直接看源码,@EnableWebMvc实际上引入一个DelegatingWebMvcConfiguration。
@Retention(RetentionPolicy.RUNTIME) @Target({ElementType.TYPE}) @Documented @Import({DelegatingWebMvcConfiguration.class}) public @interface EnableWebMvc { }DelegatingWebMvcConfiguration继承了WebMvcConfigurationSupport
@Configuration public class DelegatingWebMvcConfiguration extends WebMvcConfigurationSupport { ...所以@EnableWebMvc=继承DelegatingWebMvcConfiguration=继承WebMvcConfigurationSupport
@EnableAutoConfiguration是springboot项目的启动类注解@SpringBootApplication的子元素，主要功能为自动配置。
@Target({ElementType.TYPE}) @Retention(RetentionPolicy.RUNTIME) @Documented @Inherited @SpringBootConfiguration @EnableAutoConfiguration @ComponentScan( excludeFilters = {@Filter( type = FilterType.CUSTOM, classes = {TypeExcludeFilter.class} ), @Filter( type = FilterType.CUSTOM, classes = {AutoConfigurationExcludeFilter.class} )} ) public @interface SpringBootApplication { ... }@EnableAutoConfiguration实际是导入了EnableAutoConfigurationImportSelector和Registrar两个类
@Target({ElementType.TYPE}) @Retention(RetentionPolicy.RUNTIME) @Documented @Inherited @AutoConfigurationPackage @Import({AutoConfigurationImportSelector.class}) public @interface EnableAutoConfiguration { ... } @Target({ElementType.TYPE}) @Retention(RetentionPolicy.RUNTIME) @Documented @Inherited @Import({Registrar.class}) public @interface AutoConfigurationPackage { }这两个类的具体原理有些复杂，不太清除，主要内容是通过SpringFactoriesLoader.loadFactoryNames()导入jar下面的配置文件META-INF/spring.factories protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) { List<String> configurations = SpringFactoriesLoader.loadFactoryNames(this.getSpringFactoriesLoaderFactoryClass(), this.getBeanClassLoader()); Assert.notEmpty(configurations, "No auto configuration classes found in META-INF/spring.factories. If you are using a custom packaging, make sure that file is correct."); return configurations; } 配置文件中的内容如下 # Auto Configure org.springframework.boot.autoconfigure.EnableAutoConfiguration=\ org.springframework.boot.autoconfigure.admin.SpringApplicationAdminJmxAutoConfiguration,\ ... org.springframework.boot.autoconfigure.web.servlet.HttpEncodingAutoConfiguration,\ org.springframework.boot.autoconfigure.web.servlet.MultipartAutoConfiguration,\ org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration,\ ... 其中有WebMvcAutoConfiguration,WebMvcAutoConfiguration源码如下 @Configuration @ConditionalOnWebApplication( type = Type.SERVLET ) @ConditionalOnClass({Servlet.class, DispatcherServlet.class, WebMvcConfigurer.class}) @ConditionalOnMissingBean({WebMvcConfigurationSupport.class}) @AutoConfigureOrder(-2147483638) @AutoConfigureAfter({DispatcherServletAutoConfiguration.class, ValidationAutoConfiguration.class}) public class WebMvcAutoConfiguration { ... }@ConditionalOnMissingBean({WebMvcConfigurationSupport.class})意思是如果存在它修饰的类的bean,则不需要再创建这个bean。由此可得出结论：如果有配置文件继承了DelegatingWebMvcConfiguration，或者WebMvcConfigurationSupport，或者配置文件有@EnableWebMvc，那么 @EnableAutoConfiguration 中的WebMvcAutoConfiguration 将不会被自动配置，而是使用WebMvcConfigurationSupport的配置。
WebMvcConfigurationAdapter已经废弃，最好用implements WebMvcConfigurer代替
@Configuration public class MyConfig implements WebMvcConfigurer { }如果使用继承,WebMvcConfigurationSupport，DelegatingWebMvcConfiguration，或者使用@EnableWebMvc，
需要注意会覆盖application.properties中关于WebMvcAutoConfiguration的设置，需要在自定义配置中实现，如
springboot2.0、spring5.0 拦截器配置WebMvcConfigurerAdapter过时使用WebMvcConfigurationSupport来代替 新坑
示例如下
Configuration @EnableWebMvc public class MyConfig implements WebMvcConfigurer { } @Configuration public class MyConfig extends WebMvcConfigurationSupport { } @Configuration public class MyConfig extends DelegatingWebMvcConfiguration { }上面代码中需要在类中实现关于WebMvcAutoConfiguration的配置，而不是在application.properties中。总结implements WebMvcConfigurer ： 不会覆盖@EnableAutoConfiguration关于WebMvcAutoConfiguration的配置@EnableWebMvc + implements WebMvcConfigurer ： 会覆盖@EnableAutoConfiguration关于WebMvcAutoConfiguration的配置extends WebMvcConfigurationSupport ：会覆盖@EnableAutoConfiguration关于WebMvcAutoConfiguration的配置extends DelegatingWebMvcConfiguration ：会覆盖@EnableAutoConfiguration关于WebMvcAutoConfiguration的配置
转载于:https://www.cnblogs.com/sufferingStriver/p/9026764.html
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