How to Send HTTP Requests in Java using HttpUrlConnection?

Sending HTTP Requests in Java

The ability to send HTTP requests is essential for interacting with remote servers and web APIs in Java. One way to compose and transmit HTTP requests is through the java.net.HttpUrlConnection class.

Creating the HTTP Request

To create an HTTP request, you can use the following steps:

1. Create a URL object: This represents the target URL of the HTTP request.
2. Open a connection: Use the openConnection() method on the URL to establish a connection to the server.
3. Set request method: Specify the HTTP method (e.g., GET, POST, PUT) using the setRequestMethod() method.
4. Set request properties: Configure various properties of the HTTP request, such as content type, language, and cache settings.
5. Enable output: Set setDoOutput(true) to enable writing data to the request body.

Sending the HTTP Request

Once the request is formulated, you can send it to the server using a DataOutputStream:

1. Write request body: Use the writeBytes() method to write the request body (if any) to the output stream.
2. Close the output stream: This completes sending the request.

Getting the HTTP Response

Upon sending the request, you can obtain the response from the server:

1. Get input stream: Use the getInputStream() method to retrieve the input stream of the response.
2. Read response: Use a BufferedReader to read the contents of the response stream line by line.
3. Parse response body: The response body may contain the actual data returned by the server. You can parse it accordingly.

Example Code Snippet

The following Java code demonstrates how to send an HTTP POST request using the HttpUrlConnection class:

import java.net.HttpURLConnection;
import java.net.URL;
import java.io.DataOutputStream;
import java.io.InputStream;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;

public class HttpPostExample {

  public static void main(String[] args) {
    String targetURL = "https://example.com/api/endpoint";
    String urlParameters = "key1=value1&key2=value2";

    HttpURLConnection connection = null;

    try {
      URL url = new URL(targetURL);
      connection = (HttpURLConnection) url.openConnection();
      connection.setRequestMethod("POST");
      connection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
      connection.setRequestProperty("Content-Length", Integer.toString(urlParameters.getBytes().length));
      connection.setDoOutput(true);

      DataOutputStream wr = new DataOutputStream(connection.getOutputStream());
      wr.writeBytes(urlParameters);
      wr.close();

      InputStream is = connection.getInputStream();
      BufferedReader rd = new BufferedReader(new InputStreamReader(is));
      StringBuilder response = new StringBuilder();
      String line;
      while ((line = rd.readLine()) != null) {
        response.append(line);
        response.append('\r');
      }
      rd.close();
      System.out.println(response.toString());
    } catch (IOException e) {
      e.printStackTrace();
    } finally {
      if (connection != null) {
        connection.disconnect();
      }
    }
  }
}

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