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);
	}
}