加密算法比较：SHA1，SHA256，MD5_multibuffer sha256

以一个60M的文件为测试样本，经过1000次的测试平均值，三种算法的表现为：

MD5算法运行1000次的平均时间为：226ms
SHA1算法运行1000次的平均时间为：308ms
SHA256算法运行1000次的平均时间为：473ms

安全性方面，显然SHA256（又称SHA2）的安全性最高，但是耗时要比其他两种多很多。MD5相对较容易碰撞，因此，SHA1应该是这三种中性能最好的一款加密算法。

JAVA实现：

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.zip.CRC32;
 
public class FileSafeCode {
	/**
	 * 计算大文件 md5获取getMD5(); SHA1获取getSha1() CRC32获取 getCRC32()
	 */
	protected static char hexDigits[] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e',
			'f' };
	public static MessageDigest messagedigest = null;
 
	
 
	/**
	 * 对一个文件获取md5值
	 * 
	 * @return md5串
	 * @throws NoSuchAlgorithmException
	 */
	public static String getMD5(File file) throws IOException, NoSuchAlgorithmException {
 
		messagedigest = MessageDigest.getInstance("MD5");
		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());
	}
 
	/**
	 * // * @param target 字符串 求一个字符串的md5值 // * @return md5 value //
	 */
	// public static String StringMD5(String target) {
	// return DigestUtils.md5Hex(target);
	// }
 
	/***
	 * 计算SHA1码
	 * 
	 * @return String 适用于上G大的文件
	 * @throws NoSuchAlgorithmException
	 */
	public static String getSha1(File file) throws OutOfMemoryError, IOException, NoSuchAlgorithmException {
		messagedigest = MessageDigest.getInstance("SHA-1");
		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());
	}
 
	/**
	 * 获取文件SHA256码
	 * 
	 * @return String
	 */
	public static String getSha256(File file) throws OutOfMemoryError, IOException, NoSuchAlgorithmException {
		messagedigest = MessageDigest.getInstance("SHA-256");
		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());
	}
 
	/**
	 * 获取文件CRC32码
	 * 
	 * @return String
	 */
	public static String getCRC32(File file) {
		CRC32 crc32 = new CRC32();
		// MessageDigest.get
		FileInputStream fileInputStream = null;
		try {
			fileInputStream = new FileInputStream(file);
			byte[] buffer = new byte[8192];
			int length;
			while ((length = fileInputStream.read(buffer)) != -1) {
				crc32.update(buffer, 0, length);
			}
			return crc32.getValue() + "";
		} catch (FileNotFoundException e) {
			e.printStackTrace();
			return null;
		} catch (IOException e) {
			e.printStackTrace();
			return null;
		} finally {
			try {
				if (fileInputStream != null)
					fileInputStream.close();
			} catch (IOException e) {
				e.printStackTrace();
			}
		}
	}
 
	public static String getMD5String(String s) {
		return getMD5String(s.getBytes());
	}
 
	public static String getMD5String(byte[] bytes) {
		messagedigest.update(bytes);
		return bufferToHex(messagedigest.digest());
	}
 
	/**
	 * @Description 计算二进制数据
	 * @return String
	 */
	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);
	}
}