java HttpClient 发送MultipartFile

以下是Java使用HttpClient发送MultipartFile的示例代码：

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.ContentType;
import org.apache.http.entity.mime.MultipartEntityBuilder;
import org.apache.http.entity.mime.content.FileBody;
import org.apache.http.entity.mime.content.StringBody;
import org.apache.http.impl.client.HttpClientBuilder;
import org.apache.http.util.EntityUtils;
import org.springframework.web.multipart.MultipartFile;

import java.io.File;
import java.io.IOException;
import java.nio.charset.Charset;

public class HttpClientUtil {

    public static String sendMultipartFile(String url, MultipartFile file, String paramStr) throws IOException {
        HttpClient httpClient = HttpClientBuilder.create().build();
        HttpPost httpPost = new HttpPost(url);

        // 构建请求参数
        FileBody fileBody = new FileBody(convert(file));
        StringBody stringBody = new StringBody(paramStr, ContentType.create("text/plain", Charset.forName("UTF-8")));
        HttpEntity reqEntity = MultipartEntityBuilder.create()
                .addPart("file", fileBody)
                .addPart("paramStr", stringBody)
                .build();
        httpPost.setEntity(reqEntity);

        // 发送请求
        HttpResponse response = httpClient.execute(httpPost);
        HttpEntity resEntity = response.getEntity();
        String result = EntityUtils.toString(resEntity, Charset.forName("UTF-8"));

        return result;
    }

    private static File convert(MultipartFile file) throws IOException {
        File convFile = new File(file.getOriginalFilename());
        file.transferTo(convFile);
        return convFile;
    }
}

其中，`sendMultipartFile`方法接收三个参数：请求URL、MultipartFile文件和请求参数。该方法使用HttpClient发送POST请求，将文件和参数一起发送到指定的URL，并返回响应结果。