After the upgrade from Jenkins 1.515 to Jenkins 1.518 one of our Maven projects failed due to a ClassFormatException:
The issue can be found in the call stack:
The Jenkins slave calls the Maven launcher and and the Maven launcher does a callback into the Jenkins code to perform some IO operations. For those operations, the jnr-ffi library is used and this has been compiled on the 8th of June under OpenJDK 6 and under Oracle JDK 7:
The pom.xml of the library has no compiler plugin configuration and thus creates code for whatever JDK it runs on (Java 6 class version 50) and I assume that this new version of the library has been pulled in between 1.516 and 1.518 of Jenkins.
That means this new version of the jnr-ffi library drops Java 5 support for certain Maven builds.