Java按自然语言字符截取字符串

由于unicode字符在java中可能超过2个char，String类自带的substring不能很好的满足要求，可能产生? ，所以按照commons的StringUtils开发了这个方法

　　/**
     * 仿照{@link StringUtils#substring(String, int, int)}开发的自然语言截取方法，考虑到了多语言字符截取问题，
     * 配合nvarchar类型字段的截取函数使用
     * @param str 要截取的字符串
     * @param start 字符开始位置，包含
     * @param end 字符结束位置，不包含
     * @return
     */
    public static String naturalSubstring(String str, int start, int end) {
        if (str == null) {
            return null;
        }

        // handle negatives
        int naturalLength = str.codePointCount(0, str.length());
        if (end < 0) {
            end = naturalLength + end; // remember end is negative
        }
        if (start < 0) {
            start = naturalLength + start; // remember start is negative
        }

        // check length next
        if (end > naturalLength) {
            end = naturalLength;
        }

        // if start is greater than end, return ""
        if (start > end) {
            return "";
        }

        if (start < 0) {
            start = 0;
        }
        if (end < 0) {
            end = 0;
        }

        StringBuilder result = new StringBuilder();
        int codePointCounter = 0;
        int charIndex = 0;
        if (start > 0 ) {
            // 过滤起始
            for (; charIndex < str.length() && codePointCounter < start; charIndex++,codePointCounter++) {
                if (Character.isHighSurrogate(str.charAt(charIndex))) {
                    charIndex++;
                }
            }
        }
        if (end < naturalLength) {
            for (; charIndex < str.length() && codePointCounter < end; charIndex++, codePointCounter++) {
                result.append(str.charAt(charIndex));
                if (Character.isHighSurrogate(str.charAt(charIndex))) {
                    result.append(str.charAt(++charIndex));
                }
            }
        } else {
            return str.substring(charIndex, str.length());
        }
        return result.toString();
    }

测试

        // "\uD83D\uDF01" == 🜁
        // "\uD801\uDC00" == 𐐀
        String test = "🜁𐐀🜁𐐀𐐀🜁🜁𐐀𐐀𐐀";
        System.out.println(StringUtil.naturalSubstring(test, 0 ,1));
        System.out.println(StringUtil.naturalSubstring(test, 0 ,3));
        System.out.println(StringUtil.naturalSubstring(test, 1 ,3));
        System.out.println(StringUtil.naturalSubstring(test, 4 ,8));
        System.out.println(StringUtil.naturalSubstring(test, 4 ,100));
        System.out.println(test.substring(1,3)); 

显示结果

 

 符合预期