Fix PrefixResourceResolver implementation

The configured prefix should not begin with a "/", since
PublicResourceUrlProvider is already taking path mapping into account
when resolving resources and URLs.

spring-webmvc/src/main/java/org/springframework/web/servlet/resource/PrefixResourceResolver.java

@@ -50,7 +50,7 @@ public class PrefixResourceResolver extends AbstractResourceResolver {
 
 	public PrefixResourceResolver(String prefix) {
 		Assert.hasText(prefix, "prefix must not be null or empty");
-		this.prefix = prefix.startsWith("/") ? prefix : "/" + prefix;
+		this.prefix = prefix.startsWith("/") ? prefix.substring(1) : prefix;
 	}
 
 	@Override

spring-webmvc/src/test/java/org/springframework/web/servlet/resource/PrefixResourceResolverTests.java

@@ -54,14 +54,14 @@ public class PrefixResourceResolverTests {
 	public void resolveResource() {
 		String resourceId = "foo.css";
 		Resource expected = new ClassPathResource("test/foo.css", getClass());
-		Resource actual = this.chain.resolveResource(null, "/" + this.shaPrefix + "/" + resourceId, this.locations);
+		Resource actual = this.chain.resolveResource(null, this.shaPrefix + "/" + resourceId, this.locations);
 		assertEquals(expected, actual);
 	}
 
 	@Test
 	public void resolvePublicUrlPath() {
 		String resourceId = "/foo.css";
-		String url = "/" + this.shaPrefix + resourceId;
+		String url = this.shaPrefix + resourceId;
 		assertEquals(url, chain.resolvePublicUrlPath(resourceId, locations));
 	}