发送HTTP PUT请求到Cloudant

Question

我正在尝试向Cloudant数据库发送HTTP PUT请求，以将密钥“ BPInc”更新为“ N”。当前值为“ Y”。我正在使用HTTPURLConnection进行连接并发送请求。我能够成功发送GET请求并检索BPInc值。但是，当我发送PUT请求时，却收到错误代码-400。

我也研究了cloudant-client库，但是无法获取如何发送PUT请求，我只想坚持使用HTTPURLConnection方法。

这是代码，

// After retrieving _rev and _id using GET request......
String revID = "_rev of the document";
String docID = "_id of the document";
 URL postUrl = new URL("<Cloudant URL>/<DB NAME>/" + docID);
 String usernameColonPassword = "<API KEY>:<PASSWORD>";
          String basicAuthPayload = "Basic " + Base64.getEncoder().encodeToString(usernameColonPassword.getBytes());
          HttpURLConnection conn = (HttpURLConnection)postUrl.openConnection();
          conn.setRequestMethod("PUT");
          conn.setRequestProperty("Content-Type", "application/json; utf-8");
          conn.setRequestProperty("Accept", "application/json");
          conn.setRequestProperty("Authorization", basicAuthPayload);
          conn.setDoOutput(true);
          OutputStreamWriter json = new OutputStreamWriter(conn.getOutputStream());
          json.write(String.format("{\"_rev\":revID, \"BPInc\":\"Y\"}"));
          json.flush();
          json.close();

          int putResponseCode = conn.getResponseCode();

我对此很陌生，所以我想我可能做错了什么。请提出建议。