Considering legacy Java code, no matter where you look, Java 8 with lambda expressions can definitely improve quality and readability. Today let us look at ReadWriteLock and how we can make using i...
First of all, let me tell this out loud: Spring is no longer XML-heavy. As a matter of fact you can write Spring applications these days with minimal or no XML at all, using plenty of annotations, ...
Imagine a simple Akka actor system consisting of two parties: MonitoringActor and NetworkActor. Whenever someone (client) sends CheckHealth to the former one it asks the latter by sending Ping. Net...
aTwitter4J is a Java wrapper around Twitter API. While Twitter supports simple request-response interactions in this article we will explore streaming APIs. In contrary to request-response model wh...
Not too often but sometimes we are forced to write custom dynamic proxy class using java.lang.reflect.Proxy. There is really no magic in this mechanism and it’s worth knowing even you will never re...
During my talk at Warsaw Java Users Group about functional reactive programming in Java a few interesting questions came up regarding CompletableFuture capabilities. One person was interested wheth...
During job interviews we often give Scala developers a simple design task: to model a binary tree. The simplest but not necessarily best implementation involves Option idiom: case class Tree[+T](v...
Last time we developed brainfuck interpreter in Clojure. This time we will write a compiler. Compilation has two advantages over interpretation: the resulting program tends to be faster and source ...
Brainfuck is one among the most popular esoteric programming languages. Writing a Brainfuck interpreter is fun, in contrary to actually using this “language”. The syntax is dead simple and semantic...
Don’t be fooled by the “beginning” in the title. This 600-pages book is a comprehensive and complete walk-through of all components and technologies comprising Java EE 7 stack. Antonio Goncalves, J...
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 msg = //.....
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 cont...
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: ScheduledExecutorServic...
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 in a que...
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 flows becomes ...
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, evaluated, expan...
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 users were much...
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 what h...
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 to 2.1 didn’...
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 couple of approaches t...
I just published LazySeq library on GitHub - result of my Java 8 experiments recently. I hope you will enjoy it. Even if you don’t find it very useful, it’s still a great lesson of functional progr...
After thoroughly exploring CompletableFuture API in Java 8 we are prepared to write a simplistic web crawler. We solved similar problem already using ExecutorCompletionService, Guava ListenableFutu...
Java 8 is coming so it’s time to study new features. While Java 7 and Java 6 were rather minor releases, version 8 will be a big step forward. Maybe even too big? Today I will give you a thorough e...
I recently stumbled upon an article Synchronising Multithreaded Integration Tests on Captain Debug’s Blog. That post emphasizes the problem of designing integration tests involving class under test...
Lazy sequences (also known as streams) are an interesting functional data structure which you might have never heard of. Basically lazy sequence is a list that is not fully known/computed until you...
One novel feature of Logback is SiftingAppender (JavaDoc). In short it’s a proxy appender that creates one child appender per each unique value of a given runtime property. Typically this property ...
WatchService is a handy class that can notify you about any file system changes (create/update/delete of file) in a given set of directories. It is described nicely in the official documentation so...
This is a continuation of Scala traits implementation and interoperability. Part I: Basics. Dreadful diamond problem can be mitigated using Scala traits and a process called linearization. Take the...
Traits in Scala are similar to interfaces, but much more powerful. They allow implementations of some of the methods, fields, stacking, etc. But have you ever wondered how are they implemented on t...
Today as an example we will take a very simple scenario: placing an order stores it and sends an e-mail about that order: @Service class OrderService @Autowired() (orderDao: OrderDao, mailNotifier...
This article won’t be about FitNesse. As matter of fact I don’t like this tool very much and it seems to be loosing momentum, judging by the traffic on an official mailing list. Instead we will imp...
Clojure, being designed for concurrency is a natural fit for our Back to the Future series. Moreover futures are supported out-of-the-box in Clojure. Last but not least, Clojure is the first langua...
Series of articles about futures/promises without JavaScript would not be complete. Futures (more commonly named promises in JS land) are ubiquitous in JavaScript to the point where we almost don’t...
Akka is actor based, event-driven framework for building highly concurrent, reliable applications. Shouldn’t come a surprise that concept of a future is ubiquitous in a system like that. You typica...
DeferredResult is a container for possibly not-yet-finished computation that will be available in future. Spring MVC uses it to represent asynchronous computation and take advantage of Servlet 3.0 ...
Last time we familiarized ourselves with ListenableFuture. I promised to introduced more advanced techniques, namely transformations and chaining. Let’s start from something straightforward. Say we...
ListenableFuture in Guava is an attempt to define consistent API for Future objects to register completion callbacks. With the ability to add callback when Future completes, we can asynchronously a...
Everyone is talking about the future of Java, we continue our journey explaining Future<T> interface in Java. ExecutorCompletionService wrapper class tries to address one of the biggest defic...
Last time we learned the principles behind java.util.concurrent.Future<T>. We also discovered that Future<T> is typically returned by libraries or frameworks. But there is nothing stopp...
Hereby I am starting a series of articles about future concept in programming languages (also known as promises or delays) with a working title: Back to the Future. Futures are very important abstr...
When you are building a complex system, barely testing components in isolation is not enough. It’s crucial, but not enough. Imagine a car factory that manufactures and imports highest quality parts...
For years I’ve been taught that breaking continuous integration build is something that should be avoided under all circumstances. Let me first quote few classics. Uncle Bob in The Clean Coder says...
Ctrl + Alt + M is used in IntelliJ IDEA to extract method. Ctrl + Alt + M. It’s as simple as selecting a piece of code and hitting this combination. Eclipse also has it. I hate long methods. To the...
I am thrilled to announce first version of my Spring Data JDBC repository project. The purpose of this open source library is to provide generic, lightweight and easy to use DAO implementation for ...
Spring 3.1 introduced great caching abstraction layer. Finally we can abandon all home-grown aspects, decorators and code polluting our business logic related to caching. Since then we can simply a...
This is one of these very simple programming puzzles I came across recently: given a function returning random integers from 0 to 4 inclusive with equal probability, write a function returning ...
So you have your executable web application in JAR with bundled Tomcat (make sure to read that one first). However there are these annoying Tomcat logs at the beginning, independent from our applic...
When it comes to deploying your application, simplicity is the biggest advantage. You’ll understand that especially when project evolves and needs some changes in the environment. Packaging up your...
Some time ago a friend of mine asked me about the possibilities of speeding up the following process: they are generating some data in two stages, reading from a database and processing the results...
Assume our test application became a huge success and slowly a single server is not capable of handling growing traffic. We are faced with two choices: replacing our server with a better one (scali...