public class GetPropertyOfSys {
	public static void main(String args[]) {
		System.out.println(System.getProperty("os.name"));
		System.out.println(System.getProperty("webdriver.browser"));

		System.out.println("----------------------------------------------");
		System.setProperty("os.name", "linux");
		System.setProperty("webdriver.browser", "firefox");

		System.out.println(System.getProperty("os.name"));
		System.out.println(System.getProperty("webdriver.browser"));
	}
}

运行结果：

Windows 7
null
----------------------------------------------
linux

firefox

解释说明：

如果没有setProperty，直接getProperty的话，如果key包含在以下默认的key，就会得到相应的value。如果没有包含，则返回null。

Key	Description of Associated Value
java.version	Java Runtime Environment version
java.vendor	Java Runtime Environment vendor
java.vendor.url	Java vendor URL
java.home	Java installation directory
java.vm.specification.version	Java Virtual Machine specification version
java.vm.specification.vendor	Java Virtual Machine specification vendor
java.vm.specification.name	Java Virtual Machine specification name
java.vm.version	Java Virtual Machine implementation version
java.vm.vendor	Java Virtual Machine implementation vendor
java.vm.name	Java Virtual Machine implementation name
java.specification.version	Java Runtime Environment specification version
java.specification.vendor	Java Runtime Environment specification vendor
java.specification.name	Java Runtime Environment specification name
java.class.version	Java class format version number
java.class.path	Java class path
java.library.path	List of paths to search when loading libraries
java.io.tmpdir	Default temp file path
java.compiler	Name of JIT compiler to use
java.ext.dirs	Path of extension directory or directories
os.name	Operating system name
os.arch	Operating system architecture
os.version	Operating system version
file.separator	File separator ("/" on UNIX)
path.separator	Path separator (":" on UNIX)
line.separator	Line separator ("\n" on UNIX)
user.name	User's account name
user.home	User's home directory
user.dir	User's current working directory