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));
        }  
}