直接貼程式碼吧！

public class CnNumberUtils {
    private final static Logger logger = LoggerFactory.getLogger(CnNumberUtils.class);
    //阿拉伯數字對應大寫中文數字
    private final static String[] CN_NUMERALS = {"零", "壹", "貳", "叄", "肆", "伍", "陸", "柒", "捌", "玖"};
    //低單位
    private final static String[] CN_NUM_UNIT = {""
 
, "拾", "佰", "仟"};
    //萬元以上高單位
    private final static String[] CN_NUM_HIGHT_UNIT = {"", "萬", "億", "萬億"};
    //小數位單位
    private final static String[] CN_NUM_DECIMAL_UNIT = {"", "角", "分"};


    /**
     * 轉換成中文大寫金額（最高支援萬億和兩位小數）
     * @param num
     * @return
     */
    public static String toUppercase
 
(Double num){
        return toUppercase(String.valueOf(num));
    }

    /**
     * 轉換成中文大寫金額（最高支援萬億和兩位小數）
     * @param num
     * @return
     */
    public static String toUppercase(String num){
        String[] strNumArray = num.split("\\.");
        int strNumArrayLength = strNumArray.length;
        if
 
(strNumArrayLength > 2 || (strNumArrayLength == 2 && strNumArray[1].length() > 2)){
            logger.error("金額格式異常，不能有多個小數點，小數位最多隻能兩位！");
        }
        BigDecimal bigDecimal = new BigDecimal(strNumArray[0]);
        BigInteger bigInteger = bigDecimal.toBigInteger();

        char[] chars = bigInteger.toString().toCharArray();
        int intLength = chars.length;

        StringBuilder strBuilder = new StringBuilder();
        for(int i=0; i<intLength; i++){
            String curCnNum = CN_NUMERALS[charNumToInt(chars[i])];
            int ui = ((intLength-1)-i)%4;
            int hui = ((intLength-1)-i)/4;
            strBuilder.append(curCnNum);
            if(!isZero(curCnNum)){
                strBuilder.append(CN_NUM_UNIT[ui]);
                String heightUnit = CN_NUM_HIGHT_UNIT[hui];
                //如果剩餘沒有低金額單位或者後續都為零則加上高單位
                if(ui == 0 || isZeroInResidue(chars, i, ui)){
                    strBuilder.append(heightUnit);
                    //萬單位以後的千單位如果不能為零則跳過零
                    if(heightUnit.equals(CN_NUM_HIGHT_UNIT[1]) && !isZeroOfIndex(chars, (ui+1)+i)){
                        i = i+skipZero(chars, i);
                    }
                }
            }
        }
        clearZero(0, strBuilder);
        //小數位轉換
        strBuilder.append("圓");
        if(strNumArrayLength == 1 || strNumArray[1].matches("^[0]*$")){
            strBuilder.append("整");
            return strBuilder.toString();
        }
        char[] decimalChars = strNumArray[1].toCharArray();
        int decimalCharLength = decimalChars.length;
        for(int i=1; i<=decimalCharLength; i++){
            String cnNum = CN_NUMERALS[charNumToInt(decimalChars[i-1])];
            if(!isZero(cnNum)){
                strBuilder.append(cnNum).append(CN_NUM_DECIMAL_UNIT[i]);
            }else if(i == decimalCharLength){
                return strBuilder.toString();
            }else{
                strBuilder.append(cnNum);
            }
        }
        return strBuilder.toString();
    }

    /**
     * 遞迴清除多餘的零
     * @param startIndex
     * @param strBuilder
     */
    private static void clearZero(int startIndex, StringBuilder strBuilder){
        int strLength = strBuilder.length();
        int zeroIndex = strBuilder.indexOf(CN_NUMERALS[0], startIndex);
        if(zeroIndex <= -1){
            return;
        }
        if(strLength <= zeroIndex+1){
            strBuilder.deleteCharAt(zeroIndex);
            return;
        }
        if(zeroIndex > -1 && isZero(strBuilder.charAt(zeroIndex+1))){
            strBuilder.deleteCharAt(zeroIndex);
            clearZero(startIndex, strBuilder);
            return;
        }
        if(strLength > zeroIndex+1){
            clearZero(zeroIndex+1, strBuilder);
            return;
        }
    }

    private static boolean isZero(String cnNum){
        return cnNum.equals(CN_NUMERALS[0]);
    }

    private static boolean isZero(char cnNum){
        return isZero(String.valueOf(cnNum));
    }

    /**
     * 跳過為零的下標
     * @param chars
     * @param beginIndex
     * @return
     */
    private static int skipZero(char[] chars, int beginIndex){
        int newIndex = 0;
        int charLength = chars.length;
        for(int i=beginIndex+1; i<charLength; i++){
            if(isZero(CN_NUMERALS[charNumToInt(chars[i])])){
                newIndex++;
            }else{
                break;
            }
        }
        return newIndex;
    }

    /**
     * 指定下標值是否是為零
     * @param chars
     * @param index
     * @return boolean
     */
    private static boolean isZeroOfIndex(char[] chars, int index){
        int numInex = Integer.parseInt(String.valueOf(chars[index]), 10);
        String cnNum = CN_NUMERALS[numInex];
        return isZero(cnNum);
    }

    /**
     * 從begin開始至end結束是否都是零
     * @param chars
     * @param begin
     * @param end
     * @return
     */
    private static boolean isZeroInResidue(char[] chars, int begin, int end){
        for(int i=1; i<=end; i++){
            boolean r = isZeroOfIndex(chars, begin+i);
            if(!r){
                return false;
            }
        }
        return true;
    }

    /**
     * char型別數值轉換為int
     * @param charNum
     * @return
     */
    private static int charNumToInt(char charNum){
        String ns = String.valueOf(charNum);
        return Integer.parseInt(ns, 10);
    }
}

技術要點：
金額字元長度-1-i（迴圈的當前索引）%4結果得出當前金額的小單位（十百千）。
金額字元長度-1-i（迴圈的當前索引）/4結果得出當前位金額大單位（萬以上）。

例如：
10000元
長度5，-1-i（0）/4=1=單位萬。