gradlew :appengineEnhance fails

Question

I am creating a mobile backend in Java using Google App Engine with Android Studio. In order to start the local server exposing my API, I use gradlew [module name]:appengineRun.

However, when I go to http://localhost:8080/_ah/api/explorer, and try to use the API I get the following error:

apr 29, 2014 10:52:32 PM com.google.api.server.spi.SystemService invokeServiceMethod
SEVERE: The class "com.mthoresen.fest.backend.LocationBean" is not persistable. 
This means that it either hasnt been enhanced, or that the enhanced version of 
the file is not in the CLASSPATH (or is hidden by an unenhanced version), or the 
Meta-Data/annotations for the class are not found.

In addition, the process never ends - it's stuck at Building 88% > :[module name]:appengineRun

---

Edit

This mess is solved by loosebazooka's answer, but appengineRun still failes with the same error.

So I tried gradlew [module name]:appengineEnhance instead, which gives me the following output:

Relying on packaging to define the extension of the main artifact has been deprecated and is scheduled to be removed in Gradle 2.0
:backend:appengineDownloadSdk                                                        
:backend:compileJava UP-TO-DATE                                                  
:backend:appengineEnhance FAILED          

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':backend:appengineEnhance'.
> An error occurred enhancing DataNucleus classes.

* Try:         
Run with --stacktrace option to get the stack trace. Run with --info or --debug option  to get more log output.

BUILD FAILED   

--info gives me nothing else, and --debug is way to much output. --stacktrace doesn't really help either:

* Exception is:
org.gradle.api.tasks.TaskExecutionException: Execution failed for task     ':backend:appengineEnhance'.
    at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.executeActions(ExecuteActionsTaskExecuter.java:69)
    at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.execute(ExecuteActionsTaskExecuter.java:46)
    at org.gradle.api.internal.tasks.execution.PostExecutionAnalysisTaskExecuter.execute(PostExecutionAnalysisTaskExecuter.java:35)
    at org.gradle.api.internal.tasks.execution.SkipUpToDateTaskExecuter.execute(SkipUpToDateTaskExecuter.java:64)
    at org.gradle.api.internal.tasks.execution.ValidatingTaskExecuter.execute(ValidatingTaskExecuter.java:58)
    at org.gradle.api.internal.tasks.execution.SkipEmptySourceFilesTaskExecuter.execute(SkipEmptySourceFilesTaskExecuter.java:42)
    at org.gradle.api.internal.tasks.execution.SkipTaskWithNoActionsExecuter.execute(SkipTaskWithNoActionsExecuter.java:52)
    at org.gradle.api.internal.tasks.execution.SkipOnlyIfTaskExecuter.execute(SkipOnlyIfTaskExecuter.java:53)
    at org.gradle.api.internal.tasks.execution.ExecuteAtMostOnceTaskExecuter.execute(ExecuteAtMostOnceTaskExecuter.java:43)
    at org.gradle.api.internal.AbstractTask.executeWithoutThrowingTaskFailure(AbstractTask.java:289)
    at org.gradle.execution.taskgraph.AbstractTaskPlanExecutor$TaskExecutorWorker.executeTask(AbstractTaskPlanExecutor.java:79)
    at org.gradle.execution.taskgraph.AbstractTaskPlanExecutor$TaskExecutorWorker.processTask(AbstractTaskPlanExecutor.java:63)
    at org.gradle.execution.taskgraph.AbstractTaskPlanExecutor$TaskExecutorWorker.run(AbstractTaskPlanExecutor.java:51)
    at org.gradle.execution.taskgraph.DefaultTaskPlanExecutor.process(DefaultTaskPlanExecutor.java:23)
    at org.gradle.execution.taskgraph.DefaultTaskGraphExecuter.execute(DefaultTaskGraphExecuter.java:86)
    at org.gradle.execution.SelectedTaskExecutionAction.execute(SelectedTaskExecutionAction.java:29)
    at org.gradle.execution.DefaultBuildExecuter.execute(DefaultBuildExecuter.java:61)
    at org.gradle.execution.DefaultBuildExecuter.access$200(DefaultBuildExecuter.java:23)
    at org.gradle.execution.DefaultBuildExecuter$2.proceed(DefaultBuildExecuter.java:67)
    at org.gradle.execution.DryRunBuildExecutionAction.execute(DryRunBuildExecutionAction.java:32)
    at org.gradle.execution.DefaultBuildExecuter.execute(DefaultBuildExecuter.java:61)
    at org.gradle.execution.DefaultBuildExecuter.execute(DefaultBuildExecuter.java:54)
    at org.gradle.initialization.DefaultGradleLauncher.doBuildStages(DefaultGradleLauncher.java:166)
    at org.gradle.initialization.DefaultGradleLauncher.doBuild(DefaultGradleLauncher.java:113)
    at org.gradle.initialization.DefaultGradleLauncher.run(DefaultGradleLauncher.java:81)
    at org.gradle.launcher.exec.InProcessBuildActionExecuter$DefaultBuildController.run(InProcessBuildActionExecuter.java:64)
    at org.gradle.launcher.cli.ExecuteBuildAction.run(ExecuteBuildAction.java:33)
    at org.gradle.launcher.cli.ExecuteBuildAction.run(ExecuteBuildAction.java:24)
    at org.gradle.launcher.exec.InProcessBuildActionExecuter.execute(InProcessBuildActionExecuter.java:35)
    at org.gradle.launcher.exec.InProcessBuildActionExecuter.execute(InProcessBuildActionExecuter.java:26)
    at org.gradle.launcher.cli.RunBuildAction.run(RunBuildAction.java:50)
    at org.gradle.internal.Actions$RunnableActionAdapter.execute(Actions.java:171)
    at org.gradle.launcher.cli.CommandLineActionFactory$ParseAndBuildAction.execute(CommandLineActionFactory.java:201)
    at org.gradle.launcher.cli.CommandLineActionFactory$ParseAndBuildAction.execute(CommandLineActionFactory.java:174)
    at org.gradle.launcher.cli.CommandLineActionFactory$WithLogging.execute(CommandLineActionFactory.java:170)
    at org.gradle.launcher.cli.CommandLineActionFactory$WithLogging.execute(CommandLineActionFactory.java:139)
    at org.gradle.launcher.cli.ExceptionReportingAction.execute(ExceptionReportingAction.java:33)
    at org.gradle.launcher.cli.ExceptionReportingAction.execute(ExceptionReportingAction.java:22)
    at org.gradle.launcher.Main.doAction(Main.java:46)
    at org.gradle.launcher.bootstrap.EntryPoint.run(EntryPoint.java:45)
    at org.gradle.launcher.Main.main(Main.java:37)
    at org.gradle.launcher.bootstrap.ProcessBootstrap.runNoExit(ProcessBootstrap.java:50)
    at org.gradle.launcher.bootstrap.ProcessBootstrap.run(ProcessBootstrap.java:32)
    at org.gradle.launcher.GradleMain.main(GradleMain.java:23)
    at org.gradle.wrapper.BootstrapMainStarter.start(BootstrapMainStarter.java:33)
    at org.gradle.wrapper.WrapperExecutor.execute(WrapperExecutor.java:130)
    at org.gradle.wrapper.GradleWrapperMain.main(GradleWrapperMain.java:48)
Caused by: org.gradle.api.GradleException: An error occurred enhancing DataNucleus classes.
    at com.google.appengine.task.EnhanceTask.enhanceClasses(EnhanceTask.groovy:58)
    at com.google.appengine.task.EnhanceTask.executeTask(EnhanceTask.groovy:34)
    at com.google.appengine.task.AbstractTask.start(AbstractTask.groovy:38)
    at org.gradle.internal.reflect.JavaMethod.invoke(JavaMethod.java:63)
    at org.gradle.api.internal.project.taskfactory.AnnotationProcessingTaskFactory$StandardTaskAction.doExecute(AnnotationProcessingTaskFactory.java:219)
    at org.gradle.api.internal.project.taskfactory.AnnotationProcessingTaskFactory$StandardTaskAction.execute(AnnotationProcessingTaskFactory.java:212)
    at org.gradle.api.internal.project.taskfactory.AnnotationProcessingTaskFactory$StandardTaskAction.execute(AnnotationProcessingTaskFactory.java:201)
    at org.gradle.api.internal.AbstractTask$TaskActionWrapper.execute(AbstractTask.java:533)
    at org.gradle.api.internal.AbstractTask$TaskActionWrapper.execute(AbstractTask.java:516)
    at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.executeAction(ExecuteActionsTaskExecuter.java:80)
    at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.executeActions(ExecuteActionsTaskExecuter.java:61)
    ... 46 more
Caused by: : Java returned: 1
    at org.apache.tools.ant.taskdefs.Java.execute(Java.java:111)
    at com.google.appengine.tools.enhancer.EnhancerTask.execute(EnhancerTask.java:97)
    at org.apache.tools.ant.UnknownElement.execute(UnknownElement.java:292)
    at org.apache.tools.ant.dispatch.DispatchUtils.execute(DispatchUtils.java:106)
    at org.gradle.api.internal.project.ant.BasicAntBuilder.nodeCompleted(BasicAntBuilder.java:71)
    at org.gradle.api.internal.project.ant.BasicAntBuilder.doInvokeMethod(BasicAntBuilder.java:86)
    at org.gradle.api.internal.project.DefaultAntBuilder.super$3$invokeMethod(DefaultAntBuilder.groovy)
    at org.gradle.api.internal.project.DefaultAntBuilder.invokeMethod(DefaultAntBuilder.groovy:37)
    at com.google.appengine.task.EnhanceTask.enhanceClasses(EnhanceTask.groovy:42)
    ... 56 more

All documentation I can find from Google is using Eclipse with maven and ant, but Android Studio has a Google App Engine plugin, so it wouldn't make sense to say it isn't supported.

The java class I want to save:

import javax.jdo.annotations.IdGeneratorStrategy;
import javax.jdo.annotations.IdentityType;
import javax.jdo.annotations.Key;
import javax.jdo.annotations.PersistenceCapable;
import javax.jdo.annotations.Persistent;
import javax.jdo.annotations.PrimaryKey;

@PersistenceCapable(identityType = IdentityType.APPLICATION)
public class LocationBean {

    @PrimaryKey
    @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
    private Key key;
    @Persistent
    private double lat;
    @Persistent
    private double lng;
    @Persistent
    private double rad;
    @Persistent
    private long endtime;

    /** Getters and setters */
}

Digging in the output from --debug, I found the following line:

Encountered a problem: Unexpected exception
Please see the logs [C:\Users\<username>\AppData\Local\Temp\enhance4980231719213251330.log] for further information.

So I did. This is the logfile:

java.lang.RuntimeException: Unexpected exception
at com.google.appengine.tools.enhancer.Enhancer.execute(Enhancer.java:76)
at com.google.appengine.tools.enhancer.Enhance.<init>(Enhance.java:71)
at com.google.appengine.tools.enhancer.Enhance.main(Enhance.java:51)
Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at com.google.appengine.tools.enhancer.Enhancer.execute(Enhancer.java:74)
... 2 more
Caused by: org.datanucleus.exceptions.NucleusException: Plugin (Bundle) "org.datanucleus.enhancer" is already registered. Ensure you dont have multiple JAR versions of the same plugin in the classpath. The URL "file:/C:/Users/Martin/.gradle/caches/modules-2/files-2.1/org.datanucleus/datanucleus-enhancer/3.1.1/b141c67d55cc19f14639f091b84e692e2198dc50/datanucleus-enhancer-3.1.1.jar" is already registered, and you are trying to register an identical plugin located at URL "file:/C:/Users/Martin/.gradle/appengine-sdk/appengine-java-sdk-1.9.3/lib/opt/tools/datanucleus/v1/datanucleus-enhancer-1.1.4.jar."
at org.datanucleus.plugin.NonManagedPluginRegistry.registerBundle(NonManagedPluginRegistry.java:541)
at org.datanucleus.plugin.NonManagedPluginRegistry.registerBundle(NonManagedPluginRegistry.java:395)
at org.datanucleus.plugin.NonManagedPluginRegistry.registerExtensions(NonManagedPluginRegistry.java:219)
at org.datanucleus.plugin.NonManagedPluginRegistry.registerExtensionPoints(NonManagedPluginRegistry.java:160)
at org.datanucleus.plugin.PluginManager.<init>(PluginManager.java:65)
at org.datanucleus.plugin.PluginManager.createPluginManager(PluginManager.java:427)
at org.datanucleus.NucleusContext.<init>(NucleusContext.java:224)
at org.datanucleus.NucleusContext.<init>(NucleusContext.java:204)
at org.datanucleus.enhancer.DataNucleusEnhancer.<init>(DataNucleusEnhancer.java:160)
at org.datanucleus.enhancer.DataNucleusEnhancer.main(DataNucleusEnhancer.java:1133)
... 7 more

The interesting line being

Plugin (Bundle) "org.datanucleus.enhancer" is already registered. Ensure you dont have multiple JAR versions of the same plugin in the classpath. The URL 
"file:/C:/Users/<username>/.gradle/caches/modules-2/files-2.1/org.datanucleus/datanucleus-enhancer/3.1.1/b141c67d55cc19f14639f091b84e692e2198dc50/datanucleus-enhancer-3.1.1.jar" 
is already registered, and you are trying to register an identical plugin located at URL 
"file:/C:/Users/<username>/.gradle/appengine-sdk/appengine-java-sdk-1.9.3/lib/opt/tools/datanucleus/v1/datanucleus-enhancer-1.1.4.jar."

So it looks like two widely different versions of datanucleus-enhancer is present. Somehow, gradlew downloads version 3.1.1 (which I have specified in build.gradle), while a part of the process wants to use version 1.1.4. Again, I can't find any resources on how to change this, as every single tutorial on the web are using Maven.

Answer 1

Update:

This answer has gone a little out of date, if you're using gradle-appengine-plugin version 1.9.5 or higher, you should use the new configuration

appengine {
  enhancer {
    version = "v2"
    enhanceOnBuild = true
  }
}

instead of what follows below.

Original Answer:

You probably need to configure the enhancer to use v2 of the enhancer.

in your build.gradle file

appengine {
  enhancerVersion = "v2"
}

[Edit] To make enhance run automatically before creating the war

in your build.gradle file

war.dependsOn appengineEnhance

Answer 2

I've had similar problem, but I'm using JPA instead. I've made :appengineEnhance run by specifying api:

enhancer {
    version = "v2"
    api="jpa"  // or jdo
    enhanceOnBuild = true
}

Answer 3

I had the same problem ("org.datanucleus.enhancer" is already registered) and i found the solution.

First i've use the code posted by @loosebazooka in my build.gradle PLUS:

dependencies {
    appengineSdk 'com.google.appengine:appengine-java-sdk:1.9.8'
    compile 'com.google.appengine:appengine-endpoints:1.9.8'
    compile 'com.google.appengine:appengine-endpoints-deps:1.9.8'
    compile 'com.google.appengine.orm:datanucleus-appengine:2.1.2'
    compile 'javax.servlet:servlet-api:2.5'
    compile 'javax.jdo:jdo2-api:2.3-eb'
    compile 'org.datanucleus:datanucleus-api-jdo:3.1.3' // WE NEED THIS
    //compile 'javax.jdo:jdo-api:3.0.1' // ALREADY IN datanucleus-appengine
    //compile 'org.datanucleus:datanucleus-core:3.1.4' // ALREADY IN datanucleus-appengine
    //compile 'org.datanucleus:datanucleus-enhancer:3.1.1' // ALREADY IN datanucleus-appengine
}

I'm running on Android Studio 0.8.10

Now gradle does the appengine:appengineEnhance task and the service is up and working!

Answer 4

Not a solution to your problem. But may be helpful for others who get this exception:

TaskExecutionException: Execution failed for task     ':backend:appengineEnhance'
Caused by: org.gradle.api.GradleException: An error occurred enhancing DataNucleus classes.
Caused by: : Java returned: 1

It may happen if you have declared an entity class without a primary key.