Making RESTful Calls in Java

Making RESTful calls is a fundamental aspect of many modern web applications. In this tutorial, we will explore how to make RESTful calls in Java using various libraries and frameworks.

Introduction to RESTful Calls

REST (Representational State of Resource) is an architectural style for designing networked applications. It relies on stateless, client-server architecture where the client makes requests to the server to access or modify resources. RESTful calls can be made using HTTP methods such as GET, POST, PUT, and DELETE.

Using Java’s Built-in HttpURLConnection

Java provides a built-in class called HttpURLConnection that can be used to make RESTful calls. Here is an example of how to use it:

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.URL;
import java.net.URLConnection;

public class Main {
    public static void main(String[] args) throws IOException {
        URL url = new URL("http://example.com/resource");
        URLConnection connection = url.openConnection();
        BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream()));
        String line;
        while ((line = reader.readLine()) != null) {
            System.out.println(line);
        }
        reader.close();
    }
}

Using Apache HttpClient

Apache HttpClient is a more robust and flexible library for making HTTP requests in Java. Here is an example of how to use it:

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;

public class Main {
    public static void main(String[] args) throws IOException {
        CloseableHttpClient client = HttpClients.createDefault();
        HttpGet request = new HttpGet("http://example.com/resource");
        HttpResponse response = client.execute(request);
        HttpEntity entity = response.getEntity();
        System.out.println(EntityUtils.toString(entity));
        client.close();
    }
}

Using OkHttp

OkHttp is a modern and efficient library for making HTTP requests in Java. Here is an example of how to use it:

import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;

public class Main {
    public static void main(String[] args) throws IOException {
        OkHttpClient client = new OkHttpClient();
        Request request = new Request.Builder()
                .url("http://example.com/resource")
                .build();
        Response response = client.newCall(request).execute();
        System.out.println(response.body().string());
        client.dispatcher().executorService().shutdown();
    }
}

Using Spring’s RestTemplate

Spring provides a convenient class called RestTemplate that can be used to make RESTful calls. Here is an example of how to use it:

import org.springframework.http.ResponseEntity;
import org.springframework.web.client.RestTemplate;

public class Main {
    public static void main(String[] args) {
        RestTemplate restTemplate = new RestTemplate();
        String resourceUrl = "http://example.com/resource";
        ResponseEntity<String> response = restTemplate.getForEntity(resourceUrl, String.class);
        System.out.println(response.getBody());
    }
}

Conclusion

In this tutorial, we have explored how to make RESTful calls in Java using various libraries and frameworks. We have seen examples of using Java’s built-in HttpURLConnection, Apache HttpClient, OkHttp, and Spring’s RestTemplate. Each library has its own strengths and weaknesses, and the choice of which one to use depends on the specific requirements of your project.