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Tag Archives: Java 8

Clean JUnit Throwable-Tests with Java 8 Lambdas

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Recently I was involved in a short online discussion on twitter and google+ which concerned the question why the arrival of Java 8 Lambda expressions makes the catch-exception library1 obsolete. This was triggered by a brief announcement that the library won’t be longer maintained as lambdas will make it redundant. The answer I came up with at that time has ...

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Grouping, sampling and batching – custom collectors in Java 8

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Continuing first article, this time we will write some more useful custom collectors: for grouping by given criteria, sampling input, batching and sliding over with fixed size window. Grouping (counting occurrences, histogram) Imagine you have a collection of some items and you want to calculate how many times each item (with respect toequals()) appears in this collection. This can be achieved ...

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Introduction to writing custom collectors in Java 8

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Java 8 introduced the concept of collectors. Most of the time we barely use factory methods from Collectors class, e.g. collect(toList()), toSet() or maybe something more fancy like counting() or groupingBy(). Not many of us actually bother to look how collectors are defined and implemented. Let’s start from analysing what Collector<T, A, R> really is and how it works. Collector<T, A, R> works as a “sink” for streams – stream pushes ...

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Java 8 Friday: More Functional Relational Transformation

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In the past, we’ve been providing you with a new article every Friday about what’s new in Java 8. It has been a very exciting blog series, but we would like to focus again more on our core content, which is Java and SQL. We will still be occasionally blogging about Java 8, but no longer every Friday (as some ...

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JUnit: testing exception with Java 8 and Lambda Expressions

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In JUnit there are many ways of testing exceptions in test code, including try-catch idiom, JUnit @Rule, with catch-exception library. As of Java 8 we have another way of dealing with exceptions: with lambda expressions. In this short blog post I will demonstrate a simple example how one can utilize the power of Java 8 and lambda expressions to test ...

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6 Reasons Not to Switch to Java 8 Just Yet

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Java 8 is awesome. Period. But… after we had the chance to have fun and play around with it, the time has come to quit avoiding the grain of salt. All good things come with a price and in this post I will share the main pain points of Java 8. Make sure you’re aware of these before upgrading and letting ...

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RxJava + Java8 + Java EE 7 + Arquillian = Bliss

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Microservices are an architectural style where each service is implemented as an independent system. They can use their own persistence system (although it is not mandatory), deployment, language, … Because a system is composed by more than one service, each service will communicate with other services, typically using a lightweight protocol like HTTP and following a Restful Web approach. You ...

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Turning recursive file system traversal into Stream

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When I was learning programming, back in the days of Turbo Pascal, I managed to list files in directory usingFindFirst, FindNext and FindClose functions. First I came up with a procedure printing contents of a given directory. You can imagine how proud I was to discover I can actually call that procedure from itself to traverse file system recursively. Well, I didn’t know the ...

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Type safe dependency injection using Java 8.0

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So I sometimes really miss old school Dependency Injection. Back when Spring was still “lightweight” we happily configured all our beans in an application.xml file with the “learn-in-a-day” Spring bean xml configuration. The downsides to this were of course a loss of type safety. I can think of quite a few test cases whose sole purpose was to bootstrap the Spring ...

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