Java实现简易文件上传工具教学

import java.io.*;
import java.net.HttpURLConnection;
import java.net.URL;

public class FileUploader {
    public static void upload(String filePath, String uploadUrl) throws Exception {
        File file = new File(filePath);
        URL url = new URL(uploadUrl);
        HttpURLConnection connection = (HttpURLConnection) url.openConnection();
        
        // 设置请求方式和头信息
        connection.setDoOutput(true);
        connection.setRequestMethod("POST");
        connection.setRequestProperty("Content-Type", "multipart/form-data; boundary=" + boundary);

        String boundary = "----WebKitFormBoundary7MA4YWxkTrZu0gW";

        try (DataOutputStream out = new DataOutputStream(connection.getOutputStream());
             FileInputStream fileInputStream = new FileInputStream(file)) {

            // 写入表单字段（文件部分）
            out.writeBytes("--" + boundary + "\r\n");
            out.writeBytes("Content-Disposition: form-data; name=\"file\"; filename=\"" + file.getName() + "\"\r\n");
            out.writeBytes("Content-Type: " + getContentType(file.getName()) + "\r\n\r\n");

            // 读取文件内容并写入输出流
            byte[] buffer = new byte[4096];
            int bytesRead;
            while ((bytesRead = fileInputStream.read(buffer)) != -1) {
                out.write(buffer, 0, bytesRead);
            }
            out.writeBytes("\r\n");
            out.writeBytes("--" + boundary + "--\r\n");

            out.flush();
        }

        // 检查响应状态
        int responseCode = connection.getResponseCode();
        if (responseCode == 200) {
            System.out.println("文件上传成功");
        } else {
            System.out.println("上传失败，响应码：" + responseCode);
        }
    }

    private static String getContentType(String fileName) {
        if (fileName.endsWith(".jpg") || fileName.endsWith(".jpeg")) {
            return "image/jpeg";
        } else if (fileName.endsWith(".png")) {
            return "image/png";
        } else if (fileName.endsWith(".pdf")) {
            return "application/pdf";
        } else {
            return "application/octet-stream";
        }
    }
}

import org.springframework.web.bind.annotation.*;
import org.springframework.web.multipart.MultipartFile;

import java.io.FileOutputStream;
import java.io.InputStream;

@RestController
public class UploadController {

    @PostMapping("/upload")
    public String handleFileUpload(@RequestParam("file") MultipartFile file) {
        try (InputStream in = file.getInputStream()) {
            FileOutputStream fos = new FileOutputStream("uploaded_" + file.getOriginalFilename());
            byte[] buffer = new byte[4096];
            int len;
            while ((len = in.read(buffer)) > 0) {
                fos.write(buffer, 0, len);
            }
            fos.close();
            return "文件保存成功: " + file.getOriginalFilename();
        } catch (Exception e) {
            return "上传失败: " + e.getMessage();
        }
    }
}

spring.servlet.multipart.max-file-size=10MB
spring.servlet.multipart.max-request-size=10MB