截取字符串 中文按两个字符长度处理情况

public class SubStringTest {
/**
 * 
 * @param src 源字符串
 * @param subLength   需要截取的长度
 * @return
 */
	public static String subString(String src, int subLength) {
		if(src == null){
			return null;
		}
		if(subLength == 0){
			return "";
		}
		StringBuffer sb = new StringBuffer();
		char[] chars = src.toCharArray();
		for (char a : chars) {
			if (isContinueAppend(sb, a, subLength)) {
				sb.append(a);
			}
			else{
				break;
			}
		}
		return sb.toString();
	}
/**
 * 
 * @param sb 已截到的字符串
 * @param a  当前要被装进sb的字符
 * @param subLength  需要截取的长度
 * @return
 */
	public static boolean isContinueAppend(StringBuffer sb, char a,
			int subLength) {
		int currentLength = 0;
		for (char temp : sb.toString().toCharArray()) {
			currentLength += (temp >> 8 == 0) ? 1 : 2;
		}
		return (currentLength + (a >> 8 == 0 ? 1 : 2)) <= subLength;
	}

	public static void main(String[] args) {
		System.out.println(subString("我是一a个中国人",7));
	}
}