java判断输出字符串个数，并将截取字符以"..."代替

public class teast {
    private String str;
    private int counterOfDoubleByte;
    private byte b[];

    /**
     * 设置需要被限制长度的字符串
     * @param str 需要被限制长度的字符串
     */
    public teast(String str) {
        this.str = str;
    }
    public static void main(String[] args) throws Exception {
        String name="java_mature";
        teast str = new teast(name);
        String afterStr = str.getLimitLengthString(8,"...");
        System.err.println(afterStr);
    }

    /**
     * @param len 需要显示的长度(注意：长度是以byte为单位的，一个汉字是2个byte)
     * @param symbol 用于表示省略的信息的字符，如“...”,“>>>”等。
     * @return 返回处理后的字符串
     */
    public String getLimitLengthString(int len, String symbol) throws Exception{
        counterOfDoubleByte = 0;
        b = str.getBytes("GBK");
        if (b.length <= len)
            return str;
        for (int i = 0; i < len; i++) {
            if (b[i] < 0)
                counterOfDoubleByte++;
        }

        if (counterOfDoubleByte % 2 == 0)
            return new String(b, 0, len, "GBK") + symbol;
        else
            return new String(b, 0, len - 1, "GBK") + symbol;
    }
}