How to parse JSON in Java

// Java program for write JSON to a file

import java.io.FileNotFoundException;
import java.io.PrintWriter;
import java.util.LinkedHashMap;
import java.util.Map;
import org.json.simple.JSONArray;
import org.json.simple.JSONObject;

public class JSONWriteExample
{
    public static void main(String[] args) throws FileNotFoundException 
    {
        // creating JSONObject
        JSONObject jo = new JSONObject();
        
        // putting data to JSONObject
        jo.put("firstName", "John");
        jo.put("lastName", "Smith");
        jo.put("age", 25);
        
        // for address data, first create LinkedHashMap
        Map m = new LinkedHashMap(4);
        m.put("streetAddress", "21 2nd Street");
        m.put("city", "New York");
        m.put("state", "NY");
        m.put("postalCode", 10021);
        
        // putting address to JSONObject
        jo.put("address", m);
        
        // for phone numbers, first create JSONArray 
        JSONArray ja = new JSONArray();
        
        m = new LinkedHashMap(2);
        m.put("type", "home");
        m.put("number", "212 555-1234");
        
        // adding map to list
        ja.add(m);
        
        m = new LinkedHashMap(2);
        m.put("type", "fax");
        m.put("number", "212 555-1234");
        
        // adding map to list
        ja.add(m);
        
        // putting phoneNumbers to JSONObject
        jo.put("phoneNumbers", ja);
        
        // writing JSON to file:"JSONExample.json" in cwd
        PrintWriter pw = new PrintWriter("JSONExample.json");
        pw.write(jo.toJSONString());
        
        pw.flush();
        pw.close();
    }
}

// Java program to read JSON from a file

import java.io.FileReader;
import java.util.Iterator;
import java.util.Map;

import org.json.simple.JSONArray;
import org.json.simple.JSONObject;
import org.json.simple.parser.*;

public class JSONReadExample 
{
    public static void main(String[] args) throws Exception 
    {
        // parsing file "JSONExample.json"
        Object obj = new JSONParser().parse(new FileReader("JSONExample.json"));
        
        // typecasting obj to JSONObject
        JSONObject jo = (JSONObject) obj;
        
        // getting firstName and lastName
        String firstName = (String) jo.get("firstName");
        String lastName = (String) jo.get("lastName");
        
        System.out.println(firstName);
        System.out.println(lastName);
        
        // getting age
        long age = (long) jo.get("age");
        System.out.println(age);
        
        // getting address
        Map address = ((Map)jo.get("address"));
        
        // iterating address Map
        Iterator<Map.Entry> itr1 = address.entrySet().iterator();
        while (itr1.hasNext()) {
            Map.Entry pair = itr1.next();
            System.out.println(pair.getKey() + " : " + pair.getValue());
        }
        
        // getting phoneNumbers
        JSONArray ja = (JSONArray) jo.get("phoneNumbers");
        
        // iterating phoneNumbers
        Iterator itr2 = ja.iterator();
        
        while (itr2.hasNext()) 
        {
            itr1 = ((Map) itr2.next()).entrySet().iterator();
            while (itr1.hasNext()) {
                Map.Entry pair = itr1.next();
                System.out.println(pair.getKey() + " : " + pair.getValue());
            }
        }
    }
}