Android获取文件的MD5值

public class DemoActivity 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));
 }

/**
 * 获取单个文件的MD5值
 * @param file 文件
 * @param radix  位 16 32 64
 *
 * @return
 */

public static String getFileMD5s(File file,int radix) {
    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(radix);
}

 /**
  * 获取文件夹中文件的MD5值
  * 
  * @param file
  * @param listChild
  *            ;true递归子目录中的文件
  * @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;
}
}

最后不要忘了在manifest中添加权限

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