Java中用内存映射处理大文件

在处理大文件时，如果利用普通的FileInputStream 或者FileOutputStream 抑或RandomAccessFile 来进行频繁的读写操作，都将导致进程因频繁读写外存而降低速度.如下为一个对比实验。
[java]
package test;

import java.io.BufferedInputStream;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;

public class Test {


    public static void main(String[] args) {
        try {
            FileInputStream fis=new FileInputStream("/home/tobacco/test/res.txt");
            int sum=0;
            int n;
            long t1=System.currentTimeMillis();
            try {
                while((n=fis.read())>=0){
                    sum+=n;
                }
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            long t=System.currentTimeMillis()-t1;
            System.out.println("sum:"+sum+" time:"+t);
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        try {
            FileInputStream fis=new FileInputStream("/home/tobacco/test/res.txt");
            BufferedInputStream bis=new BufferedInputStream(fis);
            int sum=0;
            int n;
            long t1=System.currentTimeMillis();
            try {
                while((n=bis.read())>=0){
                    sum+=n;
                }
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            long t=System.currentTimeMillis()-t1;
            System.out.println("sum:"+sum+" time:"+t);
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        MappedByteBuffer buffer=null;
        try {
            buffer=new RandomAccessFile("/home/tobacco/test/res.txt","rw").getChannel().map(FileChannel.MapMode.READ_WRITE, 0, 1253244);
            int sum=0;
            int n;
            long t1=System.currentTimeMillis();
            for(int i=0;i<1253244;i++){
                n=0x000000ff&buffer.get(i);
                sum+=n;
            }
            long t=System.currentTimeMillis()-t1;
            System.out.println("sum:"+sum+" time:"+t);
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }

}

    测试文件为一个大小为1253244字节的文件。测试结果：
sum:220152087 time:1464
sum:220152087 time:72
sum:220152087 time:25
    说明读数据无误。删去其中的数据处理部分。
[java]
package test;

import java.io.BufferedInputStream;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;

public class Test {


    public static void main(String[] args) {

补充：软件开发 , Java ,