DWR Java AJAX Applications

Table of Contents

DWR Java AJAX Applications

Credits

About the Author

About the Reviewers

Preface

What This Book Covers

What You Need for This Book

Who is This Book For

Conventions

Reader Feedback

Customer Support

Downloading the Example Code for the Book

Errata

Piracy

Questions

1. Introduction

What is AJAX?

DWR: AJAX for Java Developers

The DWR Community

Summary

2. DWR Features

Ease of Use

Reverse AJAX

Piggyback

Polling

Comet

DWR JavaScript Libraries

engine.js

util.js

gi.js

Converters

Creators, Filters, and Signatures

Integration with Other Projects

Security

Minimize Risks

Summary

3. Getting Started

Supported Browsers and Environments

Configuration

web.xml

dwr.xml

Using Creator and Its Attributes

Using the Converter Element

Working with Annotations

Using Fluent Configuration with DWR

Setting up a Development Environment

Development Environment with DWR and Firefox

Development Environment with Eclipse

Apache Geronimo

Testing and Debugging

Error Handling

Packaging and Deployment

Deployment Using the Administration Console

Deployment Using the Deployer Tool

Deployment Using Hot Deployment

Summary

4. User Interface: Basic Elements

Creating a Dynamic User Interface

Creating a New Web Project

Configuring the Web Application

Developing the Web Application

Testing the Web Application

Developing Web Pages

Callback Functions

Afterword

Implementing Tables and Lists

Server Code for Tables and Lists

Client Code for Tables and Lists

Testing Tables and Lists

Afterword

Implementing Field Completion

Server Code for Field Completion

Client Code for Field Completion

Afterword

Summary

5. User Interface: Advanced Elements

Creating Forms

Developing the User Interface

Creating the FormHandler Class

Testing the Form

Afterword

Building a Navigation Tree

Developing the User Interface

Creating the NavigationTree Class

Developing the User Interface, Part 2

Testing the Navigation Tree

Afterword

Map Scrolling Using DWR

Developing the User Interface

Creating the MapScroller Java Class

Testing the Map Scroller

Afterword

Summary

6. Backend Integration

Integrating a Database with DWR

Configuring the Database in Geronimo

Creating a CountryDerbyDB Java Class

Testing the Database Integration

Afterword

Integrating with Web Services

Developing the Web Service Client

Implementing the Web Service Call

Testing Web Services Integration

Afterword

Integrating with a Messaging System

Setting up Queues in Geronimo

Developing the OrderSystem Java Class

Setting up the Application for Messaging

Testing with the Backend OrderSystem

Afterword

Summary

7. Sample Applications

Collaborative Book Authoring

Starting the Project

Developing the User Interface

index.jsp

loginFailed.html

mainpage.jsp

Configuring the Web Application

Developing the Java Classes

Login.java

UserDatabase.java

Util.java

Book.java

BookDatabase.java

Testing Collaborative Book Authoring

Afterword

Chatroom

Starting the Project and Configuration

Developing the User Interface

Developing the Java Code

Testing the Chat

Afterword

Summary

Index

DWR Java AJAX Applications

Sami Salkosuo

DWR Java AJAX Applications

Copyright © 2008 Packt Publishing

All rights reserved. No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, without the prior written permission of the publisher, except in the case of brief quotations embedded in critical articles or reviews.

Every effort has been made in the preparation of this book to ensure the accuracy of the information presented. However, the information contained in this book is sold without warranty, either express or implied. Neither the author, Packt Publishing, nor its dealers or distributors will be held liable for any damages caused or alleged to be caused directly or indirectly by this book.

Packt Publishing has endeavored to provide trademark information about all the companies and products mentioned in this book by the appropriate use of capitals. However, Packt Publishing cannot guarantee the accuracy of this information.

First published: October 2008

Production Reference: 1151008

Published by Packt Publishing Ltd.

32 Lincoln Road

Olton

Birmingham, B27 6PA, UK.

ISBN 978-1-847192-93-6

www.packtpub.com

Cover Image by Parag Kadam (<Paragvkadam@gmail.com>)

Credits

Author

Sami Salkosuo

Reviewers

Jason Crow

Matthew Henry

Sujit Pal

Acquisition Editor

Adil Ahmed

Development Editor

Usha Iyer

Technical Editor

Darshana D. Shinde

Copy Editor

Sumathi Sridhar

Editorial Team Leader

Mithil Kulkarni

Project Manager

Abhijeet Deobhakta

Project Coordinator

Rajashree Hamine

Indexer

Rekha Nair

Proofreader

Chris Smith

Production Coordinator

Rajni R. Thorat

Cover Work

Rajni R. Thorat

About the Author

Sami Salkosuo is a Software IT Architect at IBM Software Group, Finland. He has over ten years of experience in Java, Web, and integration technologies.

Sami has written several articles for IBM developerWorks, and is also the co-author of an IBM Redbook: Portalizing Domino Applications.

I am thankful to the reviewers Sujit Pal, Matthew Henry, and Jason Crow for their comments that helped me improve my writing. My thanks to Rajashree Hamine, Usha Iyer, Darshana Shinde, and others at Packt Publishing for making this book come true.

My sincere thanks also for my family for their patience and support.

About the Reviewers

Jason Crow is the lead Java Developer for Office Depot, Inc. in Delray Beach, Florida. He specializes in blending his expertise in Java, DWR, HTML, CSS, and jQuery to enhance usability and to bring dynamic features to officedepot.com. He actively contributes back to the community through his blog http://greatwebguy.com.

Matthew Henry is the Programming Services Manager at LeTourneau University. Matthew has worked in IT and computer related fields as a programmer for 30 years. Matthew co-authored Upgrading to Lotus Notes 7 and has written various articles for specific computer industry magazines.

Sujit Pal started programming some 20 years ago, and has never looked back since. He currently works at Healthline Networks, Inc., a search vertical focused on health, as part of its Research and Development team. Apart from his work, his favorite pastime is to explore new software technologies, techniques, and languages, and he writes about his experiments at sujitpal.blogspot.com.

Preface

AJAX enables a rich desktop-like user interface in the browser and enables interactive interfaces that can even replace traditional user interfaces. Communication between browser and server is done in the background and because only the data is transferred between the browser and the server, AJAX applications seem to be, and are actually, fast and responsive to the users.

DWR, Direct Web Remoting, is an Open Source Java framework, licensed under the commercial-friendly Apache Software License v2 for building AJAX applications. DWR's main idea is to hide AJAX implementation details, like XMLHttpRequest and such, from developers. Developers can concentrate on developing the application and business objects and leave the AJAX details behind the scenes where they belong.

DWR allows server-side Java classes to be used in the browser (it's like an RPC between JavaScript functions and the server-side Java) and also allows JavaScript functions to be used in the server (Reverse AJAX). DWR dynamically generates JavaScript functions from Java classes via XML-based configuration, which can be called from browser via the DWR JavaScript library. A DWR servlet on the server side receives requests and calls the actual Java implementation. DWR includes a couple of JavaScript libraries that are required for DWR to work, and are also helpful for developers.

The term Reverse AJAX is used when a server is used to query and/or control the client browser behavior. DWR supports three different methods to do reverse AJAX in applications: Piggyback, Polling (by the client), and Comet (server push).

You may have an on-going project where you may want to use a framework such as JSF or Spring for building the whole solution. In these cases, AJAX and DWR are just a part of the overall picture, and so DWR needs to integrate with other frameworks nicely, and does that successfully!

The DWR project has thought about security very thoroughly. The DWR framework has taken into account many security issues and there is a lot of discussion about security at the DWR website.

This book is written for professional Java developers who are interested in learning DWR and AJAX framework. It starts with a tutorial on DWR's main features and functions. Then it covers setting up the development environment. It concludes with some sample applications.

The later chapters are full of example code for sample applications, to aid comprehension.

What This Book Covers

Chapter 1 is a brief introduction to AJAX technology and DWR. It also discusses the DWR community and describes briefly what information can be found about DWR on the Internet.

Chapter 2 describes DWR features that we use in the samples of this book—a high-level view of how DWR makes a developer's life easier. It discusses reverse AJAX, DWR JavaScript libraries, converters, creators, filters, and signatures. It also contains a section on integrating DWR with other projects and another on security.

Chapter 3 sets the stage for development by describing how to set up the development environment and how to test and debug our sample applications. It covers DWR-supported browsers and environments, configuration, error handling, packaging, and deployment.

Chapter 4 is the first chapter dedicated to sample code. The examples in this chapter include typical user interface elements such as tables and lists, and how they can be implemented using DWR. It also has an example for field completion.

Chapter 5 discusses how to use DWR in more advanced user interface elements such as forms, navigation tree, and scrolling a map.

Chapter 6 shows how DWR applications are integrated to a database, a web service, or a messaging system.

Chapter 7 includes two sample applications: Collaborative Book Authoring, which shows how DWR is used to create a web based multi-user authoring environment, and Chatroom—a typical multi-user chat room application using DWR.

What You Need for This Book

This book is for professional Java developers and architects who want to learn about DWR by examples. Several skills are needed or are beneficial to get the most out of this book.

First of all, Java development skills are needed. Especially web development using Java technologies like Java Enterprise Edition (JEE), Servlets, and JSPs. Experience about other web technologies like JavaScript, HTML, and CSS is also useful.

Eclipse tooling should be familiar and other useful skills are knowledge about JEE application servers and experience about common technologies like XML.

Knowledge about the basics of AJAX technology is helpful. However, the basics of AJAX are introduced in this book.

Who is This Book For

This book is written for competent Java developers and assumes that you are a professional rather than a hobbyist. You should be familiar with the concepts of programming, Web 2.0, and AJAX.

Conventions

In this book, you will find a number of styles of text that distinguish between different kinds of information. Here are some examples of these styles, and an explanation of their meaning.

Code words in text are shown as follows: We can include other contexts through the use of the include directive.

A block of code will be