URL Class in JAVA

Presentation

1. URL Class In JAVA

2. Uniform Resource Locator: URL
FHierarchy of Classes
FMethods of the Class
FExamples of Using the Class

3. Hierarchy of Classes
Object
DatagramPacket
InetAddress
ServerSocket
Socket
URL
DatagramSocket
URLConnection
URLEncode
r

4. URL Class
FClass URL is a description of a resource location on the
Internet.
FComplete URL: http://www.cs.joensuu.fi:1547/~john/pub/index.html
-- protocol : http://
-- host : www.cs.joensuu.fi
-- port : 1547
-- path : ~smith/pub/index.html
FJava provides a class—java.net.URL—to manipulate
URLs.

5. Methods of URL Class
FMain methods of the class URL:
·URL(String url): create an object using the string parameter
(exception MalformedURLException ).
·URL(String, String, String) : protocol, host, path of the resource.
·String toString(): return the URL as a strings.
·String getHost(): return the name of the host linked to this URL.
·String getProtocol(): return le protocol of this URL.
·String getPort(): return the number of the associate port.

6. Methods of URL Class
·InputStream openStream(): realize the connection to the
URL previously instantiated.
·An InputStream object is returned and permits to retrieve
information specified into the URL.
·If the connection fails, the exception IOException is raised.

7. Creating a URL Instance
The following statement creates a Java URL object:
String str = "http://www.sun.com”;
try
{
URL location = new URL(str);
}
catch(MalformedURLException ex)
{}

8. Example 18.6: Retrieving Remote Files
Rather than reading the file from the local system, this example
reads the file from a Web server.
private void showFile() {
URL url = null;
try {
url = new URL(urlString);
InputStream is = url.openStream();
infile = new BufferedReader(
new InputStreamReader(is));
}
catch (FileNotFoundException e) { ... }
catch (IOException e) { ... }

9. Viewing HTML Pages
FGiven the URL of the page, a Web browser can view an
HTML page—for example, http://www.sun.com.
FHTTP (Hypertext Transfer Protocol) is the common
standard used for communication between a Web
server and the Internet. You can open a URL and
view a Web page in a Java applet.

10. Example 18.5 Viewing HTML Pages from Java
The following figure shows the process by which an
applet/application reads the files on the Web server:

11. Example 18.5 Viewing HTML Pages from Java
The following figure shows the process by which an
applet/application reads the files on the Web server: