fido

src/main/java/Main.java

@@ -1,7 +1,94 @@
+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 Main {
+
     public static void main(String[] args) {
-        //ask for a url
-        // fetch the url
-        // print the url
+        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://"))) {
+            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: If
+           getContentType() method were called before getting the input
+           stream, it is possible for contentType to be null only because
+           no connection can be made.  The getInputStream() method will
+           throw an error if no connection can be made. */
+
+        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