User`s manual

Example – Reading a URL
5-63
Example – Reading a URL
This program, URLdemo, opens a connection to a web site specified by a URL
(Uniform Resource Locator), for the purpose of reading text from a file at that
site. It constructs an object of the Java API class,
java.net.URL, which enables
convenient handling of URLs. Then, it calls a method on the URL object, to
open a connection.
To read and display the lines of text at the site,
URLdemo uses classes from the
Java I/O package
java.io. It creates an InputStreamReader object, and then
uses that object to construct a
BufferedReader object. Finally, it calls a method
on the
BufferedReader object to read the specified number of lines from the
site.
Description of URLdemo
The major tasks performed by URLdemo are:
1. Construct a URL Object
The example first calls a constructor on java.net.URL and assigns the
resulting object to variable
url. The URL constructor takes a single argument,
the name of the URL to be accessed, as a string. The constructor checks
whether the input URL has a valid form.
url = java.net.URL(...
'http://www.ncsa.uiuc.edu/demoweb/url-primer.html')
2. Open a Connection to the URL
The second statement of the example calls the method, openStream, on the URL
object
url, to establish a connection with the web site named by the object. The
method returns an
InputStream object to variable, is, for reading bytes from
the site.
is = openStream(url)
3. Set Up a Buffered Stream Reader
The next two lines create a buffered stream reader for characters. The
java.io.InputStreamReader constructor is called with the input stream is, to
return to variable
isr an object that can read characters. Then, the
java.io.BufferedReader constructor is called with isr, to return a