[pull] master from iluwatar:master

.all-contributorsrc

@@ -3728,6 +3728,51 @@
       "contributions": [
         "translation"
       ]
+    },
+    {
+      "login": "priyanshuvishwakarma273403",
+      "name": "Priyanshu",
+      "avatar_url": "https://avatars.githubusercontent.com/u/222148451?v=4",
+      "profile": "https://www.priyanshu-portfolio.co.in",
+      "contributions": [
+        "code"
+      ]
+    },
+    {
+      "login": "arnabnandy7",
+      "name": "Arnab Nandy",
+      "avatar_url": "https://avatars.githubusercontent.com/u/5053648?v=4",
+      "profile": "https://github.com/arnabnandy-cognizant",
+      "contributions": [
+        "doc"
+      ]
+    },
+    {
+      "login": "MohamedMBG",
+      "name": "BAGHDAD Mohamed",
+      "avatar_url": "https://avatars.githubusercontent.com/u/123114744?v=4",
+      "profile": "https://github.com/MohamedMBG",
+      "contributions": [
+        "code"
+      ]
+    },
+    {
+      "login": "AnveshSrivastava",
+      "name": "Anvesh Srivastava",
+      "avatar_url": "https://avatars.githubusercontent.com/u/170334970?v=4",
+      "profile": "https://github.com/AnveshSrivastava",
+      "contributions": [
+        "code"
+      ]
+    },
+    {
+      "login": "Mukul-Howale",
+      "name": "Mukul Howale",
+      "avatar_url": "https://avatars.githubusercontent.com/u/110479646?v=4",
+      "profile": "https://github.com/Mukul-Howale",
+      "contributions": [
+        "code"
+      ]
     }
   ],
   "contributorsPerLine": 6,

README.md

@@ -6,7 +6,7 @@
 [![Coverage](https://sonarcloud.io/api/project_badges/measure?project=iluwatar_java-design-patterns&metric=coverage)](https://sonarcloud.io/dashboard?id=iluwatar_java-design-patterns)
 [![Join the chat at https://gitter.im/iluwatar/java-design-patterns](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/iluwatar/java-design-patterns?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
 <!-- ALL-CONTRIBUTORS-BADGE:START - Do not remove or modify this section -->
-[![All Contributors](https://img.shields.io/badge/all_contributors-409-orange.svg?style=flat-square)](#contributors-)
+[![All Contributors](https://img.shields.io/badge/all_contributors-414-orange.svg?style=flat-square)](#contributors-)
 <!-- ALL-CONTRIBUTORS-BADGE:END -->
 
 <br/>
@@ -607,6 +607,11 @@ This project is licensed under the terms of the MIT license.
     </tr>
     <tr>
       <td align="center" valign="top" width="16.66%"><a href="https://github.com/SrGiuliano77"><img src="https://avatars.githubusercontent.com/u/128543464?v=4?s=100" width="100px;" alt="Giuliano Oliveira"/><br /><sub><b>Giuliano Oliveira</b></sub></a><br /><a href="#translation-SrGiuliano77" title="Translation">🌍</a></td>
+      <td align="center" valign="top" width="16.66%"><a href="https://www.priyanshu-portfolio.co.in"><img src="https://avatars.githubusercontent.com/u/222148451?v=4?s=100" width="100px;" alt="Priyanshu"/><br /><sub><b>Priyanshu</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=priyanshuvishwakarma273403" title="Code">💻</a></td>
+      <td align="center" valign="top" width="16.66%"><a href="https://github.com/arnabnandy-cognizant"><img src="https://avatars.githubusercontent.com/u/5053648?v=4?s=100" width="100px;" alt="Arnab Nandy"/><br /><sub><b>Arnab Nandy</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=arnabnandy7" title="Documentation">📖</a></td>
+      <td align="center" valign="top" width="16.66%"><a href="https://github.com/MohamedMBG"><img src="https://avatars.githubusercontent.com/u/123114744?v=4?s=100" width="100px;" alt="BAGHDAD Mohamed"/><br /><sub><b>BAGHDAD Mohamed</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=MohamedMBG" title="Code">💻</a></td>
+      <td align="center" valign="top" width="16.66%"><a href="https://github.com/AnveshSrivastava"><img src="https://avatars.githubusercontent.com/u/170334970?v=4?s=100" width="100px;" alt="Anvesh Srivastava"/><br /><sub><b>Anvesh Srivastava</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=AnveshSrivastava" title="Code">💻</a></td>
+      <td align="center" valign="top" width="16.66%"><a href="https://github.com/Mukul-Howale"><img src="https://avatars.githubusercontent.com/u/110479646?v=4?s=100" width="100px;" alt="Mukul Howale"/><br /><sub><b>Mukul Howale</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=Mukul-Howale" title="Code">💻</a></td>
     </tr>
   </tbody>
 </table>

backends-for-frontends/README.md

@@ -0,0 +1,148 @@
+---
+title: "Backends For Frontends Pattern in Java: Tailoring APIs to Client Needs"
+shortTitle: Backends For Frontends
+description: "Learn the Backends For Frontends (BFF) design pattern in Java. Understand how to give each client type its own dedicated backend service, with real-world examples, code, and diagrams."
+category: Architectural
+language: en
+tag:
+  - API design
+  - Architecture
+  - Client-server
+  - Decoupling
+  - Microservices
+---
+
+## Also known as
+
+* Backend For Frontend
+* BFF Pattern
+
+## Intent of Backends For Frontends Pattern
+
+Provide each client-side application (mobile, desktop, chatbot, and so on) with its own dedicated
+backend service, so every client gets an API shaped exactly for its own needs instead of sharing
+one general-purpose backend with every other client.
+
+## Detailed Explanation of Backends For Frontends Pattern with Real-World Examples
+
+Real-world example
+
+> Imagine a retail company whose mobile app, desktop back-office tool, and support chatbot all
+> need customer, cart, order and supplier data -- but a phone screen wants a short summary while
+> the back-office desktop tool wants full order and stock detail. Rather than exposing one shared
+> API that every client has to filter or over-fetch from, the company stands up a small BFF service
+> for the mobile clients and a separate BFF service for the intranet clients. Each BFF calls only
+> the downstream microservices its client needs and returns a payload shaped for that client.
+
+In plain words
+
+> Give every kind of client its own tailor-made backend, instead of forcing all clients through one
+> one-size-fits-all API.
+
+Sam Newman, who popularized the pattern, says
+
+> Create separate backend services to be consumed by specific frontend applications or interfaces.
+
+## Architecture Diagram
+
+```
+node mobile{
+ component iosapp as "ios app"
+ component androidapp as "android app"
+}
+node intranet{
+ component desktop as "desktop app"
+ component chatbot
+}
+component bff as "BFF server"{
+ component iosbff as "ios BFF"
+ component androidbff as "android BFF"
+ component chatbotbff as "chatbot BFF"
+ component desktopbff as "desktop BFF"
+}
+node intranetserv as "intranet services server"{
+ component ss as "supplier service API"
+}
+cloud onlypublic as "public cloud"{
+ component cas as "customer authentication service API"
+ component cs as "cart service API"
+}
+cloud cloudserv as "managed cloud"{
+ component os as "order service API"
+}
+iosapp -- iosbff
+androidapp -- androidbff
+chatbot -- chatbotbff
+desktop -- desktopbff
+iosbff -- cas
+androidbff -- cas
+iosbff -- cs
+androidbff -- cs
+iosbff -- os
+androidbff -- os
+chatbotbff -- os
+desktopbff -- os
+chatbotbff -- ss
+desktopbff -- ss
+```
+
+This example implements a simplified version of the diagram above with two client-facing BFFs
+instead of four, to keep the demo focused: a **Mobile BFF** standing in for the ios/android BFFs,
+and a **Desktop BFF** standing in for the desktop/chatbot BFFs. Both call into the same shared
+downstream services (`AuthService`, `OrderService`), while `CartService` is only used by the
+Mobile BFF and `SupplierService` is only reachable from the Desktop BFF, matching the fan-out
+shown in the diagram.
+
+## Class Diagram
+
+![Backends For Frontends class diagram](./etc/backends-for-frontends.png)
+
+## When to Use the Backends For Frontends Pattern in Java
+
+* Different client types (mobile, web, desktop, voice/chat) need meaningfully different shapes,
+  granularity, or aggregation of the same underlying data.
+* A single shared API has grown a large number of client-specific conditional branches, optional
+  fields, or query parameters to accommodate every consumer.
+* Different client teams need to iterate on their own API independently without coordinating
+  changes through one shared backend team.
+* Some clients (e.g. mobile) need aggressively trimmed payloads for bandwidth/latency reasons,
+  while others (e.g. an internal desktop tool) need much richer data.
+
+## Benefits and Trade-offs of Backends For Frontends Pattern
+
+Benefits:
+
+* Each client gets an API optimized for its own needs, improving performance and simplicity on
+  the client side.
+* Client teams can evolve their BFF independently, reducing cross-team coordination.
+* Downstream microservices stay generic and reusable; client-specific logic lives in the BFF
+  layer instead of leaking into shared services.
+
+Trade-offs:
+
+* Introduces additional services to build, deploy, and operate.
+* Logic that is genuinely shared across clients can end up duplicated across BFFs if not
+  carefully factored out.
+* Adds an extra network hop between the client and the downstream services.
+
+## How to Implement Backends For Frontends Pattern in Java
+
+1. Identify the distinct client types that need meaningfully different data shapes.
+2. Define the downstream services each client's data actually depends on (`AuthService`,
+   `CartService`, `OrderService`, `SupplierService` in this example).
+3. Create one BFF per client type, implementing a shared `ClientBff<T>` contract, where each BFF
+   only depends on the downstream services its client needs.
+4. Have each BFF aggregate and reshape the downstream data into a response DTO tailored to its
+   client (`MobileDashboardResponse`, `DesktopDashboardResponse`).
+5. Wire the client applications to call their own BFF rather than the downstream services
+   directly.
+
+## Source Code
+
+* [Pattern: Backends For Frontends](https://samnewman.io/patterns/architectural/bff/) by Sam Newman
+* [Microservices Patterns: With examples in Java](https://www.amazon.com/Microservices-Patterns-examples-Chris-Richardson/dp/1617294543) by Chris Richardson
+
+## References and Credits
+
+* [Building Microservices](https://www.oreilly.com/library/view/building-microservices-2nd/9781492034018/) by Sam Newman
+* [Pattern: Backend for frontend (microservices.io)](https://microservices.io/patterns/apigateway.html)

backends-for-frontends/etc/backends-for-frontends.urm.puml

@@ -0,0 +1,130 @@
+@startuml
+package com.iluwatar.bff {
+  class App {
+    - LOGGER : Logger {static}
+    - USER_ID : String {static}
+    - PRODUCT_ID : String {static}
+    - DEMO_PRICE_USD : double {static}
+    - DEMO_STOCK_LEVEL : int {static}
+    + App()
+    + main(args : String[]) {static}
+  }
+}
+package com.iluwatar.bff.bff {
+  interface ClientBff<T> {
+    + getDashboard(userId : String) : T {abstract}
+  }
+  class DesktopBff {
+    - authService : AuthService
+    - orderService : OrderService
+    - supplierService : SupplierService
+    + DesktopBff(auth : AuthService, orders : OrderService, suppliers : SupplierService)
+    + getDashboard(userId : String) : DesktopDashboardResponse
+  }
+  class MobileBff {
+    - MAX_RECENT_ORDERS : int {static}
+    - authService : AuthService
+    - cartService : CartService
+    - orderService : OrderService
+    + MobileBff(auth : AuthService, cart : CartService, orders : OrderService)
+    + getDashboard(userId : String) : MobileDashboardResponse
+  }
+}
+package com.iluwatar.bff.dto {
+  class DesktopDashboardResponse {
+    - greeting : String
+    - loyaltyTier : String
+    - orderStatuses : List<String>
+    - supplierStockSummaries : List<String>
+    + DesktopDashboardResponse(greeting : String, loyaltyTier : String, orderStatuses : List<String>, supplierStockSummaries : List<String>)
+  }
+  class MobileDashboardResponse {
+    - greeting : String
+    - cartItemCount : int
+    - cartTotalUsd : double
+    - recentOrderSummaries : List<String>
+    + MobileDashboardResponse(greeting : String, cartItemCount : int, cartTotalUsd : double, recentOrderSummaries : List<String>)
+  }
+}
+package com.iluwatar.bff.model {
+  class CartItem {
+    - product : Product
+    - quantity : int
+    + CartItem(product : Product, quantity : int)
+    + lineTotal() : double
+  }
+  class Order {
+    - id : String
+    - productName : String
+    - status : String
+    + Order(id : String, productName : String, status : String)
+  }
+  class Product {
+    - id : String
+    - name : String
+    - priceUsd : double
+    + Product(id : String, name : String, priceUsd : double)
+  }
+  class SupplierRecord {
+    - productId : String
+    - supplierName : String
+    - stockLevel : int
+    + SupplierRecord(productId : String, supplierName : String, stockLevel : int)
+  }
+  class User {
+    - id : String
+    - displayName : String
+    - loyaltyTier : String
+    + User(id : String, displayName : String, loyaltyTier : String)
+  }
+}
+package com.iluwatar.bff.service {
+  interface AuthService {
+    + getUser(userId : String) : User {abstract}
+  }
+  interface CartService {
+    + getCart(userId : String) : List<CartItem> {abstract}
+  }
+  interface OrderService {
+    + getOrders(userId : String) : List<Order> {abstract}
+  }
+  interface SupplierService {
+    + getSupplierRecords(productId : String) : List<SupplierRecord> {abstract}
+  }
+}
+package com.iluwatar.bff.service.impl {
+  class InMemoryAuthService {
+    - users : Map<String, User>
+    + InMemoryAuthService(userData : Map<String, User>)
+    + getUser(userId : String) : User
+  }
+  class InMemoryCartService {
+    - cartsByUserId : Map<String, List<CartItem>>
+    + InMemoryCartService(carts : Map<String, List<CartItem>>)
+    + getCart(userId : String) : List<CartItem>
+  }
+  class InMemoryOrderService {
+    - ordersByUserId : Map<String, List<Order>>
+    + InMemoryOrderService(orders : Map<String, List<Order>>)
+    + getOrders(userId : String) : List<Order>
+  }
+  class InMemorySupplierService {
+    - recordsByProductId : Map<String, List<SupplierRecord>>
+    + InMemorySupplierService(records : Map<String, List<SupplierRecord>>)
+    + getSupplierRecords(productId : String) : List<SupplierRecord>
+  }
+}
+DesktopBff ..|> ClientBff
+MobileBff ..|> ClientBff
+DesktopBff --> "-authService" AuthService
+DesktopBff --> "-orderService" OrderService
+DesktopBff --> "-supplierService" SupplierService
+MobileBff --> "-authService" AuthService
+MobileBff --> "-cartService" CartService
+MobileBff --> "-orderService" OrderService
+InMemoryAuthService ..|> AuthService
+InMemoryCartService ..|> CartService
+InMemoryOrderService ..|> OrderService
+InMemorySupplierService ..|> SupplierService
+CartItem --> "-product" Product
+@enduml