Velocity - VTL Reference Guide

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About this Guide

This guide is the reference for the Velocity Template Language (VTL). For more information, please also refer to the Velocity User Guide.

References

Variables

Notation:

$ [ ! ][ { ][ a..z, A..Z ][ a..z, A..Z, 0..9, -, _ ][ } ]

Examples:

Normal notation: $mud-Slinger_9

Silent notation: $!mud-Slinger_9

Formal notation: ${mud-Slinger_9}

Properties

Notation:

$ [ { ][ a..z, A..Z ][ a..z, A..Z, 0..9, -, _ ]* .[a..z, A..Z ][ a..z, A-Z, 0..9, -, _ ]* [ } ]

Examples:

Regular Notation: $customer.Address

Formal Notation: ${purchase.Total}

Methods

Notation:

$ [ { ][ a..z, A..Z ][ a..z, A..Z, 0..9, -, _ ]* .[ a..z, A..Z ][ a..z, A..Z, 0..9, -, _ ]*( [ optional parameter list... ] ) [ } ]

Examples:

Regular Notation: $customer.getAddress()

Formal Notation: ${purchase.getTotal()}

Regular Notation with Parameter List: $page.setTitle( "My Home Page" )

VTL Properties can be used as a shorthand notation for VTL Methods that take get and set. Either $object.getMethod() or $object.setMethod() can be abbreviated as $object.Method. 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.

Directives

#set - Establishes the value of a reference

Format:

# [ { ] set [ } ] ( $ref = [ ", ' ]arg[ ", ' ] )

Usage:

$ref - The LHS of the assignment must be a variable reference or a property reference.

arg - The RHS of the assignment, arg is parsed if enclosed in double quotes, and not parsed if enclosed in single quotes. If the RHS evaluates to null, it is not assigned to the LHS.

Examples:

Variable reference: #set( $monkey = $bill )

String literal: #set( $monkey.Friend = 'monica' )

Property reference: #set( $monkey.Blame = $whitehouse.Leak )

Method reference: #set( $monkey.Plan = $spindoctor.weave($web) )

Number literal: #set( $monkey.Number = 123 )

Range operator: #set( $monkey.Numbers = [1..3] )

Object array: #set( $monkey.Say = ["Not", $my, "fault"] )

The RHS can also be a simple arithmetic expression, such as:

Addition: #set( $value = $foo + 1 )

Subtraction: #set( $value = $bar - 1 )

Multiplication: #set( $value = $foo * $bar )

Division: #set( $value = $foo / $bar )

Remainder: #set( $value = $foo % $bar )

#if / #elseif / #else - output conditional on truth of statements

Format:

# [ { ] if [ } ] ( [condition] ) [output] [ # [ { ] elseif [ } ] ( [condition] ) [output] ]* [ # [ { ] else [ } ] [output] ] # [ { ] end [ } ]

Usage:

condition - If a boolean, considered true if it has a true false; if not a boolean, considered true if not null.

output - May contain VTL.

Examples:

Equivalent Operator: #if( $foo == $bar )

Greater Than: #if( $foo > 42 )

Less Than: #if( $foo < 42 )

Greater Than or Equal To: #if( $foo >= 42 )

Less Than or Equal To: #if( $foo <= 42 )

Equals Number: #if( $foo == 42 )

Equals String: #if( $foo == "bar" )

Boolean NOT: #if( !$foo )

using brackets to delimit directive: #if( $foo == $bar)it's true!#{else}it's not!#end
#foreach - Loops through a list of objects
Format:

# [ { ] foreach [ } ] ( $ref in arg ) statement # [ { ] end [ } ]

Usage:

$ref - The first variable reference is the item.

arg - 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.

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

Examples of the #foreach(), omitting the statement block :

Reference: #foreach ( $item in $items )

Array list: #foreach ( $item in ["Not", $my, "fault"] )

Range operator: #foreach ( $item in [1..3] )

Velocity provides an easy way to get the loop counter so that you can do something like the following:
<table>
#foreach( $customer in $customerList )
    <tr><td>$velocityCount</td><td>$customer.Name</td></tr>
#end
</table>
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 velocity.properties file. Here's what the loop counter properties section of the velocity.properties file appears:
# 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
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:
# The maximum allowed number of loops.
directive.foreach.maxloops = -1
#include - Renders local file(s) that are not parsed by Velocity

Format:

# [ { ] include [ } ] ( arg[, arg2, ... argn] )

arg - Refers to a valid file under TEMPLATE_ROOT.

Examples:

String: #include( "disclaimer.txt", "opinion.txt" )

Variable: #include( $foo, $bar )

#parse - Renders a local template that is parsed by Velocity

Format:

# [ { ] parse [ } ] ( arg )

arg - Refers to a template under TEMPLATE_ROOT.

Examples:

String: #parse( "lecorbusier.vm" )

Variable: #parse( $foo )

Recursion permitted. See parse_directive.maxdepth in velocity.properties to change from parse depth. (The default parse depth is 10.)

#stop - Stops the template engine

Format:

# [ { ] stop [ } ]

Usage:

This will stop execution of the current template. This is good for debugging a template.
#macro - Allows users to define a Velocimacro (VM), a repeated segment of a VTL template, as required
Format:

# [ { ] macro [ } ] ( vmname $arg1 [ $arg2 $arg3 ... $argn ] ) [ VM VTL code... ] # [ { ] #end [ } ]

vmname - Name used to call the VM (#vmname)

$arg1 $arg2 [ ... ] - 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.

[ VM VTL code... ] - Any valid VTL code, anything you can put into a template, can be put into a VM.

Once defined, the VM is used like any other VTL directive in a template.
#vmname( $arg1 $arg2 )
VMs can be defined in one of two places:

Template library: can be either VMs pre-packaged with Velocity or custom-made, user-defined, site-specific VMs; available from any template

Inline: found in regular templates, only usable when velocimacro.permissions.allowInline=true in velocity.properties.

Comments

Comments are not rendered at runtime.

Single Line

Example:

## This is a comment.

Multi Line

Example:

#*
This is a multiline comment.
This is the second line
*#