Creating The Skeleton Application

Before we can get down to the fun, we have to create an empty application. Tapestry uses a feature of Maven to do this: archetypes (a too-clever way of saying "project templates").

What we'll do is create an empty shell application using Maven, then import the application into Eclipse to do the rest of the work.

For the tutorial, we're using a fresh install of Eclipse and an empty workspace at /Users/Howard/Documents/workspace<style type='text/css'> .FootnoteMarker, .FootnoteNum a { background: transparent url(/confluence/download/resources/com.adaptavist.confluence.footnoteMacros:footnote/gfx/footnote.png) no-repeat top right; padding: 1px 2px 0px 1px; border-left: 1px solid #8898B8; border-bottom: 1px solid #6B7C9B; margin: 1px; text-decoration: none; } .FootnoteNum a { margin-top: 2px; margin-right: 0px; } .FootnoteNum { font-size: x-small; text-align: right; padding-bottom: 4px; } .footnote-th1 { text-align: right; } .Footnote { padding-left: 7px; margin-bottom: 4px; border: 1px none #DDDDDD; writingMode: tb-rl; } .accessibility { display: none; visibility: hidden; } @media aural,braille,embossed { .FootnoteMarker, .FootnoteNum a { border: 1px solid #000000; background: #ffffff none; } .accessibility { display: run-in; visibility: visible; } } </style> <script type='text/javascript' language='JavaScript'> //<!--\n var effectInProgress = {}; var despamEffect = function (id,effectType,duration) { if ((effectInProgress[id]) || (typeof(Effect)=="undefined") || (typeof(Effect[effectType])=="undefined")) return; new Effect[effectType](id); effectInProgress[id]=true; setTimeout('effectInProgress[\"'+id+'\"]=false;',duration*1000); }; var oldFootnoteId = ''; var footnoteHighlight = function(id,pulsateNum) { if (oldFootnoteId!='') document.getElementById('Footnote'+oldFootnoteId).style['borderStyle'] = 'none'; oldFootnoteId = id; document.getElementById('Footnote'+id).style['borderStyle'] = 'solid'; despamEffect('Footnote'+id,'Highlight',1) if (pulsateNum) despamEffect('FootnoteNum'+id,'Pulsate',3) } var footnoteMarkerHighlight = function(id) { if (oldFootnoteId!='') document.getElementById('Footnote'+oldFootnoteId).style['borderStyle'] = 'none'; oldFootnoteId = ''; despamEffect('FootnoteMarker'+id,'Pulsate',3) } //--> </script> ¹ . You may need to adjust a few things for other operating systems or local paths.

From our workspace directory, we'll use Maven to create a skeleton Tapestry project.

Before proceeding, we have to decide on four things: A Maven group id and artifact id for our project, a version, and a base package name.

Maven uses the group id and artifact id to provide a unique identity for the application, and Tapestry needs to have a base package name so it knows where to look for pages and components.

For this example, we'll use the group id com.example, artifact id tutorial1, version 1.0-SNAPSHOT and we'll use com.example.tutorial as the base package.

Our final command line is:

mvn archetype:generate -DarchetypeCatalog=http://tapestry.apache.org

It will then prompt you to pick the archetype - choose Tapestry 5.2.4 Quickstart Project, enter the group id, artifact id, version and package when prompted.

~/Documents/workspace
$ mvn archetype:generate -DarchetypeCatalog=http://tapestry.apache.org
[INFO] Scanning for projects...
[INFO] Searching repository for plugin with prefix: 'archetype'.
[INFO] ------------------------------------------------------------------------
[INFO] Building Maven Default Project
[INFO]    task-segment: [archetype:generate] (aggregator-style)
[INFO] ------------------------------------------------------------------------
[INFO] Preparing archetype:generate
[INFO] No goals needed for project - skipping
[INFO] [archetype:generate {execution: default-cli}]
[INFO] Generating project in Interactive mode
[INFO] No archetype defined. Using maven-archetype-quickstart (org.apache.maven.archetypes:maven-archetype-quickstart:1.0)
Choose archetype:
1: http://tapestry.apache.org -> quickstart (Tapestry 5.2.4 Quickstart Project)
2: http://tapestry.apache.org -> tapestry-archetype (Tapestry 4.1.6 Archetype)
Choose a number: : 1
Choose version: 
1: 5.1.0.5
2: 5.0.19
3: 5.2.4
Choose a number: 3: 3
Define value for property 'groupId': : com.example
Define value for property 'artifactId': : tutorial1
Define value for property 'version': 1.0-SNAPSHOT: 
Define value for property 'package': com.example: com.example.tutorial
Confirm properties configuration:
groupId: com.example
artifactId: tutorial1
version: 1.0-SNAPSHOT
package: com.example.tutorial
Y: 
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESSFUL
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 1 minute 41 seconds
[INFO] Finished at: Wed Nov 17 17:00:16 PST 2010
[INFO] Final Memory: 16M/81M
[INFO] ------------------------------------------------------------------------
~/Documents/workspace
$ 

After executing the command, you'll see a new directory, tutorial1.

<settings>
  <proxies>
    <proxy>
      <active>true</active>
      <protocol>http</protocol>
      <host>myProxyServer.com</host>
      <port>8080</port>
      <username>joeuser</username>
      <password>myPassword</password>
      <nonProxyHosts></nonProxyHosts>
    </proxy>
  </proxies>
  <localRepository>C:/Documents and Settings/joeuser/.m2/repository</localRepository>
</settings>

Running the New Application in Jetty

One of the first things you can do is use Maven to run Jetty directly.

Change into the newly created directory, and execute the command:

mvn jetty:run

Again, the first time, there's a dizzying number of downloads, but before you know it, the Jetty servlet container is up and running.

Once Jetty is initialized (which only takes a few seconds), you'll see the following in your console:

                               URLRewriter: DEFINED
                         UpdateListenerHub: REAL
                    ValidateBindingFactory: DEFINED
             ValidationConstraintGenerator: DEFINED
                  ValidationMessagesSource: DEFINED
                            ValidatorMacro: DEFINED
                        ValueEncoderSource: DEFINED

85.00% unrealized services (153/180)

2010-11-17 17:06:30.630::INFO:  Started SelectChannelConnector@0.0.0.0:8080
[INFO] Started Jetty Server

You can now open a web browser to http://localhost:8080/tutorial1/ to see the running application:

The date and time in the middle of the page proves that this is a live application.

This is a complete little application; it doesn't do much, but it demonstrate how to create a number of pages sharing a common layout, and demonstrates some simple navigation.

Loading the Project into Eclipse

Let's look at what Maven has generated for us. To do this, we're going to load the project inside Eclipse and continue from there.

Start by hitting Control-C in the Terminal window to close down Jetty.

Next, we'll ask Maven to create our Eclipse project for us:

$ mvn eclipse:eclipse -DdownloadSources=true
[INFO] Scanning for projects...
[INFO] Searching repository for plugin with prefix: 'eclipse'.
[INFO] org.apache.maven.plugins: checking for updates from apache-snapshots
[INFO] org.codehaus.mojo: checking for updates from apache-snapshots
[INFO] artifact org.apache.maven.plugins:maven-eclipse-plugin: checking for updates from apache-snapshots
[INFO] snapshot org.apache.maven.plugins:maven-eclipse-plugin:2.9-SNAPSHOT: checking for updates from apache-snapshots
Downloading: http://repository.apache.org/snapshots//org/apache/maven/plugins/maven-eclipse-plugin/2.9-SNAPSHOT/maven-eclipse-plugin-2.9-20101117.070458-148.pom
11K downloaded  (maven-eclipse-plugin-2.9-20101117.070458-148.pom)
Downloading: http://repository.apache.org/snapshots//org/apache/maven/plugins/maven-eclipse-plugin/2.9-SNAPSHOT/maven-eclipse-plugin-2.9-20101117.070458-148.jar
194K downloaded  (maven-eclipse-plugin-2.9-20101117.070458-148.jar)
[INFO] ------------------------------------------------------------------------
[INFO] Building tutorial1 Tapestry 5 Application
[INFO]    task-segment: [eclipse:eclipse]
[INFO] ------------------------------------------------------------------------
[INFO] Preparing eclipse:eclipse
[INFO] No goals needed for project - skipping
[INFO] [eclipse:eclipse {execution: default-cli}]
[INFO] Using Eclipse Workspace: /Users/Howard/Documents/workspace
[INFO] Adding default classpath container: org.eclipse.jdt.launching.JRE_CONTAINER
[INFO] Wrote settings to /Users/Howard/Documents/workspace/tutorial1/.settings/org.eclipse.jdt.core.prefs
[INFO] Wrote Eclipse project for "tutorial1" to /Users/Howard/Documents/workspace/tutorial1.
[INFO] 
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESSFUL
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 5 seconds
[INFO] Finished at: Wed Nov 17 17:13:11 PST 2010
[INFO] Final Memory: 21M/81M
[INFO] ------------------------------------------------------------------------
~/Documents/workspace/tutorial1
$ 

At this point, Maven has created the Eclipse .project and .classpath files, and we can import the project.

Launch Eclipse and switch over to the Java Perspective.

Right click inside the Package Explorer view and select Import ...

Choose the "existing projects" option:

Now select the folder created by Maven:

When you click the Finish button, the project will be imported into the Eclipse workspace.

However; there are many errors. Maven expects that you will configure a classpath variable, M2_REPO, that points at your local repository; a directory in your home directory that stores all those downloaded JARs and other files. Open Eclipse's preferences panel and navigate to Java > Build Path > Classpath Variables:

Click the New button, and enter the new variable (you'll have to adjust this for your operating system and local paths):

Eclipse will ask to perform a clean build, and the errors will be gone once it has done so.

Investigating the Generated Artifacts

Maven dictates the layout of the project:

• Java source files under src/main/java
• Web application files under src/main/webapp (including src/main/webapp/WEB-INF)
• Java test sources under src/test/java
• Non-code resources under src/main/resources and src/test/resources

Let's look at what the archetype has created for us, starting with the web.xml configuration file:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE web-app
        PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
        "http://java.sun.com/dtd/web-app_2_3.dtd">
<web-app>
    <display-name>tutorial1 Tapestry 5 Application</display-name>
    <context-param>
        <!-- The only significant configuration for Tapestry 5, this informs Tapestry
of where to look for pages, components and mixins. -->
        <param-name>tapestry.app-package</param-name>
        <param-value>com.example.tutorial</param-value>
    </context-param>
    <filter>
        <filter-name>app</filter-name>
        <filter-class>org.apache.tapestry5.TapestryFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>app</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>
</web-app>

This is short and sweet: you can see that the package name you provided earlier shows up as the tapestry.app-package context parameter; the TapestryFilter instance will use this information to locate the Java classes for pages and components.

Tapestry 5 operates as a servlet filter rather than as a traditional servlet. In this way, Tapestry has a chance to intercept all incoming requests, to determine which ones apply to Tapestry pages (or other resources). The net effect is that you don't have to maintain any additional configuration for Tapestry to operate, regardless of how many pages or components you add to your application.

Tapestry pages minimally consist of an ordinary Java class plus a component template file.

In the root of your web application, a page named "Index" will be used for any request that specifies no additional path after the context name.

Index Java Class

The final piece of the puzzle is the Java class for the page. Tapestry has very specific rules for where page classes go. Remember the package name (configured inside web.xml)? Tapestry adds a sub-package, "pages", to it and the Java class goes there. Thus the full Java class name is org.apache.tapestry5.tutorial.pages.Index.

package org.apache.tapestry5.tutorial.pages;

import java.util.Date;

/**
 * Start page of application tutorial1.
 */
public class Index
{
  public Date getCurrentTime()
  {
    return new Date();
  }
}

That's pretty darn simple: No classes to extend, no interfaces to implement, just a very pure POJO (Plain Old Java Object). You do have to meet the Tapestry framework halfway:

• You need to put the Java class in the expected package, org.apache.tapestry5.tutorial.pages
• The class must be public
• You need to make sure there's a public, no-arguments constructor (here, the Java compiler has silently provided one for us)

As we saw when running the application, this page displays the current date and time. the currentTime property is where that value comes from; shortly we'll see how that value is extracted from the page and output.

Tapestry always matches a page class to a template; neither is functional without the other. In fact, components within a page are treated the same way (except that components do not always have templates).

You will often hear about the Model-View-Controller pattern (MVC). In Tapestry, the page class acts as both the Model (the source of data) and the controller (the logic that responds to user interaction). The template is the View in MVC. As a model, the page exposes JavaBeans properties that can be referenced in the template.

Let's look at how the component template builds on the Java class to provide the full user interface.

Component Template

Tapestry pages are the combination of a POJO Java class with a Tapestry component template. The has the same name as the Java class, but has the extension .tml. Since the Java class here is com.example.tutorial.pages.Index, the template file will be located at src/main/resource/com/example/tutorial/pages/Index.tml. Ultimately, both the Java class and the component template file will be stored in the same folder within the deployed WAR.

Tapestry component templates are well-formed XML documents. This means that you can use any available XML editor. Templates may even have a DOCTYPE or an XML schema to validate the structure of the template.

For the most part, the template looks like ordinary XHTML:

<html t:type="layout" title="tutorial1 Index"
      t:sidebarTitle="Current Time"
      xmlns:t="http://tapestry.apache.org/schema/tapestry_5_1_0.xsd"
      xmlns:p="tapestry:parameter">
        <!-- Most of the page content, including <head>, <body>, etc. tags, comes from Layout.tml -->

    <p>${message:greeting}</p>

    <p:sidebar>

        <p>
            Just to prove this is live:
        </p>

        <p>The current time is: ${currentTime}.</p>


        <p>
            [<t:pagelink page="Index">refresh</t:pagelink>]
        </p>
    </p:sidebar>

</html>

The goal in Tapestry is for component templates, such as Index.tml, to look as much as possible like ordinary, static HTML files ² . In fact, the expectation is that in many cases, the templates will start as static HTML files, created by a web developer, and then be instrumented to act as live Tapestry pages.

Tapestry hides non-standard elements and attributes inside XML namespaces. By convention, the prefix "t:" is used for the primary namespace, but that is not a requirement.

This short template demonstrates quite a few features of Tapestry.

First of all, there are two XML namespaces defined:

  xmlns:t="http://tapestry.apache.org/schema/tapestry_5_1_0.xsd"
  xmlns:p="tapestry:parameter"

The first namespace, "t:", it used to identify Tapestry-specific elements and attributes. Although there is an XSD (that is, a XML schema definition), it is incomplete (for reasons explained shortly).

The second namespace, "p:", is a way of marking a chunk of the template as a parameter passed into another component. We'll expand on that shortly.

A Tapestry template consists mostly of standard XHTML that will pass down to the client web browser unchanged. The dynamic aspects of the template are represented by components and expansions.

Expansions in Templates

Let's start with expansions. Expansions are an easy way of including some dynamic output when rendering the page. By default, an expansion refers to a JavaBeans property of the page:

  <p>The current time is: ${currentTime}</p>

The value inside the curly braces is a property expression. Tapestry uses its own property expression language that is expressive, fast, and type-safe ³ . More advanced property expressions can traverse multiple properties (for example, user.address.city), or even invoke public methods. Here the expansion simply reads the currentTime property of the page.

Tapestry follows the rules defined by Sun's JavaBeans specification: a property name of currentTime maps to two methods: getCurrentTime() and setCurrentTime(). If you omit one or the other of these methods, the property is either read only (as here), or write only ⁴ .

Tapestry does go one step further: it ignores case when matching properties inside the expansion to properties of the page. In the template we could say ${currenttime} or ${CurrentTime} or any variation, and Tapestry will still invoke the getCurrentTime() method.

Note that in Tapestry it is not necessary to configure what object holds the currentTime property; a template and a page are always used in concert with each other; expressions are always rooted in the page instance, in this case, an instance of the Index class.

The Index.tml template includes a second expansion:

    <p>${message:greeting}</p>

Here greeting is not a property of the page; its actually a localized message key. Every page and component is allowed to have its own message catalog.

greeting=Welcome to Tapestry 5!  We hope that this project template will get you going in style.

Message catalogs are useful for storing repeating strings outside of code or templates, though their primary purpose is related to localization of the application (which will be described in more detail later). Messages that may be used across multiple pages can be stored in the application's global message catalog, src/main/webapp/WEB-INF/app.properties, instead.

This "message:" prefix is not some special case; there are actually quite a few of these "binding prefixes" built into Tapestry, each having a specific purpose. In fact, omitting a binding prefix in an expansion is exactly the same as using the "prop:" binding prefix.

Expansions are useful for extracting a piece of information and rendering it out to the client as a string, but the real heavy lifting of Tapestry occurs inside components.

Components Inside Templates

Components can be represented inside a component template in two ways ⁵ :

• As an ordinary element, but with a t:type attribute to define the type of component.

• As an element in the Tapestry namespace, in which case the element name determines the type.

Here we've used an <html> element to represent the application's Layout component.

<html t:type="layout"> 
  ...
</html>

But for the PageLink component, we've used an element in the Tapestry namespace:

<t:pagelink> ... </t:pagelink>

Which form you select is a matter of choice. In the vast majority of cases, they are exactly equivalent.

Tapestry components are configured using parameters; for each component, there is a set of parameters, each with a specific type and purpose. Some parameters are required, others are optional. Attributes of the element are used to bind parameters to values, or to page properties. Tapestry is flexible here as well; you can always place an attribute in the Tapestry namespace (using the "t:" prefix), but in most cases, this is unnecessary.

<html t:type="layout" title="tutorial1 Index"
      t:sidebarTitle="Current Time"

This binds two parameters, title and sidebarTitle of the Layout component, to the literal strings "tutorial1 Index" and "Current Time", respectively.

The Layout component will actually provide the bulk of the HTML ultimately sent to the browser; we'll look at its template in a bit. The point is, the page's template is integrated into the Layout components. The following diagram shows how parameters passed to the Layout component end up rendered in the final page:

Full Size

The interesting point here (and this is an advanced concept in Tapestry, one we'll return to later) is that we can pass a chunk of the Index.tml template to the Layout component as the sidebar parameter. That's what the tapestry:parameter namespace (the "p:" prefix) is for; the element name is matched against a parameter of the component and the entire block of the template is passed into the Layout component ... which decides where, inside its template, that block gets rendered.

<t:pagelink page="Index">refresh</t:pagelink>

This time, it's the page parameter of the PageLink component that is bound, to the literal value "Index" (which is the name of this page). This gets rendered as a URL that re-renders the page, which is how the current time gets updated. You can also create links to other pages in the application and, as we'll see in later chapters, attach additional information to the URL beyond just the page name.

Running the Application inside Eclipse

In the next chapter, we'll start to build a simple hi-lo guessing game, but we've got one more task before then, plus a magic trick.

The task is to set up Jetty to run our application directly out of our Eclipse workspace. This is a great way to develop web applications, since we don't want to have to use Maven to compile and run the application ... or worse yet, use Maven to package and deploy the application. That's for later, when we want to put the application into production. For development, we want a fast, agile environment that can keep up with our changes, and that means we can't wait for redeploys and restarts.

Choose the Run ... item from the Eclipse Run menu to get the launch configuration dialog:

Select Jetty Webapp and click the New button, then fill in a few values:

Make sure you clear the field labeled HTTPS.

You can then click Run and Jetty will launch (it takes only a few seconds):

Once you click Run, Jetty will start up and launch (it should take about two seconds).

You may now start the application with the URL http://localhost:8080/tutorial1/.

A Magic Trick

Now it's time for the magic trick. Edit Index.java and change the getCurrentTime() method to:

  public String getCurrentTime()
  {
    return "A great day to learn Tapestry";
  }

Make sure you save changes; then click the refresh link in the web browser:

This is one of Tapestry's early wow factor features: changes to your component classes are picked up immediately. No restart. No re-deploy. Make the changes and see them now. Nothing should slow you down or get in the way of you getting your job done.

But ... what if you make a mistake? What if you got the name in the template wrong. Give it a try; in the template, change ${currentTime} to, say, ${currenTime}, and see what you get:

This is Tapestry's exception report page. It's quite detailed. It clearly identifies what Tapestry was doing, and relates the problem to a specific line in the template, which is shown in context. Tapestry always expands out the entire stack of exceptions, because it is so common for exceptions to be thrown, caught, and re-thrown inside other exceptions. In fact, if we scroll down just a little bit, we see more detail about this exception, plus a little bit of help:

This is part of Tapestry's way: it not only spells out exactly what it was doing and what went wrong, but it even helps you find a solution; here it tells you the names of properties you could have used.

Tapestry displays the stack trace of the deepest exception, along with lots of details about the run-time environment: details about the current request, the HttpSession (if one exists), and even a detailed list of all JVM system properties. Scroll down to see all this information.

Now that we have our basic application set up, and ready to run (or debug) directly inside Eclipse, we can start working on implementing our Hi/Lo game in earnest.