Here comes the time to follow some good practices when implementing actors. One of the most important rules we should follow is avoiding any blocking input/output operations, polling, busy waiting,...

Sometimes our actor needs to react differently based on its internal state. Typically receiving some specific message causes the state transition which, in turns, changes the way subsequent message...

Hope you are having fun so far, but our application has serious performance defect. After measuring response times of the RandomOrgRandom class we developed in the previous part we will notice some...

In the previous part we implemented our first actor and sent message to it. Unfortunately actor was incapable of returning any result of processing this message, which rendered him rather useless. ...

Akka is a platform (framework?) inspired by Erlang, promising easier development of scalable, multi-threaded and safe applications. While in most of the popular languages concurrency is based on me...

Java language and standard library is powerful, but with great power comes great responsibility. After seeing a lot of user code misusing or abusing rare Java features on one hand and completely fo...

Declaring complex Cron expressions is still giving me some headaches, especially when some more advanced constructs are used. After all, can you tell when the following trigger will fire "0 0 17 L-...

There is an official Code Conventions for the Java Programming Language guide published on Oracle site. You would expect this 20+ pages document to be the most complete, comprehensive and authorita...

I believe that reading and understanding stack traces is an essential skill every programmer should posses in order to effectively troubleshoot problems with every JVM language (see also: Filtering...

RateLimiter class was recently added to Guava libraries (since 13.0) and it is already among my favourite tools. Have a look what the JavaDoc says: […] rate limiter distributes permits at a con...

As an exception, this article is written in Polish as it is related to my talk at Confitura 2012 conference in Warsaw. It was chosen second best talk according to attendees votes - I would like to ...

On a day-to-day basis I am using Ubuntu, which means constantly switching between terminal window and ordinary graphical application like IDE, editors, etc. Often I need to copy a bit of text from ...

What do you do when your Java application consumes 100% of the CPU? Turns out you can easily find the problematic thread(s) using built-in UNIX and JDK tools. No profilers or agents required. For t...

This article is based on my answer on StackOverflow. I am trying to explain how String class stores the texts, how interning and constant pool works. The main point to understand here is the distin...

Few days ago I had a pleasure to attend Coderetreat summer 2012 in Oslo, carried out by Johannes Brodwall. It was a great experience, I had an opportunity to do some pair programming with six diffe...

Sometimes we just need CAPTCHA, that’s a sad fact. Today we will learn how to integrate with reCAPTCHA. Because the topic itself isn’t particularly interesting and advanced, we will overengineer a ...

Some time ago I came across What’s the purpose of AsyncContext.start(…) in Servlet 3.0? question. Quoting the Javadoc of aforementioned method: Causes the container to dispatch a thread, possibly ...

foldLeft() method, available for all collections in Scala, allows to run a given 2-argument function against consecutive elements of that collection, where the result of that function is passed as ...

Sometimes Quartz is not capable of running your job at the time when you desired. There are three reasons for that: all worker threads were busy running other jobs (probably with higher priorit...

Today we will learn how Scala compiler implements very important aspect of the language known as an eta-expansion. We will see how scalac works around the limitations of JVM, in particular with the...

Although briefly described in the official documentation, I believe Quartz plugins aren’t known enough, looking at how useful they are. Essentially plugins in Quartz are convenient classes wrappin...

I am starting a little series about Quartz scheduler internals, tips and tricks, this is a chapter 0 - how to configure persistent job store. In Quartz you essentially have a choice between storing...

I love stack traces. Not because I love errors, but the moment they occur, stack trace is priceless source of information. For instance in web application the stack trace shows you the complete req...

The choice of Java monitoring tools is tremendous (random selection and order powered by Google):     javamelody psi-probe ...

Last time we have learnt the basics of WADL. The language itself is not as interesting to write a separate article about it, but the title of this article reveals why we needed that knowledge. Man...

WADL (Web Application Description Language) is to REST what WSDL is to SOAP. The mere existence of this language causes a lot of controversy (see: Do we need WADL? and To WADL or not to WADL). I ca...

Continuing our journey with JMX (see: …JMX for human beings) we will learn how to enable JMX support (typically statistics and monitoring capabilities) in some popular frameworks. Most of this info...

One of the Spring killer-features is an in-container integration testing. While EJB lacked this functionality for many years (Java EE 6 finally addressesthis, however I haven’t, ekhem, tested it), ...

Being a Spring framework user and enthusiast for many years I came across several misunderstandings and problems with this stack. Also there are places where abstractions leak terribly and to effec...

The 0.9.30 release of Logback logging library brings new awesome feature: logging stack traces starting from root (innermost) exception rather than from the outermost one. Of course my excitement h...

Looking back at the history of Spring framework you will find out that the number of ways you can implement dependency injection is growing in every release. If you’ve been working with this framew...

Despite more complex and less intuitive syntax compared to Java, Scala actually drops several features of Java, sometimes for good, other times providing replacements on the standard library level....

Recently I received a copy of EJB 3.1 Cookbook (courtesy to Packt Publishing) with a kind request to prepare a review. And since I have just got my new Kindle reader, this was a great opportunity t...

More than two years back I wrote an article on how two implement elegant CRUD in Struts2. Actually I had to devote two articles on that subject because the topic was so broad. Today I have taken mu...

A while ago we’ve faced the requirement of load-balancing web services clients based on Apache CXF. Also the clients should automatically fail-over when some of the servers are down. To make it eve...

Today I am giving you two new appenders for Logback: one for MongoDB and one which I called recording appender. Just as a reminder, appenders (both in Log4J and Logback) are an abstraction of your ...

Java Management Extensions (JMX) is a well established, but not widespread technology allowing to monitor and manage every JVM. It provides tons of useful information, like CPU, thread and memory m...

It is not a secret that Java servlet containers aren’t particularly suited for handling large amount of concurrent users. Commonly established thread-per-request model effectively limits the number...

First, there was EJB 2.1 with countless XML files all over. It won’t be such a big exaggeration to say that for every line of business code you had to create at least 10 lines of framework code and...

I was interested in Activiti process engine long before it reached its first stable 5.0 version. Now, when 5.1 was released, I decided to play a bit with this framework, especially paying attention...

The biggest problem with unit testing using Spring testing support* is the time it takes to initialize the Spring framework context. Every new test case adds precious seconds to overall build time....

Ted Newards’ talk about functional programming in Java and his workshop on Scala (hence the article title) were the most memorable events during the third JDD conference that I attended last week. ...

In his recent post the author of fantastic mocking framework Mockito collected few rules about testing exceptions. What caught my attention is the advice to use JUnit rules (nomen est omen!) for te...

Miško Hevery’s blog post about JavaScript opened my eyes and changed the way I thought about this language completely. Miško practices TDD and advices this technique at every occasion. JavaScript, ...

The strength of the Spring Framework is its emphasis on stateless services. Being totally against OOP, this approach has many pragmatic advantages, with low memory consumption, no cost of pooling a...

It is never too late to mention about such a great event like Javarsovia 2010 conference. The conference was really successful, even though I was one of the speakers ;-). If you were near Warsaw on...

It’s almost two weeks after great Javarsovia 2010 conference, but before I write few words about this event, let me mention about really clever library called Hades. I owe you this after my attenda...

There are two groups of receivers particularly interested in your application logs: human beings (you might disagree, but programmers belong to this group as well) and computers (typically shell sc...

First of all, avoid logging exceptions, let your framework or container (whatever it is) do it for you*. Logging exceptions is one of the most important roles of logging at all, but many programmer...

This is the special case of the previous tip: if you communicate with any external system, consider logging every piece of data that comes out from your application and gets in. Period. Integration...