Push to Upstream to Heroku server from Eclipse failed - eclipse

Question

I was able to commit the change but when i do push to upstream this is the message i get:
Repository git#heroku.com:protected-garden-XXXX.git
pre-receive hook declined
Compressing source files... done.
Building source:
-----> Java app detected
-----> Installing OpenJDK 1.6... done
-----> Installing Maven 3.3.1... done
-----> Executing: mvn -B -DskipTests=true clean install
Exception in thread "main" java.lang.UnsupportedClassVersionError: org/apache/maven/cli/MavenCli : Unsupported major.minor version 51.0
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:634)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:277)
at java.net.URLClassLoader.access$000(URLClassLoader.java:73)
at java.net.URLClassLoader$1.run(URLClassLoader.java:212)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
at org.codehaus.plexus.classworlds.realm.ClassRealm.loadClassFromSelf(ClassRealm.java:401)
at org.codehaus.plexus.classworlds.strategy.SelfFirstStrategy.loadClass(SelfFirstStrategy.java:42)
at org.codehaus.plexus.classworlds.realm.ClassRealm.unsynchronizedLoadClass(ClassRealm.java:271)
at org.codehaus.plexus.classworlds.realm.ClassRealm.loadClass(ClassRealm.java:254)
at org.codehaus.plexus.classworlds.realm.ClassRealm.loadClass(ClassRealm.java:239)
at org.codehaus.plexus.classworlds.launcher.Launcher.getMainClass(Launcher.java:144)
at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:266)
at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:229)
at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:415)
at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:356)
! ERROR: Failed to build app with Maven
We're sorry this build is failing! If you can't find the issue in application code,
please submit a ticket so we can help: https://help.heroku.com/
! Push rejected, failed to compile Java app
Verifying deploy...
! Push rejected to protected-garden-XXXX.
What might be the problem because I used the default example Eclipse >>> Project >>> :"Create Heroku App from Template" and chose the Embedded Jetty-Servlet Application and just changed the text in the HelloServlet line 20 and then commit.

Answer 1

Answer from heroku support team: (which solved my problem)
Maven 3, which Heroku uses to build projects with a pom.xml file, will not run on any version of Java 6. It requires Java 7 or later. Personally, I'd suggest going straight to the latest version, Java 8, since Java 7 is no longer supported by Oracle or the OpenJDK team.
You can upgrade Java in your app by specifying
java.runtime.version=1.8
in the:
system.properties
file in the root of your project, then pushing your app. You'll also want to install the same version of Java locally, so that you can test your app before you push it.