Slackdown-Java: Slack flavoured Markdown to HTML in Java using flexmark-java

MarkdownUtils.java

import com.vladsch.flexmark.html.HtmlRenderer;
import com.vladsch.flexmark.parser.Parser;
import com.vladsch.flexmark.util.ast.Node;
import com.vladsch.flexmark.util.options.MutableDataSet;

import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * @author Manish Singh
 */
public class MarkdownUtils {

    private static final Pattern SLACKDOWN_LINK_PATTERN = Pattern.compile("(<[^>]+>)");
    private static final Pattern SLACKDOWN_BOLD_PATTERN = Pattern.compile("(\\*[^\\*]+\\*)");

    public static String markdownToHtml(String markdown) {
        MutableDataSet options = new MutableDataSet();
        options.set(HtmlRenderer.SOFT_BREAK, "<br />\n");
        Parser parser = Parser.builder(options).build();
        HtmlRenderer renderer = HtmlRenderer.builder(options).build();
        // You can re-use parser and renderer instances
        Node document = parser.parse(markdown);
        return renderer.render(document);
    }

    public static String slackdownToHtml(String slackdown) {
        return markdownToHtml(slackdownToMarkdown(slackdown));
    }

    public static String slackdownToMarkdown(String slackdown) {
        return handleSlackdownBold(handleSlackdownLinks(slackdown));
    }

    private static String handleSlackdownLinks(String slackdown) {
        StringBuffer sb = new StringBuffer();
        Matcher m = SLACKDOWN_LINK_PATTERN.matcher(slackdown);
        while (m.find())
        {
            String match = m.group(1);
            String replacement;
            int pipeIndex = match.indexOf("|");
            if (pipeIndex != -1) {
                String link = match.substring(1, pipeIndex);
                String text = match.substring(pipeIndex + 1, match.length() - 1);
                replacement = String.format("[%s](%s)", text, link);
            } else {
                String link = match.substring(1, match.length() - 1);
                replacement = String.format("(%s)", link);
            }
            if (replacement != null)
                m.appendReplacement(sb, replacement);
        }
        m.appendTail(sb);
        return sb.toString();
    }

    private static String handleSlackdownBold(String slackdown) {
        StringBuffer sb = new StringBuffer();
        Matcher m = SLACKDOWN_BOLD_PATTERN.matcher(slackdown);
        while (m.find())
        {
            String match = m.group(1);
            String replacement = String.format("*%s*", match);
            m.appendReplacement(sb, replacement);
        }
        m.appendTail(sb);
        return sb.toString();
    }


}