java - Check programatically (without string-matching) whether using IPV6 or IPV4 for JVM -

i want check whether jvm options particular application (in case, matlab) have been set prefer ipv4 or if still use ipv6.

i know how set jvm prefer ipv4. in case, can done adding line

-djava.net.preferipv4stack=true

to java.opts file within $matlabroot/bin/maci64/.

i can check whether line has been added java.opts via string-matching. i've pasted current solution (a matlab script checks string-match, , adds line if not exist) @ bottom of question.

i don't know how, though, check whether ipv4 or ipv6 preferred without string-matching. seems preferred.

does know how check ipv4 vs. ipv6 in jvm without string-matching?

here's current solution, depends on string-matching:

% osx platform-specific: revert ipv4 if (computer('arch') == 'maci64')   javaoptspath = fileread([matlabroot '/bin/' computer('arch') '/java.opts']);   k = strfind(javaoptspath, '-djava.net.preferipv4stack=true');   if isempty(k)     setenv('drake_ipv4_set_matlabroot', matlabroot)     setenv('drake_ipv4_set_arch', computer('arch'))     display('since on mac, need set jvm prefer ipv4 instead of ipv6 matlab')     display('please enter sudo password below')     ! (echo "" | echo "-djava.net.preferipv4stack=true") | sudo tee -a $drake_ipv4_set_matlabroot/bin/$drake_ipv4_set_arch/java.opts   end end 

you can access underlying java system properties without parsing options string using java.lang.system class directly matlab.

for example:

ipv4_preferred = java.lang.system.getproperty('java.net.preferipv4stack') 

the result of getproperty empty if user has not set -djava.net.preferipv4stack=..., more complete solution might be:

ipv4_preferred = java.lang.system.getproperty('java.net.preferipv4stack'); if isempty(ipv4_preferred)   ipv4_preferred = false; end