Question

Is there a way to get the HashCode of an InputStream in Java, I am trying to upload a picture using the <p:fileUpload/> from PrimeFaces, converting it into a HashCode and comparing it to another picture.

At the moment I'm trying this:

public void save(FileUploadEvent event) throws IOException {
        HashCode hashCode = null;
        HashCode hashCodeCompare = null;
        hashCode = Files.asByteSource(new File(event.toString())).hash(Hashing.murmur3_128(50));
        hashCodeCompare = Files.asByteSource(new File(FilePathOfFileToCompare)).hash(Hashing.murmur3_128(50));
        boolean hashTrueFalse;
        if(hashCode.equals(hashCodeCompare)) {
            System.out.println("true");
        } else{
            System.out.println("false");
        }

        try (InputStream input = event.getFile().getInputstream()) {
            String imageName = generateFileName() + "." + fileExtensions(event.getFile().getFileName());
            String imageLink = PICTURE_DESTINATION + "\\" + imageName;


            Picture picture = new Picture();
            picture.setPictureUrl(imageLink);
            pictureService.createOrUpdate(picture);

            personForm.getCurrentPersonDTO().setPictureDTO(pictureMapper.toDTO(picture));


        } catch (IOException e) {
            e.printStackTrace();
        }
    }

Is there any way to turn the InputStream into a hashcode?

Answer 1

如果要计算包含在其上的字节的哈希值，则必须阅读InputStream。首先将InputSteam读取为byte []。

在番石榴中使用ByteStreams：

InputStream in = ...;
byte[] bytes = ByteStreams.toByteArray(in);

一种流行的替代方法是使用Commons IO：

InputStream in = ...;
byte[] bytes = IOUtils.toByteArray(in);

然后您可以在字节数组上调用Arrays.hashCode（）：

int hash = java.util.Arrays.hashCode(bytes);

但是您可能会考虑使用SHA256作为哈希函数，因为您不太可能发生冲突：

MessageDigest digest = MessageDigest.getInstance("SHA-256");
byte[] sha256Hash = digest.digest(bytes);

如果您不想将整个流读取到内存中的字节数组，则可以计算哈希值，因为其他人正在读取InputStream。例如，您可能想将InputStream流式传输到磁盘并传输到db中。 Guava提供了一个包装InputStream的类，该类为您HashingInputStream：

首先用HashinInputStream包装您的InputStream

HashingInputStream hin = new HashingInputStream(Hashing.sha256(), in);

然后以您喜欢的任何方式读取HashingInputStream

while(hin.read() != -1);

然后从HashingInputStream获取哈希

byte[] sha256Hash = hin.hash().asBytes();

Answer 2

您想要做的是ByteStreams.copy(input, Funnels.asOutputStream(hasher))，其中hasher是从Hashing.sha256().newHasher()。然后，调用hasher.hash()以得到生成的HashCode。

Answer 3

我建议使用Files.asByteSource(fileSource.getFile()).hash(hashFunction).padToLong()

Is there any way to get the hashcode of an InputStream using Guava?

3 个答案: