The Holy Java

Building the right thing, building it right, fast

Posts Tagged ‘patterns’

There will be failures – On systems that live through difficulties instead of turning them into a catastrophy

Posted by Jakub Holý on March 17, 2015

Our systems always depend on other systems and services and thus may and will be subject to failures – network glitches, dropped connections, load spikes, deadlocks, slow or crashed subsystems. We will explore how to create robust systems that can sustain blows from its users, interconnecting networks, and supposedly allied systems yet carry on as well as possible, recovering quickly – instead of aggreviating these difficulties and turning them into an extended outage and potentially substiantial financial loss. In systems not designed for robustness, even a minor and transient failure tends to cause a chain reaction of failures, spreading destruction far and wide. Here you will learn how to avoid that with a few crucial yet simple stability patterns and the main antipatterns to be aware of. Based primarily on the book Release It! and Hystrix. (Presented at Iterate winter conference 2015; re-posted from

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Patterns of Effective Delivery – Challenge Your Understanding Of Agile (RootsConf 2011)

Posted by Jakub Holý on June 22, 2013

Highlights from Dan North‘s excellent, inspiring, and insightful talk Patterns of Effective Delivery at RootConf 2011. North has a unique take on what agile development is, going beyond the established (and rather limitied and rigid) views. I really recommend this talk to learn more about effective teams, about North’s “shocking,” beyond-agile experience, and for great ideas on improving your team.

The talk challenges the absolutism of some widely accepted principles of “right” software development such as TDD, naming, the evilness of copy&paste. However the challenge is in a positive way: it makes us think in which contexts these principles really help (in many) and when it might be more effective to (temporarily) postpone them. The result is a much more balanced view and better undestanding of their value. A lot of it is inspired by the theory (and practice) of Real Options.

What are Patterns of Effective Delivery?

  • Patterns – strategies that work in a particular context – and not in another (too often we forget the context and to consider the context where a strategy doesn’t work / is contra-productive); beware: a part of the context is the experience of the developer; for unexperienced devs it might be better to just stick to a process and applying TDD etc. all the time than trying to guess when they are appropriate and when not without having the experience to decide it right
  • Effective – optimize for something: volume of SW produced? time to market? learning/discovery? certanity? user experience?
  • Delivery – get stuff that is useful out of the door; software is not important, the utility it provides is; know why you write the SW to be able to get better at it

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Most interesting links of July

Posted by Jakub Holý on August 2, 2010

This month about performance, the Java language and patterns, the development process, and a few interesting news.

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Book: Real World Java EE Patterns – Rethinking Best Practices (review & digest)

Posted by Jakub Holý on May 8, 2010

I’d like to make you aware of the excellent book Real World Java EE Patterns – Rethinking Best Practices by Adam Bien (blog), a Java Champion and renowned consultant, software architect and Java EE standardization comitee member. I’d absolutely recommend it to any architect or developer serious with Java EE 5 or 6 development, even to those not planning to use EJB 3.x (at least prior to reading the book :)). It’s a must-read complement to the now a little outdated Core J2EE patterns as it updates the patterns for the new bright world of EJB 3/3.1 while discarding some of them and introducing some new, extremely useful patterns and techniques.

The book starts with an overview of the evolution of Java Enterprise Edition and the hard issues it solves for us, continues with the new and updated patterns and strategies and concludes with an introduction of two opposite architectures you can build with Java EE 5/6, namely lean SOA and domain-driven (which itself makes it worth reading).

What I really appreciate in addition to that valuable content is that for each pattern there is a section on testing and documentation and a really good evaluation of consequences in terms of maintainability, performance and other such qualities. You will find there also many code samples and beautiful applications of the Builder and Fluent API patterns.

The main message is that EJB 3.x is so lean and powerful that we must justify why NOT using it – and when using it, you should be very pragmatic and only introduce patterns, layers and principles if they bring real value.

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PatternTesting: Automatically verifying the good application of architectural/design patterns in code

Posted by Jakub Holý on September 25, 2009

PatternTesting is a mature open-source project that enables you to automatically check at the compile- or run-time that architectural/design/implementation decisions are implemented and bad practices avoided in the code. The main differences from tools like FindBugs and PMD are that you can implement tests spanning multiple files (classes) and that aside of compile-time checks there are also run-time checks (using AOP with ApsectJ) to do things like “ensuring that there are no more than 10 calls to the database per user case” and providing better error messages in the case of e.g. IOException.

Read more in a The Server Side’s introductory article and on the project’s page.

I haven’t yet the chance to try this out but it really intrigues me.

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