Java实现断点下载服务端与客户端的示例代码

Range:bytes=300-800
//客户端需要文件300-800字节范围的数据（即500B数据）

Range:bytes=300-
//客户端需要文件300字节之后的数据

/**
 * 断点下载文件
 *
 * @return
 */
@GetMapping("download")
public void download( HttpServletRequest request, HttpServletResponse response) throws IOException {
    //todo 这里文件按照你的需求调整
    File file = new File("D:\\temp\\测试文件.zip");
    if (!file.exists()) {
        response.setStatus(HttpStatus.NOT_FOUND.value());
        return;
    }
    long fromPos = 0;
    long downloadSize = file.length();

    if (request.getHeader("Range") != null) {
        response.setStatus(HttpServletResponse.SC_PARTIAL_CONTENT);
        String[] ary = request.getHeader("Range").replaceAll("bytes=", "").split("-");
        fromPos = Long.parseLong(ary[0]);
        downloadSize = (ary.length < 2 ? downloadSize : Long.parseLong(ary[1])) - fromPos;
    }
    //注意下面设置的相关请求头
    response.setContentType(MediaType.APPLICATION_OCTET_STREAM_VALUE);
    //相当于设置请求头content-length
    response.setContentLengthLong(downloadSize);

    //使用URLEncoder处理中文名(否则会出现乱码)
    response.setHeader("Content-Disposition", "attachment;filename="   URLEncoder.encode(file.getName(), "UTF-8"));
    response.setHeader("Accept-Ranges", "bytes");
    response.setHeader("Content-Range", String.format("bytes %s-%s/%s", fromPos, (fromPos   downloadSize), downloadSize));

    RandomAccessFile randomAccessFile = new RandomAccessFile(file, "rw");
    randomAccessFile.seek(fromPos);

    FileChannel inChannel = randomAccessFile.getChannel();
    WritableByteChannel outChannel = Channels.newChannel(response.getOutputStream());

    try {
        while (downloadSize > 0) {
            long count = inChannel.transferTo(fromPos, downloadSize, outChannel);
            if (count > 0) {
                fromPos  = count;
                downloadSize -= count;
            }
        }
        inChannel.close();
        outChannel.close();
        randomAccessFile.close();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

implementation 'com.squareup.okhttp3:okhttp:3.9.0'

package com.tyky.update.utils;

import com.blankj.utilcode.util.ThreadUtils;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.math.BigDecimal;
import java.nio.ByteBuffer;
import java.nio.channels.Channels;
import java.nio.channels.FileChannel;
import java.nio.channels.ReadableByteChannel;

import okhttp3.Call;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;

public class FileDownloadUtil {

    public static void download(String url, File file, OnDownloadListener listener) {

        //http://10.232.107.44:9060/swan-business/file/download
        // 利用通道完成文件的复制(非直接缓冲区)
        ThreadUtils.getIoPool().submit(new Runnable() {
            @Override
            public void run() {
                try {

                    //续传开始的进度
                    long startSize = 0;
                    if (file.exists()) {
                        startSize = file.length();
                    }
                    OkHttpClient okHttpClient = new OkHttpClient.Builder().build();
                    Request request = new Request.Builder().url(url)
                            .addHeader("Range", "bytes="   startSize)
                            .get().build();
                    Call call = okHttpClient.newCall(request);
                    Response resp = call.execute();

                    double length = Long.parseLong(resp.header("Content-Length")) * 1.0;
                    InputStream fis = resp.body().byteStream();
                    ReadableByteChannel fisChannel = Channels.newChannel(fis);

                    RandomAccessFile randomAccessFile = new RandomAccessFile(file, "rw");
                    //从上次未完成的位置开始下载
                    randomAccessFile.seek(startSize);
                    FileChannel foschannel = randomAccessFile.getChannel();

                    // 通道没有办法传输数据，必须依赖缓冲区
                    // 分配指定大小的缓冲区
                    ByteBuffer byteBuffer = ByteBuffer.allocate(1024);

                    // 将通道中的数据存入缓冲区中
                    while (fisChannel.read(byteBuffer) != -1) {  // fisChannel 中的数据读到 byteBuffer 缓冲区中
                        byteBuffer.flip();  // 切换成读数据模式
                        // 将缓冲区中的数据写入通道
                        foschannel.write(byteBuffer);

                        final double progress = (foschannel.size() / length);
                        BigDecimal two = new BigDecimal(progress);
                        double result = two.setScale(2,BigDecimal.ROUND_HALF_UP).doubleValue();
                        //计算进度，回调
                        if (listener != null) {
                            listener.onProgress(result);
                        }
                        byteBuffer.clear();  // 清空缓冲区
                    }
                    foschannel.close();
                    fisChannel.close();
                    randomAccessFile.close();

                    if (listener != null) {
                        listener.onSuccess(file);
                    }
                } catch (IOException e) {
                    if (listener != null) {
                        listener.onError(e);
                    }

                }
            }
        });


    }

    public interface OnDownloadListener {
        void onProgress(double progress);

        void onError(Exception e);

        void onSuccess(File outputFile);
    }
}

FileDownloadUtil.download(downloadUrl, file, new FileDownloadUtil.OnDownloadListener() {
    @Override
    public void onProgress(double progress) {
        KLog.d("下载进度: "   progress);
    }

    @Override
    public void onError(Exception e) {
        KLog.e("下载错误: "   e.getMessage());
    }

    @Override
    public void onSuccess(File outputFile) {
        KLog.d("下载成功");
    }
});