import java.net.URL;
import java.net.URLConnection;
import java.util.Scanner;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;


/**
 * This short program demonstrates the URL and URLConnection classes by
 * attempting to open a connection to a URL and read text from it.  The url 
 * can be specified on the command line.  If no command line argument is
 * provided, the user is prompted for input.  It can be a complete url, including 
 * the "protocol" at the beginning ("http://", "ftp://", or "file://").   If 
 * it does not start with one of these protocols, "http://" is added to the
 * beginning of the input line.  If an error occurs while trying to fetch the data, 
 * a message is output. Otherwise, the text from the URL is copied to the screen.
 */

public class FetchURL {

    public static void main(String[] args) {
        String url;    // The url from the command line or from user input.
        String urlLC;  // The url transformed to lower case.
        if (args.length == 0) {
            Scanner stdin = new Scanner(System.in);
            System.out.print("Enter a url: ");
            url = stdin.nextLine();
        }
        else {
            url = args[0];
        }
        urlLC = url.toLowerCase();
        if ( ! (urlLC.startsWith("http://") || urlLC.startsWith("ftp://") || 
                urlLC.startsWith("file://") || urlLC.startsWith("https://") )) {
            url = "http://" + url;
            System.out.println("Using: " + url);
        }
        System.out.println();
        try {
            readTextFromURL(url);
        }
        catch (IOException e) {
            System.out.println("\n*** Sorry, an error has occurred ***\n");
            System.out.println(e);
            System.out.println();
        }  
    }

    /**
     * This subroutine attempts to copy text from the specified URL onto the screen.  
     * Any error must be handled by the caller of this subroutine.
     * @param urlString contains the URL in text form
     */
    static void readTextFromURL( String urlString ) throws IOException {

        /* Open a connection to the URL, and get an input stream
           for reading data from the URL. */

        URL url = new URL(urlString);
        URLConnection connection = url.openConnection();
        InputStream urlData = connection.getInputStream();

        /* Check that the content is some type of text.  Note: 
           connection.getContentType() should be called after
           connction.getInputStream(). */

        String contentType = connection.getContentType();
        System.out.println("Stream opened with content type: " + contentType);
        System.out.println();
        if (contentType == null || contentType.startsWith("text") == false)
            throw new IOException("URL does not seem to refer to a text file.");
        System.out.println("Fetching context from " + urlString + " ...");
        System.out.println();

        /* Copy lines of text from the input stream to the screen, until
           end-of-file is encountered  (or an error occurs). */

        BufferedReader in;  // For reading from the connection's input stream.
        in = new BufferedReader( new InputStreamReader(urlData) );

        while (true) {
            String line = in.readLine();
            if (line == null)
                break;
            System.out.println(line);
        }
        in.close();

    } // end readTextFromURL()

} // end class FetchURL