vilbara's weblog: velocity

Wednesday, December 5, 2007

How to use Velocity as a view component in Struts?

Struts provides a proved framework for building web applications in Java. It is most often used with JSP as a view component. However, other view components may be used as well.

Here I will show how to create a "hello world" application using Struts and Velocity as a view component. I assume you have already downloaded and set up necessary Struts parts.

First of all, we need to download VelocityTools package which provides easy way to use "*.vm" (Velocity Macro) templates to serve HTML pages and has some tools for Struts integration.

Extract the archive and copy following jar files to your project:

velocity-tools-1.4.jar
velocity-1.5.jar
commons-beanutils-1.7.0.jar
commons-logging-1.1.jar
commons-collections-3.2.jar
oro-2.0.8.jar
commons-digester-1.8.jar
commons-lang-2.2.jar

Add following servlet definition and mapping to your web.xml:

  <servlet>
    <servlet-name>velocity</servlet-name>
    <servlet-class>
      org.apache.velocity.tools.view.servlet.VelocityViewServlet
    </servlet-class>
  </servlet>

  <servlet-mapping>
    <servlet-name>velocity</servlet-name>
    <url-pattern>*.vm</url-pattern>
  </servlet-mapping>

Now create a hello-world.vm file in the root directory of your web resources, where you would normally put JSP files.

  <html>
  <body>
  Hello World at $currentTime!
  </body>
  </html>

If you start application and point your browser to the http://localhost:8080/struts-velocity/hello-world.vm URL, you will see following output:

  Hello World at $currentTime!

Create HelloWorldAction Struts Action to add necessary "currentTime" object to the request.

In struts-config.xml:

  <action path="/hello-world" type="vilbara.HelloWorldAction">
  <forward name="ok" path="/hello-world.vm"/>
  </action>

In HelloWorldAction class:

  request.setAttribute("currentTime", new Date());
  return actionMapping.findForward("ok");

Start application and access http://localhost:8080/struts-velocity/hello-world.do URL. You will get following output:

  Hello World at Thu Dec 06 12:36:33 CET 2007!

That was it. Now Struts uses Velocity for the view component in your application.

You may download struts-velocity.war file. Sources are included.

Use Velocity for e-mail templates

You are Java developer and need to send an e-mail. Where and how do you store e-mail content?

First, let me clarify what I mean by the "content". There are several parts of it:

subject.
body
"from" field.

Many developers use Java property resource bundles and naming convention to store 2 or 3 parts of content.

  mail.created.subject=Account for {0} has been created.
  mail.created.from=support@example.org
  mail.created.body=Account with the user ID {0} has been successfully created.\n\n\
    Please follow this link to use your account:\n  {1}\n\nYour Support Team\nexample.org

Let's look at the alternate solution using Apache's Velocity.

First, create a file in Velocity macro, e.g. mail-created.vm with following content:

  #set ($subject = "Account for $person.name has been created")
  #set ($from = 'support@example.org')
 
  Account with the user ID $person.uid has been successfully created.

  Please follow this link to use your account:
  $link

  Your Support Team
  example.org

Now, load and evaluate the template:

  Context context = new VelocityContext();
  context.put("person", new Person("Vilmantas Baranauskas", "vilbara"));
  context.put("link", "http://vilbara.blogspot.com/");

  Template template = Velocity.getTemplate("src/mail-created.vm");

  StringWriter body = new StringWriter();
  template.merge(context, body);

  String from = String.valueOf(context.get("from"));
  String subject = String.valueOf(context.get("subject"));

Compare abilities of Velocity and MessageFormat and you will see the benefits.

You may download a zip file containing this example.

vilbara's weblog

Wednesday, December 5, 2007

How to use Velocity as a view component in Struts?

Use Velocity for e-mail templates

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