How to set java net preferIPv4Stack true at runtime

Question

I need to disable IPv6  For that the java documentation indicates setting jvm property java net preferIPv4Stack true   But I don t understand how to do it from the code itself   Many forums demonstrated doing it from the command prompt  but I need to do it at runtime

User · Answer

I ran into this very problem trying to send mail with javax.mail from a web application in a web server running Java 7. Internal mail server destinations failed with "network unreachable", despite telnet and ping working from the same host, and while external mail servers worked. I tried

System.setProperty("java.net.preferIPv4Stack" , "true");

in the code, but that failed. So the parameter value was probably cached earlier by the system. Setting the VM argument

-Djava.net.preferIPv4Stack=true

in the web server startup script worked.

One further bit of evidence: in a very small targeted test program, setting the system property in the code did work. So the parameter is probably cached when the first Socket is used, probably not just as the JVM starts.

User · Answer

You can use System setProperty  java net preferIPv4Stack     true     This is equivalent to passing it in the command line via -Djava net preferIPv4Stack true

User · Answer

Another approach  if you re desperate and don t have access to  a  the code or  b  the command line  then you can use environment variables   http   docs oracle com javase 7 docs webnotes tsg TSG-Desktop html plugin html   Specifically for java web start set the environment variable   JAVAWS VM ARGS  and for applets    JPI VM OPTIONS  e g    JPI VM OPTIONS -Djava net preferIPv4Stack true  Additionally  under Windows global options  for general Java applications  can be set in the Java   control plan page under the  Java  tab

User · Answer

System setProperty is not working for applets  Because JVM already running before applet start  In this case we use applet parameters like this        deployJava runApplet           id   MyApplet           code   com mkysoft myapplet SomeClass           archive   com mkysoft myapplet jar                   java version   1 6       Target version         cache option   no           cache archive              codebase lookup  true          java arguments   -Djava net preferIPv4Stack true                 1 6     Minimum version          You can find deployJava js at https   www java com js deployJava js

User · Answer

well   I used System setProperty  java net preferIPv4Stack     true    and it works from JAVA  but it doesn t work on JBOSS AS7    Here is my work around solution   Add the below line to the end of the file   JBOSS HOME  bin standalone conf bat  just after  JAVA OPTS SET    set  JAVA OPTS  JAVA OPTS  -Djava net preferIPv4Stack true    Note  restart JBoss server

User · Answer

you can set the environment variable JAVA TOOL OPTS like as follows  which will be picked by JVM for any application      set JAVA TOOL OPTS -Djava net preferIPv4Stack true   You can set this from the command prompt or set in system environment variables  based on your need  Note that this will reflect into all the java applications that run in your machine  even if it s a java interpreter that you have in a private setup

[java] How to set java.net.preferIPv4Stack=true at runtime?

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