JavaScript文件上傳和下載

時間 2019-11-22

原文原文鏈接

前一段時間作附件的上傳和下載功能。期間遇到很多問題，網上找的方法都不算完整。這裏把前端和後端的實現都整理一下。前端

須要的東西：JQuery，Pako.js，base64.js。其中pako/base64是爲了對上傳的文件進行壓縮而使用。若是前端有對文件進行壓縮，那麼後端也應該對應進行解壓。node

上傳最簡單的實現：前端選擇一個文件-讀取文件信息-經過ajax請求後端方法把文件信息傳輸並保存(固然，當文件太大，在客戶端應該要分批讀取並上傳，在服務端也是依次分批保存)git

HTML只須要一個input
```
<input type="file" id="filePicker" />
```

JS實現

$(document).ready(function () {
    $(document).on("change", "#filePicker", onFileUpload);
});

function onFileUpload(e) {
    if (!window.FileReader) { // 使用了HTML 5 的 FileReader API。目前大部分瀏覽器都能支持。
        alert("該瀏覽器不支持HTML5，請升級或者更換其它瀏覽器。");
        return;
    }
    var fileInfo = e.currentTarget.files[0];
    var fileName = fileInfo.name;
    var fileSize = fileInfo.size;

    var fileReader = new FileReader();
    //var blob = fileInfo.slice(0, fileSize);
    //fileReader.readAsArrayBuffer(blob);
    fileReader.readAsArrayBuffer(fileInfo);
    fileReader.onload = function (result) {
        var pakoString = getUploadingFileContentString(this.result);
        $.ajax({
            url: "http://localhost/Server/ashx/FileProcess.ashx", //用通常處理程序接收請求
            type: "POST",
            data: {
                fileContent: pakoString,
                fileName: fileName
            },
            success: function (data) {
                if (data == "True") {
                    alert("上傳成功！");
                }
                else {
                    alert("上傳失敗");
                }
            },
            error: function (e) {
                alert(e.responseText);
            }
        });
    }
}

function getUploadingFileContentString(readResult) {
    if (readResult == null) {
        return null;
    }
    var fileContentArr = new Uint8Array(readResult);
    var fileContentStr = "";
    for (var i = 0; i < fileContentArr.length; i++) {
        fileContentStr += String.fromCharCode(fileContentArr[i]);
    }
    //若是不壓縮，直接轉base64 string進行傳輸
    //window.btoa: 將ascii字符串或二進制數據轉換成一個base64編碼過的字符串,該方法不能直接做用於Unicode字符串.
    //var base64FileString = window.btoa(fileContentStr);
    //return base64FileString;

    //壓縮
    var pakoBytes = pako.gzip(fileContentStr);
    var pakoString = fromByteArray(pakoBytes);
    return pakoString;
}

服務端實現

public class FileProcess : IHttpHandler
    {

        public void ProcessRequest(HttpContext context)
        {
            UploadFile(context);
        }

        private void UploadFile(HttpContext context)
        {
            var fileName = context.Request["fileName"];
            var compressedFileContent = context.Request["fileContent"];
            //若是前端沒有對文件進行壓縮，那麼直接獲取文件的字節數組便可
            //byte[] fileBytes = Convert.FromBase64String(compressedFileContent);

            //解壓
            var fileContent = GZip.GZipDecompress(compressedFileContent);
            byte[] fileBytes = Utils.ConvertJSBytes2Str(fileContent);
            bool isSavedSuccess = Utils.SaveFile2Disk(fileBytes, fileName, isUploadPartly);

            context.Response.Write(isSavedSuccess);
        }
}

//其中GZipDecompress/ConvertJSBytes2Str/SaveFile2Disk實現以下
public static string GZipDecompress(string zipString)
        {
            if (string.IsNullOrEmpty(zipString))
            {
                return string.Empty;
            }

            byte[] zipBytes = Convert.FromBase64String(zipString);
            return System.Text.Encoding.UTF8.GetString(Decompress(zipBytes));
        }

private static byte[] Decompress(byte[] zipData)
        {
            MemoryStream m = new MemoryStream(zipData);
            GZipStream zipStream = new GZipStream(m, CompressionMode.Decompress);
            MemoryStream outStream = new MemoryStream();
            byte[] buffer = new byte[1024];
            while (true)
            {
                var readCount = zipStream.Read(buffer, 0, buffer.Length);
                if (readCount <= 0)
                {
                    break;
                }
                outStream.Write(buffer, 0, readCount);
            }
            zipStream.Close();
            return outStream.ToArray();
        }

public static byte[] ConvertJSBytes2Str(string fileContent)
        {
            if (string.IsNullOrEmpty(fileContent))
            {
                return null;
            }
            // JS中，String.fromCharCode接受Unicode字符，並轉成字符串
            byte[] fileBytes = System.Text.Encoding.Unicode.GetBytes(fileContent);
            byte[] adjustedFileBytes = new byte[fileBytes.Length / 2];
            var index = 0;
            for (var i = 0; i < fileBytes.Length; i = i + 2)
            {
                adjustedFileBytes[index] = fileBytes[i];
                index++;
            }

            return adjustedFileBytes;
        }

public static bool SaveFile2Disk(byte[] fileContent, string fileName, bool isSavedPartly = false)
        {
            if (fileContent == null || fileContent.Length == 0)
            {
                throw new ArgumentNullException("文件內容不能爲空!");
            }
            if (string.IsNullOrEmpty(fileName))
            {
                throw new ArgumentNullException("文件名不能爲空!");
            }
            var targetFloder = HttpContext.Current.Server.MapPath("~/UploadFileFloder/");
            var fullPath = Path.Combine(targetFloder, fileName);
            DirectoryInfo di = new DirectoryInfo(targetFloder);
            if (di.Exists == false)
            {
                di.Create();
            }
            FileStream fileStream;
            try
            {
                if (isSavedPartly)
                {
                    fileStream = new FileStream(fullPath, FileMode.Append, FileAccess.Write, FileShare.Read, 1024);
                }
                else
                {
                    fileStream = new FileStream(fullPath, FileMode.Create, FileAccess.ReadWrite);
                }
            }
            catch (Exception ex)
            {
                //throw ex;
                //write log
                return false;
            }
            try
            {
                fileStream.Write(fileContent, 0, fileContent.Length);
            }
            catch (IOException ex)
            {
                //write log
                return false;
            }
            finally
            {
                fileStream.Flush();
                fileStream.Close();
                fileStream.Dispose();
            }
            return true;
        }

這樣，一個簡單的完整的前端到後端的文件上傳保存就完成了github

下載文件。(這裏簡化程序，服務端指定的文件夾裏面已經有待下載的file1.txt)ajax

HTML

<input type="button" id="downloadFileBtn" value="下載"/>

$(document).on("click", "#downloadFileBtn", downloadFile);

function downloadFile()
{
    var fileName = "file1.txt";
    $.ajax({
        url: "http://localhost/Server/ashx/FileProcess.ashx",
        type: "POST",
        success: function (data) {
            var fileContent = window.atob(data);
            saveFile(fileName, fileContent);
        },
        error: function (e) {
            alert(e.responseText);
        }
    });
}

function saveFile(fileName, fileContent) {
        var byteArr = new Array(fileContent.length);
        for (var i = 0; i < fileContent.length; i++) {
            byteArr[i] = fileContent.charCodeAt(i);
        }

        var blob = new Blob([new Uint8Array(byteArr)], { type: "application/octet-stream" });
        var url = window.URL.createObjectURL(blob);

        var a = document.createElement("a");
        if ("download" in a) { // 支持download屬性
            document.body.appendChild(a);
            a.style = "display:none";
            a.href = url;
            //download屬性IE不支持。。。
            a.download = fileName;
            a.click(); // 觸發下載
            //revokeObjectURL會致使firefox不能下載。。。
            //window.URL.revokeObjectURL(url);
            document.body.removeChild(a);
        }
        else { //IE 10+
            if (typeof navigator !== "undefined" && navigator.msSaveOrOpenBlob) {
                return navigator.msSaveOrOpenBlob(blob, name);
            }
        }
}

服務端實現

//ProcessRequest中調用Download

public void Download(HttpContext context)

 { var filePath = Path.Combine(HttpContext.Current.Server.MapPath("~/UploadFileFloder/"), "file1.txt"); byte[] fileContentBytes = Utils.GetByteArrayByFilePath(filePath); context.Response.Write(Convert.ToBase64String(fileContentBytes)); } //其中，GetByteArrayByFilePath實現以下
public static byte[] GetByteArrayByFilePath(string fileFullPath) { if (string.IsNullOrEmpty(fileFullPath)) { return null; } FileStream fs = null; byte[] fileContent = null; try { FileInfo fi = new FileInfo(fileFullPath); fileContent = new byte[fi.Length]; //fs = new FileStream(fileFullPath, FileMode.Open);
                fs = File.OpenRead(fileFullPath); fs.Read(fileContent, 0, fileContent.Length); } catch (Exception ex) { return null; } finally { if (fs != null) { fs.Close(); } } return fileContent; }