计算文件的md5值

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;/** * 计算文件的MD5 */public final class FileMD5 {/** * 默认的密码字符串组合，apache校验下载的文件的正确性用的就是默认的这个组合 */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 nsaex) {System.err.println(FileMD5.class.getName() + "初始化失败，MessageDigest不支持MD5Util。");nsaex.printStackTrace();}}public static void main(String[] args) throws IOException {long begin = System.currentTimeMillis();File big = new File("D:/unit1.zip");String md5 = getFileMD5String(big);long end = System.currentTimeMillis();System.out.println("md5:" + md5 + " time:" + ((end - begin) / 1000) + "s");big = new File("D:/unit.zip");md5 = getFileMD5String(big);end = System.currentTimeMillis();System.out.println("md5:" + md5 + " time:" + ((end - begin) / 1000) + "s");}/** * 适用于上G大的文件 * * @param file * @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());}public static String getMD5String(String s) {return getMD5String(s.getBytes());}public static String getMD5String(byte[] bytes) {messagedigest.update(bytes);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 boolean checkPassword(String password, String md5PwdStr) {String s = getMD5String(password);return s.equals(md5PwdStr);}}