Pizza problem- builder vs decorator

Problem Statement :
We need to build the software for a pizza company who wants to prepare different types of pizzas, e.g Chicken Pizza, Flat Bread, Pepperoni Pizza with Extra Cheese, put add on toppings on it.

Lets try to see which design pattern suits this problem statement and under what scenario.
Traditionally, for pizza problem, builder pattern is most commonly used. However there are some examples using decorator as well, both the approaches are correct but there is difference in use case.
Builder is an object creation pattern whereas decorator is used to change the already built object at runtime.
Lets try to understand this by the examples :
Read More »

Converting JSON to XML to Java Objects using XStream

XStream library can be an effective tool for converting JSON to Java to XML translations to and fro.
Lets explore each one of them one by one, and see which driver is used.

Handling JSONs

To convert JSON to Java objects all you have to do is initialize XStream object with an appropriate driver and you are ready to serialise your objects to (and from) JSON.
Read More »

Configuring chef Part-2

Lets recap what all we have done in the last blog :

1.) Setup workstation and chef-repo.
2.) Registered on chef to use hosted chef as the chef-server.
3.) Bootstrapped a node to be managed by the chef-server.
4.) Downloaded the “apache” cookbook in our chef-repo.
5.) Uploaded the “apache” cookbook to the chef-server.
6.) Added the recipe[apache] in the run-list of the node.
7.) Ran the chef-client on the client to apply the cookbook.

Now lets continue, and try to understand some more concepts around chef and see them in action.
Read More »

Configuring Chef part 1

Below are the first steps in getting started with using chef.
The three main components of chef are :
1.) Work station
This is the developer’s machine will be used to author cookbooks and recipes and upload them to the chef-server using the command line utility called knife.
2.) Chef-Server
This is the main server on which all the cookbooks, roles, policies are uploaded.
3.) Node
This is the instance which would be provisioned by applying the cookbooks uploaded on the chef-server.

So, lets get started:
Read More »

How to mock HTTP endpoints in Mule Functional Test?

Mule is an enterprise service bus (ESB) and integration framework. In Mule, we define flows and sub-flows in order to integrate applications and orchestrate services.These flows contain endpoints to integrate different applications or services. These endpoints can be HTTP, VM, JMS, etc. More details about development in mule can be found here. Below is a sample flow.
Screen Shot 2014-03-18 at 1.12.54 PM

In order to write unit test cases for mule flows, mule provides an abstract JUnit test case called org.mule.tck.junit4.FunctionalTestCase that runs Mule inside a test case and manages the lifecycle of the server.More details about can be found here.
Read More »

Vagrant – a swiss Army knife for every developer

Whenever we move to a new project, or we want to explore a new stack of technologies; we face the problem of environments. Being a developer we generally have a tendency to install everything on our local environment; which many times proves to be a disaster.

Today, modern web applications involve a lot of moving parts, numerous underlying technologies and a lot of complexity.Read More »

Implement single click deployment using Jenkins and DeployIt

Problem statement : Implement single click deployment using Jenkins and DeployIt
Tools used: Jenkins CI Server, DeplyIt Plugin for Jenkins, Github plugin for jenkins, Maven for building artifact.

Detailed use case :
Lets suppose we have our code in github in a public repository and we want that every fix which goes to “deployment” branch should get propagated to a dev environment automatically.

In order to get this set up working we would need to do:
1.) Configure Jenkins with gitHub and deployIt Plugin.
2.) Configure application placeholder and environment (including infrastructure) in which deployment would take place in DeployIt.
Read More »

chef-solo with vagrant

To learn the concepts of chef, we can start by using chef-solo with Vagrant.
See my previous post on Vagrant to install vagrant and know more about it.

Next, lets install chef-solo on our machine.
We will install chef-solo using ruby gem,(for both Linux and Mac) make sure you have ruby installed.

root@intro:~# cd ~
root@intro:~# sudo gem install chef
Thank you for installing Chef!

So, now we have installed chef-solo and vagrant on our machine.
In this exercise, we will try and install apache2 on an ubuntu virtual machine (virtual box)
using chef-solo and vagrant.
To begin we would first need to understand few concepts; which would be required to run chef-solo in Vagrant.
Read More »

What are Reentrant Locks?

In Java 5.0 a new addition was made to enhance the intrinsic locking capabilities, called as Reentrant Lock.
Prior to this, ‘synchronized’ and ‘volatile’ were the means for achieving concurrency.

public synchronized void doAtomicTransfer(){
     //enter synchronized block , acquire lock over this object.
    operation1()
    operation2();    
} // exiting synchronized block, release lock over this object.

Synchronized uses intrinsic locks or monitors. Every object in Java has an intrinsic lock associated with it. Whenever a thread tries to access a synchronized block or method it acquires the intrinsic lock or the monitor on that object. In case of static methods, the thread acquires the lock over the class object.
Intrinsic locking mechanism is a clean approach in terms of writing code and is pretty good for most of the use-cases. So why do we need additional feature of Explicit Locks? Lets discuss.

Read More »