A Java snippet which detects if input parameters have any emoji

EmojiDetector.java

/*
 * The MIT License (MIT)
 *
 * Copyright (c) 2020 Chun-Kwong Wong
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to
 * deal in the Software without restriction, including without limitation the
 * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
 * sell copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 *
 * Detects, and prints out in groups, if inputs have any emoji.
 *
 * How to use:
 *
 * $ javac ./EmojiDetector.java
 * $ java [-Xss<SIZE>] \
 *     [ -Dmaxlen=<MAX GROUP SIZE> ] \
 *     [ -Dfilemode=<true/false> ] \
 *     EmojiDetector INPUT [ INPUT [ INPUT ... ] ] ]
 *
 * NOTE:
 *
 * - use "-Dfilemode" option to treat INPUT as filepaths and read contents
 *   from them.
 *
 * - adjust option "-Xss" and "-Dmaxlen" to avoid the infamous
 *   StackOverflowError RegExp bug.  More details here:
 *   https://bugs.java.com/bugdatabase/view_bug.do?bug_id=6882582
 */
import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.util.stream.Collectors;

public class EmojiDetector
{
	final private static String HELPMSG
		= "usage: java [ OPTIONS ] EmojiDetector "
		+ "INPUT [ INPUT [ INPUT ... ] ] ]\n\n"
		+ "OPTIONS:\n"
		+ " -Dmaxlen=<SIZE>    where SIZE is the maximum number of characters of each\n"
		+ "                    group of capture. (default: 1)\n"
		+ " -Dfilemode=<BOOL>  where BOOL can be true/false to indicate whether INPUTs\n"
		+ "                    are filepaths to read contents from. (default: false)\n"
		+ " -Xss<MEMSIZE>      where MEMSIZE is the Java thread stack size.\n";

	final private static String RE_Digit = "\\u0023\\u002A\\u0030-\\u0039";

	final private static String RE_RI = "\\uD83C\\uDDE6-\\uD83C\\uDDFF";

	final private static String RE_2Byte = "\\u00A9\\u00AE\\u203C\\u2049\\u2122\\u2139\\u2194-\\u2199\\u21A9-\\u21AA\\u231A-\\u231B\\u2328\\u23CF\\u23E9-\\u23EF\\u23F0-\\u23F3\\u23F8-\\u23FA\\u24C2\\u25AA\\u25AB\\u25B6\\u25C0\\u25FB-\\u25FE\\u2600-\\u2604\\u260E\\u2611\\u2614-\\u2615\\u2618\\u261D\\u2620\\u2622-\\u2623\\u2626\\u262A\\u262E\\u262F\\u2638\\u2639\\u263A\\u2640\\u2642\\u2648-\\u2653\\u265F\\u2660\\u2663\\u2665-\\u2666\\u2668\\u267B\\u267E\\u267F\\u2692-\\u2697\\u2699\\u269B-\\u269C\\u26A0-\\u26A1\\u26A7\\u26AA-\\u26AB\\u26B0-\\u26B1\\u26BD-\\u26BE\\u26C4-\\u26C5\\u26C8\\u26CE\\u26CF\\u26D1\\u26D3\\u26D4\\u26E9\\u26EA\\u26F0-\\u26F5\\u26F7-\\u26F9\\u26FA\\u26FD\\u2702\\u2705\\u2708-\\u270C\\u270D\\u270F\\u2712\\u2714\\u2716\\u271D\\u2721\\u2728\\u2733-\\u2734\\u2744\\u2747\\u274C\\u274E\\u2753-\\u2755\\u2757\\u2763\\u2764\\u2795-\\u2797\\u27A1\\u27B0\\u27BF\\u2934-\\u2935\\u2B05-\\u2B07\\u2B1B-\\u2B1C\\u2B50\\u2B55\\u3030\\u303D\\u3297\\u3299";

	final private static String RE_3Byte = "\\uD83C\\uDC04\\uD83C\\uDCCF\\uD83C\\uDD70-\\uD83C\\uDD71\\uD83C\\uDD7E-\\uD83C\\uDD7F\\uD83C\\uDD8E\\uD83C\\uDD91-\\uD83C\\uDD9A\\uD83C\\uDDE6-\\uD83C\\uDDFF\\uD83C\\uDE01-\\uD83C\\uDE02\\uD83C\\uDE1A\\uD83C\\uDE2F\\uD83C\\uDE32-\\uD83C\\uDE3A\\uD83C\\uDE50-\\uD83C\\uDE51\\uD83C\\uDF00-\\uD83C\\uDF21\\uD83C\\uDF24-\\uD83C\\uDF2C\\uD83C\\uDF2D-\\uD83C\\uDF2F\\uD83C\\uDF30-\\uD83C\\uDF93\\uD83C\\uDF96-\\uD83C\\uDF97\\uD83C\\uDF99-\\uD83C\\uDF9B\\uD83C\\uDF9E-\\uD83C\\uDF9F\\uD83C\\uDFA0-\\uD83C\\uDFF0\\uD83C\\uDFF3-\\uD83C\\uDFF5\\uD83C\\uDFF7\\uD83C\\uDFF8-\\uD83D\\uDC29\\uD83D\\uDC2A-\\uD83D\\uDCFD\\uD83D\\uDCFF-\\uD83D\\uDD3D\\uD83D\\uDD49-\\uD83D\\uDD4E\\uD83D\\uDD50-\\uD83D\\uDD67\\uD83D\\uDD6F-\\uD83D\\uDD70\\uD83D\\uDD73-\\uD83D\\uDD7A\\uD83D\\uDD87\\uD83D\\uDD8A-\\uD83D\\uDD8D\\uD83D\\uDD90\\uD83D\\uDD95-\\uD83D\\uDD96\\uD83D\\uDDA4\\uD83D\\uDDA5\\uD83D\\uDDA8\\uD83D\\uDDB1-\\uD83D\\uDDB2\\uD83D\\uDDBC\\uD83D\\uDDC2-\\uD83D\\uDDC4\\uD83D\\uDDD1-\\uD83D\\uDDD3\\uD83D\\uDDDC-\\uD83D\\uDDDE\\uD83D\\uDDE1\\uD83D\\uDDE3\\uD83D\\uDDE8\\uD83D\\uDDEF\\uD83D\\uDDF3\\uD83D\\uDDFA-\\uD83D\\uDE4F\\uD83D\\uDE80-\\uD83D\\uDEC5\\uD83D\\uDECB-\\uD83D\\uDED2\\uD83D\\uDED5-\\uD83D\\uDED7\\uD83D\\uDEE0-\\uD83D\\uDEE5\\uD83D\\uDEE9\\uD83D\\uDEEB-\\uD83D\\uDEEC\\uD83D\\uDEF0\\uD83D\\uDEF3\\uD83D\\uDEF4-\\uD83D\\uDEFC\\uD83D\\uDFE0-\\uD83D\\uDFEB\\uD83E\\uDD0C-\\uD83E\\uDD3A\\uD83E\\uDD3C-\\uD83E\\uDD45\\uD83E\\uDD47-\\uD83E\\uDD78\\uD83E\\uDD7A-\\uD83E\\uDDCB\\uD83E\\uDDCD-\\uD83E\\uDDFF\\uD83E\\uDE70-\\uD83E\\uDE74\\uD83E\\uDE78-\\uD83E\\uDE86\\uD83E\\uDE90-\\uD83E\\uDEA8\\uD83E\\uDEB0-\\uD83E\\uDEB6\\uD83E\\uDEC0-\\uD83E\\uDEC2\\uD83E\\uDED0-\\uD83E\\uDED6";

	final private static String RE_EMod = "\\uD83C\\uDFFB-\\uD83C\\uDFFF";

	final private static String RE_Emoji = RE_2Byte + RE_3Byte;

	final private static String RE_TagMod = "[\\uDB40\\uDC20-\\uDB40\\uDC7E]+\\uDB40\\uDC7F";

	final private static String RE =
		"[" + RE_RI + "]{2}"
		+ "|[" + RE_Digit + "]\\uFE0F?\\u20E3"
		+ "|[" + RE_Emoji  + "]"
			+ "(?:[" + RE_EMod + "]"
			+ "|\\uFE0F\\u20E3?"
			+ "|" + RE_TagMod + ")?"
			+ "(?:\\u200D[" + RE_Emoji + "]"
				+ "(?:[" + RE_EMod + "]"
				+ "|\\uFE0F\\u20E3?"
				+ "|" + RE_TagMod + ")?"
			+ ")*"
		;

	final private Pattern re;

	final private boolean filemode;

	public EmojiDetector(int maxlen, boolean filemode)
	{
		if (1 == maxlen)
			this.re = Pattern.compile(RE);
		else if (0 > maxlen)
			this.re = Pattern.compile("(?:" + RE + ")+");
		else
			this.re = Pattern.compile("(?:" + RE + "){1," + maxlen + "}");

		this.filemode = filemode;
	}

	public List<String> processInput(String s)
	{
		if (this.filemode)
			return this.processFile(s);
		else
			return this.processString(s);
	}

	private List<String> processString(String s)
	{
		List<String> out = new ArrayList<>();
		Matcher m = this.re.matcher(s);
		while(m.find()) out.add(m.group());
		return out;
	}

	private List<String> processFile(String fpath)
	{
		try
		{
			BufferedReader br = new BufferedReader(new FileReader(fpath));
			return br.lines().map(l -> this.processString(l))
				.flatMap(l -> l.stream()).collect(Collectors.toList());
		}
		catch(FileNotFoundException fnfe)
		{
			System.err.println("Could not open file \"" + fpath + "\".");
		}
		return Collections.emptyList();
	}

	public static void main(String[] args)
	{
		if (0 == args.length)
		{
			System.out.println(HELPMSG);
			return;
		}

		EmojiDetector detector = new EmojiDetector
		(
			Integer.parseInt(System.getProperty("maxlen", "1"))
			, Boolean.parseBoolean(System.getProperty("filemode", "false"))
		);

		for(String arg: args)
			for(String emoji: detector.processInput(arg))
				System.out.println(emoji);
	}
}