DEV Community: Vijay SRJ

An intro to Reactive programming in Spring Boot

Vijay SRJ — Fri, 01 Jul 2022 12:45:27 +0000

An ebook with an introduction to reactive programming in Spring Boot.

Programming comes in different paradigms.
For long, we did procedural programming using languages like C where the business logic was executed step by step in a procedural manner. Then came Object Oriented Programming where you modelled your business requirement into domain objects. It represented real world more closely and has been quite successful even now.
And we also have Functional programming, Event Driven programming etc.
The latest among these is Reactive Programming.

Reactive programming is non-blocking, asynchronous , deals with data streams and supports backpressure.

This ebook gives a quick intro to Reactive Programming in Spring Boot with sample demo in both Spring Boot and Javascript.

Contents:

Reactive programming – definition
Reactive programming in Spring Boot
How to create a reactive REST API – demo
How to consume a reactive REST API – demo
Backpressure
How to consume a reactive REST API in Javascript - demo
Conclusion
Further Reading

An Intro to Reactive Programming in Spring Boot

Attribute vs Property in HTML

Vijay SRJ — Sat, 04 Dec 2021 10:14:42 +0000

The terms attribute and property can be confusing in HTML.

For example the javascript framework Angular has the concepts Property Binding and Attribute Binding . Without knowing the difference between the two it is difficult to grasp the difference between those concepts.

The major difference between the two is this:

Attribute is related to HTML

Property is related to DOM

Other differences:

Attribute and Property names are not always similar
Changing Attribute/Property values doesn't always get reflected to the other
Attribute is case sensitive , Property is not
Attribute values are always strings , Property can be of different data types

Here is an explanation with examples:
Attribute vs Property

Published my first EBook on the Gang of Four Design Patterns in Java!

Vijay SRJ — Thu, 28 Oct 2021 13:49:32 +0000

The Gang of Four Design Patterns are often hard to get .

Most of the articles on the internet are generic or too complicated to understand. I wrote a book which solves this by providing an easier explanation of all the 23 design patterns with use cases implemented in Java and with link to GitHub.

Every design pattern is presented with an use case , the solution in java and the link to Github.

Once you finish this book , you will gain more confidence about implementing design patterns in your day to day programming.

Link to the book : The Gang of Four Design Patterns Simplified

Topics covered:

Creational :

Deals with how to create objects.

Singleton – Create a single instance of an object.

Prototype– Use an existing object by cloning it.

Factory Method – Delegate creation of an object to another object.

Abstract Factory – Delegate creation of a group of related objects to another object.

Builder – Delegate creation of a complex object to another object.

Structural:

Deals with how to structure objects.

Adapter – Make two incompatible interfaces work together.

Bridge – Separate abstraction and implementation.

Composite – Treat part-whole hierarchy the same way.

Decorator – Add responsibilities to an object dynamically.

Facade – Provide a single interface for a group of related operations.

Flyweight – Reuse objects than creating new ones.

Proxy – Protect access to an object.

Behavioral

Deals with how to communicate between objects.

Chain of Responsibility – Allow different objects to carry out a responsibility.

Command – Encapsulate requests as separate objects.

Mediator – Act as a broker for communication between objects.

Template – Provide basic template of an algorithm to implement.

Strategy – Encapsulate different algorithms using separate objects which can be chosen at run time.

State – Encapsulate state specific behavior in a separate object.

Observer – Intimate group of objects when a change occurs.

Memento – Allow to revert an object’s state.

Iterator – Provide a generic way to iterate through collection of objects.

Interpreter – Represent a grammar using an object.

Visitor – Add new responsibilities to an object without changing its existing behavior.

Note : The original book by the Gang of Four was referred for these posts.

About the author:

I am Vijay , a full stack developer and a Tech Manager working in a multi national IT company. I have over 13 years of experience in the IT industry and have spent major part of my career working on Java and related technologies. In this book, I have tried to present the design patterns by the Gang of Four in a simplistic way yet not compromising on the quality of the content.

Java 17 features

Vijay SRJ — Thu, 12 Aug 2021 16:55:56 +0000

Java 17 features are finalized and sealed. As of this writing , it is going to be released next month (September 2021).

Though there are around 14 new features introduced in this release , only two of them directly help developers and they should be aware of these.

Those two are :

Pattern Matching for Switch
Sealed Classess
Pattern Matching for Switch is introduced as a preview feature and it is one among the ongoing features released by the Java team in the pattern matching series.

This is explained in detail here with examples :

Pattern Matching for Switch

Sealed classes were introduced in Java 15 as a preview feature and have now become a permanent feature in Java 17.

Here is a detailed explanation on this :

Sealed Classes

Most of the remaining features are related to the JVM .

Here is the full list :

https://openjdk.java.net/projects/jdk/17/

What is a closure in Javascript?

Vijay SRJ — Wed, 05 May 2021 15:33:59 +0000

Let’s say you declare a variable in javascript.

What is the scope of this variable?

It is the entire function in which it is declared.

What if it is declared within a particular block ?

Still it’s scope is the entire function in which it is declared.

For example:

function test(value){

     if(value==1){
             var temp = "Hello the value entered is 1";

          }
        alert(temp);       //you can access temp here!
}

In the above code even though the variable temp is declared inside the if block , the scope of the variable is the entire function test() , hence the alert statement will alert the value “Hello the value entered is 1” .

But , this will work only if the value is 1 , if the value does not match , javascript will skip the initialization of the variable and you will get undefined for the variable ‘temp’.

Let’s play a little more with scope of a variable.

Now , lets say the above function returns another function which accesses the variable “value”:

function test(value){



    return function(){

        console.log(value);

        value++;

        return value;
    }
}

Now , does the returned function has access to the variable “value” once is it is returned.

Like when you assign the returned function like this:

var returnedfunction = test(5);
and then you call the returned function:

returnedfunction();
Does the returnedfunction() now has access to the variable “value”?

It does!

The value of the variable “value” is incremented every time you call returnedfunction().

I called it thrice in my code and it returned 5,6 and 7:

<script>

function test(value){



    return function(){

        console.log(value);

        value++;

        return value;
    }
}


var returnedfunction = test(5);

returnedfunction();

returnedfunction();

returnedfunction();


</script>

The output was
5
6
7
This connection to the variable in its surrounding scope for the returned function + the returned function are together called a closure.

Repeating it again :

Closure = a function + its connection to variables in its surrounding scopes even after it leaves the scope where it was created

That’s it!

Javascript functions vs Java functions

Vijay SRJ — Tue, 04 May 2021 16:07:26 +0000

A post on how javascript functions differ from Java functions.
Would help java developers trying their hands on javascript :

You don’t specify the type of javascript parameters
Javascript functions don’t need to live inside a Class
Javascript functions can be assigned to a variable
Javascript functions can be passed as parameters to other functions
You can pass any number of parameters to a javascript function

Explanation with samples :
https://fullstackdeveloper.guru/2021/05/04/how-do-javascript-functions-differ-from-java-functions/

How does Number data type differ in Java and Javascript?

Vijay SRJ — Fri, 30 Apr 2021 11:26:10 +0000

Brendan Eich , while creating Javascript took a great influence from Java.
In fact he was asked to create the Java language on the browser by the company Netscape.

So though Javascript has a lot of similarities with Java , it varies widely in other aspects.

With respect to numbers , Javascript treats Numbers differently from Java in these ways:

All numbers are floating point numbers in Javascript
You can represent 'Not a Number' in Javascript
You can represent Infinity in Javascript
You can convert a string to number using the '+' symbol in Javascript.

Explained with examples here:

https://fullstackdeveloper.guru/2021/04/30/how-do-numbers-differ-in-javascript-and-java/

How to move a file or folder to trash in Java?

Vijay SRJ — Thu, 29 Apr 2021 17:01:57 +0000

You can move a file or a folder to trash/ recycle bin in java using the below code:

`Desktop.getDesktop().moveToTrash()'

Here is a demo:

https://fullstackdeveloper.guru/2021/04/29/how-to-move-a-file-folder-to-trash-recyclebin-in-java/

How to convert your Spring Boot app to serve over HTTPs instead of HTTP?

Vijay SRJ — Fri, 23 Apr 2021 12:19:30 +0000

Converting your spring boot app to serve on HTTPS just requires few configuration to be added in application.yml:

server:
  ssl:
    key-store: C:\softwares\jdk-16\bin\demokeystore
    key-store-password: demopass
    key-alias: demokey 
  port: 8443

The above configuration is enough. Here is the explanation behind it:

https://fullstackdeveloper.guru/2021/04/23/how-to-convert-your-spring-boot-app-to-a-https-application/

How does HTTPs work?

Vijay SRJ — Thu, 22 Apr 2021 13:56:44 +0000

Here is the basic algorithm of how HTTPS work:

1.Browser hits website protected by HTTPS
2.Server sends digital certificate
3.Browser extracts public key from certificate
4.Browser creates a session key
5.Browser encrypts the session key using the public key and sends it to server
6.Server decrypts session key using its private key
7.Browser sends requests encrypted with the session key
8.Server sends responses encrypted with the same session key

A detailed explanation:

https://fullstackdeveloper.guru/2021/04/22/how-does-https-work/

The case of the binary logical operators '&&' and '||' in Javascript

Vijay SRJ — Wed, 21 Apr 2021 12:06:01 +0000

In Javascript the binary logical operators '&&' and '||' behave differently compared to the same operators in a programming language like Java.
This is because javascript binary logical operators can return even a number or a string, not just true or false!
And again this is possible because Javascript has this concept of 'Truthy' and 'Falsy'.

Anything of the below is considered as false by javascript:
''
false
NaN
null
undefined

Everything else is considered as true

Here is a short post on how the above concept affects the binary logical operators in javascript:

https://fullstackdeveloper.guru/2021/04/21/how-the-binary-logical-operators-and-differs-in-javascript-from-java/

undefined vs null in Javascript

Vijay SRJ — Tue, 20 Apr 2021 10:40:43 +0000

If you are from the background of a programming language like Java , you might feel that the way to represent a “no value” is through the value “null”.

But Javascript has two ways to denote a “no value”.

One is “undefined”

Another is “null”

“undefined” represents “no value” whereas “null” represents “no object” to be more specific.

Thus the major difference is that null is concerned with objects only.

When does Javascript return undefined?
When a variable is declared but not initialized , javascript throws undefined.

Here is an example:

var x;
console.log(x); // the value returned here is undefined

If you try to invoke a property of an object which doesn’t exist , you get undefined:

var obj = {};
console.log(obj.name); // the value returned here is undefined

When does Javascript return null?
null means “missing”.

So you get null whenever an object is missing.

For example when you try to access a html element that does not exist , you get null.

The below code returns null if there is no html element named “name” :

<script>
console.log(document.getElementById("name"));
</script>

How to check if a function returns null or undefined?
Let’s say you are invoking a function in your javascript code and that function may return null or undefined. In that case you need to check for both null and undefined :

let output =  somefunction();

if(output === undefined || output === null){
        //logic here
}

You can combine both the checks using ! operator like this:

if(!output){
   //logic here
}

This works because both undefined and null are treated as “false” by javascript.

But you need to be cautious here , because if the output of the function in the above examples is an empty string , still the value of output is “false”.

This is because javascript treats an empty string as false.

Also the below are treated as false:

NaN

false (the boolean value false itself)

To summarize , javascript considers all these as false:

false

”

undefined

null

NaN

Reposted from :

https://fullstackdeveloper.guru/2021/04/20/undefined-vs-null-in-javascript/