How to parse JSONObjects in a JSONArray in Java?

Question

I'm trying to read data from Floodlight's (an SDN controller) REST API and input that into other software's REST API. I have this which reads from Floodlight's REST API:

private JSONArray getFlData(String path) {
    try {
        logger.info("getData URL: " + path);
        URL url = new URL("http://localhost:8080" + path);
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setDoInput(true);
        conn.setRequestMethod("GET");

        BufferedReader br = new BufferedReader(
            new InputStreamReader(conn.getInputStream()));

        String inputline;
        StringBuffer response = new StringBuffer();
        while((inputline = br.readLine()) != null) {
             response.append(inputline);
        }
        JSONArray jsonr = new JSONArray(response.toString());
        br.close();
        conn.disconnect();
        return jsonr;
    }
    catch (MalformedURLException e) {
        logger.info("Bad URL (getData) " + path);
    }
    catch (IOException e) {
        logger.info("IOException (getData)" + path);
    }
    catch (JSONException e) {
        logger.info("Bad JSON (getData)" + path);
    }
    return null;
}

Then I'm parsing that information into lists:

    JSONArray flswitches = getFlData("/wm/core/controller/switches/json");
    List<String> switchDPIDlist = new ArrayList<String>();
    List<String> switchIPlist = new ArrayList<String>();
    for (int i = 0;i < flswitches.length();i++){
        try {
            switchDPIDlist.add(flswitches.getJSONObject(i).getString("switchDPID"));
            switchIPlist.add(flswitches.getJSONObject(i).getString("inetAddress"));
            } catch (JSONException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }

Which works. However, when I try to do the same thing with the output regarding hosts in the network I'm running into problems. For reference, here's the CURL output for the simpler thing I can do it with:

curl http://127.0.0.1:8080/wm/core/controller/switches/json
[{"inetAddress":"/127.0.0.1:43663","connectedSince":1456305460978,"switchDPID":"00:00:00:00:00:00:00:01"},{"inetAddress":"/127.0.0.1:43664","connectedSince":1456305460981,"switchDPID":"00:00:00:00:00:00:00:03"},{"inetAddress":"/127.0.0.1:43665","connectedSince":1456305460984,"switchDPID":"00:00:00:00:00:00:00:02"}]

But when I try to use it with the more complex output like this, I run into problems:

curl http://127.0.0.1:8080/wm/device/
[{"entityClass":"DefaultEntityClass","mac":["86:2b:a2:f1:2b:9c"],"ipv4":["10.0.0.1"],"ipv6":[],"vlan":["0x0"],"attachmentPoint":[{"switchDPID":"00:00:00:00:00:00:00:02","port":1,"errorStatus":null}],"lastSeen":1456312407529},{"entityClass":"DefaultEntityClass","mac":["1e:94:63:67:1e:d1"],"ipv4":["10.0.0.3"],"ipv6":[],"vlan":["0x0"],"attachmentPoint":[{"switchDPID":"00:00:00:00:00:00:00:03","port":1,"errorStatus":null}],"lastSeen":1456312407625},{"entityClass":"DefaultEntityClass","mac":["06:d7:e0:c5:60:86"],"ipv4":["10.0.0.2"],"ipv6":[],"vlan":["0x0"],"attachmentPoint":[{"switchDPID":"00:00:00:00:00:00:00:02","port":2,"errorStatus":null}],"lastSeen":1456312407591},{"entityClass":"DefaultEntityClass","mac":["6e:c3:e4:5e:1f:65"],"ipv4":["10.0.0.4"],"ipv6":[],"vlan":["0x0"],"attachmentPoint":[{"switchDPID":"00:00:00:00:00:00:00:03","port":2,"errorStatus":null}],"lastSeen":1456312407626}]

For some reason just changing .getString("switchDPID") into .getString ("mac") flat out didn't work. Apparently the result from using "mac" is not a string, and I can't figure out what I should use. What am I doing wrong here and what should I change? Is it an issue with the mac-address format or is it something to do with the JSON format or something?

Answer 1

The value of mac is an array. So you'd have to use getJSONArray("mac") here. The exact syntax depends on the JSON library you are using.

You might want to have a look at Gson , which can convert JSON into regular Java objects and back again.

Answer 2

mac is a JSON array.

In this first example, the hierarchy is as follows

JSON Array -> JSON Object -> switchDPID

In the second one the hierarchy is

JSON Array -> JSON Object -> JSON Array ( mac ) -> data inside mac array.

If you see the JSON in tree structure, you can see the difference. I use http://www.jsoneditoronline.org/

You would have to fetch JSON Array ( mac ) first and then access it's first element for the data.

Answer 3

Here, mac is an array. Try to read it as an array and then get the first item in the array as string!