Possible Duplicate:
Exception in thread “main” java.lang.UnsupportedClassVersionError: a (Unsupporte d major.minor version 51.0)
i have developed an web application in java using jdk 1.7.0 ,Eclipse IDE (Indigo) and is running that application on the tomcat(apache-tomcat-7.0.23) configured in eclipse ide.
When i tried to run my application through IDE it runs fine but when i created its war and placed it in apache deployment folder(webapps) and run it from outside the IDE the start page gets successfully loaded but when i tried to do any operation over it it gives me an error
UnsupportedClassVersionError unsupported major.minor version 51.0 unable to load class bean.myclassname
i have checked the java version outside ide its jdk 1.7.0 and also the JAVA_HOME environment variable is set to C:\Program Files\Java\jdk1.7.0_01 .
Well presumably it's not using the same version of Java when running it externally. Look through the startup scripts carefully to find where it picks up the version of Java to run. You should also check the startup logs to see whether they indicate which version is running.
Alternatively, unless you need the Java 7 features, you could always change your compiler preferences in Eclipse to target 1.6 instead.
Even though your JDK in eclipse is 1.7, you need to make sure eclipse compilance level also set to 1.7. You can check compilance level--> Window-->Preferences--> Java--Compiler--compilance level.
Unsupported major minor error happens in cases where compilance level doesn't match with runtime.
java_home environment variable should point to the location of the proper version of java installation directory, so that tomcat starts with the right version. for example it you built the project with java 1.7 , then make sure that JAVA_HOME environment variable points to the jdk 1.7 installation directory in your machine.
I had same problem , when i deploy the war in tomcat and run, the link throws the error. But pointing the variable - JAVA_HOME to jdk 1.7 resolved the issue, as my war file was built in java 1.7 environment.
Try adding the following to your eclipse.ini file:
-vm
C:\Program Files\Java\jdk1.7.0_01\bin\java.exe
You might also have to change the Dosgi.requiredJavaVersion to 1.7 in the same file.
来源：https://stackoverflow.com/questions/8982730/unsupportedclassversionerror-unsupported-major-minor-version-51-0-unable-to-load