每个文件都可以用MD5验证程序算出一个固定的md5码来,它是一个文件的文件签名,可用于验证自己下载的软件是否为原版。百度网盘的“秒传”应该也用到了这个,即上传之前首先计算该文件的md5值,然后看服务器上有没有该文件,有的话从服务端直接拷贝,节省上传时间和降低网络负担。
java的MD5util类:
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;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class MD5FileUtil {
private static final Logger logger = LoggerFactory
.getLogger(MD5FileUtil.class);
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) {
logger.error("MD5FileUtil messagedigest初始化失败", e);
}
}
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);
}
public static void main(String[] args) throws IOException {
long begin = System.currentTimeMillis();
File big = new File("D:\\temp\\jre-7u11-linux-i586.tar.gz");
String md5 = getFileMD5String(big);
long end = System.currentTimeMillis();
System.out.println("md5:" + md5);
System.out.println("time:" + ((end - begin) / 1000) + "s");
}
}
php
例子1:
<?php
$filename = "test.txt";
$md5file = md5_file($filename);
echo $md5file;
?>
会输出类似下面一串字符:
5d41402abc4b2a76b9719d911017c592
例子 2 存储 "test.txt" 文件的 MD5 散列:
<?php
$md5file = md5_file("test.txt");
file_put_contents("md5file.txt",$md5file);
?>
//在本例中,我们将检测 "test.txt" 是否已被更改(即是否 MD5 散列已被更改):
<?php
$md5file = file_get_contents("md5file.txt");
if (md5_file("test.txt") == $md5file)
{
echo "The file is ok.";
}
else
{
echo "The file has been changed.";
}
?>
输出:
The file is ok.