JavaScript进阶之前端文件上传和下载示例详解

2024-04-02 19:55

短信预约 -IT技能 免费直播动态提醒

文件下载

1.通过a标签点击直接下载

<a href="https:xxx.xlsx" rel="external nofollow"  download="test">下载文件</a>

download属性标识文件需要下载且下载名称为test

如果有 Content-Disposition 响应头，则不需要设置download属性就能下载，文件名在响应头里面由后端控制

此方法有同源和请求headers鉴权的问题

2.open或location.href

window.open('xxx.zip');
location.href = 'xxx.zip';

需要注意 url 长度和编码问题

不能直接下载浏览器默认预览的文件，如txt、图片

3.Blob和Base64

function downloadFile(res, Filename) {
  // res为接口返回数据，在请求接口的时候可进行鉴权
  if (!res) return;
  // IE及IE内核浏览器
  if ("msSaveOrOpenBlob" in navigator) {
    navigator.msSaveOrOpenBlob(res, name);
    return;
  }
  const url = URL.createObjectURL(new Blob([res]));
  //  const fileReader = new FileReader();  使用 Base64 编码生成
  // fileReader.readAsDataURL(res);
  // fileReader.onload = function() { ...此处逻辑和下面创建a标签并释放代码一致，可从fileReader.result获取href值...}
  const a = document.createElement("a");
  a.style.display = "none";
  a.href = url;
  a.download = Filename;
  document.body.appendChild(a);
  a.click();
  document.body.removeChild(a);
  URL.revokeObjectURL(url); // 释放blob对象
}

注意请求发送的时候注明 responseType = "blob"，如无设置则需要 new Blob的时候传入第二个参数，如

new Blob([res], { type: xhr.getResponseHeader("Content-Type") });

此方法可以解决请求headers鉴权和下载浏览器默认直接预览的文件，并得知下载进度

文件上传

文件上传思路

File文件

MDN描述

上传单个文件-客户端

<input id="uploadFile" type="file" accept="image
async function getFileHash(fileList) {
  console.time("filehash");
  const spark = new SparkMD5.ArrayBuffer();
  // 获取全部内容
  const result = fileList.map((item, key) => {
    return getFileContent(item.file);
  });
  try {
    const contentList = await Promise.all(result);
    for (let i = 0; i < contentList.length; i++) {
      spark.append(contentList[i]);
    }
    // 生成指纹
    const res = spark.end();
    console.timeEnd("filehash");
    return res;
  } catch (e) {
    console.log(e);
  }
}

async function getFileHash2(fileList) {
  console.time("filehash");
  const spark = new SparkMD5.ArrayBuffer();
  // 获取全部内容
  const content = await getFileContent(fileList);
  try {
    spark.append(content);
    // 生成指纹
    const result = spark.end();
    console.timeEnd("filehash");
    return result;
  } catch (e) {
    console.log(e);
  }
}

function getFileContent(file) {
  return new Promise((resolve, reject) => {
    const fileReader = new FileReader();
    // 读取文件内容
    fileReader.readAsArrayBuffer(file);
    fileReader.onload = (e) => {
      // 返回读取到的文件内容
      resolve(e.target.result);
    };
    fileReader.onerror = (e) => {
      reject(fileReader.error);
      fileReader.abort();
    };
  });
}

async function uploadChunks(chunks, fileName) {
  const requestList = chunks
    .map(({ chunk, hash, fileHash, index, fileCount, size, totalSize }) => {
      //生成每个切片上传的信息
      const formData = new FormData();
      formData.append("hash", hash);
      formData.append("index", index);
      formData.append("fileCount", fileCount);
      formData.append("size", size);
      formData.append("splitSize", DefaultChunkSize);
      formData.append("fileName", fileName);
      formData.append("fileHash", fileHash);
      formData.append("chunk", chunk);
      formData.append("totalSize", totalSize);
      return { formData, index };
    })
    .map(async ({ formData, index }) =>
      singleRequest({
        url: "http://127.0.0.1:3000/uploadBigFile",
        data: formData,
      })
    );
  //全部上传
  await Promise.all(requestList);
}

function singleRequest({ url, method = "post", data, headers = {} }) {
  return new Promise((resolve) => {
    const xhr = new XMLHttpRequest();
    xhr.open(method, url);
    Object.keys(headers).forEach((key) => xhr.setRequestHeader(key, headers[key]));
    xhr.send(data);
    xhr.onload = (e) => {
      resolve({
        data: e.target.response,
      });
    };
  });
}
window.upload = {
  start: start,
};

大文件上传-服务端

...
import { checkFileIsMerge, chunkMerge } from "./upload";
const multiparty = require("multiparty");
const fse = require("fs-extra");
// 上传成功后返回URL地址
const resourceUrl = `http://127.0.0.1:${port}/`;
// 存储文件目录
const uploadDIr = path.join(__dirname, "/upload");
//设置静态访问目录
app.use(express.static(uploadDIr));
const extractExt = (filename) => filename.slice(filename.lastIndexOf("."), filename.length); // 提取后缀名
app.post("/uploadBigFile", function (req, res, _next) {
  const multipart = new multiparty.Form();
  multipart.parse(req, async (err, fields, files) => {
    if (err) {
      console.error(err);
      return res.json({
        code: 5000,
        data: null,
        msg: "上传文件失败",
      });
    }
    //取出文件内容
    const [chunk] = files.chunk;
    //当前chunk 文件hash
    const [hash] = fields.hash;
    //大文件的hash
    const [fileHash] = fields.fileHash;
    //大文件的名称
    const [fileName] = fields.fileName;
    //切片索引
    const [index] = fields.index;
    //总共切片个数
    const [fileCount] = fields.fileCount;
    //当前chunk 的大小
    // const [size] = fields.size;
    const [splitSize] = fields.splitSize;
    //整个文件大小
    const [totalSize] = fields.totalSize;
    const saveFileName = `${fileHash}${extractExt(fileName)}`;
    //获取整个文件存储路径
    const filePath = path.resolve(uploadDIr, saveFileName);
    const chunkDir = path.resolve(uploadDIr, fileHash);
    // 大文件存在直接返回,根据内容hash存储，可以实现后续秒传
    if (fse.existsSync(filePath)) {
      return res.json({
        code: 1000,
        data: { url: `${resourceUrl}${saveFileName}` },
        msg: "上传文件已存在",
      });
    }
    // 切片目录不存在，创建切片目录
    if (!fse.existsSync(chunkDir)) {
      await fse.mkdirs(chunkDir);
    }
    const chunkFile = path.resolve(chunkDir, hash);
    if (!fse.existsSync(chunkFile)) {
      await fse.move(chunk.path, path.resolve(chunkDir, hash));
    }
    const isMerge = checkFileIsMerge(chunkDir, Number(fileCount), fileHash);
    if (isMerge) {
      //合并
      await chunkMerge({
        filePath: filePath,
        fileHash: fileHash,
        chunkDir: chunkDir,
        splitSize: Number(splitSize),
        fileCount: Number(fileCount),
        totalSize: Number(totalSize),
      });
      return res.json({
        code: 1000,
        data: { url: `${resourceUrl}${saveFileName}` },
        msg: "文件上传成功",
      });
    } else {
      return res.json({
        code: 200,
        data: { url: `${resourceUrl}${filePath}` },
        msg: "文件上传成功",
      });
    }
  });
});

upload.ts

const fse = require("fs-extra");
const path = require("path");

const pipeStream = (path, writeStream) =>
    new Promise((resolve) => {
        const readStream = fse.createReadStream(path);
        readStream.on("end", () => {
            // fse.unlinkSync(path);
            resolve(null);
        });
        readStream.pipe(writeStream);
    });

export async function chunkMerge({
    filePath,
    fileHash,
    chunkDir,
    splitSize,
    fileCount,
    totalSize,
}) {
    const chunkPaths = await fse.readdir(chunkDir);
    //帅选合适的切片
    const filterPath = chunkPaths.filter((item) => {
        return item.includes(fileHash);
    });
    //数量不对，抛出错误
    if (filterPath.length !== fileCount) {
        console.log("合并错误");
        return;
    }
    // 根据切片下标进行排序,方便合并
    filterPath.sort((a, b) => a.split("-")[1] - b.split("-")[1]);
    await Promise.all(
        chunkPaths.map((chunkPath, index) => {
            //并发写入，需要知道开始和结束位置
            let end = (index + 1) * splitSize;
            if (index === fileCount - 1) {
                end = totalSize + 1;
            }
            return pipeStream(
                path.resolve(chunkDir, chunkPath),
                // 指定位置创建可写流
                fse.createWriteStream(filePath, {
                    start: index * splitSize,
                    end: end,
                })
            );
        })
    );
    //删除所有切片
    // fse.rmdirSync(chunkDir); // 合并后删除保存切片的目录
    return filePath;
}


export function checkFileIsMerge(pathName, totalCount, hash) {
    var dirs = [];
    //同步读取切片存储目录
    const readDir = fse.readdirSync(pathName);
    //判断目录下切片数量 小于 总切片数，不能合并
    if (readDir && readDir.length < totalCount) return false;
    //获取目录下所有真正属于该文件的切片，以大文件hash为准
    (function iterator(i) {
        if (i == readDir.length) {
            return;
        }
        const curFile = fse.statSync(path.join(pathName, readDir[i]));
        //提出目录和文件名不包含大文件hash的文件
        if (curFile.isFile() && readDir[i].includes(hash + "")) {
            dirs.push(readDir[i]);
        }
        iterator(i + 1);
    })(0);
    //数量一直，可以合并
    if (dirs.length === totalCount) {
        return true;
    }
    return false;
}

这里的大文件上传有几处问题，我没有解决，留给各位思考啦