springboot请求响应流程

• 2020-03-05
• 作者： 王海波
• 分类：springboot
• 访问量：1040

springboot相对于springMVC来说，只是增加了大量的自动配置，从而节省开发人员的配置，其核心部分都是使用的springMVC的。因此，两者处理流程没什么不同。

下面这张图是网上找的：

看到上图，DisPatchServelet是一个非常重要的组件。它负责接收前端请求，并进行分发，以及返回响应。

看一下它的继承关系：

Servlet是一个接口：

public interface Servlet {
    void init(ServletConfig var1) throws ServletException;

    ServletConfig getServletConfig();

    void service(ServletRequest var1, ServletResponse var2) throws ServletException, IOException;

    String getServletInfo();

    void destroy();
}

servlet是一个接口，是Java的一个Web组件，用于动态的生成内容，它运行在Servlet容器中，不可单独存在。而Tomcat就是一个著名的Servlet容器，也是一个Web服务器。

Servlet容器采用多线程单实例的模式，每当有一个新请求过来，会创建一个线程（线程池，可能是新创建的，也可能是已经初始化过的），执行Servlet的service方法。当然，这种模式要考虑线程安全性，而DispatchServlet内部机制保证了线程安全。

springboot的DisPatchServeLet并不需要再配置，而是通过SPI机制加载的。

当我们再应用入口使用注解：

@SpringBootApplication就会自动加载各种配置。

public @interface SpringBootApplication {
    @AliasFor(
        annotation = EnableAutoConfiguration.class
    )
    Class<?>[] exclude() default {};

    @AliasFor(
        annotation = EnableAutoConfiguration.class
    )
    String[] excludeName() default {};

    @AliasFor(
        annotation = ComponentScan.class,
        attribute = "basePackages"
    )
    String[] scanBasePackages() default {};

    @AliasFor(
        annotation = ComponentScan.class,
        attribute = "basePackageClasses"
    )
    Class<?>[] scanBasePackageClasses() default {};

    @AliasFor(
        annotation = Configuration.class
    )
    boolean proxyBeanMethods() default true;
}

在springboot-autoconfigure的META-INF中有spring.factories中可看到：

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
org.springframework.boot.autoconfigure.admin.SpringApplicationAdminJmxAutoConfiguration,\
org.springframework.boot.autoconfigure.aop.AopAutoConfiguration,\
org.springframework.boot.autoconfigure.amqp.RabbitAutoConfiguration,\
org.springframework.boot.autoconfigure.batch.BatchAutoConfiguration,\
org.springframework.boot.autoconfigure.cache.CacheAutoConfiguration,\
org.springframework.boot.autoconfigure.cassandra.CassandraAutoConfiguration,\
org.springframework.boot.autoconfigure.cloud.CloudServiceConnectorsAutoConfiguration,\
org.springframework.boot.autoconfigure.context.ConfigurationPropertiesAutoConfiguration,\
org.springframework.boot.autoconfigure.context.MessageSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.context.PropertyPlaceholderAutoConfiguration,\
org.springframework.boot.autoconfigure.couchbase.CouchbaseAutoConfiguration,\
org.springframework.boot.autoconfigure.dao.PersistenceExceptionTranslationAutoConfiguration,\
org.springframework.boot.autoconfigure.data.cassandra.CassandraDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.cassandra.CassandraReactiveDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.cassandra.CassandraReactiveRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.cassandra.CassandraRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseReactiveDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseReactiveRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ReactiveElasticsearchRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ReactiveRestClientAutoConfiguration,\
org.springframework.boot.autoconfigure.data.jdbc.JdbcRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.jpa.JpaRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.ldap.LdapRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.mongo.MongoDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.mongo.MongoReactiveDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.mongo.MongoReactiveRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.mongo.MongoRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.neo4j.Neo4jDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.neo4j.Neo4jRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.solr.SolrRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.redis.RedisAutoConfiguration,\
org.springframework.boot.autoconfigure.data.redis.RedisReactiveAutoConfiguration,\
org.springframework.boot.autoconfigure.data.redis.RedisRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.rest.RepositoryRestMvcAutoConfiguration,\
org.springframework.boot.autoconfigure.data.web.SpringDataWebAutoConfiguration,\
org.springframework.boot.autoconfigure.elasticsearch.jest.JestAutoConfiguration,\
org.springframework.boot.autoconfigure.elasticsearch.rest.RestClientAutoConfiguration,\
org.springframework.boot.autoconfigure.flyway.FlywayAutoConfiguration,\
org.springframework.boot.autoconfigure.freemarker.FreeMarkerAutoConfiguration,\
org.springframework.boot.autoconfigure.gson.GsonAutoConfiguration,\
org.springframework.boot.autoconfigure.h2.H2ConsoleAutoConfiguration,\
org.springframework.boot.autoconfigure.hateoas.HypermediaAutoConfiguration,\
org.springframework.boot.autoconfigure.hazelcast.HazelcastAutoConfiguration,\
org.springframework.boot.autoconfigure.hazelcast.HazelcastJpaDependencyAutoConfiguration,\
org.springframework.boot.autoconfigure.http.HttpMessageConvertersAutoConfiguration,\
org.springframework.boot.autoconfigure.http.codec.CodecsAutoConfiguration,\
org.springframework.boot.autoconfigure.influx.InfluxDbAutoConfiguration,\
org.springframework.boot.autoconfigure.info.ProjectInfoAutoConfiguration,\
org.springframework.boot.autoconfigure.integration.IntegrationAutoConfiguration,\
org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.JdbcTemplateAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.JndiDataSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.XADataSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.DataSourceTransactionManagerAutoConfiguration,\
org.springframework.boot.autoconfigure.jms.JmsAutoConfiguration,\
org.springframework.boot.autoconfigure.jmx.JmxAutoConfiguration,\
org.springframework.boot.autoconfigure.jms.JndiConnectionFactoryAutoConfiguration,\
org.springframework.boot.autoconfigure.jms.activemq.ActiveMQAutoConfiguration,\
org.springframework.boot.autoconfigure.jms.artemis.ArtemisAutoConfiguration,\
org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAutoConfiguration,\
org.springframework.boot.autoconfigure.jersey.JerseyAutoConfiguration,\
org.springframework.boot.autoconfigure.jooq.JooqAutoConfiguration,\
org.springframework.boot.autoconfigure.jsonb.JsonbAutoConfiguration,\
org.springframework.boot.autoconfigure.kafka.KafkaAutoConfiguration,\
org.springframework.boot.autoconfigure.ldap.embedded.EmbeddedLdapAutoConfiguration,\
org.springframework.boot.autoconfigure.ldap.LdapAutoConfiguration,\
org.springframework.boot.autoconfigure.liquibase.LiquibaseAutoConfiguration,\
org.springframework.boot.autoconfigure.mail.MailSenderAutoConfiguration,\
org.springframework.boot.autoconfigure.mail.MailSenderValidatorAutoConfiguration,\
org.springframework.boot.autoconfigure.mongo.embedded.EmbeddedMongoAutoConfiguration,\
org.springframework.boot.autoconfigure.mongo.MongoAutoConfiguration,\
org.springframework.boot.autoconfigure.mongo.MongoReactiveAutoConfiguration,\
org.springframework.boot.autoconfigure.mustache.MustacheAutoConfiguration,\
org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration,\
org.springframework.boot.autoconfigure.quartz.QuartzAutoConfiguration,\
org.springframework.boot.autoconfigure.rsocket.RSocketMessagingAutoConfiguration,\
org.springframework.boot.autoconfigure.rsocket.RSocketRequesterAutoConfiguration,\
org.springframework.boot.autoconfigure.rsocket.RSocketServerAutoConfiguration,\
org.springframework.boot.autoconfigure.rsocket.RSocketStrategiesAutoConfiguration,\
org.springframework.boot.autoconfigure.security.servlet.SecurityAutoConfiguration,\
org.springframework.boot.autoconfigure.security.servlet.UserDetailsServiceAutoConfiguration,\
org.springframework.boot.autoconfigure.security.servlet.SecurityFilterAutoConfiguration,\
org.springframework.boot.autoconfigure.security.reactive.ReactiveSecurityAutoConfiguration,\
org.springframework.boot.autoconfigure.security.reactive.ReactiveUserDetailsServiceAutoConfiguration,\
org.springframework.boot.autoconfigure.security.rsocket.RSocketSecurityAutoConfiguration,\
org.springframework.boot.autoconfigure.security.saml2.Saml2RelyingPartyAutoConfiguration,\
org.springframework.boot.autoconfigure.sendgrid.SendGridAutoConfiguration,\
org.springframework.boot.autoconfigure.session.SessionAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth2.client.servlet.OAuth2ClientAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth2.client.reactive.ReactiveOAuth2ClientAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth2.resource.servlet.OAuth2ResourceServerAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth2.resource.reactive.ReactiveOAuth2ResourceServerAutoConfiguration,\
org.springframework.boot.autoconfigure.solr.SolrAutoConfiguration,\
org.springframework.boot.autoconfigure.task.TaskExecutionAutoConfiguration,\
org.springframework.boot.autoconfigure.task.TaskSchedulingAutoConfiguration,\
org.springframework.boot.autoconfigure.thymeleaf.ThymeleafAutoConfiguration,\
org.springframework.boot.autoconfigure.transaction.TransactionAutoConfiguration,\
org.springframework.boot.autoconfigure.transaction.jta.JtaAutoConfiguration,\
org.springframework.boot.autoconfigure.validation.ValidationAutoConfiguration,\
org.springframework.boot.autoconfigure.web.client.RestTemplateAutoConfiguration,\
org.springframework.boot.autoconfigure.web.embedded.EmbeddedWebServerFactoryCustomizerAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.HttpHandlerAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.ReactiveWebServerFactoryAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.WebFluxAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.error.ErrorWebFluxAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.function.client.ClientHttpConnectorAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.function.client.WebClientAutoConfiguration,\
//配置DispatchServelet
org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.error.ErrorMvcAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.HttpEncodingAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.MultipartAutoConfiguration,\
//WebMVC 加载 RequestHandlerMapping Bean
org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration,\
org.springframework.boot.autoconfigure.websocket.reactive.WebSocketReactiveAutoConfiguration,\
org.springframework.boot.autoconfigure.websocket.servlet.WebSocketServletAutoConfiguration,\
org.springframework.boot.autoconfigure.websocket.servlet.WebSocketMessagingAutoConfiguration,\
org.springframework.boot.autoconfigure.webservices.WebServicesAutoConfiguration,\
org.springframework.boot.autoconfigure.webservices.client.WebServiceTemplateAutoConfiguration

上面可以看到org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration

RequestMappingHandlerMapping就是注册了Controller 和RestController注解的handler和方法，进行路由注册。

该配置就是创建DispatchServelet bean,但是ConditionalBean ，即当不存在时创建

    @Configuration(
        proxyBeanMethods = false
    )
    @Conditional({DispatcherServletAutoConfiguration.DefaultDispatcherServletCondition.class})
    @ConditionalOnClass({ServletRegistration.class})
    @EnableConfigurationProperties({HttpProperties.class, WebMvcProperties.class})
    protected static class DispatcherServletConfiguration {
        protected DispatcherServletConfiguration() {
        }

        @Bean(
            name = {"dispatcherServlet"}
        )
        public DispatcherServlet dispatcherServlet(HttpProperties httpProperties, WebMvcProperties webMvcProperties) {
            DispatcherServlet dispatcherServlet = new DispatcherServlet();
            dispatcherServlet.setDispatchOptionsRequest(webMvcProperties.isDispatchOptionsRequest());
            dispatcherServlet.setDispatchTraceRequest(webMvcProperties.isDispatchTraceRequest());
            dispatcherServlet.setThrowExceptionIfNoHandlerFound(webMvcProperties.isThrowExceptionIfNoHandlerFound());
            dispatcherServlet.setPublishEvents(webMvcProperties.isPublishRequestHandledEvents());
            dispatcherServlet.setEnableLoggingRequestDetails(httpProperties.isLogRequestDetails());
            return dispatcherServlet;
        }

        @Bean
        @ConditionalOnBean({MultipartResolver.class})
        @ConditionalOnMissingBean(
            name = {"multipartResolver"}
        )
        public MultipartResolver multipartResolver(MultipartResolver resolver) {
            return resolver;
        }
    }

上面是创建了DisPatchServlet Bean。

springboot默认情况下，在应用器动时，不会进行DispatchServlet的初始化，而是在第一次请求到来时进行。当然，这个是可以配置的，可以配置成启动时进行初始化。

这是会调用DisPatchServlet的onRefresh方法，并调用初时化方法，这时候会初时化各种组件。

  protected void onRefresh(ApplicationContext context) {
        this.initStrategies(context);
    }

    protected void initStrategies(ApplicationContext context) {
        //初始化文件解析器
        this.initMultipartResolver(context);
        this.initLocaleResolver(context);
        this.initThemeResolver(context);
         //初始化HandlerMapping
        this.initHandlerMappings(context);
        this.initHandlerAdapters(context);
   //初始化异常解析器
        this.initHandlerExceptionResolvers(context);
    // 初始化请求到视图名称翻译器
        this.initRequestToViewNameTranslator(context);
        // 初始化视图解析器
        this.initViewResolvers(context);
        this.initFlashMapManager(context);
    }

其中最最重要的，就是handlermapping的初始化，它初始化了路由和controller的映射。

 private void initHandlerMappings(ApplicationContext context) {
        this.handlerMappings = null;
        if (this.detectAllHandlerMappings) {
            Map<String, HandlerMapping> matchingBeans = BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false);
            if (!matchingBeans.isEmpty()) {
                this.handlerMappings = new ArrayList(matchingBeans.values());
                AnnotationAwareOrderComparator.sort(this.handlerMappings);
            }
        } else {
            try {
                HandlerMapping hm = (HandlerMapping)context.getBean("handlerMapping", HandlerMapping.class);
                this.handlerMappings = Collections.singletonList(hm);
            } catch (NoSuchBeanDefinitionException var3) {
                ;
            }
        }

        if (this.handlerMappings == null) {
            this.handlerMappings = this.getDefaultStrategies(context, HandlerMapping.class);
            if (this.logger.isTraceEnabled()) {
                this.logger.trace("No HandlerMappings declared for servlet '" + this.getServletName() + "': using default strategies from DispatcherServlet.properties");
            }
        }

    }

上述方法主要是从IOC容器中获取HanderMapping Bean。那么Bean是从何而来呢？

在最上面说到了springboot的自动配置以及SPI机制。AutoConfiguration中有一个

org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration

该类实例化的Bean:

 @Bean
        public RequestMappingHandlerAdapter requestMappingHandlerAdapter(@Qualifier("mvcContentNegotiationManager") ContentNegotiationManager contentNegotiationManager, @Qualifier("mvcConversionService") FormattingConversionService conversionService, @Qualifier("mvcValidator") Validator validator) {
            RequestMappingHandlerAdapter adapter = super.requestMappingHandlerAdapter(contentNegotiationManager, conversionService, validator);
            adapter.setIgnoreDefaultModelOnRedirect(this.mvcProperties == null || this.mvcProperties.isIgnoreDefaultModelOnRedirect());
            return adapter;
        }

      
        }

        @Bean
        @Primary
        public RequestMappingHandlerMapping requestMappingHandlerMapping(@Qualifier("mvcContentNegotiationManager") ContentNegotiationManager contentNegotiationManager, @Qualifier("mvcConversionService") FormattingConversionService conversionService, @Qualifier("mvcResourceUrlProvider") ResourceUrlProvider resourceUrlProvider) {
            return super.requestMappingHandlerMapping(contentNegotiationManager, conversionService, resourceUrlProvider);
        }

requestMappingHandlerMapping就是创建HandlerMapping,其会创建一个RequestMappingHandlerMapping，而该类继承了InitializingBean。

 public void afterPropertiesSet() {
        this.config = new BuilderConfiguration();
        this.config.setUrlPathHelper(this.getUrlPathHelper());
        this.config.setPathMatcher(this.getPathMatcher());
        this.config.setSuffixPatternMatch(this.useSuffixPatternMatch);
        this.config.setTrailingSlashMatch(this.useTrailingSlashMatch);
        this.config.setRegisteredSuffixPatternMatch(this.useRegisteredSuffixPatternMatch);
        this.config.setContentNegotiationManager(this.getContentNegotiationManager());
        super.afterPropertiesSet();
    }

父类的方法：

 public void afterPropertiesSet() {
        this.initHandlerMethods();
    }

    protected void initHandlerMethods() {
        String[] var1 = this.getCandidateBeanNames();
        int var2 = var1.length;

        for(int var3 = 0; var3 < var2; ++var3) {
            String beanName = var1[var3];
            if (!beanName.startsWith("scopedTarget.")) {
                this.processCandidateBean(beanName);
            }
        }

        this.handlerMethodsInitialized(this.getHandlerMethods());
    }

上述方法是循环处理侯选的bean name.具体处理方法：

 protected void processCandidateBean(String beanName) {
        Class beanType = null;

        try {
            beanType = this.obtainApplicationContext().getType(beanName);
        } catch (Throwable var4) {
            if (this.logger.isTraceEnabled()) {
                this.logger.trace("Could not resolve type for bean '" + beanName + "'", var4);
            }
        }

        if (beanType != null && this.isHandler(beanType)) {
            this.detectHandlerMethods(beanName);
        }

    }

上面的isHandler就是判断是不是Controller何RequestMapping注解的，如果是就处理。

protected boolean isHandler(Class<?> beanType) {
        return AnnotatedElementUtils.hasAnnotation(beanType, Controller.class) || AnnotatedElementUtils.hasAnnotation(beanType, RequestMapping.class);
    }

具体处理就是根据Method对象生成RequestMappingInfo对象，如果类上有@RequestMapping注解，那么也生成RequestMappingInfo对象，将这两个RequestMappingInfo对象进行合并遍历Method、RequestMappingInfo对应的map集合并注册到对应的mappingLookup、urlLookup、registry集合中。具体注册过程是加了读写锁的。

 public void register(T mapping, Object handler, Method method) {
            if (KotlinDetector.isKotlinType(method.getDeclaringClass()) && AbstractHandlerMethodMapping.KotlinDelegate.isSuspend(method)) {
                throw new IllegalStateException("Unsupported suspending handler method detected: " + method);
            } else {
                this.readWriteLock.writeLock().lock();

                try {
                    HandlerMethod handlerMethod = AbstractHandlerMethodMapping.this.createHandlerMethod(handler, method);
                    this.validateMethodMapping(handlerMethod, mapping);
                    this.mappingLookup.put(mapping, handlerMethod);
                    List<String> directUrls = this.getDirectUrls(mapping);
                    Iterator var6 = directUrls.iterator();

                    while(var6.hasNext()) {
                        String url = (String)var6.next();
                        this.urlLookup.add(url, mapping);
                    }

                    String name = null;
                    if (AbstractHandlerMethodMapping.this.getNamingStrategy() != null) {
                        name = AbstractHandlerMethodMapping.this.getNamingStrategy().getName(handlerMethod, mapping);
                        this.addMappingName(name, handlerMethod);
                    }

                    CorsConfiguration corsConfig = AbstractHandlerMethodMapping.this.initCorsConfiguration(handler, method, mapping);
                    if (corsConfig != null) {
                        this.corsLookup.put(handlerMethod, corsConfig);
                    }

                    this.registry.put(mapping, new AbstractHandlerMethodMapping.MappingRegistration(mapping, handlerMethod, directUrls, name));
                } finally {
                    this.readWriteLock.writeLock().unlock();
                }
            }
        }

上面就是DispatchServlet的一个创建过程了。

那么当一个请求过来时，具体是怎么处理的呢。

1、上面也提到了，Tomcat将请求进行处理封装，转发给Servlet容器。

2、调用DispatchServlet 的service方法。

3、DispatchServlet进行分发，找到对应的Controller方法进行处理。

参考资料：

【原创】005 | 搭上SpringBoot请求处理源码分析专车

聊聊Tomcat的架构设计

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