// newio/MappedIO.java
// (c)2016 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://mindviewinc.com/Books/OnJava/ for more book information.
import java.nio.*;
import java.nio.channels.*;
import java.io.*;

public class MappedIO {
  private static int numOfInts = 4000000;
  private static int numOfUbuffInts = 200000;
  private abstract static class Tester {
    private String name;
    public Tester(String name) { this.name = name; }
    public void runTest() {
      System.out.print(name + ": ");
      try {
        long start = System.nanoTime();
        test();
        double duration = System.nanoTime() - start;
        System.out.format("%.2f\n", duration/1.0e9);
      } catch(IOException e) {
        throw new RuntimeException(e);
      }
    }
    public abstract void test() throws IOException;
  }
  private static Tester[] tests = {
    new Tester("Stream Write") {
      @Override
      public void test() throws IOException {
        try(DataOutputStream dos = new DataOutputStream(
              new BufferedOutputStream(
                new FileOutputStream(
                  new File("temp.tmp"))))) {
          for(int i = 0; i < numOfInts; i++)
            dos.writeInt(i);
        }
      }
    },
    new Tester("Mapped Write") {
      @Override
      public void test() throws IOException {
        try(FileChannel fc =
            new RandomAccessFile("temp.tmp", "rw")
            .getChannel()) {
          IntBuffer ib = fc.map(
            FileChannel.MapMode.READ_WRITE, 0, fc.size())
            .asIntBuffer();
          for(int i = 0; i < numOfInts; i++)
            ib.put(i);
        }
      }
    },
    new Tester("Stream Read") {
      @Override
      public void test() throws IOException {
        try(DataInputStream dis = new DataInputStream(
              new BufferedInputStream(
                new FileInputStream("temp.tmp")))) {
          for(int i = 0; i < numOfInts; i++)
            dis.readInt();
        }
      }
    },
    new Tester("Mapped Read") {
      @Override
      public void test() throws IOException {
        try(FileChannel fc = new FileInputStream(
             new File("temp.tmp")).getChannel()) {
          IntBuffer ib = fc.map(
            FileChannel.MapMode.READ_ONLY, 0, fc.size())
            .asIntBuffer();
          while(ib.hasRemaining())
            ib.get();
        }
      }
    },
    new Tester("Stream Read/Write") {
      @Override
      public void test() throws IOException {
        try(RandomAccessFile raf = new RandomAccessFile(
              new File("temp.tmp"), "rw")) {
          raf.writeInt(1);
          for(int i = 0; i < numOfUbuffInts; i++) {
            raf.seek(raf.length() - 4);
            raf.writeInt(raf.readInt());
          }
        }
      }
    },
    new Tester("Mapped Read/Write") {
      @Override
      public void test() throws IOException {
        try(FileChannel fc = new RandomAccessFile(
              new File("temp.tmp"), "rw").getChannel()) {
          IntBuffer ib = fc.map(
            FileChannel.MapMode.READ_WRITE, 0, fc.size())
            .asIntBuffer();
          ib.put(0);
          for(int i = 1; i < numOfUbuffInts; i++)
            ib.put(ib.get(i - 1));
        }
      }
    }
  };
  public static void main(String[] args) {
    for(Tester test : tests)
      test.runTest();
  }
}
/* Output:
Stream Write: 0.45
Mapped Write: 0.04
Stream Read: 0.42
Mapped Read: 0.03
Stream Read/Write: 3.43
Mapped Read/Write: 0.00
*/