springboot靜態資源配置原理

springboot對靜態資源的配置可參考WebMvcAutoConfiguration這個類，在spring-boot-autoconfigure.jar中

WebMvcAutoConfiguration

@Configuration(proxyBeanMethods = false)
@ConditionalOnWebApplication(type = Type.SERVLET)
@ConditionalOnClass({ Servlet.class, DispatcherServlet.class, WebMvcConfigurer.class })
@ConditionalOnMissingBean(WebMvcConfigurationSupport.class)
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE + 10)
@AutoConfigureAfter({ DispatcherServletAutoConfiguration.class, TaskExecutionAutoConfiguration.class,
		ValidationAutoConfiguration.class })
public class WebMvcAutoConfiguration {
   ....
}

@Configuration(proxyBeanMethods = false)：告訴容器這是一個配置類，且不代理bean方法，每次調用都會創建，這樣容器啓動時無需檢查容器中是否已經存在

@ConditionalOnWebApplication(type = Type.SERVLET)：判斷當前webAplication的類型是否爲servlet，如果是則繼續執行

@ConditionalOnClass({ Servlet.class, DispatcherServlet.class, WebMvcConfigurer.class })：判斷必須存在指定的類才執行

@ConditionalOnMissingBean(WebMvcConfigurationSupport.class)：判斷必須沒有指定的類才執行

@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE + 10)：控制執行順序
@AutoConfigureAfter({ DispatcherServletAutoConfiguration.class, TaskExecutionAutoConfiguration.class,
ValidationAutoConfiguration.class })：在加載配置的類之後再加載當前類

WebMvcAutoConfigurationAdapter

在WebMvcAutoConfiguration這個類中，存在一個WebMvcAutoConfigurationAdapter 靜態內部類，用於配置靜態資源規則的。

// Defined as a nested config to ensure WebMvcConfigurer is not read when not
	// on the classpath
	@Configuration(proxyBeanMethods = false)
	@Import(EnableWebMvcConfiguration.class)
	@EnableConfigurationProperties({ WebMvcProperties.class, ResourceProperties.class })
	@Order(0)
	public static class WebMvcAutoConfigurationAdapter implements WebMvcConfigurer {
 
....

}

　這個靜態內部類中有且只有一個帶參構造方法：

public WebMvcAutoConfigurationAdapter(ResourceProperties resourceProperties, WebMvcProperties mvcProperties,
				ListableBeanFactory beanFactory, ObjectProvider<HttpMessageConverters> messageConvertersProvider,
				ObjectProvider<ResourceHandlerRegistrationCustomizer> resourceHandlerRegistrationCustomizerProvider) {
			this.resourceProperties = resourceProperties;
			this.mvcProperties = mvcProperties;
			this.beanFactory = beanFactory;
			this.messageConvertersProvider = messageConvertersProvider;
			this.resourceHandlerRegistrationCustomizer = resourceHandlerRegistrationCustomizerProvider.getIfAvailable();
		}

　　只有一個帶參構造方法時，入參會從容器中進行查找。其中的 resourceProperties和mvcProperties是通過註解@EnableConfigurationProperties導入的，其中的XXXProperties又是通過指定前綴和配置文件進行綁定的；

WebMvcProperties

@ConfigurationProperties(prefix = "spring.mvc")
public class WebMvcProperties {

ResourceProperties

@ConfigurationProperties(prefix = "spring.resources", ignoreUnknownFields = false)
public class ResourceProperties {

	private static final String[] CLASSPATH_RESOURCE_LOCATIONS = { "classpath:/META-INF/resources/",
			"classpath:/resources/", "classpath:/static/", "classpath:/public/" };

addResourceHandlers

在這個WebMvcAutoConfigurationAdapter 靜態內部類中存在一個addResourceHandlers方法，這個方法就是用於靜態資源規則配置使用的；

@Override
public void addResourceHandlers(ResourceHandlerRegistry registry) {
        //檢查是否開啓默認資源處理，默認是true,可以通過配置文件改爲false,關閉所有的靜態資源配置映射
       if (!this.resourceProperties.isAddMappings()) {
          logger.debug("Default resource handling disabled");
          return;
       }
       //同時通過配置文件可以添加緩存時間，秒爲單位
       Duration cachePeriod = this.resourceProperties.getCache().getPeriod();
       CacheControl cacheControl = this.resourceProperties.getCache().getCachecontrol().toHttpCacheControl();
       if (!registry.hasMappingForPattern("/webjars/**")) {
       
            //對於webjars的訪問全部映射到類路徑下的/META-INF/resources/webjars/
          customizeResourceHandlerRegistration(registry.addResourceHandler("/webjars/**")
                .addResourceLocations("classpath:/META-INF/resources/webjars/")
                .setCachePeriod(getSeconds(cachePeriod)).setCacheControl(cacheControl));
       }
       
       //獲取靜態資源的路徑，默認是/**
       String staticPathPattern = this.mvcProperties.getStaticPathPattern();
       if (!registry.hasMappingForPattern(staticPathPattern)) {
       
        //對於配置的靜態資源路徑都會去this.resourceProperties.getStaticLocations()進行查找
          customizeResourceHandlerRegistration(registry.addResourceHandler(staticPathPattern)
                .addResourceLocations(getResourceLocations(this.resourceProperties.getStaticLocations()))
                .setCachePeriod(getSeconds(cachePeriod)).setCacheControl(cacheControl));
       }
}

　　this.resourceProperties.getStaticLocations()：這個就對應到ResourceProperties類中的CLASSPATH_RESOURCE_LOCATIONS；

private static final String[] CLASSPATH_RESOURCE_LOCATIONS = { "classpath:/META-INF/resources/",
			"classpath:/resources/", "classpath:/static/", "classpath:/public/" };

　

spring:
#  mvc:
#    static-path-pattern: /res/**

  resources:
    add-mappings: false   禁用所有靜態資源規則

　　

歡迎頁的處理

歡迎頁使用的welcomePageHandlerMapping方法

@Bean

public WelcomePageHandlerMapping welcomePageHandlerMapping(ApplicationContext applicationContext,
      FormattingConversionService mvcConversionService, ResourceUrlProvider mvcResourceUrlProvider) {
   WelcomePageHandlerMapping welcomePageHandlerMapping = new WelcomePageHandlerMapping(
         new TemplateAvailabilityProviders(applicationContext), applicationContext, getWelcomePage(),
         this.mvcProperties.getStaticPathPattern());
   welcomePageHandlerMapping.setInterceptors(getInterceptors(mvcConversionService, mvcResourceUrlProvider));
   welcomePageHandlerMapping.setCorsConfigurations(getCorsConfigurations());
   return welcomePageHandlerMapping;
}

　　HandlerMapping：處理器映射。保存了每一個Handler能處理哪些請求。

對於這個有參構造方法：

WelcomePageHandlerMapping(TemplateAvailabilityProviders templateAvailabilityProviders,
			ApplicationContext applicationContext, Optional<Resource> welcomePage, String staticPathPattern) {
		if (welcomePage.isPresent() && "/**".equals(staticPathPattern)) {
			logger.info("Adding welcome page: " + welcomePage.get());
			setRootViewName("forward:index.html");
		}
		else if (welcomeTemplateExists(templateAvailabilityProviders, applicationContext)) {
			logger.info("Adding welcome page template: index");
			setRootViewName("index");
		}
	}

　　可以看出判斷條件，如果開啓了歡迎頁且靜態路徑必須匹配/**則會去index.html，要麼是跳轉到index的請求。

      至此可以看出springboot對靜態資源的所有默認規則。