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Long Polling Tomcat with Spring


“Ooh err Missus” as comedian Frankie Howerd would have said, but enough of British innuendo and double entendre because Long Polling Tomcat isn’t some kind of sexual deviance with next door’s moggy, it’s a technique (or more of a hack) that’s been developed as a result of Steve Jobs’s refusal to support Adobe Flash Player on the iPhone and iPad. ...

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Writing a Hadoop MapReduce task in Java


Although Hadoop Framework itself is created with Java the MapReduce jobs can be written in many different languages. In this post I show how to create a MapReduce job in Java based on a Maven project like any other Java project.                 Prepare the example input Lets start with a fictional business case. ...

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Creating a price model using k-Nearest Neighbours + Genetic Algorithm


Chapter 8 of Programming Collective Intelligence (PCI) explains the usage and implementation of the k-Nearest Neighbours algorithm. (k-NN). Simply put: k-NN is a classification algorithm that uses (k) for the number of neighbours to determine what class an item will belong to.  To determine the neighbours to be used the algorithm uses a distance / similarity score function, in this example (Euclidian Distance). ...

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From inside the code: Camel Routing Engine Part I


So I’ve recently re-kindled my interest in how Apache Camel works. Camel is such a powerful integration tool and is very widely used, but anytime I put it to work, I can’t help but think “well, how the hell does it do all that!!” … guess I just have knack for not just accepting that it’s wonderful.. I want to ...

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Optional in Java 8 cheat sheet


java.util.Optional<T> in Java 8 is a poor cousin of scala.Option[T] and Data.Maybe in Haskell. But this doesn’t mean it’s not useful. If this concept is new to you, imagine Optional as a container that may or may not contain some value. Just like all references in Java can point to some object or be null, Option may enclose some (non-null!) ...

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50 Servlet Interview Questions and Answers


Servlets are very important topic of Java EE and all of the web applications framework such as Spring and Struts are built on top of it. This makes servlet a hot topic in Java interviews. Here I am providing a list of 50 servlet interview questions with answers to help you tackle most of the interview questions related to servlets ...

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10 More Common Mistakes Java Developers Make when Writing SQL


I was positively surprised to see how popular my recent listing about 10 Common Mistakes Java Developers Make when Writing SQL was, both on my own blog and on my syndication partner DZone. The popularity shows a couple of things: How important SQL is to the professional Java world. How common it is to forget about some basic SQL things. How well SQL-centric ...

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Simple and lightweight pool implementation


Object pools are containers which contain a specified amount of objects. When an object is taken from the pool, it is not available in the pool until it is put back. Objects in the pool have a lifecycle: creation, validation, destroying, etc. A pool helps to manage available resources in a better way. There are many using examples. Especially in ...

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Async Servlet Feature of Servlet 3


Before we jump into understanding what Async Servlet is, let’s try to understand why do we need it. Let’s say we have a Servlet that takes a lot of time to process, something like below.        package com.journaldev.servlet; import; import; import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; ...

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