read json file java code example

Example 1: java load .json file

import net.sf.json.JSONObject;
import net.sf.json.JSONSerializer;
import org.apache.commons.io.IOUtils; 

    public class JsonParsing {

        public static void main(String[] args) throws Exception {
            InputStream is = 
                    JsonParsing.class.getResourceAsStream( "sample-json.txt");
            String jsonTxt = IOUtils.toString( is );

            JSONObject json = (JSONObject) JSONSerializer.toJSON( jsonTxt );        
            double coolness = json.getDouble( "coolness" );
            int altitude = json.getInt( "altitude" );
            JSONObject pilot = json.getJSONObject("pilot");
            String firstName = pilot.getString("firstName");
            String lastName = pilot.getString("lastName");

            System.out.println( "Coolness: " + coolness );
            System.out.println( "Altitude: " + altitude );
            System.out.println( "Pilot: " + lastName );
        }
    }

Example 2: how to read file in java jacakson

try {
    // create object mapper instance
    ObjectMapper mapper = new ObjectMapper();

    // convert JSON file to map
    Map<?, ?> map = mapper.readValue(Paths.get("book.json").toFile(), Map.class);

    // print map entries
    for (Map.Entry<?, ?> entry : map.entrySet()) {
        System.out.println(entry.getKey() + "=" + entry.getValue());
    }

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

Example 3: how to read from json files in java

package com.howtodoinjava.demo.jsonsimple;
 
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
 
import org.json.simple.JSONArray;
import org.json.simple.JSONObject;
import org.json.simple.parser.JSONParser;
import org.json.simple.parser.ParseException;
 
public class ReadJSONExample 
{
    @SuppressWarnings("unchecked")
    public static void main(String[] args) 
    {
        //JSON parser object to parse read file
        JSONParser jsonParser = new JSONParser();
         
        try (FileReader reader = new FileReader("employees.json"))
        {
            //Read JSON file
            Object obj = jsonParser.parse(reader);
 
            JSONArray employeeList = (JSONArray) obj;
            System.out.println(employeeList);
             
            //Iterate over employee array
            employeeList.forEach( emp -> parseEmployeeObject( (JSONObject) emp ) );
 
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (ParseException e) {
            e.printStackTrace();
        }
    }
 
    private static void parseEmployeeObject(JSONObject employee) 
    {
        //Get employee object within list
        JSONObject employeeObject = (JSONObject) employee.get("employee");
         
        //Get employee first name
        String firstName = (String) employeeObject.get("firstName");    
        System.out.println(firstName);
         
        //Get employee last name
        String lastName = (String) employeeObject.get("lastName");  
        System.out.println(lastName);
         
        //Get employee website name
        String website = (String) employeeObject.get("website");    
        System.out.println(website);
    }
}

Example 4: decode json file in java tutorial

package com.howtodoinjava.demo.jsonsimple;
 
import java.io.FileWriter;
import java.io.IOException;
 
import org.json.simple.JSONArray;
import org.json.simple.JSONObject;
 
public class WriteJSONExample
{
    @SuppressWarnings("unchecked")
    public static void main( String[] args )
    {
        //First Employee
        JSONObject employeeDetails = new JSONObject();
        employeeDetails.put("firstName", "Lokesh");
        employeeDetails.put("lastName", "Gupta");
        employeeDetails.put("website", "howtodoinjava.com");
         
        JSONObject employeeObject = new JSONObject(); 
        employeeObject.put("employee", employeeDetails);
         
        //Second Employee
        JSONObject employeeDetails2 = new JSONObject();
        employeeDetails2.put("firstName", "Brian");
        employeeDetails2.put("lastName", "Schultz");
        employeeDetails2.put("website", "example.com");
         
        JSONObject employeeObject2 = new JSONObject(); 
        employeeObject2.put("employee", employeeDetails2);
         
        //Add employees to list
        JSONArray employeeList = new JSONArray();
        employeeList.add(employeeObject);
        employeeList.add(employeeObject2);
         
        //Write JSON file
        try (FileWriter file = new FileWriter("employees.json")) {
 
            file.write(employeeList.toJSONString());
            file.flush();
 
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}