postinst is in icedtea-netx 1.2-2ubuntu1.
This file is a maintainer script. It is executed when installing (*inst) or removing (*rm) the package.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 | #! /bin/sh
set -e
multiarch=x86_64-linux-gnu
priority=1061
basedir=/usr/lib/jvm/java-6-openjdk-amd64
mandir=$basedir/jre/man
priority7=1060
base7dir=/usr/lib/jvm/java-7-openjdk-amd64
man7dir=$base7dir/jre/man
tools='javaws itweb-settings'
srcext=1.gz
dstext=1.gz
case "$1" in
configure)
   if [ -z "$2" ]; then
        update_alternatives=y
    fi
    if [ -n "$multiarch" ] && [ -n "$2" ]; then
        for i in $tools; do
            if [ -z "$(update-alternatives --list $i 2>/dev/null | grep ^$basedir/)" ]; then
                update_alternatives=y
                break
            fi
        done
    fi
    if [ "$update_alternatives" = y ]; then
    if [ -n "$multiarch" ] && [ "$DPKG_MAINTSCRIPT_ARCH" != $(dpkg --print-architecture) ]; then
        priority=$(expr $priority - 1)
        priority7=$(expr $priority7 - 1)
    fi
    for i in $tools; do
        unset slave1 || true
        if [ -e $mandir/man1/$i.$srcext ]; then
            slave1="--slave \
                /usr/share/man/man1/$i.$dstext \
                $i.$dstext \
                $mandir/man1/$i.$srcext"
        fi
        update-alternatives \
            --install \
            /usr/bin/$i \
            $i \
            $basedir/jre/bin/$i \
            $priority \
            $slave1
    done
    for i in $tools; do
        unset slave1 || true
        if [ -e $man7dir/man1/$i.$srcext ]; then
            slave1="--slave \
                /usr/share/man/man1/$i.$dstext \
                $i.$dstext \
                $man7dir/man1/$i.$srcext"
        fi
        update-alternatives \
            --install \
            /usr/bin/$i \
            $i \
            $base7dir/jre/bin/$i \
            $priority7 \
            $slave1
    done
    fi
esac
 |