端，前端通过携带文件请求该URL进行上传。
使用filename请求服务端获取临时访问文件的URL。（最长时间为7 天，想要永久性访问，需要其他设置，这里不做说明。）
下面展示页面html，使用的是VUE+element-ui进行渲染。
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<!-- import CSS -->
<link rel="stylesheet" href="https://unpkg.com/element-ui/lib/theme-chalk/index.css">
<title>上传图片</title>
</head>
<body>
<div id="app">
<el-row :gutter="2">
<el-col :span="8">
<div class="div-center-class">
<div class="">
<center><h3>传统上传</h3></center>
<el-upload
class="upload-demo"
action="#"
drag
:http-request="uploadHandle">
<i class="el-icon-upload"></i>
<div class="el-upload__text">将文件拖到此处，或<em>点击上传</em></div>
<div class="el-upload__tip" slot="tip">只能上传jpg/png文件，且不超过500kb</div>
</el-upload>
<div v-if="imgUrl">
<img :src="imgUrl" style="width: 40px;height: 40px"></img>
</div>
</div>
</div>
</el-col>
<el-col :span="8">
<div class="div-center-class">
<div class="">
<center><h3>前端formData直传</h3></center>
<el-upload
class="upload-demo"
action="#"
drag
:http-request="httpRequestHandle">
<i class="el-icon-upload"></i>
<div class="el-upload__text">将文件拖到此处，或<em>点击上传</em></div>
<div class="el-upload__tip" slot="tip">只能上传jpg/png文件，且不超过500kb</div>
</el-upload>
<div v-if="directUrl">
<img :src="directUrl" style="width: 40px;height: 40px"></img>
</div>
</div>
</div>
</el-col>
<el-col :span="8">
<div class="div-center-class">
<div class="">
<center><h3>前端Url直传</h3></center>
<el-upload
class="upload-demo"
action="#"
drag
:http-request="UrlUploadHandle">
<i class="el-icon-upload"></i>
<div class="el-upload__text">将文件拖到此处，或<em>点击上传</em></div>
<div class="el-upload__tip" slot="tip">只能上传jpg/png文件，且不超过500kb</div>
</el-upload>
<div v-if="uploadUrl">
<img :src="uploadUrl" style="width: 40px;height: 40px"></img>
</div>
</div>
</div>
</el-col>
</el-row>
</div>
</body>
<!-- import Vue before Element -->
<script src="https://unpkg.com/vue/dist/vue.js"></script>
<!-- import java script -->
<script src="https://unpkg.com/element-ui/lib/index.js"></script>
<!--import axios -->
<script src="https://unpkg.com/axios/dist/axios.min