How can I read a character from an InputStream and return it in a Supplier<Integer> (Java)

Question

So I have a method I need to implement. It gets an InputStream and returns a Supplier like this:

public Supplier<Integer> buildPipe(InputStream input)

Now I want to read a character from the InputStream (probably with the read()-method) and return it, but I have no idea how to store it as an int so I can return it with the Supplier.

I hope someone can help me out.

Answer 1

It is not really possible to go directly from an InputStream to a codepoint without going through a decoding bridge. For that you need to know that Charset, or assume it. InputStreamReader is that bridge.

for example:

InputStream is = new ByteArrayInputStream(new byte[]{1,2});
InputStreamReader reader = new InputStreamReader(is, StandardCharsets.UTF_8);

Now you can have your Supplier from a Reader rather than an input stream.

Supplier<Integer> next(InputStreamReader reader) {
    Supplier<Integer> s = () -> {
        try {
            return reader.read();
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    };
    return s;
}

Please note that InputStreamReader is stateful and hence your Supplier wont be referential transparent as one would expect.