Guava现在提供了一个新的、一致的哈希API，它比JDK中提供的各种哈希API更友好。参见哈希的解释。对于一个文件，你可以很容易地得到MD5和，CRC32(14.0+版本)或许多其他哈希值:

HashCode md5 = Files.hash(file, Hashing.md5());
byte[] md5Bytes = md5.asBytes();
String md5Hex = md5.toString();

HashCode crc32 = Files.hash(file, Hashing.crc32());
int crc32Int = crc32.asInt();

// the Checksum API returns a long, but it's padded with 0s for 32-bit CRC
// this is the value you would get if using that API directly
long checksumResult = crc32.padToLong();

使用Apache Commons Codec库中的DigestUtils:

try (InputStream is = Files.newInputStream(Paths.get("file.zip"))) {
    String md5 = org.apache.commons.codec.digest.DigestUtils.md5Hex(is);
}

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();

如果使用ANT进行构建，这非常简单。将以下内容添加到build.xml中:

<checksum file="${jarFile}" todir="${toDir}"/>

其中jarFile是要针对其生成MD5的JAR, toDir是要放置MD5文件的目录。

更多信息请点击这里。

标准Java运行时环境方式:

public String checksum(File file) {
  try {
    InputStream fin = new FileInputStream(file);
    java.security.MessageDigest md5er =
        MessageDigest.getInstance("MD5");
    byte[] buffer = new byte[1024];
    int read;
    do {
      read = fin.read(buffer);
      if (read > 0)
        md5er.update(buffer, 0, read);
    } while (read != -1);
    fin.close();
    byte[] digest = md5er.digest();
    if (digest == null)
      return null;
    String strDigest = "0x";
    for (int i = 0; i < digest.length; i++) {
      strDigest += Integer.toString((digest[i] & 0xff) 
                + 0x100, 16).substring(1).toUpperCase();
    }
    return strDigest;
  } catch (Exception e) {
    return null;
  }
}

结果等于linux md5sum实用程序。