feature: Add gateway pattern (#1297) (#2734)

* Implement Gateway pattern * Fixed docstrings * Fixed README.md * Fixed App * Fixed pom.xml * Fixed pom.xml * Fixed pom.xml * Fixed pom.xml * fixed checkstyle errors and directory names * fixed pom.xml * fixed checkstyle errors * Bug fixed * Bug fixed * Bug fixed * Bug fixed and code improvement * Bug fixed and code improvement * Bug fixed and update README.md * update APP.java * update gateway pattern * Revert "update gateway pattern" This reverts commit f31a00c268889b2c6b7690e07847df7247725999. * update gateway pattern --------- Co-authored-by: Finn <u7552286@anu.edu.au>
2026-10-14 02:16:06 +00:00 · 2024-03-10 10:55:18 +02:00
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+---
+title: Gateway
+category: Structural
+language: en
+tag:
+- Gang of Four
+- Decoupling
+
+---
+
+## Intent
+
+Provide a interface to access a set of external systems or functionalities. Gateway provides a simple uniform view of
+external resources to the internals of an application.
+
+## Explanation
+
+Real-world example
+
+> Gateway acts like a real front gate of a certain city. The people inside the city are called
+> internal system, and different outside cities are called external services. The gateway is here
+> to provide access for internal system to different external services.
+
+In plain words
+
+> Gateway can provide an interface which lets internal system to utilize external service.
+
+Wikipedia says
+
+> A server that acts as an API front-end, receives API requests, enforces throttling and security
+> policies, passes requests to the back-end service and then passes the response back to the requester.
+
+**Programmatic Example**
+
+The main class in our example is the `ExternalService` that contains items.
+
+```java
+class ExternalServiceA implements Gateway {
+    @Override
+    public void execute() throws Exception {
+        System.out.println("Executing Service A");
+        // Simulate a time-consuming task
+        Thread.sleep(1000);
+    }
+}
+
+/**
+ * ExternalServiceB is one of external services.
+ */
+class ExternalServiceB implements Gateway {
+    @Override
+    public void execute() throws Exception {
+        System.out.println("Executing Service B");
+        // Simulate a time-consuming task
+        Thread.sleep(1000);
+    }
+}
+
+/**
+ * ExternalServiceC is one of external services.
+ */
+class ExternalServiceC implements Gateway {
+    @Override
+    public void execute() throws Exception {
+        System.out.println("Executing Service C");
+        // Simulate a time-consuming task
+        Thread.sleep(1000);
+    }
+
+    public void error() throws Exception {
+        // Simulate an exception
+        throw new RuntimeException("Service C encountered an error");
+    }
+}
+```
+
+To operate these external services, Here's the `App` class:
+
+```java
+public class App {
+    /**
+     * Simulate an application calling external services.
+     */
+    public static void main(String[] args) throws Exception {
+        GatewayFactory gatewayFactory = new GatewayFactory();
+
+        // Register different gateways
+        gatewayFactory.registerGateway("ServiceA", new ExternalServiceA());
+        gatewayFactory.registerGateway("ServiceB", new ExternalServiceB());
+        gatewayFactory.registerGateway("ServiceC", new ExternalServiceC());
+
+        // Use an executor service for asynchronous execution
+        Gateway serviceA = gatewayFactory.getGateway("ServiceA");
+        Gateway serviceB = gatewayFactory.getGateway("ServiceB");
+        Gateway serviceC = gatewayFactory.getGateway("ServiceC");
+
+        // Execute external services
+        try {
+            serviceA.execute();
+            serviceB.execute();
+            serviceC.execute();
+        } catch (ThreadDeath e) {
+            System.out.println("Interrupted!" + e);
+            throw e;
+        }
+    }
+}
+```
+
+The `Gateway` interface is extremely simple.
+
+```java
+interface Gateway {
+    void execute() throws Exception;
+}
+```
+
+Program output:
+
+```java
+        Executing Service A
+        Executing Service B
+        Executing Service C
+```
+
+## Class diagram
+
+![alt text](./etc/gateway.urm.png "gateway")
+
+## Applicability
+
+Use the Gateway pattern
+
+* To access an aggregate object's contents without exposing its internal representation.
+* To integration with multiple external services or APIs.
+* To provide a uniform interface for traversing different aggregate structures.
+
+## Tutorials
+
+* [Pattern: API Gateway / Backends for Frontends](https://microservices.io/patterns/apigateway.html)
+
+## Known uses
+
+* [API Gateway](https://java-design-patterns.com/patterns/api-gateway/)
+* [10 most common use cases of an API Gateway](https://apisix.apache.org/blog/2022/10/27/ten-use-cases-api-gateway/)
+
+## Credits
+
+* [Gateway](https://martinfowler.com/articles/gateway-pattern.html)
+* [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)