概述
Spring Boot對所支持的Servlet Web服務器實現做了建模抽象:
| Servlet容器類型 | WebServer模型接口 | WebServer工廠實現類 |
| Tomcat | TomcatWebServer | TomcatServletWebServerFactory |
| Jetty | JettyWebServer | JettyServletWebServerFactory |
| Undertow | UndertowWebServer | UndertowServletWebServerFactory |
基於此模型概念,在一個Servlet Web應用中，Spring Boot會使用上表中所說的WebServer工廠組件生成相應的WebServer實例。而這里的WebServer工廠組件又是從哪里來的呢 ？ 這就是自動配置類ServletWebServerFactoryAutoConfiguration的任務了。
自動配置類ServletWebServerFactoryAutoConfiguration首先通過注解聲明自己的生效條件:類 ServletRequest 存在於 classpath 上時才生效,也就是要求javax.servlet-api包必須被引用;當前應用必須是Spring MVC應用才生效；在以上條件被滿足時，ServletWebServerFactoryAutoConfiguration引入了如下三個配置類 :
EmbeddedTomcat
EmbeddedJetty
EmbeddedUndertow
這三個配置類是ServletWebServerFactoryConfiguration的嵌套配置類，它們會分別檢測classpath上存在的類，從而判斷當前應用使用的是Tomcat/Jetty/Undertow中的哪一個Servlet Web服務器,從而決定定義相應的工廠組件bean : TomcatServletWebServerFactory/JettyServletWebServerFactory/UndertowServletWebServerFactory。
詳解：
ServletWebServerFactoryAutoConfiguration
/**
* EnableAutoConfiguration Auto-configuration for servlet web servers.
*
*/
@Configuration
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
// 僅在類 ServletRequest 存在於 classpath 上時才生效
@ConditionalOnClass(ServletRequest.class)
// 僅在當前應用是 Servlet Web 應用時才生效
@ConditionalOnWebApplication(type = Type.SERVLET)
// 確保前綴為 server 的配置參數加載到 bean ServerProperties
@EnableConfigurationProperties(ServerProperties.class)
// 1. 導入 ServletWebServerFactoryAutoConfiguration.BeanPostProcessorsRegistrar 以注冊
// BeanPostProcessor : WebServerFactoryCustomizerBeanPostProcessor 和
// ErrorPageRegistrarBeanPostProcessor
// 2. 導入 EmbeddedTomcat/EmbeddedJetty/EmbeddedUndertow 這三個屬於
// ServletWebServerFactoryConfiguration 的嵌套配置類，這三個配置類會分別檢測
// classpath上存在的類，從而判斷當前應用使用的是 Tomcat/Jetty/Undertow,
// 從而決定定義哪一個 Servlet Web服務器的工廠 bean :
// TomcatServletWebServerFactory/JettyServletWebServerFactory/UndertowServletWebServerFactory
@Import({ ServletWebServerFactoryAutoConfiguration.BeanPostProcessorsRegistrar.class,
ServletWebServerFactoryConfiguration.EmbeddedTomcat.class,
ServletWebServerFactoryConfiguration.EmbeddedJetty.class,
ServletWebServerFactoryConfiguration.EmbeddedUndertow.class })
public class ServletWebServerFactoryAutoConfiguration {
// 定義 bean ServletWebServerFactoryCustomizer，這里與properties中serverProperties配置聯系，解釋了為什么配置文件也可修改servlet容器配置
@Bean
public ServletWebServerFactoryCustomizer servletWebServerFactoryCustomizer(
ServerProperties serverProperties) {
return new ServletWebServerFactoryCustomizer(serverProperties);
}
// 針對當前Servlet容器是Tomcat時定義該 bean，用於定制化 TomcatServletWebServerFactory
@Bean
// 僅在類 org.apache.catalina.startup.Tomcat 存在於 classpath 上時才生效
@ConditionalOnClass(name = "org.apache.catalina.startup.Tomcat")
public TomcatServletWebServerFactoryCustomizer tomcatServletWebServerFactoryCustomizer(
ServerProperties serverProperties) {
return new TomcatServletWebServerFactoryCustomizer(serverProperties);
}
/**
* Registers a WebServerFactoryCustomizerBeanPostProcessor. Registered via
* ImportBeanDefinitionRegistrar for early registration.
* 這是一個 ImportBeanDefinitionRegistrar， 它會向容器注入兩個 BeanPostProcessor :
* 1. WebServerFactoryCustomizerBeanPostProcessor
* 該 BeanPostProcessor 會搜集容器中所有的 WebServerFactoryCustomizer，對當前應用所采用的
* WebServerFactory 被初始化前進行定制
* 2. ErrorPageRegistrarBeanPostProcessor
* 該 BeanPostProcessor 會搜集容器中所有的 ErrorPageRegistrar，添加到當前應用所采用的
* ErrorPageRegistry 中,實際上，這里的 ErrorPageRegistry 會是 ConfigurableWebServerFactory,
* 具體實現上來講，是一個 ConfigurableTomcatWebServerFactory,ConfigurableJettyWebServerFactory
* 或者 ConfigurableUndertowWebServerFactory,分別對應 Tomcat, Jetty, Undertow 這三種
* Servlet Web 容器的工廠類
*/
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);
}
}
}ServletWebServerFactoryConfiguration
ServletWebServerFactoryConfiguration是一個針對ServletWebServerFactory進行配置的配置類。它通過檢測應用classpath存在的類，從而判斷當前應用要使用哪個Servlet容器:Tomcat,Jetty還是Undertow。檢測出來之后，定義相應的Servlet Web服務器工廠組件bean
| Servlet容器類型 | WebServerFactory實現類 |
| Tomcat | TomcatServletWebServerFactory |
| Jetty | JettyServletWebServerFactory |
| Undertow | UndertowServletWebServerFactory |
注意，以上三個實現類都繼承自抽象基類AbstractServletWebServerFactory,實現了接口WebServerFactory,ErrorPageRegistry。該特征會被WebServerFactoryCustomizerBeanPostProcessor和ErrorPageRegistrarBeanPostProcessor使用，用於對WebServerFactory進行定制化，以及設置相應的錯誤頁面。
@Configuration
class ServletWebServerFactoryConfiguration {
@Configuration
@ConditionalOnClass({ Servlet.class, Tomcat.class, UpgradeProtocol.class })
@ConditionalOnMissingBean(value = ServletWebServerFactory.class, search = SearchStrategy.CURRENT)
public static class EmbeddedTomcat {
@Bean
public TomcatServletWebServerFactory tomcatServletWebServerFactory() {
return new TomcatServletWebServerFactory();
}
}
/**
* Nested configuration if Jetty is being used.
*/
@Configuration
@ConditionalOnClass({ Servlet.class, Server.class, Loader.class, WebAppContext.class })
@ConditionalOnMissingBean(value = ServletWebServerFactory.class, search = SearchStrategy.CURRENT)
public static class EmbeddedJetty {
@Bean
public JettyServletWebServerFactory JettyServletWebServerFactory() {
return new JettyServletWebServerFactory();
}
}
/**
* Nested configuration if Undertow is being used.
*/
@Configuration
@ConditionalOnClass({ Servlet.class, Undertow.class, SslClientAuthMode.class })
@ConditionalOnMissingBean(value = ServletWebServerFactory.class, search = SearchStrategy.CURRENT)
public static class EmbeddedUndertow {
@Bean
public UndertowServletWebServerFactory undertowServletWebServerFactory() {
return new UndertowServletWebServerFactory();
}
}
}查看代碼：
這里以TomcatServletWebServerFactory:
注意這里此方法返回值：getTomcatWebServer(tomcat);查看此方法：傳入兩個參數，只要得到端口號大於0就默認啟動
同時查看：其中TomcatWebServer類構造方法：
這時候tomcat啟動開始。查看initialize();方法
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
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();
destroySilently();
throw new WebServerException("Unable to start embedded Tomcat", ex);
}
}
}可以看到有啟動： this.tomcat.start();啟動！
思考
如何對嵌入式容器的配置修改是怎么生效的
兩種方法:1、修改properties
2、配置servlet容器定制器
@Bean
public WebServerFactoryCustomizer<TomcatServletWebServerFactory> myWebServerFactoryCustomizer() {
return new WebServerFactoryCustomizer<TomcatServletWebServerFactory>() {
public void customize(TomcatServletWebServerFactory factory) {
//設置相關配置
factory.setPort(8080);
}
};
}思考：怎么修改的原理？
springboot版本對照：
1.5.x:-->
//導入后置處理器的注冊器，作用給容器導入組件
@Import(BeanPostProcessorsRegistrar.class
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@Configuration
@ConditionalOnWebApplication
//導入后置處理器的注冊器
@Import(BeanPostProcessorsRegistrar.class)
public class EmbeddedServletContainerAutoConfiguration {.....}2.x:將其作為內部類導入組件
@Configuration
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@ConditionalOnClass(ServletRequest.class)
@ConditionalOnWebApplication(type = Type.SERVLET)
@EnableConfigurationProperties(ServerProperties.class)
@Import({ ServletWebServerFactoryAutoConfiguration.BeanPostProcessorsRegistrar.class,
ServletWebServerFactoryConfiguration.EmbeddedTomcat.class,
ServletWebServerFactoryConfiguration.EmbeddedJetty.class,
ServletWebServerFactoryConfiguration.EmbeddedUndertow.class })
public class ServletWebServerFactoryAutoConfiguration {
.....
public static class BeanPostProcessorsRegistrar implements ImportBeanDefinitionRegistrar, BeanFactoryAware {
...
@Override
public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata,BeanDefinitionRegistry registry) {
if (this.beanFactory == null) {
return;
}
//導入servlet定制器的后置處理器
registerSyntheticBeanIfMissing(registry, "webServerFactoryCustomizerBeanPostProcessor",
WebServerFactoryCustomizerBeanPostProcessor.class);
registerSyntheticBeanIfMissing(registry, "errorPageRegistrarBeanPostProcessor",
ErrorPageRegistrarBeanPostProcessor.class);
}
}
}觀察方法：BeanPostProcessorsRegistrar，導入servlet定制器的后置處理器
作用：后置處理器：bean初始化前后（創建完對象，還沒賦值賦值）執行初始化工作
WebServerFactoryCustomizerBeanPostProcessor
@Override
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
if (bean instanceof WebServerFactory) {
postProcessBeforeInitialization((WebServerFactory) bean);
}
return bean;
}初始化之前：判斷如果當前初始化組件是WebServerFactory 的一個組件，就調用postProcessBeforeInitialization此方法，
private void postProcessBeforeInitialization(WebServerFactory webServerFactory) {
LambdaSafe.callbacks(WebServerFactoryCustomizer.class, getCustomizers(), webServerFactory)
.withLogger(WebServerFactoryCustomizerBeanPostProcessor.class)
.invoke((customizer) -> customizer.customize(webServerFactory));
}此方法：獲取所有的定制器，調用每一個定制器的customize方法，來給servlet容器進行屬性賦值
getCustomizers()方法以上調用：
private Collection<WebServerFactoryCustomizer<?>> getCustomizers() {
if (this.customizers == null) {
// Look up does not include the parent context
this.customizers = new ArrayList<>(getWebServerFactoryCustomizerBeans());
this.customizers.sort(AnnotationAwareOrderComparator.INSTANCE);
this.customizers = Collections.unmodifiableList(this.customizers);
}
return this.customizers;
}
this.customizers = new ArrayList<>(getWebServerFactoryCustomizerBeans());此方法點進去：
@SuppressWarnings({ "unchecked", "rawtypes" })
private Collection<WebServerFactoryCustomizer<?>> getWebServerFactoryCustomizerBeans() {
return (Collection) this.beanFactory.getBeansOfType(WebServerFactoryCustomizer.class, false, false).values();
}作用：從容器中獲取所有該類型的組件：WebServerFactoryCustomizer這里該組件我們可以定制。
思考2？在properties中是怎樣定制servlet容器的？？
@Configuration
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@ConditionalOnClass(ServletRequest.class)
@ConditionalOnWebApplication(type = Type.SERVLET)
@EnableConfigurationProperties(ServerProperties.class)
@Import({ ServletWebServerFactoryAutoConfiguration.BeanPostProcessorsRegistrar.class,
ServletWebServerFactoryConfiguration.EmbeddedTomcat.class,
ServletWebServerFactoryConfiguration.EmbeddedJetty.class,
ServletWebServerFactoryConfiguration.EmbeddedUndertow.class })
public class ServletWebServerFactoryAutoConfiguration {......}2.x:中直接在servelt容器工廠的自動配置類：@EnableConfigurationProperties(ServerProperties.class)注解，向容器中添加ServerProperties組件，在SpringBoot中xxxProperties類都是和配置文件映射的類，用戶可以通過配置文件配置類中屬性。例如：用戶可以通過server.port配置容器端口號。
1.5.x:serverProperties中實現方法。
嵌入式servlet容器自動配置原理的步驟
1）、SpringBoot根據導入的依賴情況，容器中導入的ServletWebServerFactoryConfiguration配置類，給容器添加相應的TomcatServletWebServerFactory，通過TomcatServletWebServerFactory的getWebServer（）啟動servelt容器
2）、容器中某個組件要創建對象就會驚動后置處理器；@Import({ServletWebServerFactoryAutoConfiguration.BeanPostProcessorsRegistrar.class,
只要是嵌入式的Servlet容器工廠，后置處理器就工作，用與定制嵌入式容器的配置修改，
3）、后置處理器，執行postProcessBeforeInitialization（）方法，調用定制器的定制方法；