src/site/xdoc/guide/contexts-evaluators.xml - commons-scxml - Git at Google

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 <document>

  <properties>
   <title>API notes - Contexts and Evaluators</title>
   <author email="dev@commons.apache.org">Commons Documentation Team</author>
  </properties>

  <body>

   <section name="Commons SCXML - Pluggable expression languages">

    <p>The SCXML specification allows implementations to support
       multiple expression languages to enable using SCXML documents
       in varying environments. These expressions become part of
       attribute values for executable content, such as:

     <pre>
      &lt;var name="foo" expr="1 + 2 + bar" /&gt;
     </pre>

       or are used to evaluate the boolean guard conditions that
       decide whether or not a particular transition is followed
       once its associated trigger event is received, such as:

     <pre>
      &lt;transition event="day.close" cond="day eq 'Friday'"
                  target="weekend" /&gt;
     </pre>

       To that end, the <code>Context</code>
       and <code>Evaluator</code> interfaces serve as adapters to the
       particular expression language APIs for a given usecase.</p>

    <p>Variable resolution bubbles up from the current state up to the
       document root, similar to variable shadowing via blocks in a
       procedural language.</p>

    <subsection name="What is a Context?">
     <p>The <code>Context</code> is a collection of variables that defines
        a variable "scope". Each &lt;state&gt; element within an SCXML
        document gets its own Context or variable scope.</p>
    </subsection>

    <subsection name="What is a root context?">
     <p>The root context is the context that may be supplied to the
        Commons SCXML engine as representing the variables in the
        "host environment". See
        <code>SCXMLExecutor#setRootContext(Context)</code> from the
        <a href="../apidocs/index.html">Javadoc</a>.</p>
    </subsection>

    <subsection name="What is an Evaluator?">
     <p>The <code>Evaluator</code> is a component with the capability
        of parsing and evaluating expressions. It is the "expression
        language engine".</p>
    </subsection>

   </section>

   <section name="Available expression languages">

    <p>Commons SCXML currently supports using Commons JEXL, Javascript, XPath and
       Groovy as the expression language.
       The expressions throughout the document must be homogeneous.
       This also applies to any external documents that may be referred
       by this document, for example via "src" attributes, like so:

     <pre>
      &lt;state id="foo" src="foo.xml"&gt;
       &lt;!-- Something, possibly very interesting, here --&gt;
      &lt;/state&gt;
     </pre>

       Here, foo.xml must use the same expression language as
       the document above that hosts the state foo.<br/>

       Check out the <a href="core-engine.html">engine API docs</a>
       on how to plug in the suitable root context and evaluator
       tuple.</p>

    <subsection name="Commons JEXL">
     <p>See
     <a href="../apidocs/org/apache/commons/scxml2/env/jexl/package-summary.html">
     org.apache.commons.scxml2.env.jexl package summary</a> for the
     relevant root context and evaluator tuple to use.</p>
    </subsection>

     <subsection name="Javascript">
       <p>See
         <a href="../apidocs/org/apache/commons/scxml2/env/javascript/package-summary.html">
           org.apache.commons.scxml2.env.javascript package summary</a> for the
         relevant root context and evaluator tuple to use.</p>
     </subsection>

     <subsection name="Groovy">
     <p>See
     <a href="../apidocs/org/apache/commons/scxml2/env/groovy/package-summary.html">
     org.apache.commons.scxml2.env.groovy package summary</a> for the
     relevant root context and evaluator tuple to use.</p>
    </subsection>

   </section>

   <section name="Method invocation in expressions">

    <p>Commons SCXML uses the mechanisms provided by the expression language
    chosen for the document to support method invocation. Commons JEXL
    allow for method invocations as follows:</p>

    <subsection name="Commons JEXL">
     <p>See Commons JEXL reference for
     <a href="http://commons.apache.org/jexl/reference/syntax.html#Functions">
     builtin JEXL functions</a> and the calling methods section of the
     <a href="http://commons.apache.org/jexl/reference/examples.html">
     examples page</a>. As a summary, if the context contains an object
     under name <code>foo</code> which has an accessible method
     <code>bar()</code>, then the JEXL expression for calling the method is
     <code>foo.bar()</code></p>
    </subsection>

   </section>

  </body>

 </document>
	<?xml version="1.0" encoding="UTF-8"?>
	<!--
	* Licensed to the Apache Software Foundation (ASF) under one or more
	* contributor license agreements. See the NOTICE file distributed with
	* this work for additional information regarding copyright ownership.
	* The ASF licenses this file to You under the Apache License, Version 2.0
	* (the "License"); you may not use this file except in compliance with
	* the License. You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	-->

	<document>

	<properties>
	<title>API notes - Contexts and Evaluators</title>
	<author email="dev@commons.apache.org">Commons Documentation Team</author>
	</properties>

	<body>

	<section name="Commons SCXML - Pluggable expression languages">

	<p>The SCXML specification allows implementations to support
	multiple expression languages to enable using SCXML documents
	in varying environments. These expressions become part of
	attribute values for executable content, such as:

	<pre>
	<var name="foo" expr="1 + 2 + bar" />
	</pre>

	or are used to evaluate the boolean guard conditions that
	decide whether or not a particular transition is followed
	once its associated trigger event is received, such as:

	<pre>
	<transition event="day.close" cond="day eq 'Friday'"
	target="weekend" />
	</pre>

	To that end, the <code>Context</code>
	and <code>Evaluator</code> interfaces serve as adapters to the
	particular expression language APIs for a given usecase.</p>

	<p>Variable resolution bubbles up from the current state up to the
	document root, similar to variable shadowing via blocks in a
	procedural language.</p>

	<subsection name="What is a Context?">
	<p>The <code>Context</code> is a collection of variables that defines
	a variable "scope". Each <state> element within an SCXML
	document gets its own Context or variable scope.</p>
	</subsection>

	<subsection name="What is a root context?">
	<p>The root context is the context that may be supplied to the
	Commons SCXML engine as representing the variables in the
	"host environment". See
	<code>SCXMLExecutor#setRootContext(Context)</code> from the
	<a href="../apidocs/index.html">Javadoc</a>.</p>
	</subsection>

	<subsection name="What is an Evaluator?">
	<p>The <code>Evaluator</code> is a component with the capability
	of parsing and evaluating expressions. It is the "expression
	language engine".</p>
	</subsection>

	</section>

	<section name="Available expression languages">

	<p>Commons SCXML currently supports using Commons JEXL, Javascript, XPath and
	Groovy as the expression language.
	The expressions throughout the document must be homogeneous.
	This also applies to any external documents that may be referred
	by this document, for example via "src" attributes, like so:

	<pre>
	<state id="foo" src="foo.xml">
	<!-- Something, possibly very interesting, here -->
	</state>
	</pre>

	Here, foo.xml must use the same expression language as
	the document above that hosts the state foo.<br/>

	Check out the <a href="core-engine.html">engine API docs</a>
	on how to plug in the suitable root context and evaluator
	tuple.</p>

	<subsection name="Commons JEXL">
	<p>See
	<a href="../apidocs/org/apache/commons/scxml2/env/jexl/package-summary.html">
	org.apache.commons.scxml2.env.jexl package summary</a> for the
	relevant root context and evaluator tuple to use.</p>
	</subsection>

	<subsection name="Javascript">
	<p>See
	<a href="../apidocs/org/apache/commons/scxml2/env/javascript/package-summary.html">
	org.apache.commons.scxml2.env.javascript package summary</a> for the
	relevant root context and evaluator tuple to use.</p>
	</subsection>

	<subsection name="Groovy">
	<p>See
	<a href="../apidocs/org/apache/commons/scxml2/env/groovy/package-summary.html">
	org.apache.commons.scxml2.env.groovy package summary</a> for the
	relevant root context and evaluator tuple to use.</p>
	</subsection>

	</section>

	<section name="Method invocation in expressions">

	<p>Commons SCXML uses the mechanisms provided by the expression language
	chosen for the document to support method invocation. Commons JEXL
	allow for method invocations as follows:</p>

	<subsection name="Commons JEXL">
	<p>See Commons JEXL reference for
	<a href="http://commons.apache.org/jexl/reference/syntax.html#Functions">
	builtin JEXL functions</a> and the calling methods section of the
	<a href="http://commons.apache.org/jexl/reference/examples.html">
	examples page</a>. As a summary, if the context contains an object
	under name <code>foo</code> which has an accessible method
	<code>bar()</code>, then the JEXL expression for calling the method is
	<code>foo.bar()</code></p>
	</subsection>

	</section>

	</body>

	</document>