springboot静态资源配置原理

springboot对静态资源的配置可参考WebMvcAutoConfiguration这个类，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)：告诉容器这是一个配置类，且不代理bean方法，每次调用都会创建，这样容器启动时无需检查容器中是否已经存在

@ConditionalOnWebApplication(type = Type.SERVLET)：判断当前webAplication的类型是否为servlet，如果是则继续执行

@ConditionalOnClass({ Servlet.class, DispatcherServlet.class, WebMvcConfigurer.class })：判断必须存在指定的类才执行

@ConditionalOnMissingBean(WebMvcConfigurationSupport.class)：判断必须没有指定的类才执行

@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE + 10)：控制执行顺序
@AutoConfigureAfter({ DispatcherServletAutoConfiguration.class, TaskExecutionAutoConfiguration.class,
ValidationAutoConfiguration.class })：在加载配置的类之后再加载当前类

WebMvcAutoConfigurationAdapter

在WebMvcAutoConfiguration这个类中，存在一个WebMvcAutoConfigurationAdapter 静态内部类，用于配置静态资源规则的。

// 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 {
 
....

}

　这个静态内部类中有且只有一个带参构造方法：

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();
		}

　　只有一个带参构造方法时，入参会从容器中进行查找。其中的 resourceProperties和mvcProperties是通过注解@EnableConfigurationProperties导入的，其中的XXXProperties又是通过指定前缀和配置文件进行绑定的；

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

在这个WebMvcAutoConfigurationAdapter 静态内部类中存在一个addResourceHandlers方法，这个方法就是用于静态资源规则配置使用的；

@Override
public void addResourceHandlers(ResourceHandlerRegistry registry) {
        //检查是否开启默认资源处理，默认是true,可以通过配置文件改为false,关闭所有的静态资源配置映射
       if (!this.resourceProperties.isAddMappings()) {
          logger.debug("Default resource handling disabled");
          return;
       }
       //同时通过配置文件可以添加缓存时间，秒为单位
       Duration cachePeriod = this.resourceProperties.getCache().getPeriod();
       CacheControl cacheControl = this.resourceProperties.getCache().getCachecontrol().toHttpCacheControl();
       if (!registry.hasMappingForPattern("/webjars/**")) {
       
            //对于webjars的访问全部映射到类路径下的/META-INF/resources/webjars/
          customizeResourceHandlerRegistration(registry.addResourceHandler("/webjars/**")
                .addResourceLocations("classpath:/META-INF/resources/webjars/")
                .setCachePeriod(getSeconds(cachePeriod)).setCacheControl(cacheControl));
       }
       
       //获取静态资源的路径，默认是/**
       String staticPathPattern = this.mvcProperties.getStaticPathPattern();
       if (!registry.hasMappingForPattern(staticPathPattern)) {
       
        //对于配置的静态资源路径都会去this.resourceProperties.getStaticLocations()进行查找
          customizeResourceHandlerRegistration(registry.addResourceHandler(staticPathPattern)
                .addResourceLocations(getResourceLocations(this.resourceProperties.getStaticLocations()))
                .setCachePeriod(getSeconds(cachePeriod)).setCacheControl(cacheControl));
       }
}

　　this.resourceProperties.getStaticLocations()：这个就对应到ResourceProperties类中的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   禁用所有静态资源规则

　　

欢迎页的处理

欢迎页使用的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：处理器映射。保存了每一个Handler能处理哪些请求。

对于这个有参构造方法：

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");
		}
	}

　　可以看出判断条件，如果开启了欢迎页且静态路径必须匹配/**则会去index.html，要么是跳转到index的请求。

      至此可以看出springboot对静态资源的所有默认规则。