Communicating Across the Internet - Java 6 - page 449

Before you can load anything, you must create a new instance of the class URL that repre-
sents the address of the resource you want to load. URL is an acronym for uniform
resource locator , and it refers to the unique address of any document or other resource
accessible on the Internet.

URL is part of the java.net package, so you must import the package or refer to the class
by its full name in your programs.

To create a new URL object, use one of four constructors:

URL( String ) —Creates a URL object from a full web address such as
http://www.java21days.com or ftp://ftp.netscape.com.

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URL( URL , String ) —Creates a URL object with a base address provided by the
specified URL and a relative path provided by the String .

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URL( String , String , int , String ) —Creates a new URL object from a protocol
(such as “http” or “ftp”), hostname (such as “www.cnn.com” or “web.archive.org”),
port number (80 for HTTP), and a filename or pathname.

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URL( String , String , String ) —The same as the previous constructor minus the
port number.

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When you use the URL( String ) constructor, you must deal with MalformedURLException
objects, which are thrown if the String does not appear to be a valid URL. These objects
can be handled in a try - catch block:

try {
URL load = new URL(“http://www.samspublishing.com”);
} catch (MalformedURLException e) {
System.out.println(“Bad URL”);

}

The WebReader application in Listing 17.1 uses the four-step technique to open a connec-
tion to a website and read a text document from it. When the document is fully loaded, it
is displayed in a text area.

LISTING 17.1 The Full Text of WebReader.java

1: import javax.swing.*;
2: import java.awt.*;
3: import java.awt.event.*;
4: import java.net.*;
5: import java.io.*;
6:
7: public class WebReader extends JFrame {
8: JTextArea box = new JTextArea(“Getting data ...”);
9: