Java Magazine - Premiere Issue 2011

this class is shown in Listing 1.

The AdvancedImageContentHandler constructor uses the registry to set itself as the listener for any responses that might be required, and, therefore, it implements the invocationResponseNotify(Registry registry) method, which is empty in this example. Then, it locates the ContentHandlerServer using the static registry method getServer(String classname). The handler is then notified that all new requests for content handling are to be done by this class using the invocationRequestNotify(ContentHandler-Server handler) method. Finally, it sets up the UI to display the image and the text below it.

When a new request is initiated, the invocationRequestNotify(ContentHandler-Server handler) method is called, as shown in Listing 2.

We first check whether there is an existing request, and we let the content handler server finish that up. Next, if there is not an existing request, we get the details of the new request, and we pass the new request on to the display-Image() method with the details.

Although fairly straightforward (in the example shown in Listing 3), the display-Image() method does all the magic of displaying the image with the added text.

We opened up a connection to the requested file (using the FileConnection API), and if the image is found, we display it on the form with the added text. We do some error checking to make sure we can load the image, and if not, we display a message accordingly.

On the caller’s side, it takes only a
three-step process to call this con-
tent handler, as shown in Listing 4
in the excerpt from the calling class
(CHAPIExample).

public AdvancedImageContentHandler() {

// notify the registry that this class is a listener registry = Registry.getRegistry( this.getClass().getName()); registry.setListener(this);

// now, get the handler which was registered by making entries in the JAD // file try { handler = Registry.getServer(CH_CLASSNAME); } catch (ContentHandlerException che) { System.err.println("Registration not done! Check JAD file"); }

JAVA IN ACTION

// this class is the handler for all new requests handler.setListener(this);

// setup the ui display = Display.getDisplay(this); form = new Form("Advanced Image"); backCommand = new Command("Back", Command.BACK, 1); form.setCommandListener(this); imageItem = new ImageItem(null, null, Item.LAYOUT_CENTER, "--");