import java.io.File;  import java.io.FileInputStream;  import java.io.IOException;  import java.nio.MappedByteBuffer;  import java.nio.channels.FileChannel;  import java.security.MessageDigest;  public final class Md5Util {      private static final char hexDigits[] = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c',     'd', 'e', 'f'};      public static String encode(File file) {    FileInputStream in = null;    MessageDigest md5 = null;    try {     in = new FileInputStream(file);     FileChannel ch = in.getChannel();     MappedByteBuffer byteBuffer = ch.map(FileChannel.MapMode.READ_ONLY, 0, file.length());     md5 = MessageDigest.getInstance("MD5");     md5.update(byteBuffer);    } catch (Exception e) {     e.printStackTrace();    } finally {     try {      in.close();     } catch (IOException e) {      e.printStackTrace();     }    }    return toHex(md5.digest());   }   public static String encode(String arg) {    if (arg == null) {     arg = "";    }    MessageDigest md5 = null;    try {     md5 = MessageDigest.getInstance("MD5");     md5.update(arg.getBytes("UTF-8"));    } catch (Exception e) {     e.printStackTrace();    }    return toHex(md5.digest());   }   private static String toHex(byte[] bytes) {    StringBuffer str = new StringBuffer(32);    for (byte b : bytes) {     str.append(hexDigits[(b & 0xf0) >> 4]);     str.append(hexDigits[(b & 0x0f)]);    }    return str.toString();   }  }

来自： http://blog.csdn.net//u011067360/article/details/24417387