I'm running in an environment where I can pass parameters but not set environment variables using a normal commandline.
I would like to set environment variables nevertheless. Is there an alternative way to "fool" java that an environment variable is set, e.g. using -D parameters?
(I'm running spark in oozie through hue; all in the Cloudera stack).
The java command itself doesn't seem to allow that. It has a -D parameter, but that sets Java 'system properties':
$ java -help 2>&1 | grep -A1 '\-D'
-D<name>=<value>
set a system property
Java system properties are a sort of Java properties. Like environment variables, java properties are key-value pairs, but aren't the same thing as environment variables: If your Java application reacts to a specific environment variable, setting a system property of the same name won't have any effect unless the application explicitly reacts to that property, too.
If your environment allows you to run arbitrary Java applications and if it allows your Java applications to execute other processes, you can write a little wrapper that sets the environment variables on a ProcessBuilder (see the question Arnon linked in his comment: How do I set environment variables from Java?) to then invoke java with your actual JAR from it. You could either hard-code the environment variables to set, or set them according to system properties the wrapper receives. (Or you could even implement your own shell in Java and pass a script to it.)
Though, if you can modify the source of that actual JAR, a much more idiomatic solution would be to make it itself react to properties instead of (or additionally to) environment variables. (Unless you have to control environment variables that the java command / the JVM reacts to rather than the JAR you'd like to run. Then this approach would not be applicable, of course.)