GWT + Appengine + JPA + Eclipse + Maven: How to get them to work together - google-app-engine

Question

I have a project where I want to use the eclipse GWT tools (dev mode and debugger) to interact with the GWT/Appengine/Maven application I am writing. I have things in a somewhat working order but there are still a few things around the edges I don't have right. I will post the POM file if anyone could help me with these few issues.
When I do a Maven->Update Project, I loose the appengine nature in the eclipse project properties and have to go to Properties, Google, AppEngine and recheck Use Google App Engine. Is there something I can do in the POM where I don't loose the appengine nature? I'm using the Google appengine-maven-plugin plugin. That seems to be the official one to use.
After a maven build, I have to do a project clean to get the jpa classes enhanced before I can run them with the Run As - Web Application launcher. The maven build has test cases for the domain objects that work within the build - and I see the classes being enhance with this goal in the build 'maven-datanucleus-plugin:3.1.3:enhance (default)'. But running as a Web Application it throws out errors telling me the classes are not enhanced unless I do a project clean which cause eclipse to do it's enhance. Is there a way to avoid this extra step?
I can not run the JUnit View test runner or use a launcher that uses that view. The JUnit View complains that: "Caused by: org.datanucleus.exceptions.NucleusException: Plugin (Bundle) "org.datanucleus" is already registered. Ensure you dont have multiple JAR versions of the same plugin in the classpath. The URL "file:/C:/Users/bondsd/.m2/repository/org/datanucleus/datanucleus-core/3.1.3/datanucleus-core-3.1.3.jar" is already registered, and you are trying to register an identical plugin located at URL "file:/C:/Program%20Files/eclipse/plugins/com.google.appengine.eclipse.sdkbundle_1.7.5/appengine-java-sdk-1.7.5/lib/opt/user/datanucleus/v2/datanucleus-core-3.1.3.jar."". I have tried various things, such as removing the datanucleus plugin and/or dependencies, various configuration options, and unchecking the 'Use Datnucleus JDO/JPA to access the datastore' in the app engine properties panel. Is there a way to get this to work?
Below is the POM I used with the company and project name x'ed out. If you need the launchers I will be glad to post them too. Thanks in advance for any advice or help on this. I have searched the internet and haven't found the right solution yet.
<modelVersion>4.0.0</modelVersion>
<groupId>com.xxx.xxxx</groupId>
<artifactId>shell</artifactId>
<packaging>war</packaging>
<version>0.1.0-proto</version>
<name>XXXXXX</name>
<description>A XXXXXXXX</description>
<properties>
<webappDirectory>${project.build.directory}/${project.build.finalName}</webappDirectory>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<!-- GWT version -->
<gwt.version>2.5.1</gwt.version>
<gwt.style>PRETTY</gwt.style>
<!-- GAE version -->
<appengine.version>1.7.6</appengine.version>
<appengine.sdk.version>1.7.6</appengine.sdk.version>
<appengine.orm.version>2.1.2</appengine.orm.version>
<appengine.port>8888</appengine.port>
<datanucleus.core.version>3.1.3</datanucleus.core.version>
<datanucleus.api.version>3.1.3</datanucleus.api.version>
<datanucleus.enhancer.version>3.1.1</datanucleus.enhancer.version>
<datanucleus.plugin.version>3.1.3</datanucleus.plugin.version>
<slf4jVersion>1.6.6</slf4jVersion>
<log4j.version>1.3</log4j.version>
<junit.version>4.11</junit.version>
</properties>
<dependencies>
<dependency>
<groupId>com.google.gwt.inject</groupId>
<artifactId>gin</artifactId>
<version>2.0.0</version>
</dependency>
<dependency>
<groupId>com.google.inject.extensions</groupId>
<artifactId>guice-servlet</artifactId>
<version>3.0</version>
</dependency>
<!-- GWT dependencies -->
<dependency>
<groupId>com.google.gwt</groupId>
<artifactId>gwt-servlet</artifactId>
<version>${gwt.version}</version>
<scope>runtime</scope>
</dependency>
<dependency>
<groupId>com.google.gwt</groupId>
<artifactId>gwt-user</artifactId>
<version>${gwt.version}</version>
<scope>provided</scope>
</dependency>
<!-- GAE SDK -->
<dependency>
<groupId>com.google.appengine</groupId>
<artifactId>appengine-api-1.0-sdk</artifactId>
<version>${appengine.version}</version>
</dependency>
<!-- For the servlet filter -->
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>servlet-api</artifactId>
<version>2.5</version>
<scope>provided</scope>
</dependency>
<!-- <dependency> <groupId>jstl</groupId> <artifactId>jstl</artifactId>
<version>1.2</version> </dependency> -->
<!-- RequestFactory server -->
<dependency>
<groupId>com.trycatchsoft.gwt.requestfactory</groupId>
<artifactId>injected-requestfactory</artifactId>
<version>1.2.0-SNAPSHOT</version>
</dependency>
<dependency>
<groupId>com.google.web.bindery</groupId>
<artifactId>requestfactory-server</artifactId>
<version>${gwt.version}</version>
</dependency>
<dependency>
<groupId>com.google.web.bindery</groupId>
<artifactId>requestfactory-apt</artifactId>
<version>${gwt.version}</version>
</dependency>
<!-- RequestFactory will use JSR 303 javax.validation -->
<!-- Validation API -->
<dependency>
<groupId>javax.validation</groupId>
<artifactId>validation-api</artifactId>
<version>1.0.0.GA</version>
</dependency>
<!-- Validation Implementation -->
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-validator</artifactId>
<version>4.3.0.Final</version>
</dependency>
<!--Test Dependencies -->
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>${junit.version}</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.mockito</groupId>
<artifactId>mockito-all</artifactId>
<version>1.9.0</version>
<scope>test</scope>
</dependency>
<!-- GAE libraries for local testing as described here: http://code.google.com/appengine/docs/java/howto/unittesting.html -->
<dependency>
<groupId>com.google.appengine</groupId>
<artifactId>appengine-api-labs</artifactId>
<version>${appengine.version}</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>com.google.appengine</groupId>
<artifactId>appengine-api-stubs</artifactId>
<version>${appengine.version}</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>com.google.appengine</groupId>
<artifactId>appengine-testing</artifactId>
<version>${appengine.version}</version>
<scope>test</scope>
</dependency>
<!-- End of Test Dependencies -->
<!-- JPA 2.0 for GAE -->
<dependency>
<groupId>com.google.appengine.orm</groupId>
<artifactId>datanucleus-appengine</artifactId>
<version>${appengine.orm.version}</version>
</dependency>
<!-- Datanucleus -->
<!-- datanucleus-core is not needed for compilation. in fact, it cannot
have compile scope because the datanucleus plugin automatically adds it during
enhancement and complains if there are two copies. app should not depend
on any classes in this lib anyways. -->
<dependency>
<groupId>org.datanucleus</groupId>
<artifactId>datanucleus-core</artifactId>
<version>${datanucleus.core.version}</version>
<scope>runtime</scope>
<exclusions>
<exclusion>
<groupId>javax.transaction</groupId>
<artifactId>transaction-api</artifactId>
</exclusion>
</exclusions>
</dependency>
<!-- datanucleus-jpa is needed during compilation for its #Extension annotation
which is used throughout entity classes -->
<dependency>
<groupId>org.datanucleus</groupId>
<artifactId>datanucleus-api-jpa</artifactId>
<version>${datanucleus.api.version}</version>
</dependency>
<dependency>
<groupId>org.apache.geronimo.specs</groupId>
<artifactId>geronimo-jpa_2.0_spec</artifactId>
<version>1.0</version>
</dependency>
<dependency>
<groupId>org.eclipse.persistence</groupId>
<artifactId>javax.persistence</artifactId>
<version>2.0.0</version>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-jdk14</artifactId>
<version>1.7.2</version>
</dependency>
<!-- SLF4J logging libraries -->
<!-- <dependency> <groupId>org.slf4j</groupId> <artifactId>slf4j-api</artifactId>
<version>${slf4jVersion}</version> </dependency> <dependency> <groupId>org.slf4j</groupId>
<artifactId>slf4j-log4j12</artifactId> <version>1.7.2</version> </dependency>
<dependency> <groupId>log4j</groupId> <artifactId>log4j</artifactId> <version>1.2.16</version>
</dependency> -->
<!-- End SLF4J logging libraries -->
</dependencies>
<build>
<!-- Generate compiled stuff in the folder used for developing mode -->
<outputDirectory>${webappDirectory}/WEB-INF/classes</outputDirectory>
<resources>
<resource>
<directory>src/main/resources</directory>
</resource>
</resources>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.0</version>
<configuration>
<source>1.6</source>
<target>1.6</target>
</configuration>
<dependencies>
<!-- Need to run the RF Validation tool. This works on both the command-line
and in Eclipse, provided that m2e-apt is installed. -->
<dependency>
<groupId>com.google.web.bindery</groupId>
<artifactId>requestfactory-apt</artifactId>
<version>${gwt.version}</version>
</dependency>
</dependencies>
</plugin>
<!-- GWT Maven Plugin -->
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>gwt-maven-plugin</artifactId>
<version>2.5.1-rc1</version>
<dependencies>
<!-- Force plugin to use same gwt version -->
<dependency>
<groupId>com.google.gwt</groupId>
<artifactId>gwt-user</artifactId>
<version>${gwt.version}</version>
</dependency>
<dependency>
<groupId>com.google.gwt</groupId>
<artifactId>gwt-dev</artifactId>
<version>${gwt.version}</version>
</dependency>
</dependencies>
<configuration>
<strict>true</strict>
<extraJvmArgs>-Xss1024K -Xmx1024M -XX:MaxPermSize=256M</extraJvmArgs>
<logLevel>INFO</logLevel>
<style>${gwt.style}</style>
<copyWebapp>true</copyWebapp>
<hostedWebapp>${webappDirectory}</hostedWebapp>
<runTarget>Shell.html</runTarget>
<webappDirectory>${webappDirectory}</webappDirectory>
<module>com.ihg.dashboard.Shell</module>
<server>com.google.appengine.tools.development.gwt.AppEngineLauncher</server>
<i18nMessagesBundle>com.ihg.dashboard.client.Messages</i18nMessagesBundle>
<appEngineVersion>${appengine.version}</appEngineVersion>
<!-- Should GWT create the Story of Your Compile Report -->
<compileReport>false</compileReport>
</configuration>
<executions>
<execution>
<goals>
<goal>compile</goal>
<goal>test</goal>
<goal>i18n</goal>
</goals>
</execution>
</executions>
</plugin>
<plugin>
<groupId>com.google.appengine</groupId>
<artifactId>appengine-maven-plugin</artifactId>
<version>${appengine.version}</version>
<configuration>
<jvmFlags>
<jvmFlag>-Ddatastore.backing_store=${project.basedir}\local_db.bin</jvmFlag>
</jvmFlags>
<enhancerApi>JPA</enhancerApi>
</configuration>
</plugin>
<!-- This plug-in "enhances" your domain model objects (i.e. makes them
persistent for datanucleus) -->
<!-- Might not need this, appengine is supposed to do this appengine:enhance -->
<plugin>
<groupId>org.datanucleus</groupId>
<artifactId>maven-datanucleus-plugin</artifactId>
<version>${datanucleus.plugin.version}</version>
<configuration>
<mappingIncludes>**/domain/*.class</mappingIncludes>
<metadataIncludes>**/domain/*.class</metadataIncludes>
<verbose>false</verbose>
<enhancerName>ASM</enhancerName>
<api>JPA</api>
</configuration>
<executions>
<execution>
<phase>process-classes</phase>
<goals>
<goal>enhance</goal>
</goals>
</execution>
</executions>
<dependencies>
<dependency>
<!-- enhancement requires the gwt-user jar because many of the entity
classes implement IsSerializable and the enhancer needs it on the classpath
to function. because the gwt-user library has a scope of provided, it is
only available on the compilation and test classpath, and is not transitive
to the enhancement classpath. -->
<groupId>com.google.gwt</groupId>
<artifactId>gwt-user</artifactId>
<version>${gwt.version}</version>
</dependency>
<dependency>
<!-- force maven-datanucleus-plugin to use the same version of datanucleus-core -->
<groupId>org.datanucleus</groupId>
<artifactId>datanucleus-core</artifactId>
<version>${datanucleus.core.version}</version>
</dependency>
</dependencies>
</plugin>
<!-- Copy static web files before executing gwt:run -->
<!-- May not need this now -->
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-war-plugin</artifactId>
<version>2.1.1</version>
<executions>
<execution>
<phase>compile</phase>
<goals>
<goal>exploded</goal>
</goals>
</execution>
</executions>
<configuration>
<webXml>${webappDirectory}/WEB-INF/web.xml</webXml>
<webappDirectory>${webappDirectory}</webappDirectory>
</configuration>
</plugin>
</plugins>
<pluginManagement>
<plugins>
<!--This plugin's configuration is used to store Eclipse m2e settings
only. It has no influence on the Maven build itself. -->
<plugin>
<groupId>org.eclipse.m2e</groupId>
<artifactId>lifecycle-mapping</artifactId>
<version>1.0.0</version>
<configuration>
<lifecycleMappingMetadata>
<pluginExecutions>
<pluginExecution>
<pluginExecutionFilter>
<groupId>org.codehaus.mojo</groupId>
<artifactId>
gwt-maven-plugin
</artifactId>
<versionRange>
[2.5.1-rc1,)
</versionRange>
<goals>
<goal>i18n</goal>
</goals>
</pluginExecutionFilter>
<action>
<ignore></ignore>
</action>
</pluginExecution>
<pluginExecution>
<pluginExecutionFilter>
<groupId>
org.datanucleus
</groupId>
<artifactId>
maven-datanucleus-plugin
</artifactId>
<versionRange>
${datanucleusVersion}
</versionRange>
<goals>
<goal>enhance</goal>
</goals>
</pluginExecutionFilter>
<action>
<execute />
</action>
</pluginExecution>
</pluginExecutions>
</lifecycleMappingMetadata>
</configuration>
</plugin>
</plugins>
</pluginManagement>
</build>
=======================================
On Edit: Here is a solution to bullet point 3. Disable the JPA/JDO in the Project Properties - Google - App Engine page. Go to the build path and remove all the datanucleus libraries that are listed as top level libraries (these are put there by enabled the appengine in the project properties). Make sure the Maven dependencies are at the bottom of the list on the Order Tab.
On Edit 2: I found a way to keep the GAE project nature when I do a Maven->Update Project. I added this to the POM (even though I am using an eclipse build with m2e installed)
<plugin>
<artifactId>maven-eclipse-plugin</artifactId>
<version>2.7</version>
<configuration>
<downloadSources>true</downloadSources>
<downloadJavadocs>false</downloadJavadocs>
<wtpversion>2.0</wtpversion>
<additionalBuildcommands>
<buildCommand>
<name>com.google.gwt.eclipse.core.gwtProjectValidator</name>
</buildCommand>
</additionalBuildcommands>
<additionalProjectnatures>
<projectnature>com.google.gwt.eclipse.core.gwtNature</projectnature>
<projectnature>com.google.appengine.eclipse.core.gaeNature</projectnature>
</additionalProjectnatures>
</configuration>
</plugin>
This addresses Bullet point 1. So now I have points 1 and 3 solved (kind of). I still need a way to address bullet point 2, although the work around is easy if I remember to do it. I am more worried about the people who get the code after me remembering to do it.
I am also looking for a way to not use the eclipse launcher at all. I know it can be done with adding various profiles and configs. I just need to find the right configs to do that. By this, I mean a profile that will run the gwt code in dev mode (or super-dev mode) and also a profile that will run the debugger with the gwt code in dev mode.
On Edit 3: I solved bullet point 2. It was as simple as turning off Project->Build Automatically. I'm not sure what that was on in the first place.
That is all 3 bullet points solved. At this point I probably should create an answer for the question and mark it solved for those that are interested in this and didn't read down this far. I will do that in a day or two (when I have the time to compose a nice answer).

Answer 1

It looks like your maven setup is good, but let me make some observations that may help.
1) I would remove the enhancerApi from the appengine-maven-plugin as we're just executing the same thing as the maven-datanucleus-plugin. As a result, don't run the appengine:enhance goal along with the datanucleus plugin's goals.
2) The datanucleus plugin is setup only to enhance domain classes, which sounds right to me, but just verify this I guess.
3) I'm not the best with eclipse anymore, but I'm curious which maven plugin you are using, the m2eclipse plugin is developed by sonatype and the most accurate one in my opinion.
4) The execution of the war plugin on compile seems wrong to me, as this should default to the package phase anyway, which ensures other phases have properly executed beforehand.
5) You may need to get set up a few more execute directives for the plugins, or rely on defaults if they exist. The maven lifecycle can be a bit tricky, and I would recommend reading up on http://maven.apache.org/guides/introduction/introduction-to-the-lifecycle.html and making sure eclipse is running the correct phases before launching your application.