Android HttpURLConnection POST Multipart Form-Data - Java

In Android development, sending POST requests with multipart form-data is a common requirement. This tutorial will guide you through the process of using HttpURLConnection to send a multipart form-data POST request in Java.

Prerequisites

• Basic knowledge of Java programming language.
• Android development environment setup.

Steps to send a POST request with multipart form-data using HttpURLConnection

1. Create a new AsyncTask class to handle the HTTP request.
2. Override the doInBackground method to perform the network operation in the background thread.
3. Inside the doInBackground method, establish a connection using HttpURLConnection.
4. Set the request method to "POST" with connection.setRequestMethod("POST").
5. Enable output/input streams and disable caching with connection.setDoOutput(true), connection.setDoInput(true), and connection.setUseCaches(false).
6. Set the request property "Content-Type" to "multipart/form-data" with connection.setRequestProperty("Content-Type", "multipart/form-data").
7. Create a DataOutputStream using connection.getOutputStream() to write the request body.
8. Write each form field and file to the DataOutputStream.
9. Close the DataOutputStream after writing the request body.
10. Get the response code from the connection with connection.getResponseCode().
11. Read the response from the input stream using connection.getInputStream().
12. Parse and handle the response as needed.
13. Release the connection resources by closing the input/output streams and the connection.

import android.os.AsyncTask;

import java.io.DataOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.UnsupportedEncodingException;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLEncoder;

public class MultipartFormPostTask extends AsyncTask<Void, Void, String> {

    @Override
    protected String doInBackground(Void... voids) {
        try {
            // Step 1: Create a URL object with the server endpoint
            URL url = new URL("http://your-server-endpoint");

            // Step 2: Open the connection
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();

            // Step 3: Set the request properties
            connection.setRequestMethod("POST");
            connection.setDoOutput(true);
            connection.setDoInput(true);
            connection.setUseCaches(false);
            connection.setRequestProperty("Content-Type", "multipart/form-data");

            // Step 4: Create the request body
            String formData = getMultipartFormData(); // Method to build the form data
            byte[] formDataBytes = formData.getBytes("UTF-8");

            // Step 5: Write the request body
            DataOutputStream outputStream = new DataOutputStream(connection.getOutputStream());
            outputStream.write(formDataBytes);
            outputStream.flush();
            outputStream.close();

            // Step 6: Get the response code
            int responseCode = connection.getResponseCode();

            // Step 7: Read the response
            InputStream inputStream = (responseCode == HttpURLConnection.HTTP_OK)
                    ? connection.getInputStream()
                    : connection.getErrorStream();
            // Read and process the response as needed

            // Step 8: Release the connection
            inputStream.close();
            connection.disconnect();

            return "Request sent successfully.";
        } catch (Exception e) {
            e.printStackTrace();
            return "Error: " + e.getMessage();
        }
    }

    private String getMultipartFormData() throws UnsupportedEncodingException {
        // Build the multipart form data
        StringBuilder builder = new StringBuilder();

        // Add form fields
        builder.append("--boundary\r\n")
                .append("Content-Disposition: form-data; name=\"field1\"\r\n")
                .append("\r\n")
                .append(URLEncoder.encode("value1", "UTF-8"))
                .append("\r\n");

        builder.append("--boundary\r\n")
                .append("Content-Disposition: form-data; name=\"field2\"\r\n")
                .append("\r\n")
                .append(URLEncoder.encode("value2", "UTF-8"))
                .append("\r\n");

        // Add file
        builder.append("--boundary\r\n")
                .append("Content-Disposition: form-data; name=\"file\"; filename=\"image.jpg\"\r\n")
                .append("Content-Type: image/jpeg\r\n")
                .append("\r\n")
                .append("File content")
                .append("\r\n");

        builder.append("--boundary--");

        return builder.toString();
    }
}

Usage

To use the MultipartFormPostTask, create an instance of the class and execute it.

MultipartFormPostTask postTask = new MultipartFormPostTask();
postTask.execute();

This will send a POST request with multipart form-data to the specified server endpoint.

Please make sure to replace "http://your-server-endpoint" in the code with the actual server endpoint URL.

Conclusion

In this tutorial, you have learned how to send a POST request with multipart form-data using HttpURLConnection in Android using Java. By following the steps and code provided, you can easily incorporate this functionality into your Android applications.