Java.AiTools

🧩 Modular Monolith vs Microservices

(Choosing the Right Architecture in 2025)

🔹 Modular Monolithic Architecture

A single deployable application divided into well-defined, independent modules with strict boundaries.

Key Traits

One codebase, one deployment

Clear domain-based modules

Fast local development

Easy testing & debugging

Can evolve into microservices later

🔹 Microservices Architecture

An architecture where the system is split into independent services, each deployed and scaled separately.

Key Traits

Independent deployments

Service-level scalability

Technology freedom

Strong DevOps & observability required


🏢 Who Uses What?

Modular Monolith Advocates

Shopify – Modular monolith at massive scale

Basecamp – Famous “Majestic Monolith” approach

Microservices at Scale

Netflix – Cloud-native microservices pioneer

Amazon – Independent service ownership model

💡 Final Thought

Microservices solve scaling problems, not design problems.
Start with a Modular Monolith, then split only when scale, teams, or traffic demand it.

🔁 Repost if you agree
💬 Comment “ARCHITECTURE” if you want a Spring Boot Modular Monolith demo

#SoftwareArchitecture #ModularMonolith #Microservices #SpringBoot #SystemDesign #BackendEngineering 🚀

6 days ago | [YT] | 1

Java.AiTools

Spring Boot repositories types are mainly classified based on the interfaces they extend.


---

🔹 1️⃣ Repository (Marker Interface)

📌 Base interface
Does NOT provide any CRUD methods by default.

```java
public interface UserRepository extends Repository<User, Long> {
}
```

✔ Used when you want full control over method definitions
❌ No built-in methods like `save()`, `findAll()`

---

🔹 2️⃣ CrudRepository

📌 Provides basic CRUD operations**

```java
public interface UserRepository extends CrudRepository<User, Long> {
}
```

#-----> Key Methods

`save()`
`findById()`
`findAll()`
`deleteById()`

✔ Lightweight
✔ Good for simple CRUD

---

🔹 3️⃣ PagingAndSortingRepository

📌 Extends `CrudRepository`
📌 Adds **pagination and sorting**

```java
public interface UserRepository
extends PagingAndSortingRepository<User, Long> {
}
```

#--> Extra Features

`findAll(Pageable pageable)`
`findAll(Sort sort)`

✔ Used when large datasets need pagination

---

🔹 4️⃣ JpaRepository ⭐ (Most Used)

📌 Extends `PagingAndSortingRepository`

```java
public interface UserRepository
extends JpaRepository<User, Long> {
}
```

#---> Extra Features

`flush()`
`saveAndFlush()`
`deleteInBatch()`
`findAll()` → returns `List`

✔ **Most powerful & commonly used**
✔ Ideal for **Spring Boot + MySQL projects** (your usual stack)

---

🔹 5️⃣ Custom Repository

📌 Define your **own queries**

### Using Method Naming

```java
List<User> findByEmail(String email);
```

### Using `@Query`

```java
@Query("SELECT u FROM User u WHERE u.email = ?1")
User findUserByEmail(String email);
```

✔ For complex queries
✔ Supports JPQL & Native SQL

---

🔹 6️⃣ Reactive Repositories (WebFlux)

Used in **Reactive applications**

```java
public interface UserRepository
extends ReactiveCrudRepository<User, Long> {
}
```

✔ Uses `Mono` & `Flux`
❌ Not used in traditional MVC apps

---

🔹 7️⃣ MongoRepository (NoSQL)

For **MongoDB**

```java
public interface UserRepository
extends MongoRepository<User, String> {
}
```

---

📊 Quick Comparison Table

| Repository | CRUD | Pagination | JPA Extras | Usage
| -------------------------- | ---- | ---------- | ---------- | ------------- |
| Repository | ❌ | ❌ | ❌ | Custom only
| CrudRepository | ✅ | ❌ | ❌ | Simple CRUD
| PagingAndSortingRepository | ✅ | ✅ | ❌ | Pagination
| JpaRepository | ✅ | ✅ | ✅ | ⭐ Most used
| ReactiveCrudRepository | ✅ | ✅ | ❌ | Reactive apps
| MongoRepository | ✅ | ✅ | ✅ | MongoDB

---

## 🎯 Which One Should You Use?

✅ For 90% of Spring Boot apps → `JpaRepository`
✅ Large data → `PagingAndSortingRepository`
✅ MongoDB → `MongoRepository`
✅ WebFlux → `ReactiveCrudRepository`

1 week ago | [YT] | 1

Java.AiTools

🚀 Types of Caching Explained (Backend Developer View)

Caching is one of the most powerful performance optimizations in backend systems.
But not all caches are the same.

Let’s understand the difference 👇
---

🌐 Browser Cache

📍 Where? Client-side (User’s browser)
📦 What is cached? Static files
➡️ HTML, CSS, JS, images

✅ Benefits

Faster page load

Reduces server requests

Improves user experience

📌 Example

Once loaded, your logo image doesn’t download again on refresh.
---

🌍 CDN Cache

📍 Where? Edge servers (close to users)
📦 What is cached? Static files

✅ Benefits

Global performance improvement

Lower latency

Offloads backend servers

📌 Example

Images served from the nearest CDN location instead of your main server.
---

🖥️ Server Cache

📍 Where? Application layer (server memory)
📦 What is cached? Frequently used data

🛠 Tools

Redis

In-memory cache (EhCache, Caffeine)


✅ Benefits

Faster API responses

Reduces DB load

Ideal for frequently accessed data

---

🗄️ Database Cache

📍 Where? Database layer
📦 What is cached? Query results

✅ Benefits

Faster query execution

Reduces expensive DB operations


📌 Example

Repeated SELECT queries served from cache instead of disk.
---
⚖️ Quick Comparison

Cache Type Location Used For

Browser Cache Client Static files
CDN Cache Edge Network Static files
Server Cache App Server Frequently used data
Database Cache DB Layer Query results


---

🧠 Simple Rule to Remember

👉 Browser & CDN cache = Speed for users
👉 Server & DB cache = Speed for backend
---

📌 Final Thought

A high-performance system doesn’t rely on one cache,
it uses multiple layers of caching together 🚀

1 week ago | [YT] | 1

Java.AiTools

🔐 OAuth 2.0 vs OpenID Connect (OIDC) – Explained Simply

If you’ve worked with Spring Boot Security, you’ve definitely heard of OAuth and OIDC.
They sound similar—but they solve different problems.

Let’s simplify it 👇
---

🔑 What is OAuth 2.0?

OAuth 2.0 is an authorization framework

👉 It answers:
“What is this app allowed to access?”

✅ What OAuth does

Allows third-party apps to access resources

Shares access tokens, not passwords

Controls permissions (scopes)


📌 Example

> “Allow this app to read your emails, but not delete them.”


❌ OAuth does NOT do

It does not identify who the user is

---

🪪 What is OpenID Connect (OIDC)?

OIDC is an identity layer built on top of OAuth 2.0

👉 It answers:
“Who is this user?”

✅ What OIDC does

Provides user authentication

Returns ID Token (JWT)

Includes user details (email, name, profile)


📌 Example

> “This user is John, logged in via Google.”


---

⚖️ OAuth vs OIDC (Quick Comparison)

Feature OAuth 2.0 OIDC

Purpose Authorization. Authentication
Token Type Access Token ID Token + Access Token
Identifies user? ❌ No. ✅ Yes
Built on – OAuth 2.0
Common Use API access Login / SSO



---

🧠 Simple One-Line Difference

👉 OAuth = What you can access
👉 OIDC = Who you are


---

🌱 Spring Boot Perspective

🔹 OAuth 2.0

Used when:

Securing REST APIs

Machine-to-machine communication


🔹 OIDC

Used when:

Login with Google / Keycloak / Okta

Single Sign-On (SSO)


spring.security.oauth2.client.registration

Spring Security handles both OAuth & OIDC seamlessly 🚀

---

📌 Real-World Mapping

OAuth → API Security

OIDC → Login & Identity

Spring Boot + Spring Security → Glue that connects everything

---

💡 Final Thought

If your app needs:

🔐 Secure APIs → OAuth

👤 User login & identity → OIDC


👉 Most modern apps use OIDC (OAuth underneath)

1 week ago | [YT] | 1

Java.AiTools

🔒 Why Do We Declare Entity Fields as private in Spring Boot?

A frequently asked interview question — answered in 5 short, clear points 👇

In Spring Boot (and JPA/Hibernate), marking entity fields as private is not just a convention — it’s a best practice for clean, safe, and maintainable domain models.

✅ Top 5 Reasons to Keep Entity Variables private

1️⃣ Encapsulation
Prevents direct modification of entity state from outside the class.

2️⃣ Controlled Access (Getters/Setters)
Allows frameworks like Hibernate to interact with the entity through accessors, ensuring consistent behavior.

3️⃣ Data Integrity
Sensitive fields cannot be changed accidentally by other classes.

4️⃣ Flexibility & Maintainability
You can update internal logic anytime without breaking other parts of the code.

5️⃣ Validation & Business Rules
Setters can enforce rules (e.g., validating email, age, status) before assigning values.

💡 In Spring Boot, keeping entity fields private improves security, consistency, and ORM compatibility.

1 month ago | [YT] | 1

Java.AiTools

🤯 Debugging Nightmare Solved: The Case of the Missing Transaction\!

I just tackled a classic Spring Boot bug that caused a seemingly simple client deletion request to crash with a massive stack trace. Sharing this to save you a few hours of head-scratching\!

The Problem:

We had a frontend DELETE request that hit the backend, but the entire process failed with a *`javax.persistence.TransactionRequiredException`*.

* Error Message:"No EntityManager with actual transaction available for current thread - cannot reliably process 'remove' call."
* Context: The API was trying to delete records (client data, associated documents) using a custom repository method (`deleteAllByDocId`).

#The Mistake:

In a Spring Data JPA application, any operation that modifies the database (INSERT, UPDATE, DELETE/REMOVE) **must** run within a transactional context. My Service Layer method, `ClientServiceImpl.deleteClientById()`, was calling these repository delete methods but was missing one crucial annotation.

# The Solution: 💡 `@Transactional`

The fix was simple but non-negotiable: adding the `@Transactional` annotation to the service method.

```java
@Service
public class ClientServiceImpl implements ClientService {
// ... dependencies

@Override
@Transactional // <--- The essential fix!
public void deleteClientById(String clientId) {
// Now, all database writes run inside an active transaction.
uploadDocumentsRepository.deleteAllByDocId(clientId);
clientRepository.deleteById(clientId);
}
}
```

Key Takeaway for Developers:

If Hibernate or JPA throws a `TransactionRequiredException`, remember this simple rule: **Database write operations belong in a transactional method.** Always ensure your Service layer method that wraps the repository calls is annotated with `@Transactional`.

Has anyone else lost time to this exact bug? Let me know\! 👇

\#Springboot \#Java \#JPA \#Hibernate \#Debugging \#BackendDevelopment \#SoftwareEngineering \#TechTips

1 month ago | [YT] | 1

Java.AiTools

🚀 JPA Tips: @Embeddable vs @Embedded — What’s the difference?

Working with Spring Boot + JPA?
Then you’ve surely seen @Embeddable and @Embedded… but when should you actually use them? 🤔

Let’s simplify it 👇

🔹 @Embeddable — Create a Value Object

Use this when you want to define a reusable component that does not need its own table.

Think of things like:

Address

Coordinates

Money

Audit fields

✔ Lives inside another entity
✔ Has no @Id
✔ Perfect for grouping fields

@Embeddable class Address { private String city; private String state; private String pincode; }

🔹 @Embedded — Insert It Into an Entity

Use this inside an entity to tell JPA:

➡ “Put the fields of this object inside my table.”

@Entity class User { @Id private Long id; @Embedded private Address address; }

This means User table gets columns like city, state, pincode.

🎯 The Core Difference

@Embeddable → You define the reusable component

@Embedded → You use that component inside an entity

💡 When to use?

If you ever catch yourself repeating the same fields in multiple entities…
👉 Convert them into an @Embeddable.
👉 And use them with @Embedded.

Clean code. Reusable structures. Better domain modeling. ✨

1 month ago | [YT] | 1

Java.AiTools

🚀 Spring Boot Quick Tip: When to Use @JsonIgnore and @EqualsAndHashCode

Working with Spring Boot + JPA? Two annotations you’ll use often — but must use wisely — are @JsonIgnore and @EqualsAndHashCode.

🔹 @JsonIgnore
Use it when you don’t want a field to appear in your JSON response.
Perfect for:
• Avoiding infinite recursion in bidirectional relationships
• Hiding sensitive data (passwords, tokens)
• Removing heavy or unnecessary fields from API responses

🔹 @EqualsAndHashCode
Use it to define how your objects should be compared.
Best for:
• Entities stored in Sets or Maps
• Logical comparison between objects
• For JPA entities, prefer: @EqualsAndHashCode(of = "id")
• Avoid including lazy-loaded collections

A small change in annotations often saves you from big production surprises. ✔️

1 month ago | [YT] | 1

Java.AiTools

Hi , *Here is simple process of how you run spring boot application into AWS* .

✅ Setup AWS EC2 machine(Amazon Linux) by logging to AWS console.
✅ Connect to EC2 machine using "ssh command", and install java using "yum install"
✅ Code & testing your Spring Boot app in your local machine in IDE like Eclipse, IntelliJ, VSCode, Cursor.
✅ Build jar file of your spring boot app (mvn clean package)
✅ Using "scp" copy local machine jar into EC2 machine
✅ Start your spring boot app (java -jar myapp.jar)
✅ Enabled AWS security group configuration, for accessing your port from outside
✅ Test from local.

Just be clear with this. In Interview having basic cloud aws working. Of how you deploy & test in AWS, this will add good value. Since in projects work happen like this.

All the best 🙏

5 months ago | [YT] | 0

Java.AiTools

🔖 How to Create Custom Annotations in Java 💡

Annotations in Java provide metadata about the code, and you can also define your own custom annotations to add meaningful behavior or structure to your applications.

✅ Step-by-Step: Create a Custom Annotation

1️⃣ Define the Annotation

import java.lang.annotation.*; @Retention(RetentionPolicy.RUNTIME) // Available at runtime @Target(ElementType.METHOD) // Can be applied on methods public @interface MyAnnotation { String value() default "Default Message"; }

🔍 Annotations Meta-Tags:

@Retention: Specifies how long the annotation is retained (SOURCE, CLASS, RUNTIME)

@Target: Specifies where the annotation can be used (METHOD, FIELD, TYPE, etc.)

2️⃣ Apply the Custom Annotation

public class MyService { @MyAnnotation(value = "Hello Annotation!") public void sayHello() { System.out.println("Method executed."); } }

3️⃣ Read Annotation Using Reflection

import java.lang.reflect.Method; public class AnnotationProcessor { public static void main(String[] args) throws Exception { Method method = MyService.class.getMethod("sayHello"); if (method.isAnnotationPresent(MyAnnotation.class)) { MyAnnotation annotation = method.getAnnotation(MyAnnotation.class); System.out.println("Annotation value: " + annotation.value()); } } }

📌 Use Cases for Custom Annotations

Building frameworks

Creating custom validation

Logging, caching, security rules

Marking deprecated or experimental features

✨ Power up your Java skills by learning and creating your own annotations!

#Java #Annotations #CustomAnnotations #ReflectionAPI #CodeTips #JavaDeveloper

5 months ago | [YT] | 1