String URL = “二维码接口地址”;
  String meetingId=request.getParameter(“id”);//我自己的参数，不用管
  log.info("------------------createwxaqrcode"+meetingId);
  if(meetingId!=null&&meetingId.trim().length()>0){
   String access_token;
   InputStream is=null;
   OutputStream os=null;
   try {
    access_token = getAccess_token();//获取token，我自己写的方法，把acess_token获取出来就行
    URL = URL + “?access_token=” + access_token;
    Map<String, Object> map = new HashMap<String, Object>();
    map.put(“path”, “pages/index/index?meetingId=”+meetingId);
    map.put(“width”, 375);
    JSONObject json = new JSONObject(map);
    CloseableHttpClient client = HttpClients.createDefault();
    HttpPost post = new HttpPost(URL);
    post.addHeader(HTTP.CONTENT_TYPE, “application/json”);
    StringEntity se;
    se = new StringEntity(json.toString());
    se.setContentType(“application/json”);
    se.setContentEncoding(new BasicHeader(HTTP.CONTENT_TYPE, “UTF-8”));
    post.setEntity(se);
    StringEntity s = new StringEntity(json.toString(), “utf-8”);
    s.setContentEncoding(new BasicHeader(HTTP.CONTENT_TYPE,
      “application/json”));
    post.setEntity(s);
    HttpResponse res = client.execute(post);
    if(res!=null){
     HttpEntity resEntity = res.getEntity();
     if (resEntity != null) {
      // 获取响应输入流
       is = resEntity.getContent();
       response.setHeader(“Content-Type”,“application/x-msdownload”);
       os=response.getOutputStream();
       //os=new FileOutputStream(“D:\\test.png”);//生成图片
       int count = 0;
       byte[] buffer = new byte[1024 * 8];
       while ((count = is.read(buffer)) != -1) {
        os.write(buffer, 0, count);
        os.flush();
       }
       os.close();
       is.close();
     }
    }

我是直接把流发送到小程序端的，直接用image标签的 src属性读取的