Check available number of bytes in an input stream in Java

In this post we saw how to read the bytes contained in an input stream. The most common way to achieve it is by way of one of the read methods. The overloaded version where we provide a target byte array, an offset and a total byte count to be read is probably used most often.

It can happen in real-life situations that we provide the total number of bytes to be extracted but those bytes have not yet “arrived”, i.e. are not yet available in the input stream. This can occur when reading the bytes from a slow network connection. The bytes will eventually be available. The read method will block the thread it’s running in while it is waiting for the bytes to be loaded.

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Various ways to read bytes from an input stream in Java

Say you want to fill a byte array from a source, e.g. a from a randomly simulated data of 50 bytes like the following:

byte[] simulatedSource = new byte[50];
Random random = new Random();
random.nextBytes(simulatedSource);
InputStream inputStream = new ByteArrayInputStream(simulatedSource);  

At a basic level we can read each byte one by one from the input stream as follows:

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