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Do you really get Class loaders? Presented by Simon Maple

*Please note this is an LJC event. Skills Matter are hosting this event and are handling the attendance - it is essential that you confirm your place at this link:*

Do you really get Class loaders? Presented by Simon Maple

Class loaders are at the core of the Java language. Java EE containers, OSGi, NetBeans modules, Tapestry 5, Grails and many others use class loaders heavily. Yet when something goes wrong, would you know how to solve it?

In this session we'll take a tour of the Java class loading mechanism, both from JVM and developer point of view. We will look at typical problems that you get with class loading and how to solve them. ClassNoDefError, IncompatibleClassChangeError, LinkageError and many others are symptoms of specific things going wrong that you can usually find and fix. For each problem we'll go through a hands on demo with a corresponding solution.

We'll also take a look at how and why class loaders leak and how can you remedy that.

ZeroTurnaround learnt more than they wanted to around class loaders when creating the JRebel product, which automatically reloads classes into a live runtime. There will also be a brief demo of the tool.

There will be some powerpoint slides but the session will mostly be live demos and live coding. There will also be JRebel examples to show what is possible with class loaders.

Who Should Attend:

Suitable for: Junior to Intermediate Java developers


Simon is a Technical Evangelist at ZeroTurnaround (a company who have had more interactions with class loaders than is healthy), but is less about preaching and more about discussion and interaction. His passion is around technical communities and is an active member of the London Java Community (LJC) organising group as well as the LJC JCP EC committee. Simon used to be a tester, developer and technical evangelist for IBM on the WebSphere Application Server for over 10 years prior to joining ZeroTurnaround. He enjoys playing and watching football (spherical variety), drinking tea and spending quality time with his family.


18:30: Doors Open
18:45: A lightning talk from Robert Rees - "Feature releasing: Breaking the two-week cycle"
19:00: Main presentation - presented by Simon Maple (90 mins approx.)
20:30: After event drinks venue: The Old Ivy House Pub, 166 Goswell Road EC1V 7DT

Please Note:

Nearest tube: Barbican
Nearest Coffee Shop: Sun Coffee Shop, 55-63 Goswell Road, London, EC1V 7EN for if you arrive early

*Please note this is an LJC event. Skills Matter are hosting this event and are handling the attendance - it is essential that you confirm your place at this link:*

Refreshments sponsored by ZeroTurnaround

At ZeroTurnaround, we know how classloaders can hurt your brains. Therefore after you hear about them, there will be some swag giveaways as well as some beer to recharge at The Old Ivy House Pub. This one's on us!

Event Organised by RecWorks

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  • Mike B.

    Great talk Simon, many thanks!
    Good and practical / hands-on too.

    April 26, 2013

  • Dan H.

    Highly informative, thanks!

    April 26, 2013

  • Daniel B.

    Great talk (as always) by Simon, and this content should be mandatory watching for anyone battling in the trenches with JVM-based application containers and webapps.

    One comment I wanted to share it that it could be beneficial to give some real-world examples of these problems. It could be easy to think these Exceptions are a bit esoteric or that they don't occur in day-to-day development, but I've bumped into practically all of over my career with GlassFish/JBoss. For example, I've seen the 'cannot cast X to X' quite often when packaging an XML Parser lib into a WAR and then deploying into a container with the same (but older) version of the lib.

    Seeing real-world stuff always help solidify concepts for me, and I guess it may do for others as well? Thanks again Simon!

    April 26, 2013

  • Michael B.

    Now unable to go - can't find a way to unregister on the SkillsMatter site though

    April 22, 2013

    • Wendy D.

      We are working on a new better, which will enable you to register as well as unregister... Stay tuned?!

      April 26, 2013

  • Yaroslav L.

    Good presentation, to the point

    1 · April 25, 2013

  • Ravinder G.

    Regrettable last moment events have made it unable to attend.

    April 25, 2013

  • Peter K.

    A last minute work thing means that unfortunately I'm not going to be able to make it tonight.

    April 25, 2013

  • Anji C.

    Confirmed lightning talk presented by Robert Rees - "Feature releasing: Breaking the two-week cycle"

    April 24, 2013

  • Catherine H.

    Something came up at work and I can no longer attend :(

    April 18, 2013

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