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Google launches contract for Java

Vinay — Wed, 09 Feb 2011 23:57:56 +0000

Contracts for Java is a new open source tool from Google that makes it easier to implement contracts in Java. According to Google’s announcement, this new tool is based on Modern Jass by Johannes Rieken and inspired by the programming language Eiffel. It was created by two Google engineers – David Morgan, Andreas Leitner – using their 20% time, and was expanded as part of an internship by Nhat Minh Le.

These guys are trying to solve one basic fundamental problem in software programming i.e How do you enforce the contract of any class or method ?

Contracts for Java enables you to write annotate your code with contracts in the form of preconditions, postconditions and invariants.

These contract annotations are

easy to write and read,
and checked at runtime.

Annotating code with contracts helps you:

design,
document,
test, and
debug

your programs.

You will have to download one of the jars to start using the contracts in your code. This jar is not official yet but you can give a try.

Creating your first REST service using Jersey

Vinay — Wed, 29 Dec 2010 12:50:38 +0000

In the last post , we had talked about SOAP being retired in favor of REST based service. in which we discussed advantages of REST over SOAP.

This post will be a short tutorial on creating your first REST based service.

What is REST and how are they accesses ?

From Sun(oracle) docs

RESTful web services are built to work best on the Web. Representational State Transfer (REST) is an architectural style that specifies constraints, such as the uniform interface, that if applied to a web service induce desirable properties, such as performance, scalability, and modifiability, that enable services to work best on the Web. In the REST architectural style, data and functionality are considered resources and are accessed using Uniform Resource Identifiers (URIs), typically links on the Web. The resources are acted upon by using a set of simple, well-defined operations. The REST architectural style constrains an architecture to a client/server architecture and is designed to use a stateless communication protocol, typically HTTP. In the REST architecture style, clients and servers exchange representations of resources by using a standardized interface and protocol.

Why use JERSEY ?

Java defines standard REST support via JAX-RS (The Java API for RESTful Web Services) in JSR 311. Jersey is the open source, production quality, JAX-RS (JSR 311) Reference Implementation for building RESTful Web services

Here is the objective of our tutorial

Set up development environment and infrastructure to build first REST full app using JERSEY
Create the sample application
Deploy and run in tomcat

All right. Now let us get going.

1. Set up development environment

I have used maven to download files required to run the application. My IDE is Eclipse, server is tomcat 6.0.29

Add these dependencies to your pom.xml

com.sun.jersey
jersey-json
1.4

com.sun.jersey
jersey-atom
1.4

com.sun.jersey.contribs
jersey-spring
1.4

com.sun.jersey.contribs
jersey-apache-client
1.4

2. Here is the code

package com.skillguru.jersey;

import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.core.MediaType;

@Path(“/hellojersey”)
public class HelloJersey {

// for TEXT_PLAIN request
@GET
@Produces(MediaType.TEXT_PLAIN)
public String sayPlainTextHello() {
return “Hello Jersey text plain”;
}

// for HTML request
@GET
@Produces(MediaType.TEXT_HTML)
public String sayHtmlHello() {
return “ ” + “” + “Hello Jersey html” + “”
+ “

” + “Hello Jersey html” + “

” + “ “;
}

}

4.Chnage settings in your web .xml as

This is the code for web.xml

Jersey REST Service
com.sun.jersey.spi.container.servlet.ServletContainer

com.sun.jersey.config.property.packages
com.skillguru.jersey

1

Jersey REST Service
/rest/*

5. Package and deploy in tomcat . Start the server .

Type in this in browser

http://localhost:8080/cmd/rest/hellojersey

You should see

Hello Jersey in Html

Tips :

Once you run your application , you might get this error

com.sun.jersey.api.container.ContainerException: The ResourceConfig instance does not contain any root resource classes.

Go to tomcat , into WEB-INF/classes and look out for the classes

The package inside which your HelloJersey class resides should be in the same durectory as specified in web.xml

i.e HelloJersey.class should reside in your com.skillguru.jersey package inside WEB-INF/classes

It should solve the problem.

Some other references

https://jersey.dev.java.net/nonav/documentation/latest/chapter_deps.html

Core Java Interview Questions

Vinay — Sat, 11 Dec 2010 21:52:27 +0000

Java is one of the most popular programming languages as of now and even with introduction of hibernate , Spring, employers do expect you to be aware of core java concepts.

Here is Core Java Interview questions to test your knowledge.

Some of the questions like

What is WeakHasmap

Jdk1.5 has introduced class data sharing which reduces the start up time for java applications and to reduce the memory footprint, True or false

What characteristics of garbage collection have changed in jdk 5.0

you will definitely find interesting.

Some other Java interview questions and Java interview quiz on skill-Guru are

Java interview questions

Java interview questions 1

Apache resigns for Java Executive Committee

Vinay — Fri, 10 Dec 2010 17:13:18 +0000

In another blow in trying to bring Java Open source , Apache has resigned from Java SE/EE executive committee.

Why Apache took this step ?

The recent Java SE 7 vote was the last chance for the JCP EC to demonstrate that the EC has any intent to defend the JCP as an open specification process, and demonstrate that the letter and spirit of the law matter. To sum up the issues at stake in the vote, we believe that while continuing to fail to uphold their responsibilities under the JSPA, Oracle provided the EC with a Java SE 7 specification request and license that are self-contradictory, severely restrict distribution of independent implementations of the spec, and most importantly, prohibit the distribution of independent open source implementations of the spec. Oracle has refused to answer any reasonable and responsible questions from the EC regarding these problem

The Apache Software Foundation concludes that that JCP is not an open specification process – that Java specifications are proprietary technology that must be licensed directly from the spec lead under whatever terms the spec lead chooses; that the commercial concerns of a single entity, Oracle, will continue to seriously interfere with and bias the transparent governance of the ecosystem; that it is impossible to distribute independent implementations of JSRs under open source licenses such that users are protected from IP litigation by expert group members or the spec lead; and finally, the EC is unwilling or unable to assert the basic power of their role in the JCP governance process

This is very big step and it will again raise questions , Can java be open sourced or Oracle will try to control all aspects of Java and its licensing.

Is Java on path to lose its stature as open source programming language ? Although Java was not clearly open sourced but it was also not under so much control as Oracle is trying to exert on it.

Switching to python

Vinay — Fri, 03 Dec 2010 21:10:55 +0000

I am a java programmer and although my wife has switched to grails, I am yet to find the motivation to move on something better. If you are looking for any reasons to switch to Python, here are two excellent posts which would help you decide why Python should be your next language of choice

An excellent post by Dharmesh

Why PHP Is Fun and Easy But Python Is Marriage Material

A very informative post

Ruby is beautiful but I am moving to phython

Parsing a date with SimpleDateFormat in java

Vinay — Tue, 30 Nov 2010 02:52:48 +0000

A small code sample on how can you format java.util.date or any date into a desired format

java.util.Date todayDate = new java.util.Date()

or preferably

Date todayDate = Calendar.getInstance().getTime();
// this is the format 2010-11-25 8:30:24
SimpleDateFormat dateFormat = new SimpleDateFormat(“yyyy-MM-dd HH:mm:ss “);

String outcome = dateFormat.format(todayDate);

System.out.println(outcome);

Java Interview questions

Vinay — Fri, 19 Nov 2010 03:58:51 +0000

Java is the most popular programming language and even with onset of all new languages like Ruby, Scala, the popularity of java has only grown . Java/J2EE is the preferred enterprise solution for the business user.

So when it comes to number of jobs, no doubt java has the most most jobs. But you should also be prepared when going for interview and here is a series of tests and quiz to help you prepare for Java inerview

A free quiz to test your knowledge of core java and collections

Take java Interview questions.

This test would test you on your basic concepts of java like

What is result Set ? (A class or interface)

When I say this “is the inclusion of behavior (i.e. methods) and state (i.e. variables) of a base class in a derived class so that they are accessible in that derived class”, what I am talking about ?

How many JVM could be run on an operating system ?

Another Java Interview questions test. This test covers more on hands on programming and inner classes

How many JVM can be run on an operating system (OS) ?

Vinay — Tue, 16 Nov 2010 04:33:44 +0000

You can have one JVM per process. Since an OS supports many processes, you can have many JVMs running.

When ever we start a new java process by invoking java.exe (i.e. java [class-name] ) a new instance of JVM is created. Each java process executes in its separate JVM environment – we can specify different JVM parameter for each process.

So you can open as many as command prompt your machine allows and run as many JVM as possible. It also means you can run different versions of JVM.

Groovy: The new buzz in the Java world

Chin — Sat, 30 Oct 2010 14:51:02 +0000

Groovy is the dynamic language for the Java Virtual Machine. Inspired from Java, Ruby and Python, Groovy is an object-oriented language written in Java. Groovy is designed to help you get things done on the Java platform in a quicker, more concise and fun way – bringing the power of Python and Ruby inside the Java platform

Groovy’s addition to the application is as of enhancing the power and capabilities of java.

Like Java, everything is an object in Groovy.

The java virtual machine has no idea that its running the groovy code. Groovy is written in Java. As java library is called by the name JDK, the groovy library is enclosed and called by the name GDK – Groovy Development Kit.

It complements the productivity of the java programmers through its powerful features.

The code is written in .groovy file and it gets compiled to byte codes (.class file).
The groovy code could be directly loaded in the run time.

What is Groovy ?

In a nutshell it is the scripting language for the Java platform. There are many scripting languages like bash, PERL, python etc.., Most of them complement the UNIX platform. Groovy is one like them inspired by Ruby and Java, and had come in to complement the Java patform.

Why Groovy ?

There are many languages developed for scripting. To name a few popular ones JRuby, Jython are some of them. JRuby and Groovy has gained significant
importance in the recent years and are competing each other in the recent years.

One could choose groovy for a variety of reasons.

It has the java-like syntax
for a java programmer has a faster learning curve
contains a vast set of library features which could enhance productivity.
Provides coding structure in such a way that it is easy to achieve in a few lines of code than which could be achieved in java with much larger code steps.

As groovy is designed to run on JVM, it serves as a protector for the codes that’s been developed for years in the past.

In the first look, it may seem that groovy is confusing, but in the long run it makes a big difference.

Groovy over Java

The main advantage of having groovy over java is the rapid development of CRUD based applications and much lesser lines of code. Java’s capability to achieve things is done in much fewer lines of code.

Groovy Command Line

The groovy command line helps in executing groovy programs.
The Groovy Console

The groovy console is a GUI toolkit used to run groovy programs. A groovy program could be loaded, compiled and executed in the groovy console. Of course, you could also see the output in the bottom panel instantly.

To delineate the power of groovy, I could say that the whole chunk of code written in java to accomplice a task could be easily written in groovy in a fly.

You can download groovy @ http://groovy.codehaus.org/Download

What is coming up in JDK 7 ?

Vinay — Thu, 21 Oct 2010 03:13:07 +0000

JDK 7 which is scheduled to be release in 2011, has some new features which should make programming fun. One of them is dynamically typed language . The JSR 292 new method invocation mode : invokedynamic. With that new bytecode keyword, we can call method only known at runtime.

A new package java.dyn that will use this new functionality. That package will improve the performances of Java reflection and mainly the performances of the others languages that run in the JVM.

Then there is a new class java.util.Objects. This class contains 9 static methods to work on Objects.

See the complete list of JDK 7 features

There is a post by Arun, Advantages of Java 7- Project Coin