SpringBoot自动装配--嵌入式Servlet容器

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简介

一般做Springboot项目，都是打成jar包，并且内嵌一个Servlet容器（Tomcat,jetty，undertow）,今天就了解一下有关内嵌Servlet容器的自动装配(2.0.0版本),主要是两个类EmbeddedWebServerFactoryCustomizerAutoConfiguration和ServletWebServerFactoryAutoConfiguration

EmbeddedWebServerFactoryCustomizerAutoConfiguration

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@Configuration
@EnableConfigurationProperties(ServerProperties.class)
public class EmbeddedWebServerFactoryCustomizerAutoConfiguration {

	@ConditionalOnClass({ Tomcat.class, UpgradeProtocol.class })
	public static class TomcatWebServerFactoryCustomizerConfiguration {

		@Bean
		public TomcatWebServerFactoryCustomizer tomcatWebServerFactoryCustomizer(
				Environment environment, ServerProperties serverProperties) {
			return new TomcatWebServerFactoryCustomizer(environment, serverProperties);
		}
	}

	/**
	 * Nested configuration if Jetty is being used.
	 */
	@Configuration
	@ConditionalOnClass({ Server.class, Loader.class, WebAppContext.class })
	public static class JettyWebServerFactoryCustomizerConfiguration {

		@Bean
		public JettyWebServerFactoryCustomizer jettyWebServerFactoryCustomizer(
				Environment environment, ServerProperties serverProperties) {
			return new JettyWebServerFactoryCustomizer(environment, serverProperties);
		}

	}

	/**
	 * Nested configuration if Undertow is being used.
	 */
	@Configuration
	@ConditionalOnClass({ Undertow.class, SslClientAuthMode.class })
	public static class UndertowWebServerFactoryCustomizerConfiguration {

		@Bean
		public UndertowWebServerFactoryCustomizer undertowWebServerFactoryCustomizer(
				Environment environment, ServerProperties serverProperties) {
			return new UndertowWebServerFactoryCustomizer(environment, serverProperties);
		}

	}

}

根据导入的依赖不同，会注册不同的WebServerFactoryCustomizer(容器工厂定制器)，默认在spring-boot-starter-web中会依赖spring-boot-starter-tomcat，即默认使用的是Tomcat容器，如果想用其他的容器，就将默认的依赖删除，加入指定容器的依赖即可。就以TomcatWebServerFactoryCustomizer为例：

ServerProperties

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@ConfigurationProperties(prefix = "server", ignoreUnknownFields = true)
public class ServerProperties {}

从配置文件中读取属性值。

TomcatWebServerFactoryCustomizer

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public class TomcatWebServerFactoryCustomizer implements
		WebServerFactoryCustomizer<ConfigurableTomcatWebServerFactory>, Ordered {

	private final Environment environment;

	private final ServerProperties serverProperties;

	public TomcatWebServerFactoryCustomizer(Environment environment,
			ServerProperties serverProperties) {
		this.environment = environment;
		this.serverProperties = serverProperties;
	}

	@Override
	public void customize(ConfigurableTomcatWebServerFactory factory) {
		ServerProperties properties = this.serverProperties;
		ServerProperties.Tomcat tomcatProperties = properties.getTomcat();
		PropertyMapper propertyMapper = PropertyMapper.get();
		propertyMapper.from(tomcatProperties::getBasedir).whenNonNull()
				.to(factory::setBaseDirectory);
		propertyMapper.from(tomcatProperties::getBackgroundProcessorDelay).whenNonNull()
				.as(Duration::getSeconds).as(Long::intValue)
				.to(factory::setBackgroundProcessorDelay);
		customizeRemoteIpValve(factory);
		propertyMapper.from(tomcatProperties::getMaxThreads).when(this::isPositive)
				.to((maxThreads) -> customizeMaxThreads(factory,
						tomcatProperties.getMaxThreads()));
		propertyMapper.from(tomcatProperties::getMinSpareThreads).when(this::isPositive)
				.to((minSpareThreads) -> customizeMinThreads(factory, minSpareThreads));
		propertyMapper.from(() -> determineMaxHttpHeaderSize()).when(this::isPositive)
				.to((maxHttpHeaderSize) -> customizeMaxHttpHeaderSize(factory,
						maxHttpHeaderSize));
		propertyMapper.from(tomcatProperties::getMaxHttpPostSize)
				.when((maxHttpPostSize) -> maxHttpPostSize != 0)
				.to((maxHttpPostSize) -> customizeMaxHttpPostSize(factory,
						maxHttpPostSize));
		propertyMapper.from(tomcatProperties::getAccesslog)
				.when(ServerProperties.Tomcat.Accesslog::isEnabled)
				.to((enabled) -> customizeAccessLog(factory));
		propertyMapper.from(tomcatProperties::getUriEncoding).whenNonNull()
				.to(factory::setUriEncoding);
		propertyMapper.from(properties::getConnectionTimeout).whenNonNull()
				.to((connectionTimeout) -> customizeConnectionTimeout(factory,
						connectionTimeout));
		propertyMapper.from(tomcatProperties::getMaxConnections).when(this::isPositive)
				.to((maxConnections) -> customizeMaxConnections(factory, maxConnections));
		propertyMapper.from(tomcatProperties::getAcceptCount).when(this::isPositive)
				.to((acceptCount) -> customizeAcceptCount(factory, acceptCount));
		customizeStaticResources(factory);
		customizeErrorReportValve(properties.getError(), factory);
	}
}

TomcatWebServerFactoryCustomizer 实现了 WebServerFactoryCustomizer接口，其中有一个customize方法，是根据ServerProperties(配置文件中的配置）给容器进行初始化，打个断点，观察一下方法调用栈。

发现是WebServerFactoryCustomizerBeanPostProcessor这个后置处理器中调用的

WebServerFactoryCustomizerBeanPostProcessor

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private void postProcessBeforeInitialization(WebServerFactory webServerFactory) {
  LambdaSafe
      .callbacks(WebServerFactoryCustomizer.class, getCustomizers(),
          webServerFactory)
      .withLogger(WebServerFactoryCustomizerBeanPostProcessor.class)
      .invoke((customizer) -> customizer.customize(webServerFactory));
}

这里会获取所有的WebServerFactoryCustomizer，依次调用其中的customize方法。

WebServerFactoryCustomizer

这些都是WebServerFactoryCustomizer接口的实现类，可以发现其中的TomcatServletWebServerFactoryCustomizer，ServletWebServerFactoryCustomizer，TomcatWebServerFactoryCustomizer都是和Tomcat有关的。

  • TomcatWebServerFactoryCustomizer 配置tomcat的主要信息，包含remoteIpValue、connector(最大/最小可接收线程、最大可接收头部大小等等)、uriEncoding、connectionTimeout、maxConnection等属性
  • TomcatServletWebServerFactoryCustomizer 配置tomcat的额外信息，redirectContextRoot(是否在请求根上下文时转发，true则转发路径为/demoWeb/)和useRelativeRedirects(是否使用相对路径)等路径跳转问题处理
  • ServletWebServerFactoryCustomizer 主要配置tomcat的servlet的信息，包含端口、上下文路径、应用名、Session配置、Servlet携带的初始变量等等

ServletWebServerFactoryAutoConfiguration

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@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 {

	@Bean
	public ServletWebServerFactoryCustomizer servletWebServerFactoryCustomizer(
			ServerProperties serverProperties) {
		return new ServletWebServerFactoryCustomizer(serverProperties);
	}

	@Bean
	@ConditionalOnClass(name = "org.apache.catalina.startup.Tomcat")
	public TomcatServletWebServerFactoryCustomizer tomcatServletWebServerFactoryCustomizer(
			ServerProperties serverProperties) {
		return new TomcatServletWebServerFactoryCustomizer(serverProperties);
	}

	/**
	 * 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);
			}
		}
	}
}

可以发现，ServletWebServerFactoryAutoConfiguration这个自动装配的类中注册了这两个容器工厂定制器。并且@import(BeanPostProcessorsRegistrar),其中注册了webServerFactoryCustomizerBeanPostProcessor这个后置处理器。

自定义webServerFactoryCustomizer

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@Bean
  public WebServerFactoryCustomizer myWebServerFactoryCustomizer() {
      return (WebServerFactory factory) -> {
          System.out.println("I am myWebServerFactoryCustomizer");
          if (factory instanceof AbstractConfigurableWebServerFactory) {
              ((AbstractConfigurableWebServerFactory) factory).setPort(8002);
          }
      };
  }
//        return new WebServerFactoryCustomizer() {
//            @Override
//            public void customize(WebServerFactory factory) {
//                System.out.println("I am myWebServerFactoryCustomizer");
//                if(factory instanceof AbstractConfigurableWebServerFactory){
//                    ((AbstractConfigurableWebServerFactory) factory).setPort(8002);
//                }
//            }
//        };

可以在自定义一个WebServerFactoryCustomizer,设置自定义的属性。

总结

springboot在启动时，会自动装配EmbeddedWebServerFactoryCustomizerAutoConfiguration和ServletWebServerFactoryAutoConfiguration。其中会有一些相关的Customizer（定制器），并注册了webServerFactoryCustomizerBeanPostProcessor后置处理器。然后在创建Servlet容器时，会在这个后置处理器中遍历这些定制器，完成对Servlet容器属性的设置。


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