What is JSON-Java (org.json)?

JSON(Javascript Object Notation) is a lightweight format of data exchange and it is independent of language. It is easily read and interpreted by humans and machines. Hence nowadays, everywhere JSON is getting used for transmitting data. Let us see how to prepare JSON data by using JSON.org JSON API  in java

• JSON.simple is a library in java is used that allows parsing/generating/transforming/querying  JavaScript Object Notation, etc.,
• Necessary jar file:  json-simple-1.1.jar. It has to be available in the classpath
• In Maven-driven projects it should be present in pom.xml as follows

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

We can store the items in the form of JSONObject or JSONArray. JSONArray is nothing but the collection of multiple JSON Objects. A sample JSON object can be viewed as follows

Let us see the ways how to create a JSON object  

JsonEncodeExample.java

Java

// Importing JSON simple library
import org.json.simple.JSONObject;

// Creating a public class
public class JsonEncodeExample {

    // Calling the main method
    public static void main(String[] args)
    {
        // Creating an object of JSON class
        JSONObject geekWriterObject = new JSONObject();

        // Entering the values using the created object
        geekWriterObject.put("geekWriterId",
                             new Integer(100));
        geekWriterObject.put("geekWritterName",
                             "GeekAuthor1");
        geekWriterObject.put("status", new Boolean(true));
        geekWriterObject.put("publishedArticlesIn",
                             "Java,Python");

        // Printing the values through the created object
        System.out.print(geekWriterObject);
    }
}

On running the above program we can see the output as 

If we beautify this using the online JSON viewer, we will get the same output as appeared in the sample JSON

JsonDecodeExample.java

Java

// importing JSON simple libraries
import org.json.simple.JSONArray;
import org.json.simple.JSONObject;
import org.json.simple.parser.JSONParser;
import org.json.simple.parser.ParseException;

// Creating a public class
public class JsonDecodeExample {

    // calling the main method
    public static void main(String[] args)
    {
        // creating an object of JSONparser
        JSONParser jsonParser = new JSONParser();
        // defining and assigning value to a string
        String sampleString = "[28,{\"38\":{\"48\":{\"58\":{\"68\":[78,{\"88\":98}]}}}}]";
        try {
            Object object = jsonParser.parse(sampleString);

            // creating a JSON array
            JSONArray array = (JSONArray)object;

            System.out.println("The array's first  element is");

              // always start the index by 0
            System.out.println(array.get(0));
            System.out.println("The array's second  element is");
            System.out.println(array.get(1));
            System.out.println();

            // creating a JSON object
            JSONObject jsonObject = (JSONObject)array.get(1);
            System.out.println("Value of \"38\"");
            System.out.println(jsonObject.get("38"));
        }
        catch (ParseException pr) {
            System.out.println("The elements position is: "
                               + pr.getPosition());
            System.out.println(pr);
        }
    }
}

On running the above program, we get the output as follows

Let us see how the JSONObject and JSONArray can be written in an external file named “author.json” via

JSONWriteExample.java

Java

// importing java simple libraries and JSON libraries
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
    {
        // Json object is created
        JSONObject jsonObject = new JSONObject();

        // Adding data using the created object
        jsonObject.put("firstName", "Rachel");
        jsonObject.put("lastName", "Green");
        jsonObject.put("age", 30);
        jsonObject.put("noOfPosts", 100);
        jsonObject.put("status", "active");

        // LinkedHashMap is created for address data
        Map addressMap = new LinkedHashMap(4);
        addressMap.put("road", "MG Road Cross cut Street");
        addressMap.put("city", "Bangalore");
        addressMap.put("state", "Karnataka");
        addressMap.put("pinCode", 560064);

        // adding address to the created JSON object
        jsonObject.put("addressOfAuthor", addressMap);

        // JSONArray is created to add the phone numbers
        JSONArray phoneNumberJsonArray = new JSONArray();
        addressMap = new LinkedHashMap(2);
        addressMap.put("presentAt", "home");
        addressMap.put("phoneNumber", "1234567890");

        // adding map to list
        phoneNumberJsonArray.add(addressMap);
        addressMap = new LinkedHashMap(2);
        addressMap.put("type2", "fax1");
        addressMap.put("no1", "6366182095");

        // map is added to the list
        phoneNumberJsonArray.add(addressMap);

        // adding phone numbers to the created JSON object
        jsonObject.put("phoneNos", phoneNumberJsonArray);

        // the JSON data is written into the file
        PrintWriter printWriter = new PrintWriter("author.json");
        printWriter.write(jsonObject.toJSONString());
        printWriter.flush();
        printWriter.close();
    }
}

On running the above program, we can see the “author.json” file is created in the mentioned location and its contents are as follows  (The output is beautified and shown here as reference)

Let us see how to read the JSON via

JSOnReadExample.java

Java

// importing JSON simple libraries
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
    {
        // The file JSON.json is parsed
        Object object = new JSONParser().parse(new FileReader("author.json"));

        // objc is convereted to JSON object
        JSONObject jsonObject = (JSONObject)object;

        // obtaining the fname and lname
        String firstName = (String)jsonObject.get("firstName");
        String lastName = (String)jsonObject.get("lastName");
        System.out.println("FirstName = " + firstName);
        System.out.println("LastName = " + lastName);

        // age is obtained
        long ageOfAuthor = (long)jsonObject.get("age");
        System.out.println("Age = " + ageOfAuthor);

        // address is obtained
        System.out.println("Address details:");
        Map addressOfAuthor = ((Map)jsonObject.get("addressOfAuthor"));

        // iterating through the address
        Iterator<Map.Entry> iterator = addressOfAuthor.entrySet().iterator();
        while (iterator.hasNext()) {
            Map.Entry pair1 = iterator.next();
            System.out.println(pair1.getKey() + " : "+ pair1.getValue());
        }
        // phone numbers are obtained
        System.out.println("Phone Number details:");
        JSONArray phoneNumberJSONArray = (JSONArray)jsonObject.get("phoneNos");

        // iterating phoneNumbers
        Iterator phoneNumberIterator = phoneNumberJSONArray.iterator();
        while (phoneNumberIterator.hasNext()) {
            iterator = ((Map)phoneNumberIterator.next())
                           .entrySet()
                           .iterator();
            while (iterator.hasNext()) {
                Map.Entry pair1 = iterator.next();
                System.out.println(pair1.getKey() + " : "
                                   + pair1.getValue());
            }
        }
    }
}

On running the program, we can see the output as follows:

Conclusion

JSON is a lightweight easily readable, understandable, and iteratable transportation medium. Nowadays it is the output mechanism that got followed in any REST API calls. This way of mechanism is easily understood in android and IOS development and hence one JSON output of REST API call serves the purpose of many communications.