In today's web development, reactive programming is becoming more and more important. Akka HTTP is a high-performance HTTP framework based on Akka, suitable for building reactive REST-style APIs. This article will introduce how to use Akka HTTP to build a reactive API, while providing some practical examples. Let’s get started!

1. Why choose Akka HTTP

When developing reactive APIs, it is very important to choose the right framework. Akka HTTP is a very good choice because it has the following advantages:

1.1 Responsive and non-blocking

Akka HTTP is a very reactive framework that allows you to handle a large number of requests , without blocking your application. It uses the Actor model, which means you can use asynchronous operations to respond to requests quickly while keeping your application highly scalable.

1.2 High performance

Because it is built on the Akka framework, Akka HTTP can provide faster performance. This is because it is able to take full advantage of multiple CPUs and cores and is suitable for situations where high concurrency is used.

1.3 Easy to use and configure

Akka HTTP is very easy to configure and use. It provides a powerful set of tools that allow you to quickly configure and manage your API. You can also write your code in Scala or Java.

2. Building a reactive API

Next, we will demonstrate how to build a reactive API using Akka HTTP. We will create a simple API for managing a list of users.

2.1 Installation and Import

To use Akka HTTP, you need to add the following dependencies:

<dependency>
  <groupId>com.typesafe.akka</groupId>
  <artifactId>akka-actor_2.12</artifactId>
  <version>2.5.26</version>
</dependency>

<dependency>
  <groupId>com.typesafe.akka</groupId>
  <artifactId>akka-http_2.12</artifactId>
  <version>10.1.10</version>
</dependency>

Please make sure these dependencies are included in your Maven or Gradle project.

2.2 Create a router

Now we will create a router to receive different HTTP requests and provide corresponding responses. We will use the Route class provided by Akka HTTP to define our router and provide the corresponding routing rules.

In this example, we will create a /User path that contains the GET, POST, PUT, and DELETE methods. The GET method will return a list of users, the POST method will create a new user, the PUT method will update users, and the DELETE method will delete users.

The following is the code of our router:

import akka.http.javadsl.server.Route;
import akka.http.javadsl.server.AllDirectives;

public class UserRouter extends AllDirectives {
  
  private final UserService userService;
  
  public UserRouter(UserService userService) {
    this.userService = userService;
  }
  
  public Route createRoute() {
    return route(
      pathPrefix("users", () -> route(
        get(() -> complete(userService.getUsers())),
        post(() -> entity(
          Jackson.unmarshaller(User.class), user -> complete(
            StatusCodes.CREATED, userService.createUser(user)
          )
        )),
        put(() -> entity(
          Jackson.unmarshaller(User.class), user -> complete(
            userService.updateUser(user)
          )
        )),
        delete(() -> parameter(
          "id", id -> complete(
            userService.deleteUser(Long.parseLong(id))
          )
        ))
      ))
    );
  }
  
}

2.3 Implementing the service layer

Next, we need to implement the user service layer. The service layer will actually handle all requests and use a storage layer (such as a database) to manage user data. In this example, we will use a simple HashMap to store data.

Here is the code for our UserService class:

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.atomic.AtomicLong;

public class UserService {

  private final Map<Long, User> users = new HashMap<>();
  private final AtomicLong counter = new AtomicLong();

  public User createUser(User user) {
    long id = counter.incrementAndGet();
    user.setId(id);
    users.put(id, user);
    return user;
  }

  public User updateUser(User user) {
    users.put(user.getId(), user);
    return user;
  }

  public User deleteUser(long id) {
    return users.remove(id);
  }

  public List<User> getUsers() {
    return new ArrayList<>(users.values());
  }

}

2.4 Starting the service

Now that we have defined our router and service layer, we need to start our application . For this example, we will create a simple main method that will start the Akka HTTP server and connect to the specified port.

Here is the code for our startup class:

import akka.actor.ActorSystem;
import akka.stream.ActorMaterializer;
import akka.http.javadsl.server.HttpApp;

public class Main extends HttpApp {

  private final UserService userService = new UserService();
  private final UserRouter userRouter = new UserRouter(userService);

  public static void main(String[] args) {
    Main main = new Main();
    main.startServer("localhost", 8080, ActorSystem.create(), ActorMaterializer.create());
  }

  @Override
  protected Route routes() {
    return userRouter.createRoute();
  }
  
}

3. Test API

Now we have successfully created an Akka HTTP based react API, and can use different HTTP methods to manage a list of users. Let's test our API using a tool like Postman and make sure it's working properly.

GET method: Get user list

GET http://localhost:8080/users

POST method: Create new user

POST http://localhost:8080/users
Body: 
{
  "name": "John Smith",
  "email": "john.smith@example.com"
}

PUT method: Update existing user

PUT http://localhost:8080/users
Body: 
{
  "id": 1,
  "name": "John Smith",
  "email": "john.smith@example.com"
}

DELETE method: Delete Existing users

DELETE http://localhost:8080/users?id=1

4. Summary

Through this article, we have learned how to build a reactive API using Akka HTTP. We learned about the main benefits of the framework, how to create routers and service layers, and how to start them. We also provide some common HTTP method examples so you can test and use your API. Hope this article helps you!

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