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Why NylasHow to build a scheduling application using Java and JavaSpark
Do you want to create your own custom scheduling application with Java? Here’s an extensive guide for you including Virtual Calendars
Do you want to create your own custom scheduling application with Java? Here’s an extensive guide for you including Virtual Calendars
Let’s imagine that we own a gym equipment rental business. People can reserve our gym equipment for an hour, and we need a scheduling system that can handle these reservations. Using Nylas and the Nylas Java SDK, we can create a Java and JavaSpark scheduling system where people can log in using their Google account, select a time slot, and receive a confirmation email with an event attached.
With the Nylas Calendar API, we can easily support creating new calendars and events. Here’s how:
If you already have the Nylas Java SDK installed and your Java environment is configured, then continue reading this blog.
Otherwise, I would recommend that you read the post How to Send Emails with the Nylas Java SDK to understand the setup basics.
When we launch our webpage, we need to provide a way for people to log into their Google accounts:
When pressing the button, they will be redirected to this login screen:
If you want to use a different provider you will need to configure an app for each of them:
We choose the account we want to use and enter our password:
We need to continue, as our application is still in the testing phase:
We’re going to need to access the calendar, so we need to click continue, although we can confirm that we’re just being asked for four services related to the calendar and nothing else.
Once we are logged in, we will be greeted and presented with the available spots for that particular day:
A new event will be scheduled once we click on one:
We will receive a confirmation email as well as an event on our calendar:
Now, we can see that the time slot that we selected is no longer available:
We can only reserve one spot per day, so attempting to reserve another will result in an error message:
While we can use our default calendar, it would be better to have one specially made for this project. Instead of creating a script, let’s use the Nylas CLI.
Read how to do it on the blog post A Small Guide to Virtual Calendars.
If you haven’t created a Nylas app yet, follow these steps:
The application has been successfully created:
We need to press on Connect an email account:
Enter your email address and press Connect:
You’re going to get this:
But no worries, it’s not your fault or ours. It’s Google’s increased security. Simply, let’s move to the next step.
To save you some time and to make this post shorter, we already have all the instructions you need to follow in this blog post How to Setup Your First Google API Project
As we want to create a Java web application, our best option is to use Spark, one of the most popular Micro Frameworks in the Java world.
Our project is going to be called GymEquipment, and it will have a main class called GymSchedule.java. We will need to change the default pom.xml file and create three Handlebars templates called welcome.hbs, main.hbs and scheduled.hbs. This files should live inside a templates folders inside the resources folder.
We’re going to include some useful libraries:
This is going to be our new pom.xml file:
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>GymEquipment_Updated</groupId>
<artifactId>GymEquipment_Updated</artifactId>
<version>1.0-SNAPSHOT</version>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<maven.compiler.source>17</maven.compiler.source>
<maven.compiler.target>17</maven.compiler.target>
</properties>
<dependencies>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-simple</artifactId>
<version>1.7.25</version>
</dependency>
<dependency>
<groupId>com.sparkjava</groupId>
<artifactId>spark-core</artifactId>
<version>2.9.4</version>
</dependency>
<dependency>
<groupId>com.nylas.sdk</groupId>
<artifactId>nylas-java-sdk</artifactId>
<version>1.19.2</version>
</dependency>
<dependency>
<groupId>io.github.cdimascio</groupId>
<artifactId>dotenv-java</artifactId>
<version>2.2.4</version>
</dependency>
<dependency>
<groupId>com.sparkjava</groupId>
<artifactId>spark-template-handlebars</artifactId>
<version>2.7.1</version>
</dependency>
<dependency>
<groupId>com.googlecode.json-simple</groupId>
<artifactId>json-simple</artifactId>
<version>1.1.1</version>
</dependency>
</dependencies>
<build>
<pluginManagement>
<plugins>
<plugin>
<!-- Build an executable JAR -->
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-jar-plugin</artifactId>
<version>3.1.0</version>
<configuration>
<archive>
<manifest>
<addClasspath>true</addClasspath>
<mainClass>GymSchedule</mainClass>
</manifest>
</archive>
</configuration>
</plugin>
<plugin>
<artifactId>maven-assembly-plugin</artifactId>
<configuration>
<archive>
<manifest>
<mainClass>GymSchedule</mainClass>
</manifest>
</archive>
<descriptorRefs>
<descriptorRef>jar-with-dependencies</descriptorRef>
</descriptorRefs>
</configuration>
</plugin>
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>exec-maven-plugin</artifactId>
<version>1.2.1</version>
<executions>
<execution>
<phase>package</phase>
<goals>
<goal>java</goal>
</goals>
</execution>
</executions>
<configuration>
<mainClass>GymSchedule</mainClass>
<cleanupDaemonThreads>false</cleanupDaemonThreads>
</configuration>
</plugin>
</plugins>
</pluginManagement>
</build>
</project>
And this is going to be our GymSchedule.java file:
// Import Java Utilities
import java.io.FileWriter;
import java.nio.file.Paths;
import java.time.*;
import java.time.temporal.ChronoUnit;
import java.util.*;
import java.util.concurrent.atomic.AtomicReference;
import java.io.File;
// Import Spark and Mustache libraries
import spark.ModelAndView;
import static spark.Spark.*;
import spark.template.handlebars.HandlebarsTemplateEngine;
//Import Nylas Packages
import com.nylas.*;
//Import DotEnv to handle .env files
import io.github.cdimascio.dotenv.Dotenv;
public class GymSchedule {
public static void main(String[] args) {
staticFiles.location("/public");
// Load the .env file
Dotenv dotenv = Dotenv.load();
// Create the client object
NylasClient client = new NylasClient();
// Connect it to Nylas using the Access Token from the .env file
NylasAccount account = client.account(dotenv.get("ACCESS_TOKEN"));
// Connect to Nylas using the virtual calendar token
NylasClient virtual_client = new NylasClient();
NylasAccount virtual = virtual_client.account(dotenv.get("VIRTUAL_TOKEN"));
// Create a user client object
NylasClient api = new NylasClient();
// Connect it to Nylas using the Client Id and Client Secret from the .env file
NylasApplication application = api.application(dotenv.get("CLIENT_ID"), dotenv.get("CLIENT_SECRET"));
// Create a user account based on the access_token
AtomicReference<AccountDetail> api_account = new AtomicReference<>(new AccountDetail());
// Hashmap to send parameters to our handlebars view
Map map = new HashMap();
// Default path when we load our web application
get("/", (request, response) ->
new ModelAndView(map, "welcome.hbs"),
new HandlebarsTemplateEngine());
// Call the authorization page
get("/login/nylas/authorized", (request, response) -> {
if(request.session().attribute("email_address") == null){
NativeAuthentication authentication = application.nativeAuthentication();
String accessToken = authentication.fetchToken(request.queryParams("code")).getAccessToken();
api_account.set(api.account(accessToken).fetchAccountByAccessToken());
request.session().attribute("email_address", api_account.get().getEmailAddress());
request.session().attribute("participant", api_account.get().getName());
request.session().attribute("access_token", accessToken);
response.redirect("/login");
}
return null;
});
get("/login", (request, response) -> {
if(request.session().attribute("email_address") == null){
HostedAuthentication authentication = application.hostedAuthentication();
String hostedAuthUrl = authentication.urlBuilder()
.redirectUri("http://localhost:4567/login/nylas/authorized")
.responseType("code") // Use token for client-side apps
.scopes(Scope.CALENDAR)
.loginHint("your_email@gmail.com")
.state("mycustomstate")
.buildUrl();
response.redirect(hostedAuthUrl);
}
ArrayList<ArrayList<String>> schedules = new ArrayList<>();
List<TimeSlot> timeslots = new ArrayList<>();
TimeSlot time_slots = new TimeSlot();
Calendars calendars = virtual.calendars();
// Get today's date
LocalDate today = LocalDate.now();
Instant sixPmUtc = today.atTime(10, 0).toInstant(ZoneOffset.UTC);
// Access the Events endpoint
Events events = virtual.events();
List<FreeBusy> list_busy = new ArrayList<>();
FreeBusy free_busy = new FreeBusy();
RemoteCollection<Event> events_list = events.list(new EventQuery()
.calendarId(dotenv.get("CALENDAR_ID")));
for (Event event : events_list){
Event.Timespan timespan = (Event.Timespan) event.getWhen();
time_slots.setStartTime(timespan.getStartTime());
time_slots.setEndTime(timespan.getEndTime());
timeslots.add(time_slots);
}
free_busy.setEmail("nylas_gym_calendar");
free_busy.setTimeSlots(timeslots);
list_busy.add(free_busy);
FreeBusyCalendars freeBusyCalendars = new FreeBusyCalendars(dotenv.get("VIRTUAL_ACCOUNT"), Collections.singletonList(dotenv.get("CALENDAR_ID")));
SingleAvailabilityQuery query = new SingleAvailabilityQuery()
.durationMinutes(60)
.startTime(sixPmUtc)
.endTime(sixPmUtc.plus(5, ChronoUnit.HOURS))
.intervalMinutes(60)
.calendars(freeBusyCalendars)
//.freeBusy(objTimeSlots)
.freeBusy(list_busy)
.emails(Collections.singletonList("nylas_gym_calendar"));
Availability availability = calendars.availability(query);
List<TimeSlot> aval_time_slots = availability.getTimeSlots();
LocalDateTime ldt = LocalDateTime.now();
String start_time;
String end_time;
String minutes;
String seconds;
for(TimeSlot available : aval_time_slots){
ArrayList<String> schedule = new ArrayList<>();
ldt = LocalDateTime.ofInstant(available.getStartTime(), ZoneOffset.UTC);
if(ldt.getMinute() < 10) { minutes = ldt.getMinute() + "0"; }
else { minutes = String.valueOf(ldt.getMinute());};
if(ldt.getSecond() < 10) { seconds = ldt.getSecond() + "0"; }
else { seconds = String.valueOf(ldt.getSecond());};
start_time = ldt.getHour() + ":" + minutes + ":" + seconds;
ldt = LocalDateTime.ofInstant(available.getEndTime(), ZoneOffset.UTC);
if(ldt.getMinute() < 10) { minutes = ldt.getMinute() + "0"; }
else { minutes = String.valueOf(ldt.getMinute());};
if(ldt.getSecond() < 10) { seconds = ldt.getSecond() + "0"; }
else { seconds = String.valueOf(ldt.getSecond());};
end_time = ldt.getHour() + ":" + minutes + ":" + seconds;
schedule.add(start_time);
schedule.add(end_time);
schedules.add(schedule);
}
map.clear();
// Pass parameters for the view
map.put("participant",request.session().attribute("participant"));
map.put("schedules", schedules);
// Call the handlebars template
return new ModelAndView(map, "main.hbs");
}, new HandlebarsTemplateEngine());
// Create the event
get("/schedule", (request, response) -> {
String link = "";
Boolean registered = false;
// Check if participant has been already registered
LocalDate today = LocalDate.now();
Instant sixPmUtc = today.atTime(9, 0).toInstant(ZoneOffset.UTC);
Events events = virtual.events();
RemoteCollection<Event> events_list = events.list(new EventQuery()
.calendarId(dotenv.get("CALENDAR_ID"))
.startsAfter(sixPmUtc)
.endsBefore(sixPmUtc.plus(7,
ChronoUnit.HOURS )));
for (Event event : events_list){
for( Participant participant : event.getParticipants()){
if(participant.getEmail() == request.session().attribute("email_address")){
registered = true;
}
}
}
if(!registered){
// Get time parameters
String ts = request.queryParams("start_time");
String te = request.queryParams("end_time");
link = ts + " to " + te;
Instant event_time = today.atTime(Integer.parseInt(ts.substring(0,2)),Integer.parseInt(ts.substring(6,8))).toInstant(ZoneOffset.UTC);
// We create the event details
Event event = new Event(dotenv.get("CALENDAR_ID"),
new Event.Timespan(event_time.plus(5, ChronoUnit.HOURS), event_time.plus(6, ChronoUnit.HOURS)));
event.setTitle("Nylas' Gym Equipment Reservation");
event.setLocation("Nylas' Gym");
event.setDescription("You have reserve Gym Equipment from " + ts + " to " + te);
event.setParticipants(
Arrays.asList(new Participant(request.session().attribute("email_address")).
name(request.session().attribute("participant")))
);
event.setBusy(true);
// Create the event
virtual.events().create(event, false);
// Generate the Internet Calendar Scheduling
String icsFromEvent = events.generateICS(event);
//File myObj = new File("invite.ics");
FileWriter myWriter = new FileWriter("invite.ics");
myWriter.write(icsFromEvent);
myWriter.close();
Files files = account.files();
byte[] myFile = java.nio.file.Files.readAllBytes(Paths.get("invite.ics"));
com.nylas.File upload = files.upload("invite.ics", "application/txt", myFile);
//Create a new draft
Draft draft = new Draft();
//Set the subject of the message
draft.setSubject("Nylas\\' Gym Equipment Reservation");
draft.setBody("You have reserve Gym Equipment from " + ts + " to " + te);
draft.setTo(Arrays.asList(new NameEmail(request.session().attribute("participant"),
request.session().attribute("email_address"))));
// Attach a file to a draft
draft.attach(upload);
try {
//Send the email draft
account.drafts().send(draft);
} catch (Exception e) {
//Something went wrong, display the error
System.out.print(e.getMessage());
}
}
// Call page to confirm reservation
map.clear();
// Pass parameters for the view
map.put("link",link);
map.put("registered", registered);
return new ModelAndView(map, "scheduled.hbs");
}, new HandlebarsTemplateEngine());
// Remove auth access
get("/remove", (request, response) -> {
// Revoke the access token that was passed to the Nylas client.
NylasAccount apiaccount = api.account(request.session().attribute("access_token"));
apiaccount.revokeAccessToken();
request.session().attribute("email_address", null);
request.session().attribute("participant", null);
request.session().attribute("access_token", null);
response.redirect("/");
return null;
});
}
}
On the templates folder, we’re going to start with main.hbs:
<html>
<head>
<script src="https://cdn.tailwindcss.com"></script>
<title>Nylas' Gym Equipment</title>
</head>
<body>
<div class="bg-[#315acb] border-green-600 border-b p-4 m-4 rounded grid place-items-center">
<h1 class="text-4xl text-white">Nylas' Gym Equipment</h1>
<br>
<p class="text-3xl text-center text-white">Welcome {{participant}}</p><br>
<p class="text-3xl text-center text-white">Choose a time that's convenient for you, so that we can reserve your gym equipment.</p><br><br>
{{#each schedules}}
<a href="schedule?start_time={{this.[0]}}&end_time={{this.[1]}}"><b>{{this.[0]}} to {{this.[1]}}</b></a><br>
{{/each}}
<a href="/remove" class="text-red-200"><b>Log Out</b></a>
</div>
</body>
</html>
Then the file welcome.hbs:
<html>
<head>
<script src="https://cdn.tailwindcss.com"></script>
<title>Nylas' Gym Equipment</title>
</head>
<body>
<div class="bg-[#315acb] border-green-600 border-b p-4 m-4 rounded grid place-items-center">
<h1 class="text-4xl text-white">Welcome to Nylas' Gym Equipment</h1><br><br>
<img src="images/Nyla_Space.png"><br><br><br>
<a href="/login"><img src="images/Google.png" alt="Sign in"></a>
</div>
</body>
</html>
Now scheduled.html:
<html>
<head>
<script src="https://cdn.tailwindcss.com"></script>
<title>Nylas' Gym Equipment</title>
</head>
<body>
<div class="bg-[#315acb] border-green-600 border-b p-4 m-4 rounded grid place-items-center">
{{#if registered }}
<h1 class="text-4xl text-white">You have already scheduled the usage of Nylas' Gym Equipment. Only one time per customer.</h1><br>
<h1 class="text-4xl text-white">If you want to cancel or update your reservation, contact <b>Customer Care</b>.</h1><br>
{{ else }}
<h1 class="text-4xl text-white">You have schedule the usage of Nylas' Gym Equipment</h1><br>
<p class="text-3xl text-center text-white">You will receive a confirmation for your {{link}} reservation.</p><br>
{{/if}}
<p class="text-3xl text-center text-red">With love, Nylas.</p><br><br>
<a href="/login" class="text-red-200"><b>Go back</b></a>
</div>
</div>
</body>
</html>
On the public.images folder, we need to images:
Ngrok is a globally distributed reverse proxy that allows our local applications to be exposed on the internet. We need to create a user and then install the client.
We can install it by using brew:
$ brew install ngrok/ngrok/ngrok
Then, follow the instructions on the webpage.
The first option is the installation:
Once everything is ready, we can run it by typing the following on the terminal window:
$ ./ngrok http 4567
We need to copy the Forwarding address, which will change every time we run ngrok.
To run our Java and JavaSpark Scheduling Application, we need to update our Nylas application. Head to the application settings page, choose Authentication and then type the following on the Add you callback input box:
http://localhost:4567/login/nylas/authorized
And also the address that you copied from ngrok:
https://xxxx-xxxx-xxxx-xxxx-xxxx-xxxx-xxxx-xxxx-xxxx.ngrok.io
we just need to type the following on the terminal window:
$ mvn package $ mvn exec:java -Dexec.mainClass="GymEquipment" -Dexec.cleanupDaemonThreads=false
Our application will be running on port 4567 of localhost, so we just need to open our favourite browser and go to the following address:
http://localhost:4567
Everything should work as expected.
Our application is done and working correctly, but, how do we check for existing events? Since the virtual calendar doesn’t exist on our calendar list, this might be tricky, but luckily it is not.
If you have the Nylas CLI installed (if you don’t, here’s how Working with the Nylas CLI) then just run this:
$ nylas api events get --access_token <VIRTUAL_ACCESS_TOKEN>
If you want to learn more about the Nylas Email API, please visit our documentation Nylas Calendar Documentation.
Now that we have created a Java and JavaSpark Scheduling Application, why don’t we explore and create more.
You can sign up Nylas for free and start building!
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Blag aka Alvaro Tejada Galindo is a Senior Developer Advocate at Nylas. He loves learning about programming and sharing knowledge with the community. When he’s not coding, he’s spending time with his wife, daughter and son. He loves Punk Music and reading all sorts of books.
