Reading Writing JSON File in JAVA

JSON.simple is lightweight JSON processing library which can be used to read JSON, write JSON file. Produced JSON will be in full compliance with JSON specification (RFC4627).

In this JSON tutorial, we will see quick examples to write JSON file with JSON.simple and then we will read JSON file back.

Json.simple maven dependency

Update pom.xml with json-simple maven dependency. [Link]

<dependency>     <groupId>com.googlecode.json-simple</groupId>     <artifactId>json-simple</artifactId>     <version>1.1.1</version> </dependency>

2. Write JSON to file in Java with json-simple

To write JSON to file, we will be working to mainly two objects:

1. JSONArray : To write data in json arrays. Use its add() method to add objects of type JSONObject.
2. JSONObject : To write json objects. Use it’s put() method to populate fields.

After populating above objects, use FileWriter instance to write JSON file.

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();         }     } }

Program Output.

employees.json

[     {         "employee": {             "firstName": "Lokesh",             "lastName": "Gupta",             "website": "howtodoinjava.com"         }     },     {         "employee": {             "firstName": "Brian",             "lastName": "Schultz",             "website": "example.com"         }     } ]

3. Read JSON from file in Java with json-simple

To read JSON from file, we will be using the JSON file we created in the previous example.

1. First of all, we will create JSONParser instance to parse JSON file.
2. Use FileReader to read JSON file and pass it to parser.
3. Start reading the JSON objects one by one, based on their type i.e. JSONArray and JSONObject.

Read JSON Example

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);     } }

Program Output.

Console

[{"employee":{"firstName":"Lokesh","lastName":"Gupta","website":"howtodoinjava.com"}},{"employee":{"firstName":"Brian","lastName":"Schultz","website":"example.com"}}] Lokesh Gupta howtodoinjava.com Brian Schultz example.com