String checksum = DigestUtils.md5Hex(new FileInputStream(filePath));

谷歌guava提供了一个新的API。找到下面的一个:

public static HashCode hash(File file,
            HashFunction hashFunction)
                     throws IOException

Computes the hash code of the file using hashFunction.

Parameters:
    file - the file to read
    hashFunction - the hash function to use to hash the data
Returns:
    the HashCode of all of the bytes in the file
Throws:
    IOException - if an I/O error occurs
Since:
    12.0

在Real的Java-How-to中有一个使用MessageDigest类的例子。

请查看该页面中使用CRC32和SHA-1的示例。

import java.io.*;
import java.security.MessageDigest;

public class MD5Checksum {

   public static byte[] createChecksum(String filename) throws Exception {
       InputStream fis =  new FileInputStream(filename);

       byte[] buffer = new byte[1024];
       MessageDigest complete = MessageDigest.getInstance("MD5");
       int numRead;

       do {
           numRead = fis.read(buffer);
           if (numRead > 0) {
               complete.update(buffer, 0, numRead);
           }
       } while (numRead != -1);

       fis.close();
       return complete.digest();
   }

   // see this How-to for a faster way to convert
   // a byte array to a HEX string
   public static String getMD5Checksum(String filename) throws Exception {
       byte[] b = createChecksum(filename);
       String result = "";

       for (int i=0; i < b.length; i++) {
           result += Integer.toString( ( b[i] & 0xff ) + 0x100, 16).substring( 1 );
       }
       return result;
   }

   public static void main(String args[]) {
       try {
           System.out.println(getMD5Checksum("apache-tomcat-5.5.17.exe"));
           // output :
           //  0bb2827c5eacf570b6064e24e0e6653b
           // ref :
           //  http://www.apache.org/dist/
           //          tomcat/tomcat-5/v5.5.17/bin
           //              /apache-tomcat-5.5.17.exe.MD5
           //  0bb2827c5eacf570b6064e24e0e6653b *apache-tomcat-5.5.17.exe
       }
       catch (Exception e) {
           e.printStackTrace();
       }
   }
}

下面是一个方便的变体，它利用了Java 9中的InputStream.transferTo()和Java 11中的OutputStream.nullOutputStream()。它不需要外部库，也不需要将整个文件加载到内存中。

public static String hashFile(String algorithm, File f) throws IOException, NoSuchAlgorithmException {
    MessageDigest md = MessageDigest.getInstance(algorithm);

    try(BufferedInputStream in = new BufferedInputStream((new FileInputStream(f)));
        DigestOutputStream out = new DigestOutputStream(OutputStream.nullOutputStream(), md)) {
        in.transferTo(out);
    }

    String fx = "%0" + (md.getDigestLength()*2) + "x";
    return String.format(fx, new BigInteger(1, md.digest()));
}

and

hashFile("SHA-512", Path.of("src", "test", "resources", "some.txt").toFile());

返回

"e30fa2784ba15be37833d569280e2163c6f106506dfb9b07dde67a24bfb90da65c661110cf2c5c6f71185754ee5ae3fd83a5465c92f72abd888b03187229da29"

有一个输入流装饰器，java。security。DigestInputStream，这样您就可以像往常一样在使用输入流时计算摘要，而不必对数据进行额外的传递。

MessageDigest md = MessageDigest.getInstance("MD5");
try (InputStream is = Files.newInputStream(Paths.get("file.txt"));
     DigestInputStream dis = new DigestInputStream(is, md)) 
{
  /* Read decorated stream (dis) to EOF as normal... */
}
byte[] digest = md.digest();

String checksum = DigestUtils.md5Hex(new FileInputStream(filePath));