Main.java

import java.io.*;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;

public class Main {

    private static int length = 0x2FFFFFFF;//1G
    private abstract static class Tester {
        private String name;
        public Tester(String name) {
            this.name = name;
        }
        public void runTest() {
            System.out.print(name + ": ");
            long start = System.currentTimeMillis();
            test();
            System.out.println(System.currentTimeMillis()-start+" ms");
        }
        public abstract void test();
    }
    private static Tester[] testers = {
            /*new Tester("Stream RW") {
                public void test() {
                    try (FileInputStream fis = new FileInputStream(
                            "src/a.txt");
                         DataInputStream dis = new DataInputStream(fis);
                         FileOutputStream fos = new FileOutputStream(
                                 "src/a.txt");
                         DataOutputStream dos = new DataOutputStream(fos);) {

                        byte b = (byte)0;
                        for(int i=0;i<length;i++) {
                            dos.writeByte(b);
                            dos.flush();
                        }
                        while (dis.read()!= -1) {
                        }
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
            },*/
            new Tester("Mapped RW") {
                public void test() {
                    try (FileChannel channel = FileChannel.open(Paths.get("src/b.txt"),
                            StandardOpenOption.READ, StandardOpenOption.WRITE);) {
                        MappedByteBuffer mapBuffer = channel.map(FileChannel.MapMode.READ_WRITE, 0, length);
                        for(int i=0;i<length;i++) {
                            mapBuffer.put((byte)0);
                        }
                        mapBuffer.flip();
                        while(mapBuffer.hasRemaining()) {
                            mapBuffer.get();
                        }
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
            },
            new Tester("Mapped PRIVATE") {
                public void test() {
                    try (FileChannel channel = FileChannel.open(Paths.get("src/c.txt"),
                            StandardOpenOption.READ, StandardOpenOption.WRITE);) {
                        MappedByteBuffer mapBuffer = channel.map(FileChannel.MapMode.PRIVATE, 0, length);
                        for(int i=0;i<length;i++) {
                            mapBuffer.put((byte)0);
                        }
                        mapBuffer.flip();
                        while(mapBuffer.hasRemaining()) {
                            mapBuffer.get();
                        }
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
            }
    };

    public static void main(String[] args) {

        for(Tester tester:testers) {
            tester.runTest();
        }



    }

    /**
     *
     * head: int32
     * price: BigDecimal[20, 10]
     * preload: { id: char[32], priority: int8,   }
     *
     */
}