// Juggle the input file into a byte array for later extraction
File sourceFile = new File(STRIPPED_DIR, STRIPPED_SOURCE);
long fileSize = sourceFile.length();
System.out.format("File size: %dn", fileSize);
byte[] fileBytes = new byte[(int) fileSize];
FileInputStream fis = new FileInputStream(sourceFile);
int bytesRead = fis.read(fileBytes);
fis.close();
System.out.format("Bytes read: %dn", bytesRead);
// Parse input file.
ANTLRInputStream input = new ANTLRInputStream(new ByteArrayInputStream(fileBytes));

Dumper dumper = new Dumper(outWriter, usage, fileBytes);
walker.walk(dumper, tree);

private String originalString(int from, int till) {
    return new String(fileBytes, from, till-from+1);
}

private String originalString(ParserRuleContext ctx) {
    int from = ctx.start.getStartIndex();
    int till = ctx.stop.getStopIndex();
    return originalString(from, till);
}