About Tomasz Nurkiewicz

Java EE developer, Scala enthusiast. Enjoying data analysis and visualization. Strongly believes in the power of testing and automation.

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instanceof operator and Visitor pattern replacement in Java 8

I had a dream where instanceof operator and downcasting were no longer needed but without clumsiness and verbosity of visitor pattern. So I came up with the following DSL syntax:                 Object ...
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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 ...
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Asynchronous retry pattern

When you have a piece of code that often fails and must be retried, this Java 7/8 library provides rich and unobtrusive API with fast and scalable solution to this problem:                   ScheduledExecutorService ...
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Managing congested actors in Akka

There comes a time in an Akka application when an actor can longer handle increasing load. Since each actor can only handle one message at a time and it keeps a backlog of pending messages ...
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Fake system clock pattern in Scala with implicit parameters

Fake system clock is a design pattern addressing testability issues of programs heavily relying on system time. If business logic flow depends on current system time, testing various ...
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su and sudo in Spring Security applications

Long time ago I worked on a project that had a quite powerful feature. There were two roles: user and supervisor. Supervisor could change any document in the system in any way while ...
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Macro lifecycle in Clojure

If you still struggle to understand what are macros in Clojure and why are they so useful, I will guide you through another example today. We will learn when macros are recognized, ...
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Clojure macros for beginners

This article will guide you step-by-step (or even character-by-character) through the process of writing macros in Clojure. I will focus on fundamental macro characteristics while explaining ...
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Mapping enums done right with @Convert in JPA 2.1

If you ever worked with Java enums in JPA you are definitely aware of their limitations and traps. Using enum as a property of your @Entity is often very good choice, however JPA prior ...
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Null safety in Kotlin

Kotlin is a statically typed JVM language developed by Jetbrains. It has some good documentation so today I will focus on a tiny part of it – null safety.There are at least ...
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