Java InputStreamReader tries to read whole stream?

Question

I'm trying to read UTF-16 string from a Socket. And the point is I don't know its length in bytes before I read first few chars of the string.

So I've opened InputStreamReader like this:

InputStreamReader reader = new InputStreamReader(inputStream, "UTF-16");

And then I tried to read it char by char.

reader.read();

And it hangs while trying to read the very first char!

In a process of debugging I realized that it looks like InputStreamReader kinda tries to read WHOLE InputStream, and then converts it to UTF-16 char sequence. And of course, it goes all the way down to end of string, and it's nothing there, so it just waits for the client to send some more bytes.

Is that really the way InputStreamReader works? If it is - how can I read a PART of UTF-16 InputStream, or better one single char, without reaching end of it?

Can you try - new InputStreamReader(inputStream, Charset.forName("UTF-16")); — JavaLearner1, Jul 26 '18 at 13:22
``read()`` blocks until data is available. So if it blocks, the stream is empty. — f1sh, Jul 26 '18 at 13:23
"I assume you haven't read the documentation" - I've read it, and InputStream works as it should. Returns bytes up to the end of string and then hangs. — user1748526, Jul 26 '18 at 13:23
The InputStream is definitely not empty. I even tried to wrap it with another stream and sysout'ed all the "read()" calls. And yes, InputStreamReader calls it up to the end of stream. — user1748526, Jul 26 '18 at 13:27
Have you tried wrapping it in a `BufferedReader` like the documentation says? — Jacob G., Jul 26 '18 at 13:31
Yeah, it was wrapped from the start, and then I "unwrapped" it to solve this bug) — user1748526, Jul 26 '18 at 13:33
It may be obvious, but have you tried the tutorial at https://docs.oracle.com/javase/tutorial/networking/sockets/readingWriting.html? — beat, Jul 26 '18 at 13:45
Yes, I've tried it in despair, and obviously, it didn't work, because that "buffering" behaviour is what I'm trying to get rid of :) — user1748526, Jul 26 '18 at 13:54

score -1 · Answer 1 · answered Jul 26 '18 at 13:28

-1

if i understand you pb you should translate your inputstream into a string using a byte[] with

IOUtils.toString(inputStream, StandardCharsets.UTF_8);

then you should be able to iterate on it

or directly

FileUtils.readFileToByteArray(new File(path))

if you want to get a byte[] from the file

answered Jul 26 '18 at 13:28

Aurele Collinet

138
1
16

No, the point is "I don't know its length before I read first few chars". Therefore, I can't just read the whole stream - it will block the thread at the end. – user1748526 Jul 26 '18 at 13:31
and if you translate you input into a byte[] in order to read its length – Aurele Collinet Jul 26 '18 at 13:45
using IOUtils.toByteArray(Input) you'll get your byte[] then you can get the size – Aurele Collinet Jul 26 '18 at 13:46
I can't translate my input to a byte[], because it's a socket. And a socket works that way it WAITS endlessly for new bytes, not ends the stream. – user1748526 Jul 26 '18 at 13:48
i don't know how to help you then :/ – Aurele Collinet Jul 26 '18 at 13:49

score -1 · Answer 2 · answered Jul 26 '18 at 13:40

-1

As the BufferedInputStream method you are using does not block you get the situation that as soon as your InputStream does not have any data and is not closed you don't get a -1 but a 0. This will send your method into an endless loop.

So for reading local streams it is better to check for read() <= 0 as you usually get the data fast enough. The best way is to make sure there is an eof by closing the stream.

answered Jul 26 '18 at 13:40

MBaev

353
2
20

Hmm, wait a sec, it doesn't return 0. It blocks. – user1748526 Jul 26 '18 at 13:44
Show your code with which you are trying to do this – MBaev Jul 26 '18 at 13:47
InputStreamReader reader = new InputStreamReader(inputStream, "UTF-16"); reader.read(); – user1748526 Jul 26 '18 at 13:48
Where is your loop? – MBaev Jul 26 '18 at 13:59
There is no loop. I'm trying to read first char and it blocks. InputStream is not empty. – user1748526 Jul 26 '18 at 14:16

Java InputStreamReader tries to read whole stream?

2 Answers2