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Uniform Resource Locator: URL

Uniform Resource Locator: URL. Hierarchy of Classes Methods of the Class Examples of Using the Class . Hierarchy of Classes. URL Class. Class URL is a description of a resource location on the Internet. Complete URL: http://www.cs.joensuu.fi:1547/~john/pub/index.html

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Uniform Resource Locator: URL

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  1. Uniform Resource Locator: URL • Hierarchy of Classes • Methods of the Class • Examples of Using the Class

  2. Hierarchy of Classes

  3. URL Class • Class URL is a description of a resource location on the Internet. • Complete 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 • Java provides a class—java.net.URL—to manipulateURLs.

  4. Methods of URL Class • Main 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.

  5. Methods of URL Class • InputStream openStream(): realize the connection to the URL previously instantiated. • An InputStream object is returned and permits to retrieve informationspecified into the URL. • If the connection fails, the exception IOExceptionis raised.

  6. 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) { }

  7. 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) { ... }

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

  9. 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:

  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:

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