Java - Resetting InputStream

Question

I'm dealing with some Java code in which there's an InputStream that I read one time and then I need to read it once again in the same method.

The problem is that I need to reset it's position to the start in order to read it twice.

I've found a hack-ish solution to the problem:

is.mark(Integer.MAX_VALUE);

//Read the InputStream is fully
// { ... }

try
{
    is.reset();
}
catch (IOException e)
{
    e.printStackTrace();
}

Does this solution lead to some unespected behaviours? Or it will work in it's dumbness?

Answer 1

As written, you have no guarantees, because mark() is not required to report whether it was successful. To get a guarantee, you must first call markSupported(), and it must return true.

Also as written, the specified read limit is very dangerous. If you happen to be using a stream that buffers in-memory, it will potentially allocate a 2GB buffer. On the other hand, if you happen to be using a FileInputStream, you're fine.

A better approach is to use a BufferedInputStream with an explicit buffer.

Answer 2

It depends on the InputStream implementation. You can also think whether it will be better if you use byte[]. The easiest way is to use Apache commons-io:

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