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>
</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!
