What is Tapestry?

Tapestry is an open-source framework for creating dynamic, robust, highly scalable web applications in Java. Tapestry complements and builds upon the standard Java Servlet API, and so it works in any servlet container or application server.

Tapestry divides a web application into a set of pages, each constructed from components. This provides a consistent structure, allowing the Tapestry framework to assume responsibility for key concerns such as URL construction and dispatch, persistent state storage on the client or on the server, user input validation, localization/internationalization, and exception reporting. Developing Tapestry applications involves creating HTML templates using plain HTML, and combining the templates with small amounts of Java code. In Tapestry, you create your application in terms of objects, and the methods and properties of those objects -- and specifically not in terms of URLs and query parameters. Tapestry brings true object oriented development to Java web applications.

Tapestry is specifically designed to make creating new components very easy, as this is a routine approach when building applications.

Tapestry is architected to scale from tiny, single-page applications all the way up to massive applications consisting of hundreds of individual pages, developed by large, diverse teams. Tapestry easily integrates with any kind of backend, including JEE, HiveMind, Spring and Hibernate.

It's more than what you can do with Tapestry ... it's also how you do it! Tapestry is a vastly productive environment. Java developers love it because they can make Java code changes and see them immediately ... no redeploy, no restart! And it's blazingly fast to boot (even when files change). Designers love it because Tapestry templates are so close to ordinary HTML, without all the cruft and confusion seen in JavaServer Pages. Managers love it because it makes it easy for large teams to work together, and because they know important features (including localization) are baked right in. Once you work in Tapestry there's no going back!

Tapestry is released under the Apache Software Licence 2.0.

Third Party Libraries, Tutorials and Resources

Tapestry 5 has inspired a number of people to create third party libraries, providing a mix of new components and new and improved integrations.

New And Of Note

• At long last, an official LinkSubmit component.
• A detailed guide to Injection has been added.
• You can now configure Tapestry to move <script> links to the top of the page.
• Event handler methods for Ajax requests may now return a page name, page class or page instance to force the browser to redirect to the page.
• The Inject and InjectService annotations may now be used on fields of service implementations or other objects constructed by the IoC container. In the past, injections only occured through method or constructor parameters.
• Tapestry now bundles Prototype version 1.6.0.2.
• New methods have been added to Node to allow nodes to be moved about or otherwise manipulated.
• Application State Objects are now automatically saved back to the session at the end of the request, which ensures that ASO data is properly replicated across at cluster.
• The new @Local annotation makes it easier to reference services within the same module when injecting.
• Most general documentation has been moved from the tapestry-core module up to the project level.
• Work has started on a Tapestry Cookbook, showing how to tackle common scenarios.
• Component methods may be marked with the @Log annotation, to enable debug logging of method entry (with parameters) and exit (with return value, or thrown exception).
• It is now possible to provide method invocation advice to component methods. This opens up a very powerful Aspect Oriented Programming approach to Tapestry components.
• The Exception Report page now identifies the version of the Tapestry framework, and lists out System properties (including the Java classpath).
• The Grid component can now update itself in place, using Ajax, when paging or sorting links are clicked.
• Added a zone parameter to the BeanEditForm component, to support Ajax updates.
• The @Cached annotation has been added to allowing the caching of method results.

What's changed since Tapestry 4?

Tapestry 5 is an all new code base, written from the ground up to take Java web application development to new levels of productivity.

This new release removes many limitations of Tapestry 4:

• Components no longer extend from base classes.
• Components classes are no longer abstract. Components are pure, simple POJOs (plain old Java objects).
• Tapestry no longer uses XML page and component specification files. Information that used to be supplied in such files is now supplied directly in the Java class, using Java annotations and naming conventions.
• Changes to Tapestry component templates and classes are now picked up immediately, without any kind of restart. This will even work properly in production, not just during development.
• Blazing Speed. The new code base operates considerably faster than Tapestry 4. Critical code paths have been simplified, and the use of reflection has been virtually eliminated. Tapestry 4 was as fast as an equivalent Servlet/JSP application, Tapestry 5 is much faster.

Adaptive API

A key feature of Tapestry 5 is adaptive API.

In traditional Java frameworks, including Tapestry 4, user code is expected to conform to the framework. You create classes that extend from framework-provided base classes, or implement framework-provided interfaces.

This works well until you upgrade to the next release of the framework: with the new features of the upgrade, you will more often than not experience breaks in backwards compatibility. Interfaces or base classes will have changed and your existing code will need to be changed to match.

In Tapestry 5, the framework adapts to your code. You have control over the names of the methods, the parameters they take, and the value that is returned. This is driven by annotations, which tell Tapestry under what circumstances your methods are to be invoked.

For example, you may have a login form and have a method that gets invoked when the form is submitted:

public class Login
{
  @Persist
  @Property
  private String userId;

  @Property
  private String password;

  @Component
  private Form form;

  @Inject
  private LoginAuthenticator authenticator;

  void onValidateForm()
  {
    if (! authenticator.isValidLogin(userId, password))
    {
      form.recordError("Invalid user name or password.");
    }
  }

  Object onSuccess()
  {
    return PostLogin.class;
  }

}

This short snippet demonstrates a bit about how Tapestry operates. Pages and services within the application are injected with the @Inject annotation. The method names, onValidateForm() and onSuccess(), inform Tapestry about when the method is to be invoked. The two events validateForm and success occur when a form is submitted; "validateForm" is triggered to perform cross-field validations, and "success" is only triggered when there are no validation errors. The onSuccess() method's return value directs Tapestry on what to do next: jump to another page within the application (here identified as the class for the page, but many other options exist). When there are exceptions, the page will be redisplayed to the user.

This also represents a distinct change from Tapestry 4. In earlier versions of Tapestry, the Form component's listener parameter would be bound to the method to invoke, by name. Further, the listener method had to be public. This new approach not only support multiple listeners, but provides an improved separation of view concerns (inside the page's HTML template) and logic concerns, inside the Java class.

In many cases, additional information about the event is available, and can be passed into the method by adding parameters to the method. Again, Tapestry will adapt to your parameters, in whatever order you supply them.

Tapestry also saves you effort: the @Property annotation marks a field as readable and writable; Tapestry will provide the accessor methods automatically.

Finally, Tapestry 5 explicitly separates actions (requests that change things) and rendering (requests that render pages) into two separate requests. Performing an action, such as clicking a link or submitting a form, results in a client side redirect to the new page. This is often called "redirect after post". This helps ensure that URLs in the browser are book-markable ... but also requires that a bit more information be stored in the session between requests (using the @Persist annotation).

About Snapshots and Releases

Tapestry is built using Maven, which makes it really easy to download the source and build it yourself, either the whole project, or just one single module.

Better yet, you can pull down Tapestry modules from the central Maven repository.

The use of Maven has let us move with great speed, providing preview releases and snapshots.

Snapshots are intermediate versions of releases. As I'm writing this, the most recent preview release is 5.0.2 and the current snapshots are for 5.0.3-SNAPSHOT. Maven keys off the -SNAPSHOT suffix and handles the dependency specially. It knows that snapshot releases can change frequently, so it will keep checking (at least once a day, maybe more often) to see if there's an updated version of the snapshot.

A nightly build process on Tapestry's continuous integration server creates new snapshots emevery night/em.

Snapshots don't go in the central Maven repository (that's reserved for full releases). Instead, they go into the Tapestry snapshots repository at http://tapestry.formos.com/maven-snapshot-repository.

To access this repository, you may add -DremoteRepositories=http://tapestry.formos.com/maven-snapshot-repository to the command line when running Maven.

Your best bet is to use the quickstart Maven archetype to create your initial Tapestry project; it generates a full project directory, including a POM that links to the Apache snapshots repository.

Documentation on this site usually refers to the latest snapshot ... that is, it is usually ahead of the last official release. In some cases, it is written as if the snapshot release is stable; if documentation refers to version 5.0.x and that doesn't work, try 5.0.x-SNAPSHOT.

Principle 1 -- Static Structure, Dynamic Behavior

Tapestry is designed to be extremely scalable in several dimensions:

• Tapestry applications may contain large numbers of pages and many custom components.
• Tapestry applications may contain very complex functionality.
• Tapestry applications may be created by large, diverse teams.
• Tapestry applications can service large numbers of concurrent users.

One core architecture decision in Tapestry exists to service many of the above goals (and others that are harder to describe). Static Structure, Dynamic Behavior

In Tapestry, the structure of any particular page is static. This is necessary for several reasons, most importantly because Tapestry pages are pooled. Creating a Tapestry page is an involved process, because the page object is simply the root of a large tree of other objects including user provided components, many kinds of structural objects, template objects, and others. Creating a new page instance for each request is simply not scalable.

Instead, Tapestry pools pages. Once created, a page instance will be stored in a pool for that particular type of page, and reused in later requests. An incoming request, the result of a user clicking a link or submitting a form, will be processed by some server within a cluster, and will use some page instance within the page pool. Because page instances are static and uniform across instances and servers, Tapestry can use any available page instance, or create a new one as needed.

Tapestry does not need to store page instances inside the HttpSession. At most, it stores a smattering of persistent field values from the page, but not the entire page instance. This lean use of the HttpSession is key to Tapestry's very high scalability, especially in a clustered configuration.

In some Tapestry-like frameworks, such as Faces and Wicket, the page structure is more dynamic, at the cost of storing much, much more data in the HttpSession.

This static structure is not so limiting as you might think. With different kinds of conditional and looping components, and the ability to "jump out of the flow" and render components in an arbitrary order, you will not find Tapestry to be rigid ... anything but!

Public vs. Internal

An issue plaguing previous versions of Tapestry 4 (and earlier) was the lack of a clear delineator between private, internal APIs and public, external APIs. The fact that your code would extend from base objects but that many of the methods on those base objects were "off limits" further confused the issue. This has been identified as a key factor in the "steep learning curve of Tapestry" meme.

With the clean slate of Tapestry 5, we are being much more ruthless about internal vs. external.

First of all, anything inside the org.apache.tapestry5.internal package is internal. It is part of the implementation of Tapestry. It is the man behind the curtain. You should not ever need to directly use this code. It is a bad idea to do so, because internal code may change from one release to the next without concern for backwards compatibility.

Backwards Compatibility

Tapestry has been plagued by backwards compatibility problems with every major release. Tapestry 5 does not even attempt to be backwards compatible to Tapestry 4. Instead, it lays the ground work for true backwards compatibility going forwards.

Tapestry 5's API is based almost entirely on naming conventions and annotations. You components are just ordinary Java classes; you will annotate fields to allow Tapestry to maintain their state or to allow Tapestry to inject resources, and you will name (or annotate) methods to tell Tapestry under what circumstances a method should be invoked.

Tapestry will adapt to your classes. It will call your methods, passing in values via method parameters. Instead of the rigidness of a fixed interface to implement, Tapestry will simply adapt to your classes, using the hints provided by annotations and simple naming conventions.

Because of this, Tapestry will be able to change internally to a great degree without it affecting any of the application code you write. This should finally crack the backwards compatibility nut, allowing you to have great assurance that you can upgrade to future releases of Tapestry without breaking your existing applications.