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Diff for: ‎pom.xml

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<module>money</module>
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<module>table-inheritance</module>
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<module>bloc</module>
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<module>remote-procedure-call</module>
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</modules>
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<repositories>
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<repository>

Diff for: ‎remote-procedure-call/README.md

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---
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title: Remote Procedure Call in Java using gRPC
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shortTitle: gRPC in Java
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description: Remote Procedure Call in Java using gRPC communicating between 2 microservices product and cart application
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category: Data Transfer
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language: en
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tag:
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- Behavioral
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- Integration
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- Messaging
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- Client-Server
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- Data Transfer
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- Microservices
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- Remote Procedure Call
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- Remote Method Invocation
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---
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# Remote Method Invocation / Remote Procedure Call
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Remote Method Invocation has various different aliases, Remote Procedure Call / Remote Method Invocation or RPC for short. Is a protocol
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that one program can use to request a service from a different program located in same or another computer in a network without having to understand network details.
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RMI can be implemented in various different languages and frameworks. Technologies like REST, gRPC and Thrift can be used for RMI. In this example we
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will be using gRPC to implement Remote Procedure Call in Java.
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## Terminologies
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- Client: The client is the application that sends a request to the server.
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- Server: The server is the application that receives the request from the client and sends a response back to the client.
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- Stub: The client-side proxy for the server.
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- Skeleton: The server-side proxy for the client.
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- Protocol: The set of rules that the client and server follow to communicate with each other.
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- Stream: The sequence of messages that are sent between the client and server, understand it as list of objects.
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## What is gRPC?
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[gRPC](https://grpc.io/docs/what-is-grpc/introduction/) is a high-performance, open-source and universal RPC framework. gRPC was developed by Google but is now open-source
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and is based on the HTTP/2 protocol.
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A gRPC client can call a method on a gRPC server similar to if it was calling a method on a local object.
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This allows client and server to communicate with each other by just using method calls. gRPC internally uses [protobuf](https://protobuf.dev/) to serialize the data for communication.
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## When to use gRPC?
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gRPC should be used when you need high performance communication between client and server. It is mostly used in micro-service architecture when one
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service needs to communicate with another service.
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For communication you need to define contract / interfaces denoting the method signature, data types and parameters along with return type.
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These methods can be called by client service just like a method call, when using gRPC, a gRPC service is created which will in-turn call the
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implementation of the RPC method in the server and return the response (if any).
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Start by creating a .proto file which should have all the methods and data types you need for communication between the services.
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When you compile your code `maven/gradle gRPC` plugin will in return create objects and interfaces which you need to implement / extend in your
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server side. The client will then call the method defined in .proto file using the generated stubs by gPRC. In return inside the server the
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implementation of the method will be called and the response will be sent back to the client.
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### In this example
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We will be using 2 different micro-services
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- product-service
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- cart-service
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Along with a shopping.proto file to define the contract between the services.
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- ShoppingService
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This is a basic e-commerce simulation.
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In this simple example the `product-service` has data related to products and is used a source of truth. The `cart-service`
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needs the product data that is available in `product-service`. Certain number of products in turn may be bought by a customer,
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inside the cart service at which point the product quantity needs to be decreased in `product-service`, hence the need for bidirectional
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communication from `product-service` -> `cart-service` and vice versa they both communicate via gRPC.
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- getAllProducts() - gets all the product from state in `product-service` and stores it in `cart-service`
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- reduceProductQuantity() - reduces the quantity of a product by `id` fetched by `getAllProducts` and stored in `cart-service`
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when the method is hit, it reduces the quantity of product with same `id` in `product-service`
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## How to implement gRPC in Java?
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### .proto file
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- Create a [.proto](https://protobuf.dev/programming-guides/proto2/) file [example](./proto/shopping.proto) defining the service and message contracts
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- Define service interfaces, method signatures and data types in your .proto file
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### At the server end
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- Add gRPC and protobuf dependencies in your `pom.xml`
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- Include gRPC and protobuf plugins in `mvn build plugins`, for it to generate interfaces from your `.proto` during compilation
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- Include the .proto file directory in mvn build plugins to generate the interfaces
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- Build the project via `mvn clean install`
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- gRPC will generate the stubs and skeletons for you
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- Implement the service logic for the generated methods of skeleton in your service classes
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- Start the gRPC server at server's side on a specific port and attach the gRPC Implementation service to it
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### At the client end
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- Add gRPC and protobuf dependencies in your `pom.xml`
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- Include gRPC and protobuf plugins in `mvn build plugins`, for it to generate interfaces from your `.proto` during compilation
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- Include the .proto file directory in mvn build plugins to generate the interfaces
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- Build the project via `mvn clean install`
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- gRPC will generate the stubs and skeletons for you
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- A stub will expose the available methods to be called by the client, call the methods you need on server via the stub
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- Create Channel with server's host and port at client's end to communicate between server and client
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- Start client, and you are good to go
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## gRPC in action
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### Product Service
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#### Service
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- ProductService - API Interface for Internal logic in `product-service`
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- ProductServiceImpl - Implementation of ProductService, saves product data in memory for simplicity, exposes getter(s) for the same.
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Houses Composition of ProductService to store state.
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- ProductServiceGrpcImpl - gRPC contract implementation, methods to retrieve all products and reduce quantity of a product.
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This file implements the logic that should be executed when gRPC methods are called
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#### Model
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- Product - Product POJO Model
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#### Mocks
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- ProductMocks - Mock data of Product for testing and state initialization.
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### Cart Service
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#### Service
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- CartService - API Interface for Internal logic in `cart-service`,
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- CartServiceImpl - Implementation of CartService, methods to call the stub to populate data in cart and reduce quantities.
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This file calls the gRPC method to communicate with `product-service`.
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#### Model
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- ProductInCart - Cut from Product POJO in `product-service`
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### proto
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Proto folder contains all the proto files which define contract for the services.
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proto files end with .proto and contain the types, methods and services that are to be used in gRPC communication.
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### Good practise
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- Keep types / method names in PascalCase in .proto file
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### How to run this project
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- Clone the project
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- navigate to 'remote-procedure-call' directory via
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```shell
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cd java-design-patterns/remote-procedure-call
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```
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- build the project with, this will download dependencies, compile .proto to java interface and classes and create final jar
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```shell
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mvn clean install
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```
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- Start the `product-service` before `cart-service` as `cart-service` depends on product-service
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```shell
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mvn exec:java -Dexec.mainClass="com.iluwatar.rpc.product.Main" -pl product-service
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```
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- Start a new terminal session
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- navigate to 'remote-procedure-call' directory
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- Start the `cart-service`
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```shell
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mvn exec:java -Dexec.mainClass="com.iluwatar.rpc.cart.Main" -pl cart-service
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```
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- `cart-service` on startup will hit a gRPC call to `product-service` to get all products and populate the cart.
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- `cart-service` will then reduce the quantity of a product in `product-service` when a product is bought.
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- `cart-service` will then shut-down gracefully.
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- all the operations will be logged in the console.
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- `product-service` will continue to run and can be used for further operations by running `cart-service` again.
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- To stop the services, press `ctrl+c` in the terminal.

Diff for: ‎remote-procedure-call/cart-service/etc/cart-service.urm.png

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Diff for: ‎remote-procedure-call/cart-service/etc/cart-service.urm.puml

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@startuml
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skinparam dpi 300
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scale 0.3
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package com.iluwatar.rpc.cart.model {
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class ProductInCart {
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- id : Long
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- name : String
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- price : double
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- quantityToReduce : int
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- type : String
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}
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}
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package com.iluwatar.rpc.cart.service {
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interface CartService {
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+ getAllProducts() {abstract}
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+ getRandomProductFromCart() : ProductInCart {abstract}
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+ reduceCartQuantityFromProduct(ProductInCart) {abstract}
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}
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class CartServiceImpl {
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- log : Logger {static}
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- productsInCart : List<ProductInCart>
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- shoppingServiceBlockingStub : ShoppingServiceBlockingStub
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+ CartServiceImpl(shoppingStub : ShoppingServiceBlockingStub)
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+ getAllProducts()
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+ getRandomProductFromCart() : ProductInCart
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+ reduceCartQuantityFromProduct(product : ProductInCart)
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}
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}
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package com.iluwatar.rpc.proto {
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class Empty {}
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class ProductResponse {
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- id : long
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- name : String
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- price : double
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- type : String
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}
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class ReduceProductRequest {
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- productId : long
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- quantity : int
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}
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class ReduceProductResponse {
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- message : String
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- status : boolean
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}
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class ShoppingServiceImplBase {
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- getAllProducts(request: Empty, responseStreamObserver: StreamObserver<ProductResponse>)
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- reduceProductQuantity(request: ReduceProductRequest, responseStreamObserver : StreamObserver<ReduceProductResponse>)
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}
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}
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package com.iluwatar.rpc.cart {
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class Main {
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- HOST : String {static}
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- SERVER_PORT : int {static}
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- log : Logger {static}
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+ main(args : String[]) {static}
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}
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}
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CartServiceImpl --> "-productsInCart" ProductInCart
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CartServiceImpl ..|> CartService
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@enduml

Diff for: ‎remote-procedure-call/cart-service/pom.xml

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<?xml version="1.0" encoding="UTF-8"?>
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<!--
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This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
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The MIT License
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Copyright © 2014-2022 Ilkka Seppälä
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Permission is hereby granted, free of charge, to any person obtaining a copy
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of this software and associated documentation files (the "Software"), to deal
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in the Software without restriction, including without limitation the rights
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to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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copies of the Software, and to permit persons to whom the Software is
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furnished to do so, subject to the following conditions:
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The above copyright notice and this permission notice shall be included in
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all copies or substantial portions of the Software.
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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THE SOFTWARE.
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-->
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<project xmlns="http://maven.apache.org/POM/4.0.0"
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<parent>
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<artifactId>remote-procedure-call</artifactId>
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<groupId>com.iluwatar</groupId>
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<version>1.26.0-SNAPSHOT</version>
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</parent>
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<modelVersion>4.0.0</modelVersion>
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<artifactId>cart-service</artifactId>
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<packaging>jar</packaging>
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</project>

Diff for: ‎remote-procedure-call/cart-service/src/main/java/com/iluwatar/rpc/cart/Main.java

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/*
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* This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
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*
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* The MIT License
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* Copyright © 2014-2022 Ilkka Seppälä
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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package com.iluwatar.rpc.cart;
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import com.iluwatar.rpc.cart.service.CartServiceImpl;
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import com.iluwatar.rpc.proto.ShoppingServiceGrpc;
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import com.iluwatar.rpc.proto.ShoppingServiceGrpc.ShoppingServiceBlockingStub;
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import io.grpc.ManagedChannel;
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import io.grpc.ManagedChannelBuilder;
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import java.util.concurrent.TimeUnit;
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import org.slf4j.Logger;
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import org.slf4j.LoggerFactory;
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/**
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* Main class for the cart service.
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* Initializes the shopping channel and the cart service.
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*
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* @author CoderSleek
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* @version 1.0
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*/
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public class Main {
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private static final int SERVER_PORT = 8080;
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private static final String HOST = "localhost";
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private static final Logger log = LoggerFactory.getLogger(Main.class);
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/**
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* Main method to initialize the cart service and channel for RPC connection
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* initializes blocking stub and passes it to CartServiceImpl for constructor initialization.
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* Initializes data fetching from product-service.
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* shuts down after 1 request
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*/
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public static void main(String[] args) {
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ManagedChannel productChannel = ManagedChannelBuilder
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.forAddress(HOST, SERVER_PORT)
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.usePlaintext()
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.enableRetry()
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.keepAliveTime(10, TimeUnit.SECONDS)
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.build();
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ShoppingServiceBlockingStub blockingStub = ShoppingServiceGrpc.newBlockingStub(productChannel);
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log.info("cart-service started");
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var cartService = new CartServiceImpl(blockingStub);
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cartService.getAllProducts();
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var productInCart = cartService.getRandomProductFromCart();
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productInCart.setQuantityToReduce(10);
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cartService.reduceCartQuantityFromProduct(productInCart);
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productChannel.shutdown();
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log.info("cart-service execution successful, shutting down");
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}
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}

Diff for: ‎remote-procedure-call/cart-service/src/main/java/com/iluwatar/rpc/cart/model/ProductInCart.java

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/*
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* This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
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*
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* The MIT License
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* Copyright © 2014-2022 Ilkka Seppälä
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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package com.iluwatar.rpc.cart.model;
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import lombok.Builder;
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import lombok.Data;
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/**
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* ProductInCart is a POJO model class for product in cart.
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* ProductInCart is a cut from Product class in product-service
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*
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* @link com.iluwatar.rpc.product.model.Product
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* @author CoderSleek
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* @version 1.0
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*/
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@Data
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@Builder(toBuilder = true)
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public class ProductInCart {
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private Long id;
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private String name;
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private String type;
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private double price;
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private int quantityToReduce;
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}

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