file计算MD5

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));
        } 
}