Java 实现表单文件上传功能

在Java中我们需要模拟页面的请求，实现上传表单的功能，具体操作如下

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

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

/**
 * @author Philip Lee
 * @date 2023/3/6 10:40
 * 发送网络上传文件请求
 */
public class FileUploadTool {
    private static final Logger log = LoggerFactory.getLogger(FileUploadTool.class);

    public static String sendPostWithFile(String url, File file) {
        log.info("Get a request to upload file. What fileName is {}", file.getName());
        DataOutputStream outputStream = null;
        BufferedReader in = null;
        String result = "";
        try {
            URL realUrl = new URL(url);
            //打开和URL之间的连接
            HttpURLConnection httpURLConnection = (HttpURLConnection) realUrl.openConnection();
            //设置POST请求必须设置如下两行
            httpURLConnection.setDoOutput(true);
            httpURLConnection.setDoInput(true);

            String BOUNDARY = UUID.randomUUID().toString();
            httpURLConnection.setUseCaches(false);
            httpURLConnection.setRequestMethod("POST");
            httpURLConnection.setRequestProperty("connection", "Keep-Alive");
            httpURLConnection.setRequestProperty("user-agent", "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1;SV1)");
            httpURLConnection.setRequestProperty("Charset", "UTF-8");
            httpURLConnection.setRequestProperty("Content-Type", "multipart/form-data; boundary=" + BOUNDARY);
            httpURLConnection.connect();

            outputStream = new DataOutputStream(httpURLConnection.getOutputStream());
            byte[] end_data = ("\r\n--" + BOUNDARY + "--\r\n").getBytes();

            //添加参数 "type":"keepFiles"
            StringBuilder stringBuilder = new StringBuilder();
            stringBuilder.append("--");
            stringBuilder.append("--");
            stringBuilder.append(BOUNDARY);
            stringBuilder.append("\r\n");
            stringBuilder.append("Content-Disposition: form-data; name=\"type\"");
            stringBuilder.append("\r\n");
            stringBuilder.append("\r\n");
            stringBuilder.append("keepFiles");
            stringBuilder.append("\r\n");
            outputStream.write(stringBuilder.toString().getBytes());

            //添加文件file，对应后端controller中的file key值
            StringBuilder sb = new StringBuilder();
            sb.append("--");
            sb.append(BOUNDARY);
            sb.append("\r\n");
            sb.append("Content-Disposition: form-data; name=\"file\";filename=\"" + file.getName() + "\"");
            sb.append("\r\n");
            sb.append("Content-Type: application/octet-stream");
            sb.append("\r\n");
            sb.append("\r\n");
            outputStream.write(sb.toString().getBytes());

            DataInputStream in1 = new DataInputStream(new FileInputStream(file));
            int bytes = 0;
            byte[] bufferOut = new byte[1024];
            while ((bytes = in1.read(bufferOut)) != -1) {
                outputStream.write(bufferOut, 0, bytes);
            }

            //多个文件时，两个文件之间加入下面这行代码，如有必要重新创建一个StringBuilder，重复上面的步骤
            outputStream.write("\r\n".getBytes());


            in1.close();
            outputStream.write(end_data);

            //刷新输出流的缓冲
            outputStream.flush();
            //定义BufferedReader输出流来读取URL的响应
            in = new BufferedReader(new InputStreamReader(httpURLConnection.getInputStream()));

            String line;
            while ((line = in.readLine()) != null) {
                result += line;
            }

        } catch (Exception e) {
            //
            e.printStackTrace();
        } finally {
            try {
                if (outputStream != null) {
                    outputStream.close();
                }
                if (in != null) {
                    in.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        log.info("Upload file end, Result is {}", result);
        return result;
    }


}

以上模拟浏览器发送请求的的参数和文件需要对应controller中的@RequestParam(name = "***")

我的Server端Controller 层如下：

    @ApiOperation(value = "上传文件", notes = "上传文件到服务器")
    @ApiImplicitParams(value = {
            @ApiImplicitParam(name = "file", value = "文件", dataTypeClass = MultipartFile.class),
            @ApiImplicitParam(name = "type", value = "上传类型（我是功能是上传的图片有不同的来源，作用也不同）", dataTypeClass = String.class),
    })
    @PostMapping
    public RespModel<String> uploadFiles(@RequestParam(name = "file") MultipartFile file,
                                         @RequestParam(name = "type") String type) throws IOException {
           *************
    }

分别为 file 和 type