[Quick Start] Using QBit's Event Bus System (The Employee example)

##Overview

QBit has an event bus. The advantage of Using the event bus with QBit services is that the events come into the same queue that handles the method calls so that the events method calls are thread safe. Everything comes in on the same thread, events and methods. The event bus is very fast, expect speeds up to 10M to 100M messages per second. Also the event bus is a great way to include additional services without disrupting existing services. With QBit's event bus you can send objects, strongly typed objects, JSON, Maps, etc.

You can wire QBit Services into many event bus systems. This makes it easy to wire a service to listen to events coming from Kafka, RabbitMQ or something else.

Using QBit's Event Bus System (The Employee example)

This wiki will walk you through a simple "employee example" to demonstrate to you how to use QBit's event bus system.

What you will build

You will build a simple "employee example" that includes four services; each service will handle the following situations: when a new employees is hired, add the employee to the payroll system, enroll the employee into the benefits system, and invite them to our community outreach program.

In this example the first service will not know about the other services. And we can add more services in the future which can listen to events and participate in the new employee being hired. This will be great example to demonstrate to you how to use QBit's event bus system. When you run this example you will get the following:

Hired employee Employee{firstName='Rick', employeeId=1}
Employee added to payroll  Rick 1 100
Employee enrolled into benefits system employee Rick 1
Employee will be invited to the community outreach program Rick 1

How to complete this guide

In order to complete this example successfully you will need the following installed on your machine:

• Gradle; if you need help installing it, visit Installing Gradle.
• Your favorite IDE or text editor (we recommend [Intellig IDEA ] (https://www.jetbrains.com/idea/) latest version).
• [JDK ] (http://www.oracle.com/technetwork/java/javase/downloads/jdk8-downloads-2133151.html) 1.8 or later.
• Build and install QBit on your machine click [Building QBit ] (https://github.com/advantageous/qbit/wiki/%5BQuick-Start%5D-Building-QBit-the-microservice-lib-for-Java) for instrutions.

Now that your machine is all ready let's get started:

• [Download ] (https://github.com/fadihub/event-bus-system-qbit/archive/master.zip) and unzip the source repository for this guide, or clone it using Git:

https://github.com/fadihub/event-bus-system-qbit.git

Once this is done you can test the service, let's first explain the process:

The process will be explained in more detail under [[Detailed Tutorial] Using the Event Bus System with QBit (The Employee example)] (https://github.com/advantageous/qbit/wiki/%5BDetailed-Tutorial%5D-Using-QBit's-Event-Bus-System-(The-Employee-example))

EmployeeEventExampleUsingSystemEventBus.java Listing

src/main/java/io.advantageous.qbit.example/EmployeeEventExampleUsingSystemEventBus

/*
 * Copyright (c) 2015. Rick Hightower, Geoff Chandler
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *  		http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * QBit - The Microservice lib for Java : JSON, WebSocket, REST. Be The Web!
 */

package io.advantageous.qbit.example;

import io.advantageous.qbit.annotation.OnEvent;
import io.advantageous.qbit.events.EventManager;
import io.advantageous.qbit.service.ServiceQueue;
import io.advantageous.boon.core.Sys;

import static io.advantageous.qbit.service.ServiceBuilder.serviceBuilder;
import static io.advantageous.qbit.service.ServiceContext.serviceContext;
import static io.advantageous.qbit.service.ServiceProxyUtils.flushServiceProxy;

/**
 * Created by rhightower on 2/4/15.
 */
public class EmployeeEventExampleUsingSystemEventBus {

    public static final String NEW_HIRE_CHANNEL = "com.mycompnay.employee.new";

    public static final String PAYROLL_ADJUSTMENT_CHANNEL = "com.mycompnay.employee.payroll";

    public static void main(String... args) {


        EmployeeHiringService employeeHiring = new EmployeeHiringService();
        PayrollService payroll = new PayrollService();
        BenefitsService benefits = new BenefitsService();
        VolunteerService volunteering = new VolunteerService();


        ServiceQueue employeeHiringServiceQueue = serviceBuilder()
                .setServiceObject(employeeHiring)
                .setInvokeDynamic(false).build().startServiceQueue();


        ServiceQueue payrollServiceQueue = serviceBuilder()
                .setServiceObject(payroll)
                .setInvokeDynamic(false).build().startServiceQueue();


        ServiceQueue employeeBenefitsServiceQueue = serviceBuilder()
                .setServiceObject(benefits)
                .setInvokeDynamic(false).build().startServiceQueue();


        ServiceQueue volunteeringServiceQueue = serviceBuilder()
                .setServiceObject(volunteering)
                .setInvokeDynamic(false).build().startServiceQueue();

        EmployeeHiringServiceClient employeeHiringServiceClientProxy = employeeHiringServiceQueue.createProxy(EmployeeHiringServiceClient.class);

        employeeHiringServiceClientProxy.hireEmployee(new Employee("Rick", 1));

        flushServiceProxy(employeeHiringServiceClientProxy);

        Sys.sleep(5_000);

    }

    interface EmployeeHiringServiceClient {
        void hireEmployee(final Employee employee);

    }

    public static class Employee {
        final String firstName;
        final int employeeId;

        public Employee(String firstName, int employeeId) {
            this.firstName = firstName;
            this.employeeId = employeeId;
        }

        public String getFirstName() {
            return firstName;
        }

        public int getEmployeeId() {
            return employeeId;
        }

        @Override
        public String toString() {
            return "Employee{" +
                    "firstName='" + firstName + '\'' +
                    ", employeeId=" + employeeId +
                    '}';
        }
    }

    public static class EmployeeHiringService {


        public void hireEmployee(final Employee employee) {

            int salary = 100;
            System.out.printf("Hired employee %s\n", employee);

            //Does stuff to hire employee

            //Sends events
            final EventManager eventManager = serviceContext().eventManager();
            eventManager.send(NEW_HIRE_CHANNEL, employee);
            eventManager.sendArray(PAYROLL_ADJUSTMENT_CHANNEL, employee, salary);


        }

    }

    public static class BenefitsService {

        @OnEvent(NEW_HIRE_CHANNEL)
        public void enroll(final Employee employee) {

            System.out.printf("Employee enrolled into benefits system employee %s %d\n",
                    employee.getFirstName(), employee.getEmployeeId());

        }

    }

    public static class VolunteerService {

        @OnEvent(NEW_HIRE_CHANNEL)
        public void invite(final Employee employee) {

            System.out.printf("Employee will be invited to the community outreach program %s %d\n",
                    employee.getFirstName(), employee.getEmployeeId());

        }

    }

    public static class PayrollService {

        @OnEvent(PAYROLL_ADJUSTMENT_CHANNEL)
        public void addEmployeeToPayroll(final Employee employee, int salary) {

            System.out.printf("Employee added to payroll  %s %d %d\n",
                    employee.getFirstName(), employee.getEmployeeId(), salary);

        }

    }
}

Test The Service

With your terminal cd event-bus-system-qbit

then gradle clean build then gradle run and you should get the following:

Hired employee Employee{firstName='Rick', employeeId=1}
Employee added to payroll  Rick 1 100
Employee enrolled into benefits system employee Rick 1
Employee will be invited to the community outreach program Rick 1

Summary

You have built and tested "The Employee example" to learn about QBit's event bus system, see you in the next tutorial!