A template engine is a software development tool that allows you to create and render documents that format and present data. Template engines include features for processing plain text like variables, functions, text replacement, file inclusion, and conditional evaluation/loops. The Velocity template engine permits templates to reference Java methods and uses references and directives to embed dynamic content.

2. A template engine is a software development
tool that allows you to create and render
documents that format and present your data
.
A template engine is included as part of
a template system or application
framework
Content from a database and "presentation
specifications" (in a web template), are
combined (through the template engine) to
produce web documents.

3.  Examples are:
Engine Language
Apache Velocity Java, C#
ASP.net C#, VB.net
Casper Java, Javascript
String Template Java, Python
Cheetah Template Python

4.  Template engines generally include features common in
higher level programming with emphasis on processing
plain text
 Features include:
 Variables and functions
 Text replacement
 File inclusion
 Conditional evaluation and loops

5. Velocity Template Engine
It permits the templates to reference methods defined in Java
code using Velocity template language(VTL) statements.
VTL uses references to embed dynamic content in a text
product
References are of three types variables, properties and Methods
VTL REFERENCES
Variable ${aVariable}, $aVariable
Properties ${anIdentifier.aIdentifier}
Methods ${aIdentifier.aMethodBody(${aIdentifier})}

6.  References begin with $ and are used to get something
 Directives begin with # and are used to do something
 #set is used to assign a value to a variable
 The variable, $aVariable can the be used in the template
to output the value(i.e “aValue”)
#set($ aVariable = “aValue”)
Character
directive
Variable
Value

7. Lets Work!!
 Download velocity engine (Velocity-1.7 jar) from
http://velocity.apache.org/download.cgi
 Include the Velocity-1.7 jar jar in the lib folder of your
project folder(you may also have to include commons-
collections.jar, commons-lang and mail.jar).
 Prepare your .vsl template message
 Write your java code

8. Template Message
#*
Test E-mail Message
@zed
*#
Dear Mr $recepientName,
The management of $companyName hereby invite you for an
interview in $interviewVenue at $timeOfInterview .
Yours Sincerely,
$sendersName

9. Sample Code
public void sendMail() {
Template template = null;
template = ve.getTemplate("/myMessage.vsl");
Map<String, String> mymail = new HashMap<String, String>();
mymail.put("recepientName", infoDetail.getRecepientname());
mymail.put("companyName", infoDetail.getCompanyName());
mymail.put("interviewVenue", infoDetail.getInterviewVenue());
mymail.put("timeOfInterview", infoDetail.getTimeOfInterview());
mymail.put("sendersName", infoDetail.getSenderName());
VelocityContext context = new VelocityContext(mymail);
StringWriter writer = writer = new StringWriter();
if (template != null) {
template.merge(context, writer);
}
message = writer.toString();
}

10. Output
Dear Mr James,
The management of Seamfix hereby invite you for an
interview in Lagos at 8:00pm
Yours Sincerely,
Zebrudaya

11. QUESTIONS??