package net.tools.random;

import java.io.FileInputStream;
import java.io.IOException;
import java.nio.CharBuffer;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;
import java.util.ArrayList;
import java.util.List;

public class MemoryMappingReader {
	private String fileName;
	private List<String> lines;

	public static void main(String s[]) {
		if (s.length != 1) {
			System.out.println("Usage: java MemoryMappingReader <fileName>");
			System.exit(1);
		}

		try {
			MemoryMappingReader mmr = new MemoryMappingReader(s[0]);
			mmr.load();
			mmr.print();
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

	public MemoryMappingReader(String fileName) {
		this.fileName = fileName;
		lines = new ArrayList<String>();
	}

	public void load() throws IOException {
		FileInputStream fis = new FileInputStream(fileName);
		FileChannel fc = fis.getChannel();
		MappedByteBuffer mbb = null;
		Charset cs = Charset.forName("ISO-8859-1");
		CharsetDecoder decoder = cs.newDecoder();
		StringBuilder sb = new StringBuilder();

		long bs = 1024L; // block size
		long fs = fc.size(); // file size
		long t = 0L; // total size

		if (fs != 0) {
			while (t < fs) {
				if (t + bs > fs) {
					bs = fs - t;
				}
				mbb = fc.map(FileChannel.MapMode.READ_ONLY, t, bs);
				CharBuffer cb = decoder.decode(mbb);

				while (cb.hasRemaining()) {
					char c = cb.get();

					if (c == '\n') {
						lines.add(sb.toString());
						sb = new StringBuilder();
					} else if (c == '\r') { // Windows
						continue;
					} else {
						sb.append(c);
					}
				}
				t += bs;
			}
			// The last line may not have ended with \n
			if (sb.length() > 0) {
				lines.add(sb.toString());
			}
		}
	}

	public void print() {
		for (String line : lines) {
			System.out.println(line);
		}
	}
}