Hello,
here is Cisco answer:
Now the recommended Java version to be used on LMS 4.2.3 is Java Plug-in version 1.6.0_31 or higher (up to Java Plug-in version 1.6.0_45 )
Java 7 is not supported over LMS 4.2.3 , and it will cause topology services not to launch up correctly.
However Java 7 is planned to be used as part of LMS 4.2.4 which should be released on October.