Shift_JISの全角文字のみにマッチする正規表現ジェネレータです。

ShiftJISRegexGenerator.java

import java.io.UnsupportedEncodingException;
import java.util.LinkedList;
import java.util.Objects;
import java.util.function.BiConsumer;
import java.util.stream.Collectors;
import java.util.stream.IntStream;
import java.util.stream.Stream;

public class ShiftJISRegexGenerator {
    public static void main(String[] args) {
        byte[] moji = new byte[2];
        Stream<Integer> upperByteStream = Stream.concat(IntStream.rangeClosed(0x81, 0x9f).boxed(), IntStream.rangeClosed(0xe0, 0xef).boxed());

        LinkedList<Integer> chars = upperByteStream.flatMap(upper ->
                IntStream.rangeClosed(0x40, 0xfc).boxed().map(lower -> {
                    moji[0] = upper.byteValue();
                    moji[1] = lower.byteValue();
                    try {
                        String s = new String(moji, 0, 2, "WINDOWS-31J");
                        int p = s.codePointAt(0);
                        return p == 0xfffd ? null : p;
                    } catch (UnsupportedEncodingException e) {
                        return null;
                    }
                }).filter(Objects::nonNull))
                .sorted(Integer::compareTo)
                .collect(Collectors.toCollection(LinkedList::new));

        int from = chars.pop();
        int to = chars.pop();
        BiConsumer<Integer, Integer> outputFunc = (f, t) -> {
            if (f.equals(t)) {
                System.out.printf("%c", t);
            } else if (t-f == 1) {
                System.out.printf("%c%c", f, t);
            } else {
                System.out.printf("%c-%c", f, t);
            }
        };
        System.out.print("/^[");
        for (int c : chars) {
            if (c - to > 1) {
                outputFunc.accept(from, to);
                from = to = c;
            } else {
                to = c;
            }
        }
        outputFunc.accept(from, to);
        System.out.println("]+$/");
    }
}