Rapid java application development @ JUG.ru 25.02.2012
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Rapid java application development @ JUG.ru 25.02.2012
- 1. Rapid Java Application Development JUG.ru 25.02.2012
- 3. Turnaround Cycle Make a change Check the change Build, deploy, wait
- 5. Vendors Standards Operations dev << PROD
- 6. Turnaround Cycle Make a change Check the change Build, deploy, wait
- 7. Turnaround Time Sink Navigation OOMApplication deployment Container boot time
- 10. Build Resolve dependencies Copy static resources Compile classes Package modules into JARs Package everything into WAR/EAR
- 12. 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(); } }
- 13. “…I know about JRebel, but I cannot pay for it, so I tried Maven…” - Stackoverflow
- 14. This works: mvn jetty:run others?
- 15. getResource(“hello.html”) read(“src/main/.../hello.html”)
- 16. Build Resolve dependencies Copy static resources Compile classes Package modules into JARs Package everything into WAR/EAR
- 17. Build Resolve dependencies Copy static resources Compile classes Package modules into JARs Package everything into WAR/EAR
- 18. Why Code Reloading is Hard? Externalized Temporary State Serializable Derivative
- 19. OldClassLoader NewClassLoader MyObject.class MyObject.class Recreate object MyObject MyObject
- 20. Serialize/deserialize init() Session Session Sevlet New Sevlet Classes Classes App App New State Libraries State Libraries OldClassLoader NewClassLoader
- 21. Twin ClassLoader Issues Classes Classes Objects Objects and Code and Code Libraries Libraries OutOfMemoryError ClassCastException OldClassLoader … NewClassLoader JVM
- 23. Component State New New Class Object Class Object Old Component New Component ClassLoader ClassLoader
- 24. HotSwap Make changes in IDE OldClassLoader MyObject.class New HotSwap Code code Debugger 111000100 101000101 101010010 100010010 New code 111000100 101010010 MyObject
- 25. 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
- 26. JRebel Make changes in IDE OldClassLoader Framework MyObject.class Code 101000101 New code JRebel 100010010 111000100 101010010 MyObject Configuration (XML, annotations,..)
- 27. in action
- 28. Oh ... The Acid is Kicking In Take a break!
Notas del editor
- 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?
- 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
- Externalized ~= PHP, Database, memcachedetcTemporary ~= StatelessJava frameworks/servers often have too much derivative state and it takes too long to createSerializing helps when it can§
- If you want to preserve the state, this is what you have to do.
- 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
- DEMO (appserver simulation)New objects are not instances of old classesinstanceof returns falseCasting throws an exceptionNew classes are not members of the old packagesCan get an IllegalAccessException when calling a perfectly legal methodMemory leaks are easyIf you hold a reference to any object in the old classloader you will hold all old classes (including their static fields)
- 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)