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

PushbackInputStream will also work, as long as you know how many characters you want to be able to rewind

Answer 2

RandomAccessFile is what you want:

• fseek() is translated to RandomAccessFile#seek
• ftell() is translated to RandomAccessFile#getFilePointer
• rewind() is seek(0)

Answer 3

BufferedInputStream has mark(readlimit) and reset(). readlimit should be larger than filesize to make mark valid. file.length()+1 is OK. This means mark is valid until readlimit bytes are read, thus you can go back by reset().