问如何关闭HttpsURLConnection Java

EN

java.lang.IllegalStateException: Already connected
at sun.net.www.protocol.http.HttpURLConnection.setRequestProperty(HttpURLConnection.java:3053)
at sun.net.www.protocol.https.HttpsURLConnectionImpl.setRequestProperty(HttpsURLConnectionImpl.java:316)

private static void sendPost(String _url) throws Exception {

    String url = _url;

    URL obj = new URL(url);
    HttpsURLConnection con = (HttpsURLConnection) obj.openConnection();

    con.setRequestMethod("POST");

    int responseCode = con.getResponseCode();
    Auth(con);

    if (responseCode == 200) {
        label.setText("Sucssesfully Scanned: " + StudID.getText());
    } else {
        label.setText("Error, please scan again");
    }
    con.disconnect();
}

private static ArrayList<String> Get(String _url) throws Exception {
    ArrayList<String> list = new ArrayList<>();
    JsonParser parser = new JsonParser();

    String url = _url;

    URL obj = new URL(url);
    HttpsURLConnection con = (HttpsURLConnection) obj.openConnection();
    Auth(con);

    con.setRequestMethod("GET");

    con.setRequestProperty("Accept", "application/json");

    BufferedReader in = new BufferedReader(
            new InputStreamReader(con.getInputStream()));
    String inputLine;
    StringBuffer response = new StringBuffer();

    while ((inputLine = in.readLine()) != null) {
        response.append(inputLine);
    }

    in.close();
    con.disconnect();

    JsonElement element = parser.parse(response.toString());

    if (element.isJsonObject()) {
        JsonObject data = element.getAsJsonObject();
        for (int i = 0; i < data.get("chapels").getAsJsonArray().size(); i++) {
            JsonObject jObj = (JsonObject) data.get("chapels").getAsJsonArray().get(i);
            list.add(jObj.get("Name").toString().replaceAll("\"", "") + " - " + jObj.get("Loc").toString().replaceAll("\"", ""));
        }
    }

    return (list);
}
private static void Auth(HttpsURLConnection con){
    String encodedBytes = Base64.getEncoder().encodeToString((BCrypt.hashpw("swheeler17", BCrypt.gensalt(10)) + ":" + BCrypt.hashpw("Trinity", BCrypt.gensalt(10))).getBytes());
    con.setRequestProperty("authorization", "Basic " + encodedBytes);
}