Parse a JSON file in Java

Question

I am using Java to parse a JSON file into a hash map so that i can search by typing a date and then get the cost, tax and profit for that date.

So that if i write:

2001-09-18 13:11:01 

I get:

7.14, 1.81 and 31.10 

Here is part of the JSON file:

{ "stat":[ { "date":" 2001-09-18 13:11:01 ", "cost":" 7.14 ", "tax":" 1.81 ", "profit":" 31.10 " }, { "date":" 2001-09-18 14:15:02 ", "cost":" 7.80 ", "tax":" 0.99 ", "profit":" 30.20 " } ] } 

And my code using Jackson:

public static void main(String[] args) throws JsonGenerationException { try { ObjectMapper mapper = new ObjectMapper(); JSONParser parser = new JSONParser(); JSONObject jsonobj = (JSONObject) parser.parse(new FileReader("test.json")); JSONArray jsons = (JSONArray) jsonobj.get("stat"); Map<Integer, Map<String, String>> jsonmaps = new HashMap<Integer, Map<String, String>>(); int i=0; for (Object j : jsons) { Map<String, String> map = new HashMap<String, String>(); JSONObject o = (JSONObject) j; map = mapper.readValue(j.toString(), new TypeReference<Map<String, String>>() { }); jsonmaps.put(i, map); i++; } System.out.println(jsonmaps.get(0).get("date")); } catch (IOException e) { e.printStackTrace(); } catch (ParseException e) { // TODO Auto-generated catch block e.printStackTrace(); } } 

Answer 1

The initial value of a map variable is not used, you can avoid this assignment and inline the variable. o is not used too.

If indexes in a map is consequent then it is better to use a List instead of Map. So the part of the code can be rewritten following way:

List<Map<String, String>> jsonmaps = new ArrayList<>(); for (Object j : jsons) { jsonmaps.add(mapper.readValue(j.toString(), new TypeReference<Map<String, String>>() {})); } 

Answer 2

If you use a POJO, your code could be reduced to:

public class Stats { public List<Stat> stat; } public class Stat { public String date; public Double cost; public Double tax; public Double profit; } public static void main(String[] args) ObjectMapper mapper = new ObjectMapper(); try { Stats stats = mapper.readValue(new File("test.json"), Stats.class); System.out.println(stats.stat.get(0).date); } catch (JsonParseException e) { e.printStackTrace(); } catch (JsonMappingException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } }