mirror of
https://github.com/tiennm99/java-design-patterns.git
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Ilkka Seppälä
150 lines
4.1 KiB
Markdown
150 lines
4.1 KiB
Markdown
---
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title: Gateway
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category: Structural
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language: en
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tag:
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- Decoupling
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---
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## Intent
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Provide a interface to access a set of external systems or functionalities. Gateway provides a simple uniform view of
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external resources to the internals of an application.
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## Explanation
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Real-world example
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> Gateway acts like a real front gate of a certain city. The people inside the city are called
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> internal system, and different outside cities are called external services. The gateway is here
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> to provide access for internal system to different external services.
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In plain words
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> Gateway can provide an interface which lets internal system to utilize external service.
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Wikipedia says
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> A server that acts as an API front-end, receives API requests, enforces throttling and security
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> policies, passes requests to the back-end service and then passes the response back to the requester.
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**Programmatic Example**
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The main class in our example is the `ExternalService` that contains items.
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```java
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class ExternalServiceA implements Gateway {
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@Override
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public void execute() throws Exception {
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LOGGER.info("Executing Service A");
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// Simulate a time-consuming task
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Thread.sleep(1000);
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}
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}
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/**
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* ExternalServiceB is one of external services.
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*/
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class ExternalServiceB implements Gateway {
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@Override
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public void execute() throws Exception {
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LOGGER.info("Executing Service B");
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// Simulate a time-consuming task
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Thread.sleep(1000);
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}
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}
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/**
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* ExternalServiceC is one of external services.
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*/
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class ExternalServiceC implements Gateway {
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@Override
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public void execute() throws Exception {
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LOGGER.info("Executing Service C");
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// Simulate a time-consuming task
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Thread.sleep(1000);
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}
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public void error() throws Exception {
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// Simulate an exception
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throw new RuntimeException("Service C encountered an error");
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}
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}
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```
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To operate these external services, Here's the `App` class:
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```java
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public class App {
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/**
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* Simulate an application calling external services.
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*/
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public static void main(String[] args) throws Exception {
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GatewayFactory gatewayFactory = new GatewayFactory();
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// Register different gateways
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gatewayFactory.registerGateway("ServiceA", new ExternalServiceA());
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gatewayFactory.registerGateway("ServiceB", new ExternalServiceB());
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gatewayFactory.registerGateway("ServiceC", new ExternalServiceC());
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// Use an executor service for asynchronous execution
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Gateway serviceA = gatewayFactory.getGateway("ServiceA");
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Gateway serviceB = gatewayFactory.getGateway("ServiceB");
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Gateway serviceC = gatewayFactory.getGateway("ServiceC");
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// Execute external services
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try {
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serviceA.execute();
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serviceB.execute();
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serviceC.execute();
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} catch (ThreadDeath e) {
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LOGGER.info("Interrupted!" + e);
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throw e;
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}
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}
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}
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```
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The `Gateway` interface is extremely simple.
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```java
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interface Gateway {
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void execute() throws Exception;
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}
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```
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Program output:
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```java
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Executing Service A
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Executing Service B
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Executing Service C
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```
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## Class diagram
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## Applicability
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Use the Gateway pattern
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* To access an aggregate object's contents without exposing its internal representation.
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* To integration with multiple external services or APIs.
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* To provide a uniform interface for traversing different aggregate structures.
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## Tutorials
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* [Pattern: API Gateway / Backends for Frontends](https://microservices.io/patterns/apigateway.html)
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## Known uses
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* [API Gateway](https://java-design-patterns.com/patterns/api-gateway/)
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* [10 most common use cases of an API Gateway](https://apisix.apache.org/blog/2022/10/27/ten-use-cases-api-gateway/)
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## Credits
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* [Gateway](https://martinfowler.com/articles/gateway-pattern.html)
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* [What is the difference between Facade and Gateway design patterns?](https://stackoverflow.com/questions/4422211/what-is-the-difference-between-facade-and-gateway-design-patterns)
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