Weaving the Tapestry Framework

In a continuation of my series of articles about Java Web development frameworks, this article will look at the Tapestry framework. Because Tapestry is a rather large framework, one article is not enough to cover most of its features. I decided to split the discussion about Tapestry into two parts. In this first part, I will focus on the configuration of the framework in an enterprise-level IDE such as JBuilder 2005 and prepare the groundwork for a working example in the second part. I will also describe the structure of the framework and its main features in this article, and concentrate on more specific features and details in the second part.

Background of Tapestry

Tapestry is an open-source framework for Web development written in Java. It competes with other frameworks such as Struts, WebWork, and Turbine to be the first choice of Web developers as an application framework. It was developed by Howard Lewis Ship and is part of Jakarta project at Apache Software Foundation.

Tapestry is not like the other Web development frameworks, not only in terms of its structure and APIs but also in terms of the development process. It uses a component object model to represent the pages of a Web application. Working with Tapestry feels more like developing a desktop application with Graphical User Interface (GUI) widgets or java Swing components. Under the hood framework is written cleverly enough to make coding a Web application feel as a desktop application development. The framework does a tremendous amount of work behind the scenes and hidden from the developers, such as object pooling, multi threading, listener callbacks, garbage collections, session state, rendering, and other processes.

At first glance, Tapestry may appear to be overly complex and resource intensive; however, it actually is not. Most of the components are cached or reused and structure is intuitive for any developer who has worked with Swing or a similar GUI toolkit. The framework also uses XML intensively.

Tapestry implements the Model-View-Controller (MVC) paradigm not only for the overall separation of logic and presentation at the framework level, but also on the level of its individual components such as tables or forms, as I will explain in the next section. Additionally, numerous main components are implemented in terms of public interfaces to give developers a great deal of flexibility in using the framework.

Tapestry also offers a built-in logging mechanism that is excellent. It is extremely flexible and provides a wealth of information.

Here is a short description of the framework from the Apache site:

Tapestry reconceptualizes Web application development in terms of objects, methods, and properties instead of URLs and query parameters.

Related Articles

• Apache Struts Framework: The Big Picture
• Working with the WebWork Framework
• Modern Java Frameworks for Web Development

Tapestry is an alternative to scripting environments such as JavaServer Pages or Velocity. Tapestry goes far further, providing a complete framework for creating extremely dynamic applications with minimal amounts of coding.

Tapestry's approach, using a component object model similar to a traditional GUI, provides the following benefits:

• Very high level of reuse, within and between projects
  Everything in Tapestry is a reusable component
• Frees developers from writing boring, buggy code
  Code in terms of objects, methods, and properties, not URLs and query parameters
• Allows applications' complexity to scale well
  Framework does all the URL building and message dispatching, transparently
• Easy Internationalization/Localization
  Framework selects localized version of text, templates, and images
• Extremely robust applications
  Less code is less bugs
  Sophisticated built-in exception reporting
  Line precise error reporting
• Easy team integration
  Graphic designers and Java developers can work together without having to know each other's jobs

Tapestry components are a combination of a specification file (in XML), an HTML template, and a Java class (extending a framework class, with simple additions). Tapestry components are combined together to form larger components or complete Tapestry pages.

Structure of the Framework

"The goal of Tapestry is to eliminate most of the coding in a Web application. Under Tapestry, nearly all code is directly related to application functionality, with very little "plumbing." If you have previously developed a Web application using PHP, Microsoft Active Server Pages, JavaServer Pages, or Java Servlets, you may take all the plumbing for granted: writing servlets, assembling URLs, parsing URLs, managing objects inside the HttpSession, and so forth. Tapestry takes care of nearly all of that, for free. It allows for the development of rich, highly interactive applications." (Kevin C. Dorff, Tapestry online tutorial)

Similar to other Web development frameworks, Tapestry is configured via a set of XML property files and other resource files. There is a main [your-app-name].application config file, a set of custom application specific "jwc" and "page" resource files, and a traditional controller Servlet. But, this is where the resemblance to other MVC frameworks ends. A concept of Application Engine, a view rendering process, and templates makes Tapestry feel very different and stand our from the pack.

Every HTML page that the user sees is rendered from a template by the application engine that is initialized per user session. Additionally, view objects follow an MVC pattern and have data models with states that can be changed. For example, forms can have listeners attached to them or tables could be "restored" to a previous state.

Setup and Configuration

Before I discuss the inner working and the main components of the framework, I want to talk about the development environment and its setup.

For this article and the example in the second part, I'm using BEA WebLogic application server, JBuilder 2005 as the development IDE, and a free MySQL database for my database needs. Because J2EE has a standardized WAR and EAR packaging structure, you may use any other application server such as Apache Tomcat, any other IDE such as very popular and free Eclipse and any other database. Assuming you are savvy enough with using other tools and can comfortably create a WAR module, get it running on an application server, and connect to a database, all of my examples should work with minimal changes. But, descriptions and screenshots will reference my environment.

Note: As of this writing, Tapestry is up to version 3.0.3 and MySQL database at version 4.1 with Connector/J mysql-connector-java-3.1.11-bin.jar.

To set up Tapestry, download it at http://jakarta.apache.org/tapestry/downloads.html.

Create a new Project (call it Tapestry) in JBuilder and add Tapestry and MySQL connection libs into the project class-path.

Assuming you have installed and configured BEA WebLogic with JBuilder, assign a server to the project.

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