How to Post Data to API Using Java

This article guides you on how to post data to an API using the POST method in Java, utilizing the HttpURLConnection and org.json library to handle JSON data.

In this article, we will learn how to use HttpURLConnection to make an HTTP POST request to send JSON data to an API. The code snippet provides a detailed step-by-step explanation.

import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import org.json.JSONObject;

public class PostJsonExample {
    public static void main(String[] args) {
        try {
            // API URL
            URL url = new URL("https://api.example.com/data");

            // Create HTTP connection
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setRequestMethod("POST");
            conn.setRequestProperty("Content-Type", "application/json; utf-8");
            conn.setRequestProperty("Accept", "application/json");
            conn.setDoOutput(true);

            // JSON data to be sent
            JSONObject jsonInput = new JSONObject();
            jsonInput.put("name", "John Doe");
            jsonInput.put("email", "[email protected]");

            // Send JSON data
            try (OutputStream os = conn.getOutputStream()) {
                byte[] input = jsonInput.toString().getBytes("utf-8");
                os.write(input, 0, input.length);
            }

            // Check server response
            int responseCode = conn.getResponseCode();
            if (responseCode == HttpURLConnection.HTTP_OK) {
                System.out.println("Data was sent successfully!");
            } else {
                System.out.println("Error sending data: " + responseCode);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Detailed explanation

1. import java.io.OutputStream; and import java.net.HttpURLConnection;: Import necessary libraries to create an HTTP connection.
2. import org.json.JSONObject;: Import the org.json library to create JSON objects.
3. URL url = new URL("https://api.example.com/data");: Set the URL of the API you want to post data to.
4. HttpURLConnection conn = (HttpURLConnection) url.openConnection();: Open an HTTP connection to the API.
5. conn.setRequestMethod("POST");: Set the HTTP request method to POST.
6. conn.setRequestProperty("Content-Type", "application/json; utf-8");: Set the content type to JSON.
7. conn.setDoOutput(true);: Allow sending data through the connection.
8. JSONObject jsonInput = new JSONObject();: Create a JSON object with the data to be sent.
9. os.write(input, 0, input.length);: Send the JSON data to the API.
10. int responseCode = conn.getResponseCode();: Retrieve the API response code to check request status.

System Requirements

• Java Version: JDK 8 or later
• Library: org.json (can be downloaded via Maven or added manually)

How to install the libraries needed to run the Java code above

You can add the org.json library to your Maven project by adding the following snippet to your pom.xml file:

<dependency>
    <groupId>org.json</groupId>
    <artifactId>json</artifactId>
    <version>20210307</version>
</dependency>

Tips

• Double-check the API URL to make sure it is correct.
• Refer to the API documentation for more details about the expected data structure.
• Always check the API's response code to handle error cases appropriately.