SpringBoot2.x內置Tomcat自動配置原理

 SpringBoot內嵌的tomcat是怎樣自動配置的？

  我們怎么修改內嵌tomcat的默認參數？

帶着這2個問題，我們分析下SpringBoot的內置tomcat自動配置原理

我們知道SpringBoot的自動配置都在spring-boot-autoconfigure-xx.RELEASE.jar包下.

同時 SpringBoot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Web應用種，Springboot會使用上述web工廠組件生成相應的webserver實例。 而web工廠組件從哪里來，這就是自動配置類ServletWebServerFactoryAutoConfiguaration進行自動配置產生這個web工廠組件的任務了。

    

@Configuration
@AutoConfigureOrder(-2147483648)
@ConditionalOnClass({ServletRequest.class})
@ConditionalOnWebApplication(
    type = Type.SERVLET
)
@EnableConfigurationProperties({ServerProperties.class})
@Import({ServletWebServerFactoryAutoConfiguration.BeanPostProcessorsRegistrar.class, EmbeddedTomcat.class, EmbeddedJetty.class, EmbeddedUndertow.class})
public class ServletWebServerFactoryAutoConfiguration {
    public 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);
    }

    public static class BeanPostProcessorsRegistrar implements ImportBeanDefinitionRegistrar, BeanFactoryAware {
        private ConfigurableListableBeanFactory beanFactory;

        public BeanPostProcessorsRegistrar() {
        }

        public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
            if (beanFactory instanceof ConfigurableListableBeanFactory) {
                this.beanFactory = (ConfigurableListableBeanFactory)beanFactory;
            }

        }

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

        }
    }
}

 首先來看一下這個ServletWebServerFactoryAutoConfiguration自動配置類的幾個注解：

兩個 Condition 表示當前運行環境是基於 servlet 標准規范的 web 服務：ConditionalOnClass(ServletRequest.class) ： 表示當前必須有 servlet-api 依賴存在ConditionalOnWebApplication(type = Type.SERVLET) ：僅基於servlet的Web應用程序

 

1. @AutoConfigureOrder 這個注解是決定配置類的加載順序的，當注解里的值越小越先加載

2.@EnableConfigurationProperties開啟ServerProperties類的屬性值配置。而這個類里面包含的就是webserver的配置

3. @Import其中內部類 BeanPostProcessorsRegistrar,這個類注冊了兩個bean:

    WebServerFactoryCustomizerBeanPostProcessor和ErrorPageRegistarBeanPostProcess。關於這兩個bean的作用稍后再詳細介紹

4.@Import EmbeddedTomcat這個類

   

 @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();
        }
    }

  這個類會在存在tomcat相關jar包時添加一個TomcatServletWebServerFactory bean  

5.  除此之外，還注入了

ServletWebServerFactoryCustomizer和TomcatServletWebServerFactoryCustomizer