http://koteitan.seesaa.net/article/47717182.html
http://icu-project.org/download/
http://www7a.biglobe.ne.jp/~java-master/samples/string/index.html
!ICU4J
Java で全角半角変換やひらがなカタカナ変換を行うライブラリ

使い方（　注意：リンク先丸パクリです）
 import com.ibm.icu.text.*;
 import com.ibm.icu.util.*;
 import java.util.*;
 
 public class Main {
   
   public static void main(String args[])
   {
     String data = "AaＡアいろはｱｲｳｴイウエ";
     
     Transliterator tr1 = Transliterator.getInstance("Fullwidth-Halfwidth");
     Transliterator tr2 = Transliterator.getInstance("Katakana-Hiragana");
     Transliterator tr3 = Transliterator.getInstance("Hiragana-Latin");
     
     System.out.println(tr1.transliterate(data));
     System.out.println(tr2.transliterate(data));
     System.out.println(tr3.transliterate(data));
     
     
     DateFormat df = new SimpleDateFormat("Gy年M月d日", new DateFormatSymbols(new JapaneseCalendar(), Locale.JAPANESE));
     df.setCalendar(new JapaneseCalendar());
     
     System.out.println(df.format(new Date()));
   }
 }

日本語で使いそうなＩＤ
* Fullwidth-Halfwidth
* Halfwidth-Fullwidth
* Hiragana-Katakana
* Hiragana-Latin
* Katakana-Hiragana
* Katakana-Latin
* Latin-Hiragana
* Latin-Katakana
* Any-Hiragana
* Any-Katakana

!マッピングテーブルを作る方法
リンク先丸パクリ

 package samples.string.japanese;
 
 public class ZenkakuKatakanaToHankakuKatakana {
   private static final char[] ZENKAKU_KATAKANA = { 'ァ', 'ア', 'ィ', 'イ', 'ゥ',
       'ウ', 'ェ', 'エ', 'ォ', 'オ', 'カ', 'ガ', 'キ', 'ギ', 'ク', 'グ', 'ケ', 'ゲ',
       'コ', 'ゴ', 'サ', 'ザ', 'シ', 'ジ', 'ス', 'ズ', 'セ', 'ゼ', 'ソ', 'ゾ', 'タ',
       'ダ', 'チ', 'ヂ', 'ッ', 'ツ', 'ヅ', 'テ', 'デ', 'ト', 'ド', 'ナ', 'ニ', 'ヌ',
       'ネ', 'ノ', 'ハ', 'バ', 'パ', 'ヒ', 'ビ', 'ピ', 'フ', 'ブ', 'プ', 'ヘ', 'ベ',
       'ペ', 'ホ', 'ボ', 'ポ', 'マ', 'ミ', 'ム', 'メ', 'モ', 'ャ', 'ヤ', 'ュ', 'ユ',
       'ョ', 'ヨ', 'ラ', 'リ', 'ル', 'レ', 'ロ', 'ヮ', 'ワ', 'ヰ', 'ヱ', 'ヲ', 'ン',
       'ヴ', 'ヵ', 'ヶ' };
 
   private static final String[] HANKAKU_KATAKANA = { "ｧ", "ｱ", "ｨ", "ｲ", "ｩ",
       "ｳ", "ｪ", "ｴ", "ｫ", "ｵ", "ｶ", "ｶﾞ", "ｷ", "ｷﾞ", "ｸ", "ｸﾞ", "ｹ",
       "ｹﾞ", "ｺ", "ｺﾞ", "ｻ", "ｻﾞ", "ｼ", "ｼﾞ", "ｽ", "ｽﾞ", "ｾ", "ｾﾞ", "ｿ",
       "ｿﾞ", "ﾀ", "ﾀﾞ", "ﾁ", "ﾁﾞ", "ｯ", "ﾂ", "ﾂﾞ", "ﾃ", "ﾃﾞ", "ﾄ", "ﾄﾞ",
       "ﾅ", "ﾆ", "ﾇ", "ﾈ", "ﾉ", "ﾊ", "ﾊﾞ", "ﾊﾟ", "ﾋ", "ﾋﾞ", "ﾋﾟ", "ﾌ",
       "ﾌﾞ", "ﾌﾟ", "ﾍ", "ﾍﾞ", "ﾍﾟ", "ﾎ", "ﾎﾞ", "ﾎﾟ", "ﾏ", "ﾐ", "ﾑ", "ﾒ",
       "ﾓ", "ｬ", "ﾔ", "ｭ", "ﾕ", "ｮ", "ﾖ", "ﾗ", "ﾘ", "ﾙ", "ﾚ", "ﾛ", "ﾜ",
       "ﾜ", "ｲ", "ｴ", "ｦ", "ﾝ", "ｳﾞ", "ｶ", "ｹ" };
 
   private static final char ZENKAKU_KATAKANA_FIRST_CHAR = ZENKAKU_KATAKANA[0];
 
   private static final char ZENKAKU_KATAKANA_LAST_CHAR = ZENKAKU_KATAKANA[ZENKAKU_KATAKANA.length - 1];
   
   public static String zenkakuKatakanaToHankakuKatakana(char c) {
     if (c >= ZENKAKU_KATAKANA_FIRST_CHAR && c <= ZENKAKU_KATAKANA_LAST_CHAR) {
       return HANKAKU_KATAKANA[c - ZENKAKU_KATAKANA_FIRST_CHAR];
     } else {
       return String.valueOf(c);
     }
   }
 
   public static String zenkakuKatakanaToHankakuKatakana(String s) {
     StringBuffer sb = new StringBuffer();
     for (int i = 0; i < s.length(); i++) {
       char originalChar = s.charAt(i);
       String convertedChar = zenkakuKatakanaToHankakuKatakana(originalChar);
       sb.append(convertedChar);
     }
     return sb.toString();
 
   }
   public static void main(String[] args) {
     System.out.println(zenkakuKatakanaToHankakuKatakana("ジャヴァプログラミング"));
   }
 }

ハッシュテーブルだと、「ー」とかも対象とするときとかに応用が利くので
マッピングテーブルはハッシュテーブルにしても良いかもしれない。

{{category2 プログラミング言語,Java}}