MappedByteBuffer高速缓存文件、RandomAccessFile随机访问

public abstract class Buffer {

    // Invariants: mark <= position <= limit <= capacity
    private int mark = -1;
    private int position = 0;
    private int limit;
    private int capacity;
    long address;
    ......
}

public abstract class ByteBuffer extends Buffer implements Comparable {

    // These fields are declared here rather than in Heap-X-Buffer in order to
    // reduce the number of virtual method invocations needed to access these
    // values, which is especially costly when coding small buffers.
    //
    final byte[] hb;   // Non-null only for heap buffers
    final int offset;
    boolean isReadOnly;   // Valid only for heap buffers
    boolean bigEndian;
    boolean nativeByteOrder;
    ......
}
//字节数组final byte[] hb就是所指的那块内存缓冲区

public abstract class MappedByteBuffer extends ByteBuffer{
    private final FileDescriptor fd;
    ......
}

package com.tzx.ne;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.Buffer;
import java.nio.ByteBuffer;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;

public class MappedByteBufferDemo {
    public static void main(String[] args) throws Exception{
        /**
         * output: 0.001s(读)
         * input: 0.11s(写)
         * */
        MappedByteBufferTest();
        /**
         * size=1024*8
         * out: 0.0s
         * input: 0.014s
         * */
        /**
         * size=1024*1024*8
         * output: 0.01s
         * input: 0.014s
         * */
        /**
         * size=80
         * output: 0.0s
         * input: 0.546s
         * */
        //BufferTest();
        /**
         * time: 0.585s
         * */
        //BufferedInputStreamTest();
    }
    
    
    
    /*
     * 测试结果与Buffer size有关
     */
    // 1、使用MappedByteBuffer: 0.7s
    public static void MappedByteBufferTest() throws Exception{
        String srcFile = "F:\\Ebook\\偷天.txt";
        String destFile = "F:\\Ebook\\toutian.txt";
        RandomAccessFile rafi = new RandomAccessFile(srcFile, "r");
        RandomAccessFile rafo = new RandomAccessFile(destFile, "rw");
        FileChannel fci = rafi.getChannel();
        FileChannel fco = rafo.getChannel();
        long size = fci.size();
        byte b;
        long start = System.currentTimeMillis();
        MappedByteBuffer mbbi = fci.map(FileChannel.MapMode.READ_ONLY, 0, size);
        System.out.println("output: " + (double) (System.currentTimeMillis() - start) / 1000 + "s");
        MappedByteBuffer mbbo = fco.map(FileChannel.MapMode.READ_WRITE, 0, size);
        start = System.currentTimeMillis();
        for (int i = 0; i < size; i++) {
            b = mbbi.get(i);
            mbbo.put(i, b);
        }
        fci.close();
        fco.close();
        rafi.close();
        rafo.close();
        System.out.println("input: " + (double) (System.currentTimeMillis() - start) / 1000 + "s");
    }


    // 2、自己处理Buffer(RandomAccessFile): 0.13s    
    public static void BufferTest() throws Exception{
        String srcFile = "F:\\Ebook\\偷天.txt";
        String destFile = "F:\\Ebook\\toutian.txt";
        RandomAccessFile rafi = new RandomAccessFile(srcFile, "r");
        RandomAccessFile rafo = new RandomAccessFile(destFile, "rw");

        byte[] buf = new byte[80];
        long start = System.currentTimeMillis();
        int c = rafi.read(buf);
        System.out.println("output: " + (double) (System.currentTimeMillis() - start) / 1000 + "s");
        start = System.currentTimeMillis();
        while (c > 0) {
            if (c == buf.length) {
                rafo.write(buf);
            } else {
                rafo.write(buf, 0, c);
            }

            c = rafi.read(buf);
        }
        System.out.println("input: " + (double) (System.currentTimeMillis() - start) / 1000 + "s");
        rafi.close();
        rafo.close();

    }

    // 3、BufferedInputStream&BufferedOutputStream: 3.02s
    public static void BufferedInputStreamTest() throws Exception{
        String srcFile = "F:\\Ebook\\偷天.txt";
        String destFile = "F:\\Ebook\\toutian.txt";
        FileInputStream rafi = new FileInputStream(srcFile);
        FileOutputStream rafo = new FileOutputStream(destFile);

        BufferedInputStream bis = new BufferedInputStream(rafi, 8192);
        BufferedOutputStream bos = new BufferedOutputStream(rafo, 8192);
        long size = rafi.available();

        long start = System.currentTimeMillis();

        for (int i = 0; i < size; i++) {
            byte b = (byte) bis.read();
            bos.write(b);
        }
        rafi.close();
        rafo.close();
        System.out.println("time: " + (double) (System.currentTimeMillis() - start) / 1000 + "s");

    }
}