Polish CssLinkResourceTransformer

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

@@ -22,9 +22,10 @@ import java.nio.charset.Charset;
 import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
 import java.util.Collections;
-import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
+import java.util.SortedSet;
+import java.util.TreeSet;
 import javax.servlet.http.HttpServletRequest;
 
 import org.apache.commons.logging.Log;
@@ -82,25 +83,23 @@ public class CssLinkResourceTransformer extends ResourceTransformerSupport {
 		byte[] bytes = FileCopyUtils.copyToByteArray(resource.getInputStream());
 		String content = new String(bytes, DEFAULT_CHARSET);
 
-		List<Segment> linkSegments = new ArrayList<>(8);
+		SortedSet<ContentChunkInfo> links = new TreeSet<>();
 		for (LinkParser parser : this.linkParsers) {
-			linkSegments.addAll(parser.parseLink(content));
+			parser.parse(content, links);
 		}
 
-		if (linkSegments.isEmpty()) {
+		if (links.isEmpty()) {
 			if (logger.isTraceEnabled()) {
 				logger.trace("No links found.");
 			}
 			return resource;
 		}
 
-		Collections.sort(linkSegments);
-
 		int index = 0;
 		StringWriter writer = new StringWriter();
-		for (Segment linkSegment : linkSegments) {
-			writer.write(content.substring(index, linkSegment.getStart()));
-			String link = content.substring(linkSegment.getStart(), linkSegment.getEnd());
+		for (ContentChunkInfo linkContentChunkInfo : links) {
+			writer.write(content.substring(index, linkContentChunkInfo.getStart()));
+			String link = content.substring(linkContentChunkInfo.getStart(), linkContentChunkInfo.getEnd());
 			String newLink = null;
 			if (!hasScheme(link)) {
 				String absolutePath = toAbsolutePath(link, request);
@@ -115,7 +114,7 @@ public class CssLinkResourceTransformer extends ResourceTransformerSupport {
 				}
 			}
 			writer.write(newLink != null ? newLink : link);
-			index = linkSegment.getEnd();
+			index = linkContentChunkInfo.getEnd();
 		}
 		writer.write(content.substring(index));
 
@@ -128,60 +127,51 @@ public class CssLinkResourceTransformer extends ResourceTransformerSupport {
 	}
 
 
+	/**
+	 * Extract content chunks that represent links.
+	 */
 	@FunctionalInterface
 	protected interface LinkParser {
 
-		Set<Segment> parseLink(String content);
+		void parse(String content, SortedSet<ContentChunkInfo> result);
 
 	}
 
 
 	protected static abstract class AbstractLinkParser implements LinkParser {
 
-		/**
-		 * Return the keyword to use to search for links.
-		 */
+		/** Return the keyword to use to search for links, e.g. "@import", "url(" */
 		protected abstract String getKeyword();
 
 		@Override
-		public Set<Segment> parseLink(String content) {
-			Set<Segment> linksToAdd = new HashSet<>(8);
-			int index = 0;
-			do {
-				index = content.indexOf(getKeyword(), index);
-				if (index == -1) {
-					break;
+		public void parse(String content, SortedSet<ContentChunkInfo> result) {
+			int position = 0;
+			while (true) {
+				position = content.indexOf(getKeyword(), position);
+				if (position == -1) {
+					return;
 				}
-				index = skipWhitespace(content, index + getKeyword().length());
-				if (content.charAt(index) == '\'') {
-					index = addLink(index, "'", content, linksToAdd);
+				position += getKeyword().length();
+				while (Character.isWhitespace(content.charAt(position))) {
+					position++;
 				}
-				else if (content.charAt(index) == '"') {
-					index = addLink(index, "\"", content, linksToAdd);
+				if (content.charAt(position) == '\'') {
+					position = extractLink(position, "'", content, result);
 				}
-				else {
-					index = extractLink(index, content, linksToAdd);
-
+				else if (content.charAt(position) == '"') {
+					position = extractLink(position, "\"", content, result);
 				}
-			}
-			while (true);
-			return linksToAdd;
-		}
+				else {
+					position = extractLink(position, content, result);
 
-		private int skipWhitespace(String content, int index) {
-			while (true) {
-				if (Character.isWhitespace(content.charAt(index))) {
-					index++;
-					continue;
 				}
-				return index;
 			}
 		}
 
-		protected int addLink(int index, String endKey, String content, Set<Segment> linksToAdd) {
+		protected int extractLink(int index, String endKey, String content, SortedSet<ContentChunkInfo> linksToAdd) {
 			int start = index + 1;
 			int end = content.indexOf(endKey, start);
-			linksToAdd.add(new Segment(start, end));
+			linksToAdd.add(new ContentChunkInfo(start, end));
 			return end + endKey.length();
 		}
 
@@ -189,7 +179,8 @@ public class CssLinkResourceTransformer extends ResourceTransformerSupport {
 		 * Invoked after a keyword match, after whitespaces removed, and when
 		 * the next char is neither a single nor double quote.
 		 */
-		protected abstract int extractLink(int index, String content, Set<Segment> linksToAdd);
+		protected abstract int extractLink(int index, String content,
+				SortedSet<ContentChunkInfo> linksToAdd);
 
 	}
 
@@ -202,7 +193,7 @@ public class CssLinkResourceTransformer extends ResourceTransformerSupport {
 		}
 
 		@Override
-		protected int extractLink(int index, String content, Set<Segment> linksToAdd) {
+		protected int extractLink(int index, String content, SortedSet<ContentChunkInfo> linksToAdd) {
 			if (content.substring(index, index + 4).equals("url(")) {
 				// Ignore, UrlLinkParser will take care
 			}
@@ -222,20 +213,20 @@ public class CssLinkResourceTransformer extends ResourceTransformerSupport {
 		}
 
 		@Override
-		protected int extractLink(int index, String content, Set<Segment> linksToAdd) {
+		protected int extractLink(int index, String content, SortedSet<ContentChunkInfo> linksToAdd) {
 			// A url() function without unquoted
-			return addLink(index - 1, ")", content, linksToAdd);
+			return extractLink(index - 1, ")", content, linksToAdd);
 		}
 	}
 
 
-	private static class Segment implements Comparable<Segment> {
+	private static class ContentChunkInfo implements Comparable<ContentChunkInfo> {
 
 		private final int start;
 
 		private final int end;
 
-		public Segment(int start, int end) {
+		ContentChunkInfo(int start, int end) {
 			this.start = start;
 			this.end = end;
 		}
@@ -249,7 +240,7 @@ public class CssLinkResourceTransformer extends ResourceTransformerSupport {
 		}
 
 		@Override
-		public int compareTo(Segment other) {
+		public int compareTo(ContentChunkInfo other) {
 			return (this.start < other.start ? -1 : (this.start == other.start ? 0 : 1));
 		}
 
@@ -258,8 +249,8 @@ public class CssLinkResourceTransformer extends ResourceTransformerSupport {
 			if (this == obj) {
 				return true;
 			}
-			if (obj instanceof Segment) {
-				Segment other = (Segment) obj;
+			if (obj instanceof ContentChunkInfo) {
+				ContentChunkInfo other = (ContentChunkInfo) obj;
 				return (this.start == other.start && this.end == other.end);
 			}
 			return false;