Question

I’m trying to build my application for GoogleAppEngine using maven. I’ve added the following to my pom which should “enhance” my classes after building, as suggested on the DataNucleus documentation

<plugin>
                <groupId>org.datanucleus</groupId>
                <artifactId>maven-datanucleus-plugin</artifactId>
                <version>1.1.4</version>
                <configuration>
                    <log4jConfiguration>${basedir}/log4j.properties</log4jConfiguration>
                    <verbose>true</verbose>
                </configuration>
                <executions>
                    <execution>
                        <phase>process-classes</phase>
                        <goals>
                            <goal>enhance</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>

According to the documentation on GoogleAppEngine, you have the choice to use JDO or JPA, I’ve chosen to use JPA since I have used it in the past. When I try to build my project (before I upload to GAE) using mvn clean package I get the following output

[ERROR] BUILD ERROR
[INFO] ------------------------------------------------------------------------
[INFO] Failed to resolve artifact.

Missing:
----------
1) javax.jdo:jdo2-api:jar:2.3-ec

  Try downloading the file manually from the project website.

  Then, install it using the command: 
      mvn install:install-file -DgroupId=javax.jdo -DartifactId=jdo2-api -Dversion=2.3-ec -Dpackaging=jar -Dfile=/path/to/file

  Alternatively, if you host your own repository you can deploy the file there: 
      mvn deploy:deploy-file -DgroupId=javax.jdo -DartifactId=jdo2-api -Dversion=2.3-ec -Dpackaging=jar -Dfile=/path/to/file -Durl=[url] -DrepositoryId=[id]

  Path to dependency: 
    1) org.datanucleus:maven-datanucleus-plugin:maven-plugin:1.1.4
    2) javax.jdo:jdo2-api:jar:2.3-ec

----------
1 required artifact is missing.

for artifact: 
  org.datanucleus:maven-datanucleus-plugin:maven-plugin:1.1.4

from the specified remote repositories:
  __jpp_repo__ (file:///usr/share/maven2/repository),
  DN_M2_Repo (http://www.datanucleus.org/downloads/maven2/),
  central (http://repo1.maven.org/maven2)


[INFO] ------------------------------------------------------------------------
[INFO] For more information, run Maven with the -e switch
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 3 seconds
[INFO] Finished at: Sat Apr 03 16:02:39 BST 2010
[INFO] Final Memory: 31M/258M
[INFO] ------------------------------------------------------------------------

Any ideas why I should get such an error? I’ve searched through my entire source code and I’m not referencing JDO anywhere, so unless the app engine libraries require it, I’m not sure why I get this message.

Answer 1

The DataNucleus Maven plugin requires the JDO2 API JAR (even for JPA) as documented here and as reported in the trace:

  Path to dependency: 
    1) org.datanucleus:maven-datanucleus-plugin:maven-plugin:1.1.4
    2) javax.jdo:jdo2-api:jar:2.3-ec

The odd part is that jdo2-api-2.3-ec.jar is in the DataNucleus Maven repository (that is declared in the POM of the plugin) and Maven has checked this repository as we can see in the trace.

Update: Ok, this is definitely weird and I don’t know why the build is failing exactly (maybe a problem with dependencies ranges). As a workaround, declare the JDO2 API JAR as dependency in the plugin:

<project>
  ...
  <build>
    <plugins>
      <plugin>
        <groupId>org.datanucleus</groupId>
        <artifactId>maven-datanucleus-plugin</artifactId>
        <version>1.1.4</version>
        <configuration>
            <log4jConfiguration>${basedir}/log4j.properties</log4jConfiguration>
            <verbose>true</verbose>
        </configuration>
        <executions>
            <execution>
                <phase>process-classes</phase>
                <goals>
                    <goal>enhance</goal>
                </goals>
            </execution>
        </executions>
        <dependencies>
          <dependency>
            <groupId>javax.jdo</groupId>
            <artifactId>jdo2-api</artifactId>
            <version>2.3-ec</version>
            <scope>runtime</scope>
          </dependency>
        </dependencies>        
      </plugin>
      ...
    </plugins>
    ...
  </build>

</project>

With this dependency declared, the JAR gets downloaded.