Caveats when upgrading from Java 6 to Java 7 on hundreds of production servers

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http://serverfault.com – I am about to upgrade the JDK version from Java 1.6.0_37-b06 to Java 1.7.0_11.64 in a few hundreds of production servers, which run Tomcat servlets. The upgrade is a part of a large system upgrade from RHEL 5 to RHEL 6. The upgrade will be tested on a staging environment on virtual machines before production deployment. Are there any known Backward-compatibility issues between these two versions? (HowTos)