Using a URLConnection using Java

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Using a URLConnection using Java

The URLConnection class establishes a connection to a URL. The openStream( ) method of URL we used in Example 5-1 is merely a convenience method that creates a URLConnection object and calls its getInputStream( ) method. By using a URLConnection object directly instead of relying on openStream( ), you have much more control over the process of downloading the contents of a URL.

Example 5-2 is a simple program that shows how to use a URLConnection to obtain the content type, size, last-modified date, and other information about the resource referred to by a URL. If the URL uses the HTTP protocol, it also demonstrates how to use theHttpURLConnection subclass to obtain additional information about the connection.

Note the use of the java.util.Date class to convert a timestamp (a long that contains the number of milliseconds since midnight, January 1, 1970 GMT) to a human-readable date and time string.

1. Example 5-2. GetURLInfo.java
   
2. package je3.net;
   
3. import java.net.*;
   
4. import java.io.*;
   
5. import java.util.Date;
   
6. 
   
7. /**
   
8. * A class that displays information about a URL.
   
9. **/
   
10. public class GetURLInfo {
    
11.     /** Use the URLConnection class to get info about the URL */
    
12.     public static void printinfo(URL url) throws IOException {
    
13.         URLConnection c = url.openConnection( );  // Get URLConnection from URL
    
14.         c.connect( );                             // Open a connection to URL
    
15.         
    
16.         // Display some information about the URL contents
    
17.         System.out.println("  Content Type: " + c.getContentType( ));
    
18.         System.out.println("  Content Encoding: " + c.getContentEncoding( ));
    
19.         System.out.println("  Content Length: " + c.getContentLength( ));
    
20.         System.out.println("  Date: " + new Date(c.getDate( )));
    
21.         System.out.println("  Last Modified: " +new Date(c.getLastModified( )));
    
22.         System.out.println("  Expiration: " + new Date(c.getExpiration( )));
    
23.         
    
24.         // If it is an HTTP connection, display some additional information.
    
25.         if (c instanceof HttpURLConnection) {
    
26.             HttpURLConnection h = (HttpURLConnection) c;
    
27.             System.out.println("  Request Method: " + h.getRequestMethod( ));
    
28.             System.out.println("  Response Message: " +h.getResponseMessage( ));
    
29.             System.out.println("  Response Code: " + h.getResponseCode( ));
    
30.         }
    
31.     }
    
32.    
    
33.     /** Create a URL, call printinfo( ) to display information about it. */
    
34.     public static void main(String[  ] args) {
    
35.         try { printinfo(new URL(args[0])); }
    
36.         catch (Exception e) {
    
37.             System.err.println(e);
    
38.             System.err.println("Usage: java GetURLInfo <url>");
    
39.         }
    
40.     }
    
41. }

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