String httpMethod = "";

RestTemplate restTemplate = new RestTemplate();

String args = "";

MultiValueMap<String, Object> paramMap = new LinkedMultiValueMap<>();

paramMap.add("args", args);

paramMap.add("sign", "");

File file=new File("D:\\5a658c98Nd0abcb82.jpg");

byte[] bytesArray = new byte[(int) file.length()];

FileInputStream fis = new FileInputStream(file);

fis.read(bytesArray); //read file into bytes[]

fis.close();

ByteArrayResource contentsAsResource = new ByteArrayResource(bytesArray) {

    @Override

    public String getFilename() {

        return "img";

    }

};

paramMap.add("img", contentsAsResource);

JSONObject json = restTemplate.postForObject(httpMethod, paramMap, JSONObject.class);

System.out.println("post json : " + json);