Spring Boot – 自動配置

首頁>技術>java乾貨2019-11-27 18:56

Spring Boot – 自動配置

他生莫作有情痴，人間無地著相思。

概述

spring boot 是很容易上手的，它在內部做了很多你不知道的事情。將來，一個好的開發人員將確切地知道SpringBoot自動配置背後發生了什麼，如何對你有利地使用它，以及如何禁用某些你不想在專案中使用的部分。

為了了解Spring Boot背後的大多數基本內容，我們將建立一個具有單個依賴項和單個啟動類檔案的最小啟動應用程式。然後，我們將分析啟動日誌以獲取見解。

使用啟動類建立Spring Boot應用程式

在Eclipse中建立一個新的Maven專案，原型為maven-archetype-quickstart。使用spring-boot-starter-web依賴項和外掛資訊更新pom.xml檔案 <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd;<modelVersion>4.0.0</modelVersion><groupId>com.howtodoinjava</groupId><artifactId>springbootdemo</artifactId><version>0.0.1-SNAPSHOT</version><packaging>jar</packaging><name>springbootdemo</name><url>http://maven.apache.org</url><parent><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-parent</artifactId><version>2.0.0.RELEASE</version></parent><properties><java.version>1.8</java.version><project.build.sourceEncoding>UTF-8</project.build.sourceEncoding></properties><dependencies><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId></dependency></dependencies><build><plugins><plugin><groupId>org.springframework.boot</groupId><artifactId>spring-boot-maven-plugin</artifactId></plugin></plugins></build><repositories><repository><id>repository.spring.release</id><name>Spring GA Repository</name><url>http://repo.spring.io/release</url></repository></repositories></project>建立啟動類 package cn.howtodoinjava.demo;import org.springframework.boot.SpringApplication;import org.springframework.boot.autoconfigure.SpringBootApplication;import org.springframework.context.ApplicationContext;@SpringBootApplicationpublic class App {public static void main(String[] args) {ApplicationContext ctx = SpringApplication.run(App.class, args);}}啟動類做了些什麼？上面的類稱為Spring Boot應用程式啟動類。它通過Java main（）方法引導和啟動Spring應用程式。它通常會執行以下操作–建立Spring的ApplicationContext的例項。允許該功能接受命令列引數並將它們作為Spring屬性公開。根據配置載入所有Spring bean，還可以根據專案需要進行其他操作。

@SpringBootApplication註解

此註解是在一條語句中應用3個註解的快捷語句–

@SpringBootConfiguration@SpringBootConfiguration是Spring boot 2中的新註解。之前，我們一直在使用@Configuration註解。你也可以使用@Configuration代替它。兩者都是同一回事。它表明類提供了Spring啟動應用程式@Configuration。它只是意味著帶註解的類是一個配置類，應該掃描它以獲得進一步的配置和bean定義。@EnableAutoConfiguration該註解用於啟用Spring Application Context的自動配置，嘗試猜測和配置你可能需要的bean。通常根據你的類路徑和定義的bean來應用自動配置類。自動配置會嘗試儘可能智慧化，並且在你定義更多自己的配置時會自動退出。你始終可以使用兩種方法手動排除你不想應用的任何配置-. 使用 excludeName() -. 配置檔案中使用spring.autoconfigure.exclude property @EnableAutoConfiguration(excludeName = {"multipartResolver","mbeanServer"})自動配置始終在註冊使用者定義的bean之後應用。@ComponentScan該註解支援與Spring XML context:component-scan並行可以指定basePackageClasses（）或basePackages（）來定義要掃描的特定程式包。如果未定義特定的程式包，則將從宣告此註解的類的程式包中進行掃描

執行啟動應用程式並檢查日誌

在IDE中，右鍵單擊應用程式類，然後將其作為Java應用程式執行。為了了解已註冊的bean，我添加了如下修改的啟動應用程式。

@SpringBootApplicationpublic class App { public static void main(String[] args)  { ApplicationContext ctx = SpringApplication.run(App.class, args); String[] beanNames = ctx.getBeanDefinitionNames(); Arrays.sort(beanNames); for (String beanName : beanNames) { System.out.println(beanName); } }}

日誌輸入如下

 . ____ _ __ _ _ /\\\\ / ___&#39;_ __ _ _(_)_ __ __ _ \\ \\ \\ \\( ( )\\___ | &#39;_ | &#39;_| | &#39;_ \\/ _` | \\ \\ \\ \\ \\\\/ ___)| |_)| | | | | || (_| | ) ) ) ) &#39; |____| .__|_| |_|_| |_\\__, | / / / / =========|_|==============|___/=/_/_/_/ :: Spring Boot :: (v2.0.0.RELEASE)2018-04-02 13:09:41.100 INFO 11452 --- [ main] com.howtodoinjava.demo.App : Starting App on FFC15B4E9C5AA with PID 11452 (C:\\Users\\zkpkhua\\IDPPaymentTransfers_Integrated\\springbootdemo\\target\\classes started by zkpkhua in C:\\Users\\zkpkhua\\IDPPaymentTransfers_Integrated\\springbootdemo)2018-04-02 13:09:41.108 INFO 11452 --- [ main] com.howtodoinjava.demo.App : No active profile set, falling back to default profiles: default2018-04-02 13:09:41.222 INFO 11452 --- [ main] ConfigServletWebServerApplicationContext : Refreshing org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext@4450d156: startup date [Mon Apr 02 13:09:41 IST 2018]; root of context hierarchy2018-04-02 13:09:43.474 INFO 11452 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with port(s): 8080 (http)2018-04-02 13:09:43.526 INFO 11452 --- [ main] o.apache.catalina.core.StandardService : Starting service [Tomcat]2018-04-02 13:09:43.526 INFO 11452 --- [ main] org.apache.catalina.core.StandardEngine : Starting Servlet Engine: Apache Tomcat/8.5.282018-04-02 13:09:43.748 INFO 11452 --- [ost-startStop-1] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext2018-04-02 13:09:43.748 INFO 11452 --- [ost-startStop-1] o.s.web.context.ContextLoader : Root WebApplicationContext: initialization completed in 2531 ms2018-04-02 13:09:43.964 INFO 11452 --- [ost-startStop-1] o.s.b.w.servlet.ServletRegistrationBean : Servlet dispatcherServlet mapped to [/]2018-04-02 13:09:43.969 INFO 11452 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean : Mapping filter: &#39;characterEncodingFilter&#39; to: [/*]2018-04-02 13:09:43.970 INFO 11452 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean : Mapping filter: &#39;hiddenHttpMethodFilter&#39; to: [/*]2018-04-02 13:09:43.970 INFO 11452 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean : Mapping filter: &#39;httpPutFormContentFilter&#39; to: [/*]2018-04-02 13:09:43.970 INFO 11452 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean : Mapping filter: &#39;requestContextFilter&#39; to: [/*]2018-04-02 13:09:44.480 INFO 11452 --- [ main] s.w.s.m.m.a.RequestMappingHandlerAdapter : Looking for @ControllerAdvice: org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext@4450d156: startup date [Mon Apr 02 13:09:41 IST 2018]; root of context hierarchy2018-04-02 13:09:44.627 INFO 11452 --- [ main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped &#34;{[/error]}&#34; onto public org.springframework.http.ResponseEntity&lt;java.util.Map&lt;java.lang.String, java.lang.Object&gt;&gt; org.springframework.boot.autoconfigure.web.servlet.error.BasicErrorController.error(javax.servlet.http.HttpServletRequest)2018-04-02 13:09:44.630 INFO 11452 --- [ main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped &#34;{[/error],produces=}&#34; onto public org.springframework.web.servlet.ModelAndView org.springframework.boot.autoconfigure.web.servlet.error.BasicErrorController.errorHtml(javax.servlet.http.HttpServletRequest,javax.servlet.http.HttpServletResponse)2018-04-02 13:09:44.681 INFO 11452 --- [ main] o.s.w.s.handler.SimpleUrlHandlerMapping : Mapped URL path [/webjars/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]2018-04-02 13:09:44.682 INFO 11452 --- [ main] o.s.w.s.handler.SimpleUrlHandlerMapping : Mapped URL path [/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]2018-04-02 13:09:44.747 INFO 11452 --- [ main] o.s.w.s.handler.SimpleUrlHandlerMapping : Mapped URL path [/**/favicon.ico] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]2018-04-02 13:09:45.002 INFO 11452 --- [ main] o.s.j.e.a.AnnotationMBeanExporter : Registering beans for JMX exposure on startup2018-04-02 13:09:45.070 INFO 11452 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8080 (http) with context path &#39;&#39;2018-04-02 13:09:45.076 INFO 11452 --- [ main] com.howtodoinjava.demo.App : Started App in 4.609 seconds (JVM running for 5.263)appbasicErrorControllerbeanNameHandlerMappingbeanNameViewResolvercharacterEncodingFilterconventionErrorViewResolverdefaultServletHandlerMappingdefaultValidatordefaultViewResolverdispatcherServletdispatcherServletRegistrationerrorerrorAttributeserrorPageCustomizererrorPageRegistrarBeanPostProcessorfaviconHandlerMappingfaviconRequestHandlerhandlerExceptionResolverhiddenHttpMethodFilterhttpPutFormContentFilterhttpRequestHandlerAdapterjacksonCodecCustomizerjacksonObjectMapperjacksonObjectMapperBuilderjsonComponentModulelocaleCharsetMappingsCustomizermappingJackson2HttpMessageConvertermbeanExportermbeanServermessageConvertersmethodValidationPostProcessormultipartConfigElementmultipartResolvermvcContentNegotiationManagermvcConversionServicemvcHandlerMappingIntrospectormvcPathMatchermvcResourceUrlProvidermvcUriComponentsContributormvcUrlPathHelpermvcValidatormvcViewResolverobjectNamingStrategyorg.springframework.boot.autoconfigure.AutoConfigurationPackagesorg.springframework.boot.autoconfigure.condition.BeanTypeRegistryorg.springframework.boot.autoconfigure.context.ConfigurationPropertiesAutoConfigurationorg.springframework.boot.autoconfigure.context.PropertyPlaceholderAutoConfigurationorg.springframework.boot.autoconfigure.http.HttpMessageConvertersAutoConfigurationorg.springframework.boot.autoconfigure.http.HttpMessageConvertersAutoConfiguration$StringHttpMessageConverterConfigurationorg.springframework.boot.autoconfigure.http.JacksonHttpMessageConvertersConfigurationorg.springframework.boot.autoconfigure.http.JacksonHttpMessageConvertersConfiguration$MappingJackson2HttpMessageConverterConfigurationorg.springframework.boot.autoconfigure.http.codec.CodecsAutoConfigurationorg.springframework.boot.autoconfigure.http.codec.CodecsAutoConfiguration$JacksonCodecConfigurationorg.springframework.boot.autoconfigure.info.ProjectInfoAutoConfigurationorg.springframework.boot.autoconfigure.internalCachingMetadataReaderFactoryorg.springframework.boot.autoconfigure.jackson.JacksonAutoConfigurationorg.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration$Jackson2ObjectMapperBuilderCustomizerConfigurationorg.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration$JacksonObjectMapperBuilderConfigurationorg.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration$JacksonObjectMapperConfigurationorg.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration$ParameterNamesModuleConfigurationorg.springframework.boot.autoconfigure.jmx.JmxAutoConfigurationorg.springframework.boot.autoconfigure.security.reactive.ReactiveSecurityAutoConfigurationorg.springframework.boot.autoconfigure.validation.ValidationAutoConfigurationorg.springframework.boot.autoconfigure.web.client.RestTemplateAutoConfigurationorg.springframework.boot.autoconfigure.web.embedded.EmbeddedWebServerFactoryCustomizerAutoConfigurationorg.springframework.boot.autoconfigure.web.embedded.EmbeddedWebServerFactoryCustomizerAutoConfiguration$TomcatWebServerFactoryCustomizerConfigurationorg.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfigurationorg.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration$DispatcherServletConfigurationorg.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration$DispatcherServletRegistrationConfigurationorg.springframework.boot.autoconfigure.web.servlet.HttpEncodingAutoConfigurationorg.springframework.boot.autoconfigure.web.servlet.MultipartAutoConfigurationorg.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfigurationorg.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryConfiguration$EmbeddedTomcatorg.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfigurationorg.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration$EnableWebMvcConfigurationorg.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration$WebMvcAutoConfigurationAdapterorg.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration$WebMvcAutoConfigurationAdapter$FaviconConfigurationorg.springframework.boot.autoconfigure.web.servlet.error.ErrorMvcAutoConfigurationorg.springframework.boot.autoconfigure.web.servlet.error.ErrorMvcAutoConfiguration$DefaultErrorViewResolverConfigurationorg.springframework.boot.autoconfigure.web.servlet.error.ErrorMvcAutoConfiguration$WhitelabelErrorViewConfigurationorg.springframework.boot.autoconfigure.websocket.servlet.WebSocketServletAutoConfigurationorg.springframework.boot.autoconfigure.websocket.servlet.WebSocketServletAutoConfiguration$TomcatWebSocketConfigurationorg.springframework.boot.context.properties.ConfigurationBeanFactoryMetadataorg.springframework.boot.context.properties.ConfigurationPropertiesBindingPostProcessororg.springframework.context.annotation.internalAutowiredAnnotationProcessororg.springframework.context.annotation.internalCommonAnnotationProcessororg.springframework.context.annotation.internalConfigurationAnnotationProcessororg.springframework.context.annotation.internalRequiredAnnotationProcessororg.springframework.context.event.internalEventListenerFactoryorg.springframework.context.event.internalEventListenerProcessorparameterNamesModulepreserveErrorControllerTargetClassPostProcessorpropertySourcesPlaceholderConfigurerrequestContextFilterrequestMappingHandlerAdapterrequestMappingHandlerMappingresourceHandlerMappingrestTemplateBuilderserver-org.springframework.boot.autoconfigure.web.ServerPropertiesservletWebServerFactoryCustomizersimpleControllerHandlerAdapterspring.http.encoding-org.springframework.boot.autoconfigure.http.HttpEncodingPropertiesspring.info-org.springframework.boot.autoconfigure.info.ProjectInfoPropertiesspring.jackson-org.springframework.boot.autoconfigure.jackson.JacksonPropertiesspring.mvc-org.springframework.boot.autoconfigure.web.servlet.WebMvcPropertiesspring.resources-org.springframework.boot.autoconfigure.web.ResourcePropertiesspring.security-org.springframework.boot.autoconfigure.security.SecurityPropertiesspring.servlet.multipart-org.springframework.boot.autoconfigure.web.servlet.MultipartPropertiesstandardJacksonObjectMapperBuilderCustomizerstringHttpMessageConvertertomcatServletWebServerFactorytomcatServletWebServerFactoryCustomizertomcatWebServerFactoryCustomizerviewControllerHandlerMappingviewResolverwebServerFactoryCustomizerBeanPostProcessorwebsocketContainerCustomizerwelcomePageHandlerMapping

你會看到有多少個bean自動註冊。如果你想更深入地研究為什麼要註冊任何特定的bean？通過在應用程式啟動時加入debug標誌，你可以看到這一點。

只需將-Ddebug = true作為VM引數傳遞。

現在，當你執行該應用程式時，您將獲得許多debug日誌，它們具有類似的資訊：

CodecsAutoConfiguration.JacksonCodecConfiguration matched: - @ConditionalOnClass found required class &#39;com.fasterxml.jackson.databind.ObjectMapper&#39;; @ConditionalOnMissingClass did not find unwanted class (OnClassCondition)CodecsAutoConfiguration.JacksonCodecConfiguration#jacksonCodecCustomizer matched: - @ConditionalOnBean (types: com.fasterxml.jackson.databind.ObjectMapper; SearchStrategy: all) found bean &#39;jacksonObjectMapper&#39; (OnBeanCondition)DispatcherServletAutoConfiguration.DispatcherServletConfiguration matched: - @ConditionalOnClass found required class &#39;javax.servlet.ServletRegistration&#39;; @ConditionalOnMissingClass did not find unwanted class (OnClassCondition) - Default DispatcherServlet did not find dispatcher servlet beans (DispatcherServletAutoConfiguration.DefaultDispatcherServletCondition)DispatcherServletAutoConfiguration.DispatcherServletRegistrationConfiguration matched: - @ConditionalOnClass found required class &#39;javax.servlet.ServletRegistration&#39;; @ConditionalOnMissingClass did not find unwanted class (OnClassCondition) - DispatcherServlet Registration did not find servlet registration bean (DispatcherServletAutoConfiguration.DispatcherServletRegistrationCondition) ... ... ...

上面的日誌說明了為什麼將特定的bean註冊到spring上下文中。當你除錯自動配置問題時，此資訊非常有用。

同樣，每次我們向Spring Boot專案新增新的依賴項時，Spring Boot自動配置都會自動嘗試基於依賴項配置Bean。

原文連結：Spring Boot2 @SpringBootApplication Auto Configuration

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