How to Send HTTP Requests in Java Using `HttpUrlConnection`?

Composing and Sending HTTP Requests in Java

To harness the power of HTTP requests in Java, you can utilize the java.net.HttpUrlConnection class. It provides a comprehensive API for creating and dispatching HTTP requests to any web server.

Creating the Connection

To establish the connection, you'll create a URL object and use it to establish an HttpUrlConnection connection. Specify the request method (e.g., POST, GET) and set necessary headers, such as Content-Type and Content-Length.

Preparing the HTTP Request

For a POST request, format the request parameters as a query string (e.g., "name=John&age=30"). Use DataOutputStream to write the parameters to the output stream.

Sending the Request

Once the request is ready, send it by using DataOutputStream.writeBytes() to transmit the request body. The web server will respond with the requested resource.

Receiving the Response

InputStream is used to retrieve the response from the server. Use BufferedReader to read the response line by line and construct the final response body.

Sample Code

Here's a code snippet that showcases how to execute an HTTP POST request using the aforementioned techniques:

import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLEncoder;
import java.io.OutputStreamWriter;
import java.io.IOException;

public static void sendHttpRequest() throws IOException {
    // Create the connection
    URL url = new URL("http://example.com/");
    HttpURLConnection connection = (HttpURLConnection) url.openConnection();
    connection.setRequestMethod("POST");
    connection.setDoOutput(true);
    connection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");

    // Build the request parameters
    String postData = URLEncoder.encode("name", "UTF-8") + "=" + URLEncoder.encode("John", "UTF-8");

    // Send the request
    OutputStreamWriter writer = new OutputStreamWriter(connection.getOutputStream());
    writer.write(postData);
    writer.flush();

    // Get the response
    int responseCode = connection.getResponseCode();
    if (responseCode == HttpURLConnection.HTTP_OK) {
        BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream()));
        String line;
        while ((line = reader.readLine()) != null) {
            System.out.println(line);
        }
        reader.close();
    }

    connection.disconnect();
}

By following these steps and utilizing the HttpUrlConnection class, you can effortlessly compose and transmit HTTP requests in your Java applications.

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