Performance issue with regex in HtmlConverterCoreNodeRenderer

[praveen-diffbot]

HtmlConverterCoreNodeRenderer.handleTableCell has a call to String.replaceAll("\\s*\n\\s*", " ") which can be quite slow. The regex is quite simple and can be sped up by removing the regex.

To Reproduce

See attached file test.html.txt

public class LoadingTest {
  public static void main(final String[] args) throws Exception {
    final String STR = java.nio.file.Files.readString(java.nio.file.Path.of("test.html.txt"));
    final long tic = System.currentTimeMillis();
    com.diffbot.websearch.html.MarkdownNormalizer.markdown(STR);
    System.out.println("took: " + (System.currentTimeMillis() - tic));
  }
}

Expected behavior
The code takes >4000 ms to run on my laptop.

took: 4024

It should take much lesser time.

[praveen-diffbot]

I replaced the regex call with an approximation which is probably ok for html

 private String replaceMultipleBlankSpace(String cellText) {
     StringBuilder result = new StringBuilder();
     boolean wasSpace = false;

     for (char c : cellText.toCharArray()) {
         if (Character.isWhitespace(c)) {
             if (!wasSpace) {
                 result.append(' ');
                 wasSpace = true;
             }
         } else {
             result.append(c);
             wasSpace = false;
         }
     }

     return result.toString();
}

String cellText = replaceMultipleBlankSpace(context.processTextNodes(element).trim());

The same file takes about 150ms to process