Java InputStream：复制到同时计算hash

发布于04月14日

以下是我的两个代码片段:

public class Uploader {

  private static final String SHA_256 = "SHA-256";

  public String getFileSHA2Checksum(InputStream fis) throws IOException {
    try {
      MessageDigest md5Digest = MessageDigest.getInstance(SHA_256);
      return getFileChecksum(md5Digest, fis);
    } catch (NoSuch算法rithmException e) {
      return "KO";
    }
  }

  public void transferTo(InputStream fis) throws IOException {
    FileUtils.copyInputStreamToFile(fis, file2);
  }

我的代码将此类用作:

有没有可能同时利用InputStream打开copyToFile和calculateChecksum？

推荐答案

下面是一个使用DigestInputStream的例子，它基于Mark Rotteveel的建议(我很喜欢):

Path input = Paths.get("input_file");
Path output = Paths.get("output_file");
MessageDigest algorithm = MessageDigest.getInstance("SHA-256");
try (InputStream is = Files.newInputStream(input);
     DigestInputStream hashingStream = new DigestInputStream(is, algorithm)) {
    Files.copy(hashingStream, output);
}
byte[] digest = algorithm.digest();
// this line uses Apache Commons Codec to show the hex representation of the byte[]
String hash = Hex.encodeHexString(digest);