从SpringBoot源码看资源映射原理

<mvc:resources mapping="/js/**" location="/js/" />
<mvc:resources mapping="/css/**" location="/css/" />
<mvc:resources mapping="/img/**" location="/img/" />

<mvc:resources mapping="/**" location="/" />

    /**
     * Override this method to add resource handlers for serving static resources.
     * @see ResourceHandlerRegistry
     */
    protected void addResourceHandlers(ResourceHandlerRegistry registry) {
    }

 /* <p>To create a resource handler, use {@link #addResourceHandler(String...)} providing the URL path patterns
 / * for which the handler should be invoked to serve static resources (e.g. {@code "/resources/**"}).

    /**
     * Add a resource handler for serving static resources based on the specified URL path patterns.
     * The handler will be invoked for every incoming request that matches to one of the specified
     * path patterns.
     * <p>Patterns like {@code "/static/**"} or {@code "/css/{filename:\\w+\\.css}"} are allowed.
     * See {@link org.springframework.util.AntPathMatcher} for more details on the syntax.
     * @return a {@link ResourceHandlerRegistration} to use to further configure the
     * registered resource handler
     */
    public ResourceHandlerRegistration addResourceHandler(String... pathPatterns) {
        ResourceHandlerRegistration registration = new ResourceHandlerRegistration(pathPatterns);
        this.registrations.add(registration);
        return registration;
    }

    /**
     * Add one or more resource locations from which to serve static content.
     * Each location must point to a valid directory. Multiple locations may
     * be specified as a comma-separated list, and the locations will be checked
     * for a given resource in the order specified.
     * <p>For example, {{@code "/"}, {@code "classpath:/META-INF/public-web-resources/"}}
     * allows resources to be served both from the web application root and
     * from any JAR on the classpath that contains a
     * {@code /META-INF/public-web-resources/} directory, with resources in the
     * web application root taking precedence.
     * <p>For {@link org.springframework.core.io.UrlResource URL-based resources}
     * (e.g. files, HTTP URLs, etc) this method supports a special prefix to
     * indicate the charset associated with the URL so that relative paths
     * appended to it can be encoded correctly, e.g.
     * {@code [charset=Windows-31J]https://example.org/path}.
     * @return the same {@link ResourceHandlerRegistration} instance, for
     * chained method invocation
     */
    public ResourceHandlerRegistration addResourceLocations(String... resourceLocations) {
        this.locationValues.addAll(Arrays.asList(resourceLocations));
        return this;
    }

import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.ResourceHandlerRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurationSupport;
/**
 * @author liumeng
 * @Date: 2020/9/25 09:20
 * @Description:
 */
@Configuration
public class SpringMvcConfig extends WebMvcConfigurationSupport {
    @Override
    protected void addResourceHandlers(ResourceHandlerRegistry registry) {        registry.addResourceHandler("/**").addResourceLocations("/");
    }
}

　　　　@Override
        public void addResourceHandlers(ResourceHandlerRegistry registry) {
            if (!this.resourceProperties.isAddMappings()) {
                logger.debug("Default resource handling disabled");
                return;
            }            Duration cachePeriod = this.resourceProperties.getCache().getPeriod();
            CacheControl cacheControl = this.resourceProperties.getCache().getCachecontrol().toHttpCacheControl();
            if (!registry.hasMappingForPattern("/webjars/**")) {
                customizeResourceHandlerRegistration(registry.addResourceHandler("/webjars/**")
                        .addResourceLocations("classpath:/META-INF/resources/webjars/")
                        .setCachePeriod(getSeconds(cachePeriod)).setCacheControl(cacheControl));            }            String staticPathPattern = this.mvcProperties.getStaticPathPattern();
            if (!registry.hasMappingForPattern(staticPathPattern)) {
                customizeResourceHandlerRegistration(registry.addResourceHandler(staticPathPattern)                        .addResourceLocations(getResourceLocations(this.resourceProperties.getStaticLocations()))
                        .setCachePeriod(getSeconds(cachePeriod)).setCacheControl(cacheControl));            }        }

　　　　　　　String staticPathPattern = this.mvcProperties.getStaticPathPattern();
            if (!registry.hasMappingForPattern(staticPathPattern)) {
                customizeResourceHandlerRegistration(registry.addResourceHandler(staticPathPattern)                        .addResourceLocations(getResourceLocations(this.resourceProperties.getStaticLocations()))
                        .setCachePeriod(getSeconds(cachePeriod)).setCacheControl(cacheControl));            }
我们看一下getStaticPathPattern()方法的实现，发现获得的就是

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

    private String[] staticLocations = CLASSPATH_RESOURCE_LOCATIONS;

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

    static String[] getResourceLocations(String[] staticLocations) {
        String[] locations = new String[staticLocations.length + SERVLET_LOCATIONS.length];
        System.arraycopy(staticLocations, 0, locations, 0, staticLocations.length);
        System.arraycopy(SERVLET_LOCATIONS, 0, locations, staticLocations.length, SERVLET_LOCATIONS.length);
        return locations;
    }

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

"classpath:/META-INF/resources/" , "classpath:/resources/", "classpath:/static/", "classpath:/public/"，“/”

spring.resources.static-locations=classpath:/
spring.mvc.static-path-pattern=/**

@ConfigurationProperties(prefix = "spring.mvc")

@ConfigurationProperties(prefix = "spring.resources", ignoreUnknownFields = false)

import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.ResourceHandlerRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;
@Configuration
public class ResourcesConfig implements WebMvcConfigurer
{    @Override
    public void addResourceHandlers(ResourceHandlerRegistry registry)    {        registry.addResourceHandler( "/**").addResourceLocations("classpath:/aaa");
    }
}