SpringBoot - 静态资源映射处理

上一篇博文说明了SpringBoot对WebJars的支持，那么项目中还有其他静态资源文件，如自定义CSS、JS、image等，SpringBoot同样提供了映射支持。

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【1】静态资源文件映射规则

同样查看WebMVCAutoConfiguration源码如下：

        @Override
        public void addResourceHandlers(ResourceHandlerRegistry registry) {
            if (!this.resourceProperties.isAddMappings()) {
                logger.debug("Default resource handling disabled");
                return;
            }
            Integer cachePeriod = this.resourceProperties.getCachePeriod();
            if (!registry.hasMappingForPattern("/webjars/**")) {
                customizeResourceHandlerRegistration(
                        registry.addResourceHandler("/webjars/**")
                                .addResourceLocations(
                                        "classpath:/META-INF/resources/webjars/")
                        .setCachePeriod(cachePeriod));
            }
            // 对静态资源文件映射支持
            String staticPathPattern = this.mvcProperties.getStaticPathPattern();
            if (!registry.hasMappingForPattern(staticPathPattern)) {
                customizeResourceHandlerRegistration(
                        registry.addResourceHandler(staticPathPattern)
                                .addResourceLocations(
                                        this.resourceProperties.getStaticLocations())
                        .setCachePeriod(cachePeriod));
            }
        }

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具体支持代码如下：

    String staticPathPattern = this.mvcProperties.getStaticPathPattern();
            if (!registry.hasMappingForPattern(staticPathPattern)) {
                customizeResourceHandlerRegistration(
                        registry.addResourceHandler(staticPathPattern)
                                .addResourceLocations(
                                        this.resourceProperties.getStaticLocations())
                        .setCachePeriod(cachePeriod));
            }

---

第一步拿到staticPathPattern；

    /**
     * Path pattern used for static resources.
     */
    private String staticPathPattern = "/**";

---

第二步如果资源请求没有对应映射，就添加资源处理器及资源找寻位置并设置缓存

if (!registry.hasMappingForPattern(staticPathPattern)) {
                customizeResourceHandlerRegistration(
                        registry.addResourceHandler(staticPathPattern)
                                .addResourceLocations(
                                        this.resourceProperties.getStaticLocations())
                        .setCachePeriod(cachePeriod));
            }

其中 staticLocations在ResourceProperties类中，源码如下：

/**
 * Properties used to configure resource handling.
 *
 * @author Phillip Webb
 * @author Brian Clozel
 * @author Dave Syer
 * @author Venil Noronha
 * @since 1.1.0
 */
@ConfigurationProperties(prefix = "spring.resources", ignoreUnknownFields = false)
public class ResourceProperties implements ResourceLoaderAware {

    private static final String[] SERVLET_RESOURCE_LOCATIONS = { "/" };

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

    private static final String[] RESOURCE_LOCATIONS;

    static {
        RESOURCE_LOCATIONS = new String[CLASSPATH_RESOURCE_LOCATIONS.length
                + SERVLET_RESOURCE_LOCATIONS.length];
        System.arraycopy(SERVLET_RESOURCE_LOCATIONS, 0, RESOURCE_LOCATIONS, 0,
                SERVLET_RESOURCE_LOCATIONS.length);
        System.arraycopy(CLASSPATH_RESOURCE_LOCATIONS, 0, RESOURCE_LOCATIONS,
                SERVLET_RESOURCE_LOCATIONS.length, CLASSPATH_RESOURCE_LOCATIONS.length);
    }

    /**
     * Locations of static resources. Defaults to classpath:[/META-INF/resources/,
     * /resources/, /static/, /public/] plus context:/ (the root of the servlet context).
     */
    private String[] staticLocations = RESOURCE_LOCATIONS;

---

即："/**"访问当前项目的任何资源，只要没有匹配的处理映射，则都去静态资源的文件夹找映射

"classpath:/META‐INF/resources/",
"classpath:/resources/",
"classpath:/static/",
"classpath:/public/"
"/"：当前项目的根路径

---

如下图，访问static/asserts/img/bootstrap-solid.svg：

URL ： http://localhost:8083/asserts/img/bootstrap-solid.svg；

这里注意URL上面不要添加静态资源文件夹(路径)的名字，如static、public等等。

---

【2】默认欢迎页的映射

代码如下：

        @Bean
        public WelcomePageHandlerMapping welcomePageHandlerMapping(
                ResourceProperties resourceProperties) {
            return new WelcomePageHandlerMapping(resourceProperties.getWelcomePage(),
                    this.mvcProperties.getStaticPathPattern());
        }

注册了WelcomePageHandlerMappingBean来处理项目的默认欢迎页面,构造器有两个参数，第一个是项目中存在的欢迎页资源，第二个是静态资源路径映射规则。

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① 获取欢迎页资源

其中跟踪resourceProperties.getWelcomePage()源码：

    public Resource getWelcomePage() {
        for (String location : getStaticWelcomePageLocations()) {
            Resource resource = this.resourceLoader.getResource(location);
            try {
                if (resource.exists()) {
                    resource.getURL();
                    return resource;
                }
            }
            catch (Exception ex) {
                // Ignore
            }
        }
        return null;
    }

即找到存在的欢迎页的资源，继续跟getStaticWelcomePageLocations()源码：

private String[] getStaticWelcomePageLocations() {
        String[] result = new String[this.staticLocations.length];
        for (int i = 0; i < result.length; i++) {
            String location = this.staticLocations[i];
            if (!location.endsWith("/")) {
                location = location + "/";
            }
            result[i] = location + "index.html";
        }
        return result;
    }

即 欢迎页的位置为第【1】部分中静态资源文件路径下的index.html。

如下所示：

"classpath:/META‐INF/resources/index.html",
"classpath:/resources/index.html",
"classpath:/static/index.html",
"classpath:/public/index.html"
"/"：/index.html

---

② 静态路径映射规则

    /**
     * Path pattern used for static resources.
     */
    private String staticPathPattern = "/**";

---

③ WelcomePageHandlerMapping类

static final class WelcomePageHandlerMapping extends AbstractUrlHandlerMapping {

        private static final Log logger = LogFactory
                .getLog(WelcomePageHandlerMapping.class);

        private WelcomePageHandlerMapping(Resource welcomePage,
                String staticPathPattern) {
            if (welcomePage != null && "/**".equals(staticPathPattern)) {
                logger.info("Adding welcome page: " + welcomePage);
                ParameterizableViewController controller = new ParameterizableViewController();
                controller.setViewName("forward:index.html");
                setRootHandler(controller);
                setOrder(0);
            }
        }

        @Override
        public Object getHandlerInternal(HttpServletRequest request) throws Exception {
            for (MediaType mediaType : getAcceptedMediaTypes(request)) {
                if (mediaType.includes(MediaType.TEXT_HTML)) {
                    return super.getHandlerInternal(request);
                }
            }
            return null;
        }

        private List<MediaType> getAcceptedMediaTypes(HttpServletRequest request) {
            String acceptHeader = request.getHeader(HttpHeaders.ACCEPT);
            return MediaType.parseMediaTypes(
                    StringUtils.hasText(acceptHeader) ? acceptHeader : "*/*");
        }

    }

总结：项目访问时，请求如http://localhost:8083/，则SpringBoot会从静态资源文件路径下找index.html，如果存在一个这样的资源，就转发请求到该页面。

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【3】项目浏览器图标的映射

SpringBoot同样对项目浏览器图标请求映射做了默认配置。浏览器图片即项目访问时，浏览器页面上呈现的图标，如CSDN图标如下

---

代码如下：

        @Configuration
        @ConditionalOnProperty(value = "spring.mvc.favicon.enabled", matchIfMissing = true)
        public static class FaviconConfiguration {

            private final ResourceProperties resourceProperties;

            public FaviconConfiguration(ResourceProperties resourceProperties) {
                this.resourceProperties = resourceProperties;
            }

            @Bean
            public SimpleUrlHandlerMapping faviconHandlerMapping() {
                SimpleUrlHandlerMapping mapping = new SimpleUrlHandlerMapping();
                mapping.setOrder(Ordered.HIGHEST_PRECEDENCE + 1);
                mapping.setUrlMap(Collections.singletonMap("**/favicon.ico",
                        faviconRequestHandler()));
                return mapping;
            }

            @Bean
            public ResourceHttpRequestHandler faviconRequestHandler() {
                ResourceHttpRequestHandler requestHandler = new ResourceHttpRequestHandler();
                requestHandler
                        .setLocations(this.resourceProperties.getFaviconLocations());
                return requestHandler;
            }

        }

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跟踪源码this.resourceProperties.getFaviconLocations()如下：

List<Resource> getFaviconLocations() {
        List<Resource> locations = new ArrayList<Resource>(
                this.staticLocations.length + 1);
        if (this.resourceLoader != null) {
            for (String location : this.staticLocations) {
                locations.add(this.resourceLoader.getResource(location));
            }
        }
        locations.add(new ClassPathResource("/"));
        return Collections.unmodifiableList(locations);
    }

即在静态资源文件下找所有的favicon.ico ！