前端

FileReader 将文件转换为 Base64 编码字符串，然后将其作为请求体发送到后端。

<input type="file" id="fileInput" />
<button onclick="uploadFileAsBase64()">上传文件</button>

<script>
  function uploadFileAsBase64() {
    const fileInput = document.getElementById("fileInput");
    const file = fileInput.files[0];

    if (file) {
      const reader = new FileReader();

      // 当文件读取完成时
      reader.onload = function (event) {
        // 获取 Base64 编码的字符串
        const base64String = event.target.result.split(",")[1]; // 去掉前面的data:URL前缀

        // 发送到后端
        fetch("/upload", {
          method: "POST",
          headers: {
            "Content-Type": "application/json",
          },
          body: JSON.stringify({
            fileName: file.name,
            fileType: file.type,
            fileData: base64String,
          }),
        })
          .then((response) => response.json())
          .then((data) => {
            console.log("上传成功:", data);
          })
          .catch((error) => {
            console.error("上传失败:", error);
          });
      };

      // 读取文件为 Data URL
      reader.readAsDataURL(file);
    } else {
      alert("请选择文件");
    }
  }
</script>

后端

需要解析接收到的 Base64 字符串并将其解码回二进制数据，以保存文件或进行其他操作。

const express = require('express');
const fs = require('fs');
const path = require('path');
const app = express();
app.use(express.json({ limit: '10mb' })); // 增加限制以处理大文件

app.post('/upload', (req, res) => {
  const { fileName, fileType, fileData } = req.body;

  // 将 Base64 字符串解码为二进制数据
  const base64Data = fileData.replace(/^data:image\/\w+;base64,/, ''); // 对于图片，移除 MIME 类型前缀
  const buffer = Buffer.from(base64Data, 'base64');

  // 将文件保存到磁盘
  fs.writeFile(path.join(__dirname, 'uploads', fileName), buffer, (err) => {
    if (err) {
      console.error('保存文件时出错:', err);
      return res.status(500).json({ status: 'error', message: '上传失败' });
    }
    res.json({ status: 'success', message: '文件上传成功' });
  });
});

app.listen(3000, () => {
  console.log('服务器正在监听端口 3000');
});

import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.multipart.MultipartFile;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.Base64;

@RestController
public class FileUploadController {

    @PostMapping("/upload")
    public String uploadFile(@RequestBody FileUploadRequest request) {
        try {
            // 将 Base64 字符串解码为二进制数据
            byte[] data = Base64.getDecoder().decode(request.getFileData());
            
            // 将文件保存到磁盘
            File file = new File("./uploads/" + request.getFileName());
            try (FileOutputStream fos = new FileOutputStream(file)) {
                fos.write(data);
            }
            return "File uploaded successfully";
        } catch (IOException e) {
            e.printStackTrace();
            return "File upload failed";
        }
    }

    static class FileUploadRequest {
        private String fileName;
        private String fileData;

        // Getters and setters
    }
}