public class ReadFileForRegex {
	//Converts the contents of a file into a CharSequence
	    // suitable for use by the regex package.
	public CharSequence fromFile(String filename) throws IOException {
	        FileInputStream fis = new FileInputStream(filename);
	        FileChannel fc = fis.getChannel();

	        // Create a read-only CharBuffer on the file
	        ByteBuffer bbuf = fc.map(FileChannel.MapMode.READ_ONLY, 0, (int)fc.size());
	        CharBuffer cbuf = Charset.forName("8859_1").newDecoder().decode(bbuf);
	        return cbuf;
    }
	public static void main(String[] args){
		    Pattern pattern = Pattern.compile("oi");
	        Matcher matcher = pattern.matcher(fromFile("file.txt"));
	        ..
	}

}