SpringBoot静态资源配置原理

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SpringBoot中与静态资源配置有关的代码在自动配置类WebMvcAutoConfiguration里（org.springframework.boot.autoconfigure.web.servlet包下）。

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@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 {
}

其中有一个重要的静态内部类WebMvcAutoConfigurationAdapter是静态资源加载原理的核心。

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@Configuration(proxyBeanMethods = false)
@Import(EnableWebMvcConfiguration.class)
@EnableConfigurationProperties({ WebMvcProperties.class, ResourceProperties.class })
@Order(0)
public static class WebMvcAutoConfigurationAdapter implements WebMvcConfigurer {
}

@EnableConfigurationProperties({ WebMvcProperties.class, ResourceProperties.class })注解使配置文件与WebMvcProperties类和ResourceProperties类进行绑定后分别转换为bean，从源码可以看出WebMvcProperties和spring.mvc为前缀的配置相关联，ResourceProperties和spring.resources为前缀的配置相关联。

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

由于WebMvcAutoConfigurationAdapter只有一个有参构造器，说明其构造器中传入的值都是从ioc中获取的。

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public WebMvcAutoConfigurationAdapter(ResourceProperties resourceProperties, WebMvcProperties mvcProperties,
		ListableBeanFactory beanFactory, ObjectProvider<HttpMessageConverters> messageConvertersProvider,
		ObjectProvider<ResourceHandlerRegistrationCustomizer> resourceHandlerRegistrationCustomizerProvider,
		ObjectProvider<DispatcherServletPath> dispatcherServletPath,
		ObjectProvider<ServletRegistrationBean<?>> servletRegistrations) {
          //从容器中找到ResourceProperties组件(和spring.resource绑定的所有的值的对象)
	this.resourceProperties = resourceProperties;
          //从容器中找到WebMvcProperties组件(和spring.mvc绑定的所有的值的对象)
	this.mvcProperties = mvcProperties;
          //从容器中找到Spring的bean工厂
	this.beanFactory = beanFactory;
          //从容器中找到所有的消息转换器
	this.messageConvertersProvider = messageConvertersProvider;
          //从容器中找到资源处理器的自定义器
	this.resourceHandlerRegistrationCustomizer = resourceHandlerRegistrationCustomizerProvider.getIfAvailable();
          //从容器中找到dispatcherServlet能处理的路径
	this.dispatcherServletPath = dispatcherServletPath;
          //从容器中找到能给应用注册Servlet、Filter的组件
	this.servletRegistrations = servletRegistrations;
}

资源处理的默认规则配置在addResourceHandlers()中。

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@Configuration(proxyBeanMethods = false)
@Import(EnableWebMvcConfiguration.class)
@EnableConfigurationProperties({ WebMvcProperties.class, ResourceProperties.class })
@Order(0)
public static class WebMvcAutoConfigurationAdapter implements WebMvcConfigurer {
       @Override
	public void addResourceHandlers(ResourceHandlerRegistry registry) {
           //如果在配置文件中配置spring.resources.add-mappings=false则禁用所有静态资源规则
		if (!this.resourceProperties.isAddMappings()) {
			logger.debug("Default resource handling disabled");
			return;
		}
           //可通过设置spring.resources.cache.period的值来配置静态资源缓存时间
		Duration cachePeriod = this.resourceProperties.getCache().getPeriod();
		CacheControl cacheControl = this.resourceProperties.getCache().getCachecontrol().toHttpCacheControl();
           //请求是/webjars/**时会到类路径的/META-INF/resources/webjars/下找寻静态资源并返回给用户，并设置上面设定的缓存时间
		if (!registry.hasMappingForPattern("/webjars/**")) {
			customizeResourceHandlerRegistration(registry.addResourceHandler("/webjars/**")
					.addResourceLocations("classpath:/META-INF/resources/webjars/")
					.setCachePeriod(getSeconds(cachePeriod)).setCacheControl(cacheControl));
		}
           //获取到spring.mvc.static-path-pattern的配置，默认是/**
		String staticPathPattern = this.mvcProperties.getStaticPathPattern();
           //请求是staticPathPattern时会映射到this.resourceProperties.getStaticLocations()目录下，即{ "classpath:/META-INF/resources/","classpath:/resources/", "classpath:/static/", "classpath:/public/" }，同时并设置上面设定的缓存时间
		if (!registry.hasMappingForPattern(staticPathPattern)) {
			customizeResourceHandlerRegistration(registry.addResourceHandler(staticPathPattern)
				.addResourceLocations(getResourceLocations(this.resourceProperties.getStaticLocations()))
					.setCachePeriod(getSeconds(cachePeriod)).setCacheControl(cacheControl));
		}
	}
   }

欢迎页的处理规则在另一个静态内部类EnableWebMvcConfiguration中。

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@Configuration(proxyBeanMethods = false)
public static class EnableWebMvcConfiguration extends DelegatingWebMvcConfiguration implements ResourceLoaderAware {        
	@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;
	}
   }
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final class WelcomePageHandlerMapping extends AbstractUrlHandlerMapping {
	WelcomePageHandlerMapping(TemplateAvailabilityProviders templateAvailabilityProviders,
			ApplicationContext applicationContext, Optional<Resource> welcomePage, String staticPathPattern) {
        //如果欢迎界面存在并且/**是staticPathPattern(默认是/**)则转发到欢迎界面，这里说明如果我们更改了默认的spring.mvc.static-path-pattern=/**则不会转发到欢迎界面
		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");
		}
	}
}