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二说不说，直接上代码
/** * */package cn.sigangjun.util;import java.io.File;import java.io.FileInputStream;import java.io.IOException;import java.io.InputStream;import java.security.MessageDigest;import java.security.NoSuchAlgorithmException;/** *Title: MD5 util
*Description: MD5 util
* @since 2013-8-12 下午3:56:22 * @version 1.0 * @author sigangjun */public class MD5Util { /** * 默认的密码字符串组合，用来将字节转换成 16 进制表示的字符,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 e) { e.printStackTrace(); } } public static String getFileMD5String(File file) throws IOException { InputStream fis; fis = new FileInputStream(file); byte[] buffer = new byte[1024]; int numRead = 0; while ((numRead = fis.read(buffer)) > 0) { messagedigest.update(buffer, 0, numRead); } fis.close(); 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];// 取字节中高 4 位的数字转换 // 为逻辑右移，将符号位一起右移,此处未发现两种符号有何不同 char c1 = hexDigits[bt & 0xf];// 取字节中低 4 位的数字转换 stringbuffer.append(c0); stringbuffer.append(c1); } public static String calcMD5(String s) { try { byte[] strTemp = s.getBytes(); MessageDigest mdTemp = MessageDigest.getInstance("MD5"); mdTemp.update(strTemp); byte[] md = mdTemp.digest(); int j = md.length; char str[] = new char[j * 2]; int k = 0; for (int i = 0; i < j; i++) { byte byte0 = md[i]; str[k++] = hexDigits[byte0 >>> 4 & 0xf]; str[k++] = hexDigits[byte0 & 0xf]; } return new String(str); } catch (Exception e) { e.printStackTrace(); return null; } } public static void main(String[] args) throws IOException { long start = System.currentTimeMillis(); File file = new File("D:/aaa.txt"); String md5 = getFileMD5String(file); System.out.println("md5:" + md5); System.out.println("time is:"+(System.currentTimeMillis()-start)); System.out.println(calcMD5("aaa")); } }