Java计算文件MD5值代码

原文：http://www.open-open.com/code/view/1424930488031

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;
import java.security.NoSuchAlgorithmException;

public class FileMd5Utils {
     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) {
                System.err.println(FileMd5Utils.class.getName()+"初始化失败，MessageDigest不支持MD5Util.");
                e.printStackTrace();
            }
        }  

        /**
         * 计算文件的MD5
         * @param fileName 文件的绝对路径
         * @return
         * @throws IOException
         */
        public static String getFileMD5String(String fileName) throws IOException{
            File f = new File(fileName);
            return getFileMD5String(f);
        }  

        /**
         * 计算文件的MD5，重载方法
         * @param file 文件对象
         * @return
         * @throws IOException
         */
        public static String getFileMD5String(File file) throws IOException{
            FileInputStream in = new FileInputStream(file);
            FileChannel ch = in.getChannel();
            MappedByteBuffer byteBuffer = ch.map(FileChannel.MapMode.READ_ONLY, 0, file.length());
            messageDigest.update(byteBuffer);
            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];
           char c1 = hexDigits[bt & 0xf];
           stringbuffer.append(c0);
           stringbuffer.append(c1);
        }  

        public static void main(String[] args) throws IOException {
            String fileName = "F:\\test01\\1.txt";
            String str = "d0970714757783e6cf17b26fb8e2298f";
            String str2 = "ea3ed20b6b101a09085ef09c97da1597";
            System.out.println(str.equals(str2));
            System.out.println(getFileMD5String(fileName));
        }
}