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Introduction to JSON in Java: Serialization and Deserialization

Introduction:
JSON (JavaScript Object Notation) is a lightweight data interchange format widely used for data exchange between different systems.
In Java, JSON can be used to serialize Java objects into JSON format and deserialize JSON data into Java objects.
This lecture will cover the basics of using JSON in Java, including how it works and how to perform serialization and deserialization.
JSON Basics:
JSON is a text-based format that uses human-readable key-value pairs.
It is language-independent and can be easily understood by humans and parsed by machines.
JSON data is organized into two structures:
Objects: Enclosed in curly braces {} and consist of key-value pairs.
Arrays: Enclosed in square brackets [] and contain ordered lists of values.
JSON Libraries in Java:
There are several popular JSON libraries available in Java, such as:
JSON.simple: A lightweight library for parsing and generating JSON data.
Jackson: A high-performance library with support for streaming, databinding, and tree-model processing.
Gson: A library developed by Google that provides simple APIs for parsing and generating JSON data.
For this lecture, we will focus on the Gson library.
Serialization:
Serialization is the process of converting Java objects into JSON format.
Gson provides an easy way to serialize Java objects to JSON.
Steps for serialization using Gson:
Create a Gson object.
Use the toJson() method to convert the Java object to JSON format.
Optional: Customize the serialization process using annotations or Gson configurations.
Deserialization:
Deserialization is the process of converting JSON data into Java objects.
Gson also provides powerful deserialization capabilities.
Steps for deserialization using Gson:
Create a Gson object.
Use the fromJson() method to convert JSON data into the desired Java object.
Optional: Customize the deserialization process using annotations or Gson configurations.
Handling Complex JSON Structures:
JSON data can have nested structures and complex hierarchies.
Gson provides support for handling nested objects, arrays, and custom data types.
Annotations like @SerializedName can be used to map JSON keys to Java object fields or properties.
Conclusion:
JSON is a widely used format for data exchange in various applications and systems.
In Java, Gson is a popular library for handling JSON serialization and deserialization.
By understanding how to use Gson, you can seamlessly convert Java objects to JSON and vice versa.
Utilizing JSON in Java allows for easy integration with other systems and enables efficient data transfer.

Code Lab: A Java Program that creates and consumes JSON. Some classes make JSON and send to some consumer classes. Do an example of a ticket selling app
Here's an example of a Java program that simulates a ticket selling app using JSON for communication between classes:
javaCopy code
import org.json.JSONArray;
import org.json.JSONObject;

import java.util.ArrayList;
import java.util.List;

// Class representing a Ticket
class Ticket {
private String event;
private String date;
private String location;
private int price;

public Ticket(String event, String date, String location, int price) {
this.event = event;
this.date = date;
this.location = location;
this.price = price;
}

public JSONObject toJSON() {
JSONObject ticketJson = new JSONObject();
ticketJson.put("event", event);
ticketJson.put("date", date);
ticketJson.put("location", location);
ticketJson.put("price", price);
return ticketJson;
}
}

// Class representing the Ticket Provider
class TicketProvider {
public JSONArray getAllTickets() {
List<Ticket> tickets = new ArrayList<>();
tickets.add(new Ticket("Concert", "2023-07-15", "City Stadium", 50));
tickets.add(new Ticket("Sports Match", "2023-07-20", "Sports Arena", 30));
tickets.add(new Ticket("Theater Play", "2023-07-25", "Grand Theater", 80));

JSONArray ticketsJson = new JSONArray();
for (Ticket ticket : tickets) {
ticketsJson.put(ticket.toJSON());
}

return ticketsJson;
}
}

// Class representing the Ticket Consumer
class TicketConsumer {
public void displayTickets(JSONArray ticketsJson) {
System.out.println("Available Tickets:");
for (int i = 0; i < ticketsJson.length(); i++) {
JSONObject ticketJson = ticketsJson.getJSONObject(i);
String event = ticketJson.getString("event");
String date = ticketJson.getString("date");
String location = ticketJson.getString("location");
int price = ticketJson.getInt("price");

System.out.println("Event: " + event);
System.out.println("Date: " + date);
System.out.println("Location: " + location);
System.out.println("Price: $" + price);
System.out.println();
}
}
}

public class TicketSellingApp {
public static void main(String[] args) {
TicketProvider ticketProvider = new TicketProvider();
JSONArray ticketsJson = ticketProvider.getAllTickets();

TicketConsumer ticketConsumer = new TicketConsumer();
ticketConsumer.displayTickets(ticketsJson);
}
}

In this program, we have three classes: Ticket, TicketProvider, and TicketConsumer.
The Ticket class represents a ticket and contains properties such as event name, date, location, and price. It provides a toJSON method that converts a Ticket object to a JSONObject.
The TicketProvider class acts as the ticket provider and generates an array of tickets. It creates Ticket objects, converts them to JSON using the toJSON method, and adds them to a JSONArray. The getAllTickets method returns this JSON array containing all the tickets.
The TicketConsumer class represents the ticket consumer and displays the tickets. It takes the JSON array of tickets as input and iterates through each ticket JSON object, extracting the necessary details and displaying them on the console.
In the main method of the TicketSellingApp class, we create an instance of TicketProvider and call the getAllTickets method to get the JSON array of tickets. Then, we create an instance of TicketConsumer and pass the JSON array to the displayTickets method to display the tickets.
When you run the program, you will see the tickets being displayed on the console. Here's the completed code for the TicketConsumer class and the main method of the TicketSellingApp class:
javaCopy code
import org.json.JSONArray;
import org.json.JSONObject;

public class TicketConsumer {
public void displayTickets(JSONArray ticketsJson) {
System.out.println("Available Tickets:");
for (int i = 0; i < ticketsJson.length(); i++) {
JSONObject ticketJson = ticketsJson.getJSONObject(i);
String event = ticketJson.getString("event");
String date = ticketJson.getString("date");
String location = ticketJson.getString("location");
int price = ticketJson.getInt("price");

System.out.println("Event: " + event);
System.out.println("Date: " + date);
System.out.println("Location: " + location);
System.out.println("Price: $" + price);
System.out.println();
}
}

public static void main(String[] args) {
TicketProvider ticketProvider = new TicketProvider();
JSONArray ticketsJson = ticketProvider.getAllTickets();

TicketConsumer ticketConsumer = new TicketConsumer();
ticketConsumer.displayTickets(ticketsJson);
}
}

When you execute the main method of the TicketSellingApp class, it creates an instance of TicketProvider and calls the getAllTickets method to obtain the JSON array of tickets. Then, it creates an instance of TicketConsumer and passes the JSON array to the displayTickets method, which iterates through each ticket JSON object, extracts the necessary details, and displays them on the console.
The output will be:
yamlCopy code
Available Tickets:
Event: Concert
Date: 2023-07-15
Location: City Stadium
Price: $50

Event: Sports Match
Date: 2023-07-20
Location: Sports Arena
Price: $30

Event: Theater Play
Date: 2023-07-25
Location: Grand Theater
Price: $80

This demonstrates how the TicketConsumer class consumes the JSON array of tickets and displays the ticket details, providing information about the available tickets to potential buyers.
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