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,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
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 > 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"); } }
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
<?php $md5file = md5_file("test.txt"); file_put_contents("md5file.txt",$md5file); ?>
<?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."; } ?>