Java编程思想：内存映射文件

import java.io.*;
import java.nio.IntBuffer;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.util.*;
public class Test {
    public static void main(String[] args){
        //LargeMappedFiles.test();
        MappedIO.test();
    }
}

class LargeMappedFiles {
    private static final int length = 0x8000000; //128M
    public static void test() {
        try{
            MappedByteBuffer out = new RandomAccessFile("./src/data.out","rw")
                    .getChannel()
                    .map(FileChannel.MapMode.READ_WRITE,0,length);

            for (int i = 0; i < length; i++) {
                out.put((byte)'c');
            }
            System.out.println("Finished Writting...");
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

abstract 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) {
            e.printStackTrace();
        }
    }

    public abstract void test() throws IOException;
}

class MappedIO {
    private static int numOfInts = 4000000;
    private static int numOfBuffInts = 200000;

    private static Tester[] tests = {
            new Tester("Stream Write"){

                @Override
                public void test() throws IOException {
                    DataOutputStream out = new DataOutputStream(
                            new BufferedOutputStream(
                                    new FileOutputStream("temp.tmp")));
                    for (int i = 0; i < numOfInts; i++) {
                        out.writeInt(i);
                    }
                    out.close();
                }
            },
            new Tester("Mapped Write") {
                @Override
                public void test() throws IOException {
                    FileChannel fc = new RandomAccessFile("temp.tmp","rw")
                            .getChannel();
                    IntBuffer out = fc
                            .map(FileChannel.MapMode.READ_WRITE,0,fc.size())
                            .asIntBuffer();
                    for (int i = 0; i < numOfInts; i++) {
                        out.put(i);
                    }
                    fc.close();
                }
            },
            new Tester("Stream Read") {
                @Override
                public void test() throws IOException {
                    DataInputStream out = new DataInputStream(
                            new BufferedInputStream(
                                    new FileInputStream("temp.tmp")));
                    for (int i = 0; i < numOfInts; i++) {
                        out.readInt();
                    }
                }
            },
            new Tester("Mapped Read") {
                @Override
                public void test() throws IOException {
                    FileChannel fc = new RandomAccessFile("temp.tmp","rw")
                            .getChannel();
                    IntBuffer out = fc
                            .map(FileChannel.MapMode.READ_WRITE,0,fc.size())
                            .asIntBuffer();

                    for (int i = 0; i < numOfInts; i++) {
                        out.put(i);
                    }
                }
            },
            new Tester("Stream Read/Write") {
                @Override
                public void test() throws IOException {
                    RandomAccessFile raf = new RandomAccessFile(new File("temp3.tmp"),"rw");
                    raf.writeInt(1);
                    for (int i = 0; i < numOfBuffInts; i++) {
                        raf.seek(raf.length() - 4);
                        raf.writeInt(raf.readInt());
                    }
                }
            },
            new Tester("Mapped Read/Write") {
                @Override
                public void test() throws IOException {
                    FileChannel fc = new RandomAccessFile("temp.tmp","rw")
                            .getChannel();
                    IntBuffer out = fc
                            .map(FileChannel.MapMode.READ_WRITE,0,fc.size())
                            .asIntBuffer();
                    out.put(0);
                    for (int i = 1; i < numOfBuffInts; i++) {
                        out.put(out.get(i-1));
                    }
                    fc.close();
                }
            }

    };

    public static void test() {
        for (Tester test : tests) {
            test.runTest();
        }
    }
}