@EnableWebMvc,WebMvcConfigurationSupport,WebMvcConfigurer和WebMvcConfigurationAdapter区别

@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
 
 

 

posted @ 2018-05-11 21:57  sufferingStriver  阅读(16106)  评论(1编辑  收藏  举报