Push-based synchronized slideshow web application – implemented using WebSockets and Kaazing WebSocket Gateway9
In the last few articles, I have discussed downloading, installing and running demos for a number of different tools, frameworks and libraries that support push-style (web) applications in one way or another. I have looked into ‘classic’ comet with Grizzly, Atmosphere and CometD as well as ADF Active Data Service and WebLogic Pub/Sub (Bayeux) Channels. I have also looked to WebSockets with jWebSocket, again Atmosphere and CometD and also with Kaazing. I intend to now take a closer look at some of these frameworks, by taking a simple push-style application and implementing it using each of these frameworks. The functionality I will be implementing is simple:
- the selection of the image is communicated to the server (background WebSocket based or alternatively regular AJAX)Comet (Bayeux)/Long Poll style)
- the server informs all connected clients about the selected image through a pushed message (background WebSocket based or alternatively Comet (Bayeux)/Long Poll style); these clients all synchronize that slide selection
- a Java (server side) component can also connect to the More >
The situation: in an ADF Faces 11g page, we have a popup with two buttons: one to start a download and one to cancel the popup. When the users presses the download button, a fileDownloadActionListener is activated, the corresponding server side method is invoked to start producing the content to be downloaded and eventually the browser will prompt the user to open or save (or cancel in the case of IE) the download.
The challenge: when the download commences, the download and cancel buttons should be disabled and perhaps an animated gif should be shown to suggest progress (we want to at least prevent the user from clicking the download button or getting frustrated in other ways while she is waiting for the report to be produced on the server side). When the download is complete – that means: when through the browser interaction the user has saved, opened or canceled the actual content download to the browser – the buttons should be enabled again and the animated gif can be removed.
In short: we want to be able to react – both to the beginning of the download as well as to the completion.
Leveraging HTML 5 Navigator API to show the browser's current location on an ADF Faces 11gR2 Thematic Map component0
The page developed in this article will essentially look as is shown in the next figure:
The HTML 5 Navigator API is available in most modern browsers – including Firefox 3.5+, Chrome 5.0+, Safari 5.0+, IE 9, iPhone 3.0+ and Android 2.0+. Note that the user should explicitly allow an application to learn about his or her location – and not get a handle on it just like that.
See Dive into HTML 5 for more details: http://diveintohtml5.org/geolocation.html
This very brief article demonstrates how a fairly complex, nested JSON document can be created using a single SQL query. The main features used in the SQL statement are the WITH clause to define the inline views per object (Department, Manager, Employee), Scalar Subquery to retrieve the result from an inline view as string into the overall JSON string and LISTAGG to collect multiple elements into a JSON list.
The article shows a very simple application of this JSON creation through a simple HTML page – served by a PL/SQL package. This page does not contain any data. Right after loading, the onLoad event triggers a listener that invokes – through AJAX – the PL/SQL package’s other procedure. This procedure returns the JSON object – courtesy of that fabulous SQL query – and uses it to write the company details on the fly into the page.
A little debugging using Firefox quickly made it clear that the submitForm() method is invoked when a command button is activated and that it in turn (indirectly) makes use of the function processValidators() on the AdfHtmlPage object. This function will return true or false, depending on whether any validation error messages were produced by the collected validators that fire.
The steps are:
In this article, we will continue a discussion on asynchronous processing started in a previous article that introduced asynchronous and parallel processing Java using Executors, Futures, Callable Objects and the underlying thread model in Java 5 and 6.
While a stand alone Java application – without UI – is a rare thing in my world, a Java Web application certainly is not. And performance, especially perceived performance, is pretty important in that world. The first page load is the most important measure I suppose for what the user feels is the performance of the web application. The fact that after the initial load, additional elements can be loaded into the page – asynchronously – is fine. The intial page load and the browser’s indication that the load is done (and the hourglass disappears) is what is most important for the happiness of the user.
We will see three stages in this article, of a very simple web page. It is a JSF (JavaServer Faces) page, that contains some very simple elements of which one displays an ‘expensive’ value – a value that takes some time to get hold of. Maybe because a database query is involved or web service is called. Whatever the cause, this one More >