Try solving the below problem without java.exe

public class StaticUnderstanding {
	public static void main(String[] args) {
		SubClass.dummyMethod();
	}
}
class SuperClass {
	static {
		System.out.println("In superclass...");
	}
	protected static void dummyMethod(){
		System.out.println("In dummy method...");
	}
}
class SubClass extends SuperClass {
	static {
		System.out.println("In subclass...");
	}
}

If you come with any answer other than the below, then you need to read  JLS 12.4 – Initialization of Classes and Interfaces.

In superclass…

In dummy method…

Thanks to Sai for getting this awesome data !!

1. Java –version

The very first solution that came to my mind is to parse the output of java –version assuming the output to have some details about the bit support level. Happily the below output from Linux 64 bit server supports my assumption


java version “1.6.0_20″
Java(TM) SE Runtime Environment (build 1.6.0_20-b02)
Java HotSpot(TM) 64-Bit Server VM (build 16.3-b01, mixed mode)


Sadly, similar output, stating the bit support level, is not shown in Solaris 64 bit SPARC server.


java version “1.6.0_22″
Java(TM) SE Runtime Environment (build 1.6.0_22-b04)
Java HotSpot(TM) Client VM (build 17.1-b03, mixed mode, sharing)

2. file command

Those worked in nix* systems should be familiar of the file command. For others, file command determines the type of the file. Again, in Linux the output shows that java.exe is 64 bit compiled however in Solaris it is not so. Output from both the OS are as below


Linux: java: ELF 64-bit LSB executable, [snipped]
Solaris: java: ELF 32-bit MSB executable SPARC Version 1, dynamically linked, not stripped, no debugging information available

The disparity of output between the OSes is because 64 bit version of java in Solaris SPARC is actually a patch over corresponding 32 bit version. Not sure of this special treatment for Solaris SPARC. Let me know if you have idea on this.

Caveat: All the java installation notes mentions installation of 64 bit java in a 64 bit Solaris SPARC server is two step process. The first step is to install 32 bit java and then install “supplemental files” for 64-bit support. However the download page doesn’t indicate any file as supplemental files. See below,

 



File names and description on download

Both the file has the same name and description too. Even the installation doesn’t give any indication to the user. This is the starting point for most of the confusion. Will Oracle fix this?

3. 64 bit OS is not default

This is something interesting. Java provides a property “sun.arch.data.model” that provides the bit support of the JVM. Executing a simple code that prints the output of the above property reveals that Solaris SPARC servers doesn’t take 64 bit by default. If 64 bit support is needed then it should be indicated with the option –d[support_level]

Point 3 reveals a new way to find out the bit support level in java for both Solaris and Linux OSes. Proper completion of the command java –d64 –version shows that 64 bit java is installed in the server. If there is some error then probable causes could be no java is installed or installed java supports only 32 bit. By executing java –version we could find the exact cause.
Snippet

 Java -d64 -version 2>/dev/null
 if [ $? -eq 0 ]
then 
	echo “64 bit”
else
	echo “32 bit”

Let me know if you have some efficient way than this

object AutoBoxing extends Application
{
   val intVariable = 2;
    System.out.printf("%d",2); //this line fails during implicit conversion
}

The above code suffers during implicit conversion from Int to Object with an error

AutoBoxing.scala:4: error: type mismatch;
found : Int
required: java.lang.Object
Note that implicit conversions are not applicable because they are ambiguous:
both method int2Integer in object Predef of type (Int)java.lang.Integer
and method intWrapper in object Predef of type (Int)scala.runtime.RichInt
are possible conversion functions from Int to java.lang.Object
System.out.printf(“%d”,intVariable);
^
one error found

On skimming through the API documentation of Scala , I came to know of the following object hierarchy

• Int subclass of AnyVal
• AnyVal subclass of Any
• AnyRef subclass of Any
• Object subclass of AnyRef

As a java programmer we all are aware that System.out.printf accepts object as its second parameter

  public PrintStream printf(String format, Object ... args) {
  }

By now you should have sensed the issue, yes Scala fails when it tries to convert Int to Object (which is of type AnyRef, not in the hierarchy). However the error is not explicit to reason that out. There are few ways to resolve the issue

• Solution 1 : Using console.printf(…)
  

            Console.printf("%d",2);
       

• Solution 2 : Converting explicitly to java.lang.Integer using asInstanceOf
  

            System.out.printf("%d",
                               intVariable.asInstanceOf[java.lang.Integer]);
            System.out.printf("%d",intVariable : java.lang.Integer);
       

• Solution 3 : Converting to java.lang.Integer using int2Integer
  

           System.out.printf("%d",int2Integer(intVariable));
       

Do you know more way to do this? Eager to learn from you, let me know it !!

Similar problem could occur for any other type of AnyVal. Being said all these; I could find certain enhancement request on Scala with regard to this http://lampsvn.epfl.ch/trac/scala/ticket/496.

Disclaimer: I am a beginner in Scala, pardon my ignorance

public void setSubnetMask(int slashNotation) {
try {
   byte[] ipaddress = new byte[4];
   for (int i = 0; i < ipaddress.length; i++, slashNotation -= 8){
      ipaddress[i] = (byte) ((255 << (8 - (slashNotation < 9 ? slashNotation: 8))) & 255);
   }
   InetAddress address = InetAddress.getByAddress(ipaddress);
   this.subnetMask = address.getHostAddress();
  } catch (UnknownHostException e) {
      e.printStackTrace();
      this.subnetMask = "";
  }
}

Hope you find this useful. Let us know if you have a simpler approach.

Question for readers :- How will you approach the problem to achieve the vice versa functionality, i.e. converting the subnet address from dot notation (255.255.255.0) to slash notation (/24)

1. How to start with Dynamips/GNS3
2. How to emulate a switch using Dynamips/GNS3
3. How to save configuration in Dynamips/GNS3

Almost a month after updated my blog with a short screencast. Hope many more articles will flow in soon. Let us know your further questions on Dynamips/GNS3 through comments.

After finding few answers other than the one mentioned in the above article, I put the same question to some of my colleagues/friends. Most of them (99% of people, including me) immediately came up with the following answer “recursive (Number/2)==0, then power of 2” or continuous multiplication with 2 gives that number, as shown below

int number = 8;
int tempNumber = 1;
while(tempNumber<number){
    tempNumber*=2;
}
if(tempNumber==number){
   System.out.println("Power of");
else{
   System.out.println("Not a power of");
}

Yes, the above solve the problem in hand, but is this an efficient one? Will this work for large numbers or gives overflow issues? For sure I can’t see this solution as an efficient one. So I contacted my genius friend Sree. Not to the surprise, he came up with a more efficient solution. I and 99% of my friends have seen the problem in decimal but Sree has seen it in bits. Without further ado let us see the (one line) code

 System.out.println(((number&(number-1))==0)?"Power of":"Not a power of");

Hope you too accept it to be more efficient than mine  One other solution proposed by Josh Bloch in the article http://www.artima.com/wbc/interprog.html (now read it) is

System.out.println(((number&(-number))==number)?"Power of":"Not a power of");

Which answer you came up with? Hey did you come up with some new one? Let us know the same.

Amazon evangelist Jinesh Varia, after taking us through an introduction to Cloud Computing and its advantages talked about various cloud offerings from Amazon . In his words, Cloud Computing is one in which everything from storage, computing to network are accessed through APIs. APIs are exposed in REST, Query or SOAP/XML based.  For java developers, he has shown bunch of tools (sorry I couldn’t make note of everything) that comes handy, few to mention are typica, Eclipse Plug-in. I am able to grab one of his slides from slideshare. Jinesh also spent good time in explaining about the key offerings from AWS like

• S3 – Distributed redundant storage
• EBS – Elastic Block storage
• Amazon simple DB – Light weight database, indexed and query able database. However it is not a relational database.
• Amazon Relation Data Service – It is a MySQL relation database service
• Amazon SQS – I don’t have a proper definition of it, but from my understanding it is a Q that passes messages between applications/computers. It should be analogous to JMS queue
• EC2 – Virtual computation servers. It is where we create the instance that we need for processing. I see this as the heart of AWS.
• Elastic IP Address – Static IP Addresses for virtual instances in clouds. 8kMiles CTO, one of the participants mentioned this as “Pay when you don’t use”
• Amazon Mechanical turk – It is work force in the cloud. I need to research, what is needed to join this work force

Jinesh also mentioned about EBS snapshot and EBS load balancing. To understand most of these items I try to find an analogy out of the things I know. So, I think EBS snapshot should be like a virtual machine snapshot but former is all about data in S3.

We had a good time playing in clouds. Thanks to Amazon, for giving us a temporary account to play with clouds. After installing S3Fox a Firefox plug-in, working with S3 is almost like working in windows explorer as shown in Figure 1

Figure 1 - View of S3Fox

You can create buckets by right clicking on the cloud area (right upper part of the window). A bucket (directory) is a container that contains objects (files). Clicking on create directory shows a new window for entering bucket name and its location details as shown in Figure 2

Figure 2 - Creating Bucket

As the buckets are created you can go into any of those buckets and upload files from local folder to those buckets thereby to S3 clouds. It is also possible to change access permission of the files in the cloud as you do for files in windows

FIgure 3 - Editing ACL

Once a file is available in the cloud you will be able to access globally using normal http or through the exposed APIs, provided you have permission.

Now it’s time to play with EC2. We have installed Elastic Fox, yet another Firefox plug-in to play with EC2. Using Elastic Fox anyone could create an instance of Windows/Ubuntu/LAMP/WordPress (anything you name) instances in no time. In Amazon jargon these are called as AMI, Amazon Machine Image.

Figure 4 - ElasticFox listing AMI

I created one Windows 2003 R2 Datacenter edition server and I am able to successfully RDP to it. I am on Cloud9 when I am working on EC2 cloud for the first time . I am able to successfully run windows update in the virtual server running on the cloud. Even from my home network (128Mbps) I am having a good user experience (no delays or hiccups) with EC2 clouds. I searched for a Windows 7 AMI but I am not able to get one . When you create an instance you will be able to assign access groups and also configure services that need to be started.   Here is a short video on how to create EC2 instances using ElasticFox

Warning: These are really very few that are on top of my head and they might not be 100% perfect too. So I request you to take this as keys and search for more in Google. I also heard that Jinesh is writing white papers on these topics. So keep watch on that too.

After the conference we had a short un-conference section from RailsFactory, 8kmiles, CSS corp, Market Simplified, XlSoft, Hover.in, Vembu and Anantara representatives. We ended up the section with a nice cool video, which you too should watch (be sure you listen to lyrics, they are shown at the bottom too)

Hope the blog is informative. Without your feedback the blog is not complete, so please comment on your feedback. I will feel guilty if I close this without thanking my friend Sree for making me aware of this event. Thanks Sree!!

The example of greeting a user is used through this article to help you comprehend and assimilate the tips provided in this article. Let us start by creating the form

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
	pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
  <head>
     <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
     <title>Playing with Annotations</title>
   </head>
   <body>
      <form method="post" action="/PracticeREST/rest/helloworld/ ">
         <label>User Name:</label>
         <input type="text" name="name"></input>
         <input type="submit" value="submit"></input>
      </form>
    </body>
</html>

On submit, the form will be submitted as a POST request to the REST service deployed at PracticeREST/rest/greetings/ (same service that we wrote in our last article with certain modifications). The REST service should welcome the entered user. Pretty similar to the service that we saw in our last article with the following changes,

1. Have to handle POST request rather than GET as we did previously
2. Have to get the user name from form

Once we complete this, we will also look in to other ways of getting the user name, for example from URL and HTTPServletRequest object.

Manipulating Form Attributes:

For handling POST request, the POJO method needs to be decorated with @POST annotation as shown below,

@POST
public String sayHello(){
	//implement the business logic here
}

REST provides two annotations @MultivaluedMap and @FormParam to manipulate form attributes.  Using @FormParam(“param name”) we will be able to get the value of a particular form parameter as shown below,

public String sayHello(@FormParam("name") @DefaultValue("NoName") String name ){
	return "Howdy "+name+" !! Welcome to Jersey REST.";
}

In addition to @FormParam, REST provides @MultivaluedMap annotation to iterate over all the form parameters as shown below,

public String sayHello(MultivaluedMap<String, String> formParams){
	for (String key : formParams.keySet()) {
			formparameters = formparameters + formParams.get(key);
		}
		formparameters += "<br> Value got using FormParam " + userName;
	System.out.println(formparameters);
}

Note: Form parameters that has name attribute can only be manipulated with @MultivaluedMap and @FormParam annotations

Other ways to get user inputs

In addition to the above annotations which directly work on form parameters, REST provides @PathParam, @Context annotation to get user inputs.

Using @PathParam

To illustrate this, let us add a new link to our index.jsp as shown below

…..
<input type="text" name="name"></input>
<a href="/PracticeREST/rest/helloworld/veechand">Click Me</a>

Clicking on the link will direct the user to the service at /PracticeREST/rest/helloworld/veechand as a GET request. Assume that the username in the link, namely veechand, is dynamically populated using the logged in user. In this case our service URL should be something like /PracticeREST/rest/helloworld/[variable] and our business logic should able to get and process on the variable. @PathParam helps us in doing this,

@Path("/helloworld/{username}")
public String sayHello(@PathParam("username") @DefaultValue("NoName") String name ){
		return "Howdy "+name+" !! Welcome to Jersey REST.";
}

1. @PATH annotation has a variable embedded in it. This variable will be substituted at run time. Variable have to be represented in curly braces ‘{‘
2. Value of the URI variables can be got using @PathParam(’[variable name]‘). This annotation could take @DefaultValue to assign a default value to the variable.

Using @Context

@Context can be used for obtaining and processing information about the application deployment and individual request. Using @Context we can get handle to HttpHeaders, Request, SecurityContext, HttpServletConfig, ServletContext, HttpServletRequest, HttpServletResponse and EJB container details like @EJB, @EJBs, @WebServiceRef, @WebServiceRefs, @PersistenceContext, @PersistenceContexts, @PersistenceUnit and @PersistenceUnits. So using @Context a handle to Request object can be obtained and manipulated to get the needed parameters

public String post(@Context HttpServletRequest req) {
          String username = req.getParameter(key)
}

Hopefully you’ve found this tutorial interesting and this has been useful to you. Feel free to reuse this code elsewhere in your projects and chime in here if you are running into difficulties. Questions? Nice things to say? Criticisms? Hit the comments section and leave me a comment. Happy coding!

REST, acronym for Representational State Transfer is coined by Roy Fielding to represent architectural style of networked systems. This is not a standard but an architectural style for an application that is based on different standards like HTTP, XML, URL, MIME types.  JAX-RS specification, JSR 311 defines a set of java APIs for development of RESTful web services and RESTful java application.  Sun Jersey, JBoss RESTEasy, Apache CXF provides implementation for JSR 311. In this article we will look at the steps needed to setup Eclipse IDE for developing REST application using Jersey. We will also write our first HelloWorld service.

Step 1 : Downloading needed jars

The following jars needed to be available at compile time and runtime,

• jersey-core*.jar
• jersey-server*.jar
• jsr311-api-1.1.jar
• asm*.jar

All these jars can be downloaded in zip format at http://download.java.net/maven/2/com/sun/jersey/jersey-archive/

Note: Setup procedure is different for maven users and not covered in this blog.

Step 2 : Creating a Dynamic Web Project

Follow the step 2 mentioned in http://veechand.wordpress.com/2009/09/16/4-easy-steps-to-load-strut2inaction-source/

Note: Have the project name as PracticeREST instead of Struts2InAction

Step 3 : Configuring Build Path

Right click on the project. Choose properties and then Java Build Path > Libraries. Using “Add External Jars” option add the four jars downloaded in step 1

Figure 1 : Adding REST Jars

Also, change the Default output folder to classes directory (create newly) under WEB-INF folder. This has to be done in Source tab as shown below

Figure 2 - Changing Default output folder

Step 4 : Configuring REST servlets

To load Jersey servlets dispatcher add the following entries to PracticeREST/WebContent/WEB-INF/web.xml

<servlet>
   <servlet-name>Jersey Web Application</servlet-name>
  <servlet-class>com.sun.jersey.spi.container.servlet.ServletContainer</servlet-class>
</servlet>
<servlet-mapping>
 <servlet-name>Jersey Web Application</servlet-name>
 <url-pattern>/myrest/*</url-pattern>
</servlet-mapping>
</servlet>

Now all our REST web services will be available through …/rest/[resource]

Step 5 : Writing our first “Greetings” service

Create a new class my.practice.rest.Greetings and paste the below code


package my.practice.rest;
import javax.annotation.Resource;
import javax.ws.rs.DefaultValue;
import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.QueryParam;
/*
* @author veechand
*/
@Path("/sayhello/")
public class Greetings {
@GET
public String sayHello(@QueryParam("name") @DefaultValue ("NoName") String name ){
return "Howdy "+name+" !! Welcome to Jersey REST.";
}
}


The meaning of the annotations used in the above code are as below

Step 6 : Testing our Greetings Service

You will be able to access the Greetings service by launching   http://hostaddress:port-number/PracticeREST/rest/sayhello?name=veechand in your favorite http client

Note: You have to replace hostaddress and port-number with corresponding values.

Figure 3 - Result

Closing Notes:

List of principles of a REST web design can be read at http://www.xfront.com/REST-Web-Services.html. Yes, we are violating the 2^nd principle. I leave fixing this violation to readers. Comment if you have any issues in getting through it.

Keep watching for more write ups on Jersey REST

Note: Below steps explains about loading Struts2InAction (war). The same applies to HelloWorld.

Step 1 – Extract the war file

Open the war file using some extraction utility like Winrar. Extract the contents in to Struts2InAction(create new) directory in your workspace.

Figure 1 - Extracting

Step 2 – Create a Eclipse project

We need to create a Dynamic Web Project in eclipse.

Figure 2 - Creating a new project

Enter the project name as “Struts2InAction”. Select the directory created in Step 1 as value to project contents

Figure 3 - Dynamic Project

Click Finish. A new project will be created with all the source code imported as shown in the below figure,

Figure 4 - Wrong directory structure

Step 3: Files re-arrangement

We need to make certain re-arrangements before successfully running the applications.

1. Copy all Chapter* directories in to WebContent directory
2. Copy menu, images in to WebContent directory
3. Copy index.html in to WebContent directory
4. Replace Struts2InAction/WebContent/WEB-INF with Struts2InAction/WEB-INF

Note: Do the above steps using windows explorer. After copying refresh the project in eclipse.

Once the above steps are done, the workspace will be re-structured as shown below

Figure 5 - Project Structure

Step 4 – Run and Have fun

Now on a single click the application will be running within eclipse.

Figure 6 - Running Application

Hope this blog helps you in saving your valuable time. The same procedure applies to creation of any “Dynamic Web Project”. Let me know if you find more easier way to achieve the same.