I've already installed java8 on this server, then I want to install tomcat8 using the "apt-get" way(not the binary way).But After lots of googling,I can't find the solution，most of the solutions are using the binary way(download the apache-tomcat-8.X.X.tar.gz,then unzip it and start the tomcat...)
I believe the issue that you are running into is that no one has yet created a Debian package for the installation of Tomcat 8. Until this happens you will need to do it manually (the "unzip" method) after installing the JDK via apt.