Play 1.2.x UnexpectedException ContinuationEnhancer on helpers.CheatSheetHelper$2 invalid constant type: 15

Question

Play framework 1.2.x starts with the following error:

Oops: UnexpectedException
An unexpected error occured caused by exception UnexpectedException: While applying class play.classloading.enhancers.ContinuationEnhancer on helpers.CheatSheetHelper$2

play.exceptions.UnexpectedException: While applying play.CorePlugin@3444d69d on helpers.CheatSheetHelper$2
    at play.plugins.PluginCollection.enhance(PluginCollection.java:556)
    at play.classloading.ApplicationClasses$ApplicationClass.enhance(ApplicationClasses.java:235)
    at play.classloading.ApplicationClassloader.loadApplicationClass(ApplicationClassloader.java:167)
    at play.classloading.ApplicationClassloader.getAllClasses(ApplicationClassloader.java:431)
    at play.Play.preCompile(Play.java:600)
    at play.Play.init(Play.java:304)
    at play.server.Server.main(Server.java:162)
Caused by: play.exceptions.UnexpectedException: While applying class play.classloading.enhancers.ContinuationEnhancer on helpers.CheatSheetHelper$2
    at play.CorePlugin.enhance(CorePlugin.java:302)
    at play.plugins.PluginCollection.enhance(PluginCollection.java:551)
    ... 6 more
Caused by: java.lang.RuntimeException: java.io.IOException: invalid constant type: 15
    at javassist.CtClassType.getClassFile2(CtClassType.java:203)
    at javassist.CtClassType.subtypeOf(CtClassType.java:303)
    at javassist.CtClassType.subtypeOf(CtClassType.java:318)
    at play.classloading.enhancers.ContinuationEnhancer.enhanceThisClass(ContinuationEnhancer.java:49)
    at play.CorePlugin.enhance(CorePlugin.java:297)
    ... 7 more
Caused by: java.io.IOException: invalid constant type: 15
    at javassist.bytecode.ConstPool.readOne(ConstPool.java:1027)
    at javassist.bytecode.ConstPool.read(ConstPool.java:970)
    at javassist.bytecode.ConstPool.<init>(ConstPool.java:127)
    at javassist.bytecode.ClassFile.read(ClassFile.java:693)
    at javassist.bytecode.ClassFile.<init>(ClassFile.java:85)
    at javassist.CtClassType.getClassFile2(CtClassType.java:190)
    ... 11 more

Answer 1

This can be related to the jdk used to run play. If you use a java8 jdk you probably want to try java7 instead. This solved the Problem for me.

Answer 2

Play 1.2.5 comes with Javassist 3.9.0 that doesn't fully understand bytecode generated by JDK 8 compiler. Either compile with JDK 7 or upgrade the Javassist library under play/lib/framework/ to Javassist 3.18.0 for example.