java file input with rewind()/reset() capability

Question

I need to write a function that takes in some kind of input stream thing (e.g. an InputStream or a FileChannel) in order to read a large file in two passes: once to precompu

Answer 1

What you want is RandomAccessFileInputStream - implements InputStream interface with mark/reset, sometimes seek based on RandomAccessFiles. Some implementations exist which might do what you need.

One example complete with sources is in http://www.fuin.org/utils4j/index.html but you would find many others searching the internet and its is easy enough to code if none fits exactly.