Introduction to Apache Velocity

Apache Velocity Petteri Hietavirta [email_address] 27.10.2010

Velocity Engine
Been around since 2000, current v1.6.4
Can produce any text output
Processing - no compilation
Good separation of logic and presentation
Easier for devs and designers

Performance
Similar to JSP for dynamic pages
... but much faster to develop on

Typical uses
Web frameworks
Code generation
Document & email generation

Context + Template
Templates are written in VTL - Velocity Template Language
Velocity context has the model and other objects required for the processing

VTL Syntax
# directives
line or block directives
built in syntax or macro declarations
$ references
variables, access to properties and methods

Simple example

Demo with Tomcat
Uses VelocityViewServlet

Extension points
Macros
Context objects included in the context
Custom resource loader
Custom directives
Event handlers
Introspectors

Velocity Tools
Collection of useful classes
GenericTools
DateTool, EscapeTool, SortTool ...
VelocityView
VelocityViewServlet, web specific tools ...
VelocityStruts

Security
Can you trust your template writers?
SecurityUberSpector

Velocity oddities
-1
swallow
macro output
static methods?
context.put("Math", Math.class);
enums, static fields

Use case: Content Control
More stuff in context
Velocity Tools are not used too much
Pushing MVC boundaries
Not too many Velocity related problems
www.contentcontrol.com

References
http://wiki.apache.org/velocity/HackingVelocity
http://stackoverflow.com/questions/159292/how-do-i-create-a-custom-directive-for-apache-velocity
http://wiki.apache.org/velocity/BuildingSecureWebApplications
http://wiki.apache.org/velocity/VelocityEditors
http://wiki.apache.org/velocity/PoweredByVelocity

Introduction to Apache Velocity

by Petteri Hietavirta on Nov 02, 2010

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Introduction to Apache Velocity — Presentation Transcript