/**
   * 返回指定字节长度的字符串
   * 
   * @param str String 字符串
   * @param length int 指定长度
   * @return String 返回的字符串
   */
  public static String toLength(String str, int length) {
    if (str == null) {
      return null;
    }
    if (length <= 0) {
      return "";
    }
    try {
      if (str.getBytes("GBK").length <= length) {
        return str;
      }
    } catch (Exception ex) {
    }
    StringBuffer buff = new StringBuffer();

    int index = 0;
    char c;
    length -= 3;
    while (length > 0) {
      c = str.charAt(index);
      if (c < 128) {
        length--;
      } else {
        length--;
        length--;
      }
      buff.append(c);
      index++;
    }
    buff.append("...");
    return buff.toString();
  }

------解决方案--------------------
你们说的长度是指 字节长度吧

但我不明白1楼的程序为什么要 length -= 3;  然后又 buff.append("...");




------解决方案--------------------
可以用正则表达式来判断输入字符是否是双字节字符，如果是双字节字符就+2，否则就+1

正则表达式是：

提取信息中的双字节字符串 (汉字)：
[^\x00-\xff]*

------解决方案--------------------
Java code
public class Test {

    public static void main(String[] args) {
        String str2 = "abcdefghijklmnopq";
        String str1 = "abcdefghijklmnop";        
        String str3 = "abcdefghijklmno";
        String str4 = "一二三四五六七八九十一二三四五六";
        String str5 = "一二三四五六七八";
        String str6 = "一二三四五六七";
        String str7 = "一二三a四五六七八九十一二三四五六";
        String append = " ...";
        System.out.println(trancate(str1, 16, append));        
        System.out.println(trancate(str2, 16, append));
        System.out.println(trancate(str3, 16, append));
        System.out.println(trancate(str4, 16, append));
        System.out.println(trancate(str5, 16, append));
        System.out.println(trancate(str6, 16, append));
        System.out.println(trancate(str7, 16, append));
    }

    private static String trancate(String src, int length) {
        return trancate(src, length, "");
    }
    
    private static String trancate(String src, int length, String append) {
        int len = 0;
        char[] chars = src.toCharArray();
        StringBuffer sb = new StringBuffer();
        int i = 0;
        while(len < length) {
            if(i >= chars.length) {
                return sb.toString();
            }
            sb.append(chars[i]);
            if(chars[i++] > 0xff) {
                len += 2;                
            }else{
                len++;
            }
        }        
        if(sb.toString().equals(src)) {
            return sb.toString();
        }else{
            sb.append(append);
            return sb.toString();
        }        
    }
}

------解决方案--------------------