1 SpringBoot支援的容器

Tomcat:
	預設使用
	
Jetty:
	長連線,eg:聊天系統

Undertow:
	不支援jsp
	高效能,非阻塞

2 將預設容器設為jetty

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"
 
>
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.springboot</groupId>
    <artifactId>springboot-21</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>springboot-21</name>
    <description
 
>Demo project for Spring Boot</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.0.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
 

    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>

            <!--排除內嵌的tomcat-->
            <exclusions>
                <exclusion>
                    <groupId>org.springframework.boot</groupId>
                    <artifactId>spring-boot-starter-tomcat</artifactId>
                </exclusion>
            </exclusions>
        </dependency>

        <!--引入其他的Servlet容器-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-jetty</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

3 嵌入式Servlet容器自動配置原理

@Configuration
@AutoConfigureOrder(-2147483648)
@ConditionalOnClass({ServletRequest.class})
@ConditionalOnWebApplication(
    type = Type.SERVLET
)
@EnableConfigurationProperties({ServerProperties.class})

// BeanPostProcessorsRegistrar(後置處理器)：向容器中匯入元件(Spring註解版)
// 匯入了WebServerFactoryCustomizerBeanPostProcessor
// 後置處理器：bean初始化前後（建立完物件，還沒賦值賦值）執行初始化工作
@Import({ServletWebServerFactoryAutoConfiguration.BeanPostProcessorsRegistrar.class, EmbeddedTomcat.class, EmbeddedJetty.class, EmbeddedUndertow.class})
public class ServletWebServerFactoryAutoConfiguration {
	...
}

• EmbeddedTomcat.class, EmbeddedJetty.class, EmbeddedUndertow.class

@Configuration
class ServletWebServerFactoryConfiguration {
    ServletWebServerFactoryConfiguration() {
    }

    @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();
        }
    }

    @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();
        }
    }

    @Configuration
	// 判斷當前是否引入了Tomcat依賴(pom.xml)
    @ConditionalOnClass({Servlet.class, Tomcat.class, UpgradeProtocol.class})
	
	// 判斷當前容器是否有使用者自己定義ServletWebServerFactory：嵌入式的Servlet容器工廠；
	// 作用：建立嵌入式的Servlet容器
    @ConditionalOnMissingBean(
        value = {ServletWebServerFactory.class},
        search = SearchStrategy.CURRENT
    )
    public static class EmbeddedTomcat {
        public EmbeddedTomcat() {
        }

        @Bean
        public TomcatServletWebServerFactory tomcatServletWebServerFactory() {
            return new TomcatServletWebServerFactory();
        }
    }
}

• TomcatServletWebServerFactory

public WebServer getWebServer(ServletContextInitializer... initializers) {

	// 建立一個Tomcat
	Tomcat tomcat = new Tomcat();
	
	// 配置Tomcat
	File baseDir = this.baseDirectory != null ? this.baseDirectory : this.createTempDir("tomcat");
	tomcat.setBaseDir(baseDir.getAbsolutePath());
	Connector connector = new Connector(this.protocol);
	tomcat.getService().addConnector(connector);
	this.customizeConnector(connector);
	tomcat.setConnector(connector);
	tomcat.getHost().setAutoDeploy(false);
	this.configureEngine(tomcat.getEngine());
	Iterator var5 = this.additionalTomcatConnectors.iterator();

	while(var5.hasNext()) {
		Connector additionalConnector = (Connector)var5.next();
		tomcat.getService().addConnector(additionalConnector);
	}

	this.prepareContext(tomcat.getHost(), initializers);
	
	// 將配置完成的Tomcat傳入，返回TomcatWebServer,啟動Tomcat伺服器
	return this.getTomcatWebServer(tomcat);
}

4 嵌入式容器的配置修改原理

4.1 通過application.properties修改

• org.springframework.boot.autoconfigure.web.ServerProperties

4.2 通過WebServerFactoryCustomizer修改

• org.springframework.boot.web.server.ConfigurableWebServerFactory

5 BeanPostProcessorsRegistrar(後置處理器)

public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
	if (this.beanFactory != null) {
		this.registerSyntheticBeanIfMissing(registry, "webServerFactoryCustomizerBeanPostProcessor", WebServerFactoryCustomizerBeanPostProcessor.class);
		this.registerSyntheticBeanIfMissing(registry, "errorPageRegistrarBeanPostProcessor", ErrorPageRegistrarBeanPostProcessor.class);
	}
}

• WebServerFactoryCustomizerBeanPostProcessor

public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
	//如果初始化的是WebServerFactory型別的元件
	if (bean instanceof WebServerFactory) {
		this.postProcessBeforeInitialization((WebServerFactory)bean);
	}

	return bean;
}

private void postProcessBeforeInitialization(WebServerFactory webServerFactory) {
	// 獲取所有的定製器，呼叫每個定製器的customize方法來給Servlet容器進行屬性賦值；
	((Callbacks)LambdaSafe.callbacks(WebServerFactoryCustomizer.class, this.getCustomizers(), webServerFactory, new Object[0]).withLogger(WebServerFactoryCustomizerBeanPostProcessor.class)).invoke((customizer) -> {
		customizer.customize(webServerFactory);
	});
}


private void postProcessBeforeInitialization(
			ConfigurableEmbeddedServletContainer bean) {
    //獲取所有的定製器，呼叫每一個定製器的customize方法來給Servlet容器進行屬性賦值；
    for (EmbeddedServletContainerCustomizer customizer : getCustomizers()) {
        customizer.customize(bean);
    }
}

private Collection<WebServerFactoryCustomizer<?>> getCustomizers() {
	if (this.customizers == null) {
		
		this.customizers = new ArrayList(this.getWebServerFactoryCustomizerBeans());
		this.customizers.sort(AnnotationAwareOrderComparator.INSTANCE);
		this.customizers = Collections.unmodifiableList(this.customizers);
	}

	return this.customizers;
}

private Collection<WebServerFactoryCustomizer<?>> getWebServerFactoryCustomizerBeans() {
	// 從容器中獲取所有這葛型別的元件：WebServerFactoryCustomizer
	// 定製Servlet容器:給容器中可以新增一個WebServerFactoryCustomizer型別的元件
	return this.beanFactory.getBeansOfType(WebServerFactoryCustomizer.class, false, false).values();
}

6 總結

1: 自動配置類生效ServletWebServerFactoryAutoConfiguration,根據依賴新增嵌入式容器工廠TomcatServletWebServerFactory
2: 容器中元件建立物件時,會呼叫後置處理器,WebServerFactoryCustomizerBeanPostProcessor
3: 後置處理器，從容器中獲取所有的WebServerFactoryCustomizer.class，呼叫定製器的定製方法