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Groovelts and Groovy Server Pages are unbelievably simple to set-up and use, quick and dirty web-api’s and proof of concept can be implemented in no time!

Using groovy as a serverlet (also known as Groovlet) is a really cool thing. Grails is a must if you want to develop a complex web-app, but what about the small quickies that can be done in minutes? groovlets are surely the answer.

In just one-liner groovlet I could solve a problem at work that has been outstanding for weeks.

Here is how to set it up :

1. Download and unzip groovy binary package and  jetty servlet engine. in my case the two folders are ~/Development/jetty-6.1.11 and ~/Development/groovy-1.5.6. Needless to say, you need Java (Standard Edition JDK) preferably the latest release (mine is 1.6).
2. Create your groovlet webapp folder structure

    mkdir -p ~/Development/jetty-6.1.11/webapps/glet/WEB-INF/lib/

3. Copy groovy run-time jar file to your servlet lib folder

   cp ~/Development/groovy-1.5.6/embeddable/groovy-all-1.5.6.jar \ 
   ~/Development/jetty-6.1.11/webapps/glet/WEB-INF/lib/

4. Create ~/Development/jetty-6.1.11/webapps/glet/WEB-INF/web.xml file with the following content

   <web-app version="2.4"
       xmlns="http://java.sun.com/xml/ns/j2ee"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee web-app_2_4.xsd" >
       <!-- Setup Groovlets -->
       <servlet>
           <servlet-name>glet</servlet-name>
           <servlet-class>groovy.servlet.GroovyServlet</servlet-class>
       </servlet>
       <servlet-mapping>
           <servlet-name>glet</servlet-name>
           <url-pattern>*.glet</url-pattern>
       </servlet-mapping>
    
       <!-- Setup Groovy Server Pages (GSP) -->
       <servlet>
           <servlet-name>GroovyTemplate</servlet-name>
           <servlet-class>groovy.servlet.TemplateServlet</servlet-class>    
       </servlet>
       <servlet-mapping>
           <servlet-name>GroovyTemplate</servlet-name>
           <url-pattern>*.gsp</url-pattern>
       </servlet-mapping>
    
       <!-- The Welcome File List -->
       <welcome-file-list>
           <welcome-file>index.glet</welcome-file>
       </welcome-file-list>
   </web-app>

5. The Groovlet : Create ~/Development/jetty-6.1.11/webapps/glet/index.glet with the following content

   def mylist = ["Hello", "World!"]
    
   html.html {
     head {
       title("My nice index page")
     }
     body {
       table {
         tr {
           td {
             span("This is a test page ...")
             br()
             i("In case you want italic")
           }
         }
         tr {
           td {
             mylist.each {
               html.span(it)
               html.br()
             }
           }
         }
       }
                   span("Hello there")
                   h1("Hala")
                   h2{
                           i("nice meeting you")
                   }
                   b("cake")
    
                   (0..3).each { p (it) }
    
           println "hala 3ammi"
    
    
           h1 "XML encoding with Groovy"
           p "this format can be used as an alternative markup to XML"
    
           /* an element with attributes and text content */
           a href:'http://groovy.codehaus.org', "Groovy"
    
           p "some text"
    
           p ( ["this is some", b ("mixed"), "text."])
           pre (["a", "b"]) {
                   (0..3).each {println "danni"}
           }
           p "other text"
     }
   }

   The above html style is called HTML Builder, and it gives a different paradigm for servlet development.
   Another dummy example .. :

   if (!session) 
     session = request.getSession(true);
    
   if (!session.counter) 
         session.counter = 1
    
   html.html {    // html is implicitly bound to new MarkupBuilder(out)
     head { title("Groovy Servlet") }
     body {
       h1("Hello, ${request.remoteHost}:")
       p("${session.counter}! ${new Date()}")
     }
   }
   session.counter = session.counter.toInteger() + 1

   More on groovlets

6. The Groovy Server Page Create ~/Development/jetty-6.1.11/webapps/glet/mypage.gsp with the following content

   <html>
   <head><title>mypage.gsp</title></head>
   <body>
   <b><% println "mypage gsp" %></b>
   <p>
   <% wrd = "Groovy"
      for (i in wrd){ 
    %>
    <h1> <%=i%> <br/>
    
    <%} %>
   </p>
   </body>
   </html>

   Just for the record, this is not exactly the same GSP that comes with grails. The GSP module that comes with grails offers more features.

7. Start jetty and browse to http://localhost:8080/glet

You can also do it in other ways, like using print “<html> … “  instead of the html DSL.

Here is a oneliner example groovlet :

println "<h1> Hello  ${params["name"]} to the world of groovlets</h1>"

put this line in say this file :jetty-6.1.11/webapps/glet/hello.glet

then call it from here : http://localhost:8080/glet/hello.glet?name=kefah

I thought glet is a nice shortname for groovlet.

The nice thing about groovlets is that you can edit them and create new ones and they will work on the fly. no need to restart jetty or recompile code.

Enjoy.

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