What Does 'java.net.UnknownHostException: Unable to Resolve Host' Mean and How to Fix It?

What are the common causes and solutions for the 'java.net.UnknownHostException: Unable to resolve host' error in Android applications?

// Example of handling networking tasks in an AsyncTask
private class LoadQuestions extends AsyncTask<Integer, Void, JSONArray> {
    @Override
    protected JSONArray doInBackground(Integer... params) {
        return getJSONfromURL(params[0]); // Handles network call
    }
}

The 'java.net.UnknownHostException' occurs when the application cannot resolve the hostname to an IP address, meaning it cannot connect to the designated server. This can happen due to various reasons, including network issues, incorrect URLs, or DNS resolution problems.

try {
    URL url = new URL("https://www.yourapi.com/endpoint");
    HttpURLConnection connection = (HttpURLConnection) url.openConnection();
    connection.setRequestMethod("GET");
    InputStream inputStream = connection.getInputStream();
} catch (UnknownHostException e) {
    Log.e("NetworkError", "Unable to resolve host: " + e.getMessage());
} catch (IOException e) {
    Log.e("NetworkError", "I/O Exception: " + e.getMessage());
}

Causes

• The device is not connected to the internet or has a weak connection.
• The hostname is incorrectly specified or does not exist.
• DNS issues are causing the hostname to fail resolution.
• There are firewall restrictions or network configurations blocking access.

Solutions

• Verify that the device has internet access and is not on Airplane Mode.
• Double-check the URL for correctness (e.g., syntax, spelling).
• Try to ping the hostname from a different device to see if it resolves correctly.
• Consider using a different DNS server (e.g., Google DNS: 8.8.8.8).
• Add error handling in the code to manage the exception gracefully and provide feedback to the user.

Mistake: Forgetting to include INTERNET permissions in the AndroidManifest.xml.

Solution: Make sure to add:<uses-permission android:name="android.permission.INTERNET"/> in your AndroidManifest.xml.

Mistake: Hardcoding network responses or not handling errors properly.

Solution: Implement robust error handling to catch and manage network-related exceptions.