How to read the contents of a JSON file using Java?

JSON or JavaScript Object Notation is a lightweight text-based open standard designed for human-readable data interchange. Conventions used by JSON are known to programmers and include C, C++, Java, Python, Perl, etc. Sample JSON document ?

{
   "book": [  
      {
         "id": "01",
         "language": "Java",
         "edition": "third",
         "author": "Herbert Schildt"
      },
      {
         "id": "07",
         "language": "C++",
         "edition": "second",
         "author": "E.Balagurusamy"
      }
   ]
}

Json-simple library

The json-simple is a lightweight library which is used to process JSON objects. Using this, you can read or write the contents of a JSON document using a Java program.

JSON-Simple Maven Dependency

Following is the maven dependency for the JSON-simple library ?

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

Paste this within the <dependencies> </dependencies> tag at the end of your pom.xml file (before the </project> tag).

Example

First of all, let us create a JSON document with name sample.json with the 6 key-value pairs as shown below ?

{
   "ID": "1",
   "First_Name": "Shikhar",
   "Last_Name": "Dhawan",
   "Date_Of_Birth": "1981-12-05",
   "Place_Of_Birth":"Delhi",
   "Country": "India"
}

To read the contents of a JSON file using a Java program Follow the steps given below −

Step 1: Instantiate the JSONParser class of the json-simple library.

JSONParser jsonParser = new JSONParser();

Step 2: Parse the contents of the obtained object using the parse() method.

//Parsing the contents of the JSON file
FileReader fReader = new FileReader("E:/players_data.json")
JSONObject jsonObject = (JSONObject) jsonParser.parse(fReader);

Step 3: Retrieve the value associated with a key using the get() method.

String value = (String) jsonObject.get("key_name");

The following Java program parses the above-created sample.json file, reads its contents, and displays them.

import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import org.json.simple.JSONObject;
import org.json.simple.parser.JSONParser;
import org.json.simple.parser.ParseException;
public class ReadingJSON {
   public static void main(String args[]) {
      //Creating a JSONParser object
      JSONParser jsonParser = new JSONParser();
      try {
         //Parsing the contents of the JSON file
         JSONObject jsonObject = (JSONObject) jsonParser.parse(new FileReader("E:/sample.json"));
         String id = (String) jsonObject.get("ID");
         String first_name = (String) jsonObject.get("First_Name");
         String last_name = (String) jsonObject.get("Last_Name");
         String date_of_birth = (String) jsonObject.get("Date_Of_Birth");
         String place_of_birth = (String) jsonObject.get("Place_Of_Birth");
         String country = (String) jsonObject.get("Country");
         //Forming URL
         System.out.println("Contents of the JSON are: ");
         System.out.println("ID :" + id);
         System.out.println("First name: " + first_name);
         System.out.println("Last name: " + last_name);
         System.out.println("Date of birth: " + date_of_birth);
         System.out.println("Place of birth: " + place_of_birth);
         System.out.println("Country: " + country);
         System.out.println(" ");
      } catch (FileNotFoundException e) {
         e.printStackTrace();
      } catch (IOException e) {
         e.printStackTrace();
      } catch (ParseException e) {
         e.printStackTrace();
      }
   }
}

Output

Contents of the JSON are:
ID :1
First name: Shikhar
Last name: Dhawan
Date of birth :1981-12-05
Place of birth: Delhi
Country: India

Using Jackson Library

The Jackson library is also a powerful library for reading content JSON in Java. Below is a program to demonstrate how we can use this library:

import com.fasterxml.jackson.databind.ObjectMapper;
import java.io.File;
import java.io.IOException;

public class ReadingJSONWithJackson {
   public static void main(String[] args) {
      ObjectMapper objectMapper = new ObjectMapper();
      try {
         Person person = objectMapper.readValue(new File("E:/sample.json"), Person.class);
         System.out.println(person);
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

class Person {
   public String ID;
   public String First_Name;
   public String Last_Name;
   public String Date_Of_Birth;
   public String Place_Of_Birth;
   public String Country;

   @Override
   public String toString() {
      return "ID: " + ID + ", First Name: " + First_Name + ", Last Name: " + Last_Name + ", Date Of Birth: " + Date_Of_Birth + ", Place Of Birth: " + Place_Of_Birth + ", Country: " + Country;
   }
}

Using Gson Library

The Gson library is developed by Google and it also helps us to read JSON content in java. The below program demonstrates the process to achieve it −

import com.google.gson.Gson;
import java.io.FileReader;
import java.io.IOException;

public class ReadingJSONWithGson {
   public static void main(String[] args) {
      Gson gson = new Gson();
      try (FileReader reader = new FileReader("E:/sample.json")) {
         Person person = gson.fromJson(reader, Person.class);
         System.out.println(person);
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}