浅谈一下Java多线程断点复制

public void schedule(TimerTask task, long delay, long period)

package draGon.local;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectOutputStream;
import java.util.List;
import java.util.Timer;
import java.util.TimerTask;

public class RecordTask extends TimerTask {
	public static final String filename = "breakPointRecord.txt";
	private Timer timer;
	private List<FileCopyThread> copyThreads;
	private String outputPath;
	
	public RecordTask(Timer timer, List<FileCopyThread> copyThreads, String outputPath) {
		this.timer = timer;
		this.copyThreads = copyThreads;
		this.outputPath = outputPath;
	}
	
	@Override
	public void run() {
		try {
			this.breakPointRecord();
		} catch (IOException e) {
			e.printStackTrace();
		}
	}
	
	public void breakPointRecord() throws FileNotFoundException, IOException {
		int aliveThreadNum = 0;  //存活线程数目
		//不使用追加方式，这里只需要最新的记录即可。
		File recordFile = new File(outputPath, filename);
		try (ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(recordFile))){
			//每次记录一个线程的下载位置，但是取出来又需要进行转换，太麻烦了。
			//我们直接使用序列化来进行操作，哈哈！
			long[] curlen = new long[4];
			int index = 0;
			for (FileCopyThread copyThread : copyThreads) {
				if (copyThread.isAlive()) {
					aliveThreadNum++;
				}
				curlen[index++] = copyThread.getCurlen();
				System.out.println(index+" curlen: "+copyThread.getCurlen());
			}
			//创建 Record 对象，并序列化。
			oos.writeObject(new Record(curlen));
		}
		//当所有的线程都死亡时，关闭计时器，删除记录文件。（所有线程死亡的话，就是文件已经复制完成了！）
		if (aliveThreadNum == 0) {
			timer.cancel();
			recordFile.delete();
		}
		System.out.println("线程数量： "+aliveThreadNum);
	}
}

if (aliveThreadNum == 0) {
	timer.cancel();
	recordFile.delete();
}

package dragon.local;

import java.io.Serializable;

public class Record implements Serializable{
	
	private static final long serialVersionUID = 1L;
	private long[] curlen;
	
	public Record(long[] curlen) {
		this.curlen = curlen;
	} 
	
	public long[] getCurlen() {
		return this.curlen;
	}
}

package dragon.local;

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

public class FileCopyThread extends Thread {
	private int index;
	private long position;
	private long size;
	private File targetFile;
	private File outputFile;
	private long curlen;      //当前下载的长度
	
	public FileCopyThread(int index, long position, long size, File targetFile, File outputFile) {
		this.index = index;
		this.position = position;
		this.size = size;
		this.targetFile = targetFile;
		this.outputFile = outputFile;
		this.curlen = 0L;
	}
	
	@Override
	public void run() {
		try (
			BufferedInputStream bis = new BufferedInputStream(new FileInputStream(targetFile));
			RandomAccessFile raf = new RandomAccessFile(outputFile, "rw")){
			bis.skip(position);  //跳过不需要读取的字节数，注意只能先后跳
			raf.seek(position);  //跳到需要写入的位置，没有这句话，会出错，但是很难改。
			int hasRead = 0;
			byte[] b = new byte[1024];
			
			while(curlen < size && (hasRead = bis.read(b)) != -1) {
				raf.write(b, 0, hasRead);
				curlen += (long)hasRead;
				//强制停止程序。
//				if (curlen > 17_000_000) {
//					System.exit(0);
//				}
			}

			System.out.println(index+" "+position+" "+curlen+" "+size);
		} catch (IOException e) {
			e.printStackTrace();
		}
	}
	
	public long getCurlen() {   //获取当前的进度，用于记录，以便必要时恢复读取进度。
		return position+this.curlen;
	}
}

				//强制停止程序。
//				if (curlen > 17_000_000) {
//					System.exit(0);
//				}

package dragon.local;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.RandomAccessFile;
import java.util.ArrayList;
import java.util.List;
import java.util.Timer;





public class FileCopyUtil {
	//设置一个常量，复制线程的数量
	private static final int THREAD_NUM = 4;
	
	private FileCopyUtil() {}
	
	
	public static void transferFile(String targetPath, String outputPath) throws IOException, ClassNotFoundException {
		File targetFile = new File(targetPath);
		File outputFilePath = new File(outputPath);
		if (!targetFile.exists() || targetFile.isDirectory()) {   //目标文件不存在，或者是一个文件夹，则抛出异常
			throw new FileNotFoundException("目标文件不存在："+targetPath);
		}
		if (!outputFilePath.exists()) {     //如果输出文件夹不存在，将会尝试创建，创建失败，则抛出异常。
			if(!outputFilePath.mkdir()) {
				throw new FileNotFoundException("无法创建输出文件："+outputPath);
			}
		}
		
		long len = targetFile.length();
		
		File outputFile = new File(outputFilePath, "copy"+targetFile.getName());
		createOutputFile(outputFile, len);    //创建输出文件，设置好大小。
		
		//创建计时器 Timer 对象
		Timer timer = new Timer();
	
		long[] position = new long[4];
		//每一个线程需要复制文件的起点
		long size = len / FileCopyUtil.THREAD_NUM + 1;     //保存复制线程的集合
		List<FileCopyThread> copyThreads = new ArrayList<>();
		Record record = getRecord(outputPath);
		
		for (int i = 0; i < FileCopyUtil.THREAD_NUM; i++) {
			//如果已经有了 记录文件，就从使用记录数据，否则就是新的下载。
			position[i] = record == null ? i*size : record.getCurlen()[i];
			FileCopyThread copyThread = new FileCopyThread(i, position[i], size, targetFile, outputFile);
			copyThread.start();     //启动复制线程
			copyThreads.add(copyThread);   //将复制线程添加到集合中。
		}
	
		timer.schedule(new RecordTask(timer, copyThreads, outputPath), 0L, 100L);  //立即启动计时器，每隔10秒记录一次位置。
		System.out.println("开始了！");
	}
	
	//创建输出文件，设置好大小。
	private static void createOutputFile(File file, long length) throws IOException {
		try (   
			RandomAccessFile raf = new RandomAccessFile(file, "rw")){
			raf.setLength(length);
		}
	}
	
	//获取以及下载的位置
	private static Record getRecord(String outputPath) throws FileNotFoundException, IOException, ClassNotFoundException {
		File recordFile = new File(outputPath, RecordTask.filename);
		if (recordFile.exists()) {
			try (ObjectInputStream ois = new ObjectInputStream(new FileInputStream(recordFile))){
				return (Record) ois.readObject();
			}
		}
		return null;
	}
}

private static Record getRecord(String outputPath) throws FileNotFoundException, IOException, ClassNotFoundException {
		File recordFile = new File(outputPath, RecordTask.filename);
		if (recordFile.exists()) {
			try (ObjectInputStream ois = new ObjectInputStream(new FileInputStream(recordFile))){
				return (Record) ois.readObject();
			}
		}
		return null;
	}

//如果已经有了 记录文件，就从使用记录数据，否则就是新的下载。
position[i] = record == null ? i*size : record.getCurlen()[i];