java-springmvc 01

springmvc也是在spring framework中的，不是一个单独的项目

MVC就是和Tomcat有关。
01.MVC启动的第一步，启动Tomcat（这个和springboot的run方法启动Tomcat有关）

02.SpringMVC中，最为核心的就是DispatcherServlet，在启动Tomcat的过程中：

1. Tomcat会先创建DispatcherServlet对象(这一步在手写springboot框架中已经写到，Tomcat在启动的时候会启动DispatcherServlet)
2. 然后调用DispatcherServlet对象的init()

---

DispatcherServlet加载到Tomcat中，依然还是靠SpringBoot的自动配置DispatcherServletAutoConfiguration。

实际上该类的逻辑就是定义了四个类，分别是：

1.DispatcherServletRegistrationCondition：决定是否注册DispatcherServlet到Servlet容器，beanFactory中有，servlet中没有，则加载
2.DefaultDispatcherServletCondition：决定是否加载DispatcherServlet
3.DispatcherServletRegistrationConfiguration：负责注册DispatcherServlet到Servlet容器，并进行一些设置。
4.DispatcherServletConfiguration：负责加载DispatcherServlet并进行一些配置

@AutoConfigureOrder(-2147483648)
@Configuration(
    proxyBeanMethods = false
)
@ConditionalOnWebApplication(
    type = Type.SERVLET
)
//存在DispatcherServlet.class文件才加载
@ConditionalOnClass({DispatcherServlet.class})
//在webServerFactory自动配置完成后才加载，防止工厂还没设置好
@AutoConfigureAfter({ServletWebServerFactoryAutoConfiguration.class})
public class DispatcherServletAutoConfiguration {
    public static final String DEFAULT_DISPATCHER_SERVLET_BEAN_NAME = "dispatcherServlet";
    public static final String DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME = "dispatcherServletRegistration";

    public DispatcherServletAutoConfiguration() {
    }
    
    //第一个类,决定是否注册DispatcherServlet到web容器
    @Order(2147483637)
    private static class DispatcherServletRegistrationCondition extends SpringBootCondition {
        private DispatcherServletRegistrationCondition() {
        }

        public ConditionOutcome getMatchOutcome(ConditionContext context, AnnotatedTypeMetadata metadata) {
            ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
            ConditionOutcome outcome = this.checkDefaultDispatcherName(beanFactory);
            return !outcome.isMatch() ? outcome : this.checkServletRegistration(beanFactory);
        }

        private ConditionOutcome checkDefaultDispatcherName(ConfigurableListableBeanFactory beanFactory) {
            List<String> servlets = Arrays.asList(beanFactory.getBeanNamesForType(DispatcherServlet.class, false, false));
            boolean containsDispatcherBean = beanFactory.containsBean("dispatcherServlet");
            return containsDispatcherBean && !servlets.contains("dispatcherServlet") ? ConditionOutcome.noMatch(this.startMessage().found("non dispatcher servlet").items(new Object[]{"dispatcherServlet"})) : ConditionOutcome.match();
        }

        private ConditionOutcome checkServletRegistration(ConfigurableListableBeanFactory beanFactory) {
            Builder message = this.startMessage();
            List<String> registrations = Arrays.asList(beanFactory.getBeanNamesForType(ServletRegistrationBean.class, false, false));
            boolean containsDispatcherRegistrationBean = beanFactory.containsBean("dispatcherServletRegistration");
            if (registrations.isEmpty()) {
                return containsDispatcherRegistrationBean ? ConditionOutcome.noMatch(message.found("non servlet registration bean").items(new Object[]{"dispatcherServletRegistration"})) : ConditionOutcome.match(message.didNotFind("servlet registration bean").atAll());
            } else if (registrations.contains("dispatcherServletRegistration")) {
                return ConditionOutcome.noMatch(message.found("servlet registration bean").items(new Object[]{"dispatcherServletRegistration"}));
            } else {
                return containsDispatcherRegistrationBean ? ConditionOutcome.noMatch(message.found("non servlet registration bean").items(new Object[]{"dispatcherServletRegistration"})) : ConditionOutcome.match(message.found("servlet registration beans").items(Style.QUOTE, registrations).append("and none is named dispatcherServletRegistration"));
            }
        }

        private Builder startMessage() {
            return ConditionMessage.forCondition("DispatcherServlet Registration", new Object[0]);
        }
    }
    //第二个类，决定是否创建DispatcherServlet对象
    @Order(2147483637)
    private static class DefaultDispatcherServletCondition extends SpringBootCondition {
        private DefaultDispatcherServletCondition() {
        }

        public ConditionOutcome getMatchOutcome(ConditionContext context, AnnotatedTypeMetadata metadata) {
            Builder message = ConditionMessage.forCondition("Default DispatcherServlet", new Object[0]);
            ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
            List<String> dispatchServletBeans = Arrays.asList(beanFactory.getBeanNamesForType(DispatcherServlet.class, false, false));
            if (dispatchServletBeans.contains("dispatcherServlet")) {
                return ConditionOutcome.noMatch(message.found("dispatcher servlet bean").items(new Object[]{"dispatcherServlet"}));
            } else if (beanFactory.containsBean("dispatcherServlet")) {
                return ConditionOutcome.noMatch(message.found("non dispatcher servlet bean").items(new Object[]{"dispatcherServlet"}));
            } else {
                return dispatchServletBeans.isEmpty() ? ConditionOutcome.match(message.didNotFind("dispatcher servlet beans").atAll()) : ConditionOutcome.match(message.found("dispatcher servlet bean", "dispatcher servlet beans").items(Style.QUOTE, dispatchServletBeans).append("and none is named dispatcherServlet"));
            }
        }
    }

    @Configuration(
        proxyBeanMethods = false
    )
    //负责将DispatcherServlet注册到servlet容器中，即tomcat中
    //原理是创建一个DispatcherServletRegistrationBean对象
    @Conditional({DispatcherServletAutoConfiguration.DispatcherServletRegistrationCondition.class})
    @ConditionalOnClass({ServletRegistration.class})
    @EnableConfigurationProperties({WebMvcProperties.class})
    @Import({DispatcherServletAutoConfiguration.DispatcherServletConfiguration.class})
    protected static class DispatcherServletRegistrationConfiguration {
        protected DispatcherServletRegistrationConfiguration() {
        }

        @Bean(
            name = {"dispatcherServletRegistration"}
        )
        @ConditionalOnBean(
            value = {DispatcherServlet.class},
            name = {"dispatcherServlet"}
        )
        public DispatcherServletRegistrationBean dispatcherServletRegistration(DispatcherServlet dispatcherServlet, WebMvcProperties webMvcProperties, ObjectProvider<MultipartConfigElement> multipartConfig) {
            //创建DispatcherServletRegistrationBean，
            //包含一个DispatcherServlet和一个urlMapping
            //即DispatcherServlet负责处理的请求路径
            DispatcherServletRegistrationBean registration = new DispatcherServletRegistrationBean(dispatcherServlet, webMvcProperties.getServlet().getPath());
            registration.setName("dispatcherServlet");
            registration.setLoadOnStartup(webMvcProperties.getServlet().getLoadOnStartup());
            multipartConfig.ifAvailable(registration::setMultipartConfig);
            return registration;
        }
    }

    @Configuration(
        proxyBeanMethods = false
    )
   //负责加载DispatcherServlet
    @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;
        }
    }
}


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