package my.bag;

import Java.io.File;
import java.io.FileInputStream;
import java.math.BigInteger;
import java.security.MessageDigest;
import java.util.HashMap;
import java.util.Map;

import Android.app.Activity;
import android.os.Bundle;
import android.util.Log;

public class FileDigest extends Activity {

 @Override
 protected void onCreate(Bundle savedInstanceState) {
  // TODO Auto-generated method stub
  super.onCreate(savedInstanceState);
  File file = new File("/mnt/sdcard/123.txt");
  Log.e("MD5", getFileMD5(file));
 }

 /**
  * 獲取單個檔案的MD5值！

  * @param file
  * @return
  */

 public static String getFileMD5(File file) {
  if (!file.isFile()) {
   return null;
  }
  MessageDigest digest = null;
  FileInputStream in = null;
  byte buffer[] = new byte[1024];
  int len;
  try {
   digest = MessageDigest.getInstance("MD5");
   in = new FileInputStream(file);
   while ((len = in.read(buffer, 0, 1024)) != -1) {
    digest.update(buffer, 0, len);
   }
   in.close();
  } catch (Exception e) {
   e.printStackTrace();
   return null;
  }
  BigInteger bigInt = new BigInteger(1, digest.digest());
  return bigInt.toString(16);
 }

 /**
  * 獲取資料夾中檔案的MD5值
  *
  * @param file
  * @param listChild
  *            ;true遞迴子目錄中的檔案
  * @return
  */
 public static Map<String, String> getDirMD5(File file, boolean listChild) {
  if (!file.isDirectory()) {
   return null;
  }
  Map<String, String> map = new HashMap<String, String>();
  String md5;
  File files[] = file.listFiles();
  for (int i = 0; i < files.length; i++) {
   File f = files[i];
   if (f.isDirectory() && listChild) {
    map.putAll(getDirMD5(f, listChild));
   } else {
    md5 = getFileMD5(f);
    if (md5 != null) {
     map.put(f.getPath(), md5);
    }
   }
  }
  return map;
 }

}

最後不要忘了在manifest中新增許可權

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>