Since it is common for Java source tarball to ship jar files of thirdparty libraries, creating a repack script to remove them from the upstream tarball is mandatory.
Packages must be built with default-jdk. This package provides a dependency on the recommended Java Development Kit. If needed, the right JAVA_HOME is /usr/lib/jvm/default-java/
The javahelper package provides helper to build either with CDBS or dh. They are strongly recommended for Java packaging.
For Maven based packages, the usage of maven-debian-helper is recommended.