@EnableWebMvc,WebMvcConfigurationSupport,WebMvcConfigurer和WebMvcConfigurationAdapter区别
If you want to keep those Spring Boot MVC customizations and make more MVC customizations (interceptors, formatters, view controllers, and other features), you can add your own @Configuration class of type WebMvcConfigurer but without @EnableWebMvc.
If you want to provide custom instances of RequestMappingHandlerMapping, RequestMappingHandlerAdapter, or ExceptionHandlerExceptionResolver, and still keep the Spring Boot MVC customizations, you can declare a bean of type WebMvcRegistrations and use it to provide custom instances of those components. The custom instances will be subject to further initialization and configuration by Spring MVC. To participate in, and if desired, override that subsequent processing, a WebMvcConfigurer should be used.
If you want to provide custom instances of RequestMappingHandlerMapping, RequestMappingHandlerAdapter, or ExceptionHandlerExceptionResolver, and still keep the Spring Boot MVC customizations, you can declare a bean of type WebMvcRegistrations and use it to provide custom instances of those components. The custom instances will be subject to further initialization and configuration by Spring MVC. To participate in, and if desired, override that subsequent processing, a WebMvcConfigurer should be used.
If you do not want to use the auto-configuration and want to take complete control of Spring MVC, add your own @Configuration annotated with @EnableWebMvc. Alternatively, add your own @Configuration-annotated DelegatingWebMvcConfiguration as described in the Javadoc of @EnableWebMvc.If you do not want to use the auto-configuration and want to take complete control of Spring MVC, add your own @Configuration annotated with @EnableWebMvc. Alternatively, add your own @Configuration-annotated DelegatingWebMvcConfiguration as described in the Javadoc of @EnableWebMvc.
@EnableWebMvc是什么
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
@EnableWebMvc和@EnableAutoConfiguration的关系
- @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。
@EnableWebMvc,WebMvcConfigurationSupport,WebMvcConfigurer和WebMvcConfigurationAdapter使用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