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Complete Guide to Write Vaadin application in Clojure

In this article I'm going to show you how to write a simple vaadin application in clojure. Before start you need some tools. All of the tools are free downloadable.

Assume you have some basic knowledge about vaadin and clojure.

It is not necessary to use IDE(Intellij IDEA, Eclipse, Netbeans) to write the clojure code. You can use a emacs or vi editor to write the code. But using an IDE can obtain lot of advantages. 

If you'r using an IDE install the corresponding clojure plugin. 

So now if you have all the tools we can start the coding.

First step is the project creation.
  • lein new example 
Using the above command you can create the project and the following files are created.
  • project.clj
  • README
  • src
    • example/core.clj
  • test
    • example/test/core.clj
In order to develop vaadin web application we need the web.xml file. To generate the web.xml file
  • lein war
Now the above command will create the web.xml file inside the src directory.

It's all about project creation. Now you need to edit the files to create the vaadin app.

2nd Step

Edit the project.clj file

(defproject example "1.0.0-SNAPSHOT"
:description "FIXME: write description"
:dependencies [[org.clojure/clojure "1.2.1"]
[org.clojure/clojure-contrib "1.2.0"]
[com.vaadin/vaadin "6.6.0"]
[javax.servlet/servlet-api "2.5"]]

:dev-dependencies [[uk.org.alienscience/leiningen-war "0.0.1"]]
:aot[example.vapp example.vaadin-servlet]
:war {:name "example.war"}
)


In order to compile the project you need the above dependencies.

3rd Step


Delete the core.clj file and create a file called vapp.clj

(ns example.vapp
(:gen-class
:extends com.vaadin.Application
:name example.VApp
:init cjinit)
(:import (com.vaadin.ui Embedded ))
(:import (com.vaadin.terminal ThemeResource ExternalResource Sizeable))
(:import (com.vaadin.ui Alignment))
)

(defn -cjinit []
[[] (ref {})])

(defn -init [this]
(println "Starting vaadin application")
(let [window (com.vaadin.ui.Window. "sample clojure vaadin application")]
(.setMainWindow this window)
(.setTheme window "runo")
(let [grid (com.vaadin.ui.GridLayout. 3 3)]
(.setSpacing grid true)
(.setWidth grid "600px")
(.setHeight grid "600px")
(.addComponent window grid)
(let [nav_panel (com.vaadin.ui.Panel. "Sample Panel")]
(.setWidth nav_panel (Sizeable/SIZE_UNDEFINED) 0)
(let [form (com.vaadin.ui.FormLayout. )]
(.setMargin form true)
(let [link1 (com.vaadin.ui.Link. "Link 1" (ExternalResource. "http://www.google.com" )) ]
(.addComponent form link1 )
)
(let [link2 (com.vaadin.ui.Link. "Link 2" (ExternalResource. "http://www.google.com" )) ]
(.addComponent form link2 )
)
(.setContent nav_panel form)
)
(.addComponent grid nav_panel 1 2)
)
)
)
)




Now create the vaadin_servlet.clj in src/example directory.

(ns example.vaadin-servlet
(:gen-class
:extends com.vaadin.terminal.gwt.server.AbstractApplicationServlet
:name example.VaadinServlet))

(defn ^Class -getApplicationClass [this]
example.VApp)

(defn ^example.VApp -getNewApplication [this request]
(example.VApp.))


Now Edit the web.xml file as follows.


<web-app>
  <!-- Servlet class taken from first :aot namespace -->
  <servlet>
     <servlet-name>example</servlet-name>
     <servlet-class>example.VaadinServlet</servlet-class>
  </servlet>
  <!-- Servlet is mapped to / by default  -->
  <servlet-mapping>
     <servlet-name>example</servlet-name>
     <url-pattern>/*</url-pattern>
  </servlet-mapping>
</web-app>


Now compile the project using following command.

  • lein compile
It will download all the dependencies and compile the code.
If there is any error it gives some exceptions.

4th Step
To build the war file use the below command.
  • lein uberwar
It will create the war file that you given in the project.clj.

Copy the war file into tomcat and the start the server. 
  • localhost:8080/example 
You can see the menu button.

Reference : http://clojure.org/
                : http://vaadin.com/home

How To Run Vaadin Applications in Intellij IDEA [Video]

How To Run Vaadin Applications in Intellij IDEA

In this article I'm going to show you how to run vaadin applications with Intellij IDEA. Vaadin provide some plugins for Eclipse and Netbeans. But for Intellij IDEA there are no plugins yet. But to deploy vaadin app is easier than other two IDEs.

Here are the steps that you want to follow.

1. First Create a New Project , File --> New Project --> Create Project From Scratch --> Give sample_vaadin as application name and select Java module click Next --> Next.
Now Select Web Application as Technology and click Finish.



2. Now create a lib folder in web/WEB-INF/lib and copy the vaadin jar file into the folder. You can get the latest vaadin jar file http://vaadin.com/home . Now the Project hierarchy looks like this.




3.After that File --> Project Structure --> Artifacts . In below you can see some error and click Fix button. That will add vaadin jar file to your exploded war. Now Click OK.



4. To deploy your application you need a web server. So in here I use tomcat 7. To config it,
Run --> Edit Configuration --> Click + sign -->Select Tomcat --> localhost .
Give vaadin as Name and Select tomcat as Application Server (If the server is not there Click configure and goto the tomcat path it will automatically recognize it)



5. Now create some hello world programme according to vaadin book and click the Run button to deploy it.

java.lang Package

In this tutorial I'll show you the main classes and methods in java.lang package.

Here are the main classes in java.lang package.

  • classses
    • Boolean
    • Byte
    • Character
    • Character.Subset
    • Character.UnicodeBlock
    • Class<T>
    • ClassLoader
    • Compiler
    • Double
    • Enum<E extends Enum<E>>
    • Float
    • InheritableThreadLocal<T>
    • Integer
    • Long
    • Math
    • Number
    • Object
    • Package
    • Process
    • ProcessBuilder
    • Runtime
    • RuntimePermission
    • SecurityManager
    • Short
    • StackTraceElement
    • StrictMath
    • String
    • StringBuffer
    • StringBuilder
    • System
    • Thread
    • ThreadGroup
    • ThreadLocal<T>
    • Throwable
    • Void
  • Interfaces
    • Appendable
    • CharSequence
    • Cloneable
    • Comparable<T>
    • Iteratable<T>
    • Readable
    • Runnable
    • Thread.UncaughtExceptionHandler

First we take a look at the most important class Object class. Object class has several methods. Some methods are very useful. Here are the methods in Object class.
  • protected Object clone()
  • boolean equals(Object obj)
  • protected void finalize()
  • Class<?> getClass()
  • int hashCode()
  • void notify()
  • void notifyAll()
  • String toString()
  • void wait()
  • void wait(long timeout)
  • void wait(long timeout, int nanos)
Now We take a look at some examples of these methods.

  • protected void finalize() throws Throwable
    • Called by garbage collector. (System.gc)
    • We can override this method to cleanup some resources
    • Not invoked more than once by a virtual machine for given object.