Eclipse: java.lang.UnsupportedClassVersionError: Bad version number in .class file

When JVM tries to load a class and found that class file version is not supported it throws UnSupportedClassVersionError.

It generally occurs if a higher jdk version is used to compile the source file and lower jdk version is used to run the program.

Example: If you compile your java source file in jdk1.6 and try to run it on jdk 1.5, JVM will throw "java.lang.UnsupportedClassVersionError: Bad version number in .class file".

How to fix UnSupportedClassVersionError?

· Try to compile source code of that jar with the same JDK version which we are using to run the program (if source is available).

· If you don't have source try to find the compatible version of that library.

· Increase the jre version that is used to run the program.

I faced this problem while running an application on Web application on Eclipse and Tomcat. This is because there was version difference of Eclipse and Tomcat (lower jdk version in Tomcat).

I changed jre version of Tomcat to fix this problem.