React 文件上传组件 File Upload-阿里云开发者社区

引言

文件上传是现代 Web 应用中不可或缺的功能之一。无论是用户头像、文档附件还是多媒体文件，都需要一个高效且可靠的文件上传组件来处理。React 作为当前最流行的前端框架之一，提供了丰富的工具和库来简化文件上传的实现。本文将从基础开始，逐步深入介绍如何在 React 中实现文件上传组件，并探讨一些常见的问题、易错点及如何避免这些问题。

基础实现

1. 创建基本的文件上传组件

首先，我们创建一个简单的文件上传组件，使用 HTML 的 <input type="file"> 元素来选择文件。

import React, { useState } from 'react';

const FileUpload = () => {
  const [file, setFile] = useState(null);

  const handleFileChange = (event) => {
    setFile(event.target.files[0]);
  };

  const handleUpload = () => {
    if (file) {
      console.log('Selected file:', file);
    } else {
      console.log('No file selected');
    }
  };

  return (
    <div>
      <input type="file" onChange={handleFileChange} />
      <button onClick={handleUpload}>Upload</button>
    </div>
  );
};

export default FileUpload;

2. 发送文件到服务器

接下来，我们将文件发送到服务器。这里使用 fetch API 来实现。

import React, { useState } from 'react';

const FileUpload = () => {
  const [file, setFile] = useState(null);

  const handleFileChange = (event) => {
    setFile(event.target.files[0]);
  };

  const handleUpload = async () => {
    if (!file) {
      alert('Please select a file first');
      return;
    }

    const formData = new FormData();
    formData.append('file', file);

    try {
      const response = await fetch('https://api.example.com/upload', {
        method: 'POST',
        body: formData,
      });

      if (response.ok) {
        const data = await response.json();
        console.log('File uploaded successfully:', data);
      } else {
        console.error('File upload failed');
      }
    } catch (error) {
      console.error('Error uploading file:', error);
    }
  };

  return (
    <div>
      <input type="file" onChange={handleFileChange} />
      <button onClick={handleUpload}>Upload</button>
    </div>
  );
};

export default FileUpload;

常见问题及易错点

1. 文件大小限制

问题：用户上传的文件过大，导致请求失败。
解决方法：在前端进行文件大小校验，并在后端设置文件大小限制。

const handleFileChange = (event) => {
  const selectedFile = event.target.files[0];
  const maxSize = 5 * 1024 * 1024; // 5MB

  if (selectedFile.size > maxSize) {
    alert('File size exceeds the limit of 5MB');
    return;
  }

  setFile(selectedFile);
};

2. 文件类型限制

问题：用户上传了不支持的文件类型。
解决方法：在前端进行文件类型校验，并在后端设置文件类型限制。

const handleFileChange = (event) => {
  const selectedFile = event.target.files[0];
  const allowedTypes = ['image/jpeg', 'image/png', 'application/pdf'];

  if (!allowedTypes.includes(selectedFile.type)) {
    alert('Unsupported file type. Please upload a JPEG, PNG, or PDF file.');
    return;
  }

  setFile(selectedFile);
};

3. 并发上传

问题：用户同时上传多个文件，导致服务器压力增大。
解决方法：限制同时上传的文件数量，或者使用队列机制逐个上传文件。

const [files, setFiles] = useState([]);

const handleFileChange = (event) => {
  const selectedFiles = Array.from(event.target.files);
  const allowedTypes = ['image/jpeg', 'image/png', 'application/pdf'];
  const maxSize = 5 * 1024 * 1024; // 5MB

  const validFiles = selectedFiles.filter(file => allowedTypes.includes(file.type) && file.size <= maxSize);

  if (validFiles.length === 0) {
    alert('No valid files selected');
    return;
  }

  setFiles([...files, ...validFiles]);
};

const handleUpload = async () => {
  if (files.length === 0) {
    alert('Please select at least one file');
    return;
  }

  for (const file of files) {
    const formData = new FormData();
    formData.append('file', file);

    try {
      const response = await fetch('https://api.example.com/upload', {
        method: 'POST',
        body: formData,
      });

      if (response.ok) {
        const data = await response.json();
        console.log('File uploaded successfully:', data);
      } else {
        console.error('File upload failed');
      }
    } catch (error) {
      console.error('Error uploading file:', error);
    }
  }

  setFiles([]);
};

4. 进度条显示

问题：用户无法知道文件上传的进度。
解决方法：使用 fetch 的 onUploadProgress 回调来显示上传进度。

import React, { useState } from 'react';
import axios from 'axios';

const FileUpload = () => {
  const [file, setFile] = useState(null);
  const [progress, setProgress] = useState(0);

  const handleFileChange = (event) => {
    const selectedFile = event.target.files[0];
    const maxSize = 5 * 1024 * 1024; // 5MB

    if (selectedFile.size > maxSize) {
      alert('File size exceeds the limit of 5MB');
      return;
    }

    setFile(selectedFile);
  };

  const handleUpload = async () => {
    if (!file) {
      alert('Please select a file first');
      return;
    }

    const formData = new FormData();
    formData.append('file', file);

    try {
      const response = await axios.post('https://api.example.com/upload', formData, {
        onUploadProgress: (progressEvent) => {
          const percentCompleted = Math.round((progressEvent.loaded * 100) / progressEvent.total);
          setProgress(percentCompleted);
        },
      });

      if (response.status === 200) {
        console.log('File uploaded successfully:', response.data);
      } else {
        console.error('File upload failed');
      }
    } catch (error) {
      console.error('Error uploading file:', error);
    }
  };

  return (
    <div>
      <input type="file" onChange={handleFileChange} />
      <button onClick={handleUpload}>Upload</button>
      {progress > 0 && <p>Upload Progress: {progress}%</p>}
    </div>
  );
};

export default FileUpload;

高级功能与优化

1. 多文件上传

在实际应用中，用户可能需要一次上传多个文件。我们可以使用 multiple 属性来允许用户选择多个文件，并批量上传。

import React, { useState } from 'react';
import axios from 'axios';

const MultiFileUpload = () => {
  const [files, setFiles] = useState([]);
  const [progress, setProgress] = useState(0);

  const handleFileChange = (event) => {
    const selectedFiles = Array.from(event.target.files);
    const maxSize = 5 * 1024 * 1024; // 5MB
    const allowedTypes = ['image/jpeg', 'image/png', 'application/pdf'];

    const validFiles = selectedFiles.filter(file => allowedTypes.includes(file.type) && file.size <= maxSize);

    if (validFiles.length === 0) {
      alert('No valid files selected');
      return;
    }

    setFiles([...files, ...validFiles]);
  };

  const handleUpload = async () => {
    if (files.length === 0) {
      alert('Please select at least one file');
      return;
    }

    for (const file of files) {
      const formData = new FormData();
      formData.append('file', file);

      try {
        const response = await axios.post('https://api.example.com/upload', formData, {
          onUploadProgress: (progressEvent) => {
            const percentCompleted = Math.round((progressEvent.loaded * 100) / progressEvent.total);
            setProgress(percentCompleted);
          },
        });

        if (response.status === 200) {
          console.log('File uploaded successfully:', response.data);
        } else {
          console.error('File upload failed');
        }
      } catch (error) {
        console.error('Error uploading file:', error);
      }
    }

    setFiles([]);
  };

  return (
    <div>
      <input type="file" multiple onChange={handleFileChange} />
      <button onClick={handleUpload}>Upload</button>
      {progress > 0 && <p>Upload Progress: {progress}%</p>}
    </div>
  );
};

export default MultiFileUpload;

2. 断点续传

问题：大文件上传过程中网络中断，导致上传失败。
解决方法：实现断点续传功能，允许用户在网络恢复后继续上传未完成的部分。

import React, { useState } from 'react';
import axios from 'axios';

const ResumableFileUpload = () => {
  const [file, setFile] = useState(null);
  const [progress, setProgress] = useState(0);

  const handleFileChange = (event) => {
    setFile(event.target.files[0]);
  };

  const handleUpload = async () => {
    if (!file) {
      alert('Please select a file first');
      return;
    }

    const chunkSize = 1024 * 1024; // 1MB
    const totalChunks = Math.ceil(file.size / chunkSize);

    for (let i = 0; i < totalChunks; i++) {
      const start = i * chunkSize;
      const end = Math.min(start + chunkSize, file.size);
      const chunk = file.slice(start, end);

      const formData = new FormData();
      formData.append('file', chunk);
      formData.append('chunkIndex', i);
      formData.append('totalChunks', totalChunks);

      try {
        const response = await axios.post('https://api.example.com/upload', formData, {
          onUploadProgress: (progressEvent) => {
            const percentCompleted = Math.round(((i * chunkSize + progressEvent.loaded) * 100) / file.size);
            setProgress(percentCompleted);
          },
        });

        if (response.status === 200) {
          console.log(`Chunk ${i + 1}/${totalChunks} uploaded successfully`);
        } else {
          console.error(`Chunk ${i + 1}/${totalChunks} upload failed`);
        }
      } catch (error) {
        console.error(`Error uploading chunk ${i + 1}/${totalChunks}:`, error);
      }
    }

    setProgress(100);
    alert('File uploaded successfully');
  };

  return (
    <div>
      <input type="file" onChange={handleFileChange} />
      <button onClick={handleUpload}>Upload</button>
      {progress > 0 && <p>Upload Progress: {progress}%</p>}
    </div>
  );
};

export default ResumableFileUpload;

3. 文件预览

问题：用户无法预览上传的文件，特别是图片文件。
解决方法：在前端生成文件的预览 URL，并显示给用户。

import React, { useState } from 'react';

const FilePreviewUpload = () => {
  const [file, setFile] = useState(null);
  const [previewUrl, setPreviewUrl] = useState('');

  const handleFileChange = (event) => {
    const selectedFile = event.target.files[0];

    if (selectedFile) {
      const reader = new FileReader();
      reader.onloadend = () => {
        setPreviewUrl(reader.result);
      };
      reader.readAsDataURL(selectedFile);
      setFile(selectedFile);
    }
  };

  const handleUpload = () => {
    if (file) {
      console.log('Selected file:', file);
    } else {
      console.log('No file selected');
    }
  };

  return (
    <div>
      <input type="file" onChange={handleFileChange} />
      <button onClick={handleUpload}>Upload</button>
      {previewUrl && <img src={previewUrl} alt="Preview" style={
  { maxWidth: '100px' }} />}
    </div>
  );
};

export default FilePreviewUpload;

总结

通过本文的介绍，我们从基础的文件上传组件开始，逐步深入探讨了常见的问题、易错点及如何避免这些问题。我们还介绍了多文件上传、断点续传和文件预览等高级功能，希望这些内容能帮助你在实际开发中更加顺利地实现文件上传功能。

如果你有任何疑问或建议，欢迎留言交流！

React 文件上传组件 File Upload

引言