For #180 - Performance: Replace collapse white-space regular expressi…

…ons with more performant loop for normal and no-wrap mode white-space settings.
danfickle · Apr 5, 2018 · 36c52aa · 36c52aa
1 parent 65b7faa
commit 36c52aa
Showing 1 changed file with 42 additions and 14 deletions.
diff --git a/openhtmltopdf-core/src/main/java/com/openhtmltopdf/layout/WhitespaceStripper.java b/openhtmltopdf-core/src/main/java/com/openhtmltopdf/layout/WhitespaceStripper.java
@@ -145,19 +145,55 @@ private static boolean stripWhitespace(InlineBox iB, boolean collapseLeading) {
         }
         return text.equals("") ? collapseLeading : collapseNext;
     }
+
+    /**
+     * Collapse whitespace for normal or no-wrap modes. Much faster (15x in simple testing)
+     * than using multiple regular expressions.
+     * 
+     * NOTE: Slightly different behavior to using regular expressions as definition of space characters
+     * differ, but I believe this is the correct definition according to CSS specifications.
+     * @param text
+     * @param collapseLeading
+     * @return
+     */
+    private static String collapseWhitespaceNormalOrNoWrap(String text, boolean collapseLeading) {
+		char[] chs = text.toCharArray();
+		StringBuilder builder = new StringBuilder(chs.length);
+		boolean spaceAdded = collapseLeading;
+
+		for (int i = 0; i < chs.length; i++) {
+			char ch = chs[i];
+
+			if (spaceAdded) {
+				if (ch != '\n' &&
+					ch != '\t' &&
+					ch != ' ') {
+					builder.append(ch);
+					spaceAdded = false;
+				}
+			} else {
+				if (ch == '\n' ||
+					ch == '\t' ||
+					ch == ' ') {
+					builder.append(' ');
+					spaceAdded = true;
+				} else {
+					builder.append(ch);
+				}
+			}
+		}
+
+		return builder.toString();
+	}
 
     private static String collapseWhitespace(InlineBox iB, IdentValue whitespace, String text, boolean collapseLeading) {
         if (whitespace == IdentValue.NORMAL || whitespace == IdentValue.NOWRAP) {
-            text = linefeed_space_collapse.matcher(text).replaceAll(EOL);
+            return collapseWhitespaceNormalOrNoWrap(text, collapseLeading);
         } else if (whitespace == IdentValue.PRE) {
             text = space_before_linefeed_collapse.matcher(text).replaceAll(EOL);
         }
 
-        if (whitespace == IdentValue.NORMAL || whitespace == IdentValue.NOWRAP) {
-            text = linefeed_to_space.matcher(text).replaceAll(SPACE);
-            text = tab_to_space.matcher(text).replaceAll(SPACE);
-            text = space_collapse.matcher(text).replaceAll(SPACE);
-        } else if (whitespace == IdentValue.PRE || whitespace == IdentValue.PRE_WRAP) {
+        if (whitespace == IdentValue.PRE || whitespace == IdentValue.PRE_WRAP) {
             int tabSize = (int) iB.getStyle().asFloat(CSSName.TAB_SIZE);
             char[] tabs = new char[tabSize];
             Arrays.fill(tabs, ' ');
@@ -167,14 +203,6 @@ private static String collapseWhitespace(InlineBox iB, IdentValue whitespace, St
             text = space_collapse.matcher(text).replaceAll(SPACE);
         }
 
-        if (whitespace == IdentValue.NORMAL || whitespace == IdentValue.NOWRAP) {
-            // collapse first space against prev inline
-            if (text.startsWith(SPACE) &&
-                    collapseLeading) {
-                text = text.substring(1, text.length());
-            }
-        }
-
         return text;
     }
 }