You can extract the HTML string from a web site with the following code:
B4X:
Sub AppStart (Form1 As Form, Args() As String)
MainForm = Form1
'MainForm.RootPane.LoadLayout("Layout1") 'Load the layout file.
' --- Needs the jOkHttpUtils2
Dim j As HttpJob
j.Initialize("", Me)
j.Download("https://www.google.com")
Wait For (j) JobDone(j As HttpJob)
If j.Success Then
Log(j.GetString)
End If
j.Release
End Sub
Depending on what you want to do a possibility is to use jSoup HTML Parser to parse the HTML string. Other inspiration can be found here