaderFilter();
FilterRegistrationBean<ForwardedHeaderFilter> registration = new FilterRegistrationBean<>(filter);
registration.setDispatcherTypes(DispatcherType.REQUEST, DispatcherType.ASYNC, DispatcherType.ERROR);
registration.setOrder(Ordered.HIGHEST_PRECEDENCE);
return registration;
}
/**
* Registers a {@link WebServerFactoryCustomizerBeanPostProcessor}. Registered via
* {@link ImportBeanDefinitionRegistrar} for early registration.
*/
public static class BeanPostProcessorsRegistrar implements ImportBeanDefinitionRegistrar, BeanFactoryAware {
private ConfigurableListableBeanFactory beanFactory;
@Override
public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
if (beanFactory instanceof ConfigurableListableBeanFactory) {
this.beanFactory = (ConfigurableListableBeanFactory) beanFactory;
}
}
@Override
public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata,
BeanDefinitionRegistry registry) {
if (this.beanFactory == null) {
return;
}
registerSyntheticBeanIfMissing(registry, "webServerFactoryCustomizerBeanPostProcessor",
WebServerFactoryCustomizerBeanPostProcessor.class);
registerSyntheticBeanIfMissing(registry, "errorPageRegistrarBeanPostProcessor",
ErrorPageRegistrarBeanPostProcessor.class);
}
private void registerSyntheticBeanIfMissing(BeanDefinitionRegistry registry, String name, Class<?> beanClass) {
if (ObjectUtils.isEmpty(this.beanFactory.getBeanNamesForType(beanClass, true, false))) {
RootBeanDefinition beanDefinition = new RootBeanDefinition(beanClass);
beanDefinition.setSynthetic(true);
registry.registerBeanDefinition(name, beanDefinition);
}
}
}
}1.1 选择导入Web工厂
@Configuration
class ServletWebServerFactoryConfiguration {
ServletWebServerFactoryConfiguration() {
}
//1.如果容器中有Servlet，Undertow，SslClientAuthMode就会创建Undertow工厂
@Configuration
@ConditionalOnClass({Servlet.class, Undertow.class, SslClientAuthMode.class})
@ConditionalOnMissingBean(
value = {ServletWebServerFactory.class},
search = SearchStrategy.CURRENT
)
public static class EmbeddedUndertow {
public EmbeddedUndertow() {
}
@Bean
public UndertowServletWebServerFactory undertowServletWebServerFactory() {
return new UndertowServletWebServerFactory();
}
}
//2.如果容器中有Servlet，Server，Loader就会创建Jetty工厂
@Configuration
@ConditionalOnClass({Servlet.class, Server.class, Loader.class, WebAppContext.class})
@ConditionalOnMissingBean(
value = {ServletWebServerFactory.class},
search = SearchStrategy.CURRENT
)
public static class EmbeddedJetty {
public EmbeddedJetty() {
}
@Bean
public JettyServletWebServerFactory JettyServletWebServerFactory() {
return new JettyServletWebServerFactory();
}
}
//3.如果容器中有Servlet，Tomcat，UpgradeProtocol就会创建Tomcat工厂
@Configuration
@ConditionalOnClass({Servlet.class, Tomcat.class, UpgradeProtocol.class})
@ConditionalOnMissingBean(
value = {ServletWebServerFactory.class},
search = SearchStrategy.CURRENT
)
public static class EmbeddedTomcat {
public EmbeddedTomcat() {
}
@Bean
public TomcatServletWebServerFactory tomcatServletWebServerFactory() {
return new TomcatServletWebServerFactory();
}
}
}二、getWebServer：获取Web服务
public static final String DEFAULT_PROTOCOL = "org.apache.coyote.http11.Http11NioProtocol";
private String protocol = DEFAULT_PROTOCOL;
public WebServer getWebServer(ServletContextInitializer... initializers) {
Tomcat tomcat = new Tomcat();
// 给嵌入式Tomcat创建一个临时文件夹，用于存放Tomcat运行中需要的文件
File baseDir = (this.baseDirectory != null) ? this.baseDirectory : createTempDir("tomcat");
tomcat.setBaseDir(baseDir.getAbsolutePath());
// Tomcat核心概念：Connector，默认放入的protocol为NIO模式
Connector connector = new Connector(this.protocol);
// 给Service添加Connector
tomcat.getService().addConnector(connector);
// 执行定制器，修改即将设置到Tomcat中的Connector
customizeConnector(connector);
tomcat.setConnector(connector);
// 关闭热部署（嵌入式Tomcat不存在修改web.xml、war包等情况）
tomcat.getHost().setAutoDeploy(false);
// 设置backgroundProcessorDelay机制
configureEngine(tomcat.getEngine());
for (Connector additionalConnector : this.additionalTomcatConnectors) {
tomcat.getService().addConnector(additionalConnector);
}
// 2.1 创建TomcatEmbeddedContext
prepareContext(tomcat.getHost(), initializers);
// 2.2. 创建TomcatWebServer
return getTomcatWebServer(tomcat);
}2.1 创建TomcatEmbeddedContext
（注释均已在源码中标注好，小伙伴们对哪一步感兴趣可以借助IDE自己动手Debug体会一下实现）
protected void prepareContext(Host host, ServletContextInitializer[] initializers) {
File documentRoot = getValidDocumentRoot();
// 创建TomcatEmbeddedContext
TomcatEmbeddedContext context = new TomcatEmbeddedContext();
if (documentRoot != null) {
context.setResources(new LoaderHidingResourceRoot(context));
}
context.setName(getContextPath());
context.setDisplayName(getDisplayName());
// 设置contextPath，很熟悉了
context.setPath(getContextPath());
// 给嵌入式Tomcat创建docbase的临时文件夹
File docBase = (documentRoot != null) ? documentRoot : createTempDir("tomcat-docbase");
context.setDocBase(docBase.getAbsolutePath());
// 注册监听器
context.addLifecycleListener(new FixContextListener());
context.setParentClassLoader((this.resourceLoader != null) ? this.resourceLoader.getClassLoader()
: ClassUtils.getDefaultClassLoader());
// 设置默认编码映射
resetDefaultLocaleMapping(context);
addLocaleMappings(context);
context.setUseRelativeRedirects(false);
try {
context.setCreateUploadTargets(true);
}
catch (NoSuchMethodError ex) {
// Tomcat is < 8.5.39. Continue.
}
configureTldSkipPatterns(context);
// 自定义的类加载器，可以加载web应用的jar包
WebappLoader loader = new WebappLoader(context.getParentClassLoader());
loader.setLoaderClass(TomcatEmbeddedWebappClassLoader.class.getName());
// 指定类加载器遵循双亲委派机制
loader.setDelegate(true);
context.setLoader(loader);
// 注册默认的Servlet
if (isRegisterDefaultServlet()) {
addDefaultServlet(context);
}
// 如果需要jsp支持，注册jsp的Servlet和Initializer
if (shouldRegisterJspServlet()) {
addJspServlet(context);
addJasperInitializer(context);
}
// 注册监听器
context.addLifecycleListener(new StaticResourceConfigurer(context));
ServletContextInitializer[] initializersToUse = mergeInitializers(initializers);
host.addChild(context);
configureContext(context, initializersToUse);
postProcessContext(context);
}2.2. 创建TomcatWebServer
protected TomcatWebServer getTomcatWebServer(Tomcat tomcat) {
return new TomcatWebServer(tomcat, getPort() >= 0, getShutdown());
}进入
TomcatWebServerpublic TomcatWebServer(Tomcat tomcat, boolean autoStart) {
Assert.notNull(tomcat, "Tomcat Server must not be null");
this.tomcat = tomcat;
this.autoStart = autoStart;
//初始化服务
initialize();
}初始化TomcatWebServer
private void initialize() throws WebServerException {
logger.info("Tomcat initialized with port(s): " + getPortsDescription(false));
synchronized (this.monitor) {
try {
//设置Engine的id
addInstanceIdToEngineName();
//获取Context（TomcatEmbeddedContext 2.1中创建出来的）
Context context = findContext();
//添加监听器 TomcatEmbeddedContext
//在服务启动时如果有连接进来先删除连接，以便在启动服务时不会发生协议绑定。
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.
//删除ServiceConnectors，以便在启动服务时不会发生协议绑定。
removeServiceConnectors();
}
});
// Start the server to trigger initialization listeners
//2.2.1 启动Tomcat
this.tomcat.start();
// We can re-throw failure exception directly in the main thread
//Tomcat启动有异常需要在主线程中抛出
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
//开启阻塞非守护线程停止web容器
startDaemonAwaitThread();
}
catch (Exception ex) {
stopSilently();
destroySilently();
throw new WebServerException("Unable to start embedded Tomcat", ex);
}
}
}2.2.1 启动Tomcat
创建和初始化Server和Service
public void start() throws LifecycleException {
//创建服务（Server和Service）
getServer();
server.start();
}启动服务
public final synchronized void start() throws LifecycleException {
//如果是正在启动或启动状态
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;
}
//如果是新建状态
if (state.equals(LifecycleState.NEW)) {
//2.2.1.1 初始化服务
init();
//如果是失败状态
} else if (state.equals(LifecycleState.FAILED)) {
//停止服务
stop();
//如果不是初始化也不是停止状态
} else if (!state.equals(LifecycleState.INITIALIZED) &&
!state.equals(LifecycleState.STOPPED)) {
//修改状态
invalidTransition(Lifecycle.BEFORE_START_EVENT);
}
try {
//修改状态为准备启动
setStateInternal(LifecycleState.STARTING_PREP, null, false);
//2.2.1.2 启动Internal
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());
}
}2.2.1.1 初始化Server
public final synchronized void init() throws LifecycleException {
if (!state.equals(LifecycleState.NEW)) {
invalidTransition(Lifecycle.BEFORE_INIT_EVENT);
}
try {
//设置状态为初始化
setStateInternal(LifecycleState.INITIALIZING, null, false);
//初始化
initInternal();
//设置状态为初始化完成
setStateInternal(LifecycleState.INITIALIZED, null, false);
} catch (Throwable t) {
handleSubClassException(t, "lifecycleBase.initFail", toString());
}
}初始化 Server
protected void initInternal() throws LifecycleException {
//调用父类初始化（设置名称：Tomcat，类型：Server）
super.initInternal();
// Initialize utility executor
reconfigureUtilityExecutor(getUtilityThreadsInternal(utilityThreads));
//注册线程池
register(utilityExecutor, "type=UtilityExecutor");
// 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
//注册字符串缓存
onameStringCache = register(new StringCache(), "type=StringCache");
// Register the MBeanFactory
MBeanFactory factory = new MBeanFactory();
factory.setContainer(this);
//注册Bean工厂
onameMBeanFactory = register(factory, "type=MBeanFactory");
// Register the naming resources
//注册命名资源
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
//2.2.1.1.1 初始化service（2.2.1最开始时创建）
for (Service service : services) {
service.init();
}
}初始化Service
public final synchronized void init() throws LifecycleException {
if (!state.equals(LifecycleState.NEW)) {
invalidTransition(Lifecycle.BEFORE_INIT_EVENT);
}
try {
//设置状态为初始化
setStateInternal(LifecycleState.INITIALIZING, null, false);
//初始化
initInternal();
//设置状态为初始化完成
setStateInternal(LifecycleState.INITIALIZED, null, false);
} catch (Throwable t) {
handleSubClassException(t, "lifecycleBase.initFail", toString());
}
}初始化Service
protected void initInternal() throws LifecycleException {
//调用父类初始化（设置名称：Tomcat，类型：Server）
super.initInternal();
//2.2.1.1.1.1 初始化engine
if (engine != null) {
engine.init();
}
// Initialize any Executors
//2.2.1.1.1.2 初始化executor
for (Executor executor : findExecutors()) {
if (executor instanceof JmxEnabled) {
((JmxEnabled) executor).setDomain(getDomain());
}
executor.init();
}
// Initialize mapper listener
//2.2.1.1.1.3 初始化mapperListener
mapperListener.init();
// Initialize our defined Connectors
//2.2.1.1.1.4 初始化connector
synchronized (connectorsLock) {
for (Connector connector : connectors) {
connector.init();
}
}
}初始化engine
protected void initInternal() throws LifecycleException {
// Ensure that a Realm is present before any attempt is made to start
// one. This will create the default NullRealm if necessary.
// 在尝试启动一个Realm之前，请确保存在一个Realm。如有必要，这将创建默认的NullRealm
getRealm();
super.initInternal();
}
public Realm getRealm() {
Realm configured = super.getRealm();
// If no set realm has been called - default to NullRealm
// This can be overridden at engine, context and host level
if (configured == null) {
configured = new NullRealm();
this.setRealm(configured);
}
return configured;
}初始化executor
它还是调的父类
LifecycleMBeanBaseprotected void initInternal() throws LifecycleException {
super.initInternal();
}初始化mapperListener
protected void initInternal() throws LifecycleException {
// If oname is not null then registration has already happened via preRegister().
// 如果oname不为null，则已经通过preRegister()进行了注册
if (oname == null) {
mserver = Registry.getRegistry(null, null).getMBeanServer();
oname = register(this, getObjectNameKeyProperties());
}
}初始化connector
protected void initInternal() throws LifecycleException {
super.initInternal();
if (protocolHandler == null) {
throw new LifecycleException(
sm.getString("coyoteConnector.protocolHandlerInstantiationFailed"));
}
// Initialize adapter
adapter = new CoyoteAdapter(this);
protocolHandler.setAdapter(adapter);
if (service != null) {
protocolHandler.setUtilityExecutor(service.getServer().getUtilityExecutor());
}
// Make sure parseBodyMethodsSet has a default
if (null == parseBodyMethodsSet) {
setParseBodyMethods(getParseBodyMethods());
}
if (protocolHandler.isAprRequired() && !AprStatus.isInstanceCreated()) {
throw new LifecycleException(sm.getString("coyoteConnector.protocolHandlerNoAprListener",
getProtocolHandlerClassName()));
}
if (protocolHandler.isAprRequired() && !AprStatus.isAprAvailable()) {
throw new LifecycleException(sm.getString("coyoteConnector.protocolHandlerNoAprLibrary",
getProtocolHandlerClassName()));
}
if (AprStatus.isAprAvailable() && AprStatus.getUseOpenSSL() &&
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