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

namespace 計算文件的MD5值
{
  class MD5_Helper
  {
    /// <summary>
    /// 文件MD5校驗
    /// </summary>
    /// <param name="pathName">文件絕對路徑</param>
    /// <returns>MD5校驗碼</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);//計算指定Stream 對象的哈希值
        oFileStream.Close();
        //由以連字符分隔的十六進制對構成的String，其中每一對表示value 中對應的元素；例如“F-2C-4A”
        strHashData = BitConverter.ToString(arrbytHashValue);
        //替換-
        strHashData = strHashData.Replace("-", "");
        strResult = strHashData;
      }
      catch (System.Exception ex)
      {

      }
      return strResult;

    }

    /// <summary>
    /// 字節(jié)數組校驗
    /// </summary>
    /// <param name="buffer">待字節(jié)數組</param>
    /// <returns>MD5校驗碼</returns>
    public string getMD5Hash(byte[] buffer)
    {
      string strResult = "";
      string strHashData = "";
      byte[] arrbytHashValue;
      MD5CryptoServiceProvider oMD5Hasher =
            new MD5CryptoServiceProvider();
      try
      {
        arrbytHashValue = oMD5Hasher.ComputeHash(buffer);//計算指定Stream 對象的哈希值
        //由以連字符分隔的十六進制對構成的String，其中每一對表示value 中對應的元素；例如“F-2C-4A”
        strHashData = BitConverter.ToString(arrbytHashValue);
        //替換-
        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 {
	/**
	 * 默認的密碼字符串組合，用來將字節(jié)轉換成 16 進制表示的字符,apache校驗下載的文件的正確性用的就是默認的這個組合
	 */
	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();//字節(jié)數組校驗
		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];// 取字節(jié)中高 4 位的數字轉換
		// 為邏輯右移，將符號位一起右移,此處未發(fā)現兩種符號有何不同
		char c1 = hexDigits[bt & 0xf];// 取字節(jié)中低 4 位的數字轉換
		stringbuffer.append(c0);
		stringbuffer.append(c1);
	}
}