Here's one way to solve this without relying on third-party libraries:

inputStream.reset();
byte[] bytes = new byte[inputStream.available()];
DataInputStream dataInputStream = new DataInputStream(inputStream);
dataInputStream.readFully(bytes);

Or if you don't mind using thirdparties (Commons IO):

byte[] bytes = IOUtils.toByteArray(is);

Guava also helps:

byte[] bytes = ByteStreams.toByteArray(inputStream);

As per InputStream.readAllBytes() method javadoc this method was introduced in Java 9.

Since:

9

It won't work when the code is compiled on lower Java version, in your case Java 8.

Use the readTree(Reader r) overloaded method to let Jackson read the stream for you:

JsonNode node;
try (Reader in = new InputStreamReader(http.getInputStream(), StandardCharsets.UTF_8)) {
    ObjectMapper mapper = new ObjectMapper();
    node = mapper.readTree(in);
}

String Stytch_user_id = node.get("user_id").textValue();
Object[] objects = getUserLogin(Stytch_user_id, "P0002","123456789");

You're misusing available(). It is not valid as a test for end of stream. See the Javadoc.

You don't need all that array copying either. Try this:

ByteArrayOutputStream out = new ByteArrayOutputStream();
while ((count = in.read(buffer)) > 0)
{
    out.write(buffer, 0, count);
}
byte[] data = out.toByteArray();

If you're storing the image at the receiving end you should just write direct to a FileOutputStream instead of the ByteArrayOutputStream above, and forget about data altogether.

Usually I prefer using a fixed size buffer when reading from input stream. As evilone pointed out, using available() as buffer size might not be a good idea because, say, if you are reading a remote resource, then you might not know the available bytes in advance. You can read the javadoc of InputStream to get more insight.

Here is the code snippet I usually use for reading input stream:

byte[] buffer = new byte[BUFFER_SIZE];

int bytesRead = 0;
while ((bytesRead = in.read(buffer)) >= 0){
  for (int i = 0; i < bytesRead; i++){
     //Do whatever you need with the bytes here
  }
}

The version of read() I'm using here will fill the given buffer as much as possible and return number of bytes actually read. This means there is chance that your buffer may contain trailing garbage data, so it is very important to use bytes only up to bytesRead.

Note the line (bytesRead = in.read(buffer)) >= 0, there is nothing in the InputStream spec saying that read() cannot read 0 bytes. You may need to handle the case when read() reads 0 bytes as special case depending on your case. For local file I never experienced such case; however, when reading remote resources, I actually seen read() reads 0 bytes constantly resulting the above code into an infinite loop. I solved the infinite loop problem by counting the number of times I read 0 bytes, when the counter exceed a threshold I will throw exception. You may not encounter this problem, but just keep this in mind :)

I probably will stay away from creating new byte array for each read for performance reasons.