Polish "Cache MimeTypes to improve performance"

Closes gh-16507

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/embedded/netty/CompressionCustomizer.java

 /*
- * Copyright 2012-2018 the original author or authors.
+ * Copyright 2012-2019 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -65,14 +65,12 @@ final class CompressionCustomizer implements NettyServerCustomizer {
 		return server;
 	}
 
-	private CompressionPredicate getMimeTypesPredicate(String[] mimeTypes) {
-		if (ObjectUtils.isEmpty(mimeTypes)) {
+	private CompressionPredicate getMimeTypesPredicate(String[] mimeTypeIds) {
+		if (ObjectUtils.isEmpty(mimeTypeIds)) {
 			return ALWAYS_COMPRESS;
 		}
-
-		List<MimeType> mimeTypeList = Arrays.stream(mimeTypes)
+		List<MimeType> mimeTypes = Arrays.stream(mimeTypeIds)
 				.map(MimeTypeUtils::parseMimeType).collect(Collectors.toList());
-
 		return (request, response) -> {
 			String contentType = response.responseHeaders()
 					.get(HttpHeaderNames.CONTENT_TYPE);
@@ -80,7 +78,7 @@ final class CompressionCustomizer implements NettyServerCustomizer {
 				return false;
 			}
 			MimeType contentMimeType = MimeTypeUtils.parseMimeType(contentType);
-			return mimeTypeList.stream()
+			return mimeTypes.stream()
 					.anyMatch((candidate) -> candidate.isCompatibleWith(contentMimeType));
 		};
 	}