java中英文字符长度截取有关问题

/**
     * 字符串按字节截取
     * @param str 原字符
     * @param len 截取长度
     * @return String
     * @author ivan
     * @since 2010.07.05
     */
     public static String splitString(String str, int len) {
            return splitString(str, len, "...");
     }

     /**
      * 字符串按字节截取
      * @param str 原字符
      * @param len 截取长度
      * @param elide 省略符
      * @return String
      * @author ivan
      * @since 2010.07.05
      */
      public static String splitString(String str,int len,String elide) {
             if (str == null) {
                    return "";
             }
             byte[] strByte = str.getBytes();
             int strLen = strByte.length;
             //int elideLen = (elide.trim().length() == 0) ? 0 : elide.getBytes().length;
             int elideLen = 0;
             if (len >= strLen || len < 1) {
                    return str;
             }
             if (len - elideLen > 0) {
                    len = len - elideLen;
             }
             int count = 0;
             for (int i = 0; i < len; i++) {
                    int value = (int) strByte[i];
                    if (value < 0) {
                           count++;
                    }
             }
             if (count % 2 != 0) {
                    len = (len == 1) ? len + 1 : len - 1;
             }
             return new String(strByte, 0, len) + elide.trim();
      }

public static String subStr(String str, int num) {
		int max = num;
		try {
			max = trimGBK(str.getBytes("GBK"),num);
		} catch (UnsupportedEncodingException e) {
			e.printStackTrace();
		}  
		int sum = 0;
		if (str != null && str.length() > max) {
			StringBuilder sb = new StringBuilder(max);
			for (int i = 0; i < str.length(); i++) {
				int c = str.charAt(i);
//				if ((c & 0xff00) != 0)
//					sum += 2;
//				else
					sum += 1;
				if (sum <= max)
					sb.append((char) c);
				else
					break;
			}
			return sb.append("...").toString();
		} else
			return str != null ? str : "";
	}
	
	public static int  trimGBK(byte[] buf,int n){  
        int num = 0;  
        boolean bChineseFirstHalf = false;
        if(buf.length < n )return buf.length;
    	for(int i=0;i<n;i++)  
        {  
            if(buf[i]<0 && !bChineseFirstHalf){  
                bChineseFirstHalf = true;  
            }else{  
                num++;  
                bChineseFirstHalf = false;                
            }  
        }  
        
        return num;  
    }