Velocity Template Tutorial _1

VELOCITY  TUTORIAL _1

TEMPLATE ENGINE :

    It is program or software which takes text files as input and process then and produces one or more output files [O/p files has content different from input text file or very few times same as input text file]

  

VELOCITY :

• Velocity is open-source template engine written in java-language .

USES OF VELOCITY:

• It is used for presenting a view to the user as like JSP.

• It is used to create any kind of pages like HTML , XML and so on.

• It can be used in standlone application to create XML files dynamically.

• We can make the whole-text file as string which is used for generating e-mail.

• It is easy to understand compared to JSP pages which uses Scriptlets, Tags .. so non-java developers can easily understand Velocity so Presentation layer and business layer is separated.

VELOCITY VS JSP :

• Velocity is faster compared to JSP [JSP involves conversion to servlet then compile and run].

• Easy to learn.

• No need for any web-container or server to run the velocity

• No expection occurs in velocity while in JSP we have Compile and runtime error.
    
  HELLO WORLD PROGRAM :

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

Steps involved in creating and running a velocity program.

• STEP 1: Intialize Velocity-Engine
  [NOTE: In version 1.1 we directly intialize velocity engine by calling “Velocity.init()” method but in 1.2 we can create VelocityEngine object and then intialize the velocity Engine as “VelocityEngine velocityEngine = new VelocityEngine(); velocityEngine.init();”]

• STEP 2: Create the Template object by calling getTemplate() method.
  [NOTE : In version 1.1 we use Velocity class to create template object as “Template template = Velocity.getTemplate("./src/directives.vm");” but in 1.2 version we can also use VelocityEngine object to create a template object as “VelocityEngine velocityEngine = new VelocityEngine(); velocityEngine.init();Template template = velocityEngine.getTemplate(/*Give the file location here*/"helloworld.txt");”]

• STEP 3: Create VelocityContext object and add values.

• STEP 4 : Process the template.

PROGRAMMING :

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 { /*STEP 1 :Create a VelocityTemplate Engine Object*/ VelocityEngine velocityEngine = new VelocityEngine(); /*STEP 2 :Initialise VelocityTemplate Engine */ velocityEngine.init(); /* * NOTE : we can directly initialise the velocity engine by calling "Velocity.init()" * Creation of VelocityEngine object is available from 1.2 version only * */ /*STEP 3: Create the template object by calling getTemplate() method in VE(VelocityEngine)*/ Template template = velocityEngine.getTemplate(/*Give the file location here*/"./src/helloworld.txt"); /*STEP 4: Create VelocityContext */ VelocityContext context = new VelocityContext(); StringWriter writer = new StringWriter(); /*STEP 5: Process the template and write the o/p to stream*/ template.merge(context, writer); /*STEP 6: Show the output */ System.out.println(writer); } }

helloworld.txt-FILE Hello java! Welcome to Velocity! Hello World NOTE : This text file is called as velocity template file

OUTPUT Hello java! Welcome to Velocity! Hello World

   

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