System.getSystemManager() got null in Tomcat

[jacksuyu]

System.getSystemManager() returns null in my javacode.

I put
grant codeBase "file:${{java.ext.dirs}}/*" {
permission java.security.SecurityPermission "*";
};

in the related java.policy file.

I am running on windows, so not sure how to specify java parameters in
startup command.

Please help, thanks