JAVA多线程文件拷贝

多线程文件拷贝，具体使用了RandomAccessFile类，对源文件进行随机读，对目标文件进行随机写入。需注意需在线程内部去实例化RandomAccessFile类，进行操作避免资源句柄共享造成异常。

import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;

public class FixedFile {

    public static void main(String[] args) throws Exception {
            File f = new File("a.txt");
            long length = f.length();
            System.out.println(length);
            int threadNum = 3;
            int split ;
            if(length%3==0){
                 split = (int) (length/3);
            } else{
                 split = (int) (length/3) + 1;
            }
            System.out.println(split);

            String src = "a.txt";
            String dest = "b.txt";
            //先建立目标文件
            RandomAccessFile destFile = new RandomAccessFile(dest,"rw");
            destFile.setLength(length);
            destFile.close();

            for(int i =0; i<threadNum;i++ ) {
                new Thread(new MultiCopy(src,dest, i*split,split) ).start();
            }
    }

}
class MultiCopy implements Runnable{

    private String from;
    private String dest;
    private int offset;
    private int length;
    public MultiCopy(String from,String dest,int offset, int length) {
        this.from = from;
        this.dest=dest;
        this.offset=offset;
        this.length=length;
    }

    @Override
    public void run() {
        RandomAccessFile srcFile = null;
        RandomAccessFile destFile = null;
        try {
            srcFile = new RandomAccessFile(from,"r");
            destFile = new RandomAccessFile(dest,"rw");
            srcFile.seek(offset);
            destFile.seek(offset);
            byte [] buff = new byte[1024]; //缓冲区大小
            int num = (length % 1024 ==0) ? (length / 1024) :(length / 1024 + 1) ; //迭代次数
            for(int i=0;i<num;i++) {
                int perLength = srcFile.read(buff);
                if(perLength != -1) {
                    destFile.write(buff);
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                destFile.close();
                srcFile.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

}