Velocity Template Tutorial_2

SCRIPTING LANGUAGE :

• It is a programming language where the program or script is directly interpreted or executed instead of compiling & then executing. Example: Javascript.

VELOCITY-TEMPLATE LANGUAGE (VTL) :

• It is a scripting language used inside the velocity template file for generating dynamic contents.

• It is a case sensitive language.

• It is white space sensitive language meaning '#end' is different from “# end”[Note: Space between “#” and “end”]

• In VTL we can specify three types of comments as like JAVA. They are :
  1.Single-line comment (##)
    Example: ## This is commented line 
  
  
  2.Multi-line comment(#*......*#)
    Example: #* The below lines will not be   processed by the velocity engine because this is multi-line command *# 
  
  
  3.Documentary comment(#**.......*#)
    Example : #** The below lines will not be processed by the velocity engine because this is multi-line command *#

• VTL has two parts DIRECTIVES and REFERENCES.
   DIRECTIVES => Used for controlling and doing action. Controlling like if,else ,else if control statement.Doing like setting variables and creating functions
  
  
   REFERENCES => Used for accessing objects and their methods.[NOTE : Directives always begin with “#” while references always beging with “$”]

 

REFERENCES :

• Always start with “$” character

Types of References : 

Variables :Used to declare variables in template-file

 

Properties:Used to access methods in objects using accessor and mutator methods like JAVABEAN accessing

 

Methods : Used to access methods in objects.

VARIABLE REFERENCES :

• Its sames as java variables.

• Always start with “$” symbol.

• When declaring variable reference in template file it should start with alpha-numeric character.

• Can have underscore(_) and hypen(-) in variable reference.

• Syntax
    $variableName
    EXAMPLE : #set($userName = “vignesh”)
    EXAMPLE 2: $userName ## userName value is in java-code. 

• Variable references can get value from #set directive or java-code.

PROGRAMMING :

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REQUIRED PACKAGES :

1.velocity-1.6.2.jar 2.commons-collections-3.2.1.jar 3.commons-lang-2.4.jar 4.oro-2.0.8.jar TO Download this files Click here

JAVA-FILE: import java.io.StringWriter; import org.apache.velocity.Template; import org.apache.velocity.VelocityContext; import org.apache.velocity.app.VelocityEngine; public class HelloWorld { public static void main(String[] args) throws Exception { VelocityEngine velocityEngine = new VelocityEngine(); velocityEngine.init(); Template template = velocityEngine.getTemplate("./src/helloworld.txt"); VelocityContext context = new VelocityContext(); context.put("password","vignesh"); // =====>STEP:1 StringWriter writer = new StringWriter(); template.merge(context, writer); System.out.println(writer); } }

helloworld.txt-FILE #set($name ="vignesh") ## =====>STEP:2 Hello $name! Welcome to Velocity! ## =====>STEP:3 Password ---> $password ## =====>STEP:4

OUTPUT Hello vignesh! Welcome to Velocity! Password ---> vignesh

EXAPLANATION : STEP: 1 ===> putting the key-value pair into velocity context.put STEP: 2 ===> Declaring the reference variable. STEP: 3 ===> Variable reference “$name” referring the value from #set directive.vm STEP: 4 ===> Variable reference “$password” referring the value from java code which is set in STEP 1.

PROPERTIE REFERENCES:

• Used to access methods in java objects.

• Used only to access or call only “getter” methods in JAVABEAN , we cannot use “setter” here.

• Can refer to velocityContext key value or JAVABEAN getter methods.

• SYNATX :
  $variableName.methods
  EXAMPLE:$customer.Address
  //Here $customer.Address can also be referring to a //method of java-bean or key in VelocityContext object. 

• VelocityEngine find wheather it referes to key in VelocityContext object or method in java bean object and return the appropriate value.

METHOD REFERENCES:

• Used to call methods in java objects.

• Can be used to call setter methods or any methods in java-object.

• Can be used to call java.array.List class methods also like $listObject.get(0);

• SYNATX :
  $variableName.methodName(parametersForMethods)
   EXAMPLE: $customer.getAddress()
            $customer.setAddress(“Bangalore”)

 

Note : If you find any thing which you can not understand or wrong please leave comments.I assure i will get back to you.

 
NOTE : TO download the velocity tutorial in word format click here