How to Send HTTP Requests in Java

HTTP (Hypertext Transfer Protocol) is a protocol used to transfer data over the web. It's the backbone of online communication. When you click a link, your browser sends an HTTP request to a web server.

In Java, HTTP requests are a fundamental part of interacting with web APIs and services. They enable you to send data to a server and receive data in return. You can use tools like the HttpURLConnection class in Java to handle these requests.

How It Works

To send HTTP requests in Java, you need a solid understanding of Java's networking capabilities. Java provides several libraries and classes for handling HTTP requests. You'll likely use HttpURLConnection, Apache HttpClient, or the newest addition, HttpClient.

HttpURLConnection is a class in the Java standard library. It allows you to open a connection to an HTTP server, send requests, and handle responses. This class is suitable for simple applications.

For more advanced features, consider using Apache HttpClient. It's a widely-used library that offers more flexibility and features than HttpURLConnection. With Apache HttpClient, you can manage cookies, compress requests, and more.

HttpClient is a modern alternative introduced in Java 11. It provides a fluent API and supports HTTP/2, making it a robust choice for current applications.

Learn more about Java servlets and networking.

Code Examples

Let's walk through some code examples to better understand how to send HTTP requests in Java.

Example 1: Using HttpURLConnection

URL url = new URL("http://example.com");
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setRequestMethod("GET");
int responseCode = connection.getResponseCode();

• URL: Create a URL object with the target URL.
• HttpURLConnection: Open a connection to the target URL.
• setRequestMethod: Set the request method, e.g., GET.
• getResponseCode: Get the response code to check the request's success.

Example 2: Using Apache HttpClient

CloseableHttpClient client = HttpClients.createDefault();
HttpGet request = new HttpGet("http://example.com");
CloseableHttpResponse response = client.execute(request);

• CloseableHttpClient: Create a client for sending requests.
• HttpGet: Create a GET request object.
• execute: Execute the request and fetch the response.

Example 3: Using Java 11 HttpClient

HttpClient client = HttpClient.newHttpClient();
HttpRequest request = HttpRequest.newBuilder()
        .uri(URI.create("http://example.com"))
        .build();
HttpResponse<String> response = client.send(request, HttpResponse.BodyHandlers.ofString());

• HttpClient: Create a new HTTP client.
• HttpRequest: Build a request with a URI.
• send: Send the request and get the response body as a string.

Read about understanding HTTP basics.

Example 4: Handling POST Requests

URL url = new URL("http://example.com");
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setRequestMethod("POST");
connection.setDoOutput(true);
OutputStream os = connection.getOutputStream();
os.write(input.getBytes());
os.flush();

• setRequestMethod: Set the request method as POST.
• setDoOutput: Enable output for sending data.
• OutputStream: Write data to the request body.

Example 5: Handling JSON Responses

HttpClient client = HttpClient.newHttpClient();
HttpRequest request = HttpRequest.newBuilder()
        .uri(URI.create("http://example.com/api/json"))
        .build();
HttpResponse<String> response = client.send(request, HttpResponse.BodyHandlers.ofString());
String responseBody = response.body();
// Convert JSON response to Java object (e.g., using Jackson)

• HttpRequest: Set the URI for the JSON endpoint.
• HttpResponse: Handle the response as a string.
• JSON Handling: Convert JSON response to a Java object.

Conclusion

You now have the tools to send HTTP requests in Java using different methods. Whether you're starting with HttpURLConnection or moving to more sophisticated libraries like HttpClient or Apache HttpClient, Java has you covered. With these examples, you're ready to make your own HTTP requests and interact with web services seamlessly.

To deepen your understanding of related concepts, check out Understanding APIs: A Beginner's Guide and What is a class in Java?. Happy coding!