Spring Boot對靜態資源的映射規則

在實際項目開發中，除了程序代碼外，還需要一些靜態資源，比如公司logo，背景圖，css樣式文件，js文件等等，這里介紹一下單體應用中Spring Boot對靜態資源的一些映射規則。(此處的單體應用指非前后端分離、非微服務、非SOA架構的簡易版項目，具體區別看下圖所示)

Spring Boot對靜態資源的映射規則

在Spring Boot中，SpringMVC的相關配置都默認在WebMvcAutoConfiguration類中，具體源碼請在IDE中自行搜索查看。

1、 所有/webjars/**（/**表示訪問此路徑下的任何資源，都會去classpath:/META-INF/resources/webjars/下尋找資源(webjars就是以jar包方式引入資源到項目中)， 相關源碼如下：

// WebMvcAutoConfiguration.java
@Override
public void addResourceHandlers(ResourceHandlerRegistry registry) {
   if (!this.resourceProperties.isAddMappings()) {
      logger.debug("Default resource handling disabled");
      return;
   }
   addResourceHandler(registry, "/webjars/**", "classpath:/META-INF/resources/webjars/");
   addResourceHandler(registry, this.mvcProperties.getStaticPathPattern(), (registration) - > {
      registration.addResourceLocations(this.resourceProperties.getStaticLocations());
      if (this.servletContext != null) {
         ServletContextResource resource = new ServletContextResource(this.servletContext, SERVLET_LOCATION);
         registration.addResourceLocations(resource);
      }
   });
}
private void addResourceHandler(ResourceHandlerRegistry registry, String pattern, String... locations) {
   addResourceHandler(registry, pattern, (registration) - > registration.addResourceLocations(locations));
}
private void addResourceHandler(ResourceHandlerRegistry registry, String pattern,
      Consumer< ResourceHandlerRegistration > customizer) {
   if (registry.hasMappingForPattern(pattern)) {
      return;
   }
   ResourceHandlerRegistration registration = registry.addResourceHandler(pattern);
   customizer.accept(registration);
   registration.setCachePeriod(getSeconds(this.resourceProperties.getCache().getPeriod()));
   registration.setCacheControl(this.resourceProperties.getCache().getCachecontrol().toHttpCacheControl());
   registration.setUseLastModified(this.resourceProperties.getCache().isUseLastModified());
   customizeResourceHandlerRegistration(registration);
}

結構如圖所示(以jquery為例)：

jquery的maven依賴如下：

< dependency >
    < groupId >org.webjars.npm< /groupId >
    < artifactId >jquery< /artifactId >
    < version >3.6.0< /version >
< /dependency >

訪問示例地址如下：

localhost:8080/webjars/jquery/3.6.0/dist/jquery.js

訪問結果如下圖所示：

2、 /**，訪問當前項目下的任何靜態資源，相關源碼如下：

// WebMvcAutoConfiguration.java
addResourceHandler(registry, this.mvcProperties.getStaticPathPattern(), (registration) - > {
   registration.addResourceLocations(this.resourceProperties.getStaticLocations());
   if (this.servletContext != null) {
      ServletContextResource resource = new ServletContextResource(this.servletContext, SERVLET_LOCATION);
      registration.addResourceLocations(resource);
   }
});


// WebMvcProperties.java
public String getStaticPathPattern() {
   return this.staticPathPattern;
}
private String staticPathPattern = "/**";


// WebProperties.java
public String[] getStaticLocations() {
   return this.staticLocations;
}
private static final String[] CLASSPATH_RESOURCE_LOCATIONS = { "classpath:/META-INF/resources/",
      "classpath:/resources/", "classpath:/static/", "classpath:/public/" };
/**
 * Locations of static resources. Defaults to classpath:[/META-INF/resources/,
 * /resources/, /static/, /public/].
 */
private String[] staticLocations = CLASSPATH_RESOURCE_LOCATIONS;

由源碼可知，靜態資源的訪問路徑有如下幾個：

1、classpath:/META-INF/resources/ ；

2、classpath:/resources/；

3、classpath:/static/；

4、classpath:/public/；

5、/ (當前項目的根路徑)。

如下圖所示：

**3、 **歡迎頁： 靜態資源文件夾下的index.html頁面，相關源碼如下：

// WebMvcAutoConfiguration.java
@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;
}


private Resource getWelcomePage() {
   for (String location : this.resourceProperties.getStaticLocations()) {
      Resource indexHtml = getIndexHtml(location);
      if (indexHtml != null) {
         return indexHtml;
      }
   }
   ServletContext servletContext = getServletContext();
   if (servletContext != null) {
      return getIndexHtml(new ServletContextResource(servletContext, SERVLET_LOCATION));
   }
   return null;
}
private Resource getIndexHtml(String location) {
   return getIndexHtml(this.resourceLoader.getResource(location));
}
private Resource getIndexHtml(Resource location) {
   try {
      Resource resource = location.createRelative("index.html");
      if (resource.exists() && (resource.getURL() != null)) {
         return resource;
      }
   }
   catch (Exception ex) {
   }
   return null;
}


// WebMvcProperties.java
public String getStaticPathPattern() {
   return this.staticPathPattern;
}
private String staticPathPattern = "/**";

根據源碼可知，歡迎頁是被/**映射，也解釋了首頁名稱為index.html的原因。

4、 自定義靜態資源文件夾，在配置文件application.properties中添加如下配置，就會覆蓋掉項目的默認配置，示例代碼如下：

spring.web.resources.static-locations=classpath:/brevity/,classpath:/github/

以上就是Spring Boot單體應用中關于靜態資源映射的說明。