/**

* 讀取指定文件塊數(shù)據(jù)Sha1

*

* @param fis

* @return

*/

private static MessageDigest calSha1(BufferedInputStream fis) {

MessageDigest sha1 = null;

try {

byte[] buffer = new byte[1024];

int numRead = 0;

int total = 0;

sha1 = MessageDigest.getInstance("SHA-1");

while ((numRead = fis.read(buffer)) > 0) {

sha1.update(buffer, 0, numRead);

total += numRead;

if (total >= BLOCK_SIZE) {//每次最多讀入4M

break;

}

}

} catch (Exception e) {

e.printStackTrace();

}

return sha1;

}

/**

* 獲取hash/etag，根據(jù)File文件計(jì)算hash值

*

* @param file 文件

* @return

*/

public static String getEtagHash(File file) {

String etagHash = null;

BufferedInputStream fis = null;

try {

if (file.exists()) {

byte[] ret = new byte[21];

long blockCount = blockCount(file.length());

fis = new BufferedInputStream(new FileInputStream(file));

if (blockCount <= 1) { // 文件塊數(shù)小于等于1塊

MessageDigest sha1 = calSha1(fis);

if (null != sha1) {

byte[] input = sha1.digest();

ret[0] = BYTE_LOW_4;

for (int i = 0; i < 20; ++i) {//SHA1算法位20字節(jié)

ret[i + 1] = input[i];

}

}

} else {//將所有sha1值按切塊順序拼接

byte[] rec = new byte[(int) blockCount * 20];

ret[0] = BYTE_OVER_4;

int i, cnt = 0;

for (i = 0; i < blockCount; i++) {//每塊文件分別計(jì)算sha1

MessageDigest sha1 = calSha1(fis);

if (null != sha1) {

byte[] tmp = sha1.digest();

for (int j = 0; j < 20; j++) {

rec[cnt++] = tmp[j];

}

}

}

MessageDigest sha1 = MessageDigest.getInstance("SHA-1");//對拼接好的數(shù)據(jù)再做sha1計(jì)算

sha1.update(rec, 0, (int) blockCount * 20);

byte[] tmp = sha1.digest();

for (i = 0; i < 20; ++i) {//在最前面拼上單個(gè)字節(jié)，值為0x96

ret[i + 1] = tmp[i];

}

}

etagHash = EncodeUtils.urlsafeEncodeString(ret);

} else {

System.out.println("File[" + file.getAbsolutePath() + "] Not Exist,Cannot Calculate Hash!");

}

} catch (Exception e) {

e.printStackTrace();

} finally {

try {

if (fis != null) {

fis.close();

fis = null;

}

} catch (IOException e) {

e.printStackTrace();

}

}

return etagHash;

}

總結(jié)

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