Introduction
In this article, we’ll explore how to use and test REST endpoints in an Axon application. Axon is a CQRS and event sourcing framework that simplifies the development of scalable and maintainable applications. We’ll learn how to expose and interact with Axon’s Command and Query APIs through REST endpoints, and we’ll cover techniques to effectively test these endpoints.
Prerequisites
Before we begin, ensure that you have the following:
- Basic knowledge of Axon framework
- JDK 8 or higher installed
- Maven or Gradle build tool installed (depending on your project setup)
Setting Up the Project
To get started, let’s set up a new Axon project or use an existing one. Ensure that the necessary dependencies for Axon and Spring Boot are added to your project’s build configuration file (e.g., pom.xml for Maven or build.gradle for Gradle).
Exposing Axon Command and Query APIs as REST Endpoints
Axon provides a convenient way to expose its Command and Query APIs as REST endpoints using Spring Boot’s @RestController annotation. Let’s create a new Java class, OrderController, and annotate it with @RestController. This class will serve as the entry point for handling HTTP requests.
@RestControllerpublic class OrderController {
// TODO: Implement REST endpoints for Command and Query APIs
}Inside the OrderController class, we’ll define methods to handle HTTP requests for Axon’s Command and Query APIs. These methods will be responsible for processing the requests, invoking the appropriate Axon components, and returning the HTTP responses.
Implementing REST Endpoints for Command APIs
To implement REST endpoints for Axon’s Command APIs, we’ll leverage the CommandGateway provided by Axon. The CommandGateway allows us to send commands to the corresponding command handlers. Let’s add a method in the OrderController class to handle the creation of new orders:
@PostMapping("/orders")public ResponseEntity<String> createOrder(@RequestBody CreateOrderCommand command) {
try {
commandGateway.sendAndWait(command);
return ResponseEntity.ok("Order created successfully");
} catch (Exception e) {
return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR).body("Failed to create order");
}
}In this example, we use the @PostMapping annotation to map the /orders URL path to the createOrder() method. The @RequestBody annotation indicates that the request payload should be mapped to the CreateOrderCommand object, which represents the command for creating a new order. We invoke the commandGateway.sendAndWait() method to send the command and wait for its execution. Depending on the outcome, we return an appropriate HTTP response.
Implementing REST Endpoints for Query APIs
To implement REST endpoints for Axon’s Query APIs, we’ll use Axon’s QueryGateway. The QueryGateway allows us to send queries and retrieve query results. Let’s add a method in the OrderController class to handle retrieving order details:
@GetMapping("/orders/{orderId}")public ResponseEntity<OrderDetails> getOrderDetails(@PathVariable String orderId) {
try {
OrderDetails orderDetails = queryGateway.query(new GetOrderDetailsQuery(orderId), ResponseTypes.instanceOf(OrderDetails.class)).join();
if (orderDetails != null) {
return ResponseEntity.ok(orderDetails);
} else {
return ResponseEntity.notFound().build();
}
} catch (Exception e) {
return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR).body(null);
}
}In this example, we use the @GetMapping annotation to map the /orders/{orderId} URL path to the getOrderDetails() method. The {orderId} path variable represents the ID of the order we want to retrieve. We invoke the queryGateway.query() method to send the GetOrderDetailsQuery query and retrieve the order details. The ResponseTypes.instanceOf(OrderDetails.class) specifies the expected response type. We use the join() method to wait for the query result and then return the appropriate HTTP response based on the retrieved order details.
Testing the REST Endpoints
Now that we have implemented the REST endpoints for Axon’s Command and Query APIs, it’s crucial to test them to ensure their correctness and functionality. We can use tools like JUnit and Spring’s MockMvc to perform unit and integration tests.
Let’s create a new test class, OrderControllerTest, and use JUnit and MockMvc to test the REST endpoints:
@RunWith(SpringRunner.class)@WebMvcTest(OrderController.class)public class OrderControllerTest {
@Autowiredprivate MockMvc mockMvc;
@MockBeanprivate CommandGateway commandGateway;
@MockBeanprivate QueryGateway queryGateway;
@Testpublic void testCreateOrder() throws Exception {
// TODO: Write test case for createOrder() endpoint
}
@Testpublic void testGetOrderDetails() throws Exception {
// TODO: Write test case for getOrderDetails() endpoint
}
}In this example, we use the @RunWith annotation to specify the SpringRunner class for running the tests. The @WebMvcTest(OrderController.class) annotation focuses the testing on the OrderController class and sets up the necessary Spring MVC components. We use the @Autowired annotation to inject the MockMvc instance, which we’ll use to perform HTTP requests and assertions.
Inside the test methods, we can use the MockMvc instance to perform HTTP requests and verify the responses. For example, to test the createOrder() endpoint, we can send a POST request and assert the expected HTTP status code and response body.
Conclusion
In this article, we learned how to use and test REST endpoints in an Axon application. We explored how to expose Axon’s Command and Query APIs as REST endpoints using Spring Boot’s @RestController annotation. We also implemented the REST endpoints for Command and Query APIs, and we covered techniques to test these endpoints using JUnit and MockMvc.
By leveraging Axon’s integration with Spring Boot and performing comprehensive testing, we can ensure the proper functionality and reliability of the REST endpoints in our Axon application.
