How do I parse JSON objects from a JSONArray?

Question

I have a very large JSON file in the following format:

[{"fullname": "name1", "id": "123"}, {"fullname": "name2", "id": "245"}, {"fullname": "name3", "id": "256"}]

It looks like a JSONArray. All the records are written in the same line.

Can you help me how can I parse this file using Java. I want to read each JSON object and display all the fullname and ids. Below is my attempt, but my code is not working:

import org.apache.commons.lang3.StringEscapeUtils;
import org.json.simple.JSONArray;
import org.json.simple.JSONObject;
import org.json.simple.parser.JSONParser;
import org.json.simple.parser.ParseException;

public class JSONFileReaderDriver {

public static void main(String[] args) throws FileNotFoundException, 
IOException, ParseException 
{
 String filename="Aarau";
 String src="C:\\"+filename+".json";
 JSONParser parser = new JSONParser();
 JSONObject obj;
 try
    {
        BufferedReader br=new BufferedReader (new FileReader(src));  
        obj = (JSONObject) new JSONParser().parse(row);
        String fullname=obj.get("fullname");
        String id=obj.get("id");
        System.out.println ("fullname: "+fullname+" id: "+id);
    }catch(Exception e)
     {e.printStackTrace();}
   br.close();
  }
 }

Do you plan to use any library like gson if that's easy way to parse? — phonemyatt
– phonemyatt, Commented Nov 22, 2017 at 13:44
In what way is your code not working? Do you see any errors? — Henrik Aasted Sørensen
– Henrik Aasted Sørensen, Commented Nov 22, 2017 at 13:45
"but my code is not working" - What specifically is not working? Are there any errors or exceptions? — phflack
– phflack, Commented Nov 22, 2017 at 13:45
Error: Unexpected token END OF FILE at position 0. at org.json.simple.parser.JSONParser.parse(JSONParser.java:257) at org.json.simple.parser.JSONParser.parse(JSONParser.java:81) at org.json.simple.parser.JSONParser.parse(JSONParser.java:75) at JSONReader.JSONFileReaderDriver.main(JSONFileReaderDriver.java:56) — user4213837
– user4213837, Commented Nov 22, 2017 at 13:54

Herr Derb · Accepted Answer · 2017-11-22 14:20:45Z

Make your life easy and use an ObjectMapper. This way you simply define a Pojo with the same properties as you json object.

In you case you need a Pojo that looks like this:

public class Person{
    private String fullname;
    private int id;

    public Person(String fullname, int id) {
        this.fullname = fullname;
        this.id = id;
    }

    public String getFullname() {
        return fullname;
    }

    public int getId() {
        return id;
    }
}

With that you only need to do:

ObjectMapper objectMapper = new ObjectMapper();
List<Person> persons = objectMapper.readValue(myInputStream, TypeFactory.defaultInstance().constructCollectionType(List.class, Person.class));

This is a hassle free and type safe approach.

Dependencies needed:

https://github.com/FasterXML/jackson-databind

<dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-databind</artifactId>
</dependency>

Rahul Rabhadiya · Accepted Answer · 2017-11-22 13:52:17Z

4

you can use Json.simple java api , below is code that can helpful to you

        byte[] bFile = Files.readAllBytes(new File("C:/xyz.json").toPath());
        JSONArray root = (JSONArray) JSONValue.parseWithException(bFile);
        JSONObject rootObj = (JSONObject) root.get(0);

You can get values from JSONObject based on key , it also depends on format of your json as there could be nested json data. So you have to extract data accordingly . Apart from this you can use jackson parser api or GSON as well.

answered Nov 22, 2017 at 13:52

Rahul Rabhadiya

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Comments

user4213837 · Accepted Answer · 2017-11-22 14:09:41Z

3

Okay folks...just solved my problem. I am posting the solution in case someone runs into the same issue again, can use my solution. My solution is partly motivated by Rahul Rabhadiya. Thanks, dude.

try{
 row=br.readLine();
            JSONArray root = (JSONArray) JSONValue.parseWithException(row);

            for (int i=0;i<root.size();i++)
            {

            JSONObject rootObj = (JSONObject) root.get(i);
            String fullname=(String) rootObj.get("fullname");

            System.out.println (fullname);
            }
    }catch(Exception e)
         {
        e.printStackTrace();
        }

answered Nov 22, 2017 at 14:09

user4213837

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1 Comment

SmugDoodleBug Over a year ago

You should have given the answer credit to Rahul Rabhadiya because he came up with this solution just before you did.

ajc · Accepted Answer · 2017-11-29 14:59:25Z

3

Your json is a JSONArray, so when you are parsing it, you need to parse it as a JSONArray.

        JSONParser jsonParser = new JSONParser();
        JSONArray a = (JSONArray) jsonParser.parse(new FileReader(src));
        for (Object o : a) {
            // access your object here. 
        }

edited Nov 29, 2017 at 14:59

answered Nov 22, 2017 at 14:08

ajc

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Gorazd Rebolj · Accepted Answer · 2017-11-22 13:47:12Z

0

I would suggest going with Jackson, in particular the Jackson Streaming API which is perfect for parsing large arrays like this.

See this answer: https://stackoverflow.com/a/24838392/3765428

answered Nov 22, 2017 at 13:47

Gorazd Rebolj

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