使用HttpClient发送InputStream--buffer对象，程序如下：

public String fileUpload(byte[] buffer, String url, int count, String classId) throws IOException {
        //创建HttpClient对象
        CloseableHttpClient client = HttpClients.createDefault();
        //构建POST请求   请求地址请更换为自己的。
        //1)
        HttpPost post = new HttpPost(url);
        InputStream inputStream = new ByteArrayInputStream(buffer);
        try {
            //文件路径请换成自己的
            //2)
            MultipartEntityBuilder builder = MultipartEntityBuilder.create();
            builder.setMode(HttpMultipartMode.BROWSER_COMPATIBLE);
            //第一个参数为 相当于 Form表单提交的file框的name值 第二个参数就是我们要发送的InputStream对象了
            //第三个参数是文件名
            //3)
            builder.addBinaryBody("fileName", inputStream, ContentType.create("multipart/form-data"), count + "_" + classId + ".jpg");
            //4)构建请求参数 普通表单项
            /*StringBody stringBody = new StringBody("12", ContentType.MULTIPART_FORM_DATA);
            builder.addPart("id",stringBody);*/
            HttpEntity entity = builder.build();
            post.setEntity(entity);
            //发送请求
            HttpResponse response = client.execute(post);
            entity = response.getEntity();
            if (entity != null) {
                inputStream = entity.getContent();
                //转换为字节输入流
                BufferedReader br = new BufferedReader(new InputStreamReader(inputStream, Consts.UTF_8));
                String body = null;
                while ((body = br.readLine()) != null) {
                    logger.info("body=" + body);
                    return body;
                }
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (inputStream != null) {
                try {
                    inputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
        return null;
    }