OkHttp初探2：如何使用OkHttp進行下載封裝？帶進度條？Kotlin+Flow版本。

本文接上一篇博文：OkHttp初探：如何使用OkHttp進行Get或Post請求？Kotlin版本，

通用模塊封裝

這里封裝一寫通用的代碼，先知道一下就可以了，

/**
 * 日志列印
 */
fun log(vararg msg: Any?) {
    val nowTime = SimpleDateFormat("HH:mm:ss:SSS").format(System.currentTimeMillis())
    println("$nowTime [${Thread.currentThread().name}] ${msg.joinToString(" ")}")
}

/**
 * 進度通用回呼  不使用flow封裝的話 使用這個
 */
internal typealias ProgressBlock = (state: DownloadState) -> Unit

/**
 * 下載狀態機
 */
sealed class DownloadState {

    /**
     * 未開始
     */
    object UnStart : DownloadState()

    /**
     * 下載中
     */
    class Progress(var totalNum: Long, var current: Long) : DownloadState()

    /**
     * 下載完成
     */
    class Complete(val file: File?) : DownloadState()

    /**
     * 下載失敗
     */
    class Failure(val e: Throwable?) : DownloadState()

    /**
     * 下載失敗
     */
    class FileExistsNoDownload(val file: File?) : DownloadState()

}

下載檔案，帶進度，一般封裝

fun downloadFile(url: String, destFileDirName: String, progressBlock: ProgressBlock) {
    //下載狀態  默認未開始
    var state: DownloadState = DownloadState.UnStart
    progressBlock(state)

    // TODO: 2021/12/27 file 創建與判斷可以封裝
    /**
     * file 創建判斷  可以封裝
     */
    val file = File(destFileDirName)
    val parentFile = file.parentFile
    if (!parentFile.exists()) {
        parentFile.mkdirs()
    }
    if (file.exists()) {
        //檔案存在 不需要下載
        state = DownloadState.FileExistsNoDownload(file)
        progressBlock(state)
        return
    } else {
        file.createNewFile()
    }

    //下載
    val okHttpClient = OkHttpClient()
    val request = Request.Builder().url(url).build()
    okHttpClient.newCall(request).enqueue(object : Callback {
        override fun onFailure(call: Call, e: IOException) {
            state = DownloadState.Failure(e)
            progressBlock(state)
        }

        override fun onResponse(call: Call, response: Response) {
            response.use { res ->
                //完整長度
                var totalLength = 0L
                //寫入位元組
                val bytes = ByteArray(2048)
                val fileOutputStream = FileOutputStream(file)
                res.body?.also { responseBody ->
                    totalLength = responseBody.contentLength()
                }?.byteStream()?.let { inputStream ->
                    try {
                        var currentProgress = 0L
                        var len = 0
						state = DownloadState.Progress(totalLength, currentProgress)
                        do {
                            if (len != 0) {
                                currentProgress += len
                                fileOutputStream.write(bytes)
                            }
                            //狀態改變
                            (state as DownloadState.Progress).current = currentProgress
                            progressBlock(state)
                            len = inputStream.read(bytes, 0, bytes.size)
                        } while (len != -1)
                        //狀態改變完成
                        state = DownloadState.Complete(file)
                        progressBlock(state)
                    } catch (e: Exception) {
                        state = DownloadState.Failure(e)
                        progressBlock(state)
                    } finally {
                        inputStream.close()
                        fileOutputStream.close()
                    }
                }
            }
        }

    })

}

使用

    downloadFile(
        "https://dldir1.qq.com/weixin/Windows/WeChatSetup.exe",
        "download/WeChatSetup.exe"
    ) { state: DownloadState ->
        when (val s = state) {
            is DownloadState.Complete -> log("下載完成 檔案路徑為 ${s.file?.absoluteFile}")
            is DownloadState.Failure -> log("下載失敗  ${s.e?.message}")
            is DownloadState.FileExistsNoDownload -> log("已經存在  ${s.file?.absoluteFile}")
            is DownloadState.Progress -> log("下載中  ${(s.current.toFloat() / s.totalNum) * 100}%")
            DownloadState.UnStart -> log("下載未開始")
        }
    }

使用flow封裝

對于上述封裝使用起來沒有問題，但是如果在android上面要把進度顯示出來的話，就需要手動切換到UI執行緒了，不太方便，既然都用kotlin了，那么為什么不解除協程Flow封裝呢？

所以，下面基于Flow的封裝就來了，直接切換到Main執行緒，美滋滋，

知識儲備：
Kotlin：Flow 全面詳細指南，附帶原始碼決議，
Flow : callbackFlow使用心得，避免踩坑！

/**
 * 使用Flow改造檔案下載
 * callbackFlow  可以保證執行緒的安全  底層是channel
 */
fun downloadFileUseFlow(url: String, destFileDirName: String) = callbackFlow<DownloadState> {
    var state: DownloadState = DownloadState.UnStart
    send(state)

    //獲取檔案物件
    val file = File(destFileDirName).also { file ->
        val parentFile = file.parentFile
        if (!parentFile.exists()) {
            parentFile.mkdirs()
        }
        if (file.exists()) {
            state = DownloadState.FileExistsNoDownload(file)
            send(state)
            //流關閉，回傳
            close()
            return@callbackFlow
        } else {
            file.createNewFile()
        }
    }
    //下載
    val okHttpClient = OkHttpClient().newBuilder()
        .dispatcher(dispatcher)
        .writeTimeout(30, TimeUnit.MINUTES)
        .readTimeout(30, TimeUnit.MINUTES)
        .build()
    val request = Request.Builder()
        .url(url)
        .build()
    okHttpClient.newCall(request).enqueue(object : Callback {
        override fun onFailure(call: Call, e: IOException) {
            //更新狀態
            state = DownloadState.Failure(e)
            this@callbackFlow.trySendBlocking(state)
            close()
        }

        override fun onResponse(call: Call, response: Response) {
            //下載
            val body = response.body
            if (response.isSuccessful && body != null) {
                //完整長度
                val totalNum: Long = body.contentLength()
                //當前下載的長度
                var currentProgress: Long = 0L
                var len = 0

                response.use {
                    //等效于   FileOutputStream(file)  輸出流
                    val outputStream = file.outputStream()
                    //輸入流
                    val byteStream = body.byteStream()
                    try {
                        val bates = ByteArray(2048)

                        //設定狀態物件拉出來，避免回圈一直創建物件
                        state = DownloadState.Progress(totalNum, currentProgress)
                        //回圈讀寫
                        do {
                            if (len != 0) {
                                currentProgress += len
                                outputStream.write(bates)
                            }
                            //更新進度
                            (state as DownloadState.Progress).current = currentProgress
                            this@callbackFlow.trySendBlocking(state)
                            len = byteStream.read(bates, 0, bates.size)
                        } while (len != -1)
                        //下載完成
                        state = DownloadState.Complete(file)
                        this@callbackFlow.trySendBlocking(state)
                    } catch (e: Exception) {
                        state = DownloadState.Failure(e)
                        this@callbackFlow.trySendBlocking(state)
                    } finally {
                        outputStream.close()
                        byteStream.close()
                        //關閉callbackFlow
                        this@callbackFlow.close()
                    }
                }

            } else {
                //更新狀態且關閉
                state = DownloadState.Failure(Exception(response.message))
                this@callbackFlow.trySendBlocking(state)
                close()
            }
        }

    })
    //使用channelFlow 必須使用awaitClose 掛起flow等待channel結束
    awaitClose {
        log("callbackFlow關閉 .")
    }
}
    .buffer(Channel.CONFLATED) //設定 立即使用最新值 buffer里面會呼叫到fuse函式，繼而呼叫到create函式重新創建channelFlow
    .flowOn(Dispatchers.Default) //直接設定callbackFlow執行在異步執行緒
    .catch { e ->
        //例外捕獲重新發射
        emit(DownloadState.Failure(e))
    }

使用

    //這里使用runBlocking只是為了跑程式，一般和lifecycleScope等合作使用
    runBlocking(Dispatchers.Main) {
        downloadFileUseFlow(
            "https://dldir1.qq.com/weixin/Windows/WeChatSetup.exe",
            "download/WeChatSetup.exe"
        ).onEach { downloadState ->
            when (downloadState) {
                is DownloadState.Complete -> log("下載完成 檔案路徑為 ${downloadState.file?.absoluteFile}")
                is DownloadState.Failure -> log("下載失敗  ${downloadState.e?.message}")
                is DownloadState.FileExistsNoDownload -> log("已經存在  ${downloadState.file?.absoluteFile}")
                is DownloadState.Progress -> log("下載中  ${(downloadState.current.toFloat() / downloadState.totalNum) * 100}%")
                DownloadState.UnStart -> log("下載未開始")
            }
        }.launchIn(this)
            .join()
    }

以上就是博主提供的兩種簡單的封裝方式了，

后面會陸續推出OkHttp高階使用，以及OkHttp原始碼分析博客，覺得不錯關注博主哈~😎
創作不易，如有幫助一鍵三連咯🙆?♀?，歡迎技術探頭噢！