Spring boot 梳理 [email
阿新 • • 發佈:2019-01-08
- @EnableWebMvc=繼承DelegatingWebMvcConfiguration=繼承WebMvcConfigurationSupport
- 直接看原始碼,@EnableWebMvc實際上引入一個DelegatingWebMvcConfiguration
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@Retention(RetentionPolicy.RUNTIME) @Target({ElementType.TYPE}) @Documented @Import({DelegatingWebMvcConfiguration.class}) public
- DelegatingWebMvcConfiguration繼承了WebMvcConfigurationSupport
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@Configuration public class DelegatingWebMvcConfiguration extends WebMvcConfigurationSupport { ...
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@EnableWebMvc,WebMvcConfigurationSupport,WebMvcConfigurer和WebMvcConfigurationAdapter使用
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WebMvcConfigurationAdapter已經廢棄,最好用implements WebMvcConfigurer代替
@Configuration public class MyConfig implements WebMvcConfigurer { }
如果使用繼承,WebMvcConfigurationSupport,DelegatingWebMvcConfiguration,或者使用@EnableWebMvc,
需要注意會覆蓋application.properties中關於WebMvcAutoConfiguration的設定,需要在自定義配置中實現,如
springboot2.0、spring5.0 攔截器配置WebMvcConfigurerAdapter過時使用WebMvcConfigurationSupport來代替 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 { }
上面程式碼中需要在類中實現關於WebMvcAutoConfiguration的配置,而不是在application.properties中。 -
總結
implements WebMvcConfigurer : 不會覆蓋@EnableAutoConfiguration關於WebMvcAutoConfiguration的配置
@EnableWebMvc + implements WebMvcConfigurer : 會覆蓋@EnableAutoConfiguration關於WebMvcAutoConfiguration的配置
extends WebMvcConfigurationSupport :會覆蓋@EnableAutoConfiguration關於WebMvcAutoConfiguration的配置
extends DelegatingWebMvcConfiguration :會覆蓋@EnableAutoConfiguration關於WebMvcAutoConfiguration的配置
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- 直接看原始碼,@EnableWebMvc實際上引入一個DelegatingWebMvcConfiguration
- @EnableAutoConfiguration
- @EnableAutoConfiguration是springboot專案的啟動類註解@SpringBootApplication的子元素,主要功能為自動配置
- @EnableAutoConfiguration實際是匯入了EnableAutoConfigurationImportSelector和Registrar兩個類
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@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 { }
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這兩個類的具體原理有些複雜,不太清除,主要內容是通過SpringFactoriesLoader.loadFactoryNames()匯入jar下面的配置檔案META-INF/spring.factories
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配置檔案中的內容如下
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# 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,\
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- 其中有WebMvcAutoConfiguration,WebMvcAutoConfiguration原始碼如下
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@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 { ...猜測,Spring boot 在此處載入 application.properties 中關於MVC的預設配置;如果@Conditional返回false,則該配置類不執行 }
- @ConditionalOnMissingBean({WebMvcConfigurationSupport.class})意思是如果存在它修飾的類的bean
,則不需要再建立這個bean。 - 由此可得出結論:
如果有配置檔案繼承了DelegatingWebMvcConfiguration,
或者WebMvcConfigurationSupport,或者配置檔案有@EnableWebMvc,那麼 @EnableAutoConfiguration 中的
WebMvcAutoConfiguration 將不會被自動配置,而是使用WebMvcConfigurationSupport的配置。
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- @SpringBootApplication
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@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 { ... }
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- 轉:https://www.cnblogs.com/sufferingStriver/p/9026764.html