DataNucleus Enhancer error while Setting up AppEngine

Question

I am trying to set up AppEngine Backend Application project according to the tutorial on this site: https://cloud.google.com/resources/articles/how-to-build-mobile-app-with-app-engine-backend-tutorial

My current Environment is as follows:

1.Eclipse 4.2 (64-bit)with ADT installed.(This was the Eclipse ADT bundle that I installed from the android sdk site itself)

2.Java 7u45(64-bit)

3.App Engine Java sdk 1.8.6.

Initially when I was using Java 6 for setting up the App engine using Generate App Engine Backend(Right click on project->Google->Generate AppEngine Backend)it was giving me a Failed to initialize App Engine:invalid App Engine at path error.

I figured out that it was a Java version error.So I installed Java 7 and the error disappeared.Now when I try to set up App engine using Generate App Engine Backend(Right click on project->Google->Generate AppEngine Backend)I get the following error:

Could not find main class: com.google.appengine.tools.enhancer.Enhance.Program will exit.

My console shows this: java.lang.UnsupportedClassVersionError: com/google/appengine/tools/enhancer/Enhance : Unsupported major.minor version 51.0

at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClassCond(Unknown Source)
at java.lang.ClassLoader.defineClass(Unknown Source)
at java.security.SecureClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.access$000(Unknown Source)
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)

Answer 1

copied from another thread. this worked for me on a mac running osx 10.9, I did not need to un-install anything and/or restart eclipse. I did delete JRE 6 from the eclipse java configuration

get jdk 7 http://www.oracle.com/technetwork/java/javase/downloads/jdk7-downloads-1880260.html

verify using: java -version javac -version

in eclipse, add to preference/java/installed JREs/

1 Go to Preferences pane of eclipse
2 Open Java on the left pane
3 Click on Installed JREs
4 Add Button ---> Standard JVM and Next
5 Insert : /Library/Java/JavaVirtualMachines/jdk1.7.0_45.jdk/Contents/Home in the JRE Home TextBox
6 Next and Save the configuration

Answer 2

"Unsupported major.minor version 51.0" is what you see when you try to execute code compiled with Java 1.7 using an earlier JRE. You probably have an older JRE/JDK on your system that some part of the aparatus is trying to use instead of 1.7. Check your environment variables to see where the JAVA ones are pointing.

Answer 3

Thanks for the answer.The problem is solved.I checked my environment Path Variable, it was pointing to the JDK7 folder. The problem was I had both Java 6 and Java 7 installed on my computer with path variable pointing to JDK7 folder.Both java -version and javac -version on cmd were indicating Java 7,don't know why my eclipse was still using jre6. What I did to solve my problem is that I uninstalled Java 6 completely from my machine and restarted eclipse and the problem disappeared.But now I got a new problem while Generating AppEngine Backend. It gave me com.google.appengine.datnucleus.query cannot be resolved to a type. I restarted eclipse and even this problem disappeared. Any idea on why this error appeared? Am I misssing something?