xdocs/docs/vtl-reference-guide.xml

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<document>

 <properties>
  <title>VTL Reference</title>
  <author email="jvanzyl@zenplex.com">Velocity Documentation Team</author>
  <author email="jcastura@apache.org">John Castura</author>
 </properties>

<body>

<section name="About this Guide" href="AboutthisGuide">
<p>
    This guide is the reference for the Velocity Template Language
    (VTL). For more information, please also refer to the <a
    href="user-guide.html">Velocity User Guide</a>.
</p>

</section>

<section name="References" href="References">
    <subsection name="Variables" href="Variables">
    <p>
    Notation:
    </p>

    <p>
    <strong>$</strong> [ <strong>!</strong> ][ <strong>{</strong> ][
    <strong>a..z</strong>, <strong>A..Z</strong> ][ <strong>a..z</strong>,
    <strong>A..Z</strong>, <strong>0..9</strong>, <strong>-</strong>,
    <strong>_</strong> ][ <strong>}</strong> ]
    </p>

    <p>
    Examples:
    </p>

    <ul>
        <li>Normal notation: <variable>$mud-Slinger_9</variable></li>
        <li>Silent notation: <variable>$!mud-Slinger_9</variable></li>
        <li>Formal notation: <variable>${mud-Slinger_9}</variable></li>
    </ul>
  </subsection>

  <subsection name="Properties" href="Properties">
    <p>
    Notation:
    </p>

    <p>
      <strong>$</strong> [ <strong>{</strong> ][ <strong>a..z</strong>,
      <strong>A..Z</strong> ][ <strong>a..z</strong>, <strong>A..Z</strong>,
      <strong>0..9</strong>, <strong>-</strong>, <strong>_</strong> ]*
      <strong>.</strong>[<strong>a..z</strong>, <strong>A..Z</strong> ][
      <strong>a..z</strong>, <strong>A-Z</strong>, <strong>0..9</strong>,
      <strong>-</strong>, <strong>_</strong> ]* [ <strong>}</strong> ]
    </p>

    <p>
    Examples:
    </p>

    <ul>
        <li>Regular Notation: $customer.Address</li>
        <li>Formal Notation: ${purchase.Total}</li>
    </ul>
  </subsection>

  <subsection name="Methods" href="Methods">
    <p>
    Notation:
    </p>

    <p>
      <strong>$</strong> [ <strong>{</strong> ][ <strong>a..z</strong>,
      <strong>A..Z</strong> ][ <strong>a..z</strong>, <strong>A..Z</strong>,
      <strong>0..9</strong>, <strong>-</strong>, <strong>_</strong> ]*
      <strong>.</strong>[ <strong>a..z</strong>, <strong>A..Z</strong> ][
      <strong>a..z</strong>, <strong>A..Z</strong>, <strong>0..9</strong>,
      <strong>-</strong>, <strong>_</strong> ]*<strong>(</strong> [
      <i>optional parameter list...</i> ] <strong>)</strong> [
      <strong> } </strong>]
    </p>

    <p>
    Examples:
    </p>

    <ul>
      <li>Regular Notation: $customer.getAddress()</li>
      <li>Formal Notation: ${purchase.getTotal()}</li>
      <li>Regular Notation with Parameter List: $page.setTitle( "My Home
      Page" )</li>
    </ul>
  </subsection>

  <p>
  VTL Properties can be used as a shorthand notation for VTL Methods
  that take <em>get</em> and <em>set</em>. Either
  <em>$object.getMethod()</em> or <em>$object.setMethod()</em> can be
  abbreviated as <em>$object.Method</em>. It is generally preferable to
  use a Property when available. The main difference between Properties
  and Methods is that you can specify a parameter list to a Method.
  </p>

</section>

<section name="Directives" href="Directives">
  <subsection name="#set - Establishes the value of a reference" href="set-Establishesthevalueofareference">
    <p>
    Format:
    </p>

    <p>
    <strong>#</strong> [ <strong>{</strong> ] <strong>set</strong> [ <strong>}</strong> ] <strong> ( $</strong>ref <strong>=</strong> [ <strong>"</strong>,
    <strong>'</strong> ]arg[ <strong>"</strong>, <strong>'</strong> ] )
    </p>

    <p>
    Usage:
    </p>

    <ul>
    <li><em>$ref</em> - The LHS of the assignment must be a variable
    reference or a property reference.</li>
    <li><em>arg</em> - The RHS of the assignment, <em>arg</em> is parsed
    if enclosed in double quotes, and not parsed if enclosed in single
    quotes.  If the RHS evaluates to <em>null</em>, it is <b>not</b>
    assigned to the LHS.</li>
    </ul>

    <p>
    Examples:
    </p>

    <ul>
      <li>Variable reference: #set( $monkey = $bill )</li>
      <li>String literal: #set( $monkey.Friend = 'monica' )</li>
      <li>Property reference: #set( $monkey.Blame = $whitehouse.Leak
      )</li>
      <li>Method reference: #set( $monkey.Plan = $spindoctor.weave($web)
      )</li>
      <li>Number literal: #set( $monkey.Number = 123 )</li>
      <li>Range operator: #set( $monkey.Numbers = [1..3] )</li>
      <li>Object array: #set( $monkey.Say = ["Not", $my, "fault"] )</li>
    </ul>

    <p>
    The RHS can also be a simple arithmetic expression, such as:
    </p>

    <ul>
      <li>Addition: #set( $value = $foo + 1 )</li>
      <li>Subtraction: #set( $value = $bar - 1 )</li>
      <li>Multiplication: #set( $value = $foo * $bar )</li>
      <li>Division: #set( $value = $foo / $bar )</li>
      <li>Remainder: #set( $value = $foo % $bar )</li>
    </ul>
  </subsection>

  <subsection name="#if/#elseif/#else-outputconditionalontruthofstatements">
    <p>
    Format:
    </p>

    <p>
    <strong>#</strong> [ <strong>{</strong> ] <strong>if</strong> [ <strong>}</strong> ] <strong>(</strong> [condition] <strong>)</strong> [output] [
    <strong>#</strong> [ <strong>{</strong> ] <strong>elseif</strong> [ <strong>}</strong> ] <strong>( </strong>[condition] <strong>)</strong> [output] ]* [
    <strong>#</strong> [ <strong>{</strong> ] <strong>else</strong> [ <strong>}</strong> ]  [output] ]
    <strong>#</strong> [ <strong>{</strong> ] <strong>end</strong> [ <strong>}</strong> ]
    </p>

    <p>
    Usage:
    </p>

    <ul>
    <li><em>condition</em> - If a boolean, considered true if it has a
    true false; if not a boolean, considered true if not null.</li>
    <li><em>output</em> - May contain VTL.</li>
    </ul>

    <p>
    Examples (showing different operators):
    </p>

    <table>
    <tr>
        <th>Operator Name</th>
        <th>Symbol</th>
        <th>Alternative Symbol</th>
        <th>Example</th>
    </tr>
    <tr>
        <td>Equals Number</td>
        <td>==</td>
        <td>eq</td>
        <td> #if( $foo == 42 )</td>
    </tr>
    <tr>
        <td>Equals String</td>
        <td>==</td>
        <td>eq</td>
        <td> #if( $foo == "bar" )</td>
    </tr>
    <tr>
        <td>Object Equivalence</td>
        <td>==</td>
        <td>eq</td>
        <td> #if( $foo == $bar )</td>
    </tr>
    <tr>
        <td>Not Equals</td>
        <td>!=</td>
        <td>ne</td>
        <td> #if( $foo != $bar )</td>
    </tr>
    <tr>
        <td>Greater Than</td>
        <td>&gt;</td>
        <td>gt</td>
        <td> #if( $foo > 42 )</td>
    </tr>
    <tr>
        <td>Less Than</td>
        <td>&lt;</td>
        <td>lt</td>
        <td> #if( $foo &lt; 42 )</td>
    </tr>
    <tr>
        <td>Greater Than or Equal To</td>
        <td>&gt;=</td>
        <td>ge</td>
        <td> #if( $foo >= 42 )</td>
    </tr>
    <tr>
        <td>Less Than or Equal To</td>
        <td>&lt;=</td>
        <td>le</td>
        <td> #if( $foo &lt;= 42 )</td>
    </tr>
    <tr>
        <td>Boolean NOT</td>
        <td>!</td>
        <td>not</td>
        <td> #if( !$foo )</td>
    </tr>
   </table>

   <p>Notes:</p>
   <ol>
	<li>
		The == operator can be used to compare numbers, strings, objects of the same class, or objects
		of different classes.  In the last case (when objects are of different classes), the toString()
		method is called on each object and the resulting Strings are compared.
	</li>
	<li>
	 You can also use brackets to delimit directives.  This is especially
    useful when text immediately follows an <code>#else</code> directive.
	</li>
   </ol>

<source><![CDATA[
#if( $foo == $bar)it's true!#{else}it's not!#end</li>
]]></source>


  </subsection>

  <subsection name="#foreach - Loops through a list of objects" href="foreach-Loopsthroughalistofobjects">
    <p>
    Format:
    </p>

    <p>
    <strong>#</strong> [ <strong>{</strong> ] <strong>foreach</strong> [ <strong>}</strong> ] <strong>(</strong> <em>$ref</em> <strong>in</strong> <em>arg</em>
    <strong>)</strong> <em>statement</em>
    <strong>#</strong> [ <strong>{</strong> ] <strong>end</strong> [ <strong>}</strong> ]
    </p>

    <p>
    Usage:
    </p>

    <ul>
    <li><em>$ref</em> - The first variable reference is the item.</li>

    <li><em>arg</em> - May be one of the following: a reference to a
        list (i.e. object array, collection, or map), an array list, or
        the range operator.</li>

    <li>
    <em>statement</em> - What is output each time Velocity finds a
    valid item in the list denoted above as <i>arg</i>.  This output is
    any valid VTL and is rendered each iteration of the loop.
    </li>

    </ul>

    <p>
    Examples of the #foreach(), omitting the statement block :
    </p>

    <ul>
      <li>Reference: #foreach ( $item in $items )</li>
      <li>Array list: #foreach ( $item in ["Not", $my, "fault"] )</li>
      <li>Range operator: #foreach ( $item in [1..3] )</li>
    </ul>

    <p>
    Velocity provides an easy way to get the loop counter so that you
    can do something like the following:
    </p>

<source><![CDATA[
<table>
#foreach( $customer in $customerList )
    <tr><td>$velocityCount</td><td>$customer.Name</td></tr>
#end
</table>
]]></source>

    <p>
    The default name for the loop counter variable reference, which is
    specified in the velocity.properties file, is $velocityCount. By
    default the counter starts at 1, but this can be set to either 0 or
    1 in the <code>velocity.properties</code> file. Here's what the loop
    counter properties section of the <code>velocity.properties</code>
    file appears:
    </p>

<source><![CDATA[
# Default name of the loop counter
# variable reference.
directive.foreach.counter.name = velocityCount

# Default starting value of the loop
# counter variable reference.
directive.foreach.counter.initial.value = 1
]]></source>

    <p>
    Additionally, the maximum allowed number of loop iterations can be
    controlled engine-wide (an ability introduced in Velocity 1.5).
    By default, there is no limit:
    </p>

<source><![CDATA[
# The maximum allowed number of loops.
directive.foreach.maxloops = -1
]]></source>

  </subsection>

  <subsection name="#include - Renders local file(s) that are not parsed by Velocity" href="include-Renderslocalfile(s)thatarenotparsedbyVelocity">
    <p>
    Format:
    </p>

    <p>
    <strong>#</strong> [ <strong>{</strong> ] <strong>include</strong> [ <strong>}</strong> ] <strong>( </strong>arg[ arg2  ... argn]<strong> )</strong>
    </p>

    <ul>
    <li><em>arg</em> - Refers to a valid file under TEMPLATE_ROOT.</li>
    </ul>

    <p>
    Examples:
    </p>

    <ul>
      <li>String: #include( "disclaimer.txt"  "opinion.txt" )</li>
      <li>Variable: #include( $foo  $bar )</li>
    </ul>
  </subsection>

  <subsection name="#parse - Renders a local template that is parsed by Velocity" href="parse-RendersalocaltemplatethatisparsedbyVelocity">
    <p>
    Format:
    </p>

    <p>
    <strong>#</strong> [ <strong>{</strong> ] <strong>parse</strong> [ <strong>}</strong> ] <strong>(</strong> arg <strong>)</strong>
    </p>

    <ul>
    <li><em>arg</em> - Refers to a template under TEMPLATE_ROOT.</li>
    </ul>

    <p>
    Examples:
    </p>

    <ul>
      <li>String: #parse( "lecorbusier.vm" )</li>
      <li>Variable: #parse( $foo )</li>
    </ul>

    <p>
    Recursion permitted. See <em>parse_directive.maxdepth</em> in
    <code>velocity.properties</code>
    to change from parse depth. (The default parse depth is 10.)
    </p>
  </subsection>

  <subsection name="#stop - Stops the template engine" href="stop-Stopsthetemplateengine">
    <p>
    Format:
    </p>

    <p>
    <strong>#</strong> [ <strong>{</strong> ] <strong>stop</strong> [ <strong>}</strong> ]
    </p>

    <p>
    Usage:
    </p>

    <p>
    This will stop execution of the current template. This is good for
    debugging a template.
    </p>
  </subsection>

  <subsection name="#macro - Allows users to define a Velocimacro (VM), a repeated segment of a VTL template, as required" href="macro-AllowsuserstodefineaVelocimacro(VM),arepeatedsegmentofaVTLtemplate,asrequired">
    <p>
    Format:
    </p>

    <p>
    <strong>#</strong> [ <strong>{</strong> ] <strong>macro</strong> [ <strong>}</strong> ] <strong>(</strong> vmname $arg1 [ $arg2 $arg3 ... $argn ]
    <strong>)</strong> [ VM VTL code... ] <strong>#</strong> [ <strong>{</strong> ] <strong>#end</strong> [ <strong>}</strong> ]
    </p>

    <ul>
    <li><em>vmname</em> - Name used to call the VM
    (<em>#vmname</em>)</li>
    <li><em>$arg1 $arg2 [ ... ]</em> - Arguments to the VM. There can be
    any number of arguments, but the number used at invocation must
    match the number specified in the definition.</li>
    <li><em>[ VM VTL code... ]</em> - Any valid VTL code, anything you
    can put into a template, can be put into a VM.</li>
    </ul>

    <p>
    Once defined, the VM is used like any other VTL directive in a
    template.
    </p>

<source><![CDATA[
#vmname( $arg1 $arg2 )
]]></source>

    <p>
    VMs can be defined in one of two places:
    </p>

    <ol>
    <li><i>Template library:</i> can be either VMs pre-packaged with
    Velocity or custom-made, user-defined, site-specific VMs;
     available from any template</li>
    <li><i>Inline:</i> found in regular templates, only usable when
    <em>velocimacro.permissions.allowInline=true</em> in
    <code>velocity.properties</code>.</li>
    </ol>
  </subsection>


</section>

<section name="Comments" href="Comments">
    <p>
    Comments are not rendered at runtime.
    </p>

    <subsection name="Single Line" href="SingleLine">
    <p>
    Example:
    </p>

    <p>
    <strong>## This is a comment.</strong>
    </p>

    </subsection>
    <subsection name="Multi Line" href="MultiLine">
    <p>
    Example:
    </p>

    <p>
    <strong>
    #*<br/>
    This is a multiline comment.<br/>
    This is the second line<br/>
    *#
    </strong>
    </p>

    </subsection>
</section>

</body>
</document>