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Double Checked Locking on Singleton Class in Java

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Singleton class is quite common among Java developers, but it poses many challenges to junior developers. One of the key challenge they face is how to keep Singleton class as Singleton? i.e. how to prevent multiple instances of a Singleton due to whatever reasons. Double checked locking of Singleton is a way to ensure only one instance of Singleton class ...

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Parsing a file with Stream API in Java 8

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Streams are everywhere in Java 8. Just look around and for sure you will find them. It also applies to java.io.BufferedReader. Parsing a file in Java 8 with Stream API is extremely easy. I have a CSV file that I want to be read. An example below:             username;visited jdoe;10 kolorobot;4 A contract for my ...

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Grails tip: refactoring your URLs

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On the current project I am working we use a lot of integration tests. For you non-Grails users out there, Integration tests test your Controller APIs, your Services and any persistence that might happen all very neatly. The only slice of the cake they don’t test from a back end perspective are your Grails filters for which you’d need something ...

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Writing Clean Tests – New Considered Harmful

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It is pretty hard to figure out a good definition for clean code because everyone of us has our own definition for the word clean. However, there is one definition which seems to be universal: Clean code is easy to read. This might come as a surprise to some of you, but I think that this definition applies to test ...

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Yet Another 10 Common Mistakes Java Developers Make When Writing SQL (You Won’t BELIEVE the Last One)

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(Sorry for that click-bait heading. Couldn’t resist!) We’re on a mission. To teach you SQL. But mostly, we want to teach you how to appreciate SQL. You’ll love it! Getting SQL right or wrong shouldn’t be about that You’re-Doing-It-Wrong™ attitude that can be encountered often when evangelists promote their object of evangelism. Getting SQL right should be about the fun ...

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The Absolute Basics of Indexing Data

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Ever wondered how a search engine works? In this post I would like to show you a high level view of the internal workings of a search engine and how it can be used to give fast access to your data. I won’t go into any technical details, what I am describing here holds true for any Lucene based search ...

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What Is Special About This? Significant Terms in Elasticseach

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I have been using Elasticsearch a few times now for doing analytics of twitter data for conferences. Popular hashtags and mentions that can be extraced using facets can show what is hot at a conference. But you can go even further and see what makes each hashtag special. In this post I would like to show you the significant terms ...

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JPA 2.1 Entity Graph – Part 1: Named entity graphs

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Lazy loading was often an issue with JPA 2.0. You have to define at the entity if you want to use FetchType.LAZY (default) or FetchType.EAGER to load the relation and this mode is always used. FetchType.EAGER is only used if we want to always load the relation. FetchType.LAZY is used in almost all of the cases to get a well ...

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Prefix and Suffix Matches in Solr

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Search engines are all about looking up strings. The user enters a query term that is then retrieved from the inverted index. Sometimes a user is looking for a value that is only a substring of values in the index and the user might be interested in those matches as well. This is especially important for languages like German that ...

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Generate your JAXB classes in a second with xjc

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Since JAXB is part of the JDK, it is one of the most often used frameworks to process XML documents. It provides a comfortable way to retrieve and store data from XML documents to Java classes. As nearly every Java developer has already used JAXB, I will not explain the different JAXB annotations. Instead I will focus on a little ...

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