java计算文件32位md5值

 protected static String getFileMD5(String fileName)
     {
         File file = new File(fileName);
         if(!file.exists() || !file.isFile()){
             return "";
         }

         byte[] buffer = new byte[2048];
         try {
             MessageDigest digest = MessageDigest.getInstance("MD5");
             FileInputStream in = new FileInputStream(file);
             while(true){
                 int len = in.read(buffer,0,2048);
                 if(len != -1){
                     digest.update(buffer, 0, len);
                 }else{
                     break;
                 }
             }
             in.close();

             byte[] md5Bytes  = digest.digest();
             StringBuffer hexValue = new StringBuffer();
             for (int i = 0; i < md5Bytes.length; i++) {
                 int val = ((int) md5Bytes[i]) & 0xff;
                 if (val < 16) {
                     hexValue.append("0");
                 }
                 hexValue.append(Integer.toHexString(val));
             }
             return hexValue.toString();

             //String hash = new BigInteger(1,digest.digest()).toString(16);
             //return hash;

         } catch (NoSuchAlgorithmException e) {
             // TODO Auto-generated catch block
             e.printStackTrace();
             return "";
         } catch (FileNotFoundException e) {
             // TODO Auto-generated catch block
             e.printStackTrace();
             return "";
         } catch (IOException e) {
             // TODO Auto-generated catch block
             e.printStackTrace();
             return "";
         }
     }

how to use:

 String file = "d://one.zip";
 String md5 = getFileMD5(file);