vue+element-ui，用el-upload实现阿里云Oss文件上传和下载

1：利用http-request自定义上传去覆盖默认上传事件。

2：由于上传的格式是FormData格式，首先需要在请求拦截的地方配置，改掉请求头部分。需要后台配置，不然显示跨域。

axios.interceptors.request.use(
  config => {
// 在这里加if语句判断，配置Content-Type 和 Access-Control-Allow-Origin
    if (
      config.headers &&
      config.headers["Content-Type"] === "multipart/form-data"
    ) {
      config.headers = {
        "Content-Type": "multipart/form-data",
        Authorization: token,
        device: "wap",
        Language: "zh-CN",
        "Access-Control-Allow-Origin": "*"
      };
    } else {
      if (typeof config.data !== "string") {
        config.data = JSON.stringify(config.data);
      }
      config.headers = {
        "Content-Type": "application/json",
        Authorization: token,
        device: "wap",
        Language: "zh-CN"
      };
    }
    return config;
  },
  error => {
    return Promise.reject(error);
  }
);

3：覆盖默认上传事件后，首先获取阿里的签名认证，再往接口里上传文件

aliaCustomReq(e) {
//这里获取阿里的签名认证
      this.$get("ailiUrl").then(res => {
        const serve = res;
// 传给后端的文件格式类型
        const formData = new FormData();
        let now = new Date().getTime();
//这一步是给fileList赋值，在做这个需求的时候，onchange拿到的参数不全，不建议用，建议在这里去赋值操作
        let newFile = {};
        for (let item in e.file) {
          newFile[item] = e.file[item];
        }
        formData.append("key", serve.dir + now + "_" + e.file.name);
        formData.append("OSSAccessKeyId", serve.accessid);
        formData.append("policy", serve.policy);
        formData.append("Signature", serve.signature);
        formData.append("callback", serve.callback);
        formData.append("success_action_status", "200");
        formData.append("file", e.file);
//传递参数，改变请求头
        this.$post(serve.host, formData, {
          "Content-Type": "multipart/form-data"
        }).then(data => {
          if (data) {
            newFile.url = data["host"] + "/" + data["filename"];
            if (!this.fileList) {
              this.fileList = [];
            }
            this.fileList.push(newFile);
          }
        });
      });
    }

4.下载功能 npm install ali-oss --save-dev 下载官网的包

AliPreview(file) {
      this.$get("aliUrl").then(res => {
        // 引入ali-oss文件
        let OSS = require("ali-oss");
        //https://help.aliyun.com/document_detail/111371.html 阿里云官方文档
        let client = new OSS({
          region: res.region,
          accessKeyId: res.accessid,
          accessKeySecret: res.accessKey,
          bucket: res.bucket
        });

        let objName = file.url
          .replace(res.host + "/", "")
          .replace(res.customName + "/", "");
        if (objName.includes("?")) {
          objName = objName.substring(0, objName.indexOf("?"));
        }
        let url = client.signatureUrl(objName, {
          response: {
            "content-disposition": `attachment; filename=${file.name}`
          }
        });
        url = url.replace(res.host, res.customName);
        console.log(url, "下载地址");
//此处为手机预览 pc预览用window.open
        window.location.href = url;
      });
    }

5.限制上传文件格式的话可在before-upload钩子函数里操作，