Nuxeo DM has been compiled against Java 5 but you should be able to run it with Java Runtime Environment 6.
Currently the build process doesn't seem to lead to a usable application
if built using the Java Development Kit 6
However you can build with JDK 5 and then run with the JRE/JDK 6.
If you encounter problems using JBoss with a Sun Java 6 runtime, you may want to set -Dsun.lang.ClassLoader.allowArraySyntax=true, as described in JBAS-4491. Other potential problems under a Java 6 runtime include:
When JBossAS 4.2.3 is compiled with Java 6, support for the extended JDBC 4 API is included in the binary, however this can only be used under a Java 6 runtime. In this case no manual configuration steps are necessary. It should be noted however that the Java 6 compiled distribution of JBoss AS 4.2.3.GA is still in experimental stage.