Examples of Velocity, xslt and StringTemplate

These template engines provide similar functionalities - transforming data into new contents based on a set of templates, and they are all compatible to java. You can pick any one of them as long as it can solve your problem. To process xml/html documents I would recommend xslt. Other text processing, I would recommend velocity. StringTemplate is powerful, but it is not well documented. If the task requires fast transformation and small memory use, dom parser based xslt transformation is not recommended. I will make a few simple examples in the article to bring you an idea of how they work.

 

Velocity,

First download velocity binary from http://velocity.apache.org/download.cgi.

Now I start eclipse and create a new project called VelocitySample, add 2 velocity jar files to build path.

 

package xish.velocity.app;

import java.io.StringWriter;

import java.io.Writer;

import java.util.ArrayList;

import java.util.Collection;

import org.apache.velocity.Template;

import org.apache.velocity.VelocityContext;

import org.apache.velocity.app.Velocity;

public class VelocityDemo {

           public static void main(String[] args) {

                      Velocity.init();

                      Template tp = Velocity.getTemplate("./template/v1.vm");

                      VelocityContext ctx = new VelocityContext();

                      Collection users = new ArrayList();

                      users.add(new User("Jemmy", "jmy32@gmail.com"));

                      users.add(new User("Funy", "fol@abcenglish.com"));

                      users.add(new User("lao", "derr@yahoo.com"));

                      ctx.put("users", users);

                      Writer writer = new StringWriter();

                      tp.merge(ctx, writer);

                      System.out.println(writer);

           }

}

VelocityDemo.java

#foreach($user in $users)

$user.Name    $user.Email

#end

#include("./template/v2.vm")

v1.vm

The End!

v2.vm

Run VelocityDemo, it will generate following output:

Jemmy    jmy32@gmail.com

Funy    fol@abcenglish.com

lao    derr@yahoo.com

The End!

Xslt,

I create a new project in eclipse called XsltSample.

 

package xish.xslt.app;

import javax.xml.transform.TransformerConfigurationException;

import javax.xml.transform.TransformerException;

import javax.xml.transform.TransformerFactoryConfigurationError;

public class XsltDemo {

           public static void main(String[] args) {

                      String xmlFile = "./data/users.xml";

                      String xsltFile = "./template/v1.xslt";

                      try {

                                 javax.xml.transform.Source xmlSource = new javax.xml.transform.stream.StreamSource(

                                                      xmlFile);

                                 javax.xml.transform.Source xsltSource = new javax.xml.transform.stream.StreamSource(

                                                      xsltFile);

                                 javax.xml.transform.Result result = new javax.xml.transform.stream.StreamResult(

                                                      System.out);

                                 javax.xml.transform.TransformerFactory transFact = javax.xml.transform.TransformerFactory

                                                      .newInstance();

                                 javax.xml.transform.Transformer trans = transFact

                                                      .newTransformer(xsltSource);

                                 trans.transform(xmlSource, result);

                      } catch (TransformerConfigurationException e) {

                                 e.printStackTrace();

                      } catch (TransformerFactoryConfigurationError e) {

                                 e.printStackTrace();

                      } catch (TransformerException e) {

                                 e.printStackTrace();

                      }

           }

}

XsltDemo.java

<?xml version="1.0" encoding="UTF-8"?>

<users>

           <user>

                      <name>Jemmy</name>

                      <email>jmy32@gmail.com</email>

           </user>

           <user>

                      <name>Funy</name>

                      <email>fol@abcenglish.com</email>

           </user>

           <user>

                      <name>lao</name>

                      <email>derr@yahoo.com</email>

           </user>

</users>

Users.xml

<?xml version="1.0" encoding="UTF-8"?>

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"

           version="1.0">

           <xsl:output method="text" indent="yes" />

           <xsl:import href="v2.xslt" />

           <xsl:template match="/">

                      <xsl:apply-templates select="users" />

                      <xsl:call-template name="end"/>

           </xsl:template>

           <xsl:template match="users">

                      <xsl:apply-templates select="user" />

           </xsl:template>

          

           <xsl:template match="user">

                      <xsl:value-of select="name" />

                      <xsl:text>    </xsl:text>

                      <xsl:value-of select="email" />

                      <xsl:text>&#xa;</xsl:text>

           </xsl:template>

</xsl:stylesheet>

v1.xslt

<?xml version="1.0" encoding="UTF-8"?>

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"

           version="1.0">

           <xsl:output method="text" indent="yes" />

          

           <xsl:template name="end">

                      <xsl:text>The End!</xsl:text>

           </xsl:template>

</xsl:stylesheet>

v2.xslt

Run XsltDemo, it will generate following output:

Jemmy    jmy32@gmail.com

Funy    fol@abcenglish.com

lao    derr@yahoo.com

The End!

StringTemplate,

Download Antlr from http://www.antlr.org/download.html.

Download StringTemplate from http://www.stringtemplate.org/download.html. Notice there are a few class name changes in comparison between v3 to v4. I downloaded the latest version v4.03 upon writing this post.

I created a new project in eclipse called StringTemplateSample, and add antlr-3.3-complete.jar and ST-4.0.3.jar to the build path.

 

package xish.stringtemplate.app;

import org.stringtemplate.v4.ST;

import org.stringtemplate.v4.STGroup;

import org.stringtemplate.v4.STGroupDir;

public class StringTemplateDemo {

          

           public static void main(String[] args) {

                      STGroup group = new STGroupDir("./template");

                      ST st = group.getInstanceOf("v1");

        st.addAggr("users.{ name, email }", "Jemmy", "jmy32@gmail.com");

        st.addAggr("users.{ name, email }", "Funy", "fol@abcenglish.com");

        st.addAggr("users.{ name, email }", "lao", "derr@yahoo.com");

       

        System.out.println(st.render());

        //v1(users) ::= "<users:{it|<it.name>    <it.email>; wrap}><\n><v2()>;"

        //System.out.println(st.render(20));

           }

}

StringTemplateDemo.java

v1(users) ::= "<users:{it|<it.name>    <it.email><\n>}><v2()>;"

v1.st

v2() ::= "The End!"

v2.st

Run StringTemplateDemo, it will generate following output:

Jemmy    jmy32@gmail.com

Funy    fol@abcenglish.com

lao    derr@yahoo.com

The End!