java断点下载文件（整合多线程）

@Resource
public RedisUtil redisUtil;

private static final String FILE_PATH = "被拷贝文件路径";
private static final String SAVE_PATH = "拷贝文件路径";
private static final int NUM_THREADS = 3;
private static int stopIndex;

@RequestMapping(value = "/")
public void EndPointTest() {
    try {
        //已经在redis中手动执行redisUtil.set("stopIndex",-1);当stopIndex为-1的时候代表没有发生过断点
        File file = new File(FILE_PATH);
        long fileSize = file.length();
        long chunkSize = fileSize / NUM_THREADS;

        stopIndex = Integer.parseInt(redisUtil.get("stopIndex"));
        if (stopIndex > 0) {
            System.out.println("执行断点下载"); //最好使用log.info
            isEndPoint = true;
            for (int i = 0; i < NUM_THREADS; i++) { 
                long startByte = (i * chunkSize);
                long endByte = (i == NUM_THREADS - 1) ? fileSize - 1 : (i + 1) * chunkSize - 1;
                Thread mergerThread = new MergerThread2(FILE_PATH, SAVE_PATH, startByte, endByte, this.redisUtil);
                mergerThread.start();
            }
        } else {
            System.out.println("执行正常下载");
            isEndPoint = false;
            for (int i = 0; i < NUM_THREADS; i++) {
                long startByte = i * chunkSize;
                long endByte = (i == NUM_THREADS - 1) ? fileSize - 1 : (i + 1) * chunkSize - 1;
                Thread mergerThread = new MergerThread2(FILE_PATH, SAVE_PATH, startByte, endByte, this.redisUtil);
                mergerThread.start();
            }
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
}

public class MergerThread2 extends Thread {

    private String filePath;
    private String savePath;
    private long startByte;
    private long endByte;
    private RedisUtil redisUtil;

    RandomAccessFile inputFile;
    RandomAccessFile outputFile;

    public MergerThread2() { 
    }

    public MergerThread2(String filePath, String savePath, long startByte, long endByte, RedisUtil redisUtil) {
        this.filePath = filePath;
        this.savePath = savePath;
        this.startByte = startByte;
        this.endByte = endByte;
        this.redisUtil = redisUtil;
    }

    public void run() {
        try {
            byte[] buffer = new byte[1];  // 不要设为1024，这样read方法如果只读了2个数据，那就会有1022个0填充数组，调用write(buffer)后，
            // 文件中会出现大量空白，设置为1是想读一个字节后立马写一个字节
            long currentIndex = 0;  //与buffer一样，千万不要写在MergerThread2实现类里面，而要写在run方法里面，不然三个线程在执行后会把
            //buffer和currentIndex变一样，另外currentIndex用于记录已经在文件的什么地方了。

            inputFile = new RandomAccessFile(filePath, "r");
            outputFile = new RandomAccessFile(savePath, "rw");


            int bytesRead = 0; //表示调用read方法后读到了多少字节，这个例子中这个值都是1，但是读到末尾时会变成-1。
            long bytesToRead = endByte - startByte + 1;//表示一共有多少字节需要读
            
            if (DemoController.isEndPoint) {
                currentIndex = Integer.parseInt(redisUtil.get("stopIndex"));
                inputFile.seek(startByte + currentIndex); //在重启程序后，startByte依然是三个线程三等分文件后分别的起始位置，
                // 要手动加上上一次发生断点时的位置，从那里开始读，并从被写入文件的同样位置开始写
                outputFile.seek(startByte + currentIndex);
                while (bytesToRead > 0 && bytesRead!=-1) { //必须要加-1判断，不然读最后一部分数据的线程会死循环。
                    bytesRead = inputFile.read(buffer, 0, 1);
                    outputFile.write(buffer, 0, 1);
                    currentIndex++;
                    redisUtil.set("stopIndex", String.valueOf(currentIndex));
                    bytesToRead -= bytesRead;
                    //Thread.sleep(1000);
                }
                inputFile.close();
                outputFile.close();
                redisUtil.set("stopIndex", "-1"); //重置
            } else {
                inputFile.seek(startByte); //正常下载时，三个线程的startByte是不一样的
                outputFile.seek(startByte);
                while (bytesToRead > 0) {
                    bytesRead = inputFile.read(buffer, 0, 1);
                    outputFile.write(buffer, 0, 1);
                    currentIndex++;
                    redisUtil.set("stopIndex", String.valueOf(currentIndex));
                    bytesToRead -= bytesRead;
                    Thread.sleep(1000); //十秒读一个字节，因为文件很小，不写这句的话文件会瞬间完成拷贝，来不及手动关闭程序设置断点，一定要这样读写文件，注意不要 for(int i=0;i<?;i++){ outputFile.write(buffer[i]); }
                }
            }
            inputFile.close();
            outputFile.close();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            System.exit(0);
        }
    }
}