SpringBoot 項目 @EnableWebMvc 注解應用總結

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SpringBoot 項目中不管是在哪個類上使用 @EnableWebMvc 注解，都将導緻所有URL通路時傳回 404 錯誤；

看到一篇文章：“

Spring4 @EnableWebMvc 純注解啟動

”，但還沒有在 Spring MVC 項目上嘗試過。

另外參考文章：“

解析@EnableWebMvc 、WebMvcConfigurationSupport和WebMvcConfigurationAdapter

”中說的：

============================

在spring-boot+spring mvc 的項目中，有些時候我們需要自己配置一些項目的設定，就會涉及到這三個，那麼，他們之間有什麼關系呢？ 

首先，@EnableWebMvc=WebMvcConfigurationSupport，使用了@EnableWebMvc注解等于擴充了WebMvcConfigurationSupport但是沒有重寫任何方法。

是以有以下幾種使用方式：

1. @EnableWebMvc+extends WebMvcConfigurationAdapter，在擴充的類中重寫父類的方法即可，這種方式會屏蔽springboot的@EnableAutoConfiguration中的設定
2. extends WebMvcConfigurationSupport，在擴充的類中重寫父類的方法即可，這種方式會屏蔽springboot的@EnableAutoConfiguration中的設定
3. extends WebMvcConfigurationAdapter，在擴充的類中重寫父類的方法即可，這種方式依舊使用springboot的@EnableAutoConfiguration中的設定

具體哪種方法适合，看個人對于項目的需求和要把控的程度

在WebMvcConfigurationSupport（@EnableWebMvc）和@EnableAutoConfiguration這兩種方式都有一些預設的設定 

而WebMvcConfigurationAdapter則是一個abstract class

具體如何類内如何進行個性化的設定，可以參考以下文章：

Spring Boot：定制HTTP消息轉換器 EnableWebMvc官方文檔

==========================

難道是因為我的項目中使用了“@EnableAutoConfiguration”，@EnableWebMvc和@EnableAutoConfiguration 這兩種方式有沖突嗎？

注釋掉 @EnableAutoConfiguration ，使用 @EnableWebMvc，得到以下錯誤：

javax.servlet.ServletException: Could not resolve view with name 'loginback' in servlet with name 'dispatcherServlet'
	at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1266) ~[spring-webmvc-4.3.13.RELEASE.jar:4.3.13.RELEASE]
	at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1041) ~[spring-webmvc-4.3.13.RELEASE.jar:4.3.13.RELEASE]
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:984) ~[spring-webmvc-4.3.13.RELEASE.jar:4.3.13.RELEASE]
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:901) ~[spring-webmvc-4.3.13.RELEASE.jar:4.3.13.RELEASE]
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970) ~[spring-webmvc-4.3.13.RELEASE.jar:4.3.13.RELEASE]
	at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861) ~[spring-webmvc-4.3.13.RELEASE.jar:4.3.13.RELEASE]
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:687) ~[javax.servlet-api-3.1.0.jar:3.1.0]
	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846) ~[spring-webmvc-4.3.13.RELEASE.jar:4.3.13.RELEASE]
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:790) ~[javax.servlet-api-3.1.0.jar:3.1.0]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) ~[tomcat-embed-websocket-8.5.23.jar:8.5.23]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.springframework.boot.web.filter.ApplicationContextHeaderFilter.doFilterInternal(ApplicationContextHeaderFilter.java:55) ~[spring-boot-1.5.9.RELEASE.jar:1.5.9.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.3.13.RELEASE.jar:4.3.13.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.springframework.boot.actuate.trace.WebRequestTraceFilter.doFilterInternal(WebRequestTraceFilter.java:110) ~[spring-boot-actuator-1.5.9.RELEASE.jar:1.5.9.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.3.13.RELEASE.jar:4.3.13.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:197) ~[spring-web-4.3.13.RELEASE.jar:4.3.13.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.3.13.RELEASE.jar:4.3.13.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.springframework.boot.actuate.autoconfigure.MetricsFilter.doFilterInternal(MetricsFilter.java:106) ~[spring-boot-actuator-1.5.9.RELEASE.jar:1.5.9.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.3.13.RELEASE.jar:4.3.13.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:199) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) [tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:478) [tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140) [tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81) [tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87) [tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342) [tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:803) [tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) [tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868) [tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1459) [tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-8.5.23.jar:8.5.23]
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [na:1.8.0_121]
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [na:1.8.0_121]
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-8.5.23.jar:8.5.23]
	at java.lang.Thread.run(Thread.java:745) [na:1.8.0_121]           

Could not resolve view with name 'loginback' in servlet with name 'dispatcherServlet'

感覺是視圖模闆沒有找到，于是在入口類（帶有 @SpringBootApplication 注解的類）中添加以下代碼，指定視圖模闆位置：

/**
	 * 配置JSP視圖解析器
	 * 如果沒有配置視圖解析器。Spring會使用BeanNameViewResolver，通過查找ID與邏輯視圖名稱比對且實作了View接口的beans
	 * 
	 * @return
	 */
	@Bean
	public InternalResourceViewResolver setupViewResolver() {
		InternalResourceViewResolver resolver = new InternalResourceViewResolver();
		/** 設定視圖路徑的字首 */
		resolver.setPrefix("/WEB-INF/jsp/");
		/** 設定視圖路徑的字尾 */
		resolver.setSuffix(".jsp");
		return resolver;
	}           

再次重新開機項目，一切正常了。

總結

使用 @EnableWebMvc 注解，需要以程式設計的方式指定視圖檔案相關配置；

使用 @EnableAutoConfiguration 注解，會讀取 application.properties 或 application.yml 檔案中的配置。