port install ntop

[olivier.servas@…]

--->  Configuring db46
Error: db46 requires the Java for Mac OS X development headers.
Error: Download the Java Developer Package from: <https://connect.apple.com/cgi-bin/WebObjects/MemberSite.woa/wa/getSoftware?bundleID=20719>
Error: Target org.macports.configure returned: missing Java headers
Log for db46 is at: /opt/local/var/macports/logs/_opt_local_var_macports_sources_rsync.macports.org_release_ports_databases_db46/main.log
Error: The following dependencies failed to build: gd2 xpm xorg-libXext xorg-libX11 xorg-libxcb python26 db46 gdbm openssl readline sqlite3 xorg-libpthread-stubs xorg-xcb-proto libxml2 xorg-util-macros xorg-xcmiscproto xorg-xextproto xorg-xf86bigfontproto xorg-xtrans xorg-libXt xorg-libsm xorg-libice libevent libgeoip libpcap rrdtool glib2 dbus intltool gnome-common p5-getopt-long p5-pathtools p5-scalar-list-utils p5-xml-parser pango Xft2 xrender xorg-renderproto cairo libpixman tcl wget libidn
Error: Status 1 encountered during processing.
To report a bug, see <http://guide.macports.org/#project.tickets>

[jmroot (Joshua Root)]

Please remember to preview and use WikiFormatting, fill in the Port field, and cc the maintainer.

The error message tells you exactly what you need to do. Do it.