AWS serverless application model(SAM) and AWS toolkit


SAM : The AWS Serverless Application Model (SAM) is an open-source framework for building serverless applications. It provides shorthand syntax to express functions, APIs, databases, and event source mappings. With just a few lines per resource, you can define the application you want and model it using YAML. During deployment, SAM transforms and expands the SAM syntax into AWS CloudFormation syntax, enabling you to build serverless applications faster. ref – AWS doc.

AWS toolkit : The AWS Toolkit is an open source plug-in that makes it easier to create, debug, and deploy Java and Python applications on Amazon Web Services. Apart from this AWS toolkit provides explorer in IDE like: CloudFormation, CloudWatch logs, DynamoDB, ECR, ECS, Lambda, S3, SqS and Schemas etc.

Assuming you have AWS CLI already install on your machine , in case if not installed, please follow this link,

Here is quick command sharing for MacOs.

#brew install awscli
#aws --version

Assuming you have already created your AWS account, now here we are going to configure aws account credentail on local machine for later use. here we will create default profile so it will be auto detected by AWS toolkit.

#aws configure
##it will ask you verious input as below
AWS Access Key ID [None]: xxxxxxxx
AWS Secret Access Key [None]: xxxxxxx
Default region name [None]: xxxxx
Default output format [None]: Json 

Now, AWS CLI is configured after above command successfully executed.

Let’s installed SAM on local machine.
(assuming you have homebrew install on mac machine)

#brew tap aws/tap
#brew install aws-sam-cli
#sam -version

In case if you are windows or Linux user please visit this link , here you will find detail installation steps.

Now, if you have successfully installed SAM on local machine, I would suggest you to install “AWS TOOLKIT” plugin into your IDE, in my case it is intellij Idea.

Once AWS toolkit successully installed, you will see the “AWS toolkit” section in bottom left corner of intelliJ idea, once you clicked on this you will see similar window.

Note – We require SAM pre-installed before AWS toolkit to generate SAM project.

Let’s jump on IDE to generate sample AWS serverless project.

Intellij Idea -> File -> Projects -> AWS -> Next -> …

after clicking on ‘create’ button you will see “HelloWorld” project generated.

This project contains source code and supporting files for a serverless application that you can deploy with the SAM CLI. It includes the following files and folders.

  • HelloWorldFunction/src/main – Code for the application’s Lambda function.
  • events – Invocation events that you can use to invoke the function.
  • HelloWorldFunction/src/test – Unit tests for the application code.
  • template.yaml – A template that defines the application’s AWS resources.

The application uses several AWS resources, including Lambda functions and an API Gateway endpoints. These resources are defined in the template.yaml file. You can update the template to add AWS resources through the same deployment process that updates your application code. more details you can find in file

Let’s build and deploy project –

#sam build
Build Succeeded

Built Artifacts  : .aws-sam/build
Built Template   : .aws-sam/build/template.yaml

Now sample project is successfully bulid , lets deploy this project, currently we don’t know about the further steps and input so we will use below command with –guided option, here you will asked multiple quesiton by SAM related to env.

#sam deploy --guided
Configuring SAM deploy

        Looking for config file [samconfig.toml] :  Not found

        Setting default arguments for 'sam deploy'
        Stack Name [sam-app]: HelloWorld
        AWS Region [ap-south-1]: ap-south-1
        Confirm changes before deploy [y/N]: y
        Allow SAM CLI IAM role creation [Y/n]: Y
        Disable rollback [y/N]: N
        Save arguments to configuration file [Y/n]: y
        SAM configuration file [samconfig.toml]: 
        SAM configuration environment [default]: 

        Looking for resources needed for deployment:
         Managed S3 bucket: aws-sam-cli-managed-default-samclisourcebucket-hyha0acabvgp
         A different default S3 bucket can be set in samconfig.toml

        Saved arguments to config file
        Running 'sam deploy' for future deployments will use the parameters saved above.
        The above parameters can be changed by modifying samconfig.toml
        Learn more about samconfig.toml syntax at

After providing all the inputs , it will initiate deployment of serverless application and provide inline status related to resource creation. let’s visit on aws console page to view, if stack is created or not.

Resources create with helloWorld example,

Now we have verified created resource and they are working fine, lets delete these resources to avoid unnsessery cost.

#sam delete --stack-name HelloWorld
 Are you sure you want to delete the stack HelloWorld in the region ap-south-1 ? [y/N]: y
        Are you sure you want to delete the folder HelloWorld in S3 which contains the artifacts? [y/N]: y
        - Deleting S3 object with key HelloWorld/6f1511bb62dde9a7dc63aab2fdc56321
        - Deleting S3 object with key HelloWorld/70a14d89c5765111d1922ecf99ce00a5.template
        - Deleting Cloudformation stack HelloWorld

Deleted successfully

Here I have tried to quickly present the simple way to kick start serverless project. let me know if you think any specfic steps should be included into this.


Service discovery with Eureka

Eureka is REST based application service, That primarily used for service register and middle-tier api load balancing.

Why Eureka required ?

There is many reason where we can consider eureka
– Service registry
– Client side load balancing
– Peer to peer connectivity between server
– Maintain self preservation state in case network collapse at certain threshold
– Scope of customisation
– Mid-tier load balancing

How Eureka work?

Eureka come up with two components. Eureka client and Eureka server. Any application who doing service discovery on Eureka server should have Eureka client enabled. actually if we complete server setup there is three application that came into picture –

  • Eureka server – that hold the client details and do mid-tier load balancing
  • Application client – That is Eureka client that called to other services.
  • Application services – That is also Eureka client but called by other services.

Let’s understand with example – Suppose we have web-application that have two services. one web client that hold front end implementation. and other backend services that hold business logics. here both backend and frontend is kind of client for Eureka server and both add eureka client component so they can send their heart bit to eureka server. and In this scenarios eureka server maintain registry of both application(web client and backend services). also web client not required to directly called to backend services. that can call to eureka server. where eureka server redirect their call to specific instance as per availability. Here Eureka server use Round-Robin algorithm to redirect request of client.

Eureka server client communication and stats ?

Register – Eureka client registers the information about the running instance to the Eureka server.
Renew – Eureka client needs to renew the lease by sending heartbeats every 30 seconds. The renewal informs the Eureka server that the instance is still alive. If the server hasn’t seen a renewal for 90 seconds, it removes the instance out of its registry. It is advisable not to change the renewal interval since the server uses that information to determine if there is a wide spread problem with the client to server communication.
Fetch registry – Eureka clients fetches the registry information from the server and caches it locally. After that, the clients use that information to find other services
Cancel – Eureka client sends a cancel request to Eureka server on shutdown. This removes the instance from the server’s instance registry thereby effectively taking the instance out of traffic.
Time lag– All operations from Eureka client may take some time to reflect in the Eureka servers and subsequently in other Eureka clients. This is because of the caching of the payload on the eureka server which is refreshed periodically to reflect new information. Eureka clients also fetch deltas periodically. Hence, it may take up to 2 mins for changes to propagate to all Eureka clients.

Let’s go through example ,
Here i’m going create these applications.
1. Eureka server – that will register all the services.
2. Application Service – This will backend application called by client but its also registered with Eureka as client
3. Application Client – this will be client application that Called Application services via eureka server.

Eureka Server

I would suggest you to visit – Spring initialiser and generate Spring application from there and don’t forget to include Eureka server dependencies. for more details please visit this page to know more details.

Once you imported the project into your IDE. then go to resource folder and open files. defined below bare minimum properties to make your server up and visible.

//YAML format
    port: 8761

        hostname: localhost
        fetch-registry: false
        register-with-eureka: false
            defaultZone: http://${eureka.instance.hostname}:${server.port}/eureka/
        prefer-file-system-access: false
        template-loader-path: classpath:/templates/
// properties format


server.port – Server port details, Here we require to define unique port no.
eureka.client.fetch-registry – mark this as false so it will not try to fetch registry details as client
eureka.client.register-with-eureka – So it will not register them self
eureka.client.serviceUrl.defaultZone – Define default zone address for the client, so client connect at this address
spring.freemarker.template-loader-path – as UI page is by default included with Eureka server. so pointed template path in class path incase if by default not detected
spring.freemarker.prefer-file-system-access – there is no need to read local file system.

Now open files and enable Eureka server using @EnableEurekaServer annotation.Then start server

public class EurekaserverApplication {

	public static void main(String[] args) {, args);

Once server up, now visit on this link – http://localhost:8761, you will see similar dashboard as below,

Eureka dashboard

Here there is no application registered with Eureka server now. Lets create Eureka Client.

Eureka Client

Same as Eureka server we require to generate project from Spring Initialiser , Once project generated and open into IDE, we require to edit file.

    name: eureka-service-client

  port: 8082

      defaultZone: http://localhost:8761/eureka

eureka.client.serviceUrl.defaultZone – Default zone for eureka client to register
server.port – server port – named the application the same will be visible to eureka server

Open files and @EnableDiscoveryClient.

public class EurekaclientApplication {

	public static void main(String[] args) {, args);


Now start the client server and check on Eureka if they are visible.


Generate Spring project base template in Java/Kotlin/Groovy

There is various way we can generate REST application base template in java. Today I’m going to share you one of the example.

Why we require to generate the template ?

Going with your own project structure is good for example or test project. but if we talking about production application or some of serious project we must require to follow the standard. generally if we talk about Framework like spring that have certain rules to read application properties and they have defined standard project structure. and that is very use-full and self explanatory.

you can see on of this example, where clearly defined ‘src’ section that contain test and main application source. apart from this there is where user can define there application details. also there is gradle config files are there that can be replace with maven if you choose maven build system.

├── build.gradle
├── gradle
│   └── wrapper
│       ├── gradle-wrapper.jar
│       └──
├── gradlew
├── gradlew.bat
├── settings.gradle
└── src
    ├── main
    │   ├── java
    │   │   └── com
    │   │       └── example
    │   │           └── demo
    │   │               └──
    │   └── resources
    │       └──
    └── test
        └── java
            └── com
                └── example
                    └── demo

Now these are The basics template every time create these structure manually is not worth to spend time. if there is already tools out there.
Spring introduced spring initialiser that can help you generate base template where developer only require to generate and import into IDE.

How to do this?

visit –

Hope you like this 🙂

Spring boot Admin


When the actuator introduced, the first thing came into my mind – What if we have a common place where I can see my all applications endpoints and I can manage them from there itself?

Thanks to the code-centric team they make this possible. if you are not aware of the Actuator, I would suggest you to first read about the actuator library.

Managing application using actuator endpoint is quite difficult, because if you have bunch of applications you won’t have a common place to see them all. But now with the help of Spring boot admin, it’s easier to view the dashboard for multiple microservices at a single place.

In this articles I’m going to describe you basic example of Spring boot admin client and server. CodeCentric has Introduce Spring boot Admin Server and it has inbuilt UI Dashboard that show the clients details. Isn’t it really amazing where you can see all your available clients at one place? Let’s see how we can implement this.

How it works?

Let’s do server and client setup

Spring boot admin server setup

First go to spring initialiser and generate sample project screenshot to generate project

Once project generated you will find below dependencies into your build.gradle file.


Now let’s enable Admin server in project using @EnableAdminServer annotation

public class SbadminserverApplication {

	public static void main(String[] args) {, args);


Logically dashboard should be secure, So let’s include basic authentication using Spring Security

implementation 'org.springframework.boot:spring-boot-starter-security'
import org.springframework.context.annotation.Configuration;

@Configuration(proxyBeanMethods = false)
public class SecuritySecureConfig extends WebSecurityConfigurerAdapter {

    protected void configure(HttpSecurity http) throws Exception {
        http.csrf().ignoringAntMatchers("/actuator/**", "/instances/**", "/logout");
        http.authorizeRequests().antMatchers("/**/*.css", "/assets/**", "/third-party/**", "/logout", "/login")
        http.httpBasic(); // Activate Http basic Auth for the server

Now assign default password to your server, if we don’t define Spring security password it will generate a random password at runtime and you can see the generated password in console.

If you want to update server ‘Titles’ you can use below properties.


Spring boot admin client setup

Generate client project

Once the project generated, configure server details into client properties files, make sure if you running both on the same machine, the port should be different to avoid a port binding error.


Now run both of the project and login into the server.

Spring boot admin server dashboard

Source link

Summary : If you are looking for a prebuilt dashboard for your microservices, you can consider it one of the options. As this project is under an open-source umbrella you can update some of the features as per your requirement.

Hope you like this 🙂


Spring boot actuator


An actuator is a spring boot sub-project that helps to expose production-ready support features against Spring boot application.

Key features offered by actuator

  • Health check : You can use health endpoint to check the status of your running application.
  • Monitoring and Management over HTTP/JMX : Actuator support HTTP endpoint as well as Java Management Extensions (JMX) to provide a standard mechanism to monitor and manage applications.
    • Logger: It provide feature to view and update the logs level.
    • Metrics: Spring Boot Actuator provides dependency management and auto-configuration for Micrometer, an application metrics facade that supports numerous monitoring systems.
    • Auditing: Once Spring Security is in play, Spring Boot Actuator has a flexible audit framework that publishes events (by default, “authentication success”, “failure” and “access denied” exceptions). This feature can be very useful for reporting and for implementing a lock-out policy based on authentication failures.
    • Http Tracing: HTTP Tracing can be enabled by providing a bean of type HttpTraceRepository in your application’s configuration. For convenience, Spring Boot offers an InMemoryHttpTraceRepository that stores traces for the last 100 request-response exchanges
    • Process Monitoring

Enable Actuator into Spring boot project

You can enable Actuator into Spring boot project by including below dependency.


Endpoint offer by Actuator

By default ‘health’ and ‘info’ endpoint are enabled

Default exposed endpoint

Other endpoints are sensitive and not advisable to expose to the production environment without security. As we are demonstrating, let’s expose all the APIs.


Include and Exclude Endpoint

Even you can include or exclude endpoint by defining below properties

# wild card to include/exclude all

# you can include specific properties like below

Customise management server address

You can customize the management server port, it will help you define the limited scope to the ports.


Expose custom endpoint

Any methods annotated with @ReadOperation@WriteOperation, or @DeleteOperation are automatically exposed over JMX and HTTP. Even you can expose technology specific endpoint by using @JmxEndpoint or @WebEndpoint.

Here i’m share you example for exposing endpoint using Spring boot 2.x

import org.springframework.boot.actuate.endpoint.annotation.ReadOperation;
import org.springframework.stereotype.Component;

@org.springframework.boot.actuate.endpoint.annotation.Endpoint(id = "say-hello")
public class Endpoint {

    public String sayHello()
        return "Hello World";


Summary : Spring boot actuator is one of the best libraries you can add in your application to enable production-ready features in less effort. it offers key features that can be used in day to day production support.


Secure properties with spring cloud config

Overview: Earlier post I was demonstrating basic of spring cloud config. Now in this post, we will see how we can use secure properties in the spring cloud config. Before continuing on this, I recommend you to first go through the previous post.

Secure properties: Almost every application has some kind of configuration that can’t be exposable, some are very sensitive and should be limited access. we generally pronounce it secure properties. 

There are multiple ways you can secure your properties like using Cerberus, Hashicorp vault with consul backend, Cyberark password vault, and aim, confidant, Credstash etc. Here we are going to use the simplest way that may not as powerful as the above tools but secure and very easy to use.

Let’s implement this, in a sample code,

First, generate a key store. assuming you are aware of keytool.

keytool -genkeypair -alias mytestkey -keyalg RSA \ -dname "CN=Web Server,OU=Unit,O=Test,L=City,S=State,C=IN" \ -keypass changeme -keystore server.jks -storepass testPassword

Then place server.jks to resource folder in cloud config server project, after that edit .yaml). and add below properties.

Properties Description
encrypt.keyStore.locationContains a resource(.jks file) location
encrypt.keyStore.passwordHolds the password that unlocks the keystore
encrypt.keyStore.aliasIdentifies which key in the store to use
encrypt.keyStore.secret secret to encrypt or decrypt


encrypt.keyStore.location=server.jks encrypt.keyStore.password=testPassword encrypt.keyStore.alias=mytestkey encrypt.keyStore.secret=changeme

That’s it and now restart config server. 

There is encryption and decryption endpoint expose by config server. 

Let’s take a simple example, where we will try to encrypt and decrypt ‘testKey’.

#curl localhost:8888/encrypt --data-urlencode testKey



#curl localhost:8888/decrypt --data-urlencode AQAYqm8ax79kPFGT0sOvV8i8uN0GDLsToULmflVNYKf95bpyAKLIV4eCFVdNJpgb7SyS808a3uTjvQBj1SrIwFlQktRpln8ykpWUG3NdPM6aPf5k4yRhNkG43S5lCckmyLTH8CIzoSSFQeKoFuk4zPiAPTMchTP9qtAYG2EwbdWU1/a9xqoDJb9OQbSsEr0wp2Ud+HlG02NGF2qmhxL7kW5BJxTsGdZG2J8qwhkPYreYF6UQlehmheWCAJBzfBw4peT9LOxi7rA0sHD78xle7Bahziyc+WOETADloKfSowERNY5FCOe4/ywhcHpJuCk+6NPok3KVI+jMTXdSpqMmfxBNc764hHjlhpablwNcRPDv8XGCdstdy4Esb9/eXTZgh0g=



As our keystore file containing public and private key so we can able to encrypt and decrypt properties.

In the case of config client, we do not have to do any extra step except below one, whenever we use encrypted property that has to start with ‘{cipher}’, for example


Caution: encrypted data should not be within single or double quotes.

In a case when a client wants to decrypt configuration locally


If you want to encrypt and decrypt endpoint not work, Then comment all properties that start with encrypt.* and include the new line as below

Include keystore(.jks) file in client project and update below properties in .yaml) file


That’s all, now client project not going to connect with the server to decrypt properties.

Summary: We can secure our external properties using spring cloud config in fewer efforts, That may easily fulfill small or mid-scale project requirement.

Hope you like this 🙂


Spring cloud config

Overview: In this tutorial, we will cover the basics of Spring cloud config server and client, where you will set up your cloud config server and access configuration through client services.

What is Spring cloud config?

Spring cloud config provides server and client side support for externalized configuration a distributed system.

Why Spring cloud config?

External configuration is the basic need of almost any application. Now we are leaving in the microservices world, that need external configuration more often. Almost every individual application has some external and dynamic properties that keep updating based on the environment or some period of time.  In case of the massive size of services, it is hard to manage or left with creating a custom solution for it.

The dilemma is how we can make our application to adopt dynamic changes more often without investing time into it and with zero downtime. Here spring cloud config comes into the picture. It will help a user to manage their external properties from multiple sources like git, local file system etc. Transfer data into encrypted form and lot more.

How it works?

Screen Shot 2018-08-26 at 9.22.06 PM.png

Above diagram, you can see multiple services that get configuration from config server where config server sync with GIT or any other VCS to get new changes.

Let’s create a simple application, that will take a message from the config server and return through the endpoint.

Implementation of spring cloud config server:

Now I’m going to visit  spring initializer page to generate demo project, where I’ve included dependencies of spring ‘web’ and ‘config server’.

Once project imported into IDE, enable config server with ‘@EnableConfigServer’ annotation

public class DemoApplication {

   public static void main(String[] args) {, args);

In this example, I’m using local git  for demo purpose

#mkdir cloud-config
#git init
message=Hello World
//wq (write and quite vi editor)
#git add
#git commit -m "initial config"

By default, config server starts on port 8080 as spring boot application.

Here is config server


server.port: We use this property to define server port if you do not define it will set 8080 as a default port. Here I’m using the same machine for client and server so one of the port needs to be updated. We define this property to fetch configuration detail from git repository.

Implementation of client application:

Now I’m again going to generate a template application using spring initializer where included ‘web’, ‘client config’ and ‘actuator’ as dependencies. Here ‘actuator’ help us to refresh configuration.

Below is message controller that return message and that message came from config properties, you will notice @RefreshScope annotation that helps to refresh configuration.

public class MessageRestController {

    private String message;

    String getMessage() {
        return this.message;

Then rename your ‘‘ file to ‘‘ and include below config,  I’ve defined application name(name of application should accurate to fetch specific data), Configuration URI(which your config server URL that holds properties details) and expose all actuator endpoint that by default disabled

management.endpoints.web.exposure.include=* Accurate name of the configuration file that defined on config server. Base url of config server

management.endpoints.web.exposure.include: By default actuator’s most features are disabled so use a wildcard to enable all. That actually not needed in case of production.

Run your application and you will see below message.

GET http://localhost:8080/message

Response :
Hello world

Let’s update the properties file, I’m going to update ‘Hello World’ to ‘Hello Test’

message= Hello Test
#git add
#git commit -m "update message"
//Once file updated then 'refresh' configuration

Once you included the @RefreshScope annotation that will expose endpoint for you to refresh application, check below.

POST http://localhost:8080/actuator/refresh

Now again hit your message API

GET http://localhost:8080/message
Hello Test

checkout example at git

Conclusion: We can use spring cloud config to any kind of application for external, distributed and centralized configuration server. There is no limitation of technology and programming languages. You can apply spring cloud config in other languages as well.

Hope you like this tutorial.



Relational to NoSQL database

Hey Everyone,

Today I’m going to share you the other experience that I’ve struggled with. I know after reading this post most of you will relate your issues with my experience and you will find a new way to deal with them.

The pain of relational database in a small project where you no need of transaction support and also not defined any complex relationship between the multiple entities.  We are very habitual with relation database we always trying to go with them. But here I’m trying to stop you, first check NoSQL, if they not meet your requirement. Then go with relational one.

Let me explain!!

What is NoSQL?

NoSql is basically a database used to manage huge sets of unstructured data, where data is not stored in a tabular relation like a relational database.

Why NoSQL?

A traditional database prefers more predictable and structured data. The technologies are increasing and we want to automate everything, in such situations we want to gather all type of data to be more predictable. Every time getting structural data is a bit difficult. Many times we need to deal with such situations where we need to store unstructured data. Here comes NoSQL as a savior.

NoSQL as per name says NOT ONLY SQL that comes with lots of more added benefit. It provides a completely new way then the Relational DB to deal with data. Managing any type of data is very simple in NoSQL then relational.

Types of NoSQL database

  • Document type: In this database, the key is paired with a complex data structured called as Document. Example: MongoDB
  • Graph stores: This types of a database is usually used to store networked data. Where we can relate data based on some existing data. Example: Neo4J
  • Key-Value stores: These are the simplest NoSql database. In this database each record store with a unique key to identify it. Example: Aerospike
  • Wide column-stores: This type of database store large data set. Example: Cassandra.

Let’s see one of the use cases (using MongoDB and MySQL):

Imagin that we have beer store database that holds beer store basic information, like beer style, beer type, and beer store addresses.

Let’s see a basic schema design in case of the relational database.

Here I have created beer_store table that holds store names then created address table that holds beer store addresses (one store can be available in multiple places)  along with country and city table. then I’ve defined beer_style and beer_type that provided by the beer stores. then defined many to many relationships between beer type and beer_store and the same in case of beer_style and beer store also.

Screen Shot 2018-04-15 at 9.06.53 PM.png

Now same beer store we can achieve in case of NoSQL (JSON-like documents). below schema.

There is two way you can design your NoSQL schema.

  1. You can store all the data into the same collection. but there is some disadvantage when some data repeat multiple times.
  2. You can store a reference to data little bit similar to SQL.

Here to avoiding confusion, I’ve separated few tables where information is fixed and that will repeat in case of another beer store record.


Screen Shot 2018-04-15 at 2.47.28 PM.png

and other tables that hold values and references


Screen Shot 2018-04-15 at 4.32.42 PM.png


Screen Shot 2018-04-15 at 4.33.26 PM.png


Screen Shot 2018-04-15 at 2.51.41 PM.png

Query Example SQL VS NoSQL


select * from beer_store;
| pkstore_id | name        |
|          1 | Magic Beer  |
|          2 | Beerland    |
|          3 | Uptown Beer |


	"_id" : ObjectId("5ad31853e5ce6fe732eb7300"),
	"name" : "The Beera",
	"address" : [
			"address1" : "sec 4",
			"address2" : "shastri cercle",
			"city" : "jaipur",
			"country" : "India"
	"beerType" : [
	"beerStyle" : [
	"_id" : ObjectId("5ad4bfa2b20cf32e1fa3cb6d"),
	"name" : "BeerLand",
	"address" : [
			"address1" : "sec 4",
			"address2" : "hiran magri",
			"city" : "udaipur",
			"country" : "India"
	"beerType" : [
	"beerStyle" : [

Above both SQL and NoSQL query requested for beer_store but as per both are different way persisted result return based on it.

Same NoSQL response we can achieve with relation database but for this, we have to do multiple joins, subqueries and inbuilt JSON converter.

Conclusion: Relation database has their own importance like supporting the ACID properties. they are well organized.  But many cases NoSQL appreciable, like when we do search operation, sorting operation filtering on one-to-many and many-to-many relationships. 

Hope you like this. Thanks for reading 🙂

Install spring boot application on linux

Today most of the people prefer to deploy the standalone application and easy to manageable instead of doing too much overhead or get expert advice on it to manage a specific web server for rest application.

dilemma: When we have a standalone jar there are few minor hacks we have to do this with it. like, configure log path, start with a specific promised user. run it with standalone process instead of inline execution.

A fully executable jar can be executed like any other executable binary or it can be registered with ‘systemd‘.  This makes it very easy to install and manage spring boot applications in common production environments.

#systemd: systemd is system and service manager for linux operating system. When run as the first process on boot (as PID 1), it acts as init system that brings up and maintains userspace services. it is a replacement of ‘Unix system v’ and BSD (Berkeley Software Distribution) init system. for more detail #man systemd

Assume that you have a linux server that has Java installed, now place your executable spring boot jar file in a /opt/apps/ directory

Now create a app.service file in a /etc/systemd/system
directory and execute below command also make sure your permission before creating a file at a particular location
#vi /etc/systemd/system/app.service

and paste script

Description=sample application



now save above script using “:wq” for more detail check vi editor helps(#man vi)

let’s enable service

#systemctl enable app.service
(check #man systemctl for more detail.)

once service enables now you can start, stop and check status of your service.

#systemctl start app.service
#systemctl stop app.service

Hope you like this. Thanks for reading 🙂

Delegates in Kotlin

Hi Everyone,

Today we gonna discuss delegates in kotlin.

The Delegation pattern has proven to be a good alternative to implementation inheritance, and kotlin supports it natively requiring zero boilerplate code.

Property delegates don’t have to implement any interface, but they have to provide a getValue() and setValue() function.

let’s see an example, that mention in Kotlin ref docs. going to define Delegate class with getValue and setValue function.

class Delegate {

    operator fun getValue(thisRef : Any?, property : KProperty<*>) : String
        return "${thisRef?.javaClass?.name}, thank you for delegating '${}' to me!"

    operator fun setValue(thisRef : Any?, property : KProperty<*>,value : String)
        println("$value has been assigned to '${}' in ${thisRef?.javaClass?.name}.")

now creating another class.

class Example {
     var p : String by Delegate()

call Example class

fun main(args : Array)
    var example = Example()
    example.p = "delegate world"

com.delegated.Example, thank you for delegating 'p' to me!
delegate world has been assigned to 'p' in com.delegated.Example.

kotlin provides few delegated properties build into the language – Lazy properties, Observable properties, and properties storing in the map.

Lazy Properties: lazy is a function that takes a lambda and returns and returns an instance of Lazy which can serve as a delegate.

let’s create an example class.

class Example {
     val lazyValue: String by lazy {
fun main(args : Array)

Observable properties: Observable takes two arguments: the initial value and a handle for modifications. the handler gets called every time we assign the property. it has three parameters: a property being assigned to, the old value and the new one.

let’s create an example class

class Example {
     var name: String by Delegates.observable("") {
          prop, old, new ->
          println("$old -> $new")
fun main(args : Array)
    var example = Example() = "first" = "second"
 -> first
first -> second

Properties storing in the map: One common use case is storing the values of properties in a map. This comes up often in applications like parsing JSON or doing other “dynamic” things. In this case, you can use the map instance itself as the delegate for a delegated property.

let’s create an example class.

class User(val map: Map<String, Any?>) {
    val name:String by map
    val age: Int by map
fun main(args : Array)
    var user = User(mapOf("name" to "Ritesh pathak", "age" to 23))
Ritesh pathak

Ref – Kotlin docs.

Hope you like this. Thanks for reading 🙂