• An Observation:
  • Stream-oriented protocols are often used to request content (e.g., HTTP)
  • The ways in which the content are requested are often very similar
• Implications:
  • We can think in the abstract about a content handler

javaexamples/contenthandlers/ImageContentHandler.java

import java.io.*;
import java.net.*;
import javax.swing.ImageIcon;


/**
 * A factory that constructs ImageContentHandler objects
 *
 * @author  Prof. David Bernstein, James Madison University
 * @version 1.0
 */
public class ImageContentHandler extends ContentHandler
{

    /**
     * Given a URL connect stream positioned at the beginning of the
     * representation of an object, this method reads that stream and
     * creates an object from it.
     *
     * @param connection           The URLConnection to read from
     */
    public Object getContent(URLConnection connection) throws IOException
    {
       byte[]             data; 
       ImageIcon          icon; 
       InputStream        is; 
       int                length;
       

       icon = null;
       
       is = connection.getInputStream();
       length = connection.getContentLength();
       data = new byte[length];
       is.read(data);
       icon = new ImageIcon(data);

       return icon;
    }
    

}
        

javaexamples/contenthandlers/ImageContentHandlerFactory.java

import java.net.*;


/**
 * A factory that constructs ImageContentHandler objects
 *
 * @author  Prof. David Bernstein, James Madison University
 * @version 1.0
 */
public class ImageContentHandlerFactory implements ContentHandlerFactory
{

    /**
     * Creates a new ContentHandler to read an object from a
     * URLStreamHandler.
     *
     * @param mimetype   The mimetype to create the content handler for
     */
    public ContentHandler createContentHandler(String mimetype)
    {
       ContentHandler      handler;
       
       handler = null;
       if (mimetype.startsWith("image"))
       {
          handler = new ImageContentHandler();
       }

       return handler;
    }
    
}
        

javaexamples/contenthandlers/ImageViewer.java (Fragment: 0)

       BufferedReader               in; 
       ImageContentHandlerFactory   factory;
       ImageIcon                    icon;
       Object                       content;       
       String                       resource;
       URL                          url;
       // Tell the URLConnection class what ContentHandlerFactory to use
       factory = new ImageContentHandlerFactory();
       URLConnection.setContentHandlerFactory(factory);
       
       
       in = new BufferedReader(new InputStreamReader(System.in));

       System.out.println("URL for the image: ");
       while ((resource = in.readLine()) != null)
       {
          // Connect to a URL
          url = new URL(resource);          

          // Get the content
          content = url.getContent();         

          if (content != null)
          {
             // Cast the content appropriately
             icon = (ImageIcon)content;       

             // Display the image
             label.setIcon(icon);
          }
          System.out.println("URL for the image: ");
       }