How do I make an extension that retrieves the source code of a web page?

[Kumaraswamy]

You need to import these:

How to do a HTTP GET request on a extension?

Import these classes java.io.BufferedReader java.io.IOException android.app.Activity java.io.InputStreamReader java.net.HttpURLConnection java.net.URL com.google.appinventor.components.runtime.util.AsynchUtil

And activity is the context.

Cannot find symbol error in extension

The problem is obvious. From where are you accessing the container variable ? You need to declare container variable in the extension class then assign the value from the constructor. public class ExtensionTemplate extends AndroidNonvisibleComponent { private ComponentContainer container; public ExtensionTemplate(ComponentContainer container) { super(container.$form()); this.container = container; }