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<h1 align="center">Extending WTP Using Project Facets</h1>

<blockquote>
<b>Summary</b><br/>
The Faceted Project Framework allows the plugin developer to think of Web Tools 
Platform (WTP) projects as composed of units of functionality, otherwise known 
as facets, that can be added and removed by the user. This tutorial walks you 
through an example of creating a couple of basic facets and in the process 
covers the majority of the framework's extension points. This tutorial has been
written for version 1.5 of the Web Tools Platform.
<br/><br/>

<b>Konstantin Komissarchik</b><br/>
BEA Systems, Inc.<br/>
September 5, 2006
</blockquote>

<hr width="100%">

<h2>Introduction</h2>

<p>Faceted Project Framework provides a powerful mechanism for extending the
capabilities of the Web Tools Platform. Project facets are typically used as
a way of adding functionality to a project. When a facet is added to the
project it can perform any necessary setup actions such as copying resources, 
installing builders, adding natures, etc. Facets can also be used as markers for
enabling user interface elements.</p>

<p>Some of the readers may be wondering how
facets are different from the project natures which are supported by the Eclipse
platform. Natures are designed to be hidden from user's view. They are
essentially markers that are set behind the scenes by tooling. Project facets,
on the other hand, have been designed from the ground up to be manipulated by
the end users. The Faceted Project Framework provides all the necessary user 
interface elements for managing the facets on a project and since facets
are self describing the user is prevented from creating invalid configurations.
Basically, it is no longer necessary to write custom project creation wizards or
the "Enable Feature X" menu actions. Common way of managing which facets are
installed on a project means less burden on the plugin writer and better end user
experience.</p>

<p>This tutorial covers the extension points and Java API that are used for 
creating project facets. The reader is assumed to be already familiar with 
developing plugins for Eclipse and to have user-level knowledge of the Web Tools 
Platform.</p>

<h2>Tutorial Scenario</h2>

<p>You are a developer for a company which develops a product called
FormGen. FormGen is basically a servlet that generates HTML forms based on XML
definition files. The product is composed of a jar containing the servlet and
some basic widgets. There is also an add-on jar with some extra widgets. Users
have been manually adding the jars into the WEB-INF/lib directories of their
web projects and setting up the servlet definitions in web.xml by hand. Your
task is to make this setup easier by writing a couple of project facets that
will perform these actions automatically.</p>

<h2>Table of Contents</h2>

<div class="block-indent">
1. <a href="#getting.started">Getting Started</a><br/>
2. <a href="#creating.basic.facets">Creating Basic Facet Definitions</a><br/>
3. <a href="#specifying.constraints">Specifying Constraints</a><br/>
4. <a href="#implementing.actions">Implementing Actions</a><br/>
5. <a href="#creating.categories">Creating Categories</a><br/>
6. <a href="#decorating">Decorating</a><br/>
7. <a href="#adding.wizard.pages">Adding Wizard Pages</a><br/>
8. <a href="#defining.presets">Defining Presets</a><br/>
9. <a href="#runtime.mappings">Specifying Runtime Support Mappings</a><br/>
10. <a href="#summary">Summary</a><br/>
Appendix A: <a href="#custom.version.comparators">Custom Version Comparators</a><br/>
Appendix B: <a href="#version.expressions">Version Expressions</a><br/>
Appendix C: <a href="#property.tester">Property Tester</a><br/>
Appendix D: <a href="#wizard.context">Wizard Context</a><br/>
</div>

<h2><a name="getting.started">1. Getting Started</a></h2>

<p>To follow along with this tutorial, you will need to have a working install 
of Web Tools Platform v1.5. The tutorial is not designed to be used with 1.0.x
version of WTP as there are numerous extension point and API differences. You 
can download the install kits for WTP and its prerequisites, including Eclipse 
Platform v3.2, at the following locations:</p>

<ul>
  <li><a href="http://download.eclipse.org/eclipse/downloads/">Eclipse Platform Download Site</a></li>
  <li><a href="http://download.eclipse.org/webtools/downloads/">Web Tools Platform Download Site</a></li>
</ul>

<p>Once the required software has been installed you will need to
create a new workspace and add the <a href="materials/starter.zip">starter project</a>
to it. The starter project includes the materials and utility code that will
be used in this tutorial. If you get stuck at any point you can take a peek at
the <a href="materials/solution.zip">solution project</a>.</p>

<h2><a name="creating.basic.facets">2. Creating Basic Facet Definitions</a></h2>

<p>Project facets are declared via the <code>org.eclipse.wst.common.project.facet.core.facets</code>
extension point. This is a pretty large extension point with lots of facilities,
but we will start small and progress incrementally while building the tutorial
facets. Here is the part of the schema that we will be working with initially:</p>

<div class="code">
<pre class="code-xml">&lt;extension point="org.eclipse.wst.common.project.facet.core.facets"&gt;

  &lt;project-facet id="<span class="schema-type">{string}</span>"&gt; <span class="schema-control">(0 or more)</span>
    &lt;label&gt;<span class="schema-type">{string}</span>&lt;/label&gt;
    &lt;description&gt;<span class="schema-type">{string}</span>&lt;/description&gt; <span class="schema-control">(optional)</span>
  &lt;/project-facet&gt;

  &lt;project-facet-version facet="<span class="schema-type">{string}</span>" version="<span class="schema-type">{string}</span>"/&gt; <span class="schema-control">(0 or more)</span>
  
&lt;/extension&gt;</pre>
</div>

<p>As you can see, there are two top-level elements in this part of the extension
point schema. The <code>&lt;project-facet&gt;</code> element is used to declare
the facet itself. The <code>&lt;project-facet-version&gt;</code> element is used
to declare versions of the facet. Every facet implementation needs to provide
at least one facet version declaration. In fact, as you will see later in this
tutorial, the bulk of the work happens in the <code>&lt;project-facet-version&gt;</code>
declaration. For now all you need to remember is that a facet cannot be used
unless it has at least one version.</p>

<div class="code">
<pre class="code-xml">&lt;extension point="<span class="code-text">org.eclipse.wst.common.project.facet.core.facets</span>"&gt;

  &lt;project-facet id="<span class="code-text">formgen.core</span>"&gt;
    &lt;label&gt;<span class="code-text">FormGen Core</span>&lt;/label&gt;
    &lt;description&gt;
      <span class="code-text">Enables generation of HTML forms based on XML definition files.</span>
    &lt;/description&gt;
  &lt;/project-facet&gt;

  &lt;project-facet-version facet="<span class="code-text">formgen.core</span>" version="<span class="code-text">1.0</span>"/&gt;

  &lt;project-facet id="<span class="code-text">formgen.ext</span>"&gt;
    &lt;label&gt;<span class="code-text">FormGen Extensions</span>&lt;/label&gt;
    &lt;description&gt;
      <span class="code-text">Enables additional FormGen widgets.</span>
    &lt;/description&gt;
  &lt;/project-facet&gt;

  &lt;project-facet-version facet="<span class="code-text">formgen.ext</span>" version="<span class="code-text">1.0</span>"/&gt;
  
&lt;/extension&gt;</pre>
</div>

<p>Insert the above code into your plugin.xml file and lets see it in action.
Launch Eclipse with your FormGen plugin and then open the Dynamic Web Project
wizard. Make sure that <code>&lt;none&gt;</code> is selected in the Target Runtime
field on the first page and go to the second page. You should see a screen that
looks like the following. Note that the FormGen facets that you have created
are displayed.</p>

<div class="screen-shot"><img src="images/screen01.gif"/></div>

<h2><a name="specifying.constraints">3. Specifying Constraints</a></h2>

<p>One of the problems with what we have so far is that the FormGen facets
appear in other module project wizards such as the EJB Project Wizard. That, of
course, makes no sense since FormGen is servlet-based technology and so is only
applicable to J2EE web applications. To solve this problem we will use the 
constraint mechanism to specify the dependencies.</p>

<p>Here is what that part of the extension point schema looks like:</p>

<div class="code">
<pre class="code-xml"><span class="context-code">&lt;extension point="org.eclipse.wst.common.project.facet.core.facets"&gt;
  &lt;project-facet-version&gt;</span>
    &lt;constraint&gt; <span class="schema-control">(optional)</span>
      <span class="schema-control">[expr]</span>
    &lt;/constraint&gt;
  <span class="context-code">&lt;/project-facet-version&gt;
&lt;/extension&gt;</span>

<span class="schema-control">[expr] =</span>
  &lt;requires facet="<span class="schema-type">{string}</span>" version="<span class="schema-type"><span class="schema-type-link">{<a href="#version.expressions">version.expr</a>}</span></span>" soft="<span class="schema-type">{boolean}</span>"/&gt; <span class="schema-control">or</span>
  &lt;conflicts facet="<span class="schema-type">{string}</span>" version="<span class="schema-type"><span class="schema-type-link">{<a href="#version.expressions">version.expr</a>}</span></span>"/&gt; <span class="schema-control">or</span>
  &lt;conflicts group="<span class="schema-type">{string}</span>"/&gt; <span class="schema-control">or</span>
  &lt;and&gt;
    <span class="schema-control">[expr]</span> <span class="schema-control">(1 or more)</span>
  &lt;/and&gt; <span class="schema-control">or</span>
  &lt;or&gt;
    <span class="schema-control">[expr]</span> <span class="schema-control">(1 or more)</span>
  &lt;/or&gt;</pre>
</div>

<p>As you can see, the constraint is an expression tree and you have four
operators at your disposal. Lets go over them one by one.</p>

<div style="margin-left: 10px">
<p><b>requires</b></p>

<p>The <code>requires</code> operator is the most frequently used of all the operators. 
It is used to specify a dependency on another facet. If the <code>version</code>
attribute is not specified, any version of the referenced facet will satisfy
the constraint. If only specific versions will do, the <code>version</code> 
attribute can contain a <a href="#version.expressions">version expression</a>.</p>

<p>The <code>soft</code> attribute is used to create a special kind of a
dependency. Facet selection will not be prevented if the dependency is not
met, but if the dependency is met, the facet is guaranteed to be installed
after the referenced facet.</p>

<p><b>conflicts</b></p>

<p>The <code>conflicts</code> constraint is used to indicate that the declaring
facet will not work correctly if installed into the same project as referenced
facets. The <code>conflicts</code> constraint comes in two flavors. You can
either specify a conflict with a single facet or with a group of facets.</p>

<p>What are groups of facets? Facet groups are a way to designate a conflict with
a certain class of facets without having to list all of the facets explicitly.
For instance, the WTP module facets all belong to the "modules" group. They also
each declare a conflict with the "modules" group. This prevents two module facets
from being installed into the same project. By declaring a conflict with a
group whose membership can expand as necessary, third parties can add module
facets on top of WTP and have the new facets interact correctly with the
built-in module facets.</p>

<p>A facet group is created the first time a facet declares group membership.
Here is the extension point schema for declaring group membership:</p>

<div class="code">
<pre class="code-xml"><span class="context-code">&lt;extension point="org.eclipse.wst.common.project.facet.core.facets"&gt;
  &lt;project-facet-version&gt;</span>
    &lt;group-member id="<span class="schema-type">{string}</span>"/&gt; <span class="schema-control">(0 or more)</span>
  <span class="context-code">&lt;/project-facet-version&gt;
&lt;/extension&gt;</span>
</pre>
</div>

<p><b>and &amp; or</b>

<p>The <code>and</code> &amp; <code>or</code> constraints are used to perform 
logical conjunction and disjunction over their operands. Although it is legal
for these operators to have only one operand, typically they will have two or
more.</p>
</div>

<p>We can now specify the constraints for the FormGen facets. The facet id that
marks a project as a J2EE web module is <code>jst.web</code>. We will setup
a dependency on it from the <code>formgen.core</code> facet. The
<code>formgen.ext</code> facet can then depend on the <code>formgen.ext</code>
facet. That latter constraint will ensure that the FormGen Extensions
are not installed without installing FormGen Core.</p>

<div class="code">
<pre class="code-xml"><span class="context-code">&lt;extension point="org.eclipse.wst.common.project.facet.core.facets"&gt;

  &lt;project-facet-version id="formgen.core" version="1.0"&gt;</span>
    &lt;constraint&gt;
      &lt;requires facet="<span class="xml-text">jst.web</span>" version="<span class="xml-text">2.2,2.3,2.4</span>"/&gt;
    &lt;/constraint&gt;
  <span class="context-code">&lt;/project-facet&gt;

  &lt;project-facet-version id="formgen.ext" version="1.0"&gt;</span>
    &lt;constraint&gt;
      &lt;requires facet="<span class="xml-text">formgen.core</span>" version="<span class="xml-text">1.0</span>"/&gt;
    &lt;/constraint&gt;
  <span class="context-code">&lt;/project-facet&gt;
  
&lt;/extension&gt;</span></pre>
</div>

<p>Once the above code is added, the FormGen facets should only appear in the
Dynamic Web Project wizard.</p>

<h2><a name="implementing.actions">4. Implementing Actions</a></h2>

<p>Let's now try selecting the FormGen Core facet on the facets selection page
of the Dynamic Web Project wizard. If you do that, you should see the
following error message appear.</p>

<div class="screen-shot"><img src="images/screen02.gif"/></div>

<p>This error message is displayed because the install action has not been
implemented for this facet. What's an action? An action is an operation that a
user can perform on a facet. There are three action types <code>INSTALL</code>,
<code>UNINSTALL</code>, and <code>VERSION_CHANGE</code>. We will now implement
the install actions for the FormGen facets.</p>

<p>Here is what that part of the extension point schema looks like:</p>

<div class="code">
<pre class="code-xml"><span class="context-code">&lt;extension point="org.eclipse.wst.common.project.facet.core.facets"&gt;</span>
  &lt;action id="<span class="schema-type">{string}</span>" facet="<span class="schema-type">{string}</span>" version="<span class="schema-type"><span class="schema-type-link">{<a href="#version.expressions">version.expr</a>}</span></span>" type="<span class="schema-type">INSTALL|UNINSTALL|VERSION_CHANGE</span>"&gt;
    &lt;delegate class="<span class="schema-type">{class:org.eclipse.wst.common.project.facet.core.IDelegate}</span>"/&gt;
    &lt;property name="<span class="schema-type">{string}</span>" value="<span class="schema-type">{string}</span>"/&gt; <span class="schema-control">(0 or more)</span>
  &lt;/action&gt;
<span class="context-code">&lt;/extension&gt;</span>
</pre>
</div>

<ul>

  <li><p>The version attribute can contain a single version or a <a href="#version.expressions">version expression</a>.
    It can also be omitted if the action applies to all versions of the facet.</p></li>
    
  <li><p>The <code>id</code> attribute is optional. If not specified, the framework
    will automatically generate one using the following pattern:</p>
    <p><code>[facet-id]#[version-expression]#[action-type](#[prop-name]=[prop-value])*</code></p>
    <p>As you can see, it is better to provide an explicit id rather than letting
    the framework generate it. Later in the tutorial we will cover extension
    points that make references to action ids.</p>
  
  <li><p>The <code>&lt;action&gt;</code> element can also be embeded inside the
    <code>&lt;project-facet-version&gt;</code> element. In that case, the
    <code>facet</code> and <code>version</code> attributes should be omitted.
    Note that if the same delegate implementation applies to multiple facet 
    versions, it is better to provide a single action declaration externally.
    This allows the framework to perform certain kinds of optimizations</p></li>
    
  <li><p>For the <code>VERSION_CHANGE</code> action, it is possible to restrict
    the applicability of the action definition with regards to the starting
    version. To do that, simply specify "from.versions" property in the action
    definition. The value is a <a href="#version.expressions">version expression</a>.
    If this property is not specified, the framework will assume that the delegate
    is capable of converting from any starting version.</p></li>
    
</ul>

<div class="code">
<pre class="java-code"><span class="java-keyword">package</span> org.eclipse.wst.common.project.facet.core;

<span class="java-keyword">import</span> org.eclipse.core.resources.IProject;
<span class="java-keyword">import</span> org.eclipse.core.runtime.CoreException;
<span class="java-keyword">import</span> org.eclipse.core.runtime.IProgressMonitor;

<span class="java-comment">/**
 * This interface is implemented in order to provide logic associated with
 * a particular event in project facet's life cycle, such as install or 
 * uninstall.
 */</span>

<span class="java-keyword">public interface</span> IDelegate 
{
    <span class="java-comment">/**
     * The method that's called to execute the delegate.
     * 
     * <span class="java-javadoc-keyword">@param</span> project the workspace project
     * <span class="java-javadoc-keyword">@param</span> fv the project facet version that this delegate is handling; this
     *   is useful when sharing the delegate among several versions of the same
     *   project facet or even different project facets
     * <span class="java-javadoc-keyword">@param</span> config the configuration object, or <code>null</code> if defaults
     *   should be used
     * <span class="java-javadoc-keyword">@param</span> monitor the progress monitor
     * <span class="java-javadoc-keyword">@throws</span> CoreException if the delegate fails for any reason
     */</span>
    
    <span class="java-keyword">void</span> execute( IProject project,
                  IProjectFacetVersion fv,
                  Object config,
                  IProgressMonitor monitor )
    
        <span class="java-keyword">throws</span> CoreException;
}
</pre>
</div>

<p>Let's now dive in and implement the install delegates for the FormGen facets.
The <code>formgen.core</code> facet should (a) copy <code>formgen-core.jar</code>
into the project's <code>WEB-INF/lib</code> directory, and (b) register the
FormGen servlet in <code>web.xml</code>. The <code>formgen.ext</code> facet should
copy the <code>formgen-ext.jar</code> into the project's <code>WEB-INF/lib</code>
directory.</p>

<div class="code">
<pre class="code-xml"><span class="context-code">&lt;extension point="org.eclipse.wst.common.project.facet.core.facets"&gt;</span>

  <span class="context-code">&lt;project-facet-version facet="formgen.core" version="1.0"&gt;</span>
    &lt;action type="<span class="xml-text">INSTALL</span>"&gt;
      &lt;delegate class="<span class="xml-text">com.formgen.eclipse.FormGenCoreFacetInstallDelegate</span>"/&gt;
    &lt;/action&gt;
  <span class="context-code">&lt;/project-facet-version&gt;</span>

  <span class="context-code">&lt;project-facet-version facet="formgen.ext" version="1.0"&gt;</span>
    &lt;action type="<span class="xml-text">INSTALL</span>"&gt;
      &lt;delegate class="<span class="xml-text">com.formgen.eclipse.FormGenExtFacetInstallDelegate</span>"/&gt;
    &lt;/action&gt;
  <span class="context-code">&lt;/project-facet-version&gt;</span>
  
<span class="context-code">&lt;/extension&gt;</span>
</pre>
</div>

<div class="code">
<pre class="java-code"><span class="java-keyword">package</span> com.formgen.eclipse;

<span class="java-keyword">import</span> org.eclipse.core.resources.IFolder;
<span class="java-keyword">import</span> org.eclipse.core.resources.IProject;
<span class="java-keyword">import</span> org.eclipse.core.runtime.CoreException;
<span class="java-keyword">import</span> org.eclipse.core.runtime.IProgressMonitor;
<span class="java-keyword">import</span> org.eclipse.core.runtime.Path;
<span class="java-keyword">import</span> org.eclipse.wst.common.project.facet.core.IDelegate;
<span class="java-keyword">import</span> org.eclipse.wst.common.project.facet.core.IProjectFacetVersion;

<span class="java-keyword">public final class</span> FormGenCoreFacetInstallDelegate <span class="java-keyword">implements</span> IDelegate
{
    <span class="java-keyword">public void</span> execute( <span class="java-keyword">final</span> IProject pj,
                         <span class="java-keyword">final</span> IProjectFacetVersion fv,
                         <span class="java-keyword">final</span> Object config,
                         <span class="java-keyword">final</span> IProgressMonitor monitor )

        <span class="java-keyword">throws</span> CoreException

    {
        monitor.beginTask( "", 2 );

        <span class="java-keyword">try</span>
        {
            <span class="java-keyword">final</span> IFolder webInfLib = Utils.getWebInfLibDir( pj );

            Utils.copyFromPlugin( new Path( "libs/formgen-core.jar" ),
                                  webInfLib.getFile( "formgen-core.jar" ) );

            monitor.worked( 1 );

            Utils.registerFormGenServlet( pj );

            monitor.worked( 1 );
        }
        <span class="java-keyword">finally</span>
        {
            monitor.done();
        }
    }
}
</pre>
</div>

<div class="code">
<pre class="java-code"><span class="java-keyword">package</span> com.formgen.eclipse;

<span class="java-keyword">import</span> org.eclipse.core.resources.IFolder;
<span class="java-keyword">import</span> org.eclipse.core.resources.IProject;
<span class="java-keyword">import</span> org.eclipse.core.runtime.CoreException;
<span class="java-keyword">import</span> org.eclipse.core.runtime.IProgressMonitor;
<span class="java-keyword">import</span> org.eclipse.core.runtime.Path;
<span class="java-keyword">import</span> org.eclipse.wst.common.project.facet.core.IDelegate;
<span class="java-keyword">import</span> org.eclipse.wst.common.project.facet.core.IProjectFacetVersion;

<span class="java-keyword">public final class</span> FormGenExtFacetInstallDelegate <span class="java-keyword">implements</span> IDelegate
{
    <span class="java-keyword">public void</span> execute( <span class="java-keyword">final</span> IProject pj,
                         <span class="java-keyword">final</span> IProjectFacetVersion fv,
                         <span class="java-keyword">final</span> Object config,
                         <span class="java-keyword">final</span> IProgressMonitor monitor )

        <span class="java-keyword">throws</span> CoreException

    {
        monitor.beginTask( "", 1 );

        <span class="java-keyword">try</span>
        {
            <span class="java-keyword">final</span> IFolder webInfLib = Utils.getWebInfLibDir( pj );

            Utils.copyFromPlugin( new Path( "libs/formgen-ext.jar" ),
                                  webInfLib.getFile( "formgen-ext.jar" ) );

            monitor.worked( 1 );
        }
        <span class="java-keyword">finally</span>
        {
            monitor.done();
        }

    }
}
</pre>
</div>

<p>Once the install actions have been implemented, you should be able to select
the FormGen facets on the Facets Selection Page of the Dynamic Web Project Wizard
without getting any error messages. You should also be able to complete the
project creation and see the following highlighted artifacts in the new project.
These artifacts have been created by the FormGen facet install delegates.</p>

<div class="screen-shot"><img src="images/screen03.gif"/></div>

<h2><a name="creating.categories">5. Creating Categories</a></h2>

<p>Project facets can be grouped into categories in order to provide the "one
click" exprience for novice users and retain the fine-grained control for advanced 
users. You are told that most of FormGen users always add both of the jars to
their web apps. These users would benefit from having the FormGen facets grouped
into a category and so we will do just that.</p>

<p>Here is what that part of the extension point schema looks like:</p>

<div class="code">
<pre class="code-xml"><span class="context-code">&lt;extension point="org.eclipse.wst.common.project.facet.core.facets"&gt;</span>
  &lt;category id="<span class="schema-type">{string}</span>"&gt;
    &lt;label&gt;<span class="schema-type">{string}</span>&lt;/label&gt;
    &lt;description&gt;<span class="schema-type">{string}</span>&lt;/description&gt; <span class="schema-control">(optional)</span>
  &lt;/category&gt;
  <span class="context-code">&lt;project-facet&gt;</span>
    &lt;category&gt;<span class="schema-type">{string}</span>&lt;/category&gt; <span class="schema-control">(optional)</span>
  <span class="context-code">&lt;/project-facet&gt;</span>
<span class="context-code">&lt;/extension&gt;</span>
</pre>
</div>

<p>We can now create a category around the FormGen facets.</p>

<div class="code">
<pre class="code-xml"><span class="context-code">&lt;extension point="org.eclipse.wst.common.project.facet.core.facets"&gt;</span>

  &lt;category id="<span class="schema-type">formgen.category</span>"&gt;
    &lt;label&gt;<span class="schema-type">FormGen</span>&lt;/label&gt;
    &lt;description&gt;<span class="schema-type">Enables generation of HTML forms based on XML definition files.</span>&lt;/description&gt;
  &lt;/category&gt;

  <span class="context-code">&lt;project-facet id="formgen.core"&gt;</span>
    &lt;category&gt;<span class="schema-type">formgen.category</span>&lt;/category&gt;
  <span class="context-code">&lt;/project-facet&gt;</span>

  <span class="context-code">&lt;project-facet id="formgen.ext"&gt;</span>
    &lt;category&gt;<span class="schema-type">formgen.category</span>&lt;/category&gt;
  <span class="context-code">&lt;/project-facet&gt;</span>

<span class="context-code">&lt;/extension&gt;</span>
</pre>
</div>

<p>Once the above change has been put in place, the facets selection page should 
look like this:</p>

<div class="screen-shot"><img src="images/screen04.gif"/></div>

<h2><a name="decorating">6. Decorating</a></h2>

<p>Custom icons can be provided for facets and categories. If an icon is not
provided, a default icon is used. The icons are helpful as a way to better
differentiate facets and to make them stand out.</p>

<p>Here is what that extension point looks like:</p>

<div class="code">
<pre class="code-xml">&lt;extension point="org.eclipse.wst.common.project.facet.ui.images"&gt;
  &lt;image facet="<span class="schema-type">{string}</span>" path="<span class="schema-type">{string}</span>"/&gt; <span class="schema-control">(0 or more)</span>
  &lt;image category="<span class="schema-type">{string}</span>" path="<span class="schema-type">{string}</span>"/&gt; <span class="schema-control">(0 or more)</span>
&lt;/extension&gt;
</pre>
</div>

<p>Your starter project came with three icons in the <code>icons</code> folder.
We will now associate them with the FormGen facets and the category.</p>

<div class="code">
<pre class="code-xml">&lt;extension point="<span class="xml-text">org.eclipse.wst.common.project.facet.ui.images</span>"&gt;
  &lt;image facet="<span class="xml-text">formgen.core</span>" path="<span class="xml-text">icons/formgen-core.gif</span>"/&gt;
  &lt;image facet="<span class="xml-text">formgen.ext</span>" path="<span class="xml-text">icons/formgen-ext.gif</span>"/&gt;
  &lt;image category="<span class="xml-text">formgen.category</span>" path="<span class="xml-text">icons/formgen-cat.gif</span>"/&gt;
&lt;/extension&gt;
</pre>
</div>

<p>Once the above snippet has been added to your plugin.xml file, the facets
selection page should look like this:</p>

<div class="screen-shot"><img src="images/screen05.gif"/></div>

<h2><a name="adding.wizard.pages">7. Adding Wizard Pages</a></h2>

<p>It is often desirable to gather user input prior to installing a facet.
The framework allows a sequence of wizard pages to be associated with facet
actions. The supplied wizard pages are shown after the facets selection
page. Based on user feedback, you known that FormGen users often customize
the URL pattern of the FormGen servlet so you would like to give them the ability
to do that in the wizard when the FormGen facets are being installed.</p>

<p>Here is what the relevant parts of the extension points look like:</p>

<div class="code">
<pre class="code-xml"><span class="context-code">&lt;extension point="org.eclipse.wst.common.project.facet.core.facets"&gt;
  &lt;action&gt;</span>
    &lt;config-factory class="<span class="schema-type">class:org.eclipse.wst.common.project.facet.core.IActionConfigFactory</span>"/&gt;
  <span class="context-code">&lt;/action&gt;
&lt;/extension&gt;</span>

&lt;extension point="<span class="xml-text">org.eclipse.wst.common.project.facet.ui.wizardPages</span>"&gt;
  &lt;wizard-pages action="<span class="schema-type">{string}</span>"&gt; <span class="schema-control">(0 or more)</span>
    &lt;page class="<span class="schema-type">{class:org.eclipse.wst.common.project.facet.ui.IFacetWizardPage}</span>"/> <span class="schema-control">(1 or more)</span>
  &lt;/wizard-pages&gt;
&lt;/extension&gt;  
</pre>
</div>

<p>One thing to note here is that in order to enable communication between the
facet action delegate and the wizard pages, we go back to the action declaration
and provide an action config factory. The object created by the factory is 
populated by the wizard pages and is read by the action delegate. No restrictions
are placed on the shape of the config object. You may choose to implement a custom
class or you can use a something generic like <code>java.util.HashMap</code>.</p>

<p>Another thing to note is that the <code>wizardPages</code> extension point refers
to the actions by their ids, so it becomes more important to explicitly specify
the id rather than letting the framework automatically generate one.</p>

<p>Here are the interfaces that are used in the above extension point schema:</p> 

<div class="code">
<pre class="java-code"><span class="java-keyword">package</span> org.eclipse.wst.common.project.facet.core;

<span class="java-keyword">import</span> org.eclipse.core.runtime.CoreException;

<span class="java-comment">/**
 * This interface is implemented in order to provide a method for creating 
 * a config object that will be used for parameterizing the facet action
 * delegate.
 */</span>

<span class="java-keyword">public interface</span> IActionConfigFactory
{
    <span class="java-comment">/**
     * Creates a new facet action configuration object. The new configuration
     * object should ideally be populated with reasonable defaults.
     * 
     * <span class="java-javadoc-keyword">@return</span> a new facet action configuration object
     * <span class="java-javadoc-keyword">@throws</span> CoreException if failed while creating the configuration object
     */</span>
    
    Object create() <span class="java-keyword">throws</span> CoreException;
}
</pre>
</div>

<div class="code">
<pre class="java-code"><span class="java-keyword">package</span> org.eclipse.wst.common.project.facet.ui;

<span class="java-keyword">import</span> org.eclipse.jface.wizard.IWizardPage;

<span class="java-comment">/**
 * This interface is implemented by the wizard pages associated with project
 * facet actions.
 */</span>

<span class="java-keyword">public interface</span> IFacetWizardPage <span class="java-keyword">extends</span> IWizardPage
{
    <span class="java-comment">/**
     * The framework will call this method in order to provide the wizard
     * context to the wizard page. The wizard context can be used to find out
     * about other actions being configured by the wizard.
     * 
     * <span class="java-javadoc-keyword">@param</span> context the wizard context
     */</span>
    
    <span class="java-keyword">void</span> setWizardContext( IWizardContext context );
    
    <span class="java-comment">/**
     * The framework will call this method in order to provide the action config
     * object that the wizard page should save user selection into. The
     * populated config object will then be passed to the action delegate.
     * 
     * <span class="java-javadoc-keyword">@param</span> config the action config object
     */</span>
    
    <span class="java-keyword">void</span> setConfig( Object config );
    
    <span class="java-comment">/**
     * This method is called after the user has pressed the <code>Finish</code>
     * button. It allows the wizard page to transfer user selection into the
     * config object. Alternative, instead of using this method, the wizard
     * page could update the model on the fly as the user is making changes.
     */</span>

    <span class="java-keyword">void</span> transferStateToConfig();
}
</pre>
</div>

<p>We will now implement a wizard page for the <code>facet.core</code> facet
install action. The wizard page will allow the user to change the default
servlet URL pattern for the FormGen servlet.</p>

<div class="code">
<pre class="code-xml"><span class="context-code">&lt;extension point="org.eclipse.wst.common.project.facet.core.facets"&gt;
  &lt;project-facet-version facet="formgen.core" version="1.0"&gt;
    &lt;action type="INSTALL"</span> id="<span class="xml-text">formgen.core.install</span>"<span class="context-code">&gt;</span>
      &lt;config-factory class="<span class="xml-text">com.formgen.eclipse.FormGenCoreFacetInstallConfig$Factory</span>"/&gt;
    <span class="context-code">&lt;/action&gt;
  &lt;/project-facet-version&gt;
&lt;/extension&gt;</span>

&lt;extension point="<span class="xml-text">org.eclipse.wst.common.project.facet.ui.wizardPages</span>"&gt;
  &lt;wizard-pages action="<span class="xml-text">formgen.core.install</span>"&gt;
    &lt;page class="<span class="schema-type">com.formgen.eclipse.FormGenCoreFacetInstallPage</span>"/>
  &lt;/wizard-pages&gt;
&lt;/extension&gt;  
</pre>
</div>

<div class="code">
<pre class="java-code"><span class="java-keyword">package</span> com.formgen.eclipse;

<span class="java-keyword">import</span> org.eclipse.wst.common.project.facet.core.IActionConfigFactory;

<span class="java-keyword">public final class</span> FormGenCoreFacetInstallConfig
{
    <span class="java-keyword">private</span> String urlPattern = <span class="java-literal">"*.form"</span>;

    <span class="java-keyword">public</span> String getUrlPattern()
    {
        <span class="java-keyword">return this</span>.urlPattern;
    }

    <span class="java-keyword">public void</span> setUrlPattern( <span class="java-keyword">final</span> String urlPattern )
    {
        <span class="java-keyword">this</span>.urlPattern = urlPattern;
    }

    <span class="java-keyword">public static final class</span> Factory <span class="java-keyword">implements</span> IActionConfigFactory
    {
        <span class="java-keyword">public</span> Object create()
        {
            <span class="java-keyword">return new</span> FormGenCoreFacetInstallConfig();
        }
    }
}
</pre>
</div>

<div class="code">
<pre class="java-code"><span class="java-keyword">package</span> com.formgen.eclipse;

<span class="java-keyword">import</span> org.eclipse.swt.SWT;
<span class="java-keyword">import</span> org.eclipse.swt.layout.GridData;
<span class="java-keyword">import</span> org.eclipse.swt.layout.GridLayout;
<span class="java-keyword">import</span> org.eclipse.swt.widgets.Composite;
<span class="java-keyword">import</span> org.eclipse.swt.widgets.Label;
<span class="java-keyword">import</span> org.eclipse.swt.widgets.Text;
<span class="java-keyword">import</span> org.eclipse.wst.common.project.facet.ui.AbstractFacetWizardPage;

<span class="java-keyword">public final class</span> FormGenCoreFacetInstallPage <span class="java-keyword">extends</span> AbstractFacetWizardPage
{
    <span class="java-keyword">private</span> FormGenCoreFacetInstallConfig config;
    <span class="java-keyword">private</span> Text urlPatternTextField;

    <span class="java-keyword">public</span> FormGenCoreFacetInstallPage()
    {
        <span class="java-keyword">super</span>( <span class="java-literal">"formgen.core.facet.install.page"</span> );

        setTitle( <span class="java-literal">"FormGen Core"</span> );
        setDescription( <span class="java-literal">"Configure the FormGen servlet."</span> );
    }

    <span class="java-keyword">public void</span> createControl( <span class="java-keyword">final</span> Composite parent )
    {
        <span class="java-keyword">final</span> Composite composite = <span class="java-keyword">new</span> Composite( parent, SWT.NONE );
        composite.setLayout( <span class="java-keyword">new</span> GridLayout( 1, <span class="java-keyword">false</span> ) );

        <span class="java-keyword">final</span> Label label = <span class="java-keyword">new</span> Label( composite, SWT.NONE );
        label.setLayoutData( gdhfill() );
        label.setText( <span class="java-literal">"URL Pattern:"</span> );

        <span class="java-keyword">this</span>.urlPatternTextField = <span class="java-keyword">new</span> Text( composite, SWT.BORDER );
        <span class="java-keyword">this</span>.urlPatternTextField.setLayoutData( gdhfill() );
        <span class="java-keyword">this</span>.urlPatternTextField.setText( this.config.getUrlPattern() );

        setControl( composite );
    }

    <span class="java-keyword">public void</span> setConfig( <span class="java-keyword">final</span> Object config )
    {
        <span class="java-keyword">this</span>.config = (FormGenCoreFacetInstallConfig) config;
    }

    <span class="java-keyword">public void</span> transferStateToConfig()
    {
        <span class="java-keyword">this</span>.config.setUrlPattern( <span class="java-keyword">this</span>.urlPatternTextField.getText() );
    }

    <span class="java-keyword">private static</span> GridData gdhfill()
    {
        <span class="java-keyword">return new</span> GridData( GridData.FILL_HORIZONTAL );
    }
}
</pre>
</div>

<div class="code">
<pre class="java-code"><span class="java-context"><span class="java-context-keyword">package</span> com.formgen.eclipse;

<span class="java-context-keyword">import</span> org.eclipse.core.resources.IFolder;
<span class="java-context-keyword">import</span> org.eclipse.core.resources.IProject;
<span class="java-context-keyword">import</span> org.eclipse.core.runtime.CoreException;
<span class="java-context-keyword">import</span> org.eclipse.core.runtime.IProgressMonitor;
<span class="java-context-keyword">import</span> org.eclipse.core.runtime.Path;
<span class="java-context-keyword">import</span> org.eclipse.wst.common.project.facet.core.IDelegate;
<span class="java-context-keyword">import</span> org.eclipse.wst.common.project.facet.core.IProjectFacetVersion;

<span class="java-context-keyword">public final class</span> FormGenCoreFacetInstallDelegate <span class="java-context-keyword">implements</span> IDelegate
{
    <span class="java-context-keyword">public void</span> execute( <span class="java-context-keyword">final</span> IProject pj,
                         <span class="java-context-keyword">final</span> IProjectFacetVersion fv,
                         <span class="java-context-keyword">final</span> Object config,
                         <span class="java-context-keyword">final</span> IProgressMonitor monitor )

        <span class="java-context-keyword">throws</span> CoreException

    {
        monitor.beginTask( "", 2 );

        try
        {</span>
            <span class="java-keyword">final</span> FormGenCoreFacetInstallConfig cfg
                = (FormGenCoreFacetInstallConfig) config;

            <span class="java-context"><span class="java-context-keyword">final</span> IFolder webInfLib = Utils.getWebInfLibDir( pj );

            Utils.copyFromPlugin( <span class="java-context-keyword">new</span> Path( "libs/formgen-core.jar" ),
                                  webInfLib.getFile( "formgen-core.jar" ) );

            monitor.worked( 1 );</span>

            Utils.registerFormGenServlet( pj, cfg.getUrlPattern() );

            <span class="java-context">monitor.worked( 1 );
        }
        <span class="java-context-keyword">finally</span>
        {
            monitor.done();
        }
    }
}</span>
</pre>
</div>

<p>Once the above code changes have been made you should see another page appear
in the Dynamic Web Project Wizard after the FormGen facets are selected. The
new page will appear after the Web Module page, which is associated with the
<code>jst.web</code> facet. That's because <code>formgen.core</code> facet
depends on the <code>jst.web</code> facet. If this dependency relationship 
was not specified the relative order of these pages would be unspecified.</p>

<div class="screen-shot"><img src="images/screen06.gif"/></div>

<h2><a name="defining.presets">8. Defining Presets</a></h2>

<p>As the number of available facets grows, it becomes increasingly difficult
for the user to figure out which combinations make sense. This is where presets
come in. Presets (or Configurations, as they are referred to in the UI) are
simply combinations of facets that someone has determined are useful in certain
situations. Presets can be created by the user or supplied via an extension
point.</p>

<p>Here is the extension point schema for declaring presets:</p>

<div class="code">
<pre class="code-xml">&lt;extension point="<span class="xml-text">org.eclipse.wst.common.project.facet.core.presets</span>"&gt;
  &lt;static-preset id="<span class="schema-type">{string}</span>" extends="<span class="schema-type">{string}</span>"&gt;
    &lt;label&gt;<span class="schema-type">{string}</span>&lt;/label&gt;
    &lt;description&gt;<span class="schema-type">{string}</span>&lt;/description&gt; <span class="schema-control">(optional)</span>
    &lt;facet id="<span class="schema-type">{string}</span>" version="<span class="schema-type">{string}</span>"/&gt; <span class="schema-control">(1 or more)</span>
  &lt;/static-preset&gt;
&lt;/extension&gt;
</pre>
</div>

<p>Note that in order for a preset to apply to a given faceted project, the
preset needs to include all of the project's "fixed facets". Fixed facets are
the facets that are key to the proper operation of that project type and so
cannot be removed. You can identify fixed facets by the lock icon.</p>

<p>Let's now create a preset that includes formgen facets.</p>

<div class="code">
<pre class="code-xml">&lt;extension point="<span class="xml-text">org.eclipse.wst.common.project.facet.core.presets</span>"&gt;
  &lt;static-preset id="<span class="xml-text">formgen.preset</span>"&gt;
    &lt;label&gt;<span class="xml-text">FormGen Web Project</span>&lt;/label&gt;
    &lt;description&gt;<span class="xml-text">Creates a web project with FormGen functionality.</span>&lt;/description&gt;
    &lt;facet id="<span class="xml-text">jst.java</span>" version="<span class="xml-text">5.0</span>"/&gt;
    &lt;facet id="<span class="xml-text">jst.web</span>" version="<span class="xml-text">2.2</span>"/&gt;
    &lt;facet id="<span class="xml-text">formgen.core</span>" version="<span class="xml-text">1.0</span>"/&gt;
    &lt;facet id="<span class="xml-text">formgen.ext</span>" version="<span class="xml-text">1.0</span>"/&gt;
  &lt;/static-preset&gt;
&lt;/extension&gt;
</pre>
</div>

<p>Here is how the preset shows up on the facets selection page:</p>

<div class="screen-shot"><img src="images/screen07.gif"/></div>

<p>The preset can also be selected on the first page of all WTP project
creation wizards. Here is how this looks in the Dynamic Web Project wizard:</p>

<div class="screen-shot"><img src="images/screen08.gif"/></div>

<h2><a name="runtime.mappings">9. Specifying Runtime Support Mappings</a></h2>

<p>One of the most important functions of the faceted project framework is to
be able to accurately model whether a certain server runtime supports a
given project. We do that by "mapping" project facets to runtime components
that support them. If the artifacts created by a facet will run on any server
that supports all of the facet's upstream dependencies, then the <code>any</code>
wildcard can be used.</p>

<p>It's important to note that every facet needs to specify a support mapping of
some kind. Facets that don't specify any support mappings are treated as not
supported by any runtime, which is not very useful.</p>

<p>Here is the extension point that's used for specifying the support mappings:</p>

<div class="code">
<pre class="code-xml">&lt;extension point="<span class="xml-text">org.eclipse.wst.common.project.facet.core.runtimes</span>"&gt;
  &lt;supported&gt; <span class="schema-control">(0 or more)</span>
    &lt;runtime-component any="<span class="schema-type">{boolean}</span>"/&gt; <span class="schema-control">(optional)</span>
    &lt;runtime-component id="<span class="schema-type">{string}</span>"/ version="<span class="schema-type"><span class="schema-type-link">{<a href="#version.expressions">version.expr</a>}</span></span>"/&gt; <span class="schema-control">(0 or more)</span>
    &lt;facet id="<span class="schema-type">{string}</span>"/ version="<span class="schema-type"><span class="schema-type-link">{<a href="#version.expressions">version.expr</a>}</span></span>"/&gt; <span class="schema-control">(1 or more)</span>
  &lt;/supported&gt;
&lt;/extension&gt;
</pre>
</div>

<p>The <code>&lt;supported&gt;</code> block can reference any number of runtime
components as well as any number of facets. The semantics of that is to declare 
as supported every combination in the resulting cross-product.</p> 

<p>The <code>version</code> attributes of the <code>&lt;runtime-component&gt;</code> 
and <code>&lt;facet&gt;</code> elements can be omitted to include all versions.</p>

<p>The FormGen facets don't have any special support requirements. They will run
on any server that supports the j2ee servlet spec. We will use the <code>any</code>
wildcard to designate that.</p>

<div class="code">
<pre class="code-xml">&lt;extension point="<span class="xml-text">org.eclipse.wst.common.project.facet.core.runtimes</span>"&gt;
  &lt;supported&gt;
    &lt;runtime-component any="<span class="xml-text">true</span>"/&gt;
    &lt;facet id="<span class="xml-text">formgen.core</span>"/&gt;
    &lt;facet id="<span class="xml-text">formgen.ext</span>"/&gt;
  &lt;/supported&gt;
&lt;/extension&gt;
</pre>
</div>

<p>Alternative, if for some reason the FormGen functionality required a specific
runtime, such as Tomcat, we would use something like the this instead:</p>

<div class="code">
<pre class="code-xml">&lt;extension point="<span class="xml-text">org.eclipse.wst.common.project.facet.core.runtimes</span>"&gt;
  &lt;supported&gt;
    &lt;runtime-component id="<span class="xml-text">org.eclipse.jst.server.tomcat</span>" version="<span class="xml-text">[5.0</span>"/&gt;
    &lt;facet id="<span class="xml-text">formgen.core</span>"/&gt;
    &lt;facet id="<span class="xml-text">formgen.ext</span>"/&gt;
  &lt;/supported&gt;
&lt;/extension&gt;
</pre>
</div>

<p>The above more restrictive specification will prevent FormGen facets from
being selected if the project is targetted to any runtime other than Apache
Tomcat 5.0 or newer.</p>

<h2><a name="summary">10. Summary</a></h2>

<p>In this tutorial we created two fully-functional project facets by specifying
constraints, implementing actions, grouping facets into categories, and creating
wizard pages to allow users to parameterize facet installation. You should now
be well prepared to create your own facets. Additional information not covered
by this tutorial can be found in the following appendix sections.</p> 

<h2><a name="custom.version.comparators">Appendix A: Custom Version Comparators</a></h2>

<p>The faceted project framework needs to be able to compare facet version
strings. The framework supplies a default version comparator that can handle
version strings encoded using the standard decimal notation (such as 1.2 or
5.66.5533), but if you want to use a different format you will need to supply
a custom version comparator.</p>

<p>Here is how you plug in a custom version comparator:</p>

<div class="code">
<pre class="code-xml"><span class="context-code">&lt;extension point="org.eclipse.wst.common.project.facet.core.facets"&gt;
  &lt;project-facet&gt;</span>
    &lt;version-comparator class="<span class="schema-type">{class:java.util.Comparator&lt;String&gt;}</span>"/&gt;
  <span class="context-code">&lt;/project-facet&gt;
&lt;/extension&gt;</span>
</pre>
</div>

<p>When implementing a version comparator you can either start from scratch
or subclass the default version comparator (<code>org.eclipse.wst.common.project.facet.core.DefaultVersionComparator</code>).
Subclassing the default version comparator makes sense if the version format
differs only slightly from the default format, such as using separators other
than dots or having non-numeric characters at certain positions. Here are the
protected methods exposed by the <code>DefaultVersionComparator</code> class
that are designed to be overridden:</p>

<div class="code">
<pre class="java-code"><span class="java-comment">/**
 * Returns the string containing the separator characters that should be
 * used when breaking the version string into segments. The default
 * implementation returns ".". Subclasses can override this method.
 * 
 * <span class="java-javadoc-keyword">@return</span> the separator characters
 */</span>
    
<span class="java-keyword">protected</span> String getSeparators();
    
<span class="java-comment">/**
 * Parses a segment of the version string. The default implementation parses
 * the first segment as an integer (leading zeroes are ignored) and the
 * rest of the segments as decimals (leading zeroes are kept). Subclasses 
 * can override this method to provide custom parsing for any number of 
 * segments.
 * 
 * <span class="java-javadoc-keyword">@param</span> version the full version string
 * <span class="java-javadoc-keyword">@param</span> segment the version segment
 * <span class="java-javadoc-keyword">@param</span> position the position of the segment in the version string
 * <span class="java-javadoc-keyword">@return</span> the parsed representation of the segment as a {@see Comparable}
 * <span class="java-javadoc-keyword">@throws</span> VersionFormatException if encountered an error while parsing
 */</span>
    
<span class="java-keyword">protected</span> Comparable parse( <span class="java-keyword">final</span> String version,
                            <span class="java-keyword">final</span> String segment,
                            <span class="java-keyword">final</span> int position )
    
    <span class="java-keyword">throws</span> VersionFormatException;
</pre>
</div>

<h2><a name="version.expressions">Appendix B: Version Expressions</a></h2>

<p>A version expression is a syntax for specifying more than one version. The
version expressions are used throughout the framework's extension points, but
you will most likely first encounter them while specifying the <code>requires</code> 
constraint.</p>

<p>A version expression is composed of multiple segments separated by commas. 
The commas function as an OR operation. Each segment is either a single version, 
a range, or a wildcard. Ranges are represented by bracket and dash notation such 
as [x-y). A bracket means inclusive, while the parenthesis means exclusive. Open 
ended ranges are also supported. A wildcard (represented by '*' character) can
be used to match any version. It is not possible to use the wildcard to match
part of the version string.</p>

<p>Here are some examples:</p>

<div class="code">
<pre class="java-code">1.2
1.2,1.5,3.2
[1.2-3.2]
[3.7-5.0)
[3.7
5.0)
1.2,[3.0-4.5),[7.3
*
</pre>
</div>

<h2><a name="property.tester">Appendix C: Property Tester</a></h2>

<p>A property tester is provided by the Faceted Project Framework that allows
the presence of the facet in a project to be tested by any extension point that
works with <code>org.eclipse.core.expressions</code> package. The most common
usage is to enable user interface elements (such as actions and project property
pages). The property name is <code>org.eclipse.wst.common.project.facet.core.projectFacet</code>
and the value is either a facet id or a facet id followed by a colon and
a <a href="#version.expressions">version expression</a>.</p>

<p>Here is an example of using facets property tester to control enablement of
a project properties page:</p>

<div class="code">
<pre class="code-xml">&lt;extension point="<span class="xml-text">org.eclipse.ui.propertyPages</span>"&gt;
  &lt;page 
    adaptable="<span class="xml-text">true</span>"
    objectClass="<span class="xml-text">org.eclipse.core.resources.IProject</span>"
    name="<span class="xml-text">FormGen Properties</span>"
    class="<span class="xml-text">com.formgen.eclipse.FormGenPropertiesPage</span>"
    id="<span class="xml-text">org.eclipse.jst.j2ee.internal.J2EEDependenciesPage</span>"&gt;
    &lt;enabledWhen&gt;
      &lt;test 
        forcePluginActivation="<span class="xml-text">true</span>"
        property="<span class="xml-text">org.eclipse.wst.common.project.facet.core.projectFacet</span>"
        value="<span class="xml-text">formgen.core</span>"/&gt;
    &lt;/enabledWhen&gt;          
  &lt;/page&gt;
&lt;/extension&gt;
</pre>
</div>

<h2><a name="wizard.context">Appendix D: Wizard Context</a></h2>

<p>Sometimes it desirable to be able to adjust the behavior of facet action 
wizard pages based on user input in the wizard pages of other facets. The
<code>IWizardContext</code> interface can be used for this purpose. The wizard
page gets a handle on <code>IWizardContext</code> interface when it's
<code>setWizardContext</code> method is called. When writing code that relies
on the wizard context, there are a couple of points you should keep in mind.</p>

<ol>

  <li><p>The facet whose value you wish to check may have already been installed
    in the past. In that case you will not find it's install configuration in
    the wizard context. You will need to write conditional logic that will
    consult the wizard context or looks at project state on disk.</p></li>
    
  <li><p>You should make sure that a reasonable default is provided in your
    config object for the API-only scenario where your wizard page will not be
    involved.</p>
    
</ol>

<p>Here is what the <code>IWizardContext</code> interface looks like:</p>

<div class="code">
<pre class="java-code"><span class="java-keyword">package</span> org.eclipse.wst.common.project.facet.ui;

<span class="java-keyword">import</span> java.util.Set;

<span class="java-keyword">import</span> org.eclipse.core.runtime.CoreException;
<span class="java-keyword">import</span> org.eclipse.wst.common.project.facet.core.IProjectFacetVersion;
<span class="java-keyword">import</span> org.eclipse.wst.common.project.facet.core.IFacetedProject.Action;
<span class="java-keyword">import</span> org.eclipse.wst.common.project.facet.core.IFacetedProject.Action.Type;

<span class="java-comment">/**
 * The interface exposed to the facet action wizard pages that allows them
 * to gather information about the wizard state.
 */</span>

<span class="java-keyword">public interface</span> IWizardContext 
{
    <span class="java-comment">/**
     * Returns the name of the project that the wizard is operating on. If the
     * wizard is in the project creation mode, the project will not yet exist
     * in the workspace.
     * 
     * <span class="java-javadoc-keyword">@return</span> the name of the project that the wizard is operating on
     */</span>
    
    String getProjectName();
    
    <span class="java-comment">/**
     * Returns the set of facets currently selected in the wizard. If the wizard
     * is in the add/remove facets mode (vs. project creation), this method will 
     * return the set of facets currently installed in a project after being 
     * modified by the current set of actions. 
     * 
     * <span class="java-javadoc-keyword">@return</span> the set of facets currently selected in the wizard (element type:
     *   {<span class="java-javadoc-keyword">@see</span> IProjectFacetVersion})
     */</span>
    
    Set getSelectedProjectFacets();
    
    <span class="java-comment">/**
     * Determines whether the specified facet is currently selected in the
     * wizard. See {@see getSelectedProjectFacets()} for more information.
     * 
     * <span class="java-javadoc-keyword">@param</span> fv the project facet version object
     * <span class="java-javadoc-keyword">@return</span> <code>true</code> if an only if the provided project facet is
     *   currently selected in the wizard
     */</span>
    
    <span class="java-keyword">boolean</span> isProjectFacetSelected( IProjectFacetVersion fv );
    
    <span class="java-comment">/**
     * Returns the set of actions currently specified by the user.
     * 
     * <span class="java-javadoc-keyword">@return</span> the set of actions currently specified by the user
     */</span>
    
    Set getActions();
    
    <span class="java-comment">/**
     * Finds the action of specified type that applies to the specified facet,
     * if such action exists. If the wizard is in the add/remove facets mode
     * (vs. project creation), you cannot depend on finding the install action
     * for a required facet as that facet may have already been installed.
     * 
     * <span class="java-javadoc-keyword">@param</span> type the action type
     * <span class="java-javadoc-keyword">@param</span> fv the project facet version object
     * <span class="java-javadoc-keyword">@return</span> the action object or <code>null</code>
     */</span>
    
    Action getAction( Action.Type type,
                      IProjectFacetVersion fv );
}
</pre>
</div>

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