Micronaut, a popular Java-based microservices framework, offers versatile tools for building web applications and services. One of its key features is the ability to create efficient HTTP clients, both at high and low levels. In this blog, we’ll explore how to write both high and low-level HTTP clients in Micronaut, providing you with the flexibility to choose the right approach for your specific use case.

High-Level HTTP Client

Micronaut’s high-level HTTP client simplifies the process of making HTTP requests to remote services or APIs. It’s a declarative and intuitive way to interact with external resources. Here’s how to get started:

1. Dependency Configuration

First, you need to include the Micronaut HTTP client dependency in your project. You can do this by adding the following to your build.gradle (for Gradle) or build.gradle.kts (for Kotlin Gradle) file:

dependencies {
    implementation "io.micronaut.http:micronaut-http-client"
}

2. Define the Client Interface

Create an interface that defines your HTTP client. This interface will contain methods representing the HTTP endpoints you want to call. For example:

import io.micronaut.http.annotation.Get;
import io.micronaut.http.client.annotation.Client;
import io.reactivex.Single;

@Client("https://api.example.com")
public interface MyHttpClient {

    @Get("/resource/{id}")
    Single<MyResource> getResourceById(Long id);

    // Other HTTP endpoints can be defined here
}

3. Inject and Use the Client

Now, you can inject and use your high-level HTTP client in your service or controller:

import javax.inject.Inject;

@Service
public class MyService {

    @Inject
    private MyHttpClient httpClient;

    public MyResource fetchResourceById(Long id) {
        return httpClient.getResourceById(id).blockingGet();
    }
}

This high-level client abstracts away many details, making it easy to use for most scenarios. However, if you need more fine-grained control or want to work with low-level details, you can use Micronaut’s low-level HTTP client.

Read Also: Harnessing the Power of HTTP Client Interceptors in Micronaut

Low-Level HTTP Client

The low-level HTTP client in Micronaut provides more control over the HTTP request and response. It’s suitable for situations where you need to customize headers, handle redirects, or work with streaming data. Here’s how to use it:

1.Create and Customize the Request

The low-level HTTP client is included by default when you add the micronaut-http dependency, so no additional dependencies are required. To use the low-level HTTP client, inject the HttpClient bean into your service or controller. With the HttpClient, you can create and customize HTTP requests, including setting headers, query parameters, and request bodies. For example:

import io.micronaut.http.HttpRequest;
import io.micronaut.http.HttpHeaders;
import io.micronaut.http.HttpMethod;
import io.micronaut.http.HttpResponse;

public void makeHttpRequest() {
    HttpRequest<String> request = HttpRequest
            .create(HttpMethod.GET, "https://api.example.com/resource/123")
            .header(HttpHeaders.ACCEPT, "application/json");

    HttpResponse<String> response = httpClient.toBlocking().exchange(request, String.class);

    // Process the response
    if (response.getStatus().getCode() == 200) {
        String body = response.body();
        // Handle the response body
    } else {
        // Handle error response
    }
}

The low-level HTTP client offers fine-grained control over requests and responses, making it suitable for advanced scenarios.

Choosing the Right Approach

In summary, Micronaut provides both high-level and low-level HTTP clients, each catering to different use cases. Use the high-level client for simplicity and rapid development when you don’t need fine-grained control. For scenarios that require advanced customization, the low-level client offers flexibility and control over the HTTP communication process.

With Micronaut’s HTTP client options, you can seamlessly integrate with external services and APIs, making it a powerful tool for building microservices and web applications. Whether you opt for the high or low-level client, Micronaut empowers you to create efficient and performant HTTP interactions in your Java applications.