system property is null even if it is defined in command line

java

Solution

You're specifying `-D` after the classname, so it's being treated as a regular command line argument to be passed on to the application itself. You would see that if you printed out the values in `args`.

Run the app like this instead:

java -cp javaapplication8.jar -Dsysprop="some value" javaapplication8.JavaApplication8

All arguments which are meant to apply to the environment rather than the application should come before the classname. If you run just `java`, you'll see usage help like this:

Usage: java [-options] class [args...]
           (to execute a class)
   or  java [-options] -jar jarfile [args...]
           (to execute a jar file)
where options include
[...]

Problem

I am debugging a problem in a large system. I was able to locate the problem in a rather basic java feature - the application is started with the -D option to specify some system properties. During run-time though, said properties are not set and their values are null. Trying to reproduce the issue I created the following very simple application: ``` public static void main(String[] args) { String propName = "sysprop"; String propValue = System.getProperty(propName); System.out.println(propName + "=" + propValue); } ``` I start the application with the following command line and to my surprise got the same result: java -cp javaapplication8.jar javaapplication8.JavaApplication8 -Dsysprop="some value" sysprop=null Apparently I am missing something obvious (or lack some basic knowledge) but what is it? Thank you.

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