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Web Push Technology

Dušan Chromý

SOA Integration Consulting

Reverse Ajax/Comet Explained

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Agenda

•Why Comet, first?

•How to Comet?

•Relation to Ajax

•Comet by Example: ODI Showcase

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Why Comet?

•The web interaction model is characterized by a client requesting information from the web server– Even Ajax, however novel, follows this model

•A web server cannot choose when to send updated information to a web browser– This makes development of a whole class of applications

difficult for the web, including:• Stock Price Tickers (and event monitoring applications in

general)• Chat & Instant Messaging• Online Multiplayer Games• Online Collaboration

•How to notify the web browser timely of server events?– Frequent polling used to be the only option…before Comet

The Challenge

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How to Comet?

1. HTTP Streaming• Never-ending stream of JavaScript tags

2. Long Polling• Slowly answered server request• via XMLHttpRequest or dynamic script tag• “Hang on - I’ll see if I have news for you”

3. HTML5 Server-Sent Events• HTTP Streaming standardized, cleaned

4. HTML5 WebSocket• Brave new upgrade of the HTTP protocol

The Approaches

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•Comet is to Ajax as– Java is to .NET

– Audi is to Mercedes

– Coke is to Pepsi

•The name “Comet” is a play on “Ajax”

•Both Ajax and Comet are umbrella terms for groups of techniques addressing different needs– Ajax enables interactive web applications

– Comet enables web applications to receive events from the server

•The Comet concept is known by several other names– Ajax Push, Reverse Ajax, Two-way-web, and others

Relation to Ajax

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Comet by Example: ODI Showcase

•The Showcase lets the user submit a file to ODI through a web page and shows the progress of the running ODI process

•Server-side Technology– ODI sends JMS progress messages

– Java Servlet delivers the messages to the client

– Oracle ADF Faces web application with JSP display technology

•Client-side Technology– Dojo Toolkit to simplify JavaScript development

•Let’s see it in action!

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Links and References

(1) Wikipedia: Comet

(2) http://cometdaily.com

(3) XML.com: JSON Dynamic Script Tags

(4) Opera Labs: Server-Sent Events

(5) My Tech Rantings: HTML5 WebSocket

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Dušan Chromý SOA Integration ConsultingEDS Operations Services GmbH Eisenstraße 56 65428 Rüsselsheim Germany Phone:+49-(0)6142 80 5431 mailto:dusan.chromy@eds.com