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Lightweight real time analytics with Spring Boot + WSO2 Siddhi by@tharinduvibuddha

Lightweight real time analytics with Spring Boot + WSO2 Siddhi

Tharindu Vibuddha Gangodagama Hacker Noon profile picture

Tharindu Vibuddha Gangodagama

Are you looking for a way to create a lightweight real time analytics engine?This article explains how to do exactly that by combining a fast, embed-able real time analytics library (WSO2 Siddhi) with an immensely popular micro services platform, Spring Boot. As a bonus I will show you how doing that under 5 minutes using with code-generation!. After following this article you can generate a full-fledged Java spring boot project with a documented REST API, friendly, responsive front-end, basic spring security, comprehensive test coverage and database integration with just a few shell commands. The generated code will be your foundation for real time micro service/ application.

Jhipster is a handy application generator that creates Spring Boot and Angular application. Jhipster is one of the best low code Development platforms in open source community. Jhipster had become very popular GitHub within short amount of time. It has a high performance Java stack on the server side with spring boot and a front-end with angular,bootstrap and react. It makes project management easy with powerful workflow , build tools like Yeoman, Webpack and Maven/Gradle. Many developers personally use it to generate multiple Spring micro services that are preconfigured to work in their company’s infrastructure. But this articles’ objective is not to give a detail explanation about Jhipster. This article will focus on how to create a Jhipster module for WSO2 Siddhi. If you are new to Jhipster or want to read more about Jhipster, please read {}.

You may have some specific real time analytics (WSO2 Siddhi) setup that you like to use in your Jhipster projects. Because you don’t want to reinvent your own wheel in every project, it makes sense to abstract all the boilerplate into your own generator. In that case you can build your own Jhipster generator for WSO2 Siddhi and use it with your every Jhipster project.

At, we heavily rely on code generation (with a custom built tool chain) to get rid of a lot of boilerplate code which we tend to program into each and every solution/project/product. When we encounter a repeatable architectural pattern we tend to apply our tool chain so next time we don’t have to code it again. Most of this work, including the tool chain is part of the Xiges low code platform.

Getting set up

This section explains how to build the basic Jhipster generator module. If you already know how to create a jhipster module, you can skip this part and go to the next section.

A Jhipster module is a Yeoman generator. Also, it is an NPM package. As a first step to generate a basic yeoman generator (which would eventually be our jhipster generator) install NodeJS. After that you’ll need to have Yeoman ,Yarn and Bower installed as well as the generator (yo) for creating generators.Please follow below commands with npm.

npm install -g generator-generator

npm install -g yeoman

npm install -g yo

To check whether Yeoman is installed correctly just type yo command on the command line which would list you all the installed generators. If you can find yeoman there, you are good to go. Finally make sure you have git installed.
First create a new directory which you’ll write your jhipster generator. This directory must be named as generator-jhipster-<name of your module(Siddhi) > . Normally a Yeoman generator is prefixed with “generator-” but Jhipster modules are prefixed with “generator-jhipster-“. Executing the below commands in order would create the folder and generate the jhipster module template.

npm install -g generator-jhipster-module
mkdir generator-jhipster-siddhi
cd generator-jhipster-siddhi
yo jhipster-module

This is not really a JHipster module, that is meant to not be used in a JHipster application. This module is used to generate a new template for coding a new JHipster module for Siddhi. A JHipster module to create a JHipster module. Answer the questions to generate the module, so we can implement the changes.

File structure

As you can see we have readme file and package.json for generator itself. Test folder holds tests for the generator. The index.js file is the entry point for the generator. It contains the template files for the boilerplate (for generating the actual scaffolding). We created the default generator. Now we can modify it and add the our custom features.

Scripting the WSO2 Siddhi generator

Now we will check how to customize the jhipster generator we created and add our own features in the generator with the following steps:

  1. Setup and import the generator-jhipster

The index.js file needs to export the generator-jhipster which will get run by Yeoman. Now I am going to clear the everything in our generator and start from the scratch. Here is what index.js file look after that.

const chalk = require(‘chalk’);
const generator = require(‘yeoman-generator’);
const packagejs = require(‘../../package.json’);
// Stores JHipster variables
const jhipsterVar = { moduleName: ‘siddhi’ };
// Stores JHipster functions
const jhipsterFunc = {};
module.exports = generator.extend({
// all your yeoman code here

We assign the extended generator to the module.exports make it available to the ecosystem. This is the typical method we use when we export modules in the Node.js. Then we can have our own functionalities to perform through methods. In every method we added to the index.js is run once the generator is called and usually in sequence. Some method names have priority in this generator. The available priorities (in running order) are in order:

  1. initializing- Initialization of your methods.(getting configs and checking project current state )
  2. prompting — prompt user preferences for the options( call this.prompt()).
  3. configuring — Saving configurations and configure the project.
  4. default — If your method name doesn’t match priority and put into this group.
  5. writing — copy template-files to the output folder and parsing (routes, controllers, etc).
  6. conflicts — Handling the conflicts.
  7. install — Where installations are run and specially add maven dependencies to the target Jhipster project pom file. (npm, bower)
  8. end — Called last, cleanup.

After implementing these methods your file should be like this.

Jhipster module uses Composability, which is one of the main functions in Yeoman. The “composeWith” (this.composeWith()) method in yeoman generators allows the generator to run parallel with another generator and it can use features from the other generator instead of having to do it all by itself. In this above example it composes with the “jhipster:modules” sub generator and get the access to Jhipster’s variables and functions.

As you can see in the code we add Jhipster function (under the install() phase) to add Maven dependencies into the pom.xml file (addMavenDependency). Also used Jhipster global variables. These are the short definition for each variable.

baseName: the name of the application

packageName: the Java package name
angularAppName: the AngularJS application name

javaDir: the directory for the Java application, including the package folder

resourceDir: the directory containing the Java resources (always src/main/resources)

webappDir: the directory containing the Web application (always src/main/webapp)

You can see java spring boot classes and resource files, add to the writing()phase and it’s done by calling the template function(all the java spring boot classes described in the next section ) . If you interested in other functions available in Jhipster module please visit —

2. Initializing the generator

We initialize our generator with package.json. In the above code Node invokes that require() function with a local file path as the function’s only argument and it gets the package.json file.This file is a Node.js module manifest. Our package.json file must contain the following.

I configured the following:

  • yo: CLI tool for running Yeoman generators.
  • generator-mocha: a generator for the mocha test-framework.
  • gulp: a front-end build tool.
  • mocha: mocha is a JavaScript test framework for Node.js programs.

3. Create gulp file

We use the gulp file as our build system. Tools like Gulp are often referred to as “build tools” because they are tools for running the tasks for building a web application.Your gulp file must be look like this.

It’s often used to do front end tasks like:

  • Spinning up a web server
  • Reloading the browser automatically whenever a file is saved
  • Using preprocessors like Sass or LESS
  • Optimizing assets like CSS, JavaScript, and images

So now we have finished the creating basics of jhipster generator for WSO2 Siddhi. But now we have to configure Spring boot with Real time analytics(WSO2 Siddhi).

Spring boot + Real time analytics

Spring boot is a very popular java-based framework for building web and enterprise based applications. Spring framework provides a wide variety of features addressing modern business needs. Spring boot makes it easy to create stand-alone, production-grade spring based applications that can “just run”. Spring boot takes an opinionated view of spring platform and combining third party libraries so developers can start with minimum fuss. Most of spring boot applications need a little bit of spring configuration. Because of this spring boot had become low code development platform. So It’s easy to embed WSO2 Siddhi to spring boot. Lets see how it’s done.

Before we go further we have to understand main concepts about real time analytics with WSO2 Siddhi. WSO2 Siddhi is a java library which carries out real time processing on complex events.The streaming SQL Language of Siddhi is being used to describe complex conditions from the data streams. Siddhi is able to perform both Stream and complex event processing. Below diagram shows the basic workflow of the WSO2 Siddhi 3.0.

Basic workflow of the WSO2 Siddhi 3.0

Now we are Embedding Siddhi in a Java Spring boot project and it allows you to use the Siddhi query language to carry out real time processing of complex events without running a WSO2 CEP server.

Implementing Business Service and adding POST Rest Service for Siddhi Application

As a first step we need to define a stream definition and Siddhi query.Stream definition always define the format of your incoming events and query is defined as below.

String definition = "define stream TempStream(roomNo int, temperature double, deviceId long);"
String query = "@info(name = 'avgTemperature') " +"from TempStream#window.time(60 sec)  " +"select avg(temperature) as temperature,deviceID " +"group by roomNo " +
"insert into AvgTempStream ;";

Step 02: Creating Siddhi runtime

This step involves creating a runtime representation of a siddhiAppRuntime by combining the stream definition and the Siddhi query you created in Step one.

SiddhiManager siddhiManager = new SiddhiManager();
//Generating runtime
SiddhiAppRuntime siddhiAppRuntime = siddhiManager .createSiddhiAppRuntime(definition+query);

The Siddhi Manager parses the Siddhi App and provides you with a Siddhi app run time. This Siddhi app run time is used to add callbacks and input handlers to the Siddhi app run time.

Step 03: Registering a Callback

Siddhi has two types of callbacks.

  • Stream Callback — this subscribes to an event stream
  • Query Callback — this subscribe to a query

We need a callback to retrieve output events from query. So we can register a callback to the Siddhi app runtime. When results are generated, they are sent to the receive method of this callback. Also, we can print the incoming events from an event printer which is added inside this callback.


siddhiAppRuntime.addCallback("AvgTempStream", new QueryCallback() {
public void receive(Event[] events) {

Step 04: Sending events

As a final step you need to send events from the event stream to the query, you need to obtain an input handler as below example.

//Retrieving input handler to push events into Siddhi        
InputHandler inputHandler =siddhiAppRuntime .getInputHandler("StockEventStream");         
//Starting event processing        
//Sending events to Siddhi        
inputHandler.send(new Object[]{2, 23.0, 100L});

Refer to these files at the bottom of the article for exact implementation of the Business Service and adding POST Rest Service for Siddhi Application.


Creating a JHipster module with WSO2 Siddhi is an easy way to simplify your micro service generation, especially if your micro service uses the same configuration. Since it is a module, it’s very easy to add functionalities and meet your needs. Our company Xiges Solutions uses this real time analytics for making real-time predictions and tracking with our IOT products.

Here is GitHub repository with the module used in this blog. Feel free to fork it and make changes to match your company requirements!

Now you can download jhipster generator for siddhi by using this command

npm install g generator-jhipster-siddhi

Then run the module on a jhipster generated application.

yo jhipster-siddhi

Soon this module will be available in the jhipster marketplace.(After JHipster team verifies it )

link for the source code-

link for the npm registry-

If you got any suggestions or enhancements you want to see in the module, please create an issue in the Xiges git hub repository —

That’s all I have for this topic. Thanks for reading. Until next time!