Beginning Apache Velocity : Creating A Simple Web Application
Today im going to try create a simple web application using Apache Velocity. From what is written on its wiki, Apache Velocty is a simple yet powerful Java-based template engine that renders data from plain Java objects to text, xml, email, SQL, Post Script, HTML etc. The template syntax and rendering engine are both easy to understand and quick to learn and implement.
In this example i’m using Velocity 1.7 and Velocity Tools View 2.0, Netbeans 6.9 and Apache Tomcat 6. Im using a simple Servlet acting as Controller, Velocity file with extension .vm as View and a simple ArrayList to mimic ResultSets as the Model.
Lets start with a simple Velocity file
<html>
<head> <title>Hello Velocity</title> </head>
<body>
<h1>Hello World..!!</h1>
<br />
## this is a comment, set variable name with "Edw" value
#set( $name = "Edw" )
<h2> $name is using velocity</h2>
## if-else statement
#if($name.equals("NotEdw"))
<br />
not an Edw
#else
<br />
Only the Paranoid Survive
#end
<br />
<br />
<table>
<tr>
<td>Name</td>
<td>Address</td>
<tr>
## for each statement to iterate over a collection
#foreach($user in $users)
<tr>
<td>$user.name</td>
<td>$user.address</td>
<tr>
#end
</table>
## simple velocity method
Today is : $date.medium
</body>
</html>
i named it index.vm and put it under the Web Pages folder.
Next is creating an xml file, toolbox.xml for registering classes that is needed by Velocity. In this example im only registering a simple DateTool class.
<toolbox>
<tool>
<key>date</key>
<scope>application</scope>
<class>org.apache.velocity.tools.generic.DateTool</class>
</tool>
</toolbox>
Next is a simple javabean
package com.edw.bean;
public class User {
private String name;
private String address;
public User() {
}
public User(String name, String address) {
this.name = name;
this.address = address;
}
// other setter - getter
}
And a simple Servlet, im using it simply just for Controller function, it forward my requests-responses to index.vm
package com.edw.servlet;
import com.edw.bean.User;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.log4j.Logger;
public class VelocityServlet extends HttpServlet {
private Logger logger = Logger.getLogger(getClass());
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
try {
// simulate a database query
List<User> users = new ArrayList<User>();
for (int i = 0; i < 5; i++) {
User user = new User("name "+i, "Address "+i);
users.add(user);
}
// set values
request.setAttribute("users", users);
// get UI
RequestDispatcher requestDispatcher = request.getRequestDispatcher("index.vm");
requestDispatcher.forward(request, response);
} catch(Exception ex){
logger.error(ex);
}
}
}
[/code]
And the most important part is web.xml
[code language="xml" highlight="10,20,25"]
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
<!-- register servlet -->
<servlet>
<servlet-name>ServletVelocity</servlet-name>
<servlet-class>com.edw.servlet.VelocityServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>ServletVelocity</servlet-name>
<url-pattern>/velocity.service</url-pattern>
</servlet-mapping>
<!-- mapping all .vm files to velocity servlets -->
<servlet>
<servlet-name>velocity</servlet-name>
<servlet-class>org.apache.velocity.tools.view.servlet.VelocityViewServlet</servlet-class>
<!-- load my toolbox -->
<init-param>
<param-name>org.apache.velocity.toolbox</param-name>
<param-value>/WEB-INF/toolbox.xml</param-value>
</init-param>
</servlet>
<servlet-mapping>
<servlet-name>velocity</servlet-name>
<url-pattern>*.vm</url-pattern>
</servlet-mapping>
<!-- session timeout -->
<session-config>
<session-timeout>
30
</session-timeout>
</session-config>
<!-- welcome file -->
<welcome-file-list>
<welcome-file>velocity.service</welcome-file>
</welcome-file-list>
</web-app>
This is my Netbeans project structure
And this is what my browser displayed
In case of anybody asked about my log4j.properties, here is my configuration
# Global logging configuration
log4j.rootLogger=DEBUG,stdout
# Console output...
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss.SSS} %-5p %c:%L - %m%n
Well it’s not too difficult isn’t it? (H)
