Apache Tapestry 5.0

By Howard M. Lewis Ship

Tapestry 5.0 is a high-productivity, component-based, open source user interface tier for Java EE web applications. It combines simple, concise page templates with minimal Java classes (to contain state and business logic), and embraces convention over configuration, dynamically locating and adapting to your classes. This refcard covers Tapestry 5.0, (released as version 5.0.18 in December 2008), and describes the structure of a Tapestry application, the format of Tapestry markup templates, the standard components, and typical configuration options.

The first decision on a new project is the root package name. Tapestry will automatically locate Tapestry pages and components under the root package. Figure 1 shows a sample project layout for a root package name of com.whizzco.snuz. Apache Tapestry 5 www.dzone.com Get More Refcarz! Visit refcardz.com #40 By Howard M. Lewis Ship Configuring the Web Application, continued Java classes to be compiled are stored under src/main/java. Additional resources to be packaged with the compiled classes are stored under src/main/resources. The web application is under src/main/webapp, complete with a WEB-INF folder and a web.xml configuration file.

Tapestry’s primary configuration comes from web.xml; this is where the application’s root package is defined.

If you are using Maven, it can build a template project for you. Enter the following all on a single line:

mvn archetype:create -DarchetypeGroupId=org.apache.tapestry \

• DarchetypeArtifactId=quickstart \
• DgroupId=com.wizzco -DartifactId=snuz
• DpackageName=com.wizzco.snuz

You can replace the parts in bold with values specific to your

Configuring the Web Application, Continued

application. Maven creates an entire project structure, including a web.xml and starter pages and classes.

Additional configuration is accomplished via Tapestry’s builtin Inversion of Control container. This takes the form of a module class that defines services and provides configuration. If an AppModule class exists in the services package (com.wizzco.snuz.services.AppModule), it is loaded automatically. Maven will create this file for you.

Let’s turn Tapestry’s production mode off, so that any exceptions will be reported in full detail:

package com.whizzco.snuz.services;

import org.apache.tapestry5.ioc.*;
import org.apache.tapestry5.SymbolConstants;

​

public class AppModule {

   public static void

contributeApplicationDefaults(MappedConfiguration<String,

String> configuration) {

   configuration.add(SymbolConstants.PRODUCTION_MODE,

   “false”);

   }

}

​

In Tapestry, each page is a specific Java class in the pages package and has a page name that is based on the Java class name. Thus com.whizzco.snuz.pages.Index is page “Index” and com.whizzco.snuz.pages.profile.Edit is page “profile/Edit”.

Each page has a Tapestry markup template file that defines what components are used by the page. Some components also have templates and their own child components.

Every component has a type and an id. The type identifies what Java class will be instantiated. The id is unique to the component’s container (the page, or containing component). Tapestry assigns an id if you don’t.

Figure 2: Pages contain components; some components contain other components.

Pages are not like servlets; they are not singletons. There will be many instances of each page. A page instance is only visible to one request at a time, and Tapestry uses a page pool to store page instances between requests.

Component classes may extend from other component classes (but not from other non-component classes). There is no required base component class in Tapestry; most components extend from Object.

Figure 3: Parameter Bindings read and update properties

A page binds the parameters of its child components. For example, a TextField component’s value parameter is bound to a property, or property expression, indicating what object property it will read (when rendering) or update (when the containing form is submitted). In Figure 3, the value parameter is bound to the Index page’s activeProfile.lastName property.

The prop: prefix indicates a property expression binding; this is often the default and is usually omitted. Other binding prefixes fulfill other purposes, such as accessing localized messages from a message catalog, and are described later.

Tapestry template files are well-formed XML documents with a .tml extension. The file name must exactly match the class name (including case). Page templates can be stored on the

Tapestry Markup Templates, Continued

classpath (under src/main/resources) or directly inside the web application (under src/main/webapp). See Figure 2. Templates are optional, and many components do not have a template.

Tapestry Namespace

Tapestry uses the namespace http://tapestry.apache.org/schema/tapestry_5_0_0.xsd for its elements and attributes, usually assigned the prefix “t”. A minimal, empty Tapestry page will define the namespace in its outermost (“html”) element:

<html xmlns:t=”http://tapestry.apache.org/schema/tapestry_5_0_0.xsd”> </html>

Any elements that are not in the Tapestry namespace will ultimately be sent to the client web browser as-is. Markup templates may contain other namespaces as well; these too are sent to the client web browser as-is.

Using Expansions

Expansions allow you to read properties of the corresponding page (or component). Expansions start with a ‘${‘ sequence and end with a ‘}’. They may appear in ordinary text, including inside attribute values:

<dt>Account Balance:</dt> <dd class=”${balanceClass}”>${balance}</dd>”

Adding Components

A Tapestry component appears in the template as an element inside the Tapestry namespace.

<t:textfield value=”activeProfile.lastName”/>

<t:pagelink page=”index”>back to home page</t:pagelink>

The element name is the component type, and matches a component class. Tapestry searches the application’s components package first, then the built-in core library if not found.

Component parameters are bound using attributes of the element.

You may assign your own id to a component with the t:id attribute. It’s always a good idea to assign an id to any form-related component, or to ActionLink components; your choice will be shorter and more mnemonic than what Tapestry assigns, and component ids sometimes appear inside URLs or client-side JavaScript.

Body Element

The <t:body/> element is a placeholder for a component’s

Tapestry Markup Templates, Continued

body: the portion of its container’s template enclosed by its element.

Component Blocks

A section of a template may be enclosed as a block: <t:block id=”nav”> … </t:block>

Blocks may contain anything: text, elements, components or ansions. Blocks do not render in the normal flow; instead they can be rendered on demand (discussed in the Component Rendering section). Blocks can be injected into a field of type Block:

@Inject
private Block nav;

Block Parameters

Some components take a parameter of type Block. You can specify these using the <t:parameter> element:

​

​

<t:grid source=”users”>

 <t:parameter name=”empty”>

  <p>No users match the filter.</p>

 </t:parameter>

</t:grid>

​

Tapestry includes a large suite of built-in components; essential components are described in the following tables. Full details of all components and component parameters are available at:
http://tapestry.apache.org/tapestry5/tapestry-core/ref/.

Tapestry’s scaffolding components allow for quick user interfaces for ordinary JavaBeans to be assembled quickly and easily.

Built-in Components, Continued

Tapestry has built-in support for many common Ajax operations, built on top of Prototype and Scriptaculous. Many of the components have Ajax related parameters, and the following table lists components that exist just for Ajax.

Tapestry uses annotations to change how fields and methods of your component classes are used.

Many additional method annotations are discussed later, in component rendering. All those annotations have a naming convention alternative.

Expressions are always evaluated in the context of a page or component. Using the . and ?. operators allows expressions to navigate a graph of objects and properties.

Property expressions are updatable only if the final form is a property, and there is a setter method for that property. The case of property and method names is ignored. The . and ?. operators can be called as many times as you need.

The default binding prefix for most component parameters is prop:, meaning a property expression. In certain cases, a particular parameter will have a different default binding prefix, often literal:.

Tapestry interacts with your application code by reading and updating properties, and by invoking event handler methods. Event handler methods may have any visibility. Component events may be triggered by a request from the client (such as a form submission) or may exist only on the server, or some mix thereof.

Events have a name: in many cases, the event name is “action”. Some components trigger other events (see their documentation). Class EventConstants defines string constants for all events provided as part of Tapestry.

Component Events, Continued

Events may have a context: one or more values that are passed as strings in the URL. Context values are converted back to appropriate types and appear as method parameters to event handler methods.

Naming Convention

​

Event handler methods are of the form “onEventName” or

“onEventNameFromComponentId”. Examples:

void onSuccess() {

  …

}

void onActionFromDelete() {

  …

}

​

@OnEvent Annotation

​

The @OnEvent annotation can be used instead of the naming

convention:

@OnEvent(EventConstants.SUCCESS)

void storeOrderInDatabase() {

  …

}

@OnEvent(component=”delete”)

void deleteLineItem() {

  …

}

​

Tip: Use the @OnEvent annotation to support more descriptive method names.

Return Values

Return values from event handler methods are used for page navigation:

Event Bubbling

When an event is triggered on a component, the first step is to look in the component itself for an event handler method, then its container, then its container’s container, and so forth. Event bubbling occurs when there is no event handler, or an event handler exists but returns null (or void). The event is re-triggered in the container. As the event bubbles, it always appears to be from the component last checked.

Form Events

The Form component fires a series of events when rendering and when processing a submission:

Tapestry breaks the rendering of a component down into phases, shown in Figure 4. Each phase corresponds to a method of the component class (possibly a method inherited from a base class). The method names match render phase names (case insensitive). Alternately, you may attach a @SetupRender, @Begin-Render, etc. annotation to a method.

Figure 4: Component Rendering Phases

Normally, each phase follows the previous (the bold lines marked “true”). A render phase method may return false to jump backwards (the dotted lines). This is how conditional components (such as If) and looping components (such as Loop and Grid) operate.

Render phase methods may be any visibility. They may either take no parameters, or take a parameter of type MarkupWriter. The MarkupWriter.element() method is used to create a new output element (along with attributes) and should always be balanced by a call to MarkupWriter.end().

Components will often start an element in the BeginRender phase, and end it in the AfterRender phase.

Components that support informal parameters should be marked with the @SupportsInformalParameters class annotation, and include a call to ComponentResources.renderInformal- Parameters():

​

@Inject

private ComponentResources resources;

void beginRender(MarkupWriter writer) {

  writer.element(“div”, “class”, “popup”);

  resources.renderInformalParameters(writer);

}

void afterRender(MarkupWriter writer) {

  writer.end();

}

​

A render phase method may also return a component instance or a Block instance; the component or Block will take over and be rendered completely before the current component advances to the next phase.

If a component has a template, it is rendered after the BeginRender phase. The template may include a <t:body/> element to render the component’s body. A component without a template is treated as if its template consists of just a <t:body/> element.

Components, as part of pages, have a specific life cycle. Components are instantiated and added to pages and containing components. Once the page is fully constructed, components receive a one-time notification that the page has loaded. For the duration of a request, a page is attached to the request: there is a notification for the page being attached and later, for the page being detached (before it is returned to the page pool).

There are three method annotations for this purpose: @Page-Loaded, @PageAttached and @PageDetached. Alternately, you can also use the method naming convention: pageLoaded(), pageAttached() and pageDetached().

Tapestry localization support is pervasive. Tapestry determines the client’s desired locale based on standard HTTP headers, or the presence of a HTTP Cookie.

Pages and components may have their own individual message catalogs.

A message catalog is a set of files with similar names: My-Component.properties for the default message catalog, or with locale names appended: MyComponent_fr.properties or MyComponent_de.properties.

Component subclasses may have message catalogs; subclass keys override super-class keys.

Applications may have a message catalog: WEB-INF/app.properties. Page and component message keys override application messages keys.

Messages are accessible inside templates: ${message:greeting}, ${user.firstName}!

You may inject your component’s message catalog as a Messages object:

@Inject private Messages messages;

Using the @Inject annotation on a field of type java.util.Locale will inject the page’s locale. This can be used to format dates and currency values.

Environmental objects are request-scoped objects that are of use to your components. The @Environmental annotation dynamically binds a component field to an environmental object. Environmental objects don’t have a name; the type of the Environmental is used to locate the object.

Environmental Objects, Continued

Tapestry includes a number of useful services that can be injected into components or other services. Other services are useful not for injection, but to be configured.

For More Information

Tapestry 5 Home Page:
http://tapestry.apache.org/tapestry5/

Detailed component reference (with examples):
http://tapestry.apache.org/tapestry5/tapestry-core/ref/

Tapestry Wiki:
http://wiki.apache.org/tapestry/