Adding a String in front and at the end of a (JSON) File?

Question

I've tried to read from a JSON-File for the first time (see code below...). Now my problem is, that my json file is auto-generated by rtl_433 and it is incomplete. In order for my code to work, I need to add the following in front and at the end of the JSON-File:

String front = "{"data":[";
String end = "]}"

Is there a way to do this in the code below? I thought about converting the data from the Filereader into a String and adding the two Strings to it before going on, processing it... I'ld also need to add "," in between a variable Number of JSON-Objects.. But it seems to me, that that's not possible.

I'm looking forwards to hearing your solution ideas! Please don't over-complicate it, I'm completely new, and coding is just a hobby - yet... :)

try{
            //Creating JSON-Parser
            JSONParser parser = new JSONParser();
            try {     
                ////Parsing the contents of the JSON file & casting received Object as JSON Object
                JSONObject obj = (JSONObject) parser.parse(new FileReader(path_json_file));
                JSONArray jsonArray = (JSONArray) obj.get("data");
                String[][] arr = new String[jsonArray.size()][3];
                
                SimpleDateFormat time_parser = new SimpleDateFormat("yyyy-MM-dd' 'HH:mm:ss");
                
                Date[] time = new Date[jsonArray.size()];
                
                System. out. println("Following data found in JSON-File:");
                
                for(int i=0; i<jsonArray.size(); i++){
                    
                    JSONObject jsonobj = (JSONObject) jsonArray.get(i);
    
                    
                    String time1 = (String) jsonobj.get("time");
                    try{
                        time[i] = time_parser.parse(time1);
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                    System.out.print("  " + time1);

Here's a example of my JSON-File, the number of JSON-Objects varies:


{"time" : "2021-01-16 21:43:53", "model" : "Fineoffset-WH2A", "id" : 252, "temperature_C" : -3.000, "humidity" : 62, "mic" : "CRC"}
{"time" : "2021-01-16 21:43:54", "model" : "Bresser-3CH", "id" : 252, "temperature_C" : -17, "humidity" : 62, "mic" : "CRC"}
{"time" : "2021-01-18 21:43:53", "model" : "Bresser-3CH", "id" : 252, "temperature_C" : -3.500, "humidity" : 62, "mic" : "CRC"}
{"time" : "2021-01-17 14:16:34", "model" : "Bresser-3CH", "id" : 246, "channel" : 3, "battery_ok" : 0, "temperature_C" : -0.500, "humidity" : 86, "mic" : "CHECKSUM"}
{"time" : "2021-01-17 14:16:43", "model" : "Fineoffset-WH2A", "id" : 252, "temperature_C" : 1.200, "humidity" : 71, "mic" : "CRC"}
{"time" : "2021-01-17 14:16:49", "model" : "Bresser-3CH", "id" : 153, "channel" : 1, "battery_ok" : 0, "temperature_C" : 0.444, "humidity" : 81, "mic" : "CHECKSUM"}

you can convert the json object to string, then you can concat the json string at the front and last of the convert json string refer - https://stackoverflow.com/questions/17651395/convert-jsonobject-to-string — Karthick, Jan 17 '21 at 13:52

score 1 · Answer 1 · answered Jan 17 '21 at 14:59

What if you don't need to modify your file at all?

Here is my suggested solution which parses each line individually instead of treating the entire file content as a json.

 public static void main(String... args) {
    try {
        JSONParser parser = new JSONParser();
        List<Date> datesFromJsonFile = Files.lines(Paths.get("path/to/file.json"))
                                            .map(jsonLine -> parseSingleLine(parser, jsonLine))
                                            .map(jsonObject -> (String) jsonObject.get("time"))
                                            .map(time -> parseDate(time))
                                            .collect(Collectors.toList());

    } catch (Exception e) {
        e.printStackTrace();
    }
}

private static Date parseDate(String time) {
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd' 'HH:mm:ss");

    try {
        return sdf.parse(time);
    } catch (java.text.ParseException e) {
        throw new RuntimeException("Cannot parse date", e);
    }
}

private static JSONObject parseSingleLine(JSONParser parser, String jsonLine) {
    try {
        return (JSONObject) parser.parse(jsonLine);
    } catch (ParseException e) {
        throw new RuntimeException("Cannot parse json", e);
    }
}

Adding a String in front and at the end of a (JSON) File?

1 Answers1