Why Java Doesn't Have Instant Turnaround
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Java does not have instant turnaround for code changes due to challenges reloading classes and preserving object state between classloader instances. Frameworks like Play, Tapestry and Grails, and tools like JRebel, help enable faster development cycles by supporting class reloading and state migration without full redeploys. JRebel in particular integrates with IDEs, build tools, containers and frameworks to allow changes to classes, methods and fields to take effect instantly in production.
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Why Java Doesn't Have Instant Turnaround
- 1. Why Doesn’t Java Have Instant Turnaround? Anton Arhipov @antonarhipov Product Lead at ZeroTurnaround
- 3. Turnaround cycle Check Make a the change change Build, deploy, wait twitter.com/ekabanov
- 4. What about others? twitter.com/ekabanov
- 5. Why Java is heavier than others? Vendors Standards Operations Dev << Prod twitter.com/ekabanov
- 6. A typical web application build Resolve dependencies Copy static resources Compile classes Package modules in JARs Package everything in a WAR/EAR twitter.com/ekabanov
- 7. Exploded layout twitter.com/ekabanov
- 8. Automatic building twitter.com/ekabanov
- 9. Deployment by linking Linux symbolic links • ln -s • Symlinks can point to any file Windows symbolic links • Sysinternals junction utility on NTFS partitions, included in Windows 7 • Can only link to local directories and must be careful when deleting twitter.com/ekabanov
- 10. 2008 => 2011 Help! is downloading the internets! twitter.com/ekabanov
- 11. 2008 => 2011 this works: mvn jetty:run others? twitter.com/ekabanov
- 12. App Server Workspace getResource(“hello.html”) read(“src/main/.../hello.html”) twitter.com/ekabanov
- 13. A typical web application build Resolve dependencies Copy static resources Compile classes Package modules in JARs Package everything in a WAR/EAR twitter.com/ekabanov
- 14. Why code reloading is so hard? Externalized Temporary State Serializable Derivative twitter.com/ekabanov
- 15. Reloading an Object OldClassLoader NewClassLoader MyObject.class MyObject.class Recreate the object MyObject MyObject twitter.com/ekabanov
- 16. Web Deployment Serialize/deserialize init() Session Session Sevlet New Sevlet Classes Classes App App New State Libraries State Libraries OldClassLoader NewClassLoader twitter.com/ekabanov
- 17. Twin ClassLoader Issues Classes Classes Objects Objects and Code and Code Libraries Libraries OutOfMemoryError ClassCastException OldClassLoader … NewClassLoader JVM twitter.com/ekabanov
- 18. 2008 => 2011 twitter.com/ekabanov
- 19. Frameworks twitter.com/ekabanov
- 20. 2008 => 2011 twitter.com/ekabanov
- 21. Component State New New Class Object Class Object Old Component New Component ClassLoader ClassLoader twitter.com/ekabanov
- 22. JVM Languages Class-based languages have same limitations as Java Groovy Jython Non-class based languages can have better support JRuby Clojure twitter.com/ekabanov
- 23. HotSwap User saves class from IDE OldClassLoader MyObject.class New Code Code HotSwap 111000100 101000101 Debugger 101010010 100010010 New Code 111000100 101010010 MyObject twitter.com/ekabanov
- 24. JRebel Class Reloading HotSwap JRebel Changing method bodies + + Adding/removing methods - + Adding/removing constructors - + Adding/removing fields - + Adding/removing classes - + Adding/removing annotations - + Replacing superclass - - Adding/removing - - implemented interfaces twitter.com/ekabanov
- 25. JRebel MyObject.class file OldClassLoader changed MyObject.class New Code Code JRebel 111000100 101000101 agent 101010010 100010010 New Code 111000100 101010010 MyObject twitter.com/ekabanov
- 26. JRebel MyObject.class file Configuration changed OldClassLoader changed Framework MyObject.class Classes New Code Code JRebel 111000100 101000101 101010010 100010010 New Code agent 111000100 101010010 MyObject Configuration (XML, annotations, …) twitter.com/ekabanov
- 27. JRebel Integration IDEs Containers Frameworks Build Tools twitter.com/ekabanov
- 28. Who is already using JRebel? Banking & FSI Web IT Telco Air / Auto Healthcare Consulting Fashion/Entertain ment twitter.com/ekabanov
- 29. (how awesome is that?) Over 40 million builds, redeploys & restarts prevented for 20,000+ Java developers twitter.com/ekabanov
- 30. Oracle Weblogic FastSwap <container-descriptor> <fast-swap>true</fast-swap> </container-descriptor> weblogic-application.xml twitter.com/ekabanov
- 31. Q: Why Doesn’t Java Have Instant Turnaround? A1: Other languages/platforms aren’t much better! A2: Reloading code is easy, preserving state is hard! A3: It’s better than it used to be! A4: Play!, Tapestry 5 and Grails do that! A5: But what about JRebel? twitter.com/ekabanov
- 32. Q? twitter.com/ekabanov
- 33. And also… Instant, online rollout and rollback of changes to production Java EE apps for any deployment size. twitter.com/ekabanov