Can't read same InputStream twice

Question

I have a an InputStream as a parameter, which works just fine when I read it for the first time, however, reading the same InputStream doesn't work. I just can't get mark() and reset()to work. Anyone know how to reset this? I'm reading a .txt file. The file contains spawn values for enemy objects that don't reappear, since the inputstream mark(?) is at the end, I guess?

readTxt(InputStream resource){
//resource is a .txt as ResourceStream
arrayList = new BufferedReader(new InputStreamReader(resource,
                StandardCharsets.UTF_8)).lines().collect(Collectors.toList());

Why don't you store values at first read ? explain more, store nameFile and stream twice not possible ? — azro, May 14 '18 at 13:33

Mạnh Quyết Nguyễn · Answer 1 · 2018-05-14T13:37:20.440

5

mark() only work if the input stream supported it (you can check by markSupported().

It does not work for every stream.

One way to read the input stream is to copy content of input stream to an array and re-read the array:

byte[] buffer = new byte[2048];

ByteArrayOutputStream output = new ByteArrayOutputStream();

int byteCount;
while ((byteCount = inputStream.read(buffer)) != -1)
{
    output.write(buffer, 0, byteCount);
}
byte[] source = output.toByteArray();

// Now you have ability to reread the "secondary" input stream:
InputStream is = new ByteArrayInputStream(source);

edited May 14 '18 at 13:37

answered May 14 '18 at 13:34

Mạnh Quyết Nguyễn

17,677
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Tested if it supports, it does. Will try to re-read with copying to array. – Ryan Sangha May 14 '18 at 13:36
If your input stream support it, you should call `mark(int byteCountAbleToReset)`. And later call `reset()` to go back `byteCountAbleToReset` bytes in stream. – Mạnh Quyết Nguyễn May 14 '18 at 14:10
Yeah, I tried `fileStream.mark(arrayList.size());`and then `fileStream.reset();` but it didn't work – Ryan Sangha May 14 '18 at 14:11
You must call `mark()` before read from input stream. And the number be passed is the number of bytes you want to go back, it's definitely greater than `list.size()` – Mạnh Quyết Nguyễn May 14 '18 at 14:12
Yeah, calling mark() before worked, I had it after the reading part – Ryan Sangha May 14 '18 at 16:33
Glad it helped! – Mạnh Quyết Nguyễn May 14 '18 at 16:34

score 2 · Answer 2 · answered May 14 '18 at 16:31

2

Since the InputStream was markSupported(), I could use the mark()and reset().

//mark 0, before you start reading your file
inputStream.mark(0);


//read your InputStream here
read(inputStream)...

//reset the stream, so it's ready to be read from the start again. 
inputStream.reset();

answered May 14 '18 at 16:31

Ryan Sangha

442
6
17

Do you know of a way to read the stream if it's been read internally. I don't receive it in my code until after Spring already called read function. Is it possible? – wheeleruniverse Nov 06 '18 at 21:37

Can't read same InputStream twice

2 Answers2