事实证明翻百度是没有用的，还是得自己写

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.ContentType;
import org.apache.http.entity.mime.MultipartEntityBuilder;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;

import java.io.BufferedReader;
import java.io.File;
import java.io.IOException;
import java.io.InputStreamReader;
import java.nio.charset.Charset;
import java.util.Map;

public class HttpFormData {

    //url为需要请求的地址
    public static String doPost(String url, Map<String, String> paramsMap, Map<String, File> fileMap) throws Exception {
        CloseableHttpClient httpclient = HttpClients.createDefault();
        MultipartEntityBuilder builder = MultipartEntityBuilder.create();

        // 解决中文乱码
        ContentType contentType = ContentType.create("text/plain",Charset.forName("UTF-8"));
        // params
        for(Map.Entry<String, String> params : paramsMap.entrySet()){
            builder.addTextBody(params.getKey(),params.getValue(),contentType);
        }
        // file
        for(Map.Entry<String, File> file : fileMap.entrySet()){
            builder.addBinaryBody(file.getKey(),file.getValue(), ContentType.MULTIPART_FORM_DATA,file.getValue().getName());
        }
        HttpEntity entity = builder.build();

        HttpPost httpPost = new HttpPost(url);

        httpPost.setEntity(entity);
        HttpResponse httpResponse = null;
        BufferedReader in = null;
        try{
            httpResponse = httpclient.execute(httpPost);
            int code = httpResponse.getStatusLine().getStatusCode();
            if(code == 200) {    //请求成功
                in = new BufferedReader(new InputStreamReader(httpResponse.getEntity()
                        .getContent(),"utf-8"));
                StringBuffer sb = new StringBuffer("");
                String line = "";
                String NL = System.getProperty("line.separator");
                while ((line = in.readLine()) != null) {
                    sb.append(line + NL);
                }
                in.close();
                System.out.println("收到的返回信息为：{}"+sb.toString());
                return sb.toString();
            }

        }catch(IOException e){
            e.printStackTrace();
        }
        return "error";
    }
}