Principle 1 – Static Structure, Dynamic Behavior

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Tapestry also makes you more agile by speeding up the development cycle with Live Class Reloading. Tapestry monitors the file system for changes to Java page classes, component classes, service implementation classes, HTML templates and component property files, and it hot-swaps the changes into the running application without requiring a restart or losing session data. This provides a very short code-save-view cycle that no other framework can touch.

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In traditional Java frameworks (including Struts, JSF and even the now-ancient 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.

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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. Pages and services within the application are injected with the @Inject annotation. The method names, onValidateFromForm() and onSuccessFromForm(), inform Tapestry about when each method is to be invoked. This naming convention identifies the event that is handled, ("validate" and "success") and the id of the component from which the event is triggered (the "form" component Wiki Markup{footnote}The component id can be omitted, leaving the method name {{onSuccess()}}, but that may cause confusion on a page that has multiple Form components triggering events, so it's best to be specific about the source of the event.{footnote}

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The "validate" event is triggered to perform cross-field validations, and the "success" event is only triggered when there are no validation errors. The onSuccessFromForm() 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.

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This is already evident in Tapestry 5.1, 5.2 and 5.3 where major new features and improvements have occurred, while remaining 100% backwards compatible to Tapestry 5.0 – as long as you've avoided the temptation to use internal APIs.

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Wiki Markup{display-footnotes}