Why Doesn't Java Has Instant Turnaround - Con-FESS 2012
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This document discusses why Java does not have instant code reloading capabilities out of the box. It describes how the typical development cycle requires building, deploying, and waiting for changes to take effect. It then explores some of the challenges around reloading classes at runtime, such as handling externalized and derivative state. The document introduces JRebel as a solution that can hotswap code changes without redeploys by leveraging different classloaders and configuration to reconnect objects to the new code.
![Jetty Launcher
public class Launcher {
public static void main(String[] args) {
Server server = new Server();
SelectChannelConnector connector
= new SelectChannelConnector();
connector.setPort(8080);
server.addConnector(connector);
WebAppContext context = new WebAppContext("war", "/");
server.setHandler(context);
server.start();
}
}](https://image.slidesharecdn.com/rapidjavaapplicationdevelopment-120508062150-phpapp02/85/Why-Doesn-t-Java-Has-Instant-Turnaround-Con-FESS-2012-15-320.jpg)
Why Doesn't Java Has Instant Turnaround - Con-FESS 2012
- 1. Why Doesn’t Java Have Instant Turnaround? Anton Arhipov | ZeroTurnaround
- 2. whoami Anton Arhipov JRebel ZeroTurnaround http://arhipov.blogspot.com @antonarhipov @javarebel
- 4. Turnaround Cycle Check Make a the change change Build, de ploy, wai t
- 5. Diversity
- 6. Vendors Standards Operations dev << PROD
- 7. Turnaround Cycle Check Make a the change change Build, de ploy, wai t
- 8. Turnaround Time Sink Navigation OOMApplication deployment Container startup time
- 12. Build Check Make a the change change Build, deploy, wait
- 13. Build Resolve dependencies Copy static resources Compile classes Package modules into JARs Package everything into WAR/EAR
- 15. Jetty Launcher public class Launcher { public static void main(String[] args) { Server server = new Server(); SelectChannelConnector connector = new SelectChannelConnector(); connector.setPort(8080); server.addConnector(connector); WebAppContext context = new WebAppContext("war", "/"); server.setHandler(context); server.start(); } }
- 16. “…I know about JRebel, but I cannot pay for it, so I tried Maven…” - Stackoverflow
- 17. This works: mvn jetty:run others?
- 18. getResource(“hello.html”) read(“src/main/.../hello.html”)
- 19. Build Resolve dependencies Copy static resources Compile classes Package modules into JARs Package everything into WAR/EAR
- 20. Build Resolve dependencies Copy static resources Compile classes Package modules into JARs Package everything into WAR/EAR
- 21. Why Code Reloading is Hard?
- 22. Why Code Reloading is Hard? Externalized Temporary State Serializable Derivative
- 23. How To Reload a Class? OldClassLoader NewClassLoader MyObject.class MyObject.class Recreate object MyObject MyObject
- 24. Serialize/deserialize init() Session Session Sevlet New Sevlet Classes Classes App App New State Libraries State Libraries OldClassLoader NewClassLoader
- 25. Session Session Sevlet New Sevlet Classes Classes App App New State State Libraries OldClassLoader NewClassLoader
- 28. Component State New New Class Object Class Object Old Component New Component ClassLoader ClassLoader
- 29. HotSwap Make changes in IDE OldClassLoader MyObject.class New HotSwap Code code Debugger 111000100 101000101 101010010 100010010 New code 111000100 101010010 MyObject
- 30. JRebel vs HotSwap 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
- 31. JRebel Make changes in IDE OldClassLoader Framework MyObject.class Code 101000101 New code JRebel 100010010 111000100 101010010 MyObject Configuration (XML, annotations,..)
- 32. in action
- 33. Oh ... The Acid is Kicking In Questions?
- 35. Remoting BETA
- 36. http://arhipov.blogspot.com @antonarhipov @javarebel
Editor's Notes
- #7: Vendors make money on production => development is secondaryOperations rule development, best practices are heavily influenced by production needsMultiple participants in the standard working groups means a choice between reducing scope of the standard or reducing its qualityStory: when we tried pitching JRebel to a large Java app server vendor the answer was: why bother?
- #18: Jetty has support for any app layout, but docs are missing. Maven Jetty plugin is the only workable application of this functionality.RAD & Websphere have decent integration that tries to copy the minimal amount of files possible. Copying isn’t a great idea, though.Weblogic has the split directory structure functionality which is powerful on paperEclipse, NetBeans and IntelliJ IDEA have support for publishing applications from the IDE, which varies from decent to awful.SpringSource has fairly decent integration between tooling and server, but only for tc Server.Jboss used to run Ant on every update in Eclipse, Netbeans still does that
- #23: Externalized ~= PHP, Database, memcachedetcTemporary ~= StatelessJava frameworks/servers often have too much derivative state and it takes too long to createSerializing helps when it can§
- #24: If you want to preserve the state, this is what you have to do.
- #25: Class loader scopeEvery deployed application gets a dedicated class loaderState recreationApplication state is recovered by reinitializationSession state is (optionally) serialized and deserialized in the new class loaderReloading timeApplication reinitialization time, typically around one minuteProblemsLeaks memoryLazy caches need to be warmed up every time
- #26: Class loader scopeEvery deployed application gets a dedicated class loaderState recreationApplication state is recovered by reinitializationSession state is (optionally) serialized and deserialized in the new class loaderReloading timeApplication reinitialization time, typically around one minuteProblemsLeaks memoryLazy caches need to be warmed up every time
- #29: Class loader scopeClass loader per component/serviceState recreationState restored by framework (component/service recreated)Reloading time(Almost) InstantProblemsOnly managed components can be reloadedManaged components referring unmanaged code can be a problem (twin class issues)