React.js，如何将 multipart/form-data 发送到服务器

Question

我们想将图像文件作为 multipart/form 发送到后端，我们尝试使用 html 表单获取文件并将文件作为 formData 发送，这里是代码

export default class Task extends React.Component {

  uploadAction() {
    var data = new FormData();
    var imagedata = document.querySelector('input[type="file"]').files[0];
    data.append("data", imagedata);

    fetch("http://localhost:8910/taskCreationController/createStoryTask", {
      mode: 'no-cors',
      method: "POST",
      headers: {
        "Content-Type": "multipart/form-data"
        "Accept": "application/json",
        "type": "formData"
      },
      body: data
    }).then(function (res) {
      if (res.ok) {
        alert("Perfect! ");
      } else if (res.status == 401) {
        alert("Oops! ");
      }
    }, function (e) {
      alert("Error submitting form!");
    });
  }

  render() {
    return (
        <form encType="multipart/form-data" action="">
          <input type="file" name="fileName" defaultValue="fileName"></input>
          <input type="button" value="upload" onClick={this.uploadAction.bind(this)}></input>
        </form>
    )
  }
}

后端的错误是 “嵌套异常是 org.springframework.web.multipart.MultipartException：无法解析多部分 servlet 请求；嵌套异常是 java.io.IOException：org.apache.tomcat.util.http.fileupload.FileUploadException：请求被拒绝，因为没有找到多部分边界”。

读完 这篇 文章后，我们尝试在 fetch 中为 headers 设置边界：

 fetch("http://localhost:8910/taskCreationController/createStoryTask", {
      mode: 'no-cors',
      method: "POST",
      headers: {
        "Content-Type": "multipart/form-data; boundary=AaB03x" +
        "--AaB03x" +
        "Content-Disposition: file" +
        "Content-Type: png" +
        "Content-Transfer-Encoding: binary" +
        "...data... " +
        "--AaB03x--",
        "Accept": "application/json",
        "type": "formData"
      },
      body: data
    }).then(function (res) {
      if (res.ok) {
        alert("Perfect! ");
      } else if (res.status == 401) {
        alert("Oops! ");
      }
    }, function (e) {
      alert("Error submitting form!");
    });
  }

这一次，后端的错误是： Servlet.service() for servlet [dispatcherServlet] in context with path [] throw exception [Request processing failed;嵌套异常是 java.lang.NullPointerException] 的根本原因

我们添加多部分边界对吗？它应该在哪里？也许我们一开始是错的，因为我们没有得到 multipart/form-data。我们怎样才能正确地得到它？

原文由 Yuehai 发布，翻译遵循 CC BY-SA 4.0 许可协议

Answer 1

我们只是尝试删除我们的标题并且它有效！

 fetch("http://localhost:8910/taskCreationController/createStoryTask", {
      mode: 'no-cors',
      method: "POST",
      body: data
    }).then(function (res) {
      if (res.ok) {
        alert("Perfect! ");
      } else if (res.status == 401) {
        alert("Oops! ");
      }
    }, function (e) {
      alert("Error submitting form!");
    });

原文由 Yuehai 发布，翻译遵循 CC BY-SA 3.0 许可协议

Answer 2

这是我通过 axios 预览图像上传的解决方案。

 import React, { Component } from 'react';
import axios from "axios";

反应组件类：

 class FileUpload extends Component {

    // API Endpoints
    custom_file_upload_url = `YOUR_API_ENDPOINT_SHOULD_GOES_HERE`;

    constructor(props) {
        super(props);
        this.state = {
            image_file: null,
            image_preview: '',
        }
    }

    // Image Preview Handler
    handleImagePreview = (e) => {
        let image_as_base64 = URL.createObjectURL(e.target.files[0])
        let image_as_files = e.target.files[0];

        this.setState({
            image_preview: image_as_base64,
            image_file: image_as_files,
        })
    }

    // Image/File Submit Handler
    handleSubmitFile = () => {

        if (this.state.image_file !== null){

            let formData = new FormData();
            formData.append('customFile', this.state.image_file);
            // the image field name should be similar to your api endpoint field name
            // in my case here the field name is customFile

            axios.post(
                this.custom_file_upload_url,
                formData,
                {
                    headers: {
                        "Authorization": "YOUR_API_AUTHORIZATION_KEY_SHOULD_GOES_HERE_IF_HAVE",
                        "Content-type": "multipart/form-data",
                    },
                }
            )
            .then(res => {
                console.log(`Success` + res.data);
            })
            .catch(err => {
                console.log(err);
            })
        }
    }

    // render from here
    render() {
        return (
            <div>
                {/* image preview */}
                <img src={this.state.image_preview} alt="image preview"/>

                {/* image input field */}
                <input
                    type="file"
                    onChange={this.handleImagePreview}
                />
                <label>Upload file</label>
                <input type="submit" onClick={this.handleSubmitFile} value="Submit"/>
            </div>
        );
    }
}

export default FileUpload;

原文由 Fatema Tuz Zuhora 发布，翻译遵循 CC BY-SA 4.0 许可协议