DEV Community: Vidya

Auto Configuration in Spring Boot

Vidya — Mon, 01 Jun 2026 05:36:07 +0000

What is Auto Configuration in Spring Boot?

Auto Configuration is one of the most powerful features of Spring Boot. It automatically configures your application based on the dependencies available in the project. This reduces manual configuration and helps developers build applications faster.

In traditional Spring applications, developers had to create many configuration classes and bean definitions manually. Spring Boot simplifies this process through Auto Configuration.

Why Do We Use Auto Configuration?

=> Reduces boilerplate configuration code.
=> Speeds up application development.
=> Minimizes manual setup.
=> Provides sensible default configurations.
=> Makes Spring applications easier to create and maintain.

How Auto Configuration Works?

When a Spring Boot application starts:
=> Spring Boot scans the dependencies in pom.xml.
=> It checks which libraries are available.
=> Based on those libraries, it automatically creates and configures the necessary beans.
=> The application becomes ready to use with minimal configuration.

The Auto Configuration feature is enabled by the @SpringBootApplication annotation.

@SpringBootApplication
public class MyApplication {
    public static void main(String[] args) {
        SpringApplication.run(MyApplication.class, args);
    }
}

The @SpringBootApplication annotation internally includes:

@Configuration
@EnableAutoConfiguration
@ComponentScan

Here, @EnableAutoConfiguration is responsible for Auto Configuration.

Real-Life Example

Think of Auto Configuration like a new smartphone.
When you insert a SIM card:
=> The phone automatically detects the network.
=> Configures mobile settings.
=> Enables calling and internet.
---> You do not manually configure everything.

Similarly, Spring Boot detects dependencies and automatically configures the required components.

Learn REST API Easily

Vidya — Thu, 28 May 2026 06:10:07 +0000

What is REST API?
A REST API (Representational State Transfer Application Programming Interface) is a way for applications to communicate with each other using HTTP methods like GET, POST, PUT, and DELETE. It allows clients and servers to exchange data, usually in JSON format. Each resource is identified using a unique URL such as http://localhost:8080/products. REST APIs are widely used in web and mobile applications because they are simple, fast, and scalable.

When we used REST API?
We use REST APIs when different applications need to communicate and share data with each other. They are commonly used to connect frontend applications with backend servers. REST APIs are also used in web and mobile applications to perform operations like creating, reading, updating, and deleting data. They help applications work efficiently across different platforms and technologies.

Example:

Example:
http://localhost:8080/users

This is a REST API endpoint used to manage user data from the server.

localhost → Your local machine where the application runs
8080 → Port number of the server
/users → Resource that contains user information

Operations:

GET /users → Get all users
GET /users/1 → Get user with ID 1
POST /users → Add a new user
PUT /users/1 → Update user details
DELETE /users/1 → Delete user with ID 1

Image Format:

API

Vidya — Wed, 27 May 2026 07:38:26 +0000

What is API?

API stands for Application Programming Interface. It is a bridge that allows two applications to communicate and exchange data with each other. APIs are used to send requests and receive responses between frontend and backend applications. They help applications fetch, store, update, and delete data from the server or database. APIs are widely used in web applications, mobile applications, and cloud services. For example, a React frontend uses APIs to get data from a Spring Boot backend.

For example:

=> React frontend
=> Spring Boot backend
=> MySQL database

The frontend cannot directly access the database.
So it sends a request through an API, and the backend returns the response.

Simple Flow

Frontend → API → Backend → Database

Real-Time Example

Consider a food delivery app.
=> The mobile app needs restaurant data
=> The data is stored in the server/database
=> The app requests data using an API
=> The server sends the response
---> So APIs help different applications communicate with each other.

Why Do We Use API?
1.Communication Between Applications

APIs allow different applications to communicate.

Example:
React ↔ Spring Boot
Mobile App ↔ Server
Website ↔ Payment Gateway

2.To Fetch Data

APIs are used to get data from the server or database.
Example:

GET /products
   This returns all products.

3. To Send Data

APIs are used to store data in the database.
Example:

POST /products
       This adds a new product.

4. To Update Data

Example:

PUT /products/1
         This updates the product with ID 1.

5. To Delete Data

Example:

DELETE /products/1
          This deletes the product with ID 1.

Annotations in Spring Boot

Vidya — Tue, 26 May 2026 06:00:28 +0000

Common Spring Boot Annotations and Why We Use Them?

@SpringBootApplication**

@SpringBootApplication
public class DemoApplication {
    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }
}

Why we use?

This is the main annotation for Spring Boot application.

It combines 3 annotations internally:

@Configuration
@EnableAutoConfiguration
@ComponentScan

Meaning:
=> Starts Spring Boot app
=> Automatically configures project
=> Scans classes like controller, service, repository

2. @RestController

@RestController
public class StudentController {

}

@RestController is used in Spring Boot to create REST APIs and send data directly to the client as an HTTP response, usually in JSON format.

Why do we use it?

We use @RestController when we want to:

=> send data to frontend applications
=> create APIs
=> return JSON/XML instead of HTML pages

3.@Controller

@Controller is used to create a web controller in Spring MVC.

It is mainly used to return:

=> HTML pages
=> JSP pages
=> Thymeleaf templates
instead of JSON data.

Why do we use @Controller?

We use @Controller when we want to:

=> handle web requests
=> return UI pages to the browser
=> build traditional web applications

Example

 @Controller
public class HomeController {

    @GetMapping("/home")
    public String home() {
        return "home";
    }
}

4.@Service

@Service is used to mark a class as a service layer in a Spring Boot application.

It contains the business logic of the application.

Why do we use @Service?

We use @Service to:

=> write business logic
=> perform calculations
=> validate data
=> process application logic
=> keep controller code clean

Example

@Service
public class StudentService {

    public String getMessage() {
        return "Welcome Student";
    }
}

5. @Repository
@Repository is used to mark a class as a repository layer in a Spring Boot application.

It is mainly used for database operations.

Why do we use @Repository?

We use @Repository to:

=> connect with the database
=> save data
=> fetch data
=> update data
=> delete data

It acts as a bridge between the application and the database.

Example

@Repository
public class StudentRepository {

}

Spring vs Spring Boot – Complete Comparison

Vidya — Tue, 12 May 2026 15:33:31 +0000

What is Spring?
=> Spring Framework is a Java framework used to build enterprise applications.
=> It provides features like Dependency Injection (DI), IoC, database handling, security, and web development.
=> In Spring, developers must configure many things manually using XML or Java configuration.
=> It is flexible and powerful but requires more setup and coding.
Spring is mainly used for large-scale Java applications.
Example: Creating web applications, banking systems, REST APIs, and microservices.

What is Spring Boot?
=> Spring Boot is built on top of Spring Framework.
=> It reduces configuration work and makes development faster and easier.
=> Spring Boot provides auto-configuration, embedded servers, and starter dependencies.
=> You can run applications directly without deploying WAR files manually.
=> It follows “convention over configuration,” so less code is needed.
Example: Quickly creating REST APIs, backend services, and microservice applications.

Why do we use Spring Boot Framework in Java instead of others?
=> Spring Boot makes Java development simple, fast, and production-ready.
=> It has built-in support for REST APIs, databases, security, and microservices.
=> Embedded servers like Tomcat help run applications easily.
=> Large community support and many companies use it in real projects.
=> It reduces boilerplate code and saves development time.
=> Compared to many frameworks, Spring Boot is easier for creating scalable enterprise applications quickly.

Image Format

Reverse Words in a Sentence

Vidya — Fri, 08 May 2026 04:38:25 +0000

JavaScript Program:

let sentence = "how are you";
let end = sentence.length - 1; 
let word = "";
let start;
for (let i = end; i >= 0; i--) {
  if (sentence[i] === " " || i === 0) {

    let start;

    if (i === 0) {
      start = i;      
    } else {
      start = i + 1;
    }

    for (let j = start; j <= end; j++) {
      word = word + sentence[j];
    }
    console.log(word);
    word = "";
    end = i - 1;  
  }
}

output:

Algorithm:

Start
Initialize a string sentence = "how are you"
Set: end = length of sentence - 1 word = "" (empty string)
Loop from end to start of the string (i = end → 0)
For each character: Check if space OR i == 0
If condition is true: Determine start index: If i == 0 → start = i Else → start = i + 1
Extract the word: Loop from start → end Add each character to word
Print the word
Reset: word = "" end = i - 1
Continue loop until i = 0
Stop

Maven in Spring Boot

Vidya — Tue, 05 May 2026 15:08:44 +0000

What is Maven?
=> Maven is a build automation and project management tool mainly used for Java applications, developed by Apache Software Foundation. It uses a file called pom.xml (Project Object Model) to define project details, dependencies, and build configuration.

=> Maven automatically downloads required libraries from online repositories, so developers don’t need to manage JAR files manually. It follows a standard project structure, making projects easy to understand and maintain.

=> Maven also manages the build lifecycle, including compile, test, package, and deploy phases. Overall, Maven simplifies development by handling dependencies, builds, and project consistency efficiently.

For example, if you add spring-boot-starter-web dependency in pom.xml, Maven will automatically download all required libraries and help you run your Spring Boot REST API easily.

Why We Used?
=> We use Maven (Apache Maven) because it simplifies project development by automating repetitive tasks and managing dependencies efficiently. Instead of manually downloading and adding JAR files, Maven automatically fetches required libraries from repositories.

=> It ensures a standard project structure, making code easier to understand and maintain across teams. Maven also handles the full build lifecycle like compiling, testing, packaging, and deploying with simple commands.

=> This reduces errors and saves time, especially in large projects. Overall, Maven improves productivity, consistency, and project management in Java applications.

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MVC Architecture Flow in Spring Boot

Vidya — Tue, 05 May 2026 08:05:26 +0000

What is MVC?
MVC stands for:

M → Model
V → View
C → Controller

It is a design pattern used to organize your code by separating concerns.

=> In Spring Boot, MVC helps structure web applications cleanly.

MVC in Spring Boot is a design pattern that separates an application into Model, View, and Controller. The Model handles data and business logic, while the View is responsible for displaying the user interface. The Controller acts as a bridge, receiving user requests and coordinating between Model and View. When a request comes in, the Controller processes it, interacts with the Model, and sends the result to the View. This separation keeps the code organized and easier to maintain. Overall, MVC improves scalability, readability, and development efficiency in web applications.

Why MVC is Used?

Without MVC, all code (logic + UI + data) gets mixed → messy

With MVC:
✔ Code is clean and organized
✔ Easy to maintain & debug
✔ Supports team development
✔ Reusable components

Components of MVC

1.Model (Data Layer)

Represents data + business logic
Usually includes:
=> Entity classes
=> Database interaction

Example:

class Student {
    int id;
    String name;
}

2.View (UI Layer)

What the user sees 👀
Can be:
-> HTML
-> JSP
-> Thymeleaf

Example:

<h1>Welcome Student</h1>
<p th:text="${name}"></p>

3.Controller (Request Handler)

=> Handles user requests
=> Connects Model and View

Example:

@RestController
public class StudentController {

    @GetMapping("/student")
    public String getStudent() {
        return "Hello Student";
    }
}

Image Format:

Map in Java

Vidya — Sat, 02 May 2026 04:49:16 +0000

What is Map in Java Collections?
A Map in Java (from Java Collections Framework) is a data structure that stores data in key–value pairs.

Each key is unique
Each value is mapped to a key
Think of it like a dictionary: word → meaning

Example:
101 → "John"
102 → "Alice"

Why do we use Map?
We use a Map when:

--> We need fast lookup using a key
--> We want to store pairs of related data
--> We need unique keys

Real-world examples:

Student ID → Name
Username → Password
Product ID → Price

Common Map Implementations
HashMap → Fast, unordered
LinkedHashMap → Maintains insertion order
TreeMap → Sorted by keys

Important Methods

put(key, value) → Insert data
get(key) → Get value
remove(key) → Delete
containsKey(key) → Check key
keySet() → Get all keys

Difference between Map vs List vs Set?

Set in Java

Vidya — Thu, 30 Apr 2026 14:57:49 +0000

What is a Set in Java Collections?
A Set is a collection in Java that:
--> Does not allow duplicate elements
--> Does not guarantee index (no ordering like List)
--> Stores only unique values

It is part of java.util.Set interface.

Main Types of Set
1. HashSet
--> No order maintained
--> Fast performance
--> Allows one null

Example

import java.util.*;

public class HashSetExample {
    public static void main(String[] args) {
        Set<String> set = new HashSet<>();

        set.add("Apple");
        set.add("Banana");
        set.add("Apple"); // duplicate ignored
        set.add("Mango");

        System.out.println(set);
    }
}      output:[Apple, Banana, Mango]

2. LinkedHashSet
--> Maintains insertion order
--> No duplicates allowed
Example

import java.util.*;

public class LinkedHashSetExample {
    public static void main(String[] args) {
        Set<Integer> set = new LinkedHashSet<>();

        set.add(10);
        set.add(30);
        set.add(20);
        set.add(10); // ignored

        System.out.println(set);
    }
}         output:[10, 30, 20]

3. TreeSet
--> Stores elements in sorted (ascending) order
--> No duplicates allowed
--> Slower than HashSet

Example:

 import java.util.*;

public class TreeSetExample {
    public static void main(String[] args) {
        Set<Integer> set = new TreeSet<>();

        set.add(50);
        set.add(10);
        set.add(30);
        set.add(20);

        System.out.println(set);
    }
}         output:[10, 20, 30, 50]

Key Features of Set
--> Unique elements only
--> No index (no get(0) like List)
--> Used in removing duplicates
--> Supports iteration (for-each loop)

Remove Space Programs

Vidya — Wed, 22 Apr 2026 04:19:17 +0000

1.Remove Front Space:

name="practice makes    perfect"
i=0
result=""
while i<len(name):
  if name[i]!=" ":
    result=result+name[i]
  else:
    if i>0 and name[i-1]!=" ":
      result=result+name[i]
  i+=1
print(result)

Output:

2.Remove Extra Space:

name="practice makes    perfect"
i=0
result=""
while i<len(name):
  if name[i]!=" ":
    result=result+name[i]
  else:
    if i>0 and name[i-1]!=" ":
      result=result+name[i]
  i+=1
print(result)

output:

3.Remove Back Space:

name = "Kill them with your success        "
result = ""

i = len(name)-1

while i >= 0:

    if name[i] == " ":
        i -= 1
        continue

    else:
        j = 0

        while j <= i:
            result += name[j]
            j += 1

        break

print(result)

output:

4.Reverse The Word:

name = "PULIKESI"
result = ""

i = len(name)-1

while i >= 0:
    result = result + name[i]
    i -= 1

print(result)

output:

5. Password Generator

import random

upper="ABCDEFGHIJKLMNOPQRSTUVWXYZ"
lower="abcdefghijklmnopqrstuvwxyz"
numbers="0123456789"
special="!@#$&"

all_chars=upper+lower+numbers+special

password=""

password=password+random.choice(upper)
password=password+random.choice(lower)
password=password+random.choice(numbers)
password=password+random.choice(special)

i=4

while i<8:
    password=password+random.choice(all_chars)
    i+=1

print("Generated Password :",password)

output:

String Programs

Vidya — Tue, 21 Apr 2026 08:45:31 +0000

1.Lowercase to Uppercase

text=input("Enter some words :")
i=0
upper=""
while i<len(text):
    ch=text[i]
    if ch>="a" and ch<="z":
        upper=upper+chr(ord(ch) - 32)
    else:
        upper=upper+ch
    i+=1
print(upper)

output

2.First Letter Uppercase

 text=input("Enter some words :")
i=0
upper=""
while i<len(text):
    ch=text[i]
    if (ch>="a" and ch<="z") and (text[i-1]==" " or i==0):
        upper=upper+chr(ord(ch) - 32)
    else:
        upper=upper+ch
    i+=1
print(upper)

output:

3.Counting Letters

 text=input("Enter some words :")
i=0
count=0
while i<len(text):
    ch=text[i]
    if (ch>="a" and ch<="z") or (ch>="A" and ch<="Z"):
        count+=1
    i+=1
print(count)

output:

4.Counting Words

 text=input("Enter some words :")
i=0
count=1
while i<len(text):
    if text[i]!=" " and text[i-1]==" ":
        count+=1
    i+=1
print(count)

output:

5.Password validator

 text=input("Create your password :")
i=0
upper=False
lower=False
number=False
spacial=False
others=True
while i<len(text):
    ch=text[i]
    if ch>="A" and ch<="Z":
        upper=True
    elif ch>="a" and ch<="z":
        lower=True
    elif ch>="0" and ch<="9":
        number=True
    elif ch=="!" or ch=="@" or ch=="#" or ch=="$" or ch=="&":
        spacial=True
    else:
        others=False
    i+=1
if upper and lower and number and spacial and others:
    print("password succesfully validate")
else:
    print("invalied try another")

output: