Next, you'll create a SubscriptionHandler.java class in the handlers package. This class includes the methods to handle the subscription requests placed from the home page.

To create a new class, select the File > New menu to open the Select a Wizard page. Select the Class option in the wizard and click Next. The New Java Class wizard will be opened. Use handlers as the package name and SubscriptionHandler.java as the class name and click Finish.

To create the subscription handler, place the following code in the class you just created. Remember to update the EPI key and the EPI ID in the appropriate fields:

package handlers;

import java.io.IOException;
import java.math.BigDecimal;
import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpHeaders;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.util.Map;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.google.gson.Gson;
import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
import com.google.gson.reflect.TypeToken;

import utils.Utils;

@WebServlet("/subscriptionhandler")
public class SubscriptionHandler extends HttpServlet {

	private static final String EPI_KEY = "<YOUR_EPI_KEY>";

	private static final String EPI_ID = "<YOUR_EPI_ID>";

	private static final String API_URL = "https://billing.epxuap.com";

	private static final long serialVersionUID = 7901708808237295496L;

	@Override
	protected void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		// Retrieve form data from the HttpServletRequest
		String firstName = request.getParameter("FirstName");
		String lastName = request.getParameter("LastName");
		String phone = request.getParameter("Phone");
		String email = request.getParameter("Email");
		String accountNumber = request.getParameter("AccountNumber");
		String expirationDate = request.getParameter("ExpirationDate");
		String cvv = request.getParameter("CVV");
		String postalCode = request.getParameter("PostalCode");
		String streetAddress = request.getParameter("StreetAddress");
		// String amount = request.getParameter("Amount");
		String frequency = request.getParameter("frequency");

		String billingDate = request.getParameter("BillingDate");
		System.out.println("date:" + billingDate);

		String numberOfPayments = request.getParameter("NumberOfPayments");

		String description = request.getParameter("Description");
		String plan = request.getParameter("plan");

		String subscriptionId = request.getParameter("subId");

		String changeSubscription = request.getParameter("changeSub");

		String responseCode = "";
String subscriptionMessage = "";

		if (subscriptionId != null && subscriptionId.equals("0")) {
			JsonObject inputJSON = generateJSONFromInput(firstName, lastName, phone, email, accountNumber,
					expirationDate, cvv, postalCode, streetAddress, frequency, billingDate, numberOfPayments,
					description, plan);
			responseCode = addSubscription(inputJSON);
			if (responseCode.equals("00")) {
subscriptionMessage = "Subscription created succesfully. ";

				redirectToProfilePage(response, email, subscriptionMessage);
			} else {
				printErrorMessage(response, responseCode);
			}

		} else {
			JsonObject jsonObject = new JsonObject();

			BigDecimal decimalValue = new BigDecimal(subscriptionId);
			int subscirptionIdInt = decimalValue.intValue();
			jsonObject.addProperty("SubscriptionID", subscirptionIdInt);

			int httpResponseCode = 0;

			if (changeSubscription != null && changeSubscription.equals("pause")) {

				jsonObject.addProperty("Paused", true);

				httpResponseCode = pauseResumeSubscription(email, jsonObject);
subscriptionMessage = "Successfully paused.";

			} else if (changeSubscription != null && changeSubscription.equals("resume")) {

				jsonObject.addProperty("Paused", false);

				httpResponseCode = pauseResumeSubscription(email, jsonObject);
subscriptionMessage = "Successfully resumed.";

			} else if (changeSubscription != null && changeSubscription.equals("cancel")) {

				httpResponseCode = cancelSubscription(email, jsonObject);
subscriptionMessage = "Successfully cancelled.";

			}

			if (httpResponseCode == 200) {

				redirectToProfilePage(response, email, subscriptionMessage);
			} else {
				printErrorMessage(response, responseCode);
			}
		}
		response.setContentType("text/html");

	}

	private void printErrorMessage(HttpServletResponse response, String responseCode) throws IOException {
		response.getWriter()
				.println("<h1>Error while creating subscription with the following response code!</h1>");
		response.getWriter().println("<h2> " + responseCode + "!</h2>");
	}

	private void redirectToProfilePage(HttpServletResponse response, String email, String subscriptionMessage) throws IOException {
		response.getWriter().println("<h1>Processed successfully!</h1>");

		String redirectURL = "/profile?mailID=" + email + "&subscriptionMessage=" + subscriptionMessage;
		response.sendRedirect(redirectURL);
	}

	private JsonObject generateJSONFromInput(String firstName, String lastName, String phone, String email,
			String accountNumber, String expirationDate, String cvv, String postalCode, String streetAddress,
			String frequency, String billingDate, String numberOfPayments, String description, String plan) {
		JsonObject customerDataJson = new JsonObject();
		customerDataJson.addProperty("FirstName", firstName);
		customerDataJson.addProperty("LastName", lastName);
		customerDataJson.addProperty("Phone", phone);
		customerDataJson.addProperty("Email", email);

		JsonObject creditCardData = new JsonObject();
		creditCardData.addProperty("AccountNumber", accountNumber);
		creditCardData.addProperty("ExpirationDate", expirationDate);
		creditCardData.addProperty("CVV", cvv);

		creditCardData.addProperty("FirstName", firstName);
		creditCardData.addProperty("LastName", lastName);
		creditCardData.addProperty("PostalCode", postalCode);
		creditCardData.addProperty("StreetAddress", streetAddress);
		// System.out.println(creditCardData.toString());

		JsonObject paymentMethod = new JsonObject();

		paymentMethod.add("CreditCardData", creditCardData);

		double amount = 0;

		if (plan.equals("basic")) {
			amount = 2121.21;
		} else if (plan.equals("premium")) {
			amount = 5000.00;
		}

		JsonObject subscriptionData = new JsonObject();

		subscriptionData.addProperty("Amount", amount);

		subscriptionData.addProperty("Frequency", frequency);

		subscriptionData.addProperty("BillingDate", billingDate);

		subscriptionData.addProperty("FailureOption", "Forward");

		subscriptionData.addProperty("NumberOfPayments", Integer.parseInt(numberOfPayments));
		subscriptionData.addProperty("Retries", 5);
		subscriptionData.addProperty("Description", description);

		JsonObject mainJson = new JsonObject();
		mainJson.add("CustomerData", customerDataJson);
		mainJson.add("PaymentMethod", paymentMethod);
		mainJson.add("SubscriptionData", subscriptionData);

		addJSONTOFireStore(email, "CustomerData", customerDataJson);
		addJSONTOFireStore(email, "CreditCardData", paymentMethod.getAsJsonObject("CreditCardData"));
		addJSONTOFireStore(email, "SubscriptionData", subscriptionData);

		return mainJson;
	}

	private void addJSONTOFireStore(String collectionName, String documentID, JsonObject jsonString) {
		TypeToken<Map<String, Object>> typeToken = new TypeToken<Map<String, Object>>() {
		};
		Map<String, Object> data = new Gson().fromJson(jsonString, typeToken.getType());
		try {
			FireStoreHandler.createDocument(collectionName, documentID, data);

		} catch (Exception e) {

			e.printStackTrace();
		}
	}

	private String addSubscription(JsonObject jsonPayload) {

		String endPoint = "/subscription";

		String requestURI = API_URL + endPoint;

		HttpResponse<String> response = executeHttpRequest(jsonPayload, endPoint, requestURI);

		String emailID = jsonPayload.getAsJsonObject("CustomerData").get("Email").getAsString();

		Gson gson = new Gson();

		JsonObject responseString = gson.fromJson(response.body(), JsonObject.class);

		JsonElement subscriptionResult = responseString.get("VerifyResult");
		String responseCode = subscriptionResult.getAsJsonObject().get("Code").getAsString();

		System.out.println(responseCode);

		if (responseCode.equals("00")) {

			addJSONTOFireStore(emailID, "SubscriptionData", responseString);

		}
		return responseCode;
	}

	private int pauseResumeSubscription(String emailId, JsonObject jsonPayload) {

		String endPoint = "/subscription/pause";

		String requestURI = API_URL + endPoint;

		HttpResponse<String> response = executeHttpRequest(jsonPayload, endPoint, requestURI);

		Gson gson = new Gson();

		JsonObject responseString = gson.fromJson(response.body(), JsonObject.class);

		addJSONTOFireStore(emailId, "SubscriptionResponse", responseString);

		return response.statusCode();

	}

	private int cancelSubscription(String emailId, JsonObject jsonPayload) {

		String endPoint = "/subscription/cancel";

		String requestURI = API_URL + endPoint;

		HttpResponse<String> response = executeHttpRequest(jsonPayload, endPoint, requestURI);

		Gson gson = new Gson();

		JsonObject responseString = gson.fromJson(response.body(), JsonObject.class);

		addJSONTOFireStore(emailId, "SubscriptionResponse", responseString);

		return response.statusCode();
	}

	private HttpResponse<String> executeHttpRequest(JsonObject jsonPayload, String endPoint, String requesURI) {

		Gson gson = new Gson();

		String jsonString = gson.toJson(jsonPayload);

		String signature = null;

		HttpClient httpClient = HttpClient.newHttpClient();

		URI uri = URI.create(requesURI);

		HttpResponse<String> response;

		try {

			signature = Utils.createSignature(endPoint, jsonString, EPI_KEY);

			HttpRequest request = HttpRequest.newBuilder(uri).header("Content-Type", "application/json")
					.header("EPI-Signature", signature).header("EPI-Id", EPI_ID)
					.POST(HttpRequest.BodyPublishers.ofString(jsonString)).build();

			response = httpClient.send(request, HttpResponse.BodyHandlers.ofString());

			int statusCode = response.statusCode();

			HttpHeaders headers = response.headers();

			String responseBody = response.body();

			System.out.println("Response Code: " + statusCode);

			System.out.println("Response Headers: " + headers);

			System.out.println("Response Body: " + responseBody);

			return response;

		} catch (NoSuchAlgorithmException | InvalidKeyException | IOException | InterruptedException e) {

			e.printStackTrace();
		}
		return null;

	}
}

The subscription handler receives the Post request from the home and profile pages and handles them as follows:

• If the subscription ID is null or 0, it adds a new subscription using the /subscription endpoint.
• If the subscription ID is not null and has a proper numeric value, it checks the change requested to the subscription, whether pause, resume, or cancel. Based on this request parameter, it calls the appropriate API endpoint.

All the API endpoints, request specifications, and response models are available in North's documentation for subscriptions.

/subscription, /subscription/pause, and /subscription/cancel are invoked using the HTTP post requests as follows:

• A request URL is created using the API URL https://billing.epxuap.com and the appropriate endpoint.
• A request signature is created using the createSignature() method and the EPI_KEY, as explained above.
• An HttpRequest is built using the JSON payload, EPI-ID, and the EPI-Signature. The request is sent, and the response is received.
• The response is added to the Firestore database for displaying the information on the profile page.

For example, while creating a new subscription, you'll invoke the /subscription endpoint. If the subscription is successful, it returns a 200 response code in the HttpResponse. In the HttpResponse body is a JSON object called VerifyResult, and inside this JSON object is a nested JSON with a key code. Its response code is 00, denoting that the subscription was successfully created.

Add this response to Firestore and redirect the user to the profile page.

Now you'll create a HomeServlet.java class in the demo package. This class includes the methods to create a home page and display the available plans as well as a button to subscribe to a plan. When the button is clicked, it'll send the appropriate request to the subscription handler to create a subscription.

Create another new class using the same steps as before, but use demo as the package name and HomeServlet.java as the class name. To create the home page, place the following code in this new class:

package demo;

import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

@WebServlet("/home")
public class HomeServlet extends HttpServlet {
    private static final long serialVersionUID = -1541805457506999385L;

	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {
        response.setContentType("text/html");
        PrintWriter out = response.getWriter();
        out.println("<html><body>");
        
        out.println("<h1>North Subscription Demo</h1>");

        out.println("<form method=\"POST\" action=\"/subscriptionhandler?subId=0\">");
        out.println("First Name: <input type=\"text\" name=\"FirstName\" value=\"Joe\"><br><br>");
        out.println("Last Name: <input type=\"text\" name=\"LastName\" value=\"Doe\"><br><br>");
        out.println("Phone: <input type=\"text\" name=\"Phone\" value=\"1234567890\"><br><br>");
        out.println("Email: <input type=\"text\" name=\"Email\" value=\"jdoe@domanin.com\"><br><br>");
        out.println("Address: <input type=\"text\" name=\"Address\" value=\"1234 Ruby Road\"><br><br>");
        out.println("Postal Code: <input type=\"text\" name=\"PostalCode\" value=\"12346\"><br><br>");
        
        out.println("<h2>Credit Card Information</h2>");
        
        out.println("Account Number: <input type=\"text\" name=\"AccountNumber\" value =\"400000000000000002\"><br><br>");
        out.println("Expiration Date: <input type=\"text\" name=\"ExpirationDate\"  placeholder=\"YYMM\" value=\"2211\" required><br><br>");
        out.println("CVV: <input type=\"text\" name=\"CVV\" value=\"123\"><br><br>");

        
        out.println("<h2>Subscription Details</h2>");
        
        out.println("Select Plan:");
        out.println("<label><input type=\"radio\" name=\"plan\" value=\"basic\" checked> Basic ($2121.21) </label>");
        out.println("<label><input type=\"radio\" name=\"plan\" value=\"premium\"> Premium ($5000.00)</label><br><br>");

        out.println("Frequency:");
        out.println("<label><input type=\"radio\" name=\"frequency\" value=\"Weekly\"> Weekly</label>");
        out.println("<label><input type=\"radio\" name=\"frequency\" value=\"Biweekly\"> Biweekly</label>");
        out.println("<label><input type=\"radio\" name=\"frequency\" value=\"Monthly\" checked> Monthly</label><br><br>");

        out.println("Billing Date: <input type=\"date\" name=\"BillingDate\"><br><br>");
        out.println("Number of Payments: <input type=\"text\" name=\"NumberOfPayments\" value =\"5\"><br><br>");
        out.println("Description: <input type=\"text\" name=\"Description\" value=\"Subscription for Streaming service\"><br><br>");

        out.println("<input type=\"submit\" value=\"Submit\">");
        out.println("</form>");

        out.println("</body></html>");

    }
}

It creates the HTML form for getting the profile, payment, and subscription information from users. It also defines that a Post request should be sent to the /subscriptionhandler with the query parameter subId=0 when the form is submitted. Here, subId=0 denotes that a new subscription must be created with the available details.

This form allows the user to enter their profile information such as name and address as well as payment information such as credit card details. They can also select the subscription plan and payment intervals (weekly, biweekly, or monthly).

Now you'll create a ProfileServlet.java class in the demo package. This class includes the methods to display the subscription details such as the username, the subscribed plan, and a button to pause or cancel the subscription. When the cancel or pause button is clicked, it'll send the appropriate request to the subscription handler to modify the subscription.

Create a new class using the same steps as before but use demo as the package name and ProfileServlet.java as the class name. Place the following code in this class to create the profile page:

package demo;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Map;

import javax.servlet.annotation.WebServlet;

import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import handlers.FireStoreHandler;

@WebServlet("/profile")
public class ProfileServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;

	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {
		response.setContentType("text/html");
		PrintWriter out = response.getWriter();
		out.println("<html><body>");
		out.println("<h1>North Profile Page</h1>");

		String emailId = request.getParameter("mailID");
		String subscriptionMessage = request.getParameter("subscriptionMessage");

		Map<String, Map<String, Object>> documents = getUserDocumentsFromFireStore(emailId);
		
		
		
		String firstName = documents.get("CustomerData").get("FirstName").toString();
		
		out.println("<h2>Welcome " + firstName + "! </h2><br><br>");

if (subscriptionMessage != null && subscriptionMessage !="") {
			out.println("<h3>Subscription Status : " + subscriptionMessage + "! </h3><br>");
		}

		out.println("<form method=\"POST\" action=\"/your-action-url\">");

		out.println("First Name: <input type=\"text\" name=\"FirstName\" value = "+ firstName + "><br><br>");
		out.println("Last Name: <input type=\"text\" name=\"LastName\" value = " + documents.get("CustomerData").get("LastName") + "><br><br>");
		out.println("Phone: <input type=\"text\" name=\"Phone\" value = " + documents.get("CustomerData").get("Phone") + "><br><br>");
		out.println("Email: <input type=\"text\" name=\"Email\" value = " + documents.get("CustomerData").get("Email") + "><br><br>");

		out.println("<h2>Credit Card Information</h2>");
		out.println("Account Number: <input type=\"text\" name=\"AccountNumber\"  value = " + documents.get("CreditCardData").get("AccountNumber") + "><br><br>");
		out.println("Expiration Date: <input type=\"text\" name=\"ExpirationDate\"  value = " + documents.get("CreditCardData").get("ExpirationDate") + "><br><br>");
		out.println("CVV: <input type=\"text\" name=\"CVV\" value = " + documents.get("CreditCardData").get("CVV") + "><br><br>");

		out.println("<h2>Subscription Details</h2>");
		out.println("Amount: <input type=\"text\" name=\"Amount\"  value = " + documents.get("SubscriptionData").get("Amount") + "><br><br>");
		out.println("Frequency: <input type=\"text\" name=\"Frequency\"  value = " + documents.get("SubscriptionData").get("Frequency") + "><br><br>");
		out.println("Billing Date: <input type=\"text\" name=\"BillingDate\"  value = " + documents.get("SubscriptionData").get("BillingDate") + "><br><br>");
		out.println("Failure Option: <input type=\"text\" name=\"FailureOption\"  value = " + documents.get("SubscriptionData").get("FailureOption") + "><br><br>");
		out.println("Number of Payments: <input type=\"text\" name=\"NumberOfPayments\"  value = " + documents.get("SubscriptionData").get("NumberOfPayments") + "><br><br>");
		out.println("Retries: <input type=\"text\" name=\"Retries\"  value = " + documents.get("SubscriptionData").get("Retries") + "><br><br>");
		out.println("Description: <input type=\"text\" name=\"Description\"  value = " + documents.get("SubscriptionData").get("Description").toString() + "><br><br>");

		String subscriptionId = documents.get("SubscriptionData").get("id").toString();
		
		out.println("<input type=\"hidden\" name=\"subscriptionid\" value=\"" + subscriptionId + "\">");
		
		
		out.println("<input type=\"button\" value=\"pause\" onclick=\"submitForm(this.value);\">");
		out.println("<input type=\"button\" value=\"resume\" onclick=\"submitForm(this.value);\">");
		out.println("<input type=\"button\" value=\"cancel\" onclick=\"submitForm(this.value);\">");
		out.println("</form>");
		out.println("<script>");
		out.println("function submitForm(buttonValue) {");
		out.println("    var form = document.createElement('form');");
		out.println("    form.setAttribute('method', 'post');");
		out.println("    form.setAttribute('action', '/subscriptionhandler');");

		out.println("    var hiddenField = document.createElement('input');");
		out.println("    hiddenField.setAttribute('type', 'hidden');");
		out.println("    hiddenField.setAttribute('name', 'Email');");
		out.println("    hiddenField.setAttribute('value', '" + emailId + "');");
		out.println("    form.appendChild(hiddenField);");

		out.println("    var changeSubField = document.createElement('input');");
		out.println("    changeSubField.setAttribute('type', 'hidden');");
		out.println("    changeSubField.setAttribute('name', 'changeSub');");
		out.println("    changeSubField.setAttribute('value', buttonValue);"); 
		out.println("    form.appendChild(changeSubField);");
		
		out.println("    var subscriptionIdField = document.createElement('input');");
		out.println("    subscriptionIdField.setAttribute('type', 'hidden');");
		out.println("    subscriptionIdField.setAttribute('name', 'subId');");
		out.println("    subscriptionIdField.setAttribute('value', '" + subscriptionId + "');"); 
		out.println("    form.appendChild(subscriptionIdField);");

		out.println("    document.body.appendChild(form);");
		out.println("    form.submit();");
		out.println("}");
		out.println("</script>");

		
		out.println("</body></html>");

	}

	private Map<String, Map<String, Object>> getUserDocumentsFromFireStore(String emailId) {
		Map<String, Map<String, Object>> documents = null;
		try {
			documents = FireStoreHandler.getAllDocuments(emailId);
		} catch (Exception e) {
			
			e.printStackTrace();
		}
		return documents;
	}
}

The profile servlet accepts a query parameter mailID. Based on this email ID, it will fetch the necessary documents from Firestore and display details such as name, address, credit card data, and other subscription details on the profile page.

It also creates buttons to pause, resume, and cancel subscriptions. When these buttons are clicked, a Post request is sent to the subscription handler with the parameters emailid, SubscriptionID, and the request type (pause, resume, or cancel). Based on these parameters, the subscription handler will process the request.