快速拷贝文件

package com.demo;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.RandomAccessFile;

public class QuickCopy {

    private static final int threshold = 10*1024;
    
    private static final int max_buf = 1024;
    
    private static final int max_worker = 4;
    
    private File targetFile;
    
    private String targetFileName;
    
    public String getTargetFileName() {
        return targetFileName;
    }

    public void setTargetFileName(String targetFileName) {
        this.targetFile = new File(targetFileName);
        
        this.targetFileName = targetFileName;
    }

    private File sourceFile;
    
    private String sourceFileName;

    public String getSourceFileName() {
        return sourceFileName;
    }

    public void setSourceFileName(String sourceFileName) throws FileNotFoundException {
        this.sourceFile = new File(sourceFileName);
        if(!this.sourceFile.exists() && !this.sourceFile.isFile()) {
            throw new FileNotFoundException();
        }
        this.sourceFileName = sourceFileName;
    }
    
    public QuickCopy(String sourceFileName, String targetFileName) throws FileNotFoundException {
        this.setSourceFileName(sourceFileName);
        this.setTargetFileName(targetFileName);
    }
    
    public void copy() throws IOException{
        createTargetFile();
        if(this.sourceFile.length() > threshold) {
            multiCopy();
        } else {
            singleCopy();
        }
    }
    
    private void createTargetFile() throws IOException {
        long length = this.sourceFile.length();
        File parent = this.targetFile.getParentFile();
        if(parent != null && !parent.exists()) {
            parent.mkdirs();
        }
        RandomAccessFile raf = 
                new RandomAccessFile(
                        this.targetFile.getAbsolutePath(), "rw");
        raf.setLength(length);
        raf.close();
    }
    
    private void singleCopy() throws IOException {
        FileInputStream in = new FileInputStream(this.sourceFile);
        FileOutputStream out = new FileOutputStream(this.targetFile);
        byte[] buf = new byte[max_buf];
        int read = 0;
        while((read = in.read(buf)) > 0) {
            out.write(buf, 0, read);
        }
        in.close();
        out.close();
    }
    
    private void multiCopy() throws IOException {
        long length = this.sourceFile.length();
        long ave = length / max_worker;
        for(int i=0; i<max_worker; i++) {
            if(i == max_worker-1) {
                multiCopy(i*ave, ave, false);
            } else {
                multiCopy(i*ave, ave, true);
            }
        }
    }
    
    private void multiCopy(long start, long total, boolean flag) {
        Thread th = new Thread(new Runnable() {

            @Override
            public void run() {
                try {
                    long ntotal = total;
                    FileInputStream in = 
                            new FileInputStream(sourceFile);
                    RandomAccessFile out = 
                            new RandomAccessFile(targetFile, "rw");
                    try {
                        in.skip(start);
                        out.seek(start);
                        byte[] buf = new byte[max_buf];
                        int read = 0;
                        while(ntotal > 0 
                                && (read = in.read(buf, 0, 
                                    !flag ? max_buf:
                                    (int)(ntotal >= max_buf ? max_buf : max_buf-ntotal))) > 0) 
                        {
                            out.write(buf, 0, read);
                            
                            if(flag) {
                                ntotal -= read;
                            }
                        }
                    } catch (IOException ex) {
                        ex.printStackTrace();
                    } finally {
                        in.close();
                        out.close();
                    }
                    
                    
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            
        });
        th.start();
    }
}