using System;
using System.IO;
using System.Security.Cryptography;

namespace 计算文件的MD5值
{
  class MD5_Helper
  {
    /// <summary>
    /// 文件MD5校验
    /// </summary>
    /// <param name="pathName">文件绝对路径</param>
    /// <returns>MD5校验码</returns>
    public string getMD5Hash(string pathName)
    {
      string strResult = "";
      string strHashData = "";
      byte[] arrbytHashValue;
      FileStream oFileStream = null;
      MD5CryptoServiceProvider oMD5Hasher =
            new MD5CryptoServiceProvider();
      try
      {
        oFileStream = new FileStream(pathName, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
        arrbytHashValue = oMD5Hasher.ComputeHash(oFileStream);//计算指定Stream 对象的哈希值
        oFileStream.Close();
        //由以连字符分隔的十六进制对构成的String，其中每一对表示value 中对应的元素；例如“F-2C-4A”
        strHashData = BitConverter.ToString(arrbytHashValue);
        //替换-
        strHashData = strHashData.Replace("-", "");
        strResult = strHashData;
      }
      catch (System.Exception ex)
      {

      }
      return strResult;

    }

    /// <summary>
    /// 字节数组校验
    /// </summary>
    /// <param name="buffer">待字节数组</param>
    /// <returns>MD5校验码</returns>
    public string getMD5Hash(byte[] buffer)
    {
      string strResult = "";
      string strHashData = "";
      byte[] arrbytHashValue;
      MD5CryptoServiceProvider oMD5Hasher =
            new MD5CryptoServiceProvider();
      try
      {
        arrbytHashValue = oMD5Hasher.ComputeHash(buffer);//计算指定Stream 对象的哈希值
        //由以连字符分隔的十六进制对构成的String，其中每一对表示value 中对应的元素；例如“F-2C-4A”
        strHashData = BitConverter.ToString(arrbytHashValue);
        //替换-
        strHashData = strHashData.Replace("-", "");
        strResult = strHashData;
      }
      catch(System.Exception ex)
      {

      }
      return strResult;

    }
  }
}

package com;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class MD5Util {
 /**
  * 默认的密码字符串组合，用来将字节转换成 16 进制表示的字符,apache校验下载的文件的正确性用的就是默认的这个组合
  */
 protected static char hexDigits[] = { '0', '1', '2', '3', '4', '5', '6','7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F' };
 protected static MessageDigest messagedigest = null;
 static {
  try {
   messagedigest = MessageDigest.getInstance("MD5");
  } catch (NoSuchAlgorithmException e) {
   e.printStackTrace();
  }
 }

 public static void main(String[] args) throws IOException {

  byte[] buffer= "HelloWorld".getBytes();//字节数组校验
  String md55 = getFileMD5String(buffer);
  System.out.println("md55:" + md55);
 }
 

 public static String getFileMD5String(File file) throws IOException {
  InputStream fis;
  fis = new FileInputStream(file);
  byte[] buffer = new byte[1024];
  int numRead = 0;
  while ((numRead = fis.read(buffer)) > 0) {
   messagedigest.update(buffer, 0, numRead);
  }
  fis.close();
  return bufferToHex(messagedigest.digest());
 }
 
 public static String getFileMD5String(byte[] buffer) throws IOException {
   messagedigest.update(buffer, 0, buffer.length);
  return bufferToHex(messagedigest.digest());
 }

 private static String bufferToHex(byte bytes[]) {
  return bufferToHex(bytes, 0, bytes.length);
 }

 private static String bufferToHex(byte bytes[], int m, int n) {
  StringBuffer stringbuffer = new StringBuffer(2 * n);
  int k = m + n;
  for (int l = m; l < k; l++) {
   appendHexPair(bytes[l], stringbuffer);
  }
  return stringbuffer.toString();
 }

 private static void appendHexPair(byte bt, StringBuffer stringbuffer) {
  char c0 = hexDigits[(bt & 0xf0) >> 4];// 取字节中高 4 位的数字转换
  // 为逻辑右移，将符号位一起右移,此处未发现两种符号有何不同
  char c1 = hexDigits[bt & 0xf];// 取字节中低 4 位的数字转换
  stringbuffer.append(c0);
  stringbuffer.append(c1);
 }
}