FYI, this happens when you accidentally install different versions of Java for compile and runtime.
E.g. Compile with javac... root@mgmtserver:~/github/cshv3/tools/apidoc# which javac /usr/bin/javac root@mgmtserver:~/github/cshv3/tools/apidoc# ls -al /usr/bin/javac lrwxrwxrwx 1 root root 23 Jul 16 19:58 /usr/bin/javac -> /etc/alternatives/javac root@mgmtserver:~/github/cshv3/tools/apidoc# ls -al /etc/alternatives/javac lrwxrwxrwx 1 root root 43 Jul 16 19:58 /etc/alternatives/javac -> /usr/lib/jvm/java-7-openjdk-amd64/bin/javac Run with java... root@mgmtserver:~/github/cshv3/tools/apidoc# which java /usr/bin/java root@mgmtserver:~/github/cshv3/tools/apidoc# ls -al /usr/bin/java lrwxrwxrwx 1 root root 22 Jul 16 17:15 /usr/bin/java -> /etc/alternatives/java root@mgmtserver:~/github/cshv3/tools/apidoc# ls -al /etc/alternatives/java lrwxrwxrwx 1 root root 46 Jul 16 17:15 /etc/alternatives/java -> /usr/lib/jvm/java-6-openjdk-amd64/jre/bin/java Fix? In my case, I wanted to try out the version 7 JRE. sudo apt-get install openjdk-7-jre This wasn't enough. I also had to purge the version 6 JRE apt-get purge openjdk-6-* Sources: http://stackoverflow.com/questions/11239086/java-lang-unsupportedclassversionerror-unsupported-major-minor-version-51-0 http://openjdk.java.net/install/ http://askubuntu.com/questions/64329/how-to-replace-openjdk-6-with-openjdk-7 > -----Original Message----- > From: MEHDI ALI SOLTANI [mailto:mehdi_alisolt...@yahoo.com] > Sent: 10 May 2013 5:01 PM > To: dev@cloudstack.apache.org > Subject: CloudStack Compile Error > > Hi > I used mvn clean install -P developer,systemvm according to > https://cwiki.apache.org/CLOUDSTACK/how-to-build-on-master- > branch.html > but i got this error > . > . > . > Exception in thread "main" java.lang.UnsupportedClassVersionError: > XmlToHtmlConverter : 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$1.run(URLClassLoader.java:212) > at java.security.AccessController.doPrivileged(Native Method) at > java.net.URLClassLoader.findClass(URLClassLoader.java:205) > at java.lang.ClassLoader.loadClass(ClassLoader.java:321) > at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294) > at java.lang.ClassLoader.loadClass(ClassLoader.java:266) > Could not find the main class: XmlToHtmlConverter. Program will exit. > [INFO] > ------------------------------------------------------------------------ > [INFO] Reactor Summary: > [INFO] > [INFO] Apache CloudStack ................................. SUCCESS [6.625s] > [INFO] > Apache CloudStack Utils ........................... SUCCESS [27.954s] [INFO] > Apache > CloudStack API ............................. SUCCESS [25.212s] [INFO] Apache > CloudStack Framework ....................... SUCCESS [0.163s] .... > .... > ... > INFO] Apache CloudStack Developer Tools ................. SUCCESS [0.159s] > [INFO] Apache CloudStack apidocs ......................... FAILURE [16.577s] > [INFO] > Apache CloudStack marvin .......................... SKIPPED [INFO] Apache > CloudStack cloudmonkey cli ................. SKIPPED [INFO] Apache CloudStack > DevCloud ........................ SKIPPED [INFO] Apache CloudStack DevCloud- > KVM .................... SKIPPED [INFO] > --------------------------------------------------- > --------------------- > [INFO] BUILD FAILURE > [INFO] > ------------------------------------------------------------------------ > [INFO] Total time: 10:53.864s > [INFO] Finished at: Fri May 10 20:21:00 IRDT 2013 [INFO] Final Memory: > 47M/329M [INFO] > ----------------------------------------------------------------------- > - > [ERROR] Failed to execute goal org.codehaus.mojo:exec-maven- > plugin:1.2.1:exec (compile) on project cloud-apidoc: Command execution > failed. Process exited with an error: 1 (Exit value: 1) -> [Help 1] [ERROR] > [ERROR] To see the full stack trace of the errors, re-run Maven with the -e > switch. > [ERROR] Re-run Maven using the -X switch to enable full debug logging. > [ERROR] > [ERROR] For more information about the errors and possible solutions, > please read the following articles: > [ERROR] [Help 1] > http://cwiki.apache.org/confluence/display/MAVEN/MojoExecutionExcepti > on > [ERROR] > [ERROR] After correcting the problems, you can resume the build with the > command [ERROR] mvn <goals> -rf :cloud-apidoc > > I tested it without developer mvn clean install -P systemvm > > but, again i got the same error. > please tell me how I can fix this error. > > Sincerely > Mehdi Ali Soltani