java md5不一致怎么办

public static String EncoderByMd5(String str) {  
    String result = "";  
    MessageDigest md5 = null;  
    try {  
        md5 = MessageDigest.getInstance("MD5");  
        // 这句是关键  
        md5.update(str.getBytes("UTF-8"));  
    } catch (NoSuchAlgorithmException e) {  
        // TODO Auto-generated catch block  
        e.printStackTrace();  
    } catch (UnsupportedEncodingException e) {  
        // TODO Auto-generated catch block  
        e.printStackTrace();  
    }  
    byte b[] = md5.digest();  
    int i;  
    StringBuffer buf = new StringBuffer("");  
    for (int offset = 0; offset < b.length; offset++) {  
        i = b[offset];  
        if (i < 0)  
            i += 256;  
        if (i < 16)  
            buf.append("0");  
        buf.append(Integer.toHexString(i));  
    }  
    result = buf.toString();  
  
    return result;  
}