OldJapaneseDate.java

import net.time4j.PlainDate;
import net.time4j.calendar.*;
import net.time4j.format.expert.*;
import java.util.Locale;
import java.text.ParseException;

public class OldJapaneseDate {
  public static void main(String... args) throws ParseException {
    ChronoFormatter<JapaneseCalendar> jf =
      ChronoFormatter.ofPattern("Gy年M月d日", PatternType.CLDR, Locale.JAPANESE,	JapaneseCalendar.axis());
	  String oldJapaneseDate = "慶応4年5月30日";
	  JapaneseCalendar jcal = jf.parse(oldJapaneseDate);
    System.out.println(jcal); // Keiō-4(1868)-5-30 (the parsed old japanese date)
    System.out.println(jcal.transform(PlainDate.axis())); // 1868-07-19 (gregorian western date)   
  }
}