springboot嵌入式servlet容器的自动配置以及原理

配置嵌入式Servlet容器

SpringBoot默认用的是Tomcat作为嵌入式的Servlet容器

如何定制和修改servlet容器的相关配置

修改和server有关的配置（ServerProperties）

    private final ServerProperties.Servlet servlet;
    private final ServerProperties.Tomcat tomcat;
    private final ServerProperties.Jetty jetty;
    private final ServerProperties.Netty netty;
    private final ServerProperties.Undertow undertow;

server.port=8080

//通用的Servler容器设置
server.xxx
//Tomcat的设置
server.tomcat.xxx
server.tomcat.uri-encoding=UTF-8
//其他的类似

编写一个 WebServerFactoryCustomizer 嵌入式的servlet容器的定制器，ConfigurableServletWebServerFactory中有很多方法调用，来修改servlet容器的配置

    @Bean
    public WebServerFactoryCustomizer<ConfigurableServletWebServerFactory> customizationBean(){
        return new WebServerFactoryCustomizer<ConfigurableServletWebServerFactory>() {
            @Override
            public void customize(ConfigurableServletWebServerFactory factory) {
                factory.setPort(8083);
            }
        };
    }

注册三大组件

注册Servlet：ServletRegistrationBean

//定制自己的servlet

public class MyServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req, resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.getWriter().write("hello MyServlet");
    }
}

@Bean
public ServletRegistrationBean MyServlet(){
    ServletRegistrationBean registrationBean = new ServletRegistrationBean(new MyServlet(),"/myServlet");
    return registrationBean;
}

注册Filter

//定制了Filter
public class MyFilter implements Filter {

@Bean
public FilterRegistrationBean MyFilter(){
    FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean();
    filterRegistrationBean.setFilter(new MyFilter());
    filterRegistrationBean.setUrlPatterns(Arrays.asList("/myServlet","/hello"));
    return filterRegistrationBean;
}

注册Listener

//定制监听器
public class MyListener implements ServletContextListener {

@Bean
public ServletListenerRegistrationBean MyListener(){
    ServletListenerRegistrationBean<MyListener> myListenerServletRegistrationBean = new ServletListenerRegistrationBean<MyListener>(new MyListener());
    return  myListenerServletRegistrationBean;
}

Spring帮我们自动配置SpringMVC的时候，自动的注册SpringMVC的前端控制器；DidpatcherServlet

@Bean(
    name = {"dispatcherServletRegistration"}
)
@ConditionalOnBean(
    value = {DispatcherServlet.class},
    name = {"dispatcherServlet"}
)
public DispatcherServletRegistrationBean dispatcherServletRegistration(DispatcherServlet dispatcherServlet, WebMvcProperties webMvcProperties, ObjectProvider<MultipartConfigElement> multipartConfig) {
    DispatcherServletRegistrationBean registration = new DispatcherServletRegistrationBean(dispatcherServlet, webMvcProperties.getServlet().getPath());
    //        private String path = "/";
    //		   默认拦截所有路径，包含静态资源
    //可以通过server.servletPath来修改拦截请求
    registration.setName("dispatcherServlet");
    registration.setLoadOnStartup(webMvcProperties.getServlet().getLoadOnStartup());
    multipartConfig.ifAvailable(registration::setMultipartConfig);
    return registration;
}

SpringBoot切换其他的Servlet容器

SpringBoot的ConfigurableServletWebServerFactory 有Jetty,Undertow,Tomcat三个实现类

默认支持这三种容器：

Tomcat
Jetty（长连接）-- web聊天
Undertow（不支持JSP）

移除tomcat后注入新的依赖切换

嵌入式Servlet容器自动配置原理（2.3.0版本）

EmbeddedWebServerFactoryCustomizerAutoConfiguration：嵌入式的servlet容器自动配置

@Configuration(
    proxyBeanMethods = false
)
@ConditionalOnWebApplication
@EnableConfigurationProperties({ServerProperties.class})
public class EmbeddedWebServerFactoryCustomizerAutoConfiguration {

该类中有对应支持的Servlet容器内部类
- TomcatWebServerFactoryCustomizerConfiguration
- JettyWebServerFactoryCustomizerConfiguration
- UndertowWebServerFactoryCustomizerConfiguration
- NettyWebServerFactoryCustomizerConfiguration

每个类都有@ConditionalOnClass注解，判断是否引入了对应的依赖，引入了对应依赖的即创建一个xxxWebServerFactoryCustomizer来构建Servlet容器工厂

//以Tomcat为例
@Configuration(
    proxyBeanMethods = false
)
@ConditionalOnClass({Tomcat.class, UpgradeProtocol.class})
public static class TomcatWebServerFactoryCustomizerConfiguration {
    public TomcatWebServerFactoryCustomizerConfiguration() {
    }

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

在TomcatWebServerFactoryCustomizer中的customize里从容器中获取了对应的ConfigurableWebServerFactory工厂来构建容器配置，被SpringBoot使用，以下以Tomcat为例

public class TomcatWebServerFactoryCustomizer implements WebServerFactoryCustomizer<ConfigurableTomcatWebServerFactory>, Ordered {
    private final Environment environment;
    private final ServerProperties serverProperties;

    public void customize(ConfigurableTomcatWebServerFactory factory) {

ConfigurableWebServerFactory 接口如下：

而SpringBoot已经通过ServletWebServerFactoryConfiguration 配置类放置了支持容器对应的ConfigurableWebServerFactory 实现类，如果用户配置了自己的servlet容器，SpringBoot则不放入默认的Servlet容器

ServletWebServerFactoryConfiguration 配置Servlet工厂，内部定义了EmbeddedTomcat，EmbeddedJetty，EmbeddedUndertow三个内部类，以下EmbeddedTomcat为例，@ConditionalOnMissingBean用来判断，如果用户没有定义自己的ServletWebServerFactory，则生效配置默认的容器TomcatServletWebServerFactory，被TomcatWebServerFactoryCustomizer调用后创建了一个Tomcat对象

@Configuration(
    proxyBeanMethods = false
)
class ServletWebServerFactoryConfiguration {
    @Configuration(
        proxyBeanMethods = false
    )
    @ConditionalOnClass({Servlet.class, Tomcat.class, UpgradeProtocol.class})
    @ConditionalOnMissingBean(
        value = {ServletWebServerFactory.class},
        search = SearchStrategy.CURRENT
    )
    static class EmbeddedTomcat {
        EmbeddedTomcat() {
        }

        @Bean
        TomcatServletWebServerFactory tomcatServletWebServerFactory(ObjectProvider<TomcatConnectorCustomizer> connectorCustomizers, ObjectProvider<TomcatContextCustomizer> contextCustomizers, ObjectProvider<TomcatProtocolHandlerCustomizer<?>> protocolHandlerCustomizers) {
            TomcatServletWebServerFactory factory = new TomcatServletWebServerFactory();
            factory.getTomcatConnectorCustomizers().addAll((Collection)connectorCustomizers.orderedStream().collect(Collectors.toList()));
            factory.getTomcatContextCustomizers().addAll((Collection)contextCustomizers.orderedStream().collect(Collectors.toList()));
            factory.getTomcatProtocolHandlerCustomizers().addAll((Collection)protocolHandlerCustomizers.orderedStream().collect(Collectors.toList()));
            return factory;
        }
    }

//TomcatServletWebServerFactory
public class TomcatServletWebServerFactory extends AbstractServletWebServerFactory implements ConfigurableTomcatWebServerFactory, ResourceLoaderAware {
    //创建Tomcat对象
        Tomcat tomcat = new Tomcat();
    //配置Tomcat的基本环节
        File baseDir = this.baseDirectory != null ? this.baseDirectory : this.createTempDir("tomcat");
        tomcat.setBaseDir(baseDir.getAbsolutePath());
        Connector connector = new Connector(this.protocol);
        connector.setThrowOnFailure(true);
        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);
    //将配置好的Tomcat传入进去，返回一个TomcatWebServer，在TomcatWebServer对象的initialize()中有个关键的代码
    //this.tomcat.start();启动Tomcat
        return this.getTomcatWebServer(tomcat);
    }

用户定义的配置修改是怎么生效的

配置文件的修改是直接修改ServletProperties的属性，对默认配置进行修改，使用的还是默认的容器

在EmbeddedWebServerFactoryCustomizerAutoConfiguration的@EnableConfigurationProperties注解里传入了一个@Import({EnableConfigurationPropertiesRegistrar.class}) 配置注册器：获取我们的配置来初始化

class EnableConfigurationPropertiesRegistrar implements ImportBeanDefinitionRegistrar {
    EnableConfigurationPropertiesRegistrar() {
    }

    public void registerBeanDefinitions(AnnotationMetadata metadata, BeanDefinitionRegistry registry) {
        //在getTypes方法中获取了
        registerInfrastructureBeans(registry);
        ConfigurationPropertiesBeanRegistrar beanRegistrar = new ConfigurationPropertiesBeanRegistrar(registry);
        //在该方法获取我们自定义的配置并初始.....(待研究)
        this.getTypes(metadata).forEach(beanRegistrar::register);
    }
    private Set<Class<?>> getTypes(AnnotationMetadata metadata) {
    return (Set)metadata.getAnnotations().stream(EnableConfigurationProperties.class).flatMap((annotation) -> {
        return Arrays.stream(annotation.getClassArray("value"));
    }).filter((type) -> {
        return Void.TYPE != type;
    }).collect(Collectors.toSet());
}

嵌入式Servlet容器启动原理

SpringBoot应用启动运行run方法

先创建IOC容器对象，初始化容器，并创建容器中的每一个组件

context = this.createApplicationContext();
exceptionReporters = this.getSpringFactoriesInstances(SpringBootExceptionReporter.class, new Class[]{ConfigurableApplicationContext.class}, context);
this.prepareContext(context, environment, listeners, applicationArguments, printedBanner);
this.refreshContext(context);

//判断创建的是不是web应用及其类型，创建相应的对象容器
protected ConfigurableApplicationContext createApplicationContext() {
    Class<?> contextClass = this.applicationContextClass;
    if (contextClass == null) {
        try {
            switch(this.webApplicationType) {
            case SERVLET:
                contextClass = Class.forName("org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext");
                break;
            case REACTIVE:
                contextClass = Class.forName("org.springframework.boot.web.reactive.context.AnnotationConfigReactiveWebServerApplicationContext");
                break;
            default:
                contextClass = Class.forName("org.springframework.context.annotation.AnnotationConfigApplicationContext");
            }
        }
    }

调用refresh刷新创建好的容器，this.refresh((ApplicationContext)context);调用了父容器的刷新方法

private void refreshContext(ConfigurableApplicationContext context) {
        this.refresh((ApplicationContext)context);

try {
    this.postProcessBeanFactory(beanFactory);
    this.invokeBeanFactoryPostProcessors(beanFactory);
    this.registerBeanPostProcessors(beanFactory);
    this.initMessageSource();
    this.initApplicationEventMulticaster();
    this.onRefresh();
    this.registerListeners();
    this.finishBeanFactoryInitialization(beanFactory);
    this.finishRefresh();

onRefresh方法：web的ioc容器重写了onRefresh方法，创建了webserver

 protected void onRefresh() {
        super.onRefresh();

        try {
            this.createWebServer();
        } catch (Throwable var2) {
            throw new ApplicationContextException("Unable to start web server", var2);
        }
    }

webserver创建第一步获取了嵌入式servlet容器工厂ServletWebServerFactory，就是上述提到的调用嵌入式servlet自动配置来判断创建哪个serlvet容器工厂

private void createWebServer() {
        WebServer webServer = this.webServer;
        ServletContext servletContext = this.getServletContext();
        if (webServer == null && servletContext == null) {
            ServletWebServerFactory factory = this.getWebServerFactory();

触发上述的EnableConfigurationPropertiesRegistrar作用，配置Servlet容器

使用容器工厂获取嵌入式的servlet容器

this.webServer = factory.getWebServer(new ServletContextInitializer[]{this.getSelfInitializer()});

嵌入式的servlet容器创建对象并启动Servlet容器，再将ioc容器中剩下没有创建出来的对象获取出来，最后才完成ioc容器的刷新
```
Tomcat tomcat = new Tomcat();
```

总结：在ioc容器启动创建嵌入式的serlver容器

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原文地址：https://www.cnblogs.com/JIATCODE/p/13169999.html