Android – OkHttp实现的断点续传

/**
 * 获取下载内容的大小
 * @param downloadUrl 文件地址
 * @return 文件字节长度
 */
private fun getContentLength(downloadUrl: String): Long {
    val request = Request.Builder().url(downloadUrl).build()
    try {
        val response = client.newCall(request).execute()
        if (response != null && response.isSuccessful) {
            val contentLength = response.body()?.contentLength() ?: 0L
            response.body()?.close()
            return contentLength
        }
    } catch (e: IOException) {
        e.printStackTrace()
    }
    return 0L
}

/**
 * 下载请求
 * @param fileName 文件名称
 * @param sourceFileName 文件名称
 * @param fileUrl 文件完整地址
 */
private fun downLoadFile(sourceFileName: String,fileName:String, fileUrl: String) {
    //已经下载的文件长度,初始化为0
    //(续载的关键点 = 每次下载的起始位置)
    var downloadLength = 0L
    //下载路径 + 文件名 在本地创建一个文件
    val file = File(downloadFileCacheDir + sourceFileName)
    if (file.exists()) {
        //如果文件存在，得到文件大小
        downloadLength = file.length()
    }
    //得到下载内容的大小
    val contentLength = getContentLength(fileUrl)
    if (contentLength == 0L) {
        //从内存中移除下载任务
        ossFileMap.remove(fileName)
        downLoadTaskMap.remove(fileName)
        onListenerCallBackError(ErrorCode.ERROR_DATA_NULL, "文件错误，长度为0")
        return
    } else if (contentLength == downloadLength) {
        //已下载字节和文件总字节相等，说明已经下载完成了
        ossFileMap.remove(fileName)
        downLoadTaskMap.remove(fileName)
        onListenerCallBackProcess(fileName, contentLength, contentLength)
        onListenerCallBackSuccess(fileName)
        return
    }

    val request = Request.Builder()
            .url(fileUrl)
            .addHeader("RANGE", "bytes=${downloadLength}-")//续传关键(请求头增加)
            .build()
    Logger.d("Down下载：Range = $downloadLength")
    val call = client.newCall(request)
    //加入传载队列
    downLoadTaskMap[fileName] = call
    saveFile(call,file, downloadLength, fileName, contentLength)
}

/**
 * 写入文件到本地
 * @param call 请求回调
 * @param file 需要写入的本地文件
 * @param downloadLength 已下载文件长度
 * @param contentLength 文件总长度
 */
private fun saveFile(call: Call, file: File?, downloadLength: Long, fileName: String, contentLength: Long) {
    var inputStream: InputStream? = null
    var savedFile: RandomAccessFile? = null
    val response = call.execute()
    try {
        if (response != null) {
            inputStream = response.body()?.byteStream()
            savedFile = RandomAccessFile(file, "rw")
            //跳过已经下载的字节
            savedFile.seek(downloadLength)
            //每次缓存字节数
            val byteArray = ByteArray(1024)
            var total = 0
            var len: Int = -1
            while (inputStream?.read(byteArray)?.also { len = it } != -1) {
                //执行缓存前都需判断该任务是否被暂停
                if (call.isCanceled) {
                    Logger.d("Down:${fileName}下载任务已取消")
                    return
                } else {
                    total += len
                    savedFile.write(byteArray, 0, len)
                    //本次下载总长
                    val currentSize = total + downloadLength
                    //回调进度
                    onListenerCallBackProcess(fileName, currentSize, contentLength)
                    //长度相等则返回成功
                    if (currentSize == contentLength) {
                        response.body()?.close()
                        Logger.d("Down:success")
                        //文件与本地路径字典记录到数据库
                        filesLocalService.saveDownPathData(DownLoadFilesValue().apply {
                            this.fileName = fileName
                            this.filePath = file?.path
                        })
                        ossFileMap.remove(fileName)
                        downLoadTaskMap.remove(fileName)
                        //删除本地传载列表
                        deleteFormLocal(fileName)
                        //成功回调
                        onListenerCallBackSuccess(fileName)
                    }
                }
            }
            response.body()?.close()
        }
    } catch (e: Exception) {
        //发生异常时关闭该下载任务
        ossFileMap.remove(fileName)
        downLoadTaskMap.remove(fileName)
        //失败回调
        onListenerCallBackError(ErrorCode.ERROR_EXCEPTION, e.message)
    } finally {
        try {
            inputStream?.close()
            savedFile?.close()
        } catch (e: Exception) {
            e.printStackTrace();
        }
    }
}