Java parse JSON array from JSON file

Question

I haven't been programming for a long time but I like it and trying to get back on track. So please excuse the nature of the problem/question here.

What I need is pretty simple in my opinion but i'm mostly struggling with using gson and json-simple to read my json file, one at a time, and be able to retrieve the values.

I have seen many approaches on here but as I said been a while and I have not done Java a lot in my career. So need some guidance/explanation on the best approach.

JSON:

[{ "car": "Toyota", "colour": "red", "qty": "1","date_manufactured":"12972632260006" }, { "car": "Hyundai", "colour": "red", "qty": "2","date_manufactured":"1360421626000" }, { "car": "Kia", "colour": "blue", "qty": "2", "date_manufactured":"1265727226000"}, ]

Any help to put me on the right track is appreciated!

Answer 1

1. Create a POJO class to represent your JSON data:

    public class CarInfo { String car; String colour; String qty; String date_manufactured; } 

2. Use GSON to parse JSON String Array

    String carInfoJson = "[{ \\"car\\": \\"Toyota\\", \\"colour\\": \\"red\\",\\"qty\\": \\"1\\",\\"date_manufactured\\":\\"12972632260006\\" }, { \\"car\\":\\"Hyundai\\", \\"colour\\":\\"red\\",\\"qty\\":\\"2\\",\\"date_manufactured\\":\\"1360421626000\\" }]"; Gson gson = new Gson(); CarInfo[] carInfoArray = gson.fromJson(carInfoJson, CarInfo[].class); 

3. Use GSON to parse JSON String Array from a file

    String carInfoJson= new String(Files.readAllBytes(Paths.get("filename.txt"))); Gson gson = new Gson(); CarInfo[] carInfoArray = gson.fromJson(carInfoJson, CarInfo[].class); 

4. Use GSON to parse JSON String Array from a file using BufferedReader

    BufferedReader reader = null; try { reader = new BufferedReader(new FileReader(file)); Gson gson = new Gson(); CarInfo[] carInfoArray = gson.fromJson(reader, CarInfo[].class); } catch (FileNotFoundException ex) { ... } finally { ... } 

5. Use GSON to parse JSON String Array from a file using JsonReader in stream mode

    try { InputStream stream = new FileInputStream("c:\\\\filename.txt"); JsonReader reader = new JsonReader(new InputStreamReader(stream, "UTF-8")); Gson gson = new Gson(); // Read file in stream mode reader.beginArray(); while (reader.hasNext()) { CarInfo carInfo = gson.fromJson(reader, CarInfo.class); } reader.endArray(); reader.close(); } catch (UnsupportedEncodingException ex) { ... } catch (IOException ex) { ... } 

Answer 2

I'm using json-simple to explain how to do this. Your json is a JSONArray (because it starts and ends with square brackets) with JSONObject (curly brackets with pair list) inside so first you've to extract the array using a JSONParser and then you can easily iterate over it and get fields from each JSONObject . Here is a simple example it just shows you an easy and understandable way:

String json = "[{ \"car\": \"Toyota\", \"colour\": \"red\", \"qty\": \"1\",\"date_manufactured\":\"12972632260006\" }, { \"car\": \"Hyundai\", \"colour\": \"red\", \"qty\": \"2\",\"date_manufactured\":\"1360421626000\" }]";
JSONParser parser = new JSONParser();
try {
    /* It's a JSONArray first. */
    JSONArray tmpArr = (JSONArray)parser.parse(json);
    for(Object obj : tmpArr){
        /* Extract each JSONObject */
        JSONObject tmpObj = (JSONObject) obj;
        System.out.println(tmpObj.get("car"));
        System.out.println(tmpObj.get("colour"));
        System.out.println(tmpObj.get("qty"));
        System.out.println(tmpObj.get("date_manufactured"));
    }
} catch (ParseException e) {
    e.printStackTrace();
}

Note that you can use Gson, it's much more complete then json-simple but a little bit trickier.