问题
I am not clear about this. When I run a java App or run an Applet in applet viewer, (in the IDE environment), System.getProperty("java.class.path") gives me the same as System.getenv("CLASSPATH") which is the CLASSPATH defined in my env variable.
But when I deploy my applet to webserver and access it from the same computer as a client, I get different results for the two. (System.getProperty("java.class.path") only points to JRE home and System.getenv("CLASSPATH") returns null).
And here is some other things that make me wonder:
For the applet part, the env var JAVA_HOME, I get the same result when deploying the applet in a browser as well as Applet Viewer.
And if I define myself a env variable at system level, and use getenv("envName") the result is null. Is there anyway I can define one and get it in my Java program?
回答1:
Environment variables are specific to the operating system. Properties are JVM only.
回答2:
System.getProperty("Propertname") **Platform Independent**
The above method will return JVM arguments and properties.
System.getenv("EnvName") **Platform Dependent**
The above method returns your operating system environment variables.
In Linux you can set a environment variable from the shell using the following command.
export SYSTEM_TYPE=PROD
In Java you can read the variable by
System.getenv("SYSTEM_TYPE")
The above code will return PROD
http://javarevisited.blogspot.in/2012/08/how-to-get-environment-variables-in.html
来源：https://stackoverflow.com/questions/2863674/whats-the-difference-between-a-system-property-and-environment-variable