Well, I thought I got automatic enhancement working in Eclipse
with Java 1.6 and annotation processing enabled, but this does not seem to be true. If I let Eclipse rebuild the project
completely (Project->clean + automatic rebuild) everything seems to
work and my classes are enhanced automatically. If however I make a change to one class in the editor and save it I get the following error message.

Message:
Exception thrown by Java annotation processor org.datanucleus.enhancer.EnhancerProcessor@1e50ba9

Exception Stack Trace:
java.lang.IllegalArgumentException: Hook previously registered
at java.lang.ApplicationShutdownHooks.add(Unknown Source)
at java.lang.Runtime.addShutdownHook(Unknown Source)
at org.datanucleus.enhancer.EnhancerProcessor.process(EnhancerProcessor.java:136)
at org.eclipse.jdt.internal.compiler.apt.dispatch.RoundDispatcher.handleProcessor(RoundDispatcher.java:
139)
at org.eclipse.jdt.internal.compiler.apt.dispatch.RoundDispatcher.round(RoundDispatcher.java:110)
at org.eclipse.jdt.internal.compiler.apt.dispatch.BaseAnnotationProcessorManager.processAnnotations(Bas
eAnnotationProcessorManager.java:159)
at org.eclipse.jdt.internal.apt.pluggable.core.dispatch.IdeAnnotationProcessorManager.processAnnotation
s(IdeAnnotationProcessorManager.java:134)
at org.eclipse.jdt.internal.compiler.Compiler.processAnnotations(Compiler.java:837)
at org.eclipse.jdt.internal.compiler.Compiler.compile(Compiler.java:428)
at org.eclipse.jdt.internal.core.builder.AbstractImageBuilder.compile(AbstractImageBuilder.java:364)
at org.eclipse.jdt.internal.core.builder.IncrementalImageBuilder.compile(IncrementalImageBuilder.java:3
21)
at org.eclipse.jdt.internal.core.builder.AbstractImageBuilder.compile(AbstractImageBuilder.java:301)
at org.eclipse.jdt.internal.core.builder.IncrementalImageBuilder.build(IncrementalImageBuilder.java:134
)
at org.eclipse.jdt.internal.core.builder.JavaBuilder.buildDeltas(JavaBuilder.java:265)
at org.eclipse.jdt.internal.core.builder.JavaBuilder.build(JavaBuilder.java:193)
at org.eclipse.core.internal.events.BuildManager$2.run(BuildManager.java:627)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:170)
at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:201)
at org.eclipse.core.internal.events.BuildManager$1.run(BuildManager.java:253)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:256)
at org.eclipse.core.internal.events.BuildManager.basicBuildLoop(BuildManager.java:309)
at org.eclipse.core.internal.events.BuildManager.build(BuildManager.java:341)
at org.eclipse.core.internal.events.AutoBuildJob.doBuild(AutoBuildJob.java:140)
at org.eclipse.core.internal.events.AutoBuildJob.run(AutoBuildJob.java:238)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:55)

Session Data:
eclipse.buildId=M20090917-0800
java.version=1.6.0_17
java.vendor=Sun Microsystems Inc.
BootLoader constants: OS=win32, ARCH=x86, WS=win32, NL=de_DE
Command-line arguments: -os win32 -ws win32 -arch x86 -data C:\Dokumente und Einstellungen\Paus\workspace_dbtest

How can this be avoided?

Michael

PS: With the Eclipse plugin I can start the enhancer as often as I like without problems.