maint-5-2/src/site/apt/index.apt

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 Apache Tapestry 5
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What is Apache Tapestry?

 Apache 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 has significant Ajax features baked right in. On the server-side, Tapestry easily integrates with any kind of backend, including JEE, 
 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 License 2.0.

New And Of Note

  * New {{{apidocs/org/apache/tapestry5/annotations/QueryParameterMapped.html}QueryParameterMapped}} annotation to
    automatically map fields of a page to query parameters.
  
  * Service <implementation> classes may now be {{{tapestry-ioc/reload.html}live reloaded}}, much like page and component classes. 

  * New {{{apidocs/org/apache/tapestry5/annotations/QueryParameter.html}QueryParameter}} annotation for parameters to event handler methods.

  * Submit components can now be used to cancel a form (bypassing client-side validation).

  * Tapestry no longer uses a StAX parser to parse templates (it uses a standard SAX parser), meaning fewer dependencies and
    better compatibility with Google App Engine.

  * A {{{guide/testing.html}guide to integration testing}} is now available.
  
  * The {{{guide/persist.html}@SessionAttribute}} annotation can be used on component fields to
    read and update HttpSession attributes.
  
  * The {{{tapestry-beanvalidator}JSR-303 Bean Validation Integration Library}} is now available.

  []
  
Roadmap

  The goal is to produce new releases on a regular schedule, every 4 - 6 months.

  High priorities for 5.2 include Spring Web Flow integration, and support for developing Tapestry applications as Portlets.

Third Party Libraries, Tutorials and Resources

  A number of Third Party Libraries, Tutorials and Resources are listed on
  the {{{http://tapestry.apache.org/}Tapestry Home Page}}.

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

  Object onSuccessFromForm()
  {
    return PostLogin.class;
  }

}
+----+

  This short snippet demonstrates a bit about how Tapestry operates.  Services
  within the application are injected with the @Inject annotation. The method names, onValidateFromForm()
  and onSuccessFromForm(),
  inform Tapestry about when the method is to be invoked.  The two events <validate> and <success> occur
  when a form is submitted; "validate" 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 supports multiple listeners, but provides an improved separation of
  view concerns (inside the page's 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.

  Tapestry also saves you effort:  the @Property annotation marks a field as readable and writable;
  Tapestry will provide the accessor methods automatically. This kind of meta-programming is common in Tapestry,
  and easy to implement yourself.

  Finally, Tapestry 5 explicitly separates actions (requests that change things) and rendering (requests that
  render pages into markup) 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 {{{http://maven.apache.org/}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 5.2.0 and the current snapshots are
  for 5.2.0-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 <every night>.
  
  Snapshots don't go in the central Maven repository (that's reserved for full releases). Instead, they go into the Apache snapshots repository
  at {{{http://http://repository.apache.org/snapshots}http://repository.apache.org/snapshots}}.
  
  To access this repository, you may add <<<-DremoteRepositories=http://repository.apache.org/snapshots>>> to the command line when
  running Maven.
  
  Your best bet is to use the {{{quickstart/}quickstart Maven archetype}} to create your initial Tapestry project; it generates a full project
  directory, including a POM that links to the Tapestry 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 5.2.x and that doesn't work, try 5.2..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.
 
 Tapestry also includes built-in mechanisms to store a limited amount of state, such as a persistent
 object id, directly into the URL used to access a page.
 
 In some Tapestry-like frameworks, such as JavaServer 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.

  This is already evident in Tapestry 5.1, where many new features and improvements have occurred, but is still
  100% backwards compatible to Tapestry 5.0, as long as you've avoided the temptation to make use of
  internal APIs.
  
  Tapestry 5.2 is continuing in this vein with improved performance and new features without sacrificing
  backwards compatibility at all.