[Java] Parse json file

Back in may 2013, I was working on a school project concerning mobile networks. So this is what I wrote one year ago while I was fighting with handover algorithm and research papers.

I’m currently building a project to simulate handover decision process in GSM/UMTS. To be able to perform the simulation, I need some parameters like mobile gain, loss, coordinates as well as informations about antennas. I’ve chose to provide these parameters to the program using a json file. So I needed to find a way to get informations from the file and parse the json in java.

I used a JSON-Java library to initialized data. Here is the code needed to parse the json belove. The jsonStr variable contains our json file as a string.

JSONObject obj = new JSONObject(jsonStr);
JSONObject objMobile = obj.getJSONObject("mobile");
JSONArray arrayPath = objMobile.getJSONArray("path");

cro = obj.getDouble("cro");
rxLevAccMin = obj.getDouble("rxlevaccmin");
msTxPwrMaxCCH = obj.getDouble("msTxPwrMaxCCH");

//Initialize Mobile Station
for(int i = 0; i < arrayPath.length(); ++i) {
 JSONObject el = arrayPath.getJSONObject(i);
 journey.add(new Coordinate(el.getInt("x"), el.getInt("y")) );
}
mobileStation = new Mobile(objMobile.getDouble("gain"),
 objMobile.getDouble("loss"), objMobile.getDouble("classPower"),
 journey, objMobile.getBoolean("voice"), 6, -102, journey.get(0));

//Initialize Antennas
JSONArray arrayAntenna = obj.getJSONArray("antenna");
for(int j = 0; j < arrayAntenna.length(); ++j) {
 JSONObject el = arrayAntenna.getJSONObject(j);
 Coordinate position = new Coordinate(el.getInt("x"), el.getInt("y"));
 antennaList.add(new Antenna(el.getInt("type"), position, 
 el.getDouble("gain"), el.getDouble("loss"), el.getDouble("power"),
 el.getDouble("frequency"), el.getDouble("coef")));
}

Once our json string has been parsed to a json object, we can extract data using:

• getJSONObject
• getJSONArray
• getBoolean
• getInt
• getDouble

Here is the json file:

{
  "rxlevaccmin": -96, 
  "cro": 0.0, 
  "msTxPwrMaxCCH": 33, 
  "mobile": { 
    "gain": 0, "loss": 0, 
    "classPower": 33, 
    "voice": false, 
    "path": [ 
      {"x": 11, "y": 0}, 
      {"x": 14, "y": 0}, 
      {"x": 16, "y": 0}, 
      {"x": 18, "y": 0}, 
      {"x": 20, "y": 0}, 
      {"x": 24, "y": 0}, 
      {"x": 25, "y": 0}, 
      {"x": 26, "y": 0} 
    ] 
  },
  "antenna": [ 
    { 
      "type": 0, 
      "x": 0, "y": 0, 
      "power": 20, 
      "gain": 0, "loss": 0, 
      "frequency": 900, 
      "coef": 1 
    }, 
    { 
      "type": 1, 
      "x": 30, "y": 0, 
      "power": 10, 
      "gain": 0, "loss": 0, 
      "frequency": 900, 
      "coef": 1 
    }, 
    {
      "type": 0, 
      "x": 20, "y": 5, 
      "power": 12, 
      "gain": 0, "loss": 0, 
      "frequency": 900, 
      "coef": 1 
    }
  ]
}

It’s funny to compare this with the one-line-way to parse json in Node.Js:

var jsonObject = require('jsonFileName');
var classPower =jsonObject.mobile.classPower