How to Send an HTTP POST Request in Java

Question

How can I send an HTTP POST request to a server in Java?

URL url = new URL("http://www.example.com/page.php");
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setRequestMethod("POST");
connection.setDoOutput(true);
OutputStream os = connection.getOutputStream();
byte[] input = "id=10".getBytes("utf-8");
os.write(input, 0, input.length);
os.close();

Answer

Sending an HTTP POST request in Java can be accomplished using the HttpURLConnection class. This allows you to connect to a web server and send data, such as parameters, to be processed by a server-side script like PHP.

import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;

public class HttpPostExample {
    public static void main(String[] args) throws Exception {
        // Define the URL
        URL url = new URL("http://www.example.com/page.php");
        HttpURLConnection connection = (HttpURLConnection) url.openConnection();

        // Set up connection properties
        connection.setRequestMethod("POST");
        connection.setDoOutput(true);

        // Prepare data to send
        String urlParameters = "id=10";

        // Send POST request
        try (OutputStream os = connection.getOutputStream()) {
            byte[] input = urlParameters.getBytes("utf-8");
            os.write(input, 0, input.length);
        }

        // Get response code
        int responseCode = connection.getResponseCode();
        System.out.println("Response Code: " + responseCode);
    }
}

Causes

Not setting the request method properly to POST.
Forgetting to enable output on the connection with setDoOutput(true).
Failing to handle encoding and converting the parameters appropriately.

Solutions

Use HttpURLConnection for handling HTTP requests.
Set the request method to POST using setRequestMethod("POST").
Prepare the output stream correctly and write the parameters using the OutputStream.

Common Mistakes

Mistake: Not handling exceptions properly during URL connection.

Solution: Surround your connection code with try-catch blocks to handle IOException.

Mistake: Sending data without a proper content type.

Solution: Set the content type using connection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded").

Helpers

Java HTTP POST request
send POST request Java
Java HttpURLConnection
Java web programming POST
HTTP requests in Java