计算文件md5 java_Java计算文件MD5值代码详解

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));

}

}