对文件做MD5摘要

package transferterminate.business.util;

import java.io.IOException;
import java.io.InputStream;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

 

/**
 * <li>Title: IntegralityUtil.java</li>
 * <li>Project: transferterminate</li>
 * <li>Package:transferterminate.business.util</li>
 * <li>Description: 摘要应用类</li>
 * <li>Copyright: Copyright (c) 2009</li>
 * <li>Company: IdealTechnologies </li>
 * <li>Created on May 8, 2009 8:23:38 AM</li>
 *
 * @author chun_chang
 * @version 1.0
 *
 */
public class IntegralityUtil {

 private static MessageDigest alg;
 private static int length;
 private static int maxBytesReadPerTime = 8192;

 static {
  try {
   alg = MessageDigest.getInstance("MD5");
   length = alg.getDigestLength();// 默认长度是16
  } catch (NoSuchAlgorithmException e) {
   e.printStackTrace();
  }
 }

 /**
  * 获取文件内容的MD5摘要
  * @param is:InputStream 源文件输入流
  * @param fileLength:long 源文件长度
  * @return byte[] 信息摘要
  * @throws IDTException
  */
 public static byte[] getMD5(InputStream is, long fileLength) throws Exception {

  byte[] bytes = new byte[maxBytesReadPerTime];
  int bytesRead = 0;
  int maxReadTimesBeforeRedigest = 100;//每100块做一次摘要
  byte[] digestOfPart = new byte[length];
  byte[] digest = new byte[length * maxReadTimesBeforeRedigest];
  int timesRead = 0;
  byte[] digestToReturn = new byte[length];

  try {
   while (fileLength > 0) {
    bytesRead = is.read(bytes);
    digestOfPart = getMD5(bytes, 0, bytesRead);
    System.arraycopy(digestOfPart, 0, digest, timesRead * length, length);
    timesRead++;
    if (timesRead == maxReadTimesBeforeRedigest) {
     digestOfPart = getMD5(digest, 0, digest.length);
     System.arraycopy(digestOfPart, 0, digest, 0, length);
     timesRead = 1;
    }
    fileLength = fileLength - bytesRead;
   }
   
   if (timesRead > 1) {
    digestOfPart = getMD5(digest, 0, timesRead * length);
    System.arraycopy(digestOfPart, 0, digestToReturn, 0, length);
   } else {
    System.arraycopy(digest, 0, digestToReturn, 0, length);
   }
   
   if (is != null) {
    is.close();
   }
  } catch (IOException e) {
   e.printStackTrace();
  }
  return digestToReturn;
 }

 /**
  * 获取MD5信息摘要
  * @param in:byte[] 源数据
  * @return byte[] 信息摘要
  * @throws Exception
  */
 public static byte[] getMD5(final byte[] in) {
  alg.update(in);
  return alg.digest();
 }

 /**
  * 获取MD5信息摘要
  * @param in:byte[] 源数据
  * @param from:int 起始字节
  * @param len:int 长度
  * @return byte[] 信息摘要
  * @throws Exception
  */
 public static byte[] getMD5(final byte[] in, int from, int len) {
  alg.update(in, from, len);
  return alg.digest();
 }

 /**
  * 获取摘要长度
  * @return int 摘要长度
  */
 public static int getDigestLength() {
  return length;
 }

 /**
  * 设置每次读文件最大长度
  * @param maxBytesReadPerTime
  */
 public static void setMaxBytesReadPerTime(int maxBytesReadPerTime) {
  IntegralityUtil.maxBytesReadPerTime = maxBytesReadPerTime;
 }
}