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3.4. Client-Side Engine
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This section gives an overview of the client-side architecture of Vaadin. Knowledge of the client-side technologies is generally not needed unless you develop or use custom GWT components. The client-side engine is based on Google Web Toolkit (GWT), which allows the development of the engine and client-side components solely with Java.

Chapter 10, Developing Custom Components provides information about the integration of GWT-based user interface components with Vaadin.

Figure 3.2. Architecture of Vaadin Client-Side Engine

Architecture of Vaadin Client-Side Engine

Figure 3.2, “Architecture of Vaadin Client-Side Engine” illustrates the architecture of the client-side engine using a button component as an example. The user interface is managed by the ApplicationConnection class, which handles AJAX requests to the server and renders the user interface according to responses. Communications are done over HTTP(S) using the JSON data interchange format and the User Interface Definition Language (UIDL). In the server-side application, the button is used with the Button class of Vaadin. On the client-side, the user interface consists of various GWT components that inherit Widget class. In the figure above, the GWT class Button is used to render the button in the browser (the inheritance of Button is simplified in the figure). Vaadin provides an VButton class, which implements the Paintable interface needed for rendering the component with GWT.

The actual initial web page that is loaded in the browser is an empty page that loads the JavaScript code of the Vaadin Client-Side Engine. After it is loaded and started, it handles the AJAX requests to the server. All server communications are done through the ApplicationConnection class.

The communication with the server is done as UIDL (User Interface Definition Language) messages using the JSON message interchange format over a HTTP(S) connection. UIDL is described in Appendix A, User Interface Definition Language (UIDL) and JSON in Section 3.2.3, “JSON” and Section A.2, “JSON Rendering”.

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3.3. Applications as Java Servlet Sessions Home 3.5. Events and Listeners

Table of Contents

Preface
1. Introduction
1.1. Overview
1.2. Example Application Walkthrough
1.3. Support for the Eclipse IDE
1.4. Goals and Philosophy
1.5. Background
2. Getting Started with Vaadin
2.1. Installing Vaadin
2.2. Setting up the Development Environment
2.3. QuickStart with Eclipse
2.4. Your First Project with Vaadin
3. Architecture
3.1. Overview
3.2. Technological Background
3.3. Applications as Java Servlet Sessions
3.4. Client-Side Engine
3.5. Events and Listeners
4. Writing a Web Application
4.1. Overview
4.2. Managing the Main Window
4.3. Child Windows
4.4. Handling Events with Listeners
4.5. Referencing Resources
4.6. Shutting Down an Application
4.7. Handling Errors
4.8. Setting Up the Application Environment
5. User Interface Components
5.1. Overview
5.2. Interfaces and Abstractions
5.3. Common Component Features
5.4. Label
5.5. Link
5.6. TextField
5.7. RichTextArea
5.8. Date and Time Input
5.9. Button
5.10. CheckBox
5.11. Selecting Items
5.12. Table
5.13. Tree
5.14. MenuBar
5.15. Embedded
5.16. Upload
5.17. Form
5.18. ProgressIndicator
5.19. Slider
5.20. Component Composition with CustomComponent
6. Managing Layout
6.1. Overview
6.2. Window and Panel Root Layout
6.3. VerticalLayout and HorizontalLayout
6.4. GridLayout
6.5. FormLayout
6.6. Panel
6.7. SplitPanel
6.8. TabSheet
6.9. Accordion
6.10. Layout Formatting
6.11. Custom Layouts
7. Visual User Interface Design with Eclipse (experimental)
7.1. Overview
7.2. Creating a New CustomComponent
7.3. Using The Visual Editor
7.4. Structure of a Visually Editable Component
8. Themes
8.1. Overview
8.2. Introduction to Cascading Style Sheets
8.3. Creating and Using Themes
8.4. Creating a Theme in Eclipse
9. Binding Components to Data
9.1. Overview
9.2. Properties
9.3. Holding properties in Items
9.4. Collecting items in Containers
10. Developing Custom Components
10.1. Overview
10.2. Doing It the Simple Way in Eclipse
10.3. Google Web Toolkit Widgets
10.4. Integrating a GWT Widget
10.5. Defining a Widget Set
10.6. Server-Side Components
10.7. Using a Custom Component
10.8. GWT Widget Development
11. Advanced Web Application Topics
11.1. Special Characteristics of AJAX Applications
11.2. Application-Level Windows
11.3. Embedding Applications in Web Pages
11.4. Debug and Production Mode
11.5. Resources
11.6. Shortcut Keys
11.7. Printing
11.8. Portal Integration
11.9. Google App Engine Integration
11.10. Common Security Issues
11.11. URI Fragment and History Management with UriFragmentUtility
11.12. Capturing HTTP Requests
A. User Interface Definition Language (UIDL)
A.1. API for Painting Components
A.2. JSON Rendering
B. Songs of Vaadin
Index