You need to iterate over the ZipEntries of the ZipInputStream.
Something like this:
//if we could gather the next zip entry, now, the zip input stream will allow reading the data associated to the current entry (i.e. the current file)...
// so just call zis.read(...)
// you may call entry.getName() and entry.getSize() to get the file name of the current file and its size.
So, you should iterate the zip entries, check with getName() whether it is the entry you want to read. Then, (assuming the file is not too big), create a byte array of length equal to entry.getSize(),
read with zis.read(...) the file content to the byte array, and finally write it to the output stream.