Tapestry Tutorial

Introduction

Welcome to Tapestry!

This is a tutorial for people who will be creating Tapestry web applications. It doesn't matter whether you have experience with earlier versions of Tapestry or other web frameworks. In fact, in some ways, the less you know about web development in general, the better off you may be ... that much less to unlearn!

You do need to have a reasonable understanding of HTML, a smattering of XML, and a good understanding of basic Java language features, including Annotations.

The Challenges of Web Application Development

If you're used to developing web applications using servlets and JSPs, or with Struts, you are simply used to a lot of pain. These are environments with few safety net; Struts and the Servlet API have no idea how your application is structured, or how the different pieces fit together. Any URL can be an action and any action can forward to any view (usually a JSP) to provide an HTML response to the web browser. The pain is the unending series of small, yet important, decisions you have to make as a developer (and communicate to the rest of your team). What are the naming conventions for actions, for pages, for attributes stored in the HttpSession or HttpServletRequest? Where do cross-cutting concerns such as database transactions, caching and security get implemented (and do you have to cut-and-paste Java or XML to make it work?) How are your packages organized ... where to the user interface classes go, and where do the data and entity objects go? How do you share code from one part of your application to another?

On top of all that, the traditional approaches thrust something most unwanted in your face: multi-threaded coding. Remember back to Object Oriented Programming 101 where an object was defined as a bundle of data and operations on that data? You have to unlearn that lesson as soon as you build a traditional web application, because web applications are multi-threaded. An application server could be handling dozens or hundreds of requests from individual users, each in their own thread, and each sharing the exact same objects. Suddenly, you can't store data inside an object (a servlet or a Struts Action) because whatever data you store for one user will be instantly overwritten by some other user.

Worse, your objects each have only one operation: doGet() or doPost().

Meanwhile, most of your day-to-day work involves deciding how to package up some data already inside a particular Java object and squeeze that data into a URL's query parameters, so that you can write more code to convert it back if the user clicks that particular link. And don't forget editing a bunch of XML files to keep the servlet container, or the Struts framework, aware of these decisions.

Just for laughs, remember that you have to rebuild, redeploy and restart your application after virtually any change. Is any of this familiar? Then perhaps you'd appreciate something a little less familiar: Tapestry.

The Tapestry Way

Tapestry uses a very different model: a structured, organized world of pages, and components within pages. Everything has a very specific name (that you provide). Once you know the name of a page, you know the location of the Java class for that page, the location of the template for that page, and the total structure of the page. Tapestry knows all this as well, and can make things just work.

As we'll see in the following pages, Tapestry lets you code in terms of your objects. You'll barely see any Tapestry classes, outside of a few Java annotations. If you have information to store, store it as fields of your classes, not inside the HttpServletRequest or HttpSession. If you need some code to execute, it's just a simple annotation or method naming convention to get Tapestry to invoke that method, at the right time, with the right data.

Tapestry also shields you from most of the multi-threaded aspects of web application development. Tapestry manages the life cycle of your page and components objects, and the fields of the pages and components, in a thread-safe way. Your page and component classes always look like simple, standard POJOs.

Tapestry began in January 2000, and it now reflects over twenty years of experience of the entire Tapestry community. Tapestry brings to the table all that experience about the best ways to build scalable, maintainable, robust, internationalized, and Ajax-enabled applications.

Getting the Tutorial Source

Although you won't need it, the source code for this tutorial is available on GitHub.

Time to Begin

Okay, enough background. Now let's dig in: Dependencies, Tools and Plugins